I installed a E-Meter many years ago, before the Tri Metric came out. It is basically the same meter, but Tri-Metric is from the next company.
It uses a shunt, and that carefully measures the amp hours leaving the battery bank, and counts all that leave at 100%.
When the battery is being recharged, the amps going back in are sent in at the 'discount rate'. In other words if you have a 400 AH battery bank, and take out 100 AH over 10 hours, then put back exactly 100 AH over say 3 hours running the generator, it will not 'fully charge' the battery, but because of battery in-efficiency, it might be at say -10 or -15 AH. The meter will adjust itself for the battery recharge process.
Also after the battery is actually full, you can keep slowly putting in amperage, and it will cause the battery water to boil away, but the battery will not become 'overfull' because it will slightly overcharge. Anyway when you start using more amperage than is going in, the meter will start counting back from 0.
So on a average day and night, I might use say 85 AH and the meter read -85 when I get up. The solar will start charging, and counting down the amps to read say -5 AH at 3 pm, and perhaps start counting upward +4 AH at 4 PM and as much as +22 AM by the time the sun goes down. It will go back to 0 AH with the first 0.2AH being consumed from the battery.
Click on the link above for Bogart Engineering and Trimetric meter. That is the best one for reading how many amp hours are leaving your battery. I think they sell a dual battery bank model too, if you happen to want to watch your engine battery as well.
I used normal 8 wire thermostat wire to hook up my shunt to the E-Meter, and it has worked fine for over 15 years.
It is very handy to have the E-meter. If I am at say -120 AH, and I know that I will not fully charge that day, but want to, I can start the generator early in the morning, while the battery is still very low voltage, and thirsty, and it will charge around 45 - 60 amps for about the first hour. AS the battery gets closer to full, it will charge much more slowly, and accept less power each hour, so running a 4000 watt noisy generator to get say 20 AH into the battery bank when it is 80% full does not make sense. It was better to run it early in the morning when it would charge at the highest rate per hour.
If I am at -100 AH, I will not run the generator at all, and rely on the solar to finish charging it. If I am at -150 or more, and plan on driving, I will not normally charge with the generator, but allow the engine to fill the battery.
If I am at say -200 AH, but plan on going home soon, and not camping again for a week or more, I will not bother charging the battery at all, but let the solar complete the charge over the next week. It will be full by sundown the second day.
Of course if I see the battery really low, I can decide to shut off the TV and go to bed, or run the generator. Or I can see if there is a significant load on the RV, such as the porch light was left on (before I converted it to LED's).
I found out about solar panels and E-Meter from the kind folks at
HomePower.com Magazine. It is written from a off grid solar powered home that has at least 1 E-meter monitoring their battery bank, solar input, ect. They adjust their loads in the winter based on how full the battery bank is. So they might delay washing clothes on a day that is not sunny, and wait a couple of days, especially if the magazine is using a lot of power. But if it is windy, they will have full batteries, and can run the washer, and perhaps the small window A/C unit too!
Good luck,
Fred.
Money can't buy happiness but somehow it's more comfortable to cry in a
Porsche or Country Coach!
If there's a WILL, I want to be in it!
I havn't been everywhere, but it's on my list.
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