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Old 11-16-2015, 01:09 AM   #21
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To address your original question, it probably is not suitable for what you want it for unless your alternators have isolated grounds. If they do you can install the shunt in series in the ground circuit. If they are grounded through the case these meters would have to be connected in the battery ground cables and would indirectly show what the alternators are doing.
The voltmeter measures volts between positive and negative. The amp meter measures the voltage between one end of the shunt and the other. This meter assumes that one end of the shunt is grounded, which means it won't be suitable for alternator output unless the alternator has a separate and electrically isolated ground cable.
If you have a separate ground cable on the alternators and if there is no continuity between the alternator case and the ground terminal (with the ground cable disconnected from the terminal) then you could install the shunt in the ground circuit and the meter will show you alternator output.
Another alternative would be to use 2 independant meters, a voltmeter that you can switch between altlernators and an ammeter that you can switch between 2 shunts in the output circuits of the alternators.
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Old 11-16-2015, 01:17 AM   #22
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I would generally agree, except this manufacturer forces a common connection between the ground and one shunt terminal.
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Old 11-16-2015, 06:59 AM   #23
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The low cost method might work for you.

While nothing beats a SOC setup perhaps this will do.

Simply install a pair of flush push in pin sockets on the dash connected to the start cable of each engine.

When interested ,plug in the VOM , observe the standing voltage and then observe the voltage while cranking.

The voltage rise after engine start will show the alt is working , and you can start the other engine.

This will catch a load of horrors like no starter cut out although it wont give the amperage of the alts.

For most the cost is very minor as most have a VOM already .
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Old 11-16-2015, 02:20 PM   #24
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Quote:
Originally Posted by av8r View Post
If you have a separate ground cable on the alternators and if there is no continuity between the alternator case and the ground terminal (with the ground cable disconnected from the terminal) then you could install the shunt in the ground circuit and the meter will show you alternator output.
I have just checked with the continuity function of my multi-meter. The ground terminal is isolated from the case of the alternator. Digital amp/volt meters on order. Will post results when installed. Thanks all.
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Old 11-16-2015, 10:10 PM   #25
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The meter doesn't know or care whether the shunt is on the negative or positive pole. Whole house meters are usually on the negative pole because that makes it easier to measure everything in the system. For alternator or solar panel output, you can just put the shuntg on the positive side and be done with it. I have an amp meter on the positive feed of my alternator and it provides useful information (Like my voltage regulator is currently toast <g>).
FWIW, I completely agree with this. The shunt doesn't know and doesn't care where in the circuit it is. It just knows that electrons are flowing through it and it counts, etc., those electrons. If it has the capacity, it will work. If it doesn't get a bigger one.
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Old 11-17-2015, 01:13 AM   #26
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Correct in principle. However take a look at the specs on this unit. It only uses 3 wires and one end of the shunt has to be grounded. Placing it in the positive side of the alternator and connecting the wires as directed may cause a dead short to ground with associated smoke and melting wires.
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Old 11-17-2015, 07:17 AM   #27
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Originally Posted by av8r View Post
Correct in principle. However take a look at the specs on this unit. It only uses 3 wires and one end of the shunt has to be grounded. Placing it in the positive side of the alternator and connecting the wires as directed may cause a dead short to ground with associated smoke and melting wires.
Grabbed this off the web site. It made it very easy to understand:

I wired mine in between the batterie negative to the chassis ground And wired all of my electronics to chassis ground

By Stephen meagher on August 31, 2015:
The black and yellow wire connect across the shunt with the black lead on the most negative side. The red wire must be connected to a positive voltage between 5 and 30volt all 3 wires are only voltage sense and carry NO current.

The wires are very flimsy so strip with care.
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Old 11-17-2015, 09:50 AM   #28
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It's not the current shunt that makes you use ground as one of the connections, it's the volt meter that reads the voltage across the shunt that is the issue here.

A shunt is nothing more than a device that takes produces 50 milivolta at it's rated current. Nothing more than a resistor.

The meter part is nothing more than a volt meter that you think is reading out in amps. In reality the meter is a 50 milivolt volt meter.

If the sensing inputs are isolated from ground then you can use the shunt any place in the DC current path. If the sensing inputs are not isolated then you'll need to install it referencing ground, which limits your options.
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