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  1. #1
    Join Date
    Aug 2004
    Location
    New Jersey
    Posts
    1,335

    Default Momentary Switch

    I'm thinking about installing a momentary switch to my electric fans to help with starting the car when hot.

    Right now with the car hot, the fans, fuel pump and MSD are all turning on with the ignition and when she is hot, it is sometimes hard to start. The systems are just drawing too much juice.

    Where can I find an automotive momentary switch that would disable the fans for a few seconds until the car starts and then close the circuit to activate the fans. I would prefer not to have a toggle, since I would probably forget to turn it on.

    Any thoughts?

    Camaro Convertible Build Pics - http://s447.photobucket.com/albums/qq198/rob07002/

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    Rob Stevens


  2. #2
    Join Date
    Dec 2006
    Location
    Burbs of Detroit
    Posts
    1,434
    Country Flag: United States

    Default

    Could also use a normally closed relay. When you hit the starter, it would automatically cut the fans
    Greg Fast
    (yes, the last name is spelled correctly)

    1970 Camaro RS Clone
    1984 el Camino
    1973 MGB vintage E/Prod race car
    (Soon to be an SCCA H/Prod limited prep)

  3. #3
    Join Date
    Feb 2008
    Posts
    44

    Default

    a spdt relay is your best bet they have 5 prongs u would use the middle prong (87a) and place it before your relays now
    tap into your solenoid lead wire and use it for the trigger wire so when its cranking they are cut off

  4. #4
    Join Date
    Sep 2006
    Location
    Southern Indiana
    Posts
    3,958
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    Default

    sounds more like you have other issues as your battery should handle this load if big enough, as a set of fans, fuel bump and msd shouldnt be pulling more than 30 amps and it really sounds like your starter cabling or to indirect of a ground path is starving the starter, remember resistance goes up as things get hot.
    I was wondering which battery are you using and what are the specs on it?

    Lets put it this way a good heavy starter even on a high compression engine shouldnt pull more than 250 amps when old. My old Pontiac had a 10.5 to 1 engine with a ridiculously low duration cam and it was a bear to start and it started with a 525 amp ac delco and boosting from my little 40 month autoworks battery and that engine even pushing nearly 275 cranking psi would fire up and never draw over 200amps.
    Few things to look for, get a good digital volt meter, set it on ac volts and look for excess ac current with car running, if it goes over 50 to 60 milliamps
    (0.050-0.060) and its better if nearer to 0.040mA AC current you have diodes bleeding too much ac current into your battery and it damages and drains them.
    another thing even most of the larger fuel pumps should pull over 10 amps and fans around 20 amps(I had a super heavy duty one I cant remember where I got it and it only pulled 12 amps on high).
    If you look for a battery look at reserve capacity and the CCA and CA. the lower the reserve the cheaper the battery and if the battery is say 600cca but 950 CA its not a good battery. kind of like the "1000" watt amps that only actually make 100 watts RMS. its bs number to sell them.
    Look for high reserve capacity and high CCA like 800-1000 and CA should be within 200-250 amps. Then go over your connections, I use 2/0 battery cable to starter I crimp and solder all my connections, and use many grounds like the woven stainless braided ones. I try to put 4 on an engine 2 front and 2 back and 2 to body for 6 total. Electricity does weird things and I have shut up many a cars radio whine when rewiring and adding grounds.

  5. #5
    Join Date
    Feb 2008
    Posts
    44

    Default

    Quote Originally Posted by MonzaRacer View Post
    sounds more like you have other issues as your battery should handle this load if big enough, as a set of fans, fuel bump and msd shouldnt be pulling more than 30 amps and it really sounds like your starter cabling or to indirect of a ground path is starving the starter, remember resistance goes up as things get hot.
    I was wondering which battery are you using and what are the specs on it?

    Lets put it this way a good heavy starter even on a high compression engine shouldnt pull more than 250 amps when old. My old Pontiac had a 10.5 to 1 engine with a ridiculously low duration cam and it was a bear to start and it started with a 525 amp ac delco and boosting from my little 40 month autoworks battery and that engine even pushing nearly 275 cranking psi would fire up and never draw over 200amps.
    Few things to look for, get a good digital volt meter, set it on ac volts and look for excess ac current with car running, if it goes over 50 to 60 milliamps
    (0.050-0.060) and its better if nearer to 0.040mA AC current you have diodes bleeding too much ac current into your battery and it damages and drains them.
    another thing even most of the larger fuel pumps should pull over 10 amps and fans around 20 amps(I had a super heavy duty one I cant remember where I got it and it only pulled 12 amps on high).
    If you look for a battery look at reserve capacity and the CCA and CA. the lower the reserve the cheaper the battery and if the battery is say 600cca but 950 CA its not a good battery. kind of like the "1000" watt amps that only actually make 100 watts RMS. its bs number to sell them.
    Look for high reserve capacity and high CCA like 800-1000 and CA should be within 200-250 amps. Then go over your connections, I use 2/0 battery cable to starter I crimp and solder all my connections, and use many grounds like the woven stainless braided ones. I try to put 4 on an engine 2 front and 2 back and 2 to body for 6 total. Electricity does weird things and I have shut up many a cars radio whine when rewiring and adding grounds.
    good stuff i usually use
    1/0ga from batt to starter considering it can flow 350amps if not more
    4ga to alternator
    2/0ga for the frame/subframe ground
    4ga for body ground
    4ga from each motor mount to frame/subframe
    8ga from back of each head to firewall

    go with a kinetik battery i have used alot and always had good results

  6. #6
    Join Date
    Aug 2004
    Location
    New Jersey
    Posts
    1,335

    Default

    Quote Originally Posted by MonzaRacer View Post
    sounds more like you have other issues as your battery should handle this load if big enough, as a set of fans, fuel bump and msd shouldnt be pulling more than 30 amps and it really sounds like your starter cabling or to indirect of a ground path is starving the starter, remember resistance goes up as things get hot.
    I was wondering which battery are you using and what are the specs on it?

    Lets put it this way a good heavy starter even on a high compression engine shouldnt pull more than 250 amps when old. My old Pontiac had a 10.5 to 1 engine with a ridiculously low duration cam and it was a bear to start and it started with a 525 amp ac delco and boosting from my little 40 month autoworks battery and that engine even pushing nearly 275 cranking psi would fire up and never draw over 200amps.
    Few things to look for, get a good digital volt meter, set it on ac volts and look for excess ac current with car running, if it goes over 50 to 60 milliamps
    (0.050-0.060) and its better if nearer to 0.040mA AC current you have diodes bleeding too much ac current into your battery and it damages and drains them.
    another thing even most of the larger fuel pumps should pull over 10 amps and fans around 20 amps(I had a super heavy duty one I cant remember where I got it and it only pulled 12 amps on high).
    If you look for a battery look at reserve capacity and the CCA and CA. the lower the reserve the cheaper the battery and if the battery is say 600cca but 950 CA its not a good battery. kind of like the "1000" watt amps that only actually make 100 watts RMS. its bs number to sell them.
    Look for high reserve capacity and high CCA like 800-1000 and CA should be within 200-250 amps. Then go over your connections, I use 2/0 battery cable to starter I crimp and solder all my connections, and use many grounds like the woven stainless braided ones. I try to put 4 on an engine 2 front and 2 back and 2 to body for 6 total. Electricity does weird things and I have shut up many a cars radio whine when rewiring and adding grounds.

    Good advice Monza, I'll take a look at my grounds, etc. For the record, I'm running a brandy new Optima Red Top, but not sure of the CCA or CA right this second. Agreed though, electricity can do wierd stuff, so worth re-checking. I just figure with 13.5 -14 volts when running, I should be good to go. I know from my race car experience, that a decent compression motor with stout timing and MSD will sometimes be hard to start when hot. We used to wire the MSD to a switch, get the car cranking with no spark, and then flip the MSD on and it would fire up no problem. This is for 12:1 and higher motors and full race apps, but it worked like a charm.
    Camaro Convertible Build Pics - http://s447.photobucket.com/albums/qq198/rob07002/

    www.musclerides.com

    Rob Stevens

  7. #7
    Join Date
    Jan 2008
    Posts
    39
    Country Flag: United States

    Default

    Did you ever notice that car radios turn off when cranking? There are circuits in your car that are disabled when the car is cranking. The extra terminal on the starter feeds these circuits. I believe (not 100% sure someone chime in) that the starter solenoid pulls in and this causes the copper disc in the starter to pull back. This breaks the circuit between the heavy terminal (from battery) and the extra terminal. Most old cars have their starters miss-wired and the circuit does not get disabled on startup. Find a circuit that is disabled on cranking and hook your relay to that circuit.



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