HiProfile
05-07-04, 07:00 PM
It sounds wierd in the title, but trust me, it'll make sense soon.
I have a bunch of electric raido-controlled cars, and they don't exacly use garden-variety batteries - 2400mAh sub-C NiCd's and 3300 mAh sub-C NiMH's. I have a high-end microprocessor-controled variable 0.5amp-7amp NiCd/NiMH battery charger, but it runs on 12v DC only. My problem is that most power supplies in the R/C industry are almost as much as the charger - $60+ for anything over 5 amps @12v, and I need a minimum of 7 amps. ATM I use an old 12v car battery that couldn't hold enough charge for an engine. Not only does it lack the power of a normal car battery, it also weighs more than my dog.
My plan was to take one of the many unused ATX psu's around my house, rig a switch to 'short it on', and enjoy well over 10amps @12v in a much smaller space & for much less than a normal charger psu. The 80mm fan can also cool the NiMH which can get searing hot if I have to charge it close to 4 amps. My problem is that I'll only be using the 12v rail, and most psu specs I see give a minimum load raiting for the 3.3v and 5v rails.
Should I get two of those ceramic resistors that can handle 10+ amps - one each for the 3.3v and 5v lines, or is it unnecessary? The PSU would have to run for at least 30 minutes each charge, and I don't know exactly how bad it is to run w/o a load on one of the rails. I don't feel like trying to remove any circuitry, mainly because I don't know which transistors handle which rail. I'm assuming that, since psu's can run with one of the rails dead or failing, it wouldn't matter if I put a load on the 3.3v or 5v rails [if I don't use it in a PC again]?
I have a bunch of electric raido-controlled cars, and they don't exacly use garden-variety batteries - 2400mAh sub-C NiCd's and 3300 mAh sub-C NiMH's. I have a high-end microprocessor-controled variable 0.5amp-7amp NiCd/NiMH battery charger, but it runs on 12v DC only. My problem is that most power supplies in the R/C industry are almost as much as the charger - $60+ for anything over 5 amps @12v, and I need a minimum of 7 amps. ATM I use an old 12v car battery that couldn't hold enough charge for an engine. Not only does it lack the power of a normal car battery, it also weighs more than my dog.
My plan was to take one of the many unused ATX psu's around my house, rig a switch to 'short it on', and enjoy well over 10amps @12v in a much smaller space & for much less than a normal charger psu. The 80mm fan can also cool the NiMH which can get searing hot if I have to charge it close to 4 amps. My problem is that I'll only be using the 12v rail, and most psu specs I see give a minimum load raiting for the 3.3v and 5v rails.
Should I get two of those ceramic resistors that can handle 10+ amps - one each for the 3.3v and 5v lines, or is it unnecessary? The PSU would have to run for at least 30 minutes each charge, and I don't know exactly how bad it is to run w/o a load on one of the rails. I don't feel like trying to remove any circuitry, mainly because I don't know which transistors handle which rail. I'm assuming that, since psu's can run with one of the rails dead or failing, it wouldn't matter if I put a load on the 3.3v or 5v rails [if I don't use it in a PC again]?