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Sizing a capacitor?

Discussion in 'Electronic Basics' started by serpa4, Oct 29, 2007.

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  1. serpa4

    serpa4 Guest

    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
    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.
  2. Eeyore

    Eeyore Guest

    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.

  3. Jamie

    Jamie Guest

    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.
  4. Run all the circuits off separate relays.

  5. 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: 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.
  6. HapticZ

    HapticZ Guest

    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?
  7. John Fields

    John Fields Guest

    Please don't top post.

    Even Google Groups advises against it.


    "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
    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
    they'll get the gist of what you're talking about."
  8. serpa4

    serpa4 Guest

    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.
  9. HapticZ

    HapticZ Guest

    using "reply to group", how does that constitute "top post"?
  10. Typing your words above those you are replying to is top
  11. HapticZ

    HapticZ Guest

    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"?
  12. 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
  13. Eeyore

    Eeyore Guest

    Oh dear. Poor baby !

  14. Suzy

    Suzy Guest

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

    Suzy Guest

    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!
  16. John Fields

    John Fields Guest

    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?

  17. John Fields

    John Fields Guest


    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. :)
  18. HapticZ

    HapticZ Guest

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

    HapticZ Guest

    protocol, rigid social levels, strict grammatix, and so forth. just bores
    me to death............
  20. Evidently, not yet.
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