Sizing a capacitor?

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. The water/
meth controller pumps a mix of water/meth into my intake manifold
based on turbo boost. When my electric fan kicks in, the controller's
reading for boost and the temperature of the exhaust on its LED
display go to zero. The display still works/lights up etc, and
displays text, but just reads zero for boost and exhaust gas
temperature (EGT). I have a mechanical turbo boost pressure gauge and
a mechanical temperature gauge for the exhaust also. These, being
mechanical, keep working fine. If the truck is making 10 lbs of boost
then the cooling fans kick in for the radiator, the boost and EGTs
drops to zero. When the fan stops, the boost and EGT readings return
from zero to whatever they should be (10 psi/800 degrees). The boost
is picked up via a plastic tube and routed to the water/meth
controller which is digital in nature. The electric fans are
controlled by a pulse width modulator to allow for a variable speed
setup. The fan controller is mounted to the radiator's metal cross
member. I have two batteries in my truck. To further isolate the
water/meth controller from interference, I completely removed the +/-
of one battery and ran both the ground and positive wire from the
water/meth controller and its injection pump to the isolated battery
for power and ground. Nothing in the water/meth controller or pump
setup touches the truck or the truck chassis and it still stops
working when the fan turns on. For more trouble shooting, I have
trapped 4 psi of air in the controller tube for trouble shooting
purposes. So, the gauge always reads 4 psi weather the truck is
running or not so I don't have to actually drive to make turbo boost.
However, the instant I connect the fan and the fan turns on, the boost
and EGT readings go to zero. Unplug the fan or turn them off, the
boost and EGT readings comes back. I'm guessing is the problem is RF
noise. How do I stop this? I don't know anything about capacitors.
However, back in my youth, the electric motors in my radio controlled
cars ran capacitors on the motors to keep from interfering with the
radios. Please don't use technical stuff like thin film or what ever,
which means nothing to me. What I'm looking for is:
Hey, put a 100 whatever capacitor between the + and - of the motor and
see if that helps. The fans are both wired to a 30 amp fuse, so I
guess the capacitor needs to be 12 v and handle up to 30 amps? Just a
guess. Thanks to anyone who can help.
Also, tonight I made a very strange discovery. The fan is multi speed.
When the fan is on low, the controller functions as stated above,
messes up the water/meth controller. HOWEVER, when the fan switches to
medium speed, the boost starts working again. Here is the funny
part..........
When the fan switches from low to medium, the MECHANICAL boost gauge
(not the one built into the water/meth controller, goes up by up to
SIX psi instantly. The turbo has veins that move to change boost and
are controlled by the truck's computer. I can hear the turbo spool
and my butt can definitely feel a slight pick up in acceleration. So,
at cruising speed of about 65mph and the turbo making about 5 psi
boost on the mechanical gauge and the fan is on low, the water/meth
controller is not working... then the fan kicks to medium, and the
controller starts working, and the mechanical boost gauge raises to 11
psi. This is a real gain in boost from the feel and from hearing the
turbo. Its not extra horse power from the water/meth since it is not
injecting AND the pump is disconnected anyway for trouble shooting.
When the fan drops to low, the water/meth controller stops reading,
and instantly the boost on the mechanical gauge drops back to 5 or
so. 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.

 

Before you post any more, may I recommend the use of paragraphs to break up up
acres of solid text. I find it virtually unreadable.

Graham

 

I would check for lack of ground straps.
it sounds like you are created a current path through the
engine block or radiator etc. the Sensors of the electronics
for the controller maybe getting nulled out.

 

Run all the circuits off separate relays.

R

 

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 photos/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.

 

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?

 

---
Please don't top post.

Even Google Groups advises against it.

From:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

"Summarize what you're following up.

When you click "Reply" under "show options" to follow up an existing
article, Google Groups includes the full article in quotes, with the
cursor at the top of the article. Tempting though it is to just
start
typing your message, please STOP and do two things first.
Look at the quoted text and remove parts that are irrelevant.
Then, go to the BOTTOM of the article and start typing there.
Doing this makes it much easier for your readers to get through your
post. They'll have a reminder of the relevant text before your
comment, but won't have to re-read the entire article.
And if your reply appears on a site before the original article
does,
they'll get the gist of what you're talking about."

 

Before you post any more, may I recommend the use of paragraphs to
break up
acres of solid text. I find it virtually unreadable.
Sorry, will do.

I would check for lack of ground straps.
It sounds like you are created a current path through the
engine block or radiator etc. the Sensors of the electronics
for the controller maybe getting nulled out.

The engine has a ground strap to the truck fire wall. The fan
controller is grounded to the frame at a pretty good location. With
the problem still there, I tried a new ground location: water meth
controller was powered and grounded to a completely separate battery
directly and the battery was not grounded to the truck.

Should I try a different place? Currently, since completely isolating
the power and ground via a completely separate battery for the water/
meth did not work I have moved the fan controller ground, water/meth
ground, and controller ground back to the radiator mount which is
reported by truck owners as a very good place to ground to.

Run all the circuits off separate relays.
There are no relays that I know of in the system. The water/meth
controller is powered from a key on location for power. It was
powered directly off a completely (second) separate battery. Neither
location had any effect. The fan system doesn't have any relays that
I know of. I believe the controller itself has the switching
mechanism in it.

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.
I'll try those magnet things. Any chance radio shack or some local
store will carry them or should I order off the internet?
Also, what size and type capacitors should I get? I have no idea.

 

using "reply to group", how does that constitute "top post"?

 

Typing your words above those you are replying to is top
posting.

 

so i have to manually move my default cursor all the way to the bottom of
the msg and then start typing? that will just wear me right out!

or should i set the option to "not include original message"?

 

You are supposed to review the quoted text and clip out any
parts that is not needed to remind others what you are
replying to, before you post. It is customary to add in
(snip) or 8< (scissors symbol) if you clip the last poster.

Then, you either insert your words directly below lines that
you are reacting to, or post your entire message at the
bottom. This is the standard for Usenet and just good
manners. Remember, this is not an email reply to one person
who knows what they have already said, but an archived post
that is part of a conversation presented to the entire
world, for anyone to join in. Normal capitalization,
spelling and punctuation are also appreciated. It is hard
enough to interpret many posts, without also having to
decode slang and abbreviations. This is not a cell phone
text message.

You are certainly free to do whatever you like, but if you
can't be bothered to think about the effort it takes others
to understand what you write, don't be surprised if many
kill file you and never see anything else you ever post.

Bye bye.

John Popelish

 

Oh dear. Poor baby !

Graham

 

No to that, as it removes the context (ie people will not know what you are
replying to)

 

Well explained John. But there is another point. If you are replying
protesting at foul language or nasty posting (a regular perpetrator of which
appears here occasionally) be careful not to requote his foulness as others
may have kill filed to avoid his nastiness!

 

---
You seem to miss the point, which is that top posting is generally
frowned on when replying to a USENET post, for many reasons.

You do know the difference between top posting, bottom posting and
inline posting, don't you?

Peruse:

http://www.google.com/search?hl=en&q=top+posting

 

---
Suzy,

Even though you may find it repugnant to read what you perceive as
"foul language" or "nasty posting", I find it even more repugnant
that you would have others censor others' posts in order to comply
with what your delicate sensibilities dictate is 'proper' behavior.

This is, after all, USENET, arguably the last bastion of truly free
speech on the planet, so if you want to play here and not be
perpetually offended by some of the other players, I suggest you
grow thicker skin.

 

ohh, such a short life to learn soooo much hoooey!

 

protocol, rigid social levels, strict grammatix, and so forth. just bores
me to death............

 

Evidently, not yet.