help troubleshooting bench power supply - Page 1
Forum section: electronics / projects

author: photonpunk
author_rank: Regular Contributor
timestamp: February 28, 2014, 03:33:29 am
content: I've been using a circuit trainer as a makeshift variable power supply for years, but I'm trying to put together a nice little lab now (on a budget), so I finally broke down and bought a vintage 30v power supply off ebay. I figured for the simple projects I typically work on, it would be sufficient. And after changing out the fuse, it powered on and successfully powered a led.Problem is it wont power anything that requires more than a couple volts. The needle wont even move if I try. Only thing I can get it to work on is leds at this point. Instead of troubleshooting it, I set it aside and just bought another cheap vintage power supply. But it had the exact same problem. Is this common? I haven't taken them apart yet, but what should I be looking for here? I'm more of a software guy, so troubleshooting circuits is new to me.

author: Rigby
author_rank: Super Contributor
timestamp: February 28, 2014, 03:50:14 am
content: makes & models?

author: photonpunk
author_rank: Regular Contributor
timestamp: February 28, 2014, 12:59:42 pm
content: Quote from: Rigby on February 28, 2014, 03:50:14 amThe first one I bought is a "Kepco ABC 30-0.3".The second one only says "Eico" on it. No model number. But the ebay listing says it's a model 1020.

author: photonpunk
author_rank: Regular Contributor
timestamp: February 28, 2014, 01:08:44 pm
content: Here's what the Eico looks like:http://www.radiomuseum.org/r/eico_transistorized_power_supply_0_30_vdc_1020.htmlAnd the same model Kepco on ebay:http://www.ebay.com/itm/KEPCO-ABC-7-5-2M-POWER-SUPPLY-/301084037255?pt=LH_DefaultDomain_0&hash=item461a01d087I tested it with my multimeter, and the voltages are good all the way up to 30v. Which makes me wonder, is it possible it doesn't have the current to push those volts out?

author: Rigby
author_rank: Super Contributor
timestamp: February 28, 2014, 01:41:39 pm
content: Yeah, it depends on what you're powering. Check that your current limit isn't set too low. In the case of the Eico, you will probably have to set it to the 6V scale to get any current. If you have an ammeter see what you can get out of them at all scales and voltages and perhaps plot that out on graph paper.In the case of the Kepco, make sure the short circuit current isn't set low, and use an ammeter to work out if maybe the meters are lying to you.

author: madires
author_rank: Super Contributor
timestamp: February 28, 2014, 01:58:12 pm
content: I'd assume that the Kepco ABC 30-0.3 delivers up to 0.3A which is not much. About the Eico 1020 I found following athttp://www.nostalgickitscentral.com/eico/products/test/1020.txt:EICO Model 1020 Power SupplyProvides continuously variable 0-30 vdc.Current range:150ma from 0-12v200ma from 12-24v300ma from 24-30vIf the load pulls more current than the PSU is able to provide (or set by the current limiter) the voltage will drop. If you're just doing low power stuff those PSUs might be fine but for the common usage I'd recommend something with 30V and 3A.

author: photonpunk
author_rank: Regular Contributor
timestamp: February 28, 2014, 02:12:00 pm
content: Quote from: Rigby on February 28, 2014, 01:41:39 pmI'll try this after work tonight. Thanks.

author: photonpunk
author_rank: Regular Contributor
timestamp: February 28, 2014, 02:14:05 pm
content: Quote from: madires on February 28, 2014, 01:58:12 pmI'm sure I'll upgrade later, but putting even a simple lab together is costing me a fortune, so I was trying to save a little money where I could. The things I normally work on don't require much power so I was hoping this would work for me for a while.

author: Rigby
author_rank: Super Contributor
timestamp: February 28, 2014, 03:09:14 pm
content: Well, one way you can get an inexpensive power supply that will work for most things (and has more than enough current) is a PC ATX power supply. They're not linear, so there's high frequency noise in them, but if you're just starting it is unlikely that you will suffer a problem because of this. They're inexpensive, deliver lots of current, but don't usually have any built-in current limiting beyond their normal failure modes.SeeedStudio has a handy way to wire them up:http://www.seeedstudio.com/depot/s/ATX.html.You can get banana terminals from Radio Shack if you want to build something like this yourself rather than buying.If you need, for example, 9V instead of 12 or 5, get some buck converters from eBay:http://www.ebay.com/itm/5Pcs-DC-Buck-Converter-Adjustable-Step-Down-Breadboard-Power-Module-1-25V-36V-5A-/221383752891?pt=LH_DefaultDomain_0&hash=item338b7ffcbbhook them up to GND and +12V and adjust them for 9V. If you order from China they are far less expensive, but will likely take longer to arrive. A similar search for 'boost converter' will get you adapters that step up voltages so you get more volts out than you put in, but at less current. None of these little cheap dudes should be driven at more than 1A, though. Some will say 3A or 5A but if you drive them at 3A for more than a minute you're going to have a very, very hot board on your hands, if the chip survives that long.Lowe's & Home Depot also have wire, alligator clips and banana plugs if you want to make your own leads. They don't have the silicone coated wire that most leads use, though, so homebrew leads without silicone insulated wire are stiff and unforgiving, unlike like real leads, but they are inexpensive to make.So, does that help?

author: photonpunk
author_rank: Regular Contributor
timestamp: March 01, 2014, 09:54:14 pm
content: Adjusting the short-circuit level seems to have done the trick on the Kepco. The Eico is being stubborn. But, having one working is enough for now. Thanks for the help.