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Registered Member #3918
Joined: Sun May 29 2011, 08:42PM
Location:
Posts: 34
I need 24v at silly amps and I need it cheap. I used to use SLA batteries, but I ended up recharging them almost constantly, which is probably not very good for them. ATX power supplies can supply the amps I need (15+) but only at 12v, putting two in series would work, but they connect the ground wire to earth, so if I connect the +12v of one to the ground of another, the overcurrent protection kicks in and it shuts it down. The only way around this that I can see is to unearth one of them, which I assume is fairly dangerous and I imagine lots of strange voltages will show up on the ground of the unearthed one. If there is a fault, the case could quite easily end up connected to line voltage (240v here) and I wouldn't know about it until I touched it.
Has anyone done this before? How quickly will I kill myself trying it?
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
This helped me: But only works if you have a TL494, HA17339, KIA494, KA7500, IR3M02, MB3759, KA7500B. You'll probably want to upgrade the components as well (mostly capacitors).
Registered Member #3918
Joined: Sun May 29 2011, 08:42PM
Location:
Posts: 34
Thanks, I've seen those mods before. I assumed the current output would be reduced if the voltage was increased, or the power supply would be converting more watts than it's rated for. For my application I need all the amps I can get.
I take it you've done the modification before? How many amps were you able to pull?
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
I wouldn't unearth it, I had an unearthed one, and there was 120volts on the case of the ATX PSU, and I touched it, and at the same time, my other hand was on my grounded table >:|
Registered Member #3918
Joined: Sun May 29 2011, 08:42PM
Location:
Posts: 34
D: I heard that is due to the noise suppression filter thing they all have, it connects the case to the centre of 2 capacitors that are connected across the mains line, if the case isn't grounded it ends up at half the mains voltage, so 120v.
(sorry double post) Hmm, if I unground one, and make sure it's ground is always connected to the 12v of the other, then that should stop the 120vac showing up on the case since it will always be at +12v with respect to ground as the other supply will always be grounded. I hope. It should also provide some form of protection, e.g. if the case goes live for whatever reason, it will trip the other supply which will let me know there's a problem, or possibly even trip the breaker if I'm lucky.
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Running ATX power supplies ungrounded
