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Old 03-08-2012, 12:02 PM   #1
Rivet Master
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
Ammeter and shunt system

I thought I might post these photos of the remote ammeter and shunt system I put in my Argosy 20'. It gives me very accurate readouts of how many amps go into and out of the two golf cart batteries that I use for my 12 volt supply.

I purchased this digital ammeter with shunt from for $68 (6/10 price). It is their m-DIG AMP100 with 100 amp shunt.

It will read from .1 amps to 100 amps. Here it is showing the charge current of .2 amps from my PD converter, when the battery is fully charged. It will show net input current with no sign, and current flow out of the battery with a - sign. It shows the net input current no matter what the source, converter, solar charge, or engine charge. If there is a net discharge current, it will show with a - sign. By turning on one item at a time without the converter on, you can find what each and every 12 volt light or device consumes. It is also great to establish if you have any loads you left on when you are not using the coach. It uses a shunt on the negative side of the battery to allow very small wires to be run to the meter, yet have very high accuracy.

The shunt is shown on the right battery side. All the current to the negative side of the battery is sent through this shunt, and the 4 small wires which feed the meter are in the silver jacketed wire you see on the right side taped to the large black negative wire. The wires on the left side of the shunt had been those attached to the negative terminal of the battery, now they go to that negative via the shunt. The small red wire with the fuse holder is the one which supplies the + 12 volts to the meter. It uses a tiny amount of current so it can be left on all the time. I used a copper bar to attach the shunt to the large negative wires as the shunt bolt was larger than the terminal holes in the existing wires and this was easier than changing the terminals to larger ones. Since it is the negative side of the system, it is not necessary to insulate against shorts as the frame of the rig is already at - potential.

I hope this gives someone more ideas.
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Old 03-08-2012, 12:11 PM   #2
Rivet Master
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
Sorry, the photo of the meter was too small to read. Here it is again
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Old 03-08-2012, 12:25 PM   #3
Wise Elder
Jammer's Avatar
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,169
Nice. Do you find that the shunt remains in place even though it isn't affixed to anything?
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Old 03-08-2012, 01:42 PM   #4
4 Rivet Member
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2005 30' Classic
Kingston , Washington
Join Date: May 2011
Posts: 471
Nice setup, i like it.
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Old 03-08-2012, 02:35 PM   #5
Site Team

, Minnesota
Join Date: Aug 2003
Posts: 7,722
Images: 59
Are you planning to add a Tri-Metric head unit to it at a later date?
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Old 03-08-2012, 07:22 PM   #6
Rivet Master
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
Yes, the shunt is quite stable where it is, due to the heavy cable up to the negative post of the battery. The two heavy black lines on the left side also stabilize it. One of those goes to the 1000 watt inverter, the other to the 12 volt (yes 12 volt) microwave I have in the rig.

At this point I have no reason to go to a Tri Metric unit. On an all solar system where you are totally dependent on batteries for a long time period, and only have solar to recharge, I think they make sense, but in my opinion, they are not necessary on the RV system.

BTW, this meter also measures the charge from my small solar system I have on the Argosy, (about 3 to 4 amps) and in addition, it tells me the charge from the TV into the batteries. On a morning when the batteries have been run down from overnight furnace and lights use, I find my TV charge current, on startup, runs about 6 amps. That is not especially great, but I expect it is similar to what a lot of AS/TV combinations run, due to the long distance from the TV alternator combined with the resistance of the TV plug and all other connections involved.

My biggest draw is the 12 volt microwave, which takes close to 60 amps when I use it. I would never buy another, I think an inverter running a small regular 120 volt household unit would be a much better setup. Live and learn. Even at 60 amps, it is a very slow microwave.
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