AGM batteries not charging on shore power

[McCormickJim]

2017 Georgetown 31L5.

Batteries are not charging on shore power. They charge fine when an external charger is attached. The converter fuses (25 amp, three fuses) have been pulled, checked, burnished, reinstalled).

At a loss for what to check next.

 

[Mr. Dan]

Your post from last April indicates you have a battery cut-off switch. Use a meter and check for continuity through the switch.

 

[Twinboat]

Is there 13.# volts output at the converter ? Is the converter getting 120 volt power ?

 

[Aussieguy]

there is usually two things between a battery and the converter
battery disconnect switch and a fuse/breaker ... check both with a meter

if your battery has some charge... and you don't have a meter (<---- bad no meter)
turn OFF shore power and any solar or generator
so only on battery is connected

turn on interior light or water pump... if they don't work you need to find the switch and fuse
you can bypass the switch if it is faulty... so you can keep going

you can get a new fuse/breaker at any autoparts store

If the lights work on battery
check converter output
disconnect battery connect shore power
now only 12v supply is converter

try the lights + pump again
If they work converter is supplying 12v


IF both tests indicate battery is connected and converter is supplying some power
a) measure the actual voltage being produced by converter
it must be HIGHER than the battery... if battery is charged ..... there will be no voltage difference so charging can not happen

b) battery can take a long time to charge
allow at least 24 hours

c) negative cables to frame... make sure you find them and ensure they are clean and tight
NO paint between lugs and frame metal.

 

[Aussieguy]

PS if you get the battery charged and it discharges in a few hours
have it tested .... if it is more than a couple years old , probably time to replace

AGM like any lead acid ..... need to be maintained on a charger
don't let them sit flat for long periods
you can charge them up in storage and let them sit disconnected for a some weeks
but always better to hook a small battery tender to them

 

[McCormickJim]

Ok, finally have a resolution, sort of. As a starting point after receiving your input was to first get the batteries charged. As pointed out above, it would be damaging to the batteries to let them sit with very low voltage.

So, with no other changes, I put an external charger on the batteries. They charged fine. Next I removed the external charger and put the RV back on shore power (in storage). The batteries showed to be maintaining on shore power so on a whim I left them there, on shore power charging to see what would happen . . . they stayed charged.

Next I took the RV off shore power. The batteries began to lose charge, but at the expected very slow rate. When the batteries reached low 11 volts, I reconnected shore power.

They Charged!

The problem hasn't been solved, but it has gone away.

I don't plan to test it, but I suspect something in the system, from the converter to the batteries, is inoperative when the batteries reach a very low voltage. To avoid the problem in the future, I just need to keep the batteries well charged.

Time will tell.

Thanks for everyone's input.

 

[TitanMike]

It doesn't sound like anything is inoperative other than the battery disconnect if you used it to shut off the batteries after charging.

Something in your 112v system is drawing the batteries down. Could be any one of several items.

Normal always on devices are the LPG/CO detector, radio channel select memory power, and possibly a TV antenna Amplifier.

For better idea on what is drawing the current a measurement of current draw would be a big help.

 

[Aussieguy]

time to invest in a shunt?
get with bluetooth... they work with lead acid and lifepo4
put a shunt on the house battery

then you can watch the charging/discharging of the battery
and even walk around turning 12v stuff OFF/ON while watching the shunt info on the phone
-------------------------------------------------
During storage... look at disconnecting both chassis and house banks and just using separate trickle chargers on the Starter and house batteries

depending on the LENGTH of time in storage you may not even need a charger, just disconnect the batteries let them sit. most fully charged batteries can last a few months without being on a charger.

BUT make sure BEFORE storage you give them full charge ,
house battery bank can take a day or two, even more to fully charge

 

[NXR]

If the batteries do not charge on shore power that should also mean they do not charge on generator power. Do they?

A 2017 Georgetown likely has the SDC-107A Battery Control Center. Docs are here and that company is reported to have great support even though FR no longer uses them: Custom RV battery control centers

Good luck,

Ray