Amp hour shunt melted

On our new-to-us 1990 GB 42 the survey called out a non-functioning amp hour meter - turns out that's because the shunt actually melted (hmm).

Ideally, we'd like to find an exact replacement - 2nd best is a newer 'compatible' shunt and of course last resort is to replace the gauge and shunt

The main part of the shunt has the inscription:

VDO Made in Germany
10/87 03 330/114

The brass terminal connector says:

108 6mV 80A

I can't tell if that's 108.6 mV (that seems odd) or 6mV? And what does 108 mean?

Does anyone know the actual spec for this shunt?

Thanks!

What is the max amp reading on the meter itself, and a part number if you can read it?

-80 to +80 Amp - alas I am away from the boat so no part number...

I've attached pics of gauge and shunt

jwag956 said:

On our new-to-us 1990 GB 42 the survey called out a non-functioning amp hour meter - turns out that's because the shunt actually melted (hmm).

Ideally, we'd like to find an exact replacement - 2nd best is a newer 'compatible' shunt and of course last resort is to replace the gauge and shunt

The main part of the shunt has the inscription:

VDO Made in Germany
10/87 03 330/114

The brass terminal connector says:

108 6mV 80A

I can't tell if that's 108.6 mV (that seems odd) or 6mV? And what does 108 mean?

Does anyone know the actual spec for this shunt?

Thanks!

Click to expand...

The part # is VDO N03-330-114.


The closest part I could find online has been discontinued (VDO N03-330-116) but available:


https://vdo-webshop.nl/en/ammeter-shunts/2739-vdo-oceanline-shunt-80a-60mv-7640178728721.html

Here's the data sheet i believe:


https://www.vdomarinegauges.com/wp-content/uploads/2020/02/TU00-0702-5804620-Ocean-Line-Ammeters.pdf


And it apparently is 108.6 mv at 80 amps of current

Before just replacing the shunt ask yourself why it melted. Most likely the draw was far beyond its capacity. Overload them badly enough and they become a fuse, a poor one though.

Look around at your electrical system:
--What is the output of the alternator?
--do you have an inverter and what can it draw? What is its output rating?
--Battery charger?
--thrusters?
and so on.


80 amps these days is not a lot with large battery banks, inverters, thrusters, larger alternators. THe load may not be continuous long term but there is a reason it melted.

C lectric said:

Before just replacing the shunt ask yourself why it melted. Most likely the draw was far beyond its capacity. Overload them badly enough and they become a fuse, a poor one though.

Look around at your electrical system:
--What is the output of the alternator?
--do you have an inverter and what can it draw? What is its output rating?
--Battery charger?
--thrusters?
and so on.


80 amps these days is not a lot with large battery banks, inverters, thrusters, larger alternators. THe load may not be continuous long term but there is a reason it melted.

Click to expand...

+1. Probably underrated.

I just installed a new blue seas DC panel for my 12 volt loads (8380). It has 22 circut breakers and a DC volt meter for 3 battery banks and an 0 - 100 amp meter. The amp meter has a shunt with a 50ma/500 amp capacity. I think you could just get a larger shunt and it should work fine.

#8:

50ma/500 amp capacity

Click to expand...

That should be 50mV/500A.

Also note that current draw can become excessive if there's too much resistance due to corrosion and/or poor connections. Wire that's gotten corroded inside the insulation can lead to problems too. The simplest way to test this is to measure voltage drop between sections while there's a load active (stuff is turned on and working).

That shunt/ammeter is not a typical type installed on boats and almost certainly is too small. You can replace it with one from Blue Seas or even better with a battery monitor that gives amps, amp hours used and percent charged. Victron makes a good one.

David

Any chance of seeing a picture of what melted? If you have power on the boat then the shunt it still working. My guess is that it's the plastic mounting around it that melted. Does the ammeter work at all?

Thanks for all the input - I realize that the question was somewhat GB specific and didn't give enough overall information.

First and most important - this ammeter/shunt is measuring (I believe) alternator to battery. With engines off, it reads 0 (on the port side that works). The result is that under power, we aren't charging batteries. On shore power etc. everything is fine. And for the record, we don't have an inverter.

The alternator was replaced by PO - it is a Wilson 90-17-8067 - which on the Wilson site claims 55A though I have seen other parts sites list it as 80A.

My *guess* is that the old alternator went berserk and fried the shunt - PO didn't notice that and just replaced alternator. Our marine survey tested that alternator functioning properly (but apparently didn't check that it was actually charging the batteries under way)

Thanks - I believe that shunt/gauges come matched - can't just replace a shunt and expect the gauge to work/be accurate.

Whenever I had a sweep amp meter like that I considered it more of a “at a glance” indicator that the alternator was working. Plus side good, minus side bad.
Now I’m more likely to replace that gauge with a volt meter. Better information in my opinion.
Everyone’s situation is different though, I understand all the things that come into play if changing out something on the dashboard. Good luck with it.

jwag956 said:

Thanks - I believe that shunt/gauges come matched - can't just replace a shunt and expect the gauge to work/be accurate.

Click to expand...

Correct. For example, all Blue Sea Systems ammeters read full scale deflection at 50mv. A 75mv or 100mv shunt would not give accurate readings.

Bmarler said:

Whenever I had a sweep amp meter like that I considered it more of a “at a glance” indicator that the alternator was working. Plus side good, minus side bad.
Now I’m more likely to replace that gauge with a volt meter. Better information in my opinion.

Click to expand...

When I replaced my amp meter with a volt meter (same brand/style fit the dash hole), I saw that the old amp meter had a nice big unfused wire running from the ER to the helm, then to the upper helm, then to ground. Not something I really wanted on a 40 year old boat given that the information provided was minimal. A fused volt meter spliced into the helm instrumentation gives the same "at a glance" info. Generally, below 12 bad, above 12 good, above 15 bad.

As part of the same project, I also installed a modern battery monitor (not in the helm cluster as it didn't match the original gauges). For $50, you get all the digital info you need (amps and volts to several decimal points), including a countdown on the actual amp hours that you have used while at anchor.

wkearney99 said:

Also note that current draw can become excessive if there's too much resistance due to corrosion and/or poor connections. Wire that's gotten corroded inside the insulation can lead to problems too. The simplest way to test this is to measure voltage drop between sections while there's a load active (stuff is turned on and working).

Click to expand...

Interesting - I was thinking of disconnecting the lead and measuring resistance. So if I am understanding your suggestion - in this case I have a (big) wire from the alternator to shunt, and one from shunt to battery. So I would measure voltage at the alternator (when running), then voltage at shunt and finally voltage at battery to make sure neither of the 2 wires is seriously compromised?

jwag956 said:

Interesting - I was thinking of disconnecting the lead and measuring resistance. So if I am understanding your suggestion - in this case I have a (big) wire from the alternator to shunt, and one from shunt to battery. So I would measure voltage at the alternator (when running), then voltage at shunt and finally voltage at battery to make sure neither of the 2 wires is seriously compromised?

Click to expand...

You can test sections of wire by setting you meter to dc volts. Put one lead on one end of the wire and the other lead on the other end. Put the leads on the terminal, not the wire. That way you get the crimp connector in the measurement.
The higher volt reading you get, the bigger the voltage drop. Your operating voltage is battery volts minus the meter reading.
Ideally, you only want to see millivolt readings.

Bmarler said:

You can test sections of wire by setting you meter to dc volts. Put one lead on one end of the wire and the other lead on the other end. Put the leads on the terminal, not the wire. That way you get the crimp connector in the measurement.
The higher volt reading you get, the bigger the voltage drop. Your operating voltage is battery volts minus the meter reading.
Ideally, you only want to see millivolt readings.

Click to expand...

This is the concept most don't understand. While you have an active load on the wire, measure from two points on the wire. You should not see much difference between the two points. If you do then that stretch between the points you're measuring is bad.

You're not checking voltage between +/-, you're, basically, using the meter as an alternative path for the electricity. If the wire is good then the flow won't favor the meter and you'll see only millivolt values. But if the flow is bad then some portion of it will try to follow the path through the meter, and that can be measured. You should do this on BOTH the positive AND the negative sides of the circuit. Because the circuit depends on all parts of it being in good shape, not just the 'hot' side.

This link covers the idea pretty well: https://www.hagerty.com/media/maintenance-and-tech/measuring-voltage-drop/

wkearney99 said:

Also note that current draw can become excessive if there's too much resistance due to corrosion and/or poor connections. Wire that's gotten corroded inside the insulation can lead to problems too. The simplest way to test this is to measure voltage drop between sections while there's a load active (stuff is turned on and working).

Click to expand...

VERY true! I had a major problem with my starting battery/starter. Not enough juice going through most of the time to even crank it. Everything looked perfect, though.


Replaced the starter and, initially, it cranked over & fired up right away. 2nd try, almost no cranking. Used another battery as an assist, still no cranking. Then, I got the smell of ozone & melting wire from the area of the new starter.


Pulled the starter, found the starter solenoid had melted.


As it was getting beyond my limited capabilities, I had a marine electronics specialist come and take a look. He found that the ground cable (well insulated, submersible, 1" thick copper strands) had wicked moisture up inside about 1 1/2 feet, and had corroded about an inch of it into green powder, with only a few thin threads of copper left.


Replaced the starter power & ground cables with new (tinned strands), and it spins over like a top now.


The old cables looked perfect. Clean, shiny copper showing at both ends..but not inside at one point.