Community Forums

Maddawg46 · 05-19-2017, 04:48 PM

2016 Bay Star- Battery usage. You would think I would have tried this by now. My batteries are fully charged and the panel says 13.3. So how do I know when to start generator. Someone told me that 11.9 to 12.0 volts means half my house battery juice has been used.
I've got 2 Interstate RV Marine batteries for the house power. My inverter is 1000w. If I watch tv in bedroom and run a 120volt fan that draws .45 amps can I last the night?

Five2o · 05-19-2017, 04:55 PM

12.2v without a load usually means battery is discharged to 50% but with your fan & tv on the monitor may read 12.0v due to the battery loads when actually the real charge is 12.4 or so. Just use trial & error to see if you can last a nite...reading voltage to determine state of charge is pretty sketchy in the first place.

C.Martin · 05-19-2017, 05:19 PM

13.3 if it just got off charge or is still float charging. Our batteries usually sit around 12.6v when off charge. You can also be seeing a slight jump from the small chassis solar panel on the roof.

It is hard to know exactly where the 50% depth of discharge line is. You'll normally be measuring the voltage with some load applied which will lower the voltage.

A good investment if camping off grid using the generator would be to add a battery monitor. It tracks the Ampheres going in and out of the battery bank using a shunt. After it learns it's reference point...and you program the 20 hr Ah rating into it...it will tell you at a glance what your State of Charge is (SOC). It will also jelp you monitor your Ah useage which is the best method of estimating how long you can go between charges...and it also is the most useful tool if deciding in the future to upgrade your battery bank, or perhaps add solar panels to closely match your utilization.

If you have a network type Magnum Inverter...they make a monitor. Bogart Engineering makes a kit many people swear by. I also like the monitor that Victron makes.

Just a thought. The more you camp off grid...the more you'll get out of it.

As to how you'll perform with TV and fan...it is not a perfect world...so the inverter will use a bit more energy than it can output...batteries have a bit of self drain, there will be small parisitic DC loads perhaps to run the LP leak detector, tank monitor, control boards on the fridge and hot water heater...etc. Again...having a battery monitor...you could simply hack the watch...zero out the monitor...and check back in two hours to see how many amps you used. If you used 14 amps in 2 hrs...then four times that amount would be a fair estimate of going 8 more hours thru the night.

Maddawg46 · 05-19-2017, 05:33 PM

So what's the point of the monitor panel in the coach if it doesn't tall me how my batteries are doing? Me confused.

twinboat · 05-19-2017, 05:33 PM

The fan at .45 amps, 120 volts, is 4.5 amps @12 volts. Give yourself another 1/2 amp for the inverter loss and your drawing 5 amps. That's 5 AH every hour.

You probably have about 160 to 190 AH in your battery bank. Run that fan for 12 hours and you used 60 AH.

Check the watts your TV draws. Watts ÷ Volts = Amps.

Lets say your TV uses 60 watts. 60÷12=6. So that TV draws 6 amps@12 volts. Watch TV for 5 hours is 30AH.

Doing what you propose should work and draw 90AH, or about 50% of your battery capacity, but you do have to start with full charged batteries.

That's another subject.

vsheetz · 05-19-2017, 05:44 PM

I use 12 volts as the target minimum. Has worked for me and I get good life from my wet batteries (be sure to check water regularly).

MisterT · 05-19-2017, 07:27 PM

50% is just a guideline, not a hard "it can never be done without ruining your batteries" number....
many of us use 12.0 as a baseline for our AGS to kick on the generator, but it's not set in stone, and I've several times gone down below 11.0 before I knew better, and my batteries still work fine after 3 years.

don't sweat it...

now, some of us have a Magnum Inverter/Charger panel that also allows you to set a 'low point' for the batteries, called a LBCO LowBatteryCutOff. It will cut off the inverter if the volts falls to this number. Mine is set at about 11.5, which serves to alert me that something is 'amiss' and I need to check on it.