High current bench power supply

djQUAN · May 4, 2014

This is not laser related but I just wanted to share my latest project.

I needed a high current power supply when testing car amps so I looked around for options. Bench supplies more than 10A are very expensive. I saw the RC guys use this Dell server power supplies for their hobby chargers so I got myself one and tweaked it for my purposes.

This is the powersupply nameplate

I needed a voltage and current meter but didn't have spare displays. I found I had the cheap hobbyking wattmeter so I tore it apart and used the board and LCD display. I also tore apart a broken cheap MP3 player and used the LCD backlight so that I can have a backlit display for the meter

It worked

I needed to make a plug to connect to the control pins of the server PSU. I used two row female pin headers and perfboard for that.

Here it is plugged in. I also soldered in 12ga silicone wire for the high current PSU output.

Instead of using the original 6" lenght of wire as the current shunt, I made my own using stainless steel plate which has a lower tempco compared to copper.

Here's the completed powersupply

This is the most power I was able to pull through it after some tweaks. But the tweaks kept on tripping the internal protection so I turned it down after taking this pic.

It can do short bursts well beyond the nameplate rating. I could have cranked the voltage up a bit more but the overvoltage protection kept tripping so I settled on a 13.55V unloaded output voltage.

if interested, more details of the build can be found here:
High current bench supply

ryansoh3 · May 4, 2014

Awesome job, thanks for sharing! :beer:

crazyspaz · May 4, 2014

Thats frickin awesome! Thanks for sharing, indeed!

djQUAN · May 4, 2014

Thanks guys. I wanted to have an output voltage of 13.8V or even 14+V but beyond about 13.6V the PSU kept on going into protect so I had to settle with 13.55V.

I believe it was rated at only 700W but was surprised when I was able to pull over 1kW from it. It got pretty hot though

but it didn't blow up.

crazyspaz · May 4, 2014

im sure theres a way to disable that protection circuit...althought its probably there for a reason

rhd · May 4, 2014

How do you accomplish the variable constant current regulation? I assume it is constant current?

DashApple · May 4, 2014

rhd said:
How do you accomplish the variable constant current regulation? I assume it is constant current?

I though server PSUs are constant voltage with voltage sensing at the load to compensate for drop over the supply lines ,

Cyparagon · May 4, 2014

rhd said:
How do you accomplish the variable constant current regulation?

There's no current limit in these, to the best of my knowledge. They just shut down if the current gets too high. Besides, car amps will get pissed if you try to operate them in constant current.

djQUAN · May 5, 2014

Yes, this operates in constant voltage output. It doesn't have a sense line so there's no way to compensate for the line drop.

If there's an overcurrent condition, it shuts down. When the voltage goes above or below an operating window, it shuts down. You'd have to cycle the power switch for it to turn on again. If the problem is still there, it shuts down again.

During bench testing, I connected a headlight lamp as a load (with high and low beams in parallel) and at cold start where the filament is basically a short circuit, it won't turn on. After the second attempt, it turns on as the filament warms up and resistance increased.

rhd · May 5, 2014

Cyparagon said:
There's no current limit in these, to the best of my knowledge. They just shut down if the current gets too high. Besides, car amps will get pissed if you try to operate them in constant current.

Reading on my phone, I missed the car amp part.

It would be great if someone made a constant current controller that could plug into a high current (but constant VOLTAGE) 12V PSU as the input.

12V 50A power supplies are ~$75 (or less). If you could stick a simply linear constant current controller on the output, you'd have something that could handle 50 Amps for the price of a bench supply that would do 5.

Hemlock_Mike · May 5, 2014

SUPER !!! Now find a water cooled laser bar head
and show us the power!!! Good Post!
HMike

Zeebit · May 5, 2014

Pics 2, 4, 8, 9 and 14 on your site are giving me a 404 error.

djQUAN · May 5, 2014

That's weird. I just checked and forced refresh and it all comes out fine both at home and at my work PC.

Meatball · May 6, 2014

Do you have any AC coupled scope measurements on the voltage rail noise? To add CC, one could use the expanded LM317 with any number of pass-bank transistors. Just don't expect fine resolution adjustment on the order of mAs. Plus the output current would be temperature sensitive. Cold start current output would differ from the long run steady state setting.

But, I'm sure there are better ways to do CC off a large supply.

djQUAN · May 6, 2014

Put a ton of AMC chips in parallel.

Kidding aside, to add CC mode, I would either use an op amp driving a large passbank and measuring current through a low ohm resistor (very inefficient) or use the op amp to control the PSU feedback (more difficult)

djQUAN · Aug 4, 2014

I read reviews of the wattmeter online and the comments were all the same. It dies after a short while of usage. I said to myself, mine's still working good so I must be lucky.

NOT! The display went blank and didn't work anymore. :wtf:

So I went to DX and bought a combination panel meter with both volts and amps in one unit. But DX seem to forgot that it should include a shunt and mine didn't have one. Going to wait for the 2nd batch of the shipment before issuing a complaint.

Here's the powersupply taken apart ready to take a new display unit