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Old 10-10-2018, 10:18 PM   #1
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Brand: Thor Motor Coach
State: Maine
Posts: 27
THOR #13246
Intermittent Chassis DC power.

I have a new to me 2017 Thor Axis. Yesterday it wouldn't start. No dc power at the dash, no lights, no relay clicking, everything dead. I did have the unit on shore power. Thought maybe it was a low chassis battery. Tried the emergency switch but still nothing at all. As I was hooking up a battery charger to the chassis battery I heard a relay connect, the headlights blinked, a chime rang. I jumped in the coach to try to start it but was too slow. Just as I turned the key the dc power dropped out again. I disconnected the shore power and then reconnected. I heard the relay again but power disappeared within a few seconds. I left the charger on for 20 minutes even though it was showing 100% charged. As I was disconnecting the charger the relay clicked and I was able to start the engine. Drove 50 miles yesterday and 50 today with a few successful restart. Hooked up to shore power and tried to plug in a small vacuum cleaner. For some reason this caused my shore power source to trip it's breaker. When shore power was lost I heard the under hood relay trip and loose DC to the chassis. I can't tell what relay is acting but the sound seems to be coming from the area of the BIM and the chassis fuse box. It seems that some power monitoring device is sensitive to electrical "tickles" or is operating close to it's switch point. The big power breakers have not tripped. Any ideas?? thanks kevin
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Old 10-10-2018, 10:42 PM   #2
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Brand: Thor Motor Coach
Model: Axis 24.1
State: Michigan
Posts: 8,143
THOR #1150
First of all: Congratulations and welcome to the site.

2nd: When plugged in do you have the use/store switch on use? Try that.

3rd: If you haven't make sure you download and read Ed's excellent crowd sourced Axis/Vegas manual found here: Link to Ed Felker's Vegas/Axis Manual
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Old 10-10-2018, 10:47 PM   #3
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Brand: Thor Motor Coach
State: Maine
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THOR #13246
thanks

Thanks for the reply. I have read Ed's manual, much better than Thor's manual. I think I've left the switch in the use position but I'll be certain to do so from now on.
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Old 10-11-2018, 01:19 PM   #4
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Brand: Thor Motor Coach
Model: 2013 ACE 30.1
State: Alberta
Posts: 921
THOR #2631
I don’t think very many new RV owners realize that just because you are plugged into AC shore power does not mean that your coach batteries are charging from the converter. The use/store or specific coach and chassis battery disconnect switches (typically located by the door) must be “on” to allow battery charging and high load coach operation. What fools many users is that the coach 12volt basic systems (like the lights) work when on shore power (via the converter), or the coach battery disconnect switch by the door may be lit.....so they assume the batteries are charging.......NOT. The best low cost investment any RV owner can make IMO is a basic multimeter (volts, ohms, amps – although amps range on many cheap multimeters is not practical for the load currents the RV uses). Learn how to use the meter safely (DC or AC volts select; correct voltage range selected; never ohm check on powered wiring etc). If you are wondering if your batteries are charging measure the DC voltage across the battery terminals when they are lightly loaded. If the reading is 13.1 approx or higher they are charging. Some batteries are hard to physically reach for measurement, but sometimes other systems (like some inverters) may include remote panels that show chassis battery voltage.
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Old 10-11-2018, 01:43 PM   #5
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Brand: Thor Motor Coach
Model: 2015 Vegas 24.1
State: Pennsylvania
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THOR #2601
Kevin sent me his question in a private message after he had read my manual. I suggested that the Isolation relay under the hood or his converter might be causing the problem. I suggested he post his question on the forum because there are way more of you out there with better electrics knowledge than me. I suggested the Isolation Relay based on him saying he was hearing relay clicking under the hood.

What I don't know is with a BIM is there internal circuitry that serves the function of the isolation relay and battery disconnect relays that many of us have with the Isolator/Trombetta/Battery Disconnect relays. If so then he might have a problem with relays in the BIM that function as the Isolator Relay or Chassis Battery Disconnect relay.

His description says there is no DC power coming from a fully charged chassis battery. So that sounds like battery disconnect relay of isolation relay -- especially when he tried the emergency start which should have shunted DC power from the house batteries to the chassis.

Thoughts?
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Old 10-11-2018, 02:11 PM   #6
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Brand: Thor Motor Coach
Model: 2013 ACE 30.1
State: Alberta
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THOR #2631
Slight correction on my comment regarding some inverters having voltage monitors.....should have said that they would show coach battery voltage not chassis battery voltage.


Regarding the fully charged coach and chassis battery not operating loads.......my first thought was use/store not on (as JamieGeek first suggested). The other thing I thought is how do you know the batteries are fully charged......measured 12.6 + volts with a meter? When the use/store or disconnect switches for coach and chassis battery latching relays are operated you should hear the clunk of the particular relay(s) operating (closing or releasing). If you do not hear the clunk......there is something wrong with the latching relay(s) or the wiring that enables the operation of the latching relays. Also when operating the emergency interconnect switch you should hear the battery interconnect relay operate. I am not familiar with the BIM operation.
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Old 10-11-2018, 02:24 PM   #7
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Brand: Thor Motor Coach
State: Maine
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THOR #13246
Thanks again everyone.



I certain the sound I hear when the problem occurs and when it resolves is the sound of a relay under the hood. With the BIM and the chassis fuse box next to each other I can't isolate it further. I'm beginning to suspect it might be a relay in the chassis box. At one point I measure 12+volts on the cable that enters the fuse box. I'll check the Ford manual to see if there is a relay controlling DC to the dash/ignition.
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