Battery Level Monitoring

McNutty195

Greetings all!

My wife and I just bought a 2018 T@G XL Outback. We've done some tent camping in the past and have always enjoyed it, this will be out very first camper. Neither of us really have much experience with campers, so this is all new to me!

I've read almost everywhere that you shouldn't let the 12v battery get down below 50% or it could damage it. Cool. However, I'm not really confident yet on how I'm supposed to go about monitoring the charge level. I bought one of these., and I understand that I can sort of tell the charge level of the battery based on the voltage, but that voltage seems to vary wildly depending on whether it is under load or not. It doesn't seem like a very reliable way to keep track of how much battery power is left.

Is there a better way? I've seen some info about PMK's on youtube and some RV sites, but they seem more geared towards the big class A's and travel trailers with built in inverters. Since the T@G doesn't have that, I'm not sure how applicable those are.

For reference, I have the stock 12v battery that came with it, as well as a 180w Zamp briefcase panel and the hookup on the battery box to plug the panel in.

Sharon_is_SAM

Correct. Your state of charge should be read about 30 minutes after removing the loads or charger. Does your charge controller have any display? If not, then probably the cheapest thing to do is either get a good battery monitor like Victron, or upgrade your charge controller to one with a display. Someone just posted an installed monitor on another thread.

McNutty195

The charge controller is built onto the portable solar panels I have. It does have a display, I messed around with it some last night and couldn't find battery charge or anything like that. I'm guessing that was lack of looking though.

I think I found the thread you were talking about. I will look into that and Victron. Would something like that interfere with the charge controller on my solar panels? I'd like to be able to see the capacity even if my solar panels aren't hooked in.

Sharon_is_SAM

You can have a battery monitor like the Victron permanently installed and use your portable panels/charge controller at intervals. The Victron uses a shunt so the only thing you would need to do is make sure that any load is wired in after the shunt. We had a permanent pigtail installed coming off the negative terminal in the junction box to connect to the negative battery port on our charge controller.

McNutty195

Awesome, thanks! That is really helpful. Out of curiosity, I saw a review of one of the Victron BMV's on amazon claiming that the monitor itself draws a small amount of current that it doesn't account for, and they found that over time this resulted in their battery dying even though the monitor read full.

Have you ever heard of anything like that happening? I'm kind of feeling like that person either had a faulty unit or something they had forgotten and left on. It seems unlikely that Victron wouldn't account for their own meter's power draw. Though I suppose it might not be able to measure that. Probably not a huge deal as it sounds like it is pretty small, but still curious.

Sharon_is_SAM

The draw from the BMV display is tiny and I do not remember what it is. I can tell you that last year we had our TaB stored for about a 4 month period and our AGM 150 amp battery was at 99% when we picked up the TaB. We had the battery switch off during that time, so the BMV was the only phantom drain. I can’t imagine why the dead battery would read full unless someone did not program the BMV correctly or it was a faulty unit. Also, there are a lot of folks who don’t understand battery limits and maintenance, so you need to consider that when you read those reviews. I learned a lot from marine blogs! We are storing our TaB for six months this year and I am anxious to see the draw down. I will say this, I make sure to fully charge our battery with a smart charger set to AGM before storing. I don’t rely on the converter as I believe it does not charge at the parameters required of our battery.

McNutty195

Sounds good, yeah I've learned to take most reviews with a grain of salt, especially on things like this that a lot of people don't seem to truly understand.

The charge controller on my solar panels actually differentiates between settings for AGM, Wet and a number of other battery types. I've got it set to wet so I think it should be charging the batteries pretty well. Thanks for all of the info, I'll definitely look at getting one of the Victron BMV's when I get a chance!

kevineso1

Hi @Sharon_is_SAM . I just picked up a Victron BMV for my T@G. I was wondering how you have it wired so that the battery shutoff doesn't kill the power to the BMV. I have my shut off switch inline on my negative side of the battery. Should I now run the positive side through the disconnect switch? Or would I want to keep my battery disconnect on the negative side in between the battery and the "shunt"....Thoughts??

Sharon_is_SAM

Our battery cut off is installed on the positive line of the battery. The Victron shunt comes off the negative battery terminal. There is a feed line that powers the display that comes directly off the positive battery terminal. I will look for a diagram that I found helpful.

Sharon_is_SAM

This is how you set it up. Anything else wired needs to come off after the shunt.

kevineso1

Sharon, Thanks

willbingham1

I installed a solar 50 watt panel to newly installed tongue box and the solar charge controller gives me a read of battery level and when charging voltage to battery from panel, etc. I rigged a cut off switch to panel input to charge controller so when on shore power I can still see battery level when it is charging off of shore power, which is about 13.8 volts until unplugged. My group 24 wet deep cycle rests at about 12.9 volts but if solar is involved, it will cycle when at about 12.4 volts to a full 14.3 volts with charge controller in charge of 4 stages of charge. Amps at max are about 2.4 at full sun. This with only 50 watt panel mounted on top of tub. This gives capability to manage my electrical needs, particularly when Norcold is running. When I am in garage, I will hook up 1.25 amp battery tender to maintain battery hooked into zamp plug on tongue box. So far so good. PS: Panel is designed to tilt up as well as be removed to place in full sun with about 10ft of #10 solar wire attached. Bill

Sharon_is_SAM

@willbingham1 - the 13.8 volts that you are seeing during shore power charging actually reflects the converter output - not the battery State of Charge (SOC). The solar charge controller wired without a shunt reflects the battery voltage under charge which is artificially high - just like the battery voltage under load is typically artificially low.

It sounds like your charge controller is bulk/absorption charging at 14.3 v which is fine for a flooded battery. Not sure what you mean “it will cycle when at about 12.4 volts”. A 2.4 amp hr charge is appropriate for a 50 watt panel. Your rested battery reading of 12.9 v reflects a ful charge.

I know that some chargers will not work via the proprietary wiring arrangement of the Zamp solar port. Did you change tge wiring at the battery terminals and use an adapter?

willbingham1

I did my own adapter for Zamp and Battery Tender. The solar charge controller is wired directly into battery not through Zamp connector. The charge controller has a four stage charge program built in (Renogy). Float is about 13.8 with no draw on battery like Norcold. As I stated, I also have a switch in line on solar panel to disconnect it from controller when plugged into shore or when using Battery Tender or trailering from car charge line. Usually I turn off car charge line and let solar charge trailer while in motion. Saves any strain on car charging system.