DC Ammeter Identification

May 28, 2015
275
Catalina 385 Long Branch, NJ
My 500A DC Ammeter suddenly started providing current readings as high as 900 Amps with no decimal and fluctuating between 150-900 amps. The boat and the ammeter are 3 years old and have worked flawlessly until today (typical range was 0-30 Amps, always with a decimal). My system is a 12 volt system and no I don't have anything that would draw anywhere near 900 amps. It showed this reading even when everything on the board was shut down.

I don't think the cause is corrosion as the shunt and connections are pretty clean.

As a first step, I'm trying to figure out the manufacturer of the Ammeter. I think it might be Paneltronics but their part number is 570-006B not 570-006.

In addition, I'm trying to figure out whether there is anyway I might be able to test whether the meter is working properly or confirm that the shunt is working properly.
Anyone know what Catalina put on their 2016 385s? I'm going to reach out to the dealer in the morning but thought someone here might know.

Any suggestions on what might have caused this, which Ammeter I have, and any other steps you might suggest?

This is the label on the Ammeter:
IMG_2524.JPG

These are the wires going into the Ammeter

IMG_2518.JPG

This is the back side of the shunt

IMG_2516.JPG

Here is the top side of the shunt:

IMG_2510.JPG
 
May 17, 2004
5,026
Beneteau Oceanis 37 Havre de Grace
The way the ammeter works is by measuring the voltage across the shunt. You could use a digital volt meter to help troubleshoot that. When you see a strange reading on the ammeter measure the voltage across the shunt. If you get something on the order of 1mV the problem is likely in the ammeter itself. If you see like 300mV then the problem could be a bad connection or failure in the shunt. To confirm test it with the ammeter disconnected from the shunt to ensure it's not putting a voltage on those wires itself.
 
Feb 10, 2004
3,917
Hunter 40.5 Warwick, RI
The label on the shut says that it is a 500A shunt and 200mv. I interpret that to means when 500A is flowing the voltage across the shunt is 200mv. That is pretty typical, but they do vary a bit. My shunt is 500A/500mv.
So the easy way to check the shunt is to turn on some loads of which you know the magnitude. If you can create a 20A load, you should measure across the shunt (20/500)*200mv or 8mv. You need a decent digital voltmeter to make this measurement. If you get anything close to the 8mv, I would believe that the shunt is working just fine.
Then you know the problem is in the display itself. And from your description of the problem, I would think that the display/circuitry to be the most likely cause anyway.
 
May 28, 2015
275
Catalina 385 Long Branch, NJ
Two Dumb questions on “measuring across the shunt”:

1. Can I use the white and purple wires?
2. Please confirm I’m measuring DC volts and not current
 
May 17, 2004
5,026
Beneteau Oceanis 37 Havre de Grace
If there purple and white wires are the ones that go to opposite sides of the shunt then yes those are the ones to measure.

Yes, definitely DC volts, with a meter that can measure in the millivolt range. That is basically the same process that the ammeter takes to show amps.
 
Jan 4, 2010
1,037
Farr 30 San Francisco
You are measuring volts, but volts and amps are related, by law V=IR . So the "shunt" is a low value resistor (R). The voltage (V) developed across that resistor is caused by the amps (I) flowing through it. It is most likely you have a bad connection somewhere, somewhat likely your meter is broken, and sort of unlikely that 900A is flowing as fuses should be popping and fires should be breaking out in that situation.