Basic Electronics question but I'm stuck

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Joined: 03/26/2014
Points: 52

I think this is a basic electronics question, but I can't easily think of a solution.
How do you limit current in a wire without dropping voltage?

So my application is I want a low current feed to the controller to do a precharge of the capacitor to 90% of pack voltage (its an option on the Curtis1244 controller).
If I jump the main contacter with something that limits current then that would allow it to precharge.
But if I just put a resistor in, it will sap most of the pack voltage and therefore the precharge wont reach 90%

Please help!

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MEroller's picture
Joined: 09/26/2011
Points: 847
Re: Basic Electronics question but I'm stuck

It WILL reach 99.999999999 eventually, as the voltage drop over the resistor is reduced as the current is reduced due to less voltage difference between battery and input capacitors of the controller. There is a reason why these resistors are referred to as precharge resistors, because that is exactly what they do, though it takes few seconds. And there is no need to precharge to 100%, as whatever you eventually use to completely connect controller and battery will have a certain current switching capacity of it's own.
I simply use a 230V~ light bulb as precharge resistor, as it's ceasing glow shows me the precharge is complete enough for my curcuit breaker to reconnect said circuit.

Check out this wikimedia charge curve of a capacitor:
from wikimedia, public domain


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