Aftermarket ammeter

[garyfish]

Anybody have one in their T4WD?

I'm considering purchasing and installing an amp gauge, because I have (or soon will have) some electrical accessories with potentially high current draw -- fog lights, etc.

But I ran across a post on this forum that indicated it may NOT be such a good idea to install an aftermarket ammeter gauge in our vehicles: viewtopic.php?f=2&t=1228

its best you hook up only voltage meter, amp meter does not get along with our alternators

Any thoughts or info on this?

[teranfirbt]

I doubt the Alternator would care. The biggest problem with an ammeter is that you're now running all of the current from your alternator to the dash and back to the battery, there's a lot of wire there, plus the gauge will cause a little resistance. If you're really running some high draw stuff, this is liable to burn out the ammeter itself, causing you to lose charging at the most inopportune moment (late at night, middle of nowhere, raining like hell).
A voltage gauge tells you a lot more about the state of your charging system than an ammeter ever will and won't cause problems with charging.
Depending on how much stuff you want to run, you may want to look into upgrading your alternator to a GM CS series (130 or 144). I've done that swap on my old 22RE and the 2RZ-FE in my Celica, and will be doing it in my Tercel when I get back to school.

[garyfish]

Thanks for the info.

Independently, I came to the same conclusion after doing some internet research:

Voltmeter, yes
Ammeter, no

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http://www.autometer.com/tech_faq_answe ... id=1&qid=5

Which is better for monitoring a vehicle's electrical system - a Voltmeter or an Ammeter?

Short answer:

A voltmeter, by far.

Electrical guru Mark Hamilton of M.A.D. Enterprises points out that amperage is a measure of current flow, so an ammeter is actually a "flow meter" that's intended to measure current flow to the battery (under normal conditions) or discharge from the battery (in the case of alternator system failure). On a typical flow meter, all output must be directed through the device to obtain an accurate reading. In the ammeter's case, that means all the alternator output used to recharge the battery must first be routed through the ammeter under the dash. Which requires a heavy-gauge cable and presents a possible fire hazard. And the ammeter itself must be able to handle all this current flow, so it must have a higher current rating than the alternator's maximum rated output.

All this might be worth the hassle if the ammeter produced reliable information. But the ammeter can only measure the amount of current output to the battery for recharging purposes: When the alternator recharges a "low" battery, the ammeter indicates a high charge rate; with a fully charged battery the voltage regulator reduces alternator output, and the ammeter is supposed to indicate a very low charge rate. But how can you really tell the regulator has reduced alternator output because the battery is fully charged? Maybe a diode in the alternator rectifier failed, or the alternator belt slipped after it warmed up, just as if the battery were fully charged. Or maybe the meter indicates a medium charge rate most of the time-does the battery want this much or could the voltage regulator be overcharging the battery?

On the other hand, a voltmeter works like a fuel pressure gauge-but instead of measuring fluid in psi, the voltmeter measures electrical system pressure in volts. Just like a fuel pressure gauge, a voltmeter only needs to tap into a circuit; all the fuel (or electricity) does not have to detour through the gauge itself. Voltmeter installation is easy, quick, and safe: It hooks up to a fused, ignition-switched "off/on" source and does not require any modification of the circuit used to recharge the battery or any part of the alternator/regulator system. In short, the voltmeter installed at the dash will be a stand-alone circuit.

The voltmeter directly measures the result of charging-system performance. With normal alternator/voltage-regulator function, battery voltage is maintained at 14.0 to 14.5 volts-and this is reported directly by the voltmeter. In the event of alternator-system failure, voltage will be low and continue to drop as the battery discharges. In the event of an "overcharge" condition, the voltmeter will climb above its normal zone. In summary, there is no chance for misinterpreting a voltmeter's readings as can happen with an ammeter.

Voltmeter vs. Ammeter?

Auto Meter offers both, but for most applications a voltmeter yields a safer installation while providing more useful information on charging-system conditions.