Charging batteries while towing

[ScottBrownstein]

That might be true for an off the shelfl tow vehicle, hence TT and 5th wheel. Class A RV generally have the charge line hooked to the chassis or house bank. On my 2015, the charge line is at bat voltage all the time and when running I a look ways see more than 14 volts from the alternator.

 

[aeblank]

Also, a gm will bump the voltage when in tow/hail or lights are on. I didn't believe it, but it's apparently true.

I have a ...battery doctor, I think it is.
It cuts the power when the source (truck) voltage is low (basically as soon as I turn it off). I don't know if it aids charging (more voltage) or not, honestly.

 

[babock]

Here it is accepting almost 12a...

https://i.imgur.com/akPmF2a.png

Are all other loads in your trailer off? This includes fridge, lights, propane detectors...

What size batteries?

Do you know what the output of the alternator is during that state? Would be interesting to know the voltage drop from the alternator to the trailer.

 

[aeblank]

Are all other loads in your trailer off? This includes fridge, lights, propane detectors...

Nope. Fridge woulda been on. Whatever the radio draws and probably the CO detector. Smoke detector is 9V battery. The screenshot is what the camper battery is seeing. The charge voltage is more than the battery voltage, so those other devices are running off the truck, at the time of the screenshot.

What size batteries?

An interstate multi-use crap that came with the camper in parallel with an older 100AH-ish deep cycle 12v that came out of dad's fishing boat (trolling motor). Certainly nothing special. Can't wait to get my 420AH, 6V, L16s... Anyway, yeah, junker batteries, basically.

Do you know what the output of the alternator is during that state? Would be interesting to know the voltage drop from the alternator to the trailer.

No idea. I'd have had the lights on, so it would be the GM's "bumped voltage" mode. Voltage drop could be calculated, I suppose.

I didn't mean to hijack, just trying to show some real world (as in, I saw it and measured it and documented it) charging rates. People often say "it's just a trickle", but I'm saying it's X amps (or can be). I don't even know the charge rate of the converter at a similar battery voltage.

 

[babock]

True, the other devices would not have made a difference...brain fart on my part.

That's actually a lot more current than I thought you would get.

Out of curiosity, do you have the size of your battery set correctly in your battery monitor? It says battery is 88% full yet it states that it is -33AH drawn from it.

 

[aeblank]

That's actually a lot more current than I thought you would get.

Mostly my point of posting it, honestly.

Out of curiosity, do you have the size of your battery set correctly in your battery monitor? It says battery is 88% full yet it states that it is -33AH drawn from it.

I do, or at least -ish. It's set at 200AH, which is overly optimistic, I think. I've struggled (and posted) about the percentage and my understanding of it. I suppose that implies that I have 137AH available total, to stay above 50%. If I have 200AH total, then that number is too high.

My previous posts were about how it was at 100% and still accepting like 5 or 6 amps. That didn't make sense to me, it should accept very little (5A doesn't seem little to me). So yeah, I don't really understand my fancy Victron battery monitor yet. I hoped that once I got known batteries with known/accurate capacities that it would all make more sense.