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Old 08-27-2017, 11:42 PM   #1
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THOR #5374
Electrical Question

While I was trouble shooting my a/c I discovered that my rv will start with the knife switch ( positive side of the battery) in the open (disconnected) position .

I would imagine that the solenoid for the emergency start , which connects the house and chassis batteries , is stuck in the closed position.

This is the only thing that I can think of that would cause this to happen.
Am I on the right track ?

If so what is that solenoid called , what does it look like and where is it located on my Vegas 24.1 ??
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Old 08-27-2017, 11:59 PM   #2
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Were you connected to shore power?
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Old 08-28-2017, 12:04 AM   #3
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Should not matter if he is connected to shore power.
I don't know where the solenoid is but you might have someone cycle the switch as you look under the hood and near the batteries......It should click, unless it is frozen solid
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Old 08-28-2017, 12:23 AM   #4
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Should not matter if he is connected to shore power.
I don't know where the solenoid is but you might have someone cycle the switch as you look under the hood and near the batteries......It should click, unless it is frozen solid
Actually, it does matter. Your RV is setup to charge the house batteries from the alternator and the chassis battery from the converter. It does this by closing the cross-connect relay when a sufficient difference in voltage is detected.

Having 13+ volts on the house batteries and 0 volts detected on the chassis battery (since the disconnect was open) would trigger the cross-connect relay allowing you to start the coach from the house batteries, just as if he had held the emergency start switch.
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Old 08-28-2017, 01:20 AM   #5
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Yes , the rig was plugged into shore power earlier in the day when it started with the chassis battery disconnected.
So I just went outside , disconnected the shore power , made sure the knife switch ( chassis battery ) was disconnected and then turned the ignition key.

It started right up !
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Old 08-28-2017, 01:26 PM   #6
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While upgrading to 4 coach batteries I noticed a was still getting minor sparks from the positve cables with both sets of batteries disconnected! I was still plugged into shore power for the fridge. So, I pushed the use/store switch to store, that stopped the sparking + the fridge was still working! dunno
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Old 08-28-2017, 01:45 PM   #7
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perhaps a stuck relay?

Just brainstorming....do you hear the relay when you push the emergency start switch?
with no shore power, no generator
chassis engine off
you should hear a thunk when you push that button.....

Relays do go bad. I replaced mine back in April after I found that the chassis was not charging the house battery

Probably time to get out the multimeter....
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Old 08-28-2017, 02:09 PM   #8
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Sounds like your initial supposition may be right. As blw2 said, "time to get out the multimeter".

Disconnect from SP and start tracing the 12 VDC back from the open knife switch. Find the relay if you can: you should have 12 VDC to ground on one side and 0 VDC on the other if working correctly.
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Old 08-28-2017, 04:10 PM   #9
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Called Thor this morning and explained my problem . Tech on phone says "that's impossible " and that the rv will not start with the positive side of the chassis battery disconnected.
He also said to let them know if I figured out the problem

He did identify the solenoid as being located in the engine compartment by the windshield washer bottle.
Went out to the rv and checked the solenoid with a test light , both sides are hot with the crossover (emergency start switch) at rest.
Called Thor back to get a part number for the solenoid , they are having trouble finding it.
They were very nice and said they will find it and call me back.

Guess I'll pull the solenoid off and see what markings are on it.
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Old 08-28-2017, 04:42 PM   #10
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Ok I think I have it figured out .
The relay / solenoid is the Trombetta , it was stuck and so hot that I almost couldn't touch it.

Don't know how long it's been bad , but it's bad.

Thor won't replace it unless I drive 3 hours to the dealer and let them condemn it.
Amazon had 1 left in stock cost me $25.00 shipped to my door .

I've had enough Thor adventures to last me for a while !
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Old 08-31-2017, 04:50 AM   #11
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I agree with you Petew.
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Old 08-31-2017, 10:20 AM   #12
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Quote:
Originally Posted by 99dart View Post
While upgrading to 4 coach batteries I noticed a was still getting minor sparks from the positve cables with both sets of batteries disconnected! I was still plugged into shore power for the fridge. So, I pushed the use/store switch to store, that stopped the sparking + the fridge was still working! dunno
Exactly as expected when plugged into shore power...
In "use", the converter/charger would be sending voltage to batteries, resulting in your sparks at the cables...
In " store",, nothing would go to batteries (stopped sparking), but the converter would still power the coach - keeping the fridge running.
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Old 09-01-2017, 10:37 AM   #13
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Electrical question

Tfryman I think you may have your logic reversed. The alternator would charge the chassis battery and the inverter charges the house battery. Some setups charge both sets of batteries at the same time.
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Old 09-01-2017, 10:49 AM   #14
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Originally Posted by Slickrick racer View Post
Tfryman I think you may have your logic reversed. The alternator would charge the chassis battery and the inverter charges the house battery. Some setups charge both sets of batteries at the same time.
No, I don't. First of all, inverters don't charge batteries, converters do, Some units have a combined converter/inverter unit, but it is the converter that has the function of charging the house batteries.

But the converter will also charge the chassis battery as I said "by closing the cross-connect relay when a sufficient difference in voltage is detected". The same way the alternator will also charge the house batteries "by closing the cross-connect relay when a sufficient difference in voltage is detected" even though the alternator will always directly charge the chassis battery.
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Old 09-02-2017, 02:41 PM   #15
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New Trombetta came yesterday and I installed it today , problem solved.
The coach will no longer start with the chassis battery disconnected.

Reconnected the chassis battery, fired it up and put a meter on all three batteries all are charging.
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