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Old 08-08-2020, 08:10 AM   #1
f balsiger
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Default 12v amps gauge

can I use a stock 6v amps gauge in 12v neg ground system?
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Old 08-08-2020, 08:34 AM   #2
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Default Re: 12v amps gauge

Yes, reverse connections for neg ground.
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Old 08-08-2020, 08:38 AM   #3
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Default Re: 12v amps gauge

Yes, although if your going to run a high current alternator you may want a shunt across the ammeter to reduce its throw. Overdeflection will kill the ammeter. An original ammeter is not something you want to waste, the repros aren't so good.
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Old 08-08-2020, 05:26 PM   #4
f balsiger
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Default Re: 12v amps gauge

ok reverse wires. alternator goes to +?
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Old 08-08-2020, 08:56 PM   #5
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Default Re: 12v amps gauge

Using a shunt across the ammeter pretty much makes the amp gauge non responsive.
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Old 08-09-2020, 08:29 AM   #6
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Default Re: 12v amps gauge

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Originally Posted by f balsiger View Post
ok reverse wires. alternator goes to +?
Facing front of ammeter, stock battery wire (yellow) goes to right side, generator wire (yellow-black) to left. Reverse those for negative ground.

Forget a shunt. Just makes normal battery current hard to read. Use common sense instead:

Sure, if you switch on your Blazing Baja Beams and Behemoth Boom Box with the engine off, you'll likely peg the meter into the Far Far West.

Don't do that.
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Old 08-09-2020, 09:06 AM   #7
30 Closed Cab PU
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Default Re: 12v amps gauge

Current draw out of the battery and charging current should be less on a 12 V system compared to a 6 V system. Assuming all the loads (horn/starter, lamps, etc) are proper for a 12 V system.



So the gauge should be OK but most likely will read less. The gauge does not care what the battery voltage is, just the load/charging amperage.
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Old 08-10-2020, 02:10 AM   #8
Richard in Anaheim CA
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Default Re: 12v amps gauge

Most alternators will put out at least 35 amps immediately after starting.
Install an aftermarket ammeter from Model A parts dealer with 30/30 reading.
They look just like the 20/20 original except the higher amp readings.
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Old 08-10-2020, 06:12 AM   #9
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Default Re: 12v amps gauge

To the OP: I agree with Badpuppy's comment, it is possible to use the stock 6 volt ammeter in a 12 volt system by reversing the leads.

This is off topic somewhat: I installed an AC unit in a recent build of a touring car. Every time the AC compressor clutch would engage, the needle would peg...hard. After a few days, the needle disappeared as it was knocked right off the pivot points. I did not know what size shunt to install so I installed a second ammeter under the hood to split the load. Both meters show a good draw when it starts...just short of pegging but so far, I have not lost sight of anymore needles.
Anyone have a guess of what size shunt is needed based on my description? Thanks Guys.
Good Day!

Last edited by Dave in MN; 08-11-2020 at 04:39 PM.
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Old 08-10-2020, 10:25 AM   #10
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Default Re: 12v amps gauge

Agree with Dave-in Minn. The current draw of a AC is almost constant load of 25/30 amps depending on the AC clutch cycling. That continuous load will cause the 30 amp meter to get hot because it is at the top of the load rating. On a cross-country road trip one of our cars, AC equipped, burned the amp meter up. Mine got very hot to the touch. I made a temporary shunt using 6 foot #16 wire wrapped around a 3/8 dowel approx. 3" long. It works well. First start of the engine the amp meter indicates about 5 amps charge very briefly.

Am experimenting to create a shunt that will indicate a charge of about 10/15 amps with full AC and Headlights load. If you have already done this please message me.
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Old 08-10-2020, 08:38 PM   #11
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Default Re: 12v amps gauge

Quote:
Originally Posted by CarlG View Post
Using a shunt across the ammeter pretty much makes the amp gauge non responsive.
You need to increase the resistance of the shunt so more goes through the ammeter. The ammeter gauge in my '32 reads almost exactly half so I just remember to double it. See photo. If I was doing it on my Model A where there is less room I would just run a second wire of the same gauge from the output of the generator or alternator to the opposite post on the ammeter.

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Old 08-11-2020, 12:15 PM   #12
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Default Re: 12v amps gauge

The ammeter shows the amps that the generator is putting out , not the voltage . I use the same ammeter with 12 volts that I use with 6 volts . The original unmodified generator will charge a twelve volt battery with no problem . I use the Fun Projects 12 volt voltage regulator that takes the place of the cut out . As has been said , the generator doesn't know the difference because the generator charges in amps . Generator out put can be controlled by the adjustable brush in the generator . Pushing the adjustable brush downward toward the ground raises the amperage out put . Raising the adjustable brush upward decreases the amperage out put . I have used the 30 amp ammeter when using the 60 amp alternator just for good measure . High amperage out put charges the battery quicker . A voltage regulator , when used prevents overcharging the system .
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Old 08-11-2020, 12:16 PM   #13
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Default Re: 12v amps gauge

I never need a shunt .
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Old 08-11-2020, 12:22 PM   #14
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Default Re: 12v amps gauge

Use nichrome wire to make an ammeter shunt. A good original ammeter is something you don't want to ruin. Size the shunt for the deflection you want, use an inline ammeter to give you the calibration factor.
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