Ammeter question
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New User
Joined: Mar 2017
Posts: 12
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From: Seymour, WI
Ammeter question
I’m converting my 51 to 12 volt and will be using a 120 amp alternator. I’ve read mixed reviews that this will overload the factory ammeter. I found a guy who converts them to voltage meters so if that’s what I need to do I will. If the factory ammeter will be fine with me running the wire through the loop then I’ll do that.
I don’t plan on using the factory distribution block that is attached to the gauge either. I was planning on running a 10 gauge b+ wire off the alternator through the ammeter loop and back to the starter solenoid. If you have a better suggestion please let me know.
I don’t plan on using the factory distribution block that is attached to the gauge either. I was planning on running a 10 gauge b+ wire off the alternator through the ammeter loop and back to the starter solenoid. If you have a better suggestion please let me know.
Cargo Master
Joined: Feb 2008
Posts: 2,795
Likes: 129
From: Windermere Valley,B.C. Ca
Not only better, but safer, and it wont burn your truck up. I'm open to correction if I am in error.
The original style ammeter as you mention has all the current for the truck going through it,(wired in series) especially with a higher output alternator. (read arc welding power) The ammeters (or charge indicators) in newer cars are not ammeters, they are voltmeters that are calibrated to look like ammeters because they just use low power battery voltage in parallel. Much safer. I would just install a volt meter, 12 volts at rest, around 14 when running.
The original style ammeter as you mention has all the current for the truck going through it,(wired in series) especially with a higher output alternator. (read arc welding power) The ammeters (or charge indicators) in newer cars are not ammeters, they are voltmeters that are calibrated to look like ammeters because they just use low power battery voltage in parallel. Much safer. I would just install a volt meter, 12 volts at rest, around 14 when running.
Fleet Owner
Joined: Jul 2004
Posts: 27,298
Likes: 1,059
From: NM
The stock ammeter operates by induction, absolutely zero current goes into the meter itself. There is always the possibility of the induction loop wearing thru the insulation on the wire passing thru it, resulting in a short, but with modern wiring (and perhaps a sleeve of heat shrink) it is unlikely.
I'm running a 65-amp alternator with my stock ammeter. No damage after 13 yrs. Why are you using a 120 amp alternator, are you really going to have that kind of load? Or is that what is on the engine you're using?
I'm running a 65-amp alternator with my stock ammeter. No damage after 13 yrs. Why are you using a 120 amp alternator, are you really going to have that kind of load? Or is that what is on the engine you're using?
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
What Ross said.
The stock ammeters use the Hall Effect, and in principle are only taking a measurement. I'm running a 85 amp alternator with AWG 6 wire through mine with no problems. The worst case scenario with your alternator is that it may bend the needle. So what gauge wire are you using for 120 amps?
And don't forget to change direction of the alternator wire through the ammeter loop if you will be negative ground.
The stock ammeters use the Hall Effect, and in principle are only taking a measurement. I'm running a 85 amp alternator with AWG 6 wire through mine with no problems. The worst case scenario with your alternator is that it may bend the needle. So what gauge wire are you using for 120 amps?
And don't forget to change direction of the alternator wire through the ammeter loop if you will be negative ground.
Thread Starter
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New User
Joined: Mar 2017
Posts: 12
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From: Seymour, WI
The stock ammeter operates by induction, absolutely zero current goes into the meter itself. There is always the possibility of the induction loop wearing thru the insulation on the wire passing thru it, resulting in a short, but with modern wiring (and perhaps a sleeve of heat shrink) it is unlikely.
I'm running a 65-amp alternator with my stock ammeter. No damage after 13 yrs. Why are you using a 120 amp alternator, are you really going to have that kind of load? Or is that what is on the engine you're using?
I'm running a 65-amp alternator with my stock ammeter. No damage after 13 yrs. Why are you using a 120 amp alternator, are you really going to have that kind of load? Or is that what is on the engine you're using?
What Ross said.
The stock ammeters use the Hall Effect, and in principle are only taking a measurement. I'm running a 85 amp alternator with AWG 6 wire through mine with no problems. The worst case scenario with your alternator is that it may bend the needle. So what gauge wire are you using for 120 amps?
i believe I put 10gauge in my original post but that was a typo. I was planning on running 6ga. Is there a better way to route the wire so I don’t have to run it from the alternator through the ammeter back to the starter? I would prefer not to run the entire charging supply all that ways, but rather just from the alternator to the starter.
And don't forget to change direction of the alternator wire through the ammeter loop if you will be negative ground.
The stock ammeters use the Hall Effect, and in principle are only taking a measurement. I'm running a 85 amp alternator with AWG 6 wire through mine with no problems. The worst case scenario with your alternator is that it may bend the needle. So what gauge wire are you using for 120 amps?
i believe I put 10gauge in my original post but that was a typo. I was planning on running 6ga. Is there a better way to route the wire so I don’t have to run it from the alternator through the ammeter back to the starter? I would prefer not to run the entire charging supply all that ways, but rather just from the alternator to the starter.
And don't forget to change direction of the alternator wire through the ammeter loop if you will be negative ground.
Cargo Master
Joined: Feb 2008
Posts: 2,795
Likes: 129
From: Windermere Valley,B.C. Ca
Is there a better way to route the wire so I don’t have to run it from the alternator through the ammeter back to the starter? I would prefer not to run the entire charging supply all that ways, but rather just from the alternator to the starter.
With the greatest of respect I think the point here is not if the old ammeter is dangerous, it is, because of the amount of current available, (risk management) and making it worse by increasing the wire size. The starter circuit never went through the ammeter, to much current, that is just a way of connecting the wires,yes it can go direct if you replace the ammeter with a voltmeter.
Fleet Owner
Joined: Jul 2004
Posts: 27,298
Likes: 1,059
From: NM
There's no way around running both the alternator and main BAT wires up under the dash if you want the ammeter to measure Net Charging. In that respect a voltmeter makes sense. My ammeter is on Zero 99% of the time anyway.
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Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
Exactly! The only time your ammeter will be reading significant amperage charge is right after you start the engine. No way is your alternator going to be putting out 120 amps continuously. Your AWG 6 wire has adequate ampacity for intermittent use with 120 amps. The stock ammeter will take up to AWG 4 wire. They are not dangerous, they are only measuring the imbalance (charge/discharge) of current flow. If you are concerned with voltage drop over the AWG 6 wire run, don't be, it's relatively short and the return path is through the chassis. But yes, you can bypass the ammeter altogether if you wanted to use a voltmeter. And I would advise installing a 120 amp circuit breaker in your alternator circuit.
Last edited by Mixer man; Jun 29, 2019 at 11:23 AM. Reason: 120
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