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load bank puzzle

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.

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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.

Reply to
John Larkin
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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?).

Reply to
Clive Arthur

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

Yes why not.. 'SSR' == solid state rectifier ? you mean relay? You get AC as input right? oh wait you mean sold state relay.... googling SSR gives among many things Wikipedia with "Soviet Socialist Republic"

We use rectangles as resistor symbol here :-)

My setup:

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uses test leads with alligator clips to switch configuration.

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. We will see where it goes now...

Reply to
Jan Panteltje

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

Reply to
John Larkin

So far, a Variac and big resistor on the output is a possibility. Or, a few paint cans full of oil, with rotary switch and immersed lower-watt resistors (Cantenna style), could work.

But, 'load' for even just a battery test can be anything from 1 ohm to hundreds, just for the batteries in my household; the only easy way to make the load you want, is to specify it first, then build one. That means the 'load board' is a connector plenum, and the loads would be plugins to that, plucked from a bucket of prebuilt options.

Eight-channel is easy: design one, build eight, and strap 'em together.

Reply to
whit3rd

fredag den 17. marts 2023 kl. 17.58.53 UTC+1 skrev John Larkin:

8*10W is going to require quite a bit of cooling

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;)

Reply to
Lasse Langwadt Christensen

Yes.

Quaint olde world customs.

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.

Most people think eating is good.

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

Reply to
John Larkin

I was thinking of kink-leading some axial wirewound resisors like they do. We'll have a lot of air flow so the cooling should be OK. Wirewound resistors can get very hot.

Reply to
John Larkin

Not on a PC board. Variacs are AC devices anyhow. Big and expensive.

This will be a product, a plugin board to a rackmount instrument.

Reply to
John Larkin

Board assembly houses should have the lead crimpers. I believe it only works with tape reel packaging. Could be wrong but check with the vendor.

Cheers

Reply to
Martin Rid

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

Does the driver really care?

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.

RL

Reply to
legg

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

Stored energy pumps current into flyback diodes or equivalent.

It certainly might.

Oh, they are just a biggish aerospace company.

No bid? Is that a good business model?

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Reply to
John Larkin

fredag den 17. marts 2023 kl. 22.13.01 UTC+1 skrev legg:

sure it can slow the current rise like an inductor but it won't keep the current flowing after turnoff

Reply to
Lasse Langwadt Christensen

clever idea using the user's arse as a power monitor.

Reply to
Tabby

sometimes it is.

Reply to
Tabby

I thought cows made methane which is a worse greenhouse gas than CO2.

Reply to
John S

Not good idea. Rheostats get hot. and ferrite rods tend to have a low Curie temperature.

Manganese-zinc ferrites have Curie temperatures from 120°C – 300°C.

Reply to
Anthony William Sloman

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

Sylvia.

Reply to
Sylvia Else

On a sunny day (Fri, 17 Mar 2023 21:36:10 -0500) it happened John S snipped-for-privacy@invalid.org wrote in <tv3831$20nan$ snipped-for-privacy@dont-email.me:

Yea, those CO2 or climate fear mongering idiots are against everything

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We should kill all dogs? those make CO2 too. and dogs shit everywhere.

It is all about selling snake oil. What needs to happen is build more nuclear power plants so we can create our own environment to keep inhabiting our locations. Heating, aircos, shelters.. But the brainless a-technical paranoid greta thunberg clueless crowd is the advertising agent for climate crap sellers.

Climate change is caused by earth orbit variations:

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Reply to
Jan Panteltje

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

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. 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.

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

Reply to
Jan Panteltje

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