(Yet another) My First Power Supply Question

[paulca]

I watched Dave's review of the cheap, cheerful DPS3003 style buck power supplies.  He sold me on them, until I actually speced one out to buy.

My use cases are basic electronics beginners stuff and Raspberry PI stuff were USB 3.3V/5V would be fine, but I also have ambitions for battery charger style circuits that would require 15V and the ability to test a 3A or 4A constant/limited current regulation circuit.  So a 30V, 5A PSU sounded ideal.

Buying for a UK seller the DP3003 30V 5A version are about £30.  Great.  However, the still require a DC power source.  That's where it all falls apart.  I simply cannot find a domestic wall-wart that will produce 30V and 5A.  The best I can find is a laptop PSU that delivers 24V and 4A and it costs £35.

Now on Farnell I can buy a professional single channel 30V 5A bench supply from Tenma for about £70.  I can get a two channel PSU for £110.

The only use case I can see for this cheap buck converter PSU is to run one or more of them in parallel off the bench supply.   So I could power two or more of the cheap PSUs from the expensive one, rather than buying the more expensive 2 or 3 channel bench supply.  Does that even work, considering impedance and what not?

Thanks,
Paul

[danadak]

You can only parallel supplies if they have current sharing circuits
built into their architecture. That architecture usually has another
pin shared between them to effect the sharing control so that one
supply is not overloaded.


Regards, Dana.

[glarsson]

You can't power two or more if these stupid modules from the same power supply. The reason us that they have their current sense on the low side and if you connect the low sides together (as we do when we for example need +5 and +12 for the same circuit) then the power senses will be shorted. You will still get your voltages but the current limiting will be disabled. Only use one power supply (isolated) for each module.

Also, verify that the high ripple/noise of the modules are acceptable to you.

[Ian.M]

http://www.google.co.uk/search?q=220V+36V+5A+PSU&tbm=shop
There's quite a few cheap options to power them, just not in a wallwart form factor.

[StillTrying]

"Buying for a UK seller the DP3003 30V 5A version are about £30."

You can get the DPS5005 50V 5A version for less than £30 from the UK.

"require 15V and the ability to test a 3A or 4A constant/limited current regulation circuit.  So a 30V, 5A PSU sounded ideal."...."24V and 4A"

24V @ 4A should easily give you 15V @ 5A, but as glarsson has just said, both sides +/- of the input supply has to be floating compared to everything else.

[paulca]

I'm a little indecisive now.  I can go for:

Cheap Chinese DC/DC module + cheap chinese AC/DC PSU and hope it works, costing about £40-50.

Or I can go for a proper supply like this:
http://uk.farnell.com/tenma/72-10495/power-supply-2ch-30v-5a-adjustable/dp/2251947

The indecision is that if I play about with things for a few weeks and then it all ends up on the shelf unused the £120 would be a waste.  However the PSU would be a good investment if I carry on through the years with electronics.

I did the same with the DMM I bought.  Hmmm'd and Haa'd and watched reviews and show downs and tried to decide on a £120 Fluke or a cheapo (in the end I aimed in the middle with an Extech).

Decisions decisions.

[StillTrying]

If you need 2 voltages and it's always going to be mains powered anyway, I don't think the DPSs are going to be much use to you.
I think that 2 channel tenma is going to be hard to beat.
You could probably get a 30V 5A, and a 18V 2A for around £95 total.
http://www.circuitspecialists.eu/power-supplies/bench-power-supplies/

[Terry01]

Get the Tenma from Farnells buddy. I got the 30v 5A one your thinking about. It's a great supply for hobby stuff. I also really like the UI too,easy to use and has all the safety stuff you could want.

I have a boost/buck 35v 6A that I was sent as a mistake when I ordered a capacitor pack. It's I my desk drawer and I use it very occasionally,I use the Tenma nearly every day. Don't forget to order leads to connect to the supply.

Hope you get what your after.

[ManuelMcLure]

Another option is to get the boost/buck module (DPH3205) and use a 12V 15+A power supply for the input. I like old server power supplies - for example the HP DPS-600PB (12V 47A) are available for $20 shipped and can easily have their outputs floated if needed - RC enthusiasts commonly put a couple of these in series (after floating the second one) to get a 24V supply to power LiPo chargers.

[paulca]

Another option is to get the boost/buck module (DPH3205) and use a 12V 15+A power supply for the input. I like old server power supplies - for example the HP DPS-600PB (12V 47A) are available for $20 shipped and can easily have their outputs floated if needed - RC enthusiasts commonly put a couple of these in series (after floating the second one) to get a 24V supply to power LiPo chargers.

I have a boost/buck (if that's the right term) LiPo (and most other battery types) charger for RC that I run off a single cheap chinese 12V 5A supply.   It's amazing.  It will happily charge a 15V lead acid to 15V CCCV at 4A.   I did manage to charge two 3s LiPo in series requiring 25.2V using a balance splitter cable (monitors and balances the 6 individual cells), but it worked out due to not being about to charge them at 5A and only getting about ~1.8A that it was faster to charge them one at a time.   It was $70 and the PSU about $10.  An Accucell 60W.  They do a bigger one, think it's 120W 10A, but I couldn't find a PSU for it.  RC folks were (as you suggest) using old PC PSUs with the main 12V rails joined and stuff.  Kinda scared me so stuck with my 60W. 

I'll mull over it a bit and decide on the chinese AC-DC power module + the cheap DC-DC one... or go for the Tenma.

Thanks for all the replies.