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Old 02-09-2008, 12:31 PM   #548 (permalink)
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PC Power supply, DC switch and fuse

Completely out of subject but still. Computer power supply and many switching power supply can run directly on DC. By design they internally get the AC to DC , and after they step it down.(you could also increase efficiency by removing/bypassing the internal bridge rectifier) Those power supply are often rated to work from 100-240 vac input (with will translate to 160 to 384 vdc (x1.6 rms to peek) ) but from experience you can often run them as low as 60vdc , but do not expect them to be able to give full power out. (aka a 400w at 60v will tend to make noise and heat when use at more than 70%ish capacity) I’ve used many of the shelf AC power supply to power electronic device on our solar car project when the vicor where broken, and even powered directly my own laptop directly out of 60v lead acid and 144v kokam lithium pack many times. Still try at your own risk with worty equipment. So , if you have a old PC power supply ling around, it could do the trick to power up the 12v appliances and event meaby the headlight is you’re over 60-80Vdc(ish)

But as motor controller, they may spark a bit more when conneted/disconected to a dc source. As you mention it before, making and especially finishing connections in DC is always a problem. One other explanation to this you didn’t mention is that on an AC circuit the current get down to 0 120 time a second (2 time by cycle) . This 0 crossing weaken the arcing and allow to cut it easily. Fuse suffer the same phenomena, always get DC rate fuses, if not, they may end up heating/exploding/burning if they ever cut the circuit as they will continue internally arc longer than designed.

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