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Old 04-06-2020, 06:19 PM   #1
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THOR #10717
2018 thor vegas converter at 13.65V but coach batteries not charging

Hi,
I just took my RV out of storage and drove it home, then plugged it into my shore power 30A. All electrical AC devices are working and so are my DC lights and DC water pump. After a few days I disconnected the shore power and noticed my coach and chassis battery were all drained down to about 3.5V. I reconnected my RV to the shore power and measured the voltage in my WFCO WF-8935 power center at 13.65V across the POS+ and NEG- and also across +VCC and NEG-. I believe the WF-89xx MBA converter is working properly and is in “absoption mode” and not 13.2 VDC range “float” mode, or 14.4 VDC range “bulk” charge mode.
I checked the thor wiring diagram and made sure that the was no voltage drop across the battery disconnect relay and also no voltage drop across the 50 AMP breaker- which leads me to believe that those devices are connected and transferring current. Both these devices are located in the battery box under the steps. I checked the coach batteries positive terminals and they are both at 3.5V. II checked the wires an none seem broken.
Does anyone else have any ideas on how I can trouble shoot this? My coach batteries should have 13.65V charging across them so there is something going on between the converter and the batteries.

Thanks
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Old 04-06-2020, 06:49 PM   #2
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THOR #7035
Sounds like you have a handle on using a voltmeter. Measure the voltage drop across the latching relay and both sides to ground.

Measure the voltage drop across the 50 amp DC breaker and both sides to ground.

The 13.65 VDC has to be dropped somewhere on the way to the batteries.
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Old 04-06-2020, 07:25 PM   #3
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THOR #10717
Thanks for the advice.
I went back and measured the voltage drop across the latching relay and both sides to ground and they were both around 3.5V. I also measured the voltage drop across the 50 amp DC breaker and both sides to ground and they were both around 3.5V.
There must be something between the WFCO converter output and the battery disconnect latching relay along the 6 AWG red wire. Is there another fuse somewhere I dont know about behind the converter box? None of the fuses seem broken inside the converter.
I cant trace the 6 AWG red wire too well back into the RV b/c its bundled inside a wire loom.
I pushed on a few various wires to see if something was loose and they all looked good.
I removed a drawer underneath the counter so i could see the wire loom going from behind the converter to the battery compartment.
I do have a AMP meter clamp on my multi-meter so I can use that to trace current but its hard to clamp on some of the wires.
Thanks for the help so far-
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Old 04-06-2020, 07:39 PM   #4
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THOR #7035
The only other thing I know of is the two large reverse polarity fuses on the DC fuse panel in your power distribution center.
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Old 04-06-2020, 08:22 PM   #5
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THOR #10717
I found the device behind the WFCO converter panel in a very hard to reach location:
KIB LR9806 Battery Disconnect Latching Relay

https://www.rvupgradestore.com/KIB-L...BoCUzsQAvD_BwE

I pulled both fuses and they looked ok but i need to trouble shoot some more and see whats going on.
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Old 04-06-2020, 08:27 PM   #6
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THOR #7035
Quote:
Originally Posted by gte534j View Post
I found the device behind the WFCO converter panel in a very hard to reach location:
KIB LR9806 Battery Disconnect Latching Relay

https://www.rvupgradestore.com/KIB-L...BoCUzsQAvD_BwE

I pulled both fuses and they looked ok but i need to trouble shoot some more and see whats going on.
So what "latching relay" were you measuring across before?
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Old 04-06-2020, 08:36 PM   #7
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THOR #10717
I was confused previously on what you referred to as latching relay and thought one of the fuses was what you were referring to as latching relay.
In my battery compartment i took a photo (attached) 50A and is yellow and the other has a blue reset button and I think is 30 or 50A.

I removed the two 5A fuses on the latch relay, reinstalled them (they were fine) and then plugged the RV back into shore power. I think that reset the latch relay and now the batteries are getting 13.6V.

Thanks for the help everyone-
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Old 04-06-2020, 08:59 PM   #8
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THOR #1150
Stupid question: Is your use/store switch in "use"?

Even if the light is on I'd switch it to on (the light being on simply means there is power--e.g. from the converter).
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Old 04-06-2020, 09:37 PM   #9
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THOR #10717
I use the use/store switch when i store the RV so that way the battery is disconnected.
According to the battery disconnect relay manual:
Relay won't engage

Check battery voltage, must be greater than 10.5 volts.
While switch is engaged, check for voltage across the coil
terminals (+ on the ""I" terminal and ground on the "S"
terminal), If 0 volts, replace panel, if + voltage, replace
relay.

Relay won't disengage
Check battery voltage, must be greater than 10.5 volts
While switch is engaged, check voltage across the coil
terminals (+ on the "S" terminal and ground on the "I"
terminal) If 0 volts, replace panel, if + voltage, replace
relay.


I am not sure exactly what happened but maybe the relay got stuck and then disconnecting it with removing and reinstalling the fuses reset the relay?

Overall- seems a concerning in that the relay wont work (either on or off) if your voltage drops below 10.5V. I do carry a portable battery jump starter just in case.

Thanks
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Old 04-06-2020, 11:03 PM   #10
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THOR #5248
The use/store relay uses the coach batteries to latch and unlatch. If the coach batteries are dead the relay won’t latch from the store position.

If you start the coach and he bird relay works, the voltage should charge the coach enough to operate the use relay.
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Old 04-06-2020, 11:08 PM   #11
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THOR #10717
Thanks for the explanation. I must have done some sort of strange combination while the coach batteries were around 10.5V.
Thanks!
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