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Thread: One Wire Alternator with Ammeter ?

  1. #1
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    One Wire Alternator with Ammeter ?

    THe generator system is shot in our 57 Hawk. I"m planning to replace it with a one
    wire alternator. I'd like to keep the ammeter. If I run a #10 wire from the alternator
    12 volt post through the ammeter and back to the battery it should work--I think.
    Anyone done this? Suggestions ? Fuze protection?
    ...Dick

  2. #2
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    Using an ammeter designed to handle 30 amps with an alternator of a much higher capability is not recommended. Chances of failure and resulting shorting and risk of fire are possible. Do an advanced search here and you will find plenty of reading on the subject. On a Hawk it would be easy to replace the ammeter with a voltmeter.
    Last edited by 41 Frank; 04-03-2011 at 07:50 PM.

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    Speedster Member 5brown1's Avatar
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    I did that with my 37 coupe using the original ammeter. It works fine with a 100 amp alternator. I rewired the whole car with an EZ Wiring harness.
    I don't believe that the wire went directly from the alternator to the ammeter so you might want to check that out. Seems that I remember wiring the ammeter from the battery but it has been a couple years so I'm not sure.
    .

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    Do not use an ammeter with a 100 amp alternator. You can get a stewart warner voltmeter to match your instrumentation.If you are compelled to use the ammeter, you need to use fusilble links on either side of it. It's dangerous, so don't do it. Thanks, m weiss

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    you can get away with this IF your electrical demand (LOAD) isn't increased beyond the current carry capability of your ampmeter. If your wanting to keep the ampmeter for originality I'd electrically remove the ampmeter from the circuit and just supply the loads direct (no wires to ampmeter) Either way use fusible links, you can buy the fusible links at napa. Use 2 sizes smaller fusible link then the wire your protecting.
    Quote Originally Posted by 5brown1 View Post
    I did that with my 37 coupe using the original ammeter. It works fine with a 100 amp alternator. I rewired the whole car with an EZ Wiring harness.
    I don't believe that the wire went directly from the alternator to the ammeter so you might want to check that out. Seems that I remember wiring the ammeter from the battery but it has been a couple years so I'm not sure.
    .

    Russ Shop Foreman \"Rusty Nut Garage\"
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    If an ammeter is wired correctly the only current that the alternator will push through it is what is sent to recharge the battery. Just because it's capable of 100 amps does mean it will have the voltage to push in into the battery except perhaps in the case of a short. It should send no more current through the ammeter to the battery than any other generator or alternator operating at the same voltage. Just use a fusible link or circuit breaker in case of a short or regulator malfunction. If it wired incorrectly it could be a problem.

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    You can put a shunt (bypass or jumper wire) across the ampmeter to carry most of the load. Most of the current will then flow past the meter. A small ammount of current will still flow thru the meter. The meter will still indicate the direction of current, charge or discharge, but it won't read the actual current flow.
    Dwight 54 Commander hardtop

  8. #8
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    I did a search before posting but found little on wiring the alternator. Probably I should put the ammeter in series
    with the load wired through the ignition switch. That way the meter should only see the load which in this car
    is less than 30 amps even with headlights and blowers on.. The fusible links are a fine idea. Am I right in assuming the one wire goes to the battery
    directly ? Seems it must but since that line is not switched, what prevents a return discharge current to the alternator when
    the car is mot running. The diodes ? The voltmeter will go in if a problem develops. I learn more from current readings
    like how much charge rate, discharge info , battery condition, and what the load is doing.

    Many thanks for the help. Ohm's law will triumph.

  9. #9
    Speedster Member Jackson's Avatar
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    This website has some great info on 10SI & 12SI alternators, one wire vs three wire and ammeter vs voltmeter. I bought the 10 SI, three wire kit for my speedster. I only have start & run connected at present, plan to use voltmeter.

    http://www.madelectrical.com/electri...hreewire.shtml

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    It's 4 gauges less for the fusible link,not two.

  11. #11
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    Ammeter in a vehicle is usually wired to show only current to and from battery. One side should hook to the battery, the alternator and feed to everything else on the other side. Hooked this way only shows charge going to battery or discharge if alternator is not putting out sufficiently to handle load.(or engine off with a load, i.e. lights) You could hook a self resetting circuit breaker on the battery side if your concerned about overloading . Fusible link would work but if you should burn it out you have to replace.

  12. #12
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    READ THE QUOTE its 2 wire sizes not 2 gauge, wire comes in even #'s.
    Thanks
    Quote Originally Posted by mrobertweiss View Post
    It's 4 gauges less for the fusible link,not two.

    Russ Shop Foreman \"Rusty Nut Garage\"
    53 2R6 289 5SpdOD (driver)
    57 SH (project)
    60 Lark VIII 2dr sd (driver)

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