AC200 charging AGM trailer battery through the 12v/10a output

[Mntnbkr83]

Using alligator clips, I connected a 79 ah AGM battery that lives on the tongue of my travel trailer to the 12v/10a XT90 output from the AC200 (battery was disconnected from trailer). It charged the AGM back up, using a steady 13.5 volts, and continued lowering the amps until it was fully charged, then stopped on its own, no faults, and everything seems fine.

Is this okay?

I am concerned that directly connecting the 12v/10a output of the AC200 to the AGM battery may harm the AGM battery.


For context, I am trying to have my AC200 connect directly to the DC side of my travel trailer, bypassing my converter (by removing 40 amp battery reverse polarity fuses). Converter draws 72 watts at minimum! (This is the reason I am disabling the converter). The AC200 inverter would power the AC side of my camper through it's existing shore power input, and the AC200 DC output would power the DC fuse box.

I have not considered any repercussions with the truck hooked up, with it's trailer trickle charger feature.

 

[snoobler]

It's kinda okay. The AGM needs to be charged to something in the 14.4-14.8V range. Alternatively, it can be fully charged by an extended float at 13.8V. The 13.5V is better than nothing, but it's not entirely sufficient.

Are you absolutely certain that the converter uses 72W at idle? Did you check this based on the input power with the 12V terminals disconnected?

 

[Mntnbkr83]

Interesting. So I am not achieving a full charge of the AGM, but I am also not harming it? Until now, I had believed I would need a DC to DC charger.

If I understand this correctly, I could wire the AC200 12v/10a directly to the AGM battery while it is in the trailer, and it would "charge" the AGM, and the AGM would still be providing 12v to the DC fuse box.

RE: 72W idle : While having the AC200 AC inverter powering the shower power of the trailer, I monitored the AC200 AC input. I turned all sorts of things on and off trying to understand what draws what. After being suspicious of high draw, I started trying to shut everything off. I isolated the converter by connecting/disconnecting the reverse polarity fuses in the DC fuse box. This is how the 72w was isolated. I do not remember if the AGM batter (trailer tongue) was connected or not. I will try this tomorrow.

 

[snoobler]

Correct. You may be long-term harming it if you're never fully charging it. Floating 12V at 13.2-13.8V AFTER a full charge to absorption voltage essentially freezes the deterioration process. Having them at lower states of charge consistently will accelerate their demise. There are 12V to 13.8V output converters, which would help get the battery at or near full charge over the course of 24 hours of charging.

That's why I'd like to see you leave the 12V attached to the converter if possible, unless you're just trying to wring out the best efficiency you can. I'll sacrifice efficiency for convenience within reason.

I suspect the battery was connected, and that's why you saw high draw. Floating an RV-size 12V typically takes less than 6W with up to 10W total consumption from the converter.

 

[Mntnbkr83]

Okay, I can expect long-term deterioration if I go this path. Thank you for explaining this.

I am hesitant to accept the 72W draw... but I sure understand convenience!

Yes, according to my manual, the converter charges the battery at 6 amps. What I cannot verify at this time is the voltage at which it charges. I think typically these converters charge in the 13.6 range... So would that mean the converter is not fully charging the AGM either?

 

[snoobler]

Converters usually operate with a 2-4 stage typical 12V charging cycle, or a 13.8V steady voltage.

Again, 72W is almost unheard of. I recommend you disconnect one of the 12V leads from the converter output and plug it directly into the AC200 with no other 12V or 120VAC loads.

Converter link?

 

[Mntnbkr83]

Well, I'll play with it again tomorrow and report back.

Power converter with distribution panel: WF-8955PEC

 

[snoobler]

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Follows a 3 stage charge profile.

14.4, 13.6 and 13.2.

 

[Mntnbkr83]

I disconnected the AGM from the converter, and was able to verify that it does shutoff with no 12v or 120v loads.

An interesting note is the Propane detector (1a fuse) causes the inverter to run continuously at 72 watts/.6a. And, as far as I can tell, I have not seen a load less than that. It's either zero, or 72w according to the AC200 AC output digital panel.

 

[snoobler]

That's pretty shocking. I had occasion to look at the numbers on my LP detector a couple weeks back, and it's 0.075A @ 12V. I don't remember the brand of my converter that simply supplies a steady 13.8V, but the inverter reports a pretty consistent 45W AC load powering 4 lights, LP detector, blink camera wifi module, a DSL modem/router and the 12V electronics for the absorption fridge.

 

[Mntnbkr83]

Interesting numbers you report. Based on your information I have investigated a bit more.

According to my LP detector, it also is 12v/75mA. I decided to unplug the fuse for it and then turn on an LED light instead, to see if that was accurate. The LED also drew 72 watts (off the AC200 AC output). The LED draws like 6w max, I know this, because if I turn on more LED lights it goes up by about 6w each. I tried other small draw items independently, and yeah, 72w was the least it would do.

Going further, I put the LP fuse back, disconnected the converter by the fuses, and then used the DC side of the Bluetti to "charge" the AGM while it was wired to the trailer.

With 4 LED lights, and the 3 way fridge electronics on, it steadily ran 13.5v/2.1a/27W.

 

[snoobler]

The second scenario sounds a lot more of what I would expect, but I guess not all converters are made the same. Both of mine are simple contained units with a grounded AC plug and 12V output terminals. They go to separate 12V fuse panel next to the AC panel (5th wheel and a motorhome). They have negligible idle power draw, but they are only about 85% efficient.

During the day with solar, I wouldn't care, but sounds like you have an alternate means of running things efficiently overnight at least.

 

[Mntnbkr83]

Very interesting lessons in real world results for me. Thank you very much for helping!