What Bench PSU for Beginner Hobbyist on a budget ?

[LeWidget]

Hi Guys,

So some time ago I converted a PC ATX PSU into a bench PSU, but was told at the time, it probably wont make a good testing PSU as it wouldnt be all too reliable.

My main uses (at this stage) would be electronic repairs. Would be nice to connect a device that has no other power source (ie. dead battery, lost power adapter etc..) too see if it's working and test etc..

I know there's probably a couple options here, either buy one... or build one.

I don;t mind building, assuming is something a beginner can handle... but what about buy? (new or used).. is there anything out there or would building work out a lot cheaper ?

I dont have a large budget.. maybe $100 (might be able to stretch to $150)

I found this one on ebay

http://www.ebay.com.au/itm/New-30V-5A-Variable-DC-Power-Supply-Digital-Display-Lab-Grade-Adjustable-/111280062283?hash=item19e8ceff4b:g:hsIAAOSwEetV794i

I know it would be a chinese PSU and it doesnt have a voltage lock .. has anyone, or Dave, done a review on this? Really not sure on quality..

I was originally going to see if I can convert the 5v rail on the ATX PSU to 3.7v (to test a phone I have) ... but (maybe someone can correct me if I'm wrong) .. if a ATX PSU is too unreliable to provide a steady-state of Voltage to a device.. that means there's a chance of voltage spikes = damage to components.. or voltage drops = unreliable to test components effectively, causing device to reboot or power off ?

The PSU in this video looks nice.. can't make out the brand though..

https://youtu.be/3GW7IYQcODY?t=3m20s


Any suggestions would be super.

 

[Simon]

You could build a linear regulator to follow on from your ATX supplies 12V rail

[LeWidget]

You could build a linear regulator to follow on from your ATX supplies 12V rail

To make it a variable voltage PSU, would I have to attach a Variable Voltage Regulator after the Linear Regulator (i.e. PSU > Lin Reg > Var Volt Reg ?)

[johnkenyon]

You could build a linear regulator to follow on from your ATX supplies 12V rail

To make it a variable voltage PSU, would I have to attach a Variable Voltage Regulator after the Linear Regulator (i.e. PSU > Lin Reg > Var Volt Reg ?)

Depends how variable you want to make the output. A variable voltage regulator should give you something like 1.2v to (Vin - Vdropout), continously variable with a pot.

If you want to have a switched variable output, use a 3v3 regulator and then lift the ground pin voltage with diodes. For example a 3v3 regulator with a reverse biased 4v7 zener between the ground pin and the 0v rail will give you 3v3+4v7 = 8v out.

A google for "low dropout variable voltage regulator" throws up the LT3083 which will supply 3A (if your upstream PSU is capable).
Low drop out means that you can get a higher maximum voltage output.

[MarkF]

I have a few HP 6216A power supplies (25V @ 400mA).  Nothing fancy but you can connect two in series or parallel for +/- voltages or higher current.  If you watch eBay you should be able to pick them up for around $50 shipping included.

[AustinTxBob]

I did one of these http://www.amazon.com/Elenco-Triple-Output-Power-Supply/dp/B0002DT0GU and it seems to be working for me on the cheap.  Here's a build and some mods. http://www.n5ese.com/xp720.htm

[LeWidget]

Thanks john

Not sure of half of what you said lol, but Ill google for the low dropout info you suggested

As for how variable, I dont think I'd need anymore than 25v output.. most of what I want to connect to it would probably be <10v (smaller electronic devices.. testing devices without a battery etc..) .. Im not sure on the requirements for larger items.. such as laptops/lcd monitors etc.. probably won;t get around to looking at those sort of items.. but good to know I can if I need to... main thing with those is how much Current they will pull..

@MarkF: I had a look, but I didn't see any in Australia, just the U.S.

@AustinTx: Thanks for the links.. they look good , How much in parts did it set you back? Did you get a PCB made for it or just use breadboard ?


Think I found that PSU from youtube I mentioned a few posts back...
http://www.goodluckbuy.com/best-1501da-15v-1a-led-display-stable-voltage-dc-power-supply.html

It's only 15v 1A .. seems low..

Thanks

[Photon939]

My suggestion: watch ebay - awesome deals come up for bench power supplies all the time. The big names like HP/Agilent/Keysight tend to attract higher premiums.

I suggest looking at used Lambda bench PSUs. They will be 10x better quality than any china clone-of-a-clone and will probably cost the same or less. (although seeing that you're in AU the market probably isn't quite as good) Keep your eyes peeled though and you should be able to find a steal.

Example:
http://www.ebay.com/itm/Lambda-LH-128-FM-Regulated-Power-Supply-A98-/272161589504?hash=item3f5e184900:g:5gwAAOSw5ZBWOr6Y

http://www.ebay.com/itm/8681-LAMBDA-LPD-422A-FM-DUAL-REGULATED-POWER-SUPPLY-0-40V-1-0-AMP-/401081987832?hash=item5d625972f8:g:kmQAAOSwx-9Wu0e~

[AustinTxBob]

Thanks john
@AustinTx: Thanks for the links.. they look good , How much in parts did it set you back? Did you get a PCB made for it or just use breadboard ?

The complete kit was $70.

[KL27x]

I have tried to save size as much as money on a compact $40.00 generic bench PSU. It died within a couple of months. The voltage starting to drift way high when it heated up.

I spent a little more on a Korad, which Dave does a review of. It has been doing the job for a couple of years, now, and I'm fully satisfied. 

If you want to have a switched variable output, use a 3v3 regulator and then lift the ground pin voltage with diodes. For example a 3v3 regulator with a reverse biased 4v7 zener between the ground pin and the 0v rail will give you 3v3+4v7 = 8v out.

I'm going to teach you something so you never have to do this terrible hack, again, lol.
1. a 3.3V regulator can't go below 3.3V
2. an adjustable linear regulator such as an LM317, et al, usually goes down to about 1.25V.

3. even if a fixed linear regulator is all you have, adding diodes to it doesn't make it "adjustable." It means you "adjusted it." And considering the "resolution" of available diodes, you can hardly call it that, even.

4. If you want to increase the voltage output of a fixed linear regulator, all you have to do it wire it up like an LM317, using the ground pin as the "ADJ" pin. And in the formula, replace "1.25V" with w/e is the voltage of your fixed linear regulator. Just be sure to know that if the device package has a heatsink, this heatsink is now going to be at Vout minus the initial voltage rating... which is a stupid number (and same as result of your diode trick). But using potentiometer, at least this way your output is actually adjustable. Please, I want to hear no more of this terrible diode hack that I have heard of for at least 10 years.

5. If you want to make multiple fixed setting to switch between, again, this is way more tunable by switching in different resistors for R2... this is not a reason to use a 3.3V fixed regulator over an adjustable regulator. The diode hack will work just as badly on an adjustable regulator.

The only thing "special" about an adjustable linear regulator is that
1. the "fixed" regulated voltage is the minimum possible to increase the range of possible output.
2. the "ground" pin is called an "ADJ" pin. (In a linear regulator, the voltage is dropped in series... the "ground" pin is just a feedback pin. The regulator keeps the voltage between output pin and "ground" pin at the "fixed" voltage - in this case it's ~1.25V.)
3. the heatsink is in continuity with the Vout, rather than the "ground," since you're going to be raising this "ground" node above ground in most applications. And having heatsink at Vout is a lot more sensible than Vout minus 1.25V.

[Leiothrix]

My suggestion: watch ebay - awesome deals come up for bench power supplies all the time. The big names like HP/Agilent/Keysight tend to attract higher premiums.

The problem is that OP is in Australia.  These things are only rarely come up locally, and we're 230V so that limits the number of devices from US we can use.  Plus shipping from US tends to cost a small fortune.

These second hand devices are often listed as "for parts".  The device may be cheap enough to gamble on, but the shipping not so much.

[exe]

I would recommend korad 3005 and its rebages/rebrands (google it). But it is single output (I think three outputs/supplies are need for a lab). Can be bought from e.g., farnell (rebranded as TENMA 72-10480 and thelike, see the site). There are two versions: 3A and 5A. People don't recommend pushing it to the limit . Beefier version is reportedly better/more reliable.

Whatever you choose first check the tear-down and tests. Many cheap PSUs have problems with noise, overshooting, overheating, etc. I wouldn't buy anything without a proper review. And do not trust specs of cheap gear. Do not let your buying instincts get over you with "wow this cheap and awesome". Tear-down first!

You can also buy a kit like http://www.banggood.com/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-p-958308.html , add a transformer, a panel meter like http://www.banggood.com/Dual-Red-Blue-LED-Digital-Voltmeter-Ammeter-Panel-Volt-Gauge-Meter-p-918687.html and it will work. Can be upgraded with a ten turn pots But the kit does not include a heatsink and I found it troublesome to find something I could attach. Be sure cooling is sufficient because it's easier to blow the output transistor than it seems to be. Of course you need to add fuses as well. Anyway, for this way to go you MUST be sure you know what you are doing because mains is no joke. So if you have no idea what a transformer is and how to use it than it's better to skip this for now.

Last resort This one is a toy and is not really capable of anything, but still fun to assemble: http://www.banggood.com/DIY-LM317-Adjustable-Voltage-Power-Supply-Board-Learning-Kit-With-Case-p-964548.html . I keep it as a supply for breadboards. It hardly can fry anything

[Muttley Snickers]

That first power supply you listed for $73 looks like it would get you out of trouble for most stuff considering that my first variable power supply was a gift from an old radio amateur almost 30 years ago and only recently gutted and discarded not because it didn’t work but because it looked like a piece of crap, I must say although very basic it did serve me well for many years.

A few years ago I went on a mission to find both good schematics and components to replace it with a larger capacity variable power supply based around the original design which incorporated an LM723 in a can package and a couple of 2N3055s, I now have enough accumulated gear to build well over a dozen power supplies and have started the ground work on a couple yet none of them are finished simply because the variable part is now me.

Dick Smith at one point were clearing out some equipment and I ended up with a few Q1770s which are a rebadged Manson 0-30 at 2.5 Amp variable supply and these have been more than adequate for day to day tinkering, they were around $100 each and I only grabbed them because I knew that Radio Parts sold a similar model for around $220, I don’t need lab grade quality and these certainly aren’t and I have plenty of larger fixed supplies if the need arises but for general bench testing and tinkering the current limiting feature is a must have as others would know.

[GreyWoolfe]

I did one of these http://www.amazon.com/Elenco-Triple-Output-Power-Supply/dp/B0002DT0GU and it seems to be working for me on the cheap.  Here's a build and some mods. http://www.n5ese.com/xp720.htm

I didn't do the DPM mode on mine, but I replaced the pots with 10 turn pots, upgraded the caps and added over and reverse voltage protection.  I also added bleeder resistors to the smoothing caps.

[bson]

Used Elenco linear supplies can usually be had for dirt cheap off eBay.  Not the greatest, and the dials may need adjustment to be ballpark, but they work and come in a metal box.

[LeWidget]

Thanks guys .. at this stage, I think I might lean more towards a pre-built Bench PSU :/ .. I really have no-idea what I'm doing and my brain hurts reading some of the tech-lingo in the comments lol..

I looked into the Korad PSU mentioned.. but I've found posts/reviews of them failing.. even Dave's video failed.. maybe they were different versions ?

I checked out Farnell/element14 for the TENMA 72-10480.. http://au.element14.com/tenma/72-10480/power-supply-1ch-30v-3a-adjustable/dp/225194602 ... though 3a max ... just wondering.. I'm not familiar with power requirements.. what sort of devices would use more than 3a ?

Thanks again guys, really appreciate all the feedback

[MrSlack]

I just bought a Mastech HY1803D for not much cash and it seems up to the job of a basic bench supply. 0-18v, 0-3a current limit. Works pretty well. I did some mods to it avoid some future problems but that was it. There are literally loads of them available at various prices everywhere.

Details of mods here: https://www.eevblog.com/forum/testgear/mastech-hy1803d-power-supply-modifications/msg890251/

I reckon you could get away with it as stock with some thermal compound on the heatsink for at least a couple of years. It's made out of standard bits so it's easy to repair if you do blow it up. The main failure mode is the pass transistor shorting which is a 10 minute replacement job and it's a standard 2n3055.

They are linear and floating so you can buy another one and hit 36v @ 3A or +/- 18v @ 3A if you need to in the future.

[exe]

what sort of devices would use more than 3a ?

Not many (instruments?). 3A is enough for almost everything for a hobbyist (I mostly use mA range).  BTW, that Tenma is rebranded korad . They used to fail, they are not perfect, but quality matches the price. After Dave's review they improved a little bit. But they are good-enough for the price and easily available.

[BillyD]

I'd also recommend getting a basic prebuilt supply and the Tenma/Korad are ok for the money.
And don't forget that as well as adjustable voltage, units like this will give you adjustable current which is almost as important.
Plus voltage and current display.
3A should be enough most of the time, on the rare occasion you need more you could probably cobble something together from an ATX supply or somesuch.

[rdl]

There's a video where one of the newer version Korads (after the initial problems were fixed, which was long ago) was abused and they couldn't make it break. I don't have the link handy though, I think it was on one of Dave's other channels. I don't think there's anything better in that price range (well, new anyway).

[ledtester]

Newark has the Tenma 72-8335a for about $30 less than everyone else:

Newark Tenma 72-8335A

Pros: linear,  variable, triple output supply (2 variable, 1 fixed at 5V), current control, tracking

Cons: only goes to 24V and 1A per variable supply; current readout has 3 digits but only shows 10's of mA; control knobs are (from left to right): voltage-current-current-voltage which can be confusing when adjusting the second supply; note that the displays are (from left to right) voltage-current-voltage-current.

You can also connect the supplies in parallel for 2A current.

For low-power work (MCUs, op-amps, 555 timer circuits, etc.) the 24V/1A limit is not a problem. Having the dual variable supplies is esp. nice for dual rail op-amp circuits. Most of the time I set the current control to 30 mA and that has saved me from the magic smoke on at least a couple of occasions.

[vince53]

Since you're in Australia, ask Dave what he's got laying around he might want to sell.

Vince