gillbot Posted March 22, 2004 Report Share Posted March 22, 2004 I have a variable voltage DC buss (0v to ~150V) and I need to pull 12-18v off of it @ ~5-10 amps. Any ideas? It's actually a car alternator sans the regulator circuit. I'd like to tap off this unregulated section after the rectifier to supply the alternator field with manually variable DC from 0~18vdc to vary the current output of the alternator itself. The down side is, I need to keep the output of the alternator unregulated voltage wise. Quote Link to comment Share on other sites More sharing options...
Akula Posted March 23, 2004 Report Share Posted March 23, 2004 Jacobs makes a variable output device for people that need clean voltage. Lots of racing VWs have them to keep the 12V stable no matter what RPM. As far as building a rectifier or something like that, go to the library or radio shack and read up on it. Quote Link to comment Share on other sites More sharing options...
gillbot Posted March 23, 2004 Author Report Share Posted March 23, 2004 I got a rectifier, I need a converter to get ~15v@5A off of a constanly variable 0-150vdc buss. Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted March 29, 2004 Report Share Posted March 29, 2004 Zener Diode wired in parallel with voltage source. PM me and I can try helping a bit more if you haven't solved the problem by now Quote Link to comment Share on other sites More sharing options...
gillbot Posted March 29, 2004 Author Report Share Posted March 29, 2004 Originally posted by nate dog: Zener Diode wired in parallel with voltage source. PM me and I can try helping a bit more if you haven't solved the problem by nowI'm not sure a zenier would work since it tries to shunt excess current to ground, wouldn't that fry it due to the high fluctuating DC buss and high current? Quote Link to comment Share on other sites More sharing options...
desperado Posted March 29, 2004 Report Share Posted March 29, 2004 Originally posted by gillbot: I'm not sure a zenier would work since it tries to shunt excess current to ground, wouldn't that fry it due to the high fluctuating DC buss and high current?Yes it would. And even if the circuit was wired correctly, with a resistor in the line before the diode, it would generate a ton of heat. The resistor would also need to be huge as far as wattage rating. It would need to be able to sink 5 amps at 145 volts 5X145=725 Watt resistor. If you could find such a thing it would be ridiclously expensive. I can't think of a voltage regulator that will allow you to have that sort of input to output ratio either. I would sugjest that you have a seperate power supply for the 5 volts. I will be MUCH easier to do that. If you are talking about your alternator welder, take some of the AC from the windings, before it's rectified and put a transformer on it and step it down. Then rectify it. Problem with that is that transformers are designed to work at 60 HZ. An alternator will vary frequency be the RPM it's spinning, so the output voltage will rise very fast, and the current draw may be rather high at higher frequencies as well. Quote Link to comment Share on other sites More sharing options...
gillbot Posted March 30, 2004 Author Report Share Posted March 30, 2004 Actually, I think I might have found a supply but unfortunately all US suppliers are out of stock. http://www.eng-tips.com/viewthread.cfm?spid=240&newpid=240&sqid=90847 Quote Link to comment Share on other sites More sharing options...
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