This is great for those times when you have to spend large amounts of time downloading large files to your car pc or configuring stuff etc. with the car parked in the garage and no engine running, and you dont want a flat battery. Sometimes a normal battery charger attached to your car battery hasnt got enough grunt to keep up with the car battery when its got a PC and everything else running off it. Most cheap crap type battery chargers fail at 2amps and the battery voltage starts to get dangerously low and then your car pc drops out/shuts down what ever
Ive done this to two PC power supplys so far, taken out of old computers, first one was a old AT type. I removed all the hdd fdd motherboard power plugs etc and opened up the power supply and looked at the board. Now im an electrician so i know what im doing, but if you dont feel comfortable doing this and you really dont know what your doing, maybe its time to close it! but if you feel ok about handling elecrtricals which have live, dangerous voltages then continue
The 12v output on some of these things can supply 4 to even 8 amps. One ive seen (but it was no good it was blown up) was capable of supplying 12amps!
But they dont work too well as a battery charger as the open circiut voltage on these switch mode supplies is just that, 12v. But you can change that
if you look at the yellow wire to the circiut board, somewhere along that track it has to lead to two resistors, in a T config. One goes to ground, one to the 12v. and the connection between goes to the regulator chip, (power supply controller)
If you change one of these resistances values, you can set your output voltage higher. Typicaly you would set it to 13.8v
I have done this on two supplies. First I lifted one leg on both these resistors and put in series with them a pot each. Usually 5k pots, set them to zero, and then with a voltmeter on the output, turn it on. It should still show 12v. When you slowly increase one of these pots, the voltage should go up. THe trick is to figure out which one needs the pot and work out how you can control the voltage externally with a permanently mounted 5k pot on the case.
I now have two switch mode battery chargers, both controllable from 10.8 volts to 14.5 volts, with pots on them so i can set the voltage.
The ATX type is the same, however it needs the low signal to the green wire to turn, so you need to put a switch in, however ive had problems with the control circiutry, shutting down the power supply when you connect a load. it seems it doenst like sudden changes in demand. There is no problem with a AT style like this.
and the performance? well my AT one, managed a max of 4.5 amps into a 50watt head lights bulb, at 13.5volts. I didnt have a higher load that would not cause the power supply to shut down.
And the ATX one, well when i managed to get it to stay on without shutting down due to its sensitivity to load, i managed a whopping 10amps at 14volts, before my meter complained!!
Even with my AT supply, i can leave it connected to the car battery, and have my car pc on, and the usb power supply for the external usb sound card, the current block, (a current and voltmeter for the amp) and the 600 watt amplifier running! With low sound level of course.
I left it running like this for several hours with music at a low level, doing other work to the pc and after i finished, the battery voltage was actually higher, proving the power supply had enough grunt to even charge the battery while everything was running.
Ill post a picture up here soon.