OT: Bench PSU 'kit'

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boriz

Senior Member
Adjustable voltage up to 22v, adjustable current limiting up to 5 Amps. 110 Watts. <£20 :)

http://dx.com/p/03100173-diy-5a-constant-led-driver-li-ion-battery-charging-module-red-169504

+

http://www.ebay.co.uk/itm/DC-24V-5A-120W-Switch-Power-Supply-Driver-For-LED-Strip-Light-Display-5-/180838279889?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1acd2ad1

+

http://www.ebay.co.uk/itm/Mini-DC-0V-To-99-9V-0-99-9v-Red-LED-Digital-Panel-Volt-Voltage-Meter-Voltmeter-/300727323022?pt=LH_DefaultDomain_0&hash=item4604bec98e

+

http://www.ebay.co.uk/itm/New-Blue-LED-Digital-Ammeter-AMP-Mini-Current-Panel-Meter-DC-0-9-99A-/180840762862?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a1af30dee
 
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D

Dippy

Moderator
How easy was it to build?
2 S/modes in a row... is it very noisy?
Is the CE genuine? Or is it simply "Chinese Export"?
 
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Paix

Senior Member
I read that as select one of two options for the basic PSU pluse one each of voltmeter/ammeter.

Build, I don't think so, maybe more speculation that the parts are readily available to do the specified job within the budget (maybe)!

Is the CE genuine? Or is it simply "Chinese Export"?
Click to expand...
Is this a string theory question or could it be a Compromising Exaggeration?

Boriz, I think you are just being coy and not rising to Dippy's bait. :)
 
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Goeytex

Senior Member
I read it as you need all 4 since #1 requires 5v - 32v input. Integration should be a snap. I would hack #1 and convert the pots to rotary type with 2 on each input to allow for coarse and fine adjustment of current & voltage. Might add an LED to indicate when current limiting kicks in.

A "repurposed" laptop adapter should be able to replace #2.

Seeing how some of these sellers fudge on specs, I would expect a total efficiency of around 75 - 80%. but who knows ?
 
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Dippy

Moderator
I had thought that boriz had selected the 'ingedients' and built a PSU.
So it was a general question about performance as I have seen some well-wobbly switchers which could be a real pain in some designs.

The CE part was a little joke after numerous experiences with claimed CE compliance.
Item 2 claims "Safety Compliance: CCC/ FCC / CE. " which isn't cheap to do if done thoroughly.
Some odd ex-Qinetiq engineers I met had suggested that CE had an alternative meaning - I really shouldn't mix with them :)
 
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boriz

Senior Member
Yep. All 4. That's what the '+' sign means. (And the price if you work it out).

A PSU, a voltage and current regulator, a digital voltmeter and digital current meter.

If I didn't already have a current control BTPSU, I'd be tempted.

Bah. I'm still tempted :)
 
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BeanieBots

Moderator
Using that current meter might be fun.
Can it measure the current drawn from the same voltage that is used to power it? Most cheap modules that I've come across cannot.
Nonetheless, some nice cheap offerings assuming they're CE marked for the reasons expected by Engineers.
 
JimPerry

JimPerry

Senior Member
I just added a breakout box to a spare ATX supply - 3V3 5V 12V and -12V from bannana post terminals + LEDs to indicate voltage - total cost less than a fiver for plastic box and terminals ( +100R 11W load resistor). only thing missing is variable current limiting - but it can suppply 20Amps! :D

You can do this without opening the PSU - so no 240/110 AC to mess with.
 
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manuka

Senior Member
Can it measure the current drawn from the same voltage that is used to power it? Most cheap modules that I've come across cannot.
Click to expand...
Indeed they can't, but many cheap DMMs take such tiny currents (~¼mA) that they can run as needed fror ~a minute on a switched in charged electrolytic. A small 12 V powered DMM recently mentioned runs reliably down to ~7V before a low battery symbol appears.
 
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inglewoodpete

Senior Member
The first supply that boriz posted (Deal Extreme) appears to be a constant current LED supply. There doesn't appear to be a control for the output voltage. Only the output current limit. For LED lighting.
 
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Goeytex

Senior Member
While it may be used an LED supply source, I see two pots ( Voltage & Current Limit ?) and the specs clearly state:

- Input voltage: 5V~32V
- Output voltage: 0.8V~30V
- Output current: Adjustable up to 5A
- Conversion rate: 95% (Max.)
- Switch frequency: 300kHz
- Output ripple: 50mV (Max.)
- Bandwidth: 20Mbps
- Loading adjustment rate: +/-0.5%
- Voltage adjustment rate: +/-2.5%
 
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BeanieBots

Moderator
Goeytex said:
While it may be used an LED supply source, I see two pots ( Voltage & Current Limit ?) and the specs clearly state:

- Input voltage: 5V~32V
- Output voltage: 0.8V~30V
- Output current: Adjustable up to 5A
- Conversion rate: 95% (Max.)
- Switch frequency: 300kHz
- Output ripple: 50mV (Max.)
- Bandwidth: 20Mbps
- Loading adjustment rate: +/-0.5%
- Voltage adjustment rate: +/-2.5%
Click to expand...
I found those numbers interesting.
If the switch frequency is 300kHz, can somebody explain to me how it manages to acheive a bandwidth of 20Mbps? Especially if the adjustment RATE is +/- 2.5% !!???!!

Based on those figures perhaps what they mean by voltage output of 0.8v ~ 30v is that you will get a voltage somewhere between 0.8 and 30v depending on what mood it's in and the pot is to adjust how quickly it changes?!
 
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Jeremy Harris

Senior Member
My experience of using a very similar CC supply was that you couldn't set the output voltage, only the output current. I have it driving some LEDs and you can add more series LEDs and the output voltage just increases in order to deliver the same set current as the total Vf of the array increases.

On the other hand, you can fairly easily modify the switched mode power supply given in one of the links to have current limit and voltage adjustments. I have a 350W version that I've modded to allow this and it works pretty well. It's not strictly speaking as flexible as a proper bench supply, as the voltage adjustment range is a bit limited, but it works OK as an adjustable current limit fairly high voltage supply (I used a 48V 250W SMPS as the basis).

If you want a display that will show current and voltage at the same time (and also power and Ah used over time) then you might want to consider one of these: http://www.ebay.com/itm/DC-DC-20A-Dual-display-Digital-LCD-Power-Current-Voltage-AMP-Meter-VA-Voltmeter-/180830130528?#ht_3217wt_1228

I have a couple, and have been using one on a bench supply/battery charger for a while now. It's pretty good for what it is and has the advantage of doing pretty much everything you want in one small display.
 
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inglewoodpete

Senior Member
Goeytex said:
While it may be used an LED supply source, I see two pots ( Voltage & Current Limit ?) and the specs clearly state:

- Input voltage: 5V~32V
- Output voltage: 0.8V~30V
- Output current: Adjustable up to 5A
- Conversion rate: 95% (Max.)
- Switch frequency: 300kHz
- Output ripple: 50mV (Max.)
- Bandwidth: 20Mbps
- Loading adjustment rate: +/-0.5%
- Voltage adjustment rate: +/-2.5%
Click to expand...
Clearly states? It "clearly states" that the output voltage can vary between 0.8 and 30v, while the output current can be adjusted up to 5A. No mention of controlling the voltage. (I have to admit that the 20MHz is out of left field, though.)

My experience appears to be backed up by Jeremy H: the voltage is controlled be the LED stack that the supply is driving. One red LED will get about 1.8v at the preset current. From memory, a stack of 6 x 1W white leds resulted in about 22v at the same current (350mA).
 
hippy

hippy

Technical Support
Staff member
I suppose this illustrates why official datasheets are so important. Without those one can only make educated guesses but only really know when one buys and tests or reverse engineers what is delivered.

I must admit that I was somewhat mystified by "bandwidth", especially being specified in "bps", presumably bits per seconds.

I would have guessed like inglewoodpete that a current can be set, voltage adjusts to provide that current, but it does seem there may be some other voltage adjustment capability. That makes sense for LED driver and battery charger; constant current but with a maximum voltage cap.
 
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