load bank puzzle...

[Jan Panteltje]

On a sunny day (Sat, 18 Mar 2023 14:09:03 +1100) it happened Sylvia Else
<sylvia@email.invalid> wrote in <k7koafF9mvU4@mid.individual.net>:

On 18-Mar-23 8:14 am, legg wrote:

Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

\"Dummy load\" seems a terminology common enough not to suggest anything
about the buyer.

Sylvia.

Yes, used all the time
https://panteltje.nl/pub/250W_1_GHz_dummy_load_IMG_4563.JPG
https://panteltje.nl/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG
especially for RF

 

[legg]

On Sat, 18 Mar 2023 14:09:03 +1100, Sylvia Else <sylvia@email.invalid>
wrote:

On 18-Mar-23 8:14 am, legg wrote:

Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

\"Dummy load\" seems a terminology common enough not to suggest anything
about the buyer.

Sylvia.

A dummy load is usually invariable and requires no
operator adjustment.

A \'dummy\' can screw up even simple switches or rheostats.

RL

 

[legg]

On Sat, 18 Mar 2023 05:52:37 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Sat, 18 Mar 2023 14:09:03 +1100) it happened Sylvia Else
sylvia@email.invalid> wrote in <k7koafF9mvU4@mid.individual.net>:

On 18-Mar-23 8:14 am, legg wrote:

Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

\"Dummy load\" seems a terminology common enough not to suggest anything
about the buyer.

Sylvia.

Yes, used all the time
https://panteltje.nl/pub/250W_1_GHz_dummy_load_IMG_4563.JPG
https://panteltje.nl/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG
especially for RF

It\'s dummy because it\'s fixed and \'foolproof\'.

RL

 

[legg]

On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.




Active I=kV with a delay would give you an inductance.


A real inductor stores energy, which a synthesized inductor usually
doesn\'t.

Stored energy pumps current into flyback diodes or equivalent.


Does the driver really care?

It certainly might.


Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

Oh, they are just a biggish aerospace company.

No bid? Is that a good business model?


RL

https://en.wikipedia.org/wiki/Dummy_load

The minute you considered variable, multicase and
especially inductive, it ceased to be idiot-proof.

Use sockets and real loads, if it\'s that important.

RL

 

[legg]

On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.




Active I=kV with a delay would give you an inductance.


A real inductor stores energy, which a synthesized inductor usually
doesn\'t.

Stored energy pumps current into flyback diodes or equivalent.


Does the driver really care?

It certainly might.


Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

Oh, they are just a biggish aerospace company.

Then offer them burn-in hardware as well as \'dummy\' loads.

No bid? Is that a good business model?


RL

https://en.wikipedia.org/wiki/Dummy_load

 

[Clive Arthur]

On 17/03/2023 16:58, John Larkin wrote:

On Fri, 17 Mar 2023 16:32:56 +0000, Clive Arthur
clive@nowaytoday.co.uk> wrote:

On 17/03/2023 15:21, John Larkin wrote:

I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

snip

Plenty of power rheostats available. eBay has loads, many new.
Inductance is a separate matter (though they will have some of course -
get tubular rheostats and bung a ferrite rod down the centre?).

We want 8 channels on a PC board, programmable resistance.

If your power source fits the obvious constraints, an SMPS with a fixed
load resistor and a programmable output voltage could work.

--
Cheers
Clive

 

[Fred Bloggs]

On Friday, March 17, 2023 at 11:21:37 AM UTC-4, John Larkin wrote:

I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

It\'s called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too.

https://forum.digikey.com/t/bending-and-forming-leads/8184

How is any of this a puzzle?

 

[John Larkin]

On Sat, 18 Mar 2023 05:43:35 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Fri, 17 Mar 2023 10:22:33 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
5l791i1hev1qsuei98p7t83mprc4881jhk@4ax.com>:

On Fri, 17 Mar 2023 16:40:09 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 08:21:23 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
u6091ide59fffa8gafp93ipmmejp424r5j@4ax.com>:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

Yes why not..
\'SSR\' == solid state rectifier ? you mean relay? You get AC as input right?
oh wait you mean sold state relay....

Yes.

googling SSR gives among many things Wikipedia with \"Soviet Socialist Republic\"


But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

We use rectangles as resistor symbol here

Quaint olde world customs.




The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

My setup:
https://panteltje.nl/pub/power_resistors_IMG_6291.JPG
uses test leads with alligator clips to switch configuration.

We have a couple of Kikusui benchtop electronic load boxes, which are
handy. They can do square wave loads, handy for checking power supply
dynamics.

I want programmable 0 to 1 zillon ohms, isolated, ac/dc, 10 or 20
watts, metered, overload protected, 8 loads per board, maybe 4 square
inches per channel.

I was wondering if anyone had cute ideas. I considered PWM-ing a big
resistor, but that has complications.


So as to Soviet Socialist Republic
Here a very funny thing happened in politics
We just had elections, and a new party, BBB (translated: farmers people movement)
wiped out all parties going from zero to more than the biggest ones.
Protest against all the CO2 idiots who want to close farms because cows make CO2.
I voted for them too
We need farmers and their produce.

Most people think eating is good.

We will see where it goes now...



People will surely get tired of crazy prices and blackouts and food
shortages and waiting hours to recharge their cars.

I did a switched inductor thing many many years ago,
it was for tuning and used relays IIRC (up to a few hundred kHz).
I see electronics to simulate inductors as a possibility.

That\'s worth discussing, but I don\'t think it\'s practical in my case,
making small, fairly inexpensive dummy loads that can behave like
solenoids or relay coils. They need to behave when the user PWMs them
or whatever.

But what sort of users need this?
Normally you would test on the real thing
any unexpected things could exist in a real system,
parasitic capacitances, lead resistance and inductances,
unexpected couplings.. what not.
Nothing like a real test.

If one is testing FADECs, for example, it might be inconvenient to
have a jet engine as part of every test bench.

Bridge rectifier with a power MOSFET in it for AC load?
Gives all sort of problems too...

A bridge ahead of some active load is an interesting idea, but it
doesn\'t look ohmic at low voltages and can\'t return energy like a real
inductor can. I have a mosfet-based load circuit that does look ohmic
for ac or dc, all the way through zero volts, but it still doesn\'t
store energy.

 

[John Larkin]

On Sat, 18 Mar 2023 07:13:33 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.




Active I=kV with a delay would give you an inductance.


A real inductor stores energy, which a synthesized inductor usually
doesn\'t.

Stored energy pumps current into flyback diodes or equivalent.


Does the driver really care?

It certainly might.


Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

Oh, they are just a biggish aerospace company.

No bid? Is that a good business model?


RL

https://en.wikipedia.org/wiki/Dummy_load


The minute you considered variable, multicase and
especially inductive, it ceased to be idiot-proof.

Use sockets and real loads, if it\'s that important.

RL

The customer has an existing design where they select and solder a
selected set of resistors and inductors per channel, unique to each
unit. We don\'t want to be in the business of doing that for them, with
every unit having its own dash number and BOM and test limits.

I\'d like to design a programmable dummy load board that we can
manufacture and stock and ship when we get an order.

It\'s looking like a straight conductance DAC is the way to go:
parallel N resistors (R, 2R, etc) with a solid-state switch per. Given
a binary control code K, net conductance is proportional to K so
resistance goes as 1/K. N=5 maybe; we\'re not simulating RTDs. That\'s
nice and simple and adds an open-circuit case for free. Two more SSRs
can add short and ground fault cases, selling points.

I like to add little goodies to products when it\'s not hard and
doesn\'t interfere with the base function. You never know if something
will appeal to someone and tip a basically emotional buy decision, as
in \"That thingie might be useful some day, let\'s buy theirs.\"

Colors matter too.

 

[John Larkin]

On Sat, 18 Mar 2023 07:08:29 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 18 Mar 2023 14:09:03 +1100, Sylvia Else <sylvia@email.invalid
wrote:

On 18-Mar-23 8:14 am, legg wrote:

Where\'d the word \'dummy\' originate in the spec? If it reflects
the attitude of the buyer, I\'d say \'No Bid\'. I\'ve had it with
idiots like that.

\"Dummy load\" seems a terminology common enough not to suggest anything
about the buyer.

Sylvia.

A dummy load is usually invariable and requires no
operator adjustment.

Why? A programmable dummy load can be very useful.

A \'dummy\' can screw up even simple switches or rheostats.

They could wire anything wrong.

A good dummy load includes measurements and waveform acquisition and
overload protections. If you see 17 volts and ask for 130 ohms and
don\'t get 130 mA, you should know that something\'s wrong.

The load is a dummy but my customers aren\'t. You trust your life to
them fairly often.

 

[Jan Panteltje]

On a sunny day (Sat, 18 Mar 2023 07:55:03 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<agjb1ih89jhol5ltl58m52cinf32eiij0t@4ax.com>:

On Sat, 18 Mar 2023 05:43:35 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 10:22:33 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
5l791i1hev1qsuei98p7t83mprc4881jhk@4ax.com>:

On Fri, 17 Mar 2023 16:40:09 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 08:21:23 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
u6091ide59fffa8gafp93ipmmejp424r5j@4ax.com>:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

Yes why not..
\'SSR\' == solid state rectifier ? you mean relay? You get AC as input right?
oh wait you mean sold state relay....

Yes.

googling SSR gives among many things Wikipedia with \"Soviet Socialist Republic\"


But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

We use rectangles as resistor symbol here

Quaint olde world customs.




The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

My setup:
https://panteltje.nl/pub/power_resistors_IMG_6291.JPG
uses test leads with alligator clips to switch configuration.

We have a couple of Kikusui benchtop electronic load boxes, which are
handy. They can do square wave loads, handy for checking power supply
dynamics.

I want programmable 0 to 1 zillon ohms, isolated, ac/dc, 10 or 20
watts, metered, overload protected, 8 loads per board, maybe 4 square
inches per channel.

I was wondering if anyone had cute ideas. I considered PWM-ing a big
resistor, but that has complications.


So as to Soviet Socialist Republic
Here a very funny thing happened in politics
We just had elections, and a new party, BBB (translated: farmers people movement)
wiped out all parties going from zero to more than the biggest ones.
Protest against all the CO2 idiots who want to close farms because cows make CO2.
I voted for them too
We need farmers and their produce.

Most people think eating is good.

We will see where it goes now...



People will surely get tired of crazy prices and blackouts and food
shortages and waiting hours to recharge their cars.

I did a switched inductor thing many many years ago,
it was for tuning and used relays IIRC (up to a few hundred kHz).
I see electronics to simulate inductors as a possibility.

That\'s worth discussing, but I don\'t think it\'s practical in my case,
making small, fairly inexpensive dummy loads that can behave like
solenoids or relay coils. They need to behave when the user PWMs them
or whatever.

But what sort of users need this?
Normally you would test on the real thing
any unexpected things could exist in a real system,
parasitic capacitances, lead resistance and inductances,
unexpected couplings.. what not.
Nothing like a real test.

If one is testing FADECs, for example, it might be inconvenient to
have a jet engine as part of every test bench.

I have no idea what a FADEC is or what its internals are
so I looked it up:
https://en.wikipedia.org/wiki/FADEC

Now I will stop flying!!!!
Carry a parachute ? Still be able to open doors?
I once was on a flight from Barcelona Spain to Amsterdam,
about 15 minutes after takeoff the \'hammer\' came on
\'Hammer\' is the alarm bells in the cockpit.
Engine on fire, we circled and dumped fuel, then landed safely on one engine.
Those alarms came on just when I was reading about Bill Clignon and Monica...
Before takeoff I did see a large pool of fluid under that engine
thought \'will not be oil, somebody must have checked\'.
Captain just walked in without even a look.
After I got back home later on an other flight I called the newspaper and they then did an article on airplane maintenance.
Much later I worked at Schiphol airport in Amsterdam... design stuff.
That was years after a 747 cargo plane flew into the flat next to were I lived 4 years earlier...
Long before all that I was in the cockpit of a F100 super sabre at an airs how on a mil airport here..
Had not had any English yet, so that big red button with \'ARM\' on it must be the start button
so I pressed it, Alarm went of and they took me out of that cockpit.
Our neighbor was a jet pilot, he had got me in.. was maybe 12 years old?
Now when the flying cup and saucers land here OK.. top secret, will be silent now..

But all that one more reason to test on the real thing!
I do see the convenience point too...
You do not need a whole jet engine in the workshop, but the relevant relays and other things that FADEC drives should not be so hard to have around?

Bridge rectifier with a power MOSFET in it for AC load?
Gives all sort of problems too...


A bridge ahead of some active load is an interesting idea, but it
doesn\'t look ohmic at low voltages and can\'t return energy like a real
inductor can. I have a mosfet-based load circuit that does look ohmic
for ac or dc, all the way through zero volts, but it still doesn\'t
store energy.

It better be very good as lives depend on it (and you maybe be sued if you screw up).
In broadcasting where I worked your job could depend on it worst case...

 

[John Larkin]

On Sat, 18 Mar 2023 15:46:03 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Sat, 18 Mar 2023 07:55:03 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
agjb1ih89jhol5ltl58m52cinf32eiij0t@4ax.com>:

On Sat, 18 Mar 2023 05:43:35 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 10:22:33 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
5l791i1hev1qsuei98p7t83mprc4881jhk@4ax.com>:

On Fri, 17 Mar 2023 16:40:09 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 08:21:23 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
u6091ide59fffa8gafp93ipmmejp424r5j@4ax.com>:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

Yes why not..
\'SSR\' == solid state rectifier ? you mean relay? You get AC as input right?
oh wait you mean sold state relay....

Yes.

googling SSR gives among many things Wikipedia with \"Soviet Socialist Republic\"


But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

We use rectangles as resistor symbol here

Quaint olde world customs.




The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

My setup:
https://panteltje.nl/pub/power_resistors_IMG_6291.JPG
uses test leads with alligator clips to switch configuration.

We have a couple of Kikusui benchtop electronic load boxes, which are
handy. They can do square wave loads, handy for checking power supply
dynamics.

I want programmable 0 to 1 zillon ohms, isolated, ac/dc, 10 or 20
watts, metered, overload protected, 8 loads per board, maybe 4 square
inches per channel.

I was wondering if anyone had cute ideas. I considered PWM-ing a big
resistor, but that has complications.


So as to Soviet Socialist Republic
Here a very funny thing happened in politics
We just had elections, and a new party, BBB (translated: farmers people movement)
wiped out all parties going from zero to more than the biggest ones.
Protest against all the CO2 idiots who want to close farms because cows make CO2.
I voted for them too
We need farmers and their produce.

Most people think eating is good.

We will see where it goes now...



People will surely get tired of crazy prices and blackouts and food
shortages and waiting hours to recharge their cars.

I did a switched inductor thing many many years ago,
it was for tuning and used relays IIRC (up to a few hundred kHz).
I see electronics to simulate inductors as a possibility.

That\'s worth discussing, but I don\'t think it\'s practical in my case,
making small, fairly inexpensive dummy loads that can behave like
solenoids or relay coils. They need to behave when the user PWMs them
or whatever.

But what sort of users need this?
Normally you would test on the real thing
any unexpected things could exist in a real system,
parasitic capacitances, lead resistance and inductances,
unexpected couplings.. what not.
Nothing like a real test.

If one is testing FADECs, for example, it might be inconvenient to
have a jet engine as part of every test bench.

I have no idea what a FADEC is or what its internals are
so I looked it up:
https://en.wikipedia.org/wiki/FADEC

Now I will stop flying!!!!

Each FADEC is redundant, and gets power from both the airframe DC
supply and from a dual alternator on its engine. Thet are very
reliable. Most engine problems are mechanical or fuel related. Birds
are bad in jet engines.

We sell alternator simulators that are used to test FADECs, which
furtunately people buy two at a time. It\'s kind of interesting, since
a PM alternator is basically a current source and the FADECs regulate
by shorting them. Our rev A box tended to blow up.


Some small planes have full-plane parachutes. They land hard but
survivably.

Carry a parachute ? Still be able to open doors?
I once was on a flight from Barcelona Spain to Amsterdam,
about 15 minutes after takeoff the \'hammer\' came on
\'Hammer\' is the alarm bells in the cockpit.
Engine on fire, we circled and dumped fuel, then landed safely on one engine.

Planes can fly on one engine, as long as the failed one doesn\'t toss
blades and tear a wing off or something like that. They have
\"containment\" that usually works. Engines are tested to destruction to
make sure the blades stay inside.

Those alarms came on just when I was reading about Bill Clignon and Monica...
Before takeoff I did see a large pool of fluid under that engine
thought \'will not be oil, somebody must have checked\'.
Captain just walked in without even a look.
After I got back home later on an other flight I called the newspaper and they then did an article on airplane maintenance.
Much later I worked at Schiphol airport in Amsterdam... design stuff.
That was years after a 747 cargo plane flew into the flat next to were I lived 4 years earlier...
Long before all that I was in the cockpit of a F100 super sabre at an airs how on a mil airport here..
Had not had any English yet, so that big red button with \'ARM\' on it must be the start button
so I pressed it, Alarm went of and they took me out of that cockpit.
Our neighbor was a jet pilot, he had got me in.. was maybe 12 years old?
Now when the flying cup and saucers land here OK.. top secret, will be silent now..

But all that one more reason to test on the real thing!
I do see the convenience point too...
You do not need a whole jet engine in the workshop, but the relevant relays and other things that FADEC drives should not be so hard to have around?



Bridge rectifier with a power MOSFET in it for AC load?
Gives all sort of problems too...


A bridge ahead of some active load is an interesting idea, but it
doesn\'t look ohmic at low voltages and can\'t return energy like a real
inductor can. I have a mosfet-based load circuit that does look ohmic
for ac or dc, all the way through zero volts, but it still doesn\'t
store energy.

It better be very good as lives depend on it (and you maybe be sued if you screw up).
In broadcasting where I worked your job could depend on it worst case...

 

[Lasse Langwadt Christensen]

lørdag den 18. marts 2023 kl. 18.28.59 UTC+1 skrev John Larkin:

On Sat, 18 Mar 2023 15:46:03 GMT, Jan Panteltje <al...@comet.invalid
wrote:

On a sunny day (Sat, 18 Mar 2023 07:55:03 -0700) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
agjb1ih89jhol5ltl...@4ax.com>:

On Sat, 18 Mar 2023 05:43:35 GMT, Jan Panteltje <al...@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 10:22:33 -0700) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
5l791i1hev1qsuei9...@4ax.com>:

On Fri, 17 Mar 2023 16:40:09 GMT, Jan Panteltje <al...@comet.invalid
wrote:

On a sunny day (Fri, 17 Mar 2023 08:21:23 -0700) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
u6091ide59fffa8ga...@4ax.com>:


I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

Yes why not..
\'SSR\' == solid state rectifier ? you mean relay? You get AC as input right?
oh wait you mean sold state relay....

Yes.

googling SSR gives among many things Wikipedia with \"Soviet Socialist Republic\"


But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

We use rectangles as resistor symbol here

Quaint olde world customs.




The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

My setup:
https://panteltje.nl/pub/power_resistors_IMG_6291.JPG
uses test leads with alligator clips to switch configuration.

We have a couple of Kikusui benchtop electronic load boxes, which are
handy. They can do square wave loads, handy for checking power supply
dynamics.

I want programmable 0 to 1 zillon ohms, isolated, ac/dc, 10 or 20
watts, metered, overload protected, 8 loads per board, maybe 4 square
inches per channel.

I was wondering if anyone had cute ideas. I considered PWM-ing a big
resistor, but that has complications.


So as to Soviet Socialist Republic
Here a very funny thing happened in politics
We just had elections, and a new party, BBB (translated: farmers people movement)
wiped out all parties going from zero to more than the biggest ones.
Protest against all the CO2 idiots who want to close farms because cows make CO2.
I voted for them too
We need farmers and their produce.

Most people think eating is good.

We will see where it goes now...



People will surely get tired of crazy prices and blackouts and food
shortages and waiting hours to recharge their cars.

I did a switched inductor thing many many years ago,
it was for tuning and used relays IIRC (up to a few hundred kHz).
I see electronics to simulate inductors as a possibility.

That\'s worth discussing, but I don\'t think it\'s practical in my case,
making small, fairly inexpensive dummy loads that can behave like
solenoids or relay coils. They need to behave when the user PWMs them
or whatever.

But what sort of users need this?
Normally you would test on the real thing
any unexpected things could exist in a real system,
parasitic capacitances, lead resistance and inductances,
unexpected couplings.. what not.
Nothing like a real test.

If one is testing FADECs, for example, it might be inconvenient to
have a jet engine as part of every test bench.

I have no idea what a FADEC is or what its internals are
so I looked it up:
https://en.wikipedia.org/wiki/FADEC

Now I will stop flying!!!!
Each FADEC is redundant, and gets power from both the airframe DC
supply and from a dual alternator on its engine. Thet are very
reliable. Most engine problems are mechanical or fuel related. Birds
are bad in jet engines.

We sell alternator simulators that are used to test FADECs, which
furtunately people buy two at a time. It\'s kind of interesting, since
a PM alternator is basically a current source and the FADECs regulate
by shorting them. Our rev A box tended to blow up.


Some small planes have full-plane parachutes. They land hard but
survivably.
Carry a parachute ? Still be able to open doors?
I once was on a flight from Barcelona Spain to Amsterdam,
about 15 minutes after takeoff the \'hammer\' came on
\'Hammer\' is the alarm bells in the cockpit.
Engine on fire, we circled and dumped fuel, then landed safely on one engine.
Planes can fly on one engine, as long as the failed one doesn\'t toss
blades and tear a wing off or something like that. They have
\"containment\" that usually works. Engines are tested to destruction to
make sure the blades stay inside.

https://www.youtube.com/shorts/yIUzWPc7pqc

 

[John Larkin]

On Sat, 18 Mar 2023 07:44:01 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Friday, March 17, 2023 at 11:21:37?AM UTC-4, John Larkin wrote:
I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

It\'s called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too.

https://forum.digikey.com/t/bending-and-forming-leads/8184

How is any of this a puzzle?

A good design is most always a puzzle, which makes design interesting.

One issue is, how much power can you dissipate in 4 square inches of
PC board with some given air flow? Big heat sink with mosfets? Small
CPU cooler? I\'m thinking of using axial-lead wirewound resistors
spaced off the board enough that the leads have enough thermal
resistance to not scorch the board when the resistor gets very hot.

 

[whit3rd]

On Saturday, March 18, 2023 at 8:20:02 AM UTC-7, John Larkin wrote:

On Sat, 18 Mar 2023 07:08:29 -0400, legg <le...@nospam.magma.ca> wrote:

A dummy load is usually invariable and requires no
operator adjustment.
Why? A programmable dummy load can be very useful.

A \'dummy\' can screw up even simple switches or rheostats.

They could wire anything wrong.

Yeah, and... for an inspection-quality load, you might want a barcode
for each of a dozen variants. At inspection time, if the right barcode isn\'t
scanned, the inspection is invalid.

Adjustable boxes aren\'t good \"standard\" loads for a formal inspection process, IMHO.
At a minimum, you\'d want a calibration date, and complete record of the settings, printed onto an
attachable sticker label, for the final report.

How does one calibrate eight different adjustable loads, each having dozens of settings?

 

[Jan Panteltje]

On a sunny day (Sat, 18 Mar 2023 10:28:46 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<kisb1ipbum7dulpqhanh1l0m95l2hglius@4ax.com>:

On Sat, 18 Mar 2023 15:46:03 GMT, Jan Panteltje <alien@comet.invalid
wrote:

I have no idea what a FADEC is or what its internals are
so I looked it up:
https://en.wikipedia.org/wiki/FADEC

Now I will stop flying!!!!

Each FADEC is redundant, and gets power from both the airframe DC
supply and from a dual alternator on its engine. Thet are very
reliable. Most engine problems are mechanical or fuel related. Birds
are bad in jet engines.

We sell alternator simulators that are used to test FADECs, which
furtunately people buy two at a time. It\'s kind of interesting, since
a PM alternator is basically a current source and the FADECs regulate
by shorting them. Our rev A box tended to blow up.


Some small planes have full-plane parachutes. They land hard but
survivably.

Engine on fire, we circled and dumped fuel, then landed safely on one engine.

Planes can fly on one engine, as long as the failed one doesn\'t toss
blades and tear a wing off or something like that. They have
\"containment\" that usually works. Engines are tested to destruction to
make sure the blades stay inside.

There is a series on German satellite TV about plane crashes that happened and they go into all the details
and follow the guys evaluating what\'s left.. to find the cause.
I have seen maybe 10 or more plain crashes analyzed now,
from the thing that got hit by birds and landed in the Hudson
to the Concord etc etc
Flight recorder voice playback, instruments status displayed, fault finding is an art.
Very nice job they do, every single part is looked at and sometimes the whole plane reconstructed
from fragments, engines taken apart, radar traces evaluated..
There is a lot that can go wrong, often pilot error like the one I followed
last week that crashed in a field near Schiphol airport,
pilot had one engine throttled down.. (propeller 2 engine plane) without knowing it (he did it himself)
so when steering towards the runway the plane tilted one way and he lost control..

And communication between captain and co-pilot, co-pilot not daring to speak up to captain who takes wrong decisions, a LOT comes into play.

Cockpit Resource Management
flyaeroguard.com/blog/2020/08/10/what-is-crew-resource-management/


Human factor...


Automation is not all that hard:
https://panteltje.nl/panteltje/quadcopter/index.html

but the more you automate the less pilots are used to flying themselves...
Sure redundancy, but at high altitude high energy particles can mess up your FADECs.
Then it becomes a matter of chance.

OTOH if you consider my laptop is now 10 years old and still going strong,
I also have a PC that is close to 20 years old now and still I use it sometimes....

I have a little 8052AH BASIC computer I build in the late eighties that still works:
https://panteltje.nl/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_inside_img_1727.jpg
even the nicads still work


So automation better than a human flying?
Maybe

But look at Tesla and the accidents that happened?

Interesting subject.
I did some manual writing for stuff like that at Schiphol airport
\'groot alarm vliegtuig\'
there are procedures in place if anything goes wrong at the airport
also security related..
...

 

[Lasse Langwadt Christensen]

lørdag den 18. marts 2023 kl. 20.30.07 UTC+1 skrev Jan Panteltje:

On a sunny day (Sat, 18 Mar 2023 10:28:46 -0700) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
kisb1ipbum7dulpqh...@4ax.com>:
On Sat, 18 Mar 2023 15:46:03 GMT, Jan Panteltje <al...@comet.invalid
wrote:
I have no idea what a FADEC is or what its internals are
so I looked it up:
https://en.wikipedia.org/wiki/FADEC

Now I will stop flying!!!!

Each FADEC is redundant, and gets power from both the airframe DC
supply and from a dual alternator on its engine. Thet are very
reliable. Most engine problems are mechanical or fuel related. Birds
are bad in jet engines.

We sell alternator simulators that are used to test FADECs, which
furtunately people buy two at a time. It\'s kind of interesting, since
a PM alternator is basically a current source and the FADECs regulate
by shorting them. Our rev A box tended to blow up.


Some small planes have full-plane parachutes. They land hard but
survivably.
Engine on fire, we circled and dumped fuel, then landed safely on one engine.

Planes can fly on one engine, as long as the failed one doesn\'t toss
blades and tear a wing off or something like that. They have
\"containment\" that usually works. Engines are tested to destruction to
make sure the blades stay inside.
There is a series on German satellite TV about plane crashes that happened and they go into all the details
and follow the guys evaluating what\'s left.. to find the cause.

\"Aircrash investigation\" I\'d guess, they are not bad but there\'s a few youtube channels*
with actual pilots going through the accident reports, watching those make you realise
the TV shows are often far from accurate

*to mention a few, Mentour Pilot and blancolirio

There is a lot that can go wrong, often pilot error like the one I followed
last week that crashed in a field near Schiphol airport,
pilot had one engine throttled down.. (propeller 2 engine plane) without knowing it (he did it himself)
so when steering towards the runway the plane tilted one way and he lost control..

There was one similar in Nepal, probably caused by the first officer pulling the wrong handle feathering the engines
instead of lowering the flaps, like because he would normally be flying in the left seat as a captain, but on this flight
he was an instructor so he was in the right seat...

 

[Fred Bloggs]

On Saturday, March 18, 2023 at 1:48:27 PM UTC-4, John Larkin wrote:

On Sat, 18 Mar 2023 07:44:01 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Friday, March 17, 2023 at 11:21:37?AM UTC-4, John Larkin wrote:
I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

It\'s called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too.

https://forum.digikey.com/t/bending-and-forming-leads/8184

How is any of this a puzzle?
A good design is most always a puzzle, which makes design interesting.

One issue is, how much power can you dissipate in 4 square inches of
PC board with some given air flow? Big heat sink with mosfets? Small
CPU cooler? I\'m thinking of using axial-lead wirewound resistors
spaced off the board enough that the leads have enough thermal
resistance to not scorch the board when the resistor gets very hot.

Keep in mind people tend to lose respect for a product that smells like it\'s burning. You should be determining the threshold case temperature at which outgassing becomes noticeable, via olfactory sensing, and see if reducing temps by half, with proper derating for ambient, does anything for you.

 

[John Larkin]

On Sat, 18 Mar 2023 15:23:20 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Saturday, March 18, 2023 at 1:48:27?PM UTC-4, John Larkin wrote:
On Sat, 18 Mar 2023 07:44:01 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Friday, March 17, 2023 at 11:21:37?AM UTC-4, John Larkin wrote:
I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

It\'s called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too.

https://forum.digikey.com/t/bending-and-forming-leads/8184

How is any of this a puzzle?
A good design is most always a puzzle, which makes design interesting.

One issue is, how much power can you dissipate in 4 square inches of
PC board with some given air flow? Big heat sink with mosfets? Small
CPU cooler? I\'m thinking of using axial-lead wirewound resistors
spaced off the board enough that the leads have enough thermal
resistance to not scorch the board when the resistor gets very hot.

Keep in mind people tend to lose respect for a product that smells like it\'s burning. You should be determining the threshold case temperature at which outgassing becomes noticeable, via olfactory sensing, and see if reducing temps by half, with proper derating for ambient, does anything for you.

Vitreous enameled resistors would be best for not outgassing. Silicone
or whatever would be worse.

Wirewound resistors tend to run at crazy temps, like 270C, at full
power. I wouldn\'t want to scorch the PCB.

There are some nice DPAK power resistors that could be clamp mounted
on heat sinks, which would provide a lot of surface area.

There are also TO-220 power resistors, which could be attached to heat
sinks with nuts and bolts.

 

[Lasse Langwadt Christensen]

lørdag den 18. marts 2023 kl. 23.57.33 UTC+1 skrev John Larkin:

On Sat, 18 Mar 2023 15:23:20 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Saturday, March 18, 2023 at 1:48:27?PM UTC-4, John Larkin wrote:
On Sat, 18 Mar 2023 07:44:01 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Friday, March 17, 2023 at 11:21:37?AM UTC-4, John Larkin wrote:
I\'ve been asked to design an 8-channel dummy load board. It\'s not very
challenging but somebody\'s got to do it. It will be used to simulate
small loads like solenoids or relays or torque motors. It needs some
inductance too, because the drivers often PWM. Maybe 10 or so watts
per channel.

I could do this electronically, but it would a lot easier and more
rugged if I use wirewound resistors. I was thinking of making a
conductance DAC, namely resistors R 2R 4R etc switched in parallel
across the inputs with an SSR per resistor.

But there is a history of clever load banks. When I was an EE student
at Tulane, two semisters of Electrical Machinery (with lab) was
mandatory. It was a pain but I learned a lot. We had a big load bank
in the machinery lab, a string of giant series resistors with a
3-position knife switch at each node. That made me think about using
series-parallel combinations to hit some target value.

https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1

The upper pic is the ancient Tulane load bank as I remember it.

I was thinking about the lower circuit for my gadget. I could use
wirewould resistors and kink the leads to space them maybe 3/4 inch
above my PCB, in the air stream. The higher value resistors might be
2512 surface mounts.

I think there is a tool to bend and kink resistor leads. Or we could
send a bunch out to a service maybe.

It\'s called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too.

https://forum.digikey.com/t/bending-and-forming-leads/8184

How is any of this a puzzle?
A good design is most always a puzzle, which makes design interesting.

One issue is, how much power can you dissipate in 4 square inches of
PC board with some given air flow? Big heat sink with mosfets? Small
CPU cooler? I\'m thinking of using axial-lead wirewound resistors
spaced off the board enough that the leads have enough thermal
resistance to not scorch the board when the resistor gets very hot.

Keep in mind people tend to lose respect for a product that smells like it\'s burning. You should be determining the threshold case temperature at which outgassing becomes noticeable, via olfactory sensing, and see if reducing temps by half, with proper derating for ambient, does anything for you.
Vitreous enameled resistors would be best for not outgassing. Silicone
or whatever would be worse.

Wirewound resistors tend to run at crazy temps, like 270C, at full
power. I wouldn\'t want to scorch the PCB.

There are some nice DPAK power resistors that could be clamp mounted
on heat sinks, which would provide a lot of surface area.

https://jlcpcb.com/help/newsdetail/62-JLCPCB-Direct-Heatsink-Copper-Cored-PCBs-Available-Now!