Re: Sizing a capacitor?

serpa4 wrote:
Hello. 1st post on any group. Hope this works. I don't know squat
about electronics. However, maybe someone here can help. I replaced
my engine driven fan on my 2007 GMC with a set of electrics fans that
are wired through a 30 amp fuse for each of the two fans. However,
the fans are messing up my water/meth injection controller.

(snip)
What do you all think? Some thing isn't right here. How can the
fan cause the boost to change unless it's also messing with the truck
computer and not just the water/meth controller? The fans have their
own temperature sender unit in the upper radiator hose and don't
interface with the factory computer in any way.
I cannot return either unit since they were installed.

Either the fan brushes or the speed control (probably a variable pulse duty cycle driver) are making radio frequency hash that is upsetting other sensitive electronics. Either you filter the fan wiring or you filter all the things that are being upset. I would start with the fans.

Look for one or a few clip on split ferrite bead that can be snapped around both fan leads (close to the fans). These will reduce the high frequency currents that travel back from the fan to the rest of the wiring harness and radiate all over the place.

The ones with a hole just large enough to pass the pair of wires will be most effective. If you can only find ones with a much larger hole, you might be able to wrap the pair around through the hole for a second pass.

This is what I am talking about:
http://rocky.digikey.com/WebLib/Steward/New%20photos/28A2026-0A2.jpg

If that helps but doesn't solve all problems, you can add more beads along the wire.

It might also help to add a capacitor across each of the motors, right at the fan, and also to add one from each terminal to the motor frame, but that is a lot more invasive than adding the beads, so it would be my second try.
.

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