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Old 05-16-2020, 02:39 PM   #1
doug.nichols
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Smile Ammeter hookup

Can someone explain the correct ammeter connection for a 12 volt system and/or send pics? Thanks.
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Old 05-16-2020, 03:13 PM   #2
Charlie Stephens
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Default Re: Ammeter hookup

It is the same as the 6 volt system shown on all of the wiring diagrams. What is the max output of your alternator/generator? If over 20 amps you may need other changes like a 30-30 ammeter or a shunt and other wiring to support it. What do you have?

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Old 05-16-2020, 03:17 PM   #3
Jim/GA
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Default Re: Ammeter hookup

Hook the solid yellow wire to one post of the ammeter; either post, just pick one. Connect the yellow/black wire to the other post.

Before installing the instrument panel, temporarily connect the battery. Turn on the parking lights and observe which direction the needle moves (engine NOT running).

If the needle swings toward the "Discharge" side of the ammeter, you have the wires correct.

If the needle moves toward "Charge", you have them backwards. Disconnect the battery and swap the wires.

Now install the instrument panel and you're done.

You have a 50-50 chance of getting it right the first time. If you guess wrong, reverse them and carry on.
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Old 05-16-2020, 03:25 PM   #4
doug.nichols
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Default Re: Ammeter hookup

I"ll need to check my alternator output specs.
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Old 05-16-2020, 03:47 PM   #5
Patrick L.
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Default Re: Ammeter hookup

What Jim says.

An alternator ? Output will surely be more than 20 amps.
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Old 05-16-2020, 05:04 PM   #6
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Default Re: Ammeter hookup

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The alternator max output has nothing to do with what shows on the amp gauge! Don't fall into that trap.

The amp gauge ONLY shows what is go in/out of the battery while running. NOT what the alternator is putting into the vehicle electrical system. You could have 1200 watts of baja lights on the roof and an alternator putting out 100 amps to light them, the ammeter would show ZERO if the battery were at full charge and not losing current to an under-supplied load.

If you have a half-charged battery and a 10,000 amp alternator with internal voltage regulation your gauge will only show about 15-18 amps going into the battery to recharge it.

Those aftermarket 30-0-30 ammeters are all garbage. Keep in mind the ammeter is attached to 16 gauge wires and they will smoke in short order if subjected to more than 15 amps or so for an extended period of time. 30 amps will smoke a 16 gauge wire in about two minutes.

Even if you push start with an almost dead battery the alternator will NEVER deliver it's full output to the battery. The amperage through the meter and into the battery is determined by a combination of wiring and internal battery resistance.



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Old 05-16-2020, 06:32 PM   #7
rotorwrench
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Default Re: Ammeter hookup

An Amp meter will show what the load is on the system. If the load is less than 20 amps them it won't ever show more than what the load is. An alternator will pick up the load when it taxes the battery's capability to keep up with it. If a person installed some high amp load components other than the normal model A complement then the amperage could go over 20-amps. A short to ground can go all the way up to the alternator and battery's maximum capacity so wires will burn fast if there are no fuses in the circuit.

12-volt systems have the capability to carry more amps through a smaller wire. A normal wire size for a light duty 6-volt circuit would be a 16-gauge wire. In a 12-volt system it would be 18-gauge. There is nothing wrong with using the larger wire but a system fuse would be a good ideal in any case. I only use a shunt if I'm running a high ampere alternator like 60 or more amps with a lot of potential load. All the 24-volt systems I work on have large alternators and either a purpose made shunt or a calibrated shunt wire set up. For a tractor or a model A with basic electrical equipment, no shunt is needed.
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Old 05-16-2020, 06:50 PM   #8
marc hildebrant
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Default Re: Ammeter hookup

rotowrench,

The amount of current in a wire is the factor that sets the needed size not the voltage.

Since power is equal to volts times amps, a 12 volt system can pass twice the amount of power through the same wire as a 6 volt system.

Marc
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Old 05-17-2020, 09:12 AM   #9
rotorwrench
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Default Re: Ammeter hookup

I'm completely familiar with Ohms Law. I wouldn't say twice if I were you. It's not that linear due to resistance in the wire. A system still only draws as much amperage as is needed for the circuit load no matter what the voltage is. The wire size depends on more than one factor.

I use this Advisory Circular chapter 11 for conductor wire and fuse sizes when I have to fabricate or modify an electrical system. Using the charts are easier than doing the calculations to find out what size wire I need.
https://www.faa.gov/regulations_poli...cumentID/99861
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Old 05-17-2020, 06:40 PM   #10
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Default Re: Ammeter hookup

O.K. then....


Marc

Last edited by marc hildebrant; 05-17-2020 at 06:47 PM.
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