Masteck linear supply, take two.

Those can sometimes be found at thrift stores for a couple of bucks. The old style, big PVC block with transformer and linear regulator in there.

I believe George was looking for something at the other end of the price scale :-)

That is my funzies name for Google (goo gull). I killed the joke by giving the hint in ().

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Well any links are potentially useful. I'm really looking for something to recommend to customers. We have a few things that assume you have access to a nice power supply.

George H.

First we'd have to know what "things" means. For some things a Lascar switcher supply would be just fine, for others not so much.

Sorry, didn't get it the first time. Might be because I do not use Google.

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Yeah the present need is for a coil, R ~ 4 to 5 ohms, I'm not sure of L. (Helmholtz coil 20 AWG wire (maybe) three foot diameter, about 20 turns.) But other times it's just a lamp, LED with resistor, TEC heater/cooler. Most times we just expect them to have something. But some customers need their hand held.

George H.

If it has to be post-doc proof use a supply with a fixed output voltage. A 12V/1A switcher wallwart of something like that. Else they may fry stuff.

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Thanks Joerg. Making things post-doc proof is hard. (Those guys think they know everything :^) I've been emailing Mastech. It maybe some sort of short circuit protection in the 5003. Here's a new supply,

with short circuit protection disabled! (So you can set the current limit.)

George H.

That's exactly the one I have, but from Mastech. I can short the output terminals and set the current. It shows zero volts when I do that. In fact, I do this a lot.

Hey! I just bought two of those. John Larkin posted about those and his post led to a company that was out of stock. However, I found another company on Ebaay that had them. They appear to be linear. The switching from voltage-to-current controlled and back is not well done, but acceptable so far.

I'd like to hear of your evaluation as well.

John

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Hi John, Well it seems I bought the wrong model. (HY5003D) This one apparently has short circuit 'protection' that is stopping it from working properly into a few ohm load. It sounds like Mastech will show me how to disable it. (and void my warranty) I'll let you know if it works. (I'm waiting on another email.)

George H.

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Success! (clipping out diode V17) No short circuit protection.

I can now set the CC limit with a short! (or put 100mA into a few ohms, what a concept :^)

George H.

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Now why is that called "no short circuit protection"? It still limits the max current. I had that happen a few days ago. Something fell over ... TUNGGGG ... the Mastech supply limited the current and nothing exploded.

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You really missed your calling, Joerg. You should have been a sound effects guy for movies.

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Yeah I have no idea. I'm just repeating what Mastech said. At my place of work we all agree it's silly. And besides which (as far as I could tell) the circuit didn't detect a short circuit. It just shut off the output when the voltage fell below ~1.5 Volts. My guess is some pointy headed manager heard about short circuit protection and told the engineer to add it. Maybe we'll see more Mastehc supplies with the short circuit protection disabled. It'd be nice if we didn't have to open up the case, clip the diode, (and loose the warranty) before shipping it to our customer.

George H.

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Can't you just heat one leg of the diode, pull it out, and when a warranty case manifests itself whistle innocently and solder it back in?

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Hmm, Is the innocent whistle going to fool St. Peter? :^) But seriously I haven't thought that far ahead. I assume we'd have to pay the shipping for the warranty service. For a $100, several pound item it may just be easier for us to eat a few warranties. It was nice of Mastech to tell me how to disable it. And I sent Sean at Mastech a 5 ohm/ 25W resistor, so he could check the 'crappy' short circuit protection for himself. Maybe he'll allow a 'non warranty' return? Hopefully they'll all just keep working for at least a year and it won't be an issue.

George H.