PC PSU Conversion.

[Gary Murphy 1]

I have just converted a PC PSU to power my charger/s.

I never liked my Pro Peak 20a,loud and always had a smell to it.

Any way,i had a good quality PSU spare and looked up how to do it,My manual skill is ok but the tech side i am very limited and i do not know what power to expect.

The PSU is a 700w, it states ,+12v max output current 25a and max combined power 552w. +5v max output current 25a and max combined power 150w.

 

I ran the wires this way, three 12v feeds and one 5v feed each has its own ground.

Each +/- feed uses 3 wire bundles.

 

I got two +12v feeds from the group that would of feed the twin graphics cards thinking these wre more powerfull?

 

Chager wise i have cellpro chargers,the 4s and 10s.would lik to use both at once with cells no more than 4s 5000mah max.

 

Can anyone let me know if this will work at what i could charge using both chargers?

 

I ws really chuffed with the finished item,very quite and no smell,looks cool also.

[Colin Naylar]

I did this conversion but had mixed results. I don't have it to hand right now but as I recall the PSU gave out exactly 12v. Connected to my charger it was good enough for a 3S lipo but the voltage dropped too low when charging a 4S lipo and the charger cut out on a 'low input' voltage' alarm. I subsequently bought a commercial power supply which has a 13.6v output for some reason.

[Gary Murphy 1]

Did not want to hear that! My reading on the 12v is 12.2v with no load.

Is there no way to bump the v up?

Lots of posts with people using psu`s i presume they are all 12v from pc`s.

Perhaps it need further modding?

[Martin Harris - Moderator]

13.6 volts is the nominal figure for the 12V lead acid battery that it's designed to be substituted for. It should maintain the voltage under load (the output voltage is regulated to 12V) up to around 25A if their figures are as claimed.

Edited By Martin Harris on 16/07/2011 15:04:17

[Peter Beeney]

Colin,

If I may speculate for a moment, that 13.6 volts you quoted might be 13.8 volts, which is the voltage at which you can permanently float a 12V battery. I’m sure your power supply is adequate now, but if you wanted a really hefty wad of watts to charge a large lipo say, you can connect a car battery, say 50 Ah, across the terminals and run your charger from that. The battery will seamlessly deliver any extra power as and when required, and as the demand lessens the PS will re-charge the battery. You can leave the PS switched on and the battery connected all the time.
It might be a bit expensive but then I don’t think any good supply is cheap. Also another little point, you are always taking more out of the supply than you are putting into the load. For instance, when my Schulze charger is charging a pack at 10 amps it’s taking 17 amps from the supply battery. That’s not quite as bad as it sounds actually, if you convert the readings to watt-hours you get an rather more accurate picture but it is running an inverter in the charger and there are always losses.

Hope I’m not repeating what you are already aware of.

PB

[PatMc]

Posted by Colin Naylar on 16/07/2011 13:22:28:
I did this conversion but had mixed results. I don't have it to hand right now but as I recall the PSU gave out exactly 12v. Connected to my charger it was good enough for a 3S lipo but the voltage dropped too low when charging a 4S lipo and the charger cut out on a 'low input' voltage' alarm. I subsequently bought a commercial power supply which has a 13.6v output for some reason.

 

Colin, did you load the +5Vm supply whilst using the 12v o/p ?

 

The +5v is the main o/p as far as a PC is concerned so if there's little or no load on it the 12v will drop. I have a couple of car bulbs connected as a load on each of the PSU's that I've converted.

 

This is one part complete being tested before I tidied up the wiring etc.

[Colin Naylar]

Hi PatMc

 

I used this website to do the job and as you can see they suggest a 10 ohm 10 watt resistor to load the +5v rail.

 

 

[Colin Naylar]

Thanks Peter for your comments - very useful. I don't have a problem with my set up at present, I just thought that I would mention the results from my pc psu conversion to Gary. I don't feel qualified to give him any advice on his question though.

[Tim Mackey]

I have done a few of these conversions now, and had two such units in the garage until recently - each being used to feed one of my several chargers. The conversion guide Colin shows is the one I used also.

I found the units struggled with the demands of larger batteries, at larger currents. Often they would simply shutdown. They were also sensitive to spikes, and would trip out if not switched on and connected to the charger in sequence. They both eventually died some months back, after I tried to do a high current charge of a 3s pack, and TBH, I simply didnt think it was worth the hassle of doing another, and bought a dual output dedicated PSU.

My chargers require something higher than 12V input in order to work at their best.

[Gary Murphy 1]

All the tech stuff is where i fall down.I could have a couple of issues here then.

I raed that some psu`s need a resistor to power up but some with a on off switch do not need that.Mine has a on off switch and it powered up with no load needed,i did connect 2 wires to jump it though,5v and grey wire.

Secondly i have no load on the 5v line,i just run one 5v feed to a terminal.

I just presumed thet because i was getting 12.2v at the terminals all was cool.

I have not used it in anger yet.

[PatMc]

Gary, you may find that when you connect a load to the 12v o/p the voltage will drop below what your charger needs. Not all PSU's are like this but a load on the +5v o/p should do the trick. As well as providing a load the car bulbs in my photo serve as a visual indicator.

One of the PSU's I adapted actually states on the label 1A min & 25A max for the +5v o/p but only max values for the other o/p's.

Edited By PatMc on 16/07/2011 21:28:26