Ammeter convert to Voltmeter

My Ammeter died so I decided to convert to a modern voltmeter.
I have the voltmeter working well. The question is what do I do with the heavy blk wire from the alternator that used to run to the Ammeter?
I'm still chasing some odds and ends of wires and waiting for new headlight switch but the wire from the alternator has me perplexed.

 

X2

An ammeter tells me EXACTLY what the charging system is doing (charging/not charging? working/not working?). Whereas the voltmeter kinda just, well, sits there and takes up space on the dash!

 

Can I run both?\
I already have the voltmeter but since I am building a custom dash instrument cluster I have room.

 

I would connect them on the positive terminal of the volt meter (You did have two wires going to your ammeter right?) That gets them out of the way and ensures they don't ground out.

Sure you can.

 

I used to believe that a ammeter would tell me if my charging system is working good, and it does but so does a voltmeter and with a lot less chance of burning the vehicle to the ground, a 12 volt battery will only produce at most about 12-12.6 volts but if you look at your voltmeter with the engine running it should never read below 14 volts if the alternator is charging the battery, therefore it does tells you that the system is charging and the battery is in good shape. When you turn the key on your jeep but don't start it look at the voltmeter if it is running very low then it means your battery is not holding the charge or you have dead cells in it, an ammeter can't do that and it can't show you what kind of shape the battery is in only that the alternator is charging or the battery is discharging. I replaced my ammeter with a voltmeter when I rewired my jeep.

 

I think the problem with an ammeter is if you put in a higher output alternator in the output of the alternator can exceed the capacity of the ammeter creating a potentially dangerous situation. I have also heard/read stories about ammeter being the source for underdash fires, but these could be nothing more than campfire stories.

You could run both. I find I get enough info from the voltmeter though. My alternator was packed pretty good with mud on a run earlier this year and it was pretty evident from the voltmeter. Exactitudes aside, you can still get a whole lot of info from a voltmeter. If the voltmeter is reading 12vdc when running then there is a problem.

 

Not a myth, I can vouch for this with 1st hand experience. A loose wire rubbed on one of the studs for the speedometer eventually shorting out on the dash and set part of the wiring on fire. This happened right after I bought my jeep back in 92".

 

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.

 

TGregg,

Your dialogue provoked a thought/comment. The newer alternators are intended to support the entire electrical system, whereas previous thinkings were that the battery supports the electrical system and the alt. maintains the battery. I suppose that that is why ammeters were used; to determine how hard the battery was working.

I like your analogy on measuring how "full" the electrical system is.

Karl

 

I wish I was that smart. It came from the company I have bought my gauges from.

 

I run both an ammeter and a voltmeter on my '68. However, I don't run the big heavy wire to the ammeter. I have what is called a shunt mounted on me firewall and the heavy wires go there. I can then run light wires to the gauge and not have to worry about the wires breaking. This is the way it's done on boats and I happened to have a set, shunt and ammeter, left over from my boating days, so I used them. Works great.