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 > Simplest battery monitor and shunt? Advice for non-expert

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Milwaukee, WI

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Posted: 12/15/21 06:08am Link  |  Quote  |  Print  |  Notify Moderator

Boon Docker wrote:

This monitor is the one I have. It is an awesome little unit.

I had one of these a couple years ago, and it was ok for some basic information, but I had a hard time setting up some of the parameters. I ended up giving it away after I had my solar system installed. But for $30, not much to lose.

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Posted: 12/15/21 06:39am Link  |  Quote  |  Print  |  Notify Moderator

corvettekent wrote:

I also like simple so I bought the Aili battery monitor. It is only $44. There are a couple options to buy a longer wire so measure before you buy.

I'll second this one. a generic version of the Victron that works just as well at 1/5 the price, just doesnt have bluetooth. very simple install remove your negitive patery cable, run a new short one from the battery to this, then your old cable you tookoff on to the other end of the shunt. run a tiny power wire to the shunt, then find a place to dril the small hole run the wire and your done. inital setting you just enter how many AH your battery is and your off.


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Milford, CT

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Posted: 12/15/21 06:57am Link  |  Quote  |  Print  |  Notify Moderator

To me the "most basic and inexpensive way" to monitor your battery voltage inside your TT is to run a pos and neg wire from your battery and terminate the wires on the front wall of your TT and check with your multimeter. I put mine on an inside wall with a std bolt head for neg and a Philips head for positive. Above this I have a chart showing what the state of charge is by voltage readings. It was a no cost way to monitor my battery SOC.


New Hope, MN

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Posted: 12/15/21 07:07am Link  |  Quote  |  Print  |  Notify Moderator

Voltage alone is a poor way to check state of charge. The batteries need to be at rest for quite a while to get a meaningful reading. This means no charge or discharge. A meter that keeps track of the amount of charge and discharge (amps in minus amps out) is a far better choice.

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Regina, SK, Canada

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Posted: 12/15/21 08:30am Link  |  Quote  |  Print  |  Notify Moderator

It is a dilemma. In order to accurately measure what is "left" in the battery, one needs to know the capacity. How many folks have actually performed a test to determine the number of amp-hours available?

But, even if one did, capacity is affected by temperature, age, demand and other factors.

I solved the issue by having a bank that was about the size of the original Tesla power wall, and solar to maintain and recharge between trips.

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The Wilderness

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Posted: 12/15/21 08:51am Link  |  Quote  |  Print  |  Notify Moderator

The first question you need to consider is if you want a coulomb counter that directly measures amp-hours in and amp-hours out of your battery to calculate state of charge, or you want a volt meter to infer state of charge from voltage and a chart with a bunch of caveats. Many of the suggestions above are volt meters.

It sounds like the OP is interested in the coulomb counter (ie with a shunt), which is a good idea. Particularly if you have solar, it is hard to interpret what the voltage means as the battery is always being charged at a variable rate during the day, so the voltage can vary wildly as a cloud moves in front of the sun. You can really only get a meaningful reading first thing in the morning.

For coulomb counters there are three basic options:
1. The no-name ebay/amazon versions (AiLi, Renogy and the like). These are the least expensive option, but have some limitations, they only provide an instantaneous value without any history or configuration, and no bluetooth connection.
2. The Victron smart shunt - which is bluetooth only, is configurable and provides history and performance metrics.
3. The Victron BMV-712 which is essentially the same as the smart shunt, but includes an LCD display to mount inside the camper.

There is a fourth option - the TriMetric, which was the bees knees 20 years ago but is now completely overpriced and out of date and not worth considering.

My suggestion (as stated before) unless you are funds limited, go with option 2 or 3. They are a bit more expensive than option 1, but provide more useful information and are the 'standard' in battery monitors. Bit if your budget is tight, option 1 will work well enough.

There is one other option, the Balmar SmartGauge, which hooks up like a voltmeter but actually measures battery capacity. It is easy to hook up and quite accurate, but is expensive and will only work with lead acid batteries.

* This post was edited 12/15/21 08:59am by FWC *

Ramblin' Ralph

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Posted: 12/15/21 09:24am Link  |  Quote  |  Print  |  Notify Moderator

I installed one these a couple of years ago and am very happy with it. No shunt to wire. Only pass the negative lead through a coil. Mine was shipped from US, but now from China, so longer delivery. Also, no bluetooth, but only $40.

Battery Monitor

Edit: Forgot to mention that it's wireless between the monitor electronics and the display.

* This post was edited 12/15/21 09:59am by Ramblin' Ralph *

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Posted: 12/15/21 09:44am Link  |  Quote  |  Print  |  Notify Moderator

I have a BM2 Bluetooth battery monitor for $30. Only measure voltage but it has history trends of battery voltage. It has been very useful and even allowed me to catch a failing battery. It's really nice to check my battery state in the morning without even getting out of bed.

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Posted: 12/15/21 10:10am Link  |  Quote  |  Print  |  Notify Moderator

What I find strange about my Victron unit is that either it or my Android phone insists location service be turned on.


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Posted: 12/15/21 11:44am Link  |  Quote  |  Print  |  Notify Moderator

I have used an Innova 3721 for 9 years now. No installation, no shunt. When you want to know your battery voltage, just plug it into a 12V socket and wait a few minutes for the reading to stabilize. I suppose you could leave it plugged in all the time, but I don't. It can move to any vehicle or camper or device with a live 12V socket. About $20. I write the readings, one for day start and one for day end, into my daily travel logbook.


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