What good is an amp meter? I've been told that's what you run with a generator and an volt meter with an alternator. Why? I'd like to know my charging system is working all the time rather than have a gauge showing zero all the time. What's the reasoning?
An ammeter on a generator 'tells' you a bit different information and that has to do with how they work. Generators are 'self exciting' (don't necessarily need a external voltage source) and can produce enough voltage but not enough current to supply all loads and adequately charge your battery. A ammeter will show this as a slight discharge. With only a voltmeter, by the time the voltage has dropped enough to really show, it's usually too late. It will also be really hard on the generator.... Alternators need an external voltage source to produce both voltage and current, so any reduction in voltage below 'spec' will directly indicate a problem. Any properly operating charging system will show a slight charge on an ammeter; enough current is being produced to supply the connected loads, what you see is the 'charge' current to the battery. The downside to ammeters is you have to run the entire vehicle electrical load (except for the starter) through the meter for it to be accurate, which isn't so easy if you have a lot of power accessories unless you can find a inductive or shunt-type ammeter (and I've never seen either one sold by the aftermarket).
Thanks for that, it all makes sense. Would a volt meter be a better indicator of an impending problem?
Be careful with the Ammeter. If you run a high current alternator (above 40 AMPS), you run the risk of an electrical fire. Depends on the gauge. I've had some 60's cars that were good to 60 amps. But they had 60 amps marked on the gauge. My Studebaker has a factory rated 40 amp alternator.
On a generator, not always. Yes if you have an alternator. If I were running a generator, I'd use an ammeter for primary charging system monitoring, a voltmeter as secondary. But make sure both the meter and the wire can carry the output current of the generator. Most 'vintage' generators were only rated for 30 amps, but some were more so it would pay to check.
After changing over to a volt meter, off the switched side of the fuse panel, and reattaching all the main power lines my old back is too sore to do anything else. I think I'll use the volt meter for a while. Especially after a new regulator and a rebuilt generator after being stranded fifty miles from home. Wouldn't a volt meter tell me if the electrical system isn't charging more effectively than an ammeter?
Idiot light will tell you if the system is working. I had a bad diode in an alt. I had switched it from one car with a voltmeter. Voltmeter was showing 13 volts. Installed the alt. on a car with the idiot light and the light didn't go out. Took it to shop who found the bad diode.
If you're running a generator, again, the answer is maybe. If the problem is not enough voltage output, the voltmeter will tell you. But if voltage is good but current is low (something that can happen with a generator), a voltmeter won't tell you that until your battery is discharged enough from lack of charging current, at which point the car probably won't start if you shut it off. What loads does your car have besides the 'basic' ones of ignition system, headlights, and taillights? Electric wipers? Heater? AC? Electric cooling fan? As a cautionary tale, I had a '64 Comet that on dark, stormy nights while running all lights (including the high beams), heater, and wipers, the stock generator (even after being rebuilt) couldn't keep up with the load. This was shown as a discharge on the ammeter, even though the lights were still bright. Drive far enough, and the battery would get low enough to notice (dim lights) but at this point if you shut the car off it wouldn't start... I swapped to an alternator. Generators were replaced with alternators for a lot of very good reasons.
Great info Crazy, thanks. Why is it that a generator will create its own field coil juice but an alternator won't? Because of the A/C?
Just the basics, lights, heater, wipers, that's it. And no, there isn't an alternator in the car's future. Thanks for your input.
They both work on the same principle, but without getting too deep into electrical theory, it's because a generator will leave residual magnetism in the field poles ('self exciting'), an alternator can't. A generator doesn't 'make' DC voltage, it makes AC, the brushes/commutator 'convert' it to DC (basically a mechanical diode). Add in the mechanical limitations of the generator and you just can't get the same output as you can from an alternator or the same reliability. Dug, you might want to have your generator load-tested to be sure it's putting out adequate/rated current. I've seen freshly rebuilt ones fail load tests....
Ammeters themselves do not start fires...FUBAR wiring does. Volt meters measure voltage - or, more precisely, the difference in voltage between two points. Ammeters measure current or 'flow' - for this reason it is necessary for an ammeter to be wired in series (all the current must flow through the ammeter), so the risk of a short is greater. Wire your car safely and use a quality ammeter rated for your generator output and you should be okay.
OT 1970s 80s Dodge trucks melt dashes in the ammeter area. No fubar there, just factory design. I think ammeters look good in theory but don't work well long term in reality. Since so much current is sent through one, the tiniest amount of corrosion causes a voltage drop to 99% of electical devices on the car. Devices meant to work at 14v+- don't work well at 9.5v for example. Ohm's Law at work. This subsequent voltage drop in effect makes the ammeter connections a LOAD. Just like headlights, horn, starter, etc are a load. Except this load does no useful work and wasn't a design feature. This load produces heat which in turn makes the corrosion worse which in turn increases voltage drop. On and on. Not good. No wonder there are fires. My vote is for an alternator system with a voltmeter AND idiot light.
The Dodge truck issues you mentioned were the result of a design flaw (who in the hell designs plastic wrapped ammeter connections?) You are correct that corrosion in the system can be bad - wire it correctly, keep it maintained (wires inspected, connections cleaned & greased) and you won't have a problem.
Yep, nothing wrong with a properly-installed ammeter; the car makers used them for years with generally no issues. But unfortunately, most builders (both home and pro) don't fully understand all the technical aspects of sizing the wire and particularly how to terminate it. It's a wonder more cars don't burn up.....
just got a stewart warner voltmeter connect it up to switched ignition and ground. it just pegs out over 16v is this a faulty meter or am i doing something wrong.
A bolt meter will tell you what is going on with the charging system much better than an amp meter will
After reading the instructions from SW, the gauge can't have any heavy voltage passing within 3" of the gauge. Try rearranging your wire harness. I know, sounds crazy but mine wasn't working correctly either until I moved some wires away from the gauge.
Amp meters are too dangerous a wiring job and one more source for bad connections to your overall system. If you just install a simple volt meter (1/2 Amp fuse with 16 Ga. wire) and observe cranking and driving condition voltages it will tell you if things are going sour. Examples: 1. During cranking the voltage shouldn't fall too low. That would indicate either an undercharged or failing battery or a starter problem developing, either of which could be caused by loose connections or a failing charging system. 2. Driving voltage starts a decline. That could be caused by a failing charging system or the wiring to it or a battery going bad. In that case, shut down any unneeded loads and head to a convenient stopping area. If you have a modern "non-points" ignition with power steering or power brakes, be ready for a complete engine failure and the loss of effective steering and/or braking.
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