Voltage Drop Question...

Discussion in 'Electrical Systems' started by badazz81z28, Dec 5, 2020.

  1. DarylD

    DarylD Veteran Member

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    I agree with using a Ford starter solenoid. Not only does it stay cooler since it's not located so close to the hot engine, but it's also much easier to crank the engine over since you aren't having to crawl under the car to attach a remote crank switch. Make sure you have the proper gauge wire from the battery. I think 01 gauge is what's required. Welding cable might be a good choice.
     
  2. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    I don’t think you’re doing your voltage drop test correctly. You should be testing one wire at a time. You put one voltmeter lead (doesn’t matter which one) at one end of the wire (in this case at the positive battery terminal). And the other voltmeter lead goes to the other end of the same wire, in this case the positive battery cable (the same cable) where it connects to the starter. It should be under 0.5 v. You should check it when the car is hot as heat affects resistance (ie the resistance number will be higher on a hot car than on a cold car). You also need to repeat the test for the ground circuit. If you have a bad ground you can also have issues. No need to run a ground from the battery to the engine if it’s in the trunk because a metal frame is much bigger than any wire you’ll buy....but you do need to make sure the ground from the battery to the frame and then up front the frame to the engine is big enough otherwise you’re creating resistance here. It’s a circuit (aka circle) and needs both sides for electricity to flow properly.

    Think of electricity like a water hose. Voltage is the same as water pressure. The smaller the hose diameter, the higher the water pressure (aka resistance). Or the more voltage needed to push the current (amperage) through. Voltage = current x resistance. The higher the resistance, the less amperage available to do work if the voltage stays the same. Length of a wire matters. The longer the wire, the more resistance. Like trying to drink through a 10 inch drinking straw versus trying to drink through a 4 foot long 1/4” diameter hose (which requires more effort).

    using the relay for the activation wire does the same thing as adding a bigger wire for the activation circuit (but doesn’t solve the too small starter motor wire from the battery if that’s the issue) and creates a circuit with less resistance and allows for more amperage to be left over to do the work (move the solenoid to engage the starter). Doing the voltage drop test on all three wires (positive battery terminal to starter motor positive terminal, negative battery terminal to starter motor body/ground, and positive battery terminal to the “s” terminal on starter) would let you know where the issue is.

    A 2 awg wire is a little small for a 12-15 ft run if your battery is in the trunk. A 1/0 or even better a 2/0 would have less resistance. A 2/0 ( aka 00 awg) is twice the diameter of a 2 awg wire. You can buy 2/0 welding wire on eBay with a 12 foot red and 6 foot black for just $37! Then add terminal ends. It will be more flexible than standard wire too because of small wire strands and annealing.

    here’s a good article:
    https://www.onallcylinders.com/2018...ubleshooting-hot-starting-problems-chevy-454/

    hope this helps. Let me know if you have questions.

    if your voltage drop test for the positive AND negative wires are both under 0.5 v, then your problem is elsewhere. But it only takes a few minutes and no money to test.
     
  3. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    The ONLY thing the FORD solenoid does is it eliminates the voltage drop in your harness ----> the excite (start) terminal. Your original harness goes:
    BATT-->distribution->fuse panel->switch->STARTER activation (which excites the electromagnet therefore making the contact disc transfer BIG BATTERY cable lug to stater motor armature field) ....so from the batt....the start wire goes a LONG way before it ever gets XXXX voltage to the start terminal. Now the MORE voltage applied AT THE START terminal....the GREATER the response of the electromagnet.
    The ford/remote solenoid system goes:
    BATT->solenoid->START terminal on starter . So you are able to get FULL voltage to the Sart TERMINAL...without going thru half the cars wiring harness. SHORTER PATH = more voltage. Thats the only thing the ford/remote relay does for you
    Now with a trunk mounted battery is your batt cable to the starter ALWAYS hot? or only hot during cranking? (as you can wire the starter a different way if cable is normally COLD)
     
  4. Fbird

    Fbird Veteran Member Lifetime Gold Member

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  5. badazz81z28

    badazz81z28 Veteran Member

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    Can totally see that...with the emphasis that the power source is shortened. If I simply just relocate the relay (ford in this case), using the same wires...it doesn't do what you're saying. The relay makes much more sense because the relay is at the starter and the power source is coming from the other lug versus coming from the power distribution. The original start wire is switching the relay. In the article, removing the wires because they are too close to the header (due to heat) and putting two wires to replace the two wires is not thinking this through lol...
     
  6. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    If your batt cable to starter is COLD.....you should jump the S --> batt lug on starter...1 less wire going all the way down there...and you can't get more voltage than what the batt cable is going to give you..
     
  7. Dichard

    Dichard Veteran Member

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    Did this start after you put a new engine in the Camaro??
    If so, maybe think your clearances are too tight when it’s hot. Had an old Chevy that would do it all the time when hot, when cold, would start right up.
    So, think about tht
     
  8. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    Absolutely correct the Ford relay doesn’t solve the problem of too much resistance in too small of a wire. Using the relay to the s terminal does because it’s changing the source of power. But you’ll only know if you need to do it if you do a voltage drop test. Which isn’t hard to do and is quick. If your meter leads are too short, you can make your own extensions. Just use thicker gauge wire or else you’ll also have voltage drop on those and false readings.

    the benefit of a Ford type relay is reducing the length of cable that is “hot” ie has electricity all the time. The relay is supposed to be close to the battery so it’s a very short run of constant voltage. And then the wire from the relay to the starter has no voltage so in an accident it doesn’t get pinched and short to ground and cause a fire. It only has voltage when the relay is activated. The same reason Nhra requires a shutoff at the battery if it’s in the trunk - so the wire running the length of the car doesn’t short to the frame/body in an accident. If it was to shut off all items in the car, they would require one all the time and not just when the battery is remote.
     
  9. badazz81z28

    badazz81z28 Veteran Member

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    The interesting thing is if you use a Ford relay, say in the trunk...I would need to run a trigger wire from the ignition all the way to the trunk. Lots of wires... lol
     
  10. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    Yes, but the current draw required to activate the solenoid is way less than that required to spin the starter motor.

    and like the other guys said, you can use a relay to trigger the solenoid. And yes I know that the solenoid is basically a mechanical relay, so you’re using a relay to trigger a relay.

    just think of the hose analogy. The longer the hose, the more resistance there is to flow. If voltage equals current times resistance, then as resistance goes up, the current available has to go down because the voltage isn’t changing. So the resistance to flow in too small of a gauge wire creates additional resistance leaving less amperage (current) available to spin the starter motor. Too big of a hose (or wire) is not a problem electrically (maybe cost or fitment wise though).
     

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