Re: Sizing a capacitor?

agreed, inline filters are good suppressors for the pwm driving the fan,
but shouldnt they be placed on the supply lines going to the PWM circuit
rather than between the fan-pwm? the entire wire length is probably
radiating all sorts of splatter emf everywhere. shortened and even shielded
may help also.

or both places?

if possible, find some tech guy to alter the PWM circuit to prevent such
drastic sharp rise times in the switch circuitry itself?


"John Popelish" <jpopelish@xxxxxxxx> wrote in message
news:JOCdnR8VVKeKJ7vanZ2dnUVZ_tyknZ2d@xxxxxxxxxxxxxx
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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