Because the way ammeters are commonly installed you are getting full alternator production amps through out the whole circuit. Voltmeters on the other hand are usually installed on a fused low amp wire ergo less amps less heating of the wire so any shorting would involve less current flow and less heating equals more TIME to investigate the problem before the shorted wire heats up something else to the point combustion starts. This is easily evidenced just by looking at the gauge of wire needed for correct installation. Ammeter large wire high current flow: short = very hot wire vs voltmeter much smaller gauge wire because less current flow short = much less hot wire. Less current flow = less heat makes for less chance of combustion. If your still not convinced do a search on all the posts of the problems Mopars had in the 60's with their FACTORY ammeters melting and shorting out whole systems and burning down whole cars. There are a few on here.
In my opinion, it depends on the era of the automobile you are building. If your building a 40s era hot rod you should be using an amp meter to be authentic.
<HR style="COLOR: #e5e5e5; BACKGROUND-COLOR: #e5e5e5" SIZE=1> <!-- / icon and title --><!-- message --> "whoever told you that was nuts. had an ammeter for 10 years in my OT truck. no problems ever." It is not wrong to have an ammeter if you wish however a volt meter on an alternator system is of the most value. In an alternator the voltage is what is controlled. The amperage is designed in and depends on the charge state of the battery. When testing an alternator a volt meter is really all that is necessary. It also does not flow current through it as does an ammeter so another HOT SPOT is eliminated. I prefer and recommend a voltmeter but you can put in what you want. Let us think this through though. Suppose you have a 40s to 50s car or truck with a 35 amp ammeter and you install a 100 Amp alternator or even a 70 which is very common in some brands. Would you want to be that ammeter rated at 35 or 40 maps having a 70 mp alternator feeding you and the cars system?(or the carrier of that cars fire insurance?) That is why. A volt meter will tell you all you need to know and will not offer any potential for trouble. Don
An ammeter really only tells you what kind of current your accessories are drawing on the charging system, they don't really tell you the state of your charging system, because an alternator is only going to put out the amount of amperage that the system requires at that point in time. In other words, even with a dying alternator, your accessories will draw current right up to the point of draining your battery dead with you having no knowledge of a problem til it's too late. IMO, with a voltmeter and some basic knowledge of a charging system, you'll see the signs of a discharge/improperly charging alternator way before you see it with an amp meter. I prefer voltmeters. Just my $.02
Automakers made the change from ammeters to voltmeters because of the ever increasing output of the alternators... necessitated by the increasing use of power accessories, a/c, etc. Having 90 (or more) amps running thru the firewall and dashboard to an ammeter is probably not wise... That being said I prefer an ammeter to a voltmeter in my old rides...
My 65 Comet came with a factory Ammeter which failed and took out the entire factory wiring loom! The car was completely stock including the alternator and was only about 7 years old at the time.I like the idea of a fusible link,most newer cars have had them for years. ROY.
I had an old ammeter in my T-bucket and decided to change to a voltmeter because I was aware of the concerns expressed in this thread. I waited until the last minute to do it after staying up all night performing several other tasks getting my car ready for a trip to the T-Bucket NATS in Colorado Springs. I should know better - I'm getting too old to miss a night of sleep. The new voltmeter worked fine and I thought I was ready for the trip. When we got there, we started the car and shut if off several times and went on a cruise. I noticed the voltmeter was showing about 12 volts but didn't go up to 14 like the one in my Avalanche. I didn't think much about it until the battery finally didn't have enough voltage to start the car. Luckily, this happened in Colorado Springs instead of Cripple Creek where we had been on the cruise that day. I jumped it off and left the jumper cables connected long enough to give me enough to get back to the motel. I then realized the problem was that when I removed the 8 gauge wires from the alternator through the ammeter to the battery, I neglected to run a wire from the alternator to the battery. I was safe from an ammeter meltdown, but had been running off the battery and it wasn't getting charged. Several of the other bucketheads helped me scrounge the necessary wire and terminals to connect the alternator. I was amazing! - the battery showed 12 volts at rest and 14 while charging when the engine was running. It was a major DUH mistake but most certainly not the last I'll make. I'm glad I made I made the change anyway and will have to be more careful (and rested) when working on wiring the next time.
Bumping this one because I think I wired my voltmeter incorrectly. It has two posts on the back. One is long and one is short. I am running a GM generator/ regulator. Does one wire go from the batt side of the reg and the other one to ground? I know it's charging because I hooked it up to my hand held meter. Thanks!
My thoughts are ammeter all the way. By the time the voltmeter tells you something it's too late. If the system isn't charging, its sure nice to know asap.
X2 Least of all the cost. When I got my 57 someone had at one time had an ammeter in the car and left the wiring in it after they took the gauge out. Couldn't get that old wiring out fast enough.
I think your understanding of what each type of the guages is telling you is mistaken. If the alternator is not up to par it's voltage output will likely drop and be seen immediately on the voltmeter. Ray
I personally like idiot lights, won't wire a car with amp gauge if brought to me. Just my opinion and i can turn the work away if I want.
I rewired my gauge. Just a line from the batt side of the reg to the + on the gauge. I then grounded the other stud to the rest of the instrument grounds. When I reconnect the battery, the gauge pegs. WTF? I have not started the vehicle again yet because it is still inside.
It sounds like you have a defective meter if it reads over battery voltage. If you hook it up backwards it usually won't hurt a voltmeter but maybe it did. It sounds like you might have a 6 volt meter or an ammeter instead of a voltmeter.
Here is the gauge in question. I did have it hooked up with power through it ( like an ammeter) originally. It didn't do anything then. I wonder if I fried it? Sent from my iPhone using TJJ sucka!
A joke right? Of course you know an ammeter wired to ground is a dead short... (for those who don't know) EDIT... I see you are talking a volt meter.... my mistake... Second edit.... If you originally wired it as a ammeter, (+ to power and - to load) the heavy current flow through the volt meter (depending on how it is made) could fry it. Also.... a 30 amp 6 volt ammeter becomes a 15 amp 12 volt ammeter....
Voltmeter will tell you all about your system. Amp readings don't really mean much if the volts are right. I've got a box of amp gauges that I would give someone, I'll never use them.
Many new cars don't have either, so you can see how they're not exactly essential. The ammeter, in my opinion is of the least value of the two. It tells you the total draw on the system from all components combined. You'll probably know somethings wrong without needing to read the gauge. The voltmeter will at least tell you if your battery is charging. The ammeter is also a single point of failure because everything has to run though it. So if it fails so does everything else. It's also not as safe because, again, everything has to go through it. Most vehicles did away with them a long time ago, probably because with all the added electrical components the increased current draw through a single device became a concern.
On my OT vehicles I have run both, in sailboats for cruising given the option 9 times out of 10 you will find ampmeters the reason is that it is much more important to know how much of a load is on the system. Voltmeters work just fine for cars and have one real advantage, KISS. What can be simpler than wiring one side positive the other side negative from the switch. An ampmeter requires a greater knowledge of your electrical system but in my opinion is a better measure of what is going on. On my build I will be using an ampmeter due to it being so much more authentic. On my OT build I will be using a voltmeter to keep things simple.
When you put an alternator with a high charging capacity in a car that originally had a generator, you can run a a parallel shunt wire from the output terminal on the alternator to the hot side of the battery. The size of the shunt wire will determine what percentage of the charging current goes from the alternator through the ammeter to the battery, and what percentage goes directly through the shunt to the battery. The ammeter will still indicate charge/discharge, but it doesn't have the entire battery charging/discharging load going through it. This is an old school, traditional forum, the dash in your traditional hot rod should have an ammeter in it. For protection, hide a fuse or breaker somewhere in the circuit. Installed correctly, and using good components, appropriately sized wiring, etc. an ammeter is not likely to cause any problems.
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