Quick gauge question

[Rat Patrol]

Probably not the best place for me to post this - but maybe Joe Dokes or someone will know...

I want to test my aftermarket Ampmeter in isolation using a multi meter

Is there any way to do it using ohms resistance measurment to see if its reading current as well as just passing voltage?

If not...

......can I connect my multi meter in series with the ampmeter - attaching a test wire from the BAT post on the Alt, to the ampmeter, from the ampmeter to the multi meter then from the multi meter to the start relay post?

 

[67Dart273]

Let's get some details here

LOL "what are you talking about?"

(I don't know what you know, so.............)

Many guys confuse ammeters and voltmeters.

Voltmeters are connected ACROSS the source, IE from pos to the ground on a battery

Ammeters are connected in SERIES with one leg of power, like a fuse.

If that is what you are doing, you need a multimeter with a similar scale. That is, you can't get a very good idea of what say, a 60A ammeter is doing when using a multimeter with a 20A scale.

The larger the ammeter, the less likely it is to be very accurate or linear

Your last part of the problem is how to provide a test load. If you are testing 20A or more, it might be difficult to come up with enough "stuff" to provide a stable load.

For LARGER loads, like starters, a carbon pile tester works:

But you could never test a dash mount auto ammeter with that

The last caveat is whether the ammeter you have is a remote shunt or high current type deal, like the old Mopar original

 

[Rat Patrol]

Im referring to an ammeter..or "amp meter" as Ive seen this term used on US forums...

I want to test a 1970s era Dixco ammeter - it has a 60 amp scale - Im not concerned about its calibration, just whether its actually reading current.

If I cant test it with a multi meter without it being connected to a circuit - then is my proposed jury-rigged circuit test suitable?

 

[Rat Patrol]

OK - got it sussed.

I connected the ammeter into series using the red ignition wire that runs from the bulk head connector to the starter relay....just for testing purposes.

Gauge showed a 30 amp deflection with the headlights on highbeam with the 50 amp factory driving lights on.

Gave up on the idea of checking the calibration against the multimeter - the gauge works well enough to tell if the alternator is charging enough - thats as good as the factory ammeter which this is replacing.

 

[Map63Vette]

I've always heard the old ammeters were pretty much just indicators anyway. I know my old one doesn't even have any numbers on it, so it's really just a relative idea of current draw, so I'd say you're fine with your replacement.

 

[67Dart273]

I've always heard the old ammeters were pretty much just indicators anyway. I know my old one doesn't even have any numbers on it, so it's really just a relative idea of current draw, so I'd say you're fine with your replacement.

This is pretty much true. They were never very accurate. The main thing is that they are OK at "center"

The age old argument, LOL "what is better, ammeter or voltmeter" I'd like to have both, but then, LOL

 

[Rat Patrol]

I would like both also - but finding a matching Dixco blue line volt meter to my ammeter and oil pressure gauges hasnt been easy

 

[Aliraza173]

I think there is an alternative where you can have the line next to the trans, but it has to be in a metal sleeve of a certain thickness. I remember something along those lines at least. It was stated something like the line needs to be properly shielded as it runs past the bellhousing and suggested something like a pipe or tube. Routing it on the outside of the frame would pretty much have the same effect.

 

[72BBSwinger]

One way I've used to measure amp "draw" is with the negative side of the battery unhooked you put the ammeter leads with positive on the negative battery post and negative lead on the battery cable. Then run the accessory and the ammeter will measure its draw.

 

[TrailBeast]

One way I've used to measure amp "draw" is with the negative side of the battery unhooked you put the ammeter leads with positive on the negative battery post and negative lead on the battery cable. Then run the accessory and the ammeter will measure its draw.

Until I saw your post I was going to suggest exactly that.

I have used a AA battery just to be sure they work at all.
(+ to one terminal and - to the other)

 

[72BBSwinger]

I have saved so many people from the dead battery in the morning issue this way I have lost count.

 

[Joe Dokes]

I agree with the other posters. Factory Ammeters are mostly to show which direction current is flowing, and are not known for being terribly accurate. Most volt meters are only good for testing a VERY small amperage, in the 1-2 amp range.

You really need something like this to measure amperage.

http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

Personally I am not a big fan of ammeters for a couple of reasons. First, all of the alternators current flows through the meter, if you are using a late model alternator that can put out over 100 Amps the stock wiring will not handle the current. (There are fixes for this though). Second, since all the current from your alternator flows through the ammeter if it fails you're screwed.

I've seen a couple of stories in magazines and online of guys hacking the dash to replace the ammeter with a volt meter. Results have been anywhere from awesome to well... less than awesome.

Regards,

Joe Dokes