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Car ammeter installation

My nephew wants to install an ammeter from Sunpro in his Chevy Avero. I have been told that one shouldn’t, because of the possibility of causing a fire due to heavy amperes. He now has installed oil pressure, oil temp, water temp, and voltmeter. I think that the voltmeter gives enough info. If he does install one, what size wire should you use? The alternator is rated at 85 amps. I would think that you must match the max alternator output to the wire size. What is the proper way to install the meter and where?

I would not like to give instructions that the gague maker disagrees with,what instructions come with the gague? does the maker have a web site?.

Actually seeing 15% less than rated alternator output still earns it a “good” rating.What gague is the big wire from the alternator? there is your absolute max gague,one perhaps two sizes down from that.

There are instructions on the Sunpro site, but I agree with OP, this requires some significant rewiring, I wouldn’t do it for the small improvement in information over the voltmeter.

Some other amp meters have a remote sensing element, so that you don’t have to run heavy wires to the meter itself. You might look for one of those. (I agree, if you have a voltmeter, you don’t really need an amp meter too.)

I’m certain that you would never run 85 amperes into a meter. The house I grew up in only had 60 ampere service. As I remember, this required #2 entrance cable from the meter. While the ammeter is effectively in series with the other resistances from the alternator, it wouldn’t take the full 85 amperes. The ammeter movement was always put in parallel with a shunt resistance. I remember doing this in the physics lab. There are hand held ammeters that read the current flow inductively from the wire leading to the alternator. I’m certain that there is an inductive pick-up that sends a small voltage to the ammeter in the kits to put an ammeter in a car.

The ammeter was useful when automobiles had generators. Even then, many people didn’t know what the gauge was for, so many auto manufacturers used a warning light to indicate that current was not flowing to the battery but away from the battery. The one time when I found the ammeter useful was when I put new brushes in the generator of my 1954 Buick and accidentally shorted the field coil of the generator to ground. This effectively let the generator run at maximum current. On cars with alternators, this wouldn’t happen and I think that an ammeter with a modern car equipped with an alternator doesn’t give much useful information.

One of the first threads I started was “ampmeter or voltmeter which one do you want” you may wish to check the responses.I believe it was more towards votlmeter but still some ampmeter fans,then the thread degraded into who is best with Ohm’s Law.

I want to thank all that answered the question about how to install the ammeter and their thoughts. What has troubled me is that you would think as triedaq states, “that the alternator would never run at 85 amperes”. I thought that running a number 14 strained wire would be just great, but I have read articles that say you must match the alternator output to the wire size. To old school you are right a volt meter gives more information than an ammeter without the worry of setting your car on fire. This is my first time on a discussion group and you guys are great. Thanks, if you have any additional info please let me know.

An ammeter would have actually been useful to me this summer, when the brushes on my rectfier/volt reg wore past the servicible limit, resulting in intermittant alternator ops. (I was able to diagnose a problem with the brush/VR assembly via other means, but an ammeter would’ve made it much easier).

An ammeter would also be useful when one has one’s car jumped: you’d know just how far you’d need to drive to be able to shut down w/ enough juice to start again.

A rule of thumb that I generally use to match wire to current is to use 300 circular mils of wire cross section area for each ampere.

85 amps X 300cm per amp = 25500 cm which would be 6 gauge. Since 85 amps is the alternator’s peak rating and not necessarily the amps it will actually be putting out continuously, you can probably get away with 8 or even 10 gauge wire. I doubt if the alternator was wound with wire that big but that wire gets cooled by a continuous blast of air from the alternator fan.