Can anyone recommend a bench power supply?


Binky

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I've been getting into electronics tinkering (arduinos, pretty leds, mutilated keyboards and a reverse geocache box) recently, and have been increasingly annoyed by my lack of a proper bench power supply.


I've been using adjustable wall-warts. batteries and voltage regulators, and an aged variable transformer. but this is getting annoying.


I know there are a few electronic engineers on these boards so though this might be a good place to find suggestions.


My provisional criteria are:

  • separate Volt- and Ammeters (preferably analogue)
  • minimum max. voltage of 24V
  • minimum max. current 3A
  • two outputs
  • enough safety features that neither the supply nor the project will explode (or release their blue smoke etc) if/when a short occurs
  • well enough built that it won't release blue smoke in the course of normal operation
  • no expensive advanced features not on the above list (which I may add to in the light of any below posts)


I don't see myself going anywhere near mains voltage stuff, can't think of a use for USB/serial connectivity (atm - (what situations are such features useful in?) and have plenty of space near my workdesk.


Having said the bit about no expensive features), money is not especially tight, so if the consensus is that anything under £200 is rubbish (for example) I would probably be prepared to buy a £250 unit instead of a £150 model.


Please do post anything you think of, as I don't know much about the market, so obvious points or links to (good) web resources would be most welcome :)
 
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TrashyMG

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I'd check Mouser or RS Components both should have good quality Bench Power Supplies..


I have a two dual bench power supplies and two single, but these were handed to be by my father who is a retired electrical engineer and didn't need them any more.. All of mine are old ranging from the 60's to early 80's they have analog meters and such.. So I don't really know who is the best manufacturer is and what not..
 
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T.T.

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Honestly, building one yourself is quite easy, the lm317 regulator is a good start if you only need 1 amp, but you want 3 so the lm1084 would be a good choice as it can handle five amps. Both of these regulators are variable by the way. The lm1084 would easily handle what you need. For the separate outputs, you'd have to use two regulators. as for the safety, fuses and circuit breakers are your friend :)

I built one as you described, I use it often, and it only cost me about 40 USD (I did have a spare transformer laying around thought)
 

TrashyMG

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You want a Transformer with a slightly higher drop down voltage than 24V since the diode bridge will cause some voltage drop..

Just a quick look through mouser, this transformer looks promising, 28VAC out, rated for 3amps according to the spec sheet... link on mouser. ~45 bucks, but the rest of the parts would be trivial in price. 

Another option would be is to take it from something like an old stereo head unit.

Edit: that was a quick search, I could of prob spent another 20 minutes finding a similarly rated transformer that was cheaper.
 
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Binky

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Hmm.

Building my own does seem like a good idea, given the huge potential savings...

I might ask round friends to see if they have any transformers lying around :)
 

urjaman

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I'll note that if you use a linear regulator like that and use it to provide lots of amps at a low voltage you will need a huge heat sink. Eg. 5V 3A from 28VDC supply gives 23V*3A => 69W of heat to dissipate. Maybe consider switching regulators. (Or atleast one switcher... there's a lot of variations you can do.) 
 

T.T.

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You are right there, but I will note that with my own supply, a heatsink from a computer northbridge and a small fan is enough for me. (though I don't think I've ever drawn more than 1 amp for extended periods of time)
 

Binky

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<Binky> Are any of the EE peoples here?
<aTc> why...
<Binky> You might be able to give advice on bench power supplies
<Binky> TrashyMG thinks I should build my own bench power supply
<aTc> yeah. something that plugs into the mains is always a great first project
<urjaman> I thinks that it is a lot of work
<aTc> not only that, but it costs you more in parts than a reasonably built one will cost
<Binky> Also, although I could probably build something that worked, I doubt it would be as reliable as a comercial unit.
<aTc> and it would look like crap :)
<urjaman> I'm mostly worried that it might not be entirely short-circuit safe
<Binky> I wouldn't know whether it was my supply, or my next project that wasn't working
<urjaman> like the way you can adjust an exact current limit with a proper bench top supply
<Binky> To sum up the  last few lines: I should fork out on a commercial unit... but which one?
<aTc> http://www.eevblog.com/forum/reviews/vellemanhq-power-ps1503sb-%28mastech-hy1503d%29-review/
<aTc> is the cheapo one i have
<Binky> Is it effective?
* Binky goes and reads up on it...
<aTc> it does everything fine.. it's just that it's a cheap one, so the terminals are just plug in things, no separate ground connector, and only a 1 turn voltage/current knob
<aTc> and just 1 on/off switch for the entire thing
<aTc> but at least it doesn't overshoot when you turn it on
<Binky> How much did it cost you?
<aTc> think it was 50 euro
<aTc> it's good enough for most basic stuff.. and if you find you need something more advanced you just get a more expensive one, since you can't have too many psus :)
<DJWillis> Yep, get lots of good bench PSU's, they are far to handy to have.
<Binky> What are the worst pitfalls with PSUs?
<DJWillis> Binky: if you want to chance it you can get very good PSU's S/H from the likes of eCrapBinBay
<Binky> Or anything to avoid generally - I don't want to end up with something worth less than I paid for it..
<DJWillis> Binky: poor build quality, flux in current and voltage outputs. General crapness, if it seems cheap and nasty it is 99.9% of the time, esp. if you are entrusting it to your fancy boards.
<DJWillis> Binky: some of mine are 25+ years old and working very well. Some a lot newer.
<dreamer> Binky: I only ever need 3 and 5V. have a breadboardable plug for that
<Binky> Is there a way to detect poor construction without either hunting for reviews or actually finding one to fiddle with in a shop?
* Binky does things with model railways at 12V
<Binky> or 16V
<dreamer> aha
<dreamer> a true 'hacker' then ;)
<Binky> or 16V PWM square-wave AC
<dreamer> you should figure it out yourself then
<urjaman> And I was going to say that I actually never provide digital logic power from a PSU directly
<DJWillis> Binky: Well I have always found Farnell's own PSU's to be very good. I use one of my old ones to put out enough current to run my Dad's train setups (fair bit of 00 and Zero One looking after trains ;) )
<urjaman> I mean an adjustable PSU. I do have 5V 1A SMPS plug for breadboarding
<Exophase> I like the Agilent PSUs at work but what do I know ;p
<Exophase> Those are probably pretty expensive.
<DJWillis> Exophase: yep, but very good. Just looked at what some of my PSU's go for on eBay, ouch, feck :eek: . Well that is worth more than I would ever pay ;)
<urjaman> I cant even recall what we have at work but they're good and propably expensive too
<Binky> has anyone else tried getting thier head around Digital Command Control?
<DJWillis> Binky: http://www.ebay.co.uk/itm/Bench-Power-Supply-30v-Farnell-/281043045474 is like the older style ones I have. Upto 30v at a good few amps and pretty accurate after many years ;) .
<Binky> Nice analogue meters :)
<Slaeshjag> I got a $30 bought in china with all labels in chinese
<Slaeshjag> What do I win?
<Slaeshjag> http://old.slaeshjag.org/filmskit/mov00758.3gp <- this is what it does when it starts
<DJWillis> Binky: DCC, only messed with the Hornby varients but not a train nut ;)
* Binky is halfway through building a DCC controller
<DJWillis> Slaeshjag: Good show.
<DJWillis> Binky: well http://www.ebay.co.uk/itm/Farnell-Dual-Power-Supply-PDD3502A-/140900115767 will get the current round the track fine, just did not realise it was worth remotely that much ;) . Now to sell mine :eek: .
<Cloudef> ah, you mean m.youtube.com
<DJWillis> Binky: does a Pandora feature in your DCC ideas/messing?
<Binky> Not yet - one arduino, one picAXE
<DJWillis> Binky: :)
<Binky> Does this look like a good buy?     http://uk.farnell.com/jsp/displayProduct.jsp?sku=1470313&CMP=e-2072-00001000&gross_price=true
<DJWillis> Binky: What sort of current will you need around the whole track?
<Binky> There are a lots of suspiciously similar 30V/3A PSUs on the market...
<Binky> http://uk.farnell.com/jsp/displayProduct.jsp?sku=1836056&CMP=e-2072-00001000&gross_price=true

Edited for relevance, readability, spelling etc
 
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TrashyMG

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<Binky> TrashyMG thinks I should build my own bench power supply 
Actually to be fair at first I pointed you to expensive quality bench supplies used in the Industry..

I only chimed in with building advice after T.T. suggested it..

Well aTc in his god like sarcasm does hit a good point, this may not be the best first project.. I figured you may of had enough electronics experience to handle a power supply.
 
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Binky

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<Binky> TrashyMG thinks I should build my own bench power supply 
Actually to be fair at first I pointed you to expensive quality bench supplies used in the Industry..


I only chimed in with building advice after T.T. suggested it..


Well aTc in his god like sarcasm does hit a good point, this may not be the best first project.. I figured you may of had enough electronics experience to handle a power supply.
True - I should have mentioned TT as well :unsure:

<Binky> Also, although I could probably build something that worked, I doubt it would be as reliable as a comercial unit.


<aTc> and it would look like crap :)
aTc isn't quite right here - have access to a laser cutter stocked with pretty, translucent acrylic paneling - So I could probably build a decent case with that

I'm still considering things, but my current leaning would be to buy one, because I have far to much stuff to do atm, and (given my luck)  it wouldn't be finished until after I needed it.

----

What do you think about the last two links mentioned above?
 
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TrashyMG

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The TENMA 72-8690 seems to have everything you need,dual supply, the current rating you were looking for. The DIGIMESS(unfortunate name) seems okay as well, it claims to have two outputs.. It must be in back of the supply, as it looks to only have one output in the front which doesn't seem that convenient.

A quick search on the web it seems both companies make both affordable and more higher end supplies.

If I had a choice between the two I would go for the TENMA 72-8690.
 
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Binky

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It looks like many of the units only have one voltmeter, and one ammeter - I might have a look to see if there are any with dedicated meters for each channel.
 

T.T.

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any you find that have a dedicated meter for each channel will probably be expensive. Something I just realized though, you could get a dual rail power supply with only one meter, and put the second one in yourself.
 

TrashyMG

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It looks like many of the units only have one voltmeter, and one ammeter - I might have a look to see if there are any with dedicated meters for each channel.
Well that Tenma has two Meters, one for each output and both Meters can be toggled from Voltmeter mode to Ammeter mode.

It maybe paranoia on my part, but I've never truly trusted a meters on Power supplies, even the Digital ones.. I tend to always double check with my fluke meter before applying to my projects.
 
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Binky

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Hah.

It sounds like they're little better than what I could make - I should probably do some more detailed research <_<
 
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