Battery/electrical problem

[maurerl]

I'm trying to troubleshoot electrical/battery problem in my 17B, and am "electrically stupid".
My two Trojan T105 6-volt batteries were running down what seemed way too fast on a recent trip. I ended up taking them out and took them to my local auto repair shop, where they tested them and told me they were beyond salvage, wouldn't hold a charge. They're 4 years old, and haven't been used at all since Covid struck, although the previous 3 years they did see around100 +/- nights use each year. I do have to admit I didn't do any maintenance or checking during the past "storage" year.
Anyway, I bought & installed two new batteries (even that was a challenge, had to travel a distance to find some, finally found them at a golf cart store! Fully charged, ready to go, they assured me).
Before installation, I "tested" them with a multimeter, and they each showed 6.96 volts. After installation, I "tested" them by unplugging the shore power cord and turning on all the systems in the trailer -- lights (all LED), fans, 1500 watt inverter (though with nothing plugged into the inverter), and frig on DC. I think the only things NOT on were furnace and hot water).
Within 90 seconds, the GoPower panel was showing battery at 38% / 11.4 volts and charging from the solar panel (in full sunlight) at 7 amps, and the battery graphic on the panel was down to one bar.
Shut everything off again, and the panel readings came back immediately (like, within seconds) to 70+% / 12.2 volts, solar charger went into boost mode, and within 30 minutes everything is back to normal.
Is something still wrong somewhere? Short? I expected pretty rapid battery depletion with everything on at once, but THAT rapid?
I'm redoing the same "test" with nothing on except the inverter with my CPAP machine (3.75 amps) plugged in, and the typical things like the propane monitor on, to see how long things will last.

[tdf-texas]

Originally Posted by maurerl

I'm trying to troubleshoot electrical/battery problem in my 17B, and am "electrically stupid".
My two Trojan T105 6-volt batteries were running down what seemed way too fast on a recent trip. I ended up taking them out and took them to my local auto repair shop, where they tested them and told me they were beyond salvage, wouldn't hold a charge. They're 4 years old, and haven't been used at all since Covid struck, although the previous 3 years they did see around100 +/- nights use each year. I do have to admit I didn't do any maintenance or checking during the past "storage" year.
Anyway, I bought & installed two new batteries (even that was a challenge, had to travel a distance to find some, finally found them at a golf cart store! Fully charged, ready to go, they assured me).
Before installation, I "tested" them with a multimeter, and they each showed 6.96 volts. After installation, I "tested" them by unplugging the shore power cord and turning on all the systems in the trailer -- lights (all LED), fans, 1500 watt inverter (though with nothing plugged into the inverter), and frig on DC. I think the only things NOT on were furnace and hot water).
Within 90 seconds, the GoPower panel was showing battery at 38% / 11.4 volts and charging from the solar panel (in full sunlight) at 7 amps, and the battery graphic on the panel was down to one bar.
Shut everything off again, and the panel readings came back immediately (like, within seconds) to 70+% / 12.2 volts, solar charger went into boost mode, and within 30 minutes everything is back to normal.
Is something still wrong somewhere? Short? I expected pretty rapid battery depletion with everything on at once, but THAT rapid?
I'm redoing the same "test" with nothing on except the inverter with my CPAP machine (3.75 amps) plugged in, and the typical things like the propane monitor on, to see how long things will last.

You can ignore the voltmeter readings you took as far as trying to determine the battery heath. Battery voltage readings will not indicate state of charge unless the batteries have been at rest for several hours. At rest means not charging or discharging - that condition is rarely met unless you force it.

https://electricalvoice.com/state-of...of-health-soh/

If you wish to monitor your batteries, you need to get a battery monitor such as a Victron 712.

[wackyburggeezer]

The GoPower panel doesn't do everything that you might ask of it. tdf is correct, and I'd recommend one of the battery monitors like the Victron 702, or 700.
As to your new batteries, when you connected a large voltage+current load to your batteries, the GoPower panel showed that you were 'pulling down' the surface charge of the batteries. The fact that the voltage rebounded after you eliminated the load, shows that your batteries are probably okay. The reason that you saw a large drop in voltage in the batteries has everything to do with lead-acid battery chemistry. The voltage rebounded because the chemistry within the batteries was equalizing throughout each cell.

[Hawkeye Ed]

Originally Posted by maurerl

I'm trying to troubleshoot electrical/battery problem in my 17B, and am "electrically stupid".

Don't think you're a dummy. There's lots to learn about RV electrical systems but many online resources to help you along.

As you probably know, the biggest life-killer of batteries is over-discharge, especially when they aren't immediately and fully recharged. Although battery voltage can be used to measure state of charge (SOC), as tdf-texas points out it's not always easy to do that.

The first thing is that batteries have to be "rested" in order for their voltage to be accurately measured: no charging or discharging for at least 2 hours, preferably overnight (and who has the time to do that when camping).

You get a false SOC voltage reading when turning on a heavy load such as an inverter. The voltage drops quickly under load but pops back up quickly when the load is turned off. That doesn't mean the battery was discharged so much when under load or that it magically recharges when the load is removed; it just means voltage measurements without sufficient battery rest periods just aren't all that accurate or helpful.

Now, having said all that, there is still a lot to be learned from watching the voltage fluctuate as you use your RV. Get one of those many cheap voltmeters that plug into a DC outlet in your RV. Then fully charge your batteries, disconnect all loads and charging, and let the batteries rest. Then see what your voltmeter says. A rested, fully charged 12V battery should read pretty close to 13 volts. Use that as your baseline.

Leave your charging systems off and, one at a time, turn on your various 12V systems for a short time and note how much of a voltage drop each of them causes when they're on. That will give you a rough idea of which systems are the biggest drain on your batteries.

I note you use an inverter to run your CPAP machine. I'll bet that's a significant drain on your batteries, perhaps big enough to be causing over-discharge. Inverters that are left one even with no load still drain batteries. And they only deliver part of their input energy to devices plugged into them. See if you can find a CPAP that runs on 12V directly from your batteries, keep the humidifier turned off and unplug it when not in use. That will save A LOT of juice.

Good luck and let us know how your tests turn out.

[maurerl]

Thank you Hawkeye Ed for about the clearest and most understandable explanation for an electrical dummy I've seen! This is the level of explanation I need, and appreciate it.
Re: My CPAP -- I use the inverter only for (got it explicitly for) the CPAP, and the inverter is turned on only when needed to run the CPAP at night. And I don't use the humidifier or a heated hose when camping. So minimal inverter use. Everything else using the batteries (normal use) is just the lights/fans/various "background" items (frig controls, propane alarms. etc).
Now off to get a cheap voltmeter.
Oh, where do I plug it in in my 17B? Where's a DC outlet? I (think I) only have standard household type plugs that only work when I'm hooked up to shore power?

[gbaglo]

My DC outlets are located under the rear dinette/bed near my propane gas detector and on the side of the wardrobe at the front dinette. I think they were both optional.