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Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Is this a good resistor to use for a voltage divider? My gun is 3 400V 470uf capacitors.
The reason for adjustable: I want it adjustable so i can change the output voltage without having to constantly change resistors for different circuits. I already own a 100KOHM pot, which is fine, just rated 50V. If I'm not mistaken, thats a 0.75 watt 500V rated one.
But do you think it would survive 3X 400V 470uf capacitors hitting it?
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
I think they aren't meant for that much voltage. I would use fixed resistors and then use a lower resistance trimmer to adjust the voltage ratio of input to output.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
That trimmer pot is rated for 500vdc insulation resistance, and 400vdc at max power rating, so that much is okay.
It won't tolerate much current, though. Note that maximum power dissipation P = VI = 0.75 watts. So if you connect one of these pots to your fully charged capacitors:
the maximum allowable current is I = P/V = (0.75)/(400) = 1.8 mA
the actual current with a 100K pot is I = V/R = (400)/(100K) = 4mA ... meltdown!
I don't see an obvious use for a little tiny wirewound trimmer pot in a coilgun, except as part of a bigger transistorized voltage controlled charging circuit.
Cheers, Barry Christmas shopping is easy this year because I'm buying everyone batteries and writing a note that says "toys not included."
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
The other main reason was to figure a NPN transistor to flip open to trigger a LED indicating its fully charged, rather than it fading to a brightness. Right now i'm only testing voltages at 200V with it, and the pot gets 30V into it, yet its rated 50V. With a 1OHM resistor, 200V the pot barely even gets 1V I should mention currently i have a 270KOHM resistor taking the capacitors power down and then hitting the pot.
its best to have one high value fixed resistor above the output, and 1 pot and 1 fixed below the resistor. This doesnt allow you as much control as with just a pot, so i have two seperate dividers on mine, one for 20-100, one for 100-450
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Working on a Voltage divider..Does this work?
