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Old 12-08-2019, 09:21 PM   #1
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Grounding a meter shunt?

I Installed an AiLi battery monitor, in my TT, and am questioning my install?
I have read several threads and watched You Tube but am still confused.
Most mention needing to put the shunt next to the batt. I am wondering how accurate that is for a TT with out a battery compartment.
My rig has the batt. box on the front A frame with a short cable attached from the neg. terminal to the frame.
Inside the TT, in cabinet, behind the fuse panel, a ground cable comes from the frame to the Neg. bus bar. I installed the shunt in this location with B- terminal to cable to frame and P- terminal to Neg, bus bar, with 4 in. short cable. Made it very easy to access an extra fused 12 V power for meter and easy to run meter control wire behind stove up to wall to mount meter on wall, above counter top.
My question is: Isn't this the same electrically as attaching the shunt at the exterior cable to battery?
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Old 12-09-2019, 12:34 AM   #2
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I would think the resistance between the battery and the bus bar through the cables and frame is enough to throw off metering amp draw. That is to say you are probably pulling more than you are measuring. That said, you’ll end up with usable data with respect to how much each item draws, just not total draw on the battery. Or I could be wrong- might be just fine. Try it both ways and see what readings you get.
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Old 12-09-2019, 05:59 AM   #3
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If you have confirmed that there are no other points of ground, for any component, what you did should work.

The distance between the battery and shunt shouldn't effect its reading, only things grounded between them.

How about your charge line from your tow vehicle, is its negetive wire run to the bus bar ?

Even a power tongue jack, often grounded to the chassis, can effect the readings. Not by much, depending on use but some.
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Old 12-09-2019, 06:15 AM   #4
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I suspect you are good..

The batteries negative terminal goes to one side of the shunt, the other side of the shunt goes to ground. All current to and from the battery must go through the shunt.

I wired one up in my Southwind this summer.

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Old 12-09-2019, 06:40 AM   #5
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Unlike voltage, current is the same everywhere in a series circuit. Meaning as long as there aren't any parallel pathways for current that go around the shunt, then it's all passing through the shunt. But being frame grounded, it's certainly possible that some of the current from connected loads passes to the battery but around the shunt unless you're sure all load Bat - leads terminate in the panel. Hence the recommendation to mount the shunt right on the battery post, so nothing sneaks past.
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Old 12-09-2019, 08:45 AM   #6
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Agree with twinboat, Waiter21 and KanzKran.
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Old 12-09-2019, 10:32 AM   #7
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you could check it by disconnecting one side of your installed shunt, if any 12 volt item in your trailer works, you will know the shunt is not 100% accurate
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Old 12-09-2019, 12:46 PM   #8
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Thanks for all the input. So if I understand correctly; Any device grounded to the frame between the shunt and the battery could use current that isn't monitored or recorded by the monitor. So I need to find out if there are any unknown connections by disconnecting the shunt and see if any devices work.
I don't know about the charge circuit from the trailer connection. I assume at some point it is grounded to the frame. So if it is grounded to the frame between the shunt and battery does that mean the charging from the alternator won't be monitored?
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Old 12-09-2019, 01:24 PM   #9
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[QUOTE=RHD51;5068953
I don't know about the charge circuit from the trailer connection. I assume at some point it is grounded to the frame. So if it is grounded to the frame between the shunt and battery does that mean the charging from the alternator won't be monitored?[/QUOTE]

That's correct. Any current you want to monitor needs to pass thru the shunt.
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