Lab power supply - which of these would you pick?

[radian]

Hi all,

I'm looking for a cheap lab power supply to get my bench up and running. I'm mostly interested in using the supply for microcontroller-based projects, spinning up motors, etc. Your basic hobbyist projects I suppose. Ideally the PSU should be as quiet as possible. I live in Canada, so the selection of power supplies are a bit limited. From my research thus far, I think I've narrowed it down to three units:

1) 30V, 5A - $58 (https://www.circuitspecialists.com/i-181791.html). Looks like a decent option. I like the form factor. A bit worried about the maximum "8 hour continuous operation time", and the obvious lack of reviews, so no guarantee on performance. Seeing as how it's a switching supply, could be harder to debug if anything were to go wrong. Should be a quiet option.

2) 30V, 5A - $63 (http://www.ebay.ca/itm/30V-5A-Digital-Precision-DC-Power-Supply-Adjustable-Stable-Lab-Grade-305D-New-/121092425979?pt=LH_DefaultDomain_2&hash=item1c31abc8fb&_uhb=1#ht_2369wt_1305). A popular choice on eBay. There seems to be hundreds of these units for sale. I've read mixed reviews, but being linear, probably would be easier to debug if anything were to go wrong. May end up being quite noisy.

3) 18V, 2A - $50 (https://www.circuitspecialists.com/bench-power-supply-csi1802x.html). Looks like a Mastech rebadge. I've heard decent reviews on Mastechs. Nice that they include the circuit diagram, that's great. Not a fan of the output voltage and current, but I could live with it. Perhaps a silent option? No fan in the schematic that I see.

Thoughts? Which would you chose? Thanks!

[wraper]

A can say that second one is complete bullshit. Such power supplies don't even have proper current limiting, they just cut output. I teared apart one of clone of such and not only it was crap which doesn't meet specs. There was fake 2N3055 transistors. I cut caps from them and crystals were 5 time smaller than genuine ones. No proper cooling, there was no proper heatsink, just aluminium plate. Even transformer was without proper insulation and with aluminium secondary winding. These are just dangerous to use. I also think that first is not better claiming such specs for $58. Third one looks better. It has proper heatsink on the back and doesn't claim impossible specs. But I personally wouldn't take any of them.

[wraper]

Just read specs of the first one. It's switching PSU, Ripple: 200mVp-p. Maybe It will work normally and even meet specs but with such ripple it has no use in electronics lab.

[BillyD]

I have the first one as a secondary power supply, purely because its size and weight make it handy for swapping it between the table and floor to save space, and sometimes the fine adjustment knobs can be useful.
However you mentioned it should be as quiet as possible and this one is not completely quiet. As a switchmode supply it makes that high pitched whine which is very noticeable in a quiet room and personally I can only tolerate using it for short periods! There is also a fan which is noisy but which only activates when necessary, which is not often.

So for me the noise and ripple would make this unsuitable as a primary power supply, but ok as an occasional backup unit.

[eevblogfan]

here some good links :

1)  http://www.ebay.com/itm/ONE-Agilent-HP-DC-Power-Supply-6200B-6201B-6202B-6206B-6281A-6289A-YOUR-CHOICE-/140966231030?pt=LH_DefaultDomain_0&hash=item20d23dfbf6

2)  http://www.ebay.com/itm/HP-Agilent-6255A-Dual-Output-Variable-DC-Power-Supply-40W-1-5A-Opt-010-040-/130899265927?pt=LH_DefaultDomain_0&hash=item1e7a344987

3) http://www.ebay.com/itm/HP-Agilent-6200B-Single-Output-30W-Variable-DC-Power-Supply-0-40V-0-75A-20V-1-5A-/130899887179?pt=LH_DefaultDomain_0&hash=item1e7a3dc44b

4)  http://www.ebay.com/itm/HP-Harrison-Agilent-6205B-DUAL-DC-Power-Supply-0-40-V-0-3-A-0-20-V-0-6-A-/140949026671?pt=LH_DefaultDomain_0&hash=item20d137776f

5)  http://www.ebay.com/itm/HP-Agilent-Hewlett-Packard-6237B-Triple-Output-20V-5A-18V-1A-Power-Supply-/151025358390?pt=LH_DefaultDomain_0&hash=item2329d01636

6)  http://www.ebay.com/itm/Agilent-HP-6255A-Dual-Output-Power-Supply-0-40V-0-1-5A-/140962782704?pt=LH_DefaultDomain_0&hash=item20d2095df0

there are more but that's good enough in order to provide you what you need ,

I would have gone for at least 2A,15V~25V power supply , preferebly dual channel

DON'T YOU DEAR TOUCHING THUSE CHEAPIES "NEW" POWER SUPPLIES ! , they are real crap , you'll regret it for sure !

Cheers

[ve7xen]

Keep in mind the 6327 doesn't have adjustable current limit.

[eevblogfan]

hey

yup indeed , BTW . 6237*

anyhow - the power supply doesn't ment to be CC one , but simply multy CH CV power supply ( IE , It is ment to feed readily working devices like op amps and anything who needs dual tracking voltages )

[ve7xen]

Definitely a useful supply, but especially for a beginner or a careless person (like me), CC mode is invaluable and will save your project more times that you care to count.

[eevblogfan]

you are correct , BUT . CC project is nice and not too costy ( simplt mosfet op amp reference and some resistors caps and pot ) not to costy I'd say , BUT power supply is very costy . Why would you buy worse power supply *only* because it can have CC as well ? while you can get some wonderfule 3 CH power supply and simply upgread it to you're needs ?

[ve7xen]

Convenience. The same reason you buy a 3CH supply instead of 3x1CH supplies. It's nice to have it all in one box because it means you'll actually use it, reduces clutter and cabling, you can do interesting projects instead of building the same boring project 3 times etc.

Also if you put a CC limit regulator outside of the CV control loop it's going to have to dissipate power.

[radian]

Thanks for all the suggestions folks. I'll take your advice and pass on option 1 and 2. Option 3 I'll admit is still enticing. Eevblog fan, those used supplies look pretty nice, but the power handling is on the low side for my applications, and they look quite hefty. Current limiting is pretty important for me, as is digital displays.

What do you think of Atten power supplies? For instance, for a bit over $100, I could get this:
http://www.ebay.ca/itm/ATTEN-Variable-DC-Power-Supply-APS3005S-30V-5A-LAB-/160684423343?pt=LH_DefaultDomain_0&hash=item256989b8af&_uhb=1#ht_5607wt_1071

A decent buy?

[ivan747]

I have seen this kind of thread before. A new member wants to get a chinese power supply for under $100. Lots of people suggest used supplies. I go for the used power supply. Almost nothing can go wrong when you have a full schematic of the power supply. These chinese power supplies are just a piece of sh!t. And trust me, I don't say that phrase often. Don't be afraid to buy test equipment on eBay. With a $50 HP power supply form the 70's there's not much that can go wrong.

There's absolutely NO WAY you can get a 30V, 5A power supply (that's 150W!) in that tiny-ass heatsink:



You should at least have something that resembles this:


And that's a 30W power supply. Granted, it doesn't have a fan, but still. Have you seen how they mount heatsinks and fans on computer processors? Those only generate 100W tops, in most cases.

There is a reason why good new power supplies cost a lot. There's heaps of metal: iron, copper, aluminium (solid and bent) everywhere. They don't cut corners.

[Monkeh]

The heatsink does not have to dissipate 150W..

[c4757p]

Probably near 75W though at low output voltages and high output currents, and that heatsink isn't going to do 75W either.

I know that many (even decent) power supplies cannot handle driving a short for very long, but I still personally think it should always be operable within its specified range, and certainly not able to self-destruct. If it can't handle that kind of dissipation, it had better damn well have a thermal cutoff, and I can say from experience that those turds do not have one.

[staxquad]

The heatsink does not have to dissipate 150W..

The HP 6002A needs 480 watts input to supply 200 watts output.  So 280 watts of heat dissipation is required for 200 watts of output power.

[c4757p]

Does it really need 480W input for that, or is that just the listed power input? Those often seem to be quite pessimistic.

[staxquad]

Does it really need 480W input for that, or is that just the listed power input? Those often seem to be quite pessimistic.

[eevblogfan]

hey

OP - the reason I told you to but those oldi(SH) power supply is the quality , those "new" cheap atten or whatever is total crap , you better buy some HP6002 for higher power stuff rather then buying stupide atten , Ind I can tell you for sure that the atten transformer is about 100W , they are abusing the damm thing in order to squeez 150W out of it ( actually more like 172.5W on the AC side ) and I can tell you that within 1 Hr the transformer will be dead !

you better build your own HIGH power supply *just* for that particular project ( some PWM motor controller ? ) . you need only one microwave oven transformer ( MOT) and a bit of knowledge in order to rewind the thing and adding some 20 turns to the primary in order not tu freaking burn thee damm thing , and then build your own high power regulator , it can be very fun and I can tell you , it will be around 100$ or even less

Good luck

[ivan747]

The heatsink does not have to dissipate 150W..

The HP won't dissipate 30W either (it has 2 modes with 2 transformer taps). Still, it cannot dissipate a whole lot of power.

Edit: it can dissipate 30W, but I doubt the Atten will have more than 4 taps. (more taps means more control over the input voltage that goes though the pass transistors and more control over power dissipation). There are some traps in tap switching, specially if it is done by software. Just watch what happened to Dave with the Korad supply.

[nctnico]

Switching between transformer windings or using an SCR are very old tricks (also seen in HP power supplies). So a small heatsink may suffice.

[nctnico]

Does it really need 480W input for that, or is that just the listed power input? Those often seem to be quite pessimistic.

No. I have a HP6002A and it doesn't need 480W input for sure. It is a very efficient power supply which uses several windings for different ranges of output voltages / currents. It says 600VA max. on the rear but you can't thumb-rule that to Watts.

[radian]

Ok, thanks everyone, I'll steer clear from those cheap supplies! The used supplies are a good option, however shipping to Canada can be quite expensive. And as much as I like the vintage analog displays, I like digital a lot more. Especially when it comes to current being drawn.

Now, let's change gears a bit. I'm going to to dig deep into my pockets to get a better supply. I like Agilent as a brand, and I found this option of Newark/Element 14. They are offering a free shipping promotion, which will help a lot.

http://canada.newark.com/agilent-technologies/u8001a/power-supply-dc-bench-30v-90w/dp/14N3964

This is a switching supply right? Anyone have any experience with this line of supplies? I also noticed some Tektronix supplies for around $400.

http://www.testequity.com/products/2579/

And lastly, what about this Sorensen?

http://www.testequity.com/products/2928/

I think I won't mind forking over a bit more cash knowing I'll be getting something with high quality and that is properly engineered.

[c4757p]

(U8001A) This is a switching supply right?

They don't seem to directly say on the official web page, but with those transient response and ripple characteristics (and low-ish power rating) it's got to be linear.

[radian]

(U8001A) This is a switching supply right?

They don't seem to directly say on the official web page, but with those transient response and ripple characteristics (and low-ish power rating) it's got to be linear.

Ah ha, well this forum just keeps on giving! A fellow member posted a teardown here. https://www.eevblog.com/forum/testgear/review-teardown-agilent-u8001a-30v-3a-linear-power-supply/

Folks replying in the thread seems to have positive words, although it sounds like the supply is on the noisy side. Hmmm...

[wraper]

That Sorensen is actually Thurlby EL302R. http://www.tti-test.com/products-tti/pdf-brochure/psu-elr-exr-series-7p.pdf. Should be very good power supply.