Ammeter Issues

[6930]

Thought I would post to see if someone might have some thoughts on this.

Last couple of flights I been getting negative amps on my ammeter in flight. The reading is really flaky….sometimes it starts off reading correctly (taxi and run up) then goes negative during flight. As I add or drop load, sometimes it changes, sometimes it doesn’t change. Sometimes it is showing correct charge rate, sometimes zero. There doesn’t seem to be any consistency to it.

Just now, I hooked up a multimeter to the posts on the back of the gauge. Master on…no reading on either the panel or multimeter. Solid zero. Add load…nav lights, landing light, radio…no change on either instrument. I assume that I should get something off my multimeter if the amp meter in the panel is bad? If that assumption is correct, then it seems like the gauge is not getting correct amp reading from what….voltage meter?

Electrons are not my forte. Any thoughts appreciated.

Thanks!

[7698]

Sounds like the ammeter is the issue.
If you have your test meter across the terminals you wont see anything on it.
If you want to see the current being used in the circuit youll need to disconnect one of the cables on the ammeter and put the multimter in between, so one lead from the multimeter on the cable you've just taken off and the other on the ammeter terminal... With the multimter on the AMPS setting ( suggests 20A range if your meter has it - dont try the landing light, it draws too much current for a 20A multimter) This will confirm the current being drawn. If the panel ammeter still doesnt read, then its duff. IMO.

A word of caution... Dont let the cable connections touch any metalwork as there is generally no fuse protection feeding the ammeter... you'll make an arc welder!!

[6930]

Got it, thanks!

I'll give that a try.

[6643]

Yes, you cannot put two ammeters in parallel. They have to be in series.

If you have a digital meter (one that can read positive and negative voltages without swapping leads) you can wire the voltmeter across the terminals of the ammeter. Reading milli-volts should track the reading on the ammeter, although the numbers will be different. A 10 amp charge and a 10 amp discharge will both always show the same voltage, but one will be plus and the other minus

An easier way to get a feel for the meter itself is to simply turn the master on (engine not running) and add and subtract loads. If the ammeter reflects the loads correctly then it's probably OK.

Another test you can do is to monitor the voltage on the bus. If the voltage drops when the ammeter does, and you haven't changed RPM or electrical load, then you have a charging problem. If it remains steady the ammeter is faulty.

More likely your generator or voltage regulator is getting flaky.

[6930]

I hooked up my multimeter in series and managed to pop the 10 amp fuse in the meter. Must have been the beacon that did it. So, I hooked the amp meter back up and simply turned the master on and added loads…radio, lights, beacon, landing light. The amp meter in the plane is stuck at 0 even though all that stuff came on and functioned properly.

Previously, it has been moving around with load, but now it is not moving at all.

So, I’m guessing it is the amp meter itself. Now I need to figure out how to get it out and what a good replacement for it will be.

Thanks for the input! Much appreciated.

[6930]

Got it out (phew, my aching back) and found this one to replace it:

https://www.aircraftspruce.com/catalog/ ... mmeter.php

I have an Aircraft Spruce near me and it's in stock, so I should be back in business on Monday. Any thoughts on whether this one is the best replacement option are welcome...but I think I should be good.

Thanks all!

[6930]

It was the ammeter. New one works great….EXCEPT….the needle really wiggles from vibration when flying (okay on the ground). I will keep it for now but probably will change it. Anybody try the Stewart Warner 82200?

I can’t seem to find a 2” FAA/PMA analog gauge anywhere. That would be my preference, of course. Anybody know of one?

[6643]

The originals were automotive gauges; there was no PMA then. All the later PMA'd ones are"standard" mounting.

[6930]

Thanks John. I kind of figured that is where this was going.