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Old 04-13-2012, 05:19 PM
Ron Chase Ron Chase is offline
Join Date: Aug 2010
Posts: 57
Cap Dump

Originally Posted by BrentA929 View Post

Two things...

1) The FET works just like you have shown. My wheel dumps at about 1.5 Amps. You are right, it is hard to tell what voltage it dumps at. I wonder if I truly understand this type of dump. My digital meter shows about 40-41V. I know the digital meter can't really see it.

2) I was wrong about my K12A. I tried it again and found that it does just like the FET and dumps at 1.5 Amps. I was so paranoid when I first did it, I had the analog meter hooked up backwards and I was to focused on the voltage on the cap. Glad to know it works. It actually works in reverse of what JB showed in the video. I wonder why? I have it hooked up like you show in your schematic in post 1830.

Guess it's time to run some tests!

Thanks, Brent


What is the reverse breakdown for the IRFP260 FET?

Thanks, Brent

Yay Brent. Start charging those batteries and begin thinking about building the second half of the wheel, the re-gauging motor.

The drain to source breakdown voltage for the IRFP260 is 200V but I wouldn't worry about that as it doesn't appear to have any relevance to the kind of cap dump function we are observing. We see dynamic charging at impossibly low current levels with all the different rated FET's we've tried so far so it has to be the RE flowing through the FET's that is doing the job regardless of what the breakdown voltage, etc. is of any particular FET. The RE doesn't care about voltage it justs wants to get to the negative pole of the battery. The higher negative potential of the cap see's the lower negative potential of the battery as positive and wants to get there anyway it can.

As far as how a FET is connected to the Cap - and the Batt - you just have to go with what works. The FET's inside SSR's often have other components associated with them such as the snubber diodes I mentioned earlier as well as how the FET was constructed all of which can affect whether it works with one connection scheme or another. The data sheet's often don't show this or even reveal the internal connections of the FET so trying to figure it all out can be maddening.

I'm just happy we've gotten to the point where we can begin building regauging motor's. Our big wheels are the perfect platform for experimenting with them.

Good Job!

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