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Old 11-30-2016, 03:29 AM   #1
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VEGAS\AXIS Emergency start

I had my chassis battery dead and tried the emergency start which did nothing. Charged the battery and has been good ever since, however, is there a way to "test" the emergency start without discharging the chassis battery to do so?

Got s 2016 25.2 coach here.
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Old 11-30-2016, 09:49 AM   #2
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My first question would be were the house batteries charged? The emergency start switch ties in house to chassis batteries, if they're dead the switch won't work.
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Old 11-30-2016, 11:38 AM   #3
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Well one way to test it would be to disconnect one of the batteries (like remove a cable from the chassis battery--then you really would need the emergency start to even crank).
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Old 11-30-2016, 03:32 PM   #4
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Originally Posted by JamieGeek View Post
Well one way to test it would be to disconnect one of the batteries (like remove a cable from the chassis battery--then you really would need the emergency start to even crank).
This is a way to test it; but you also need to see how the BIRD or BCC, which ever system you have is wired. On ours the power that feeds the BIRD and the Aux or emergency start switch was on the cranking side of the isolation, Trombetta, relay. Thus when our cranking battery was dead, 4.5 volts, we were unable to pick up, energize the isolation relay which ties the house and cranking batteries together.
I posted a pic in another thread. I'll try to find it.
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Old 11-30-2016, 04:05 PM   #5
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Quote:
Originally Posted by scrubjaysnest
This is a way to test it; but you also need to see how the BIRD or BCC, which ever system you have is wired. On ours the power that feeds the BIRD and the Aux or emergency start switch was on the cranking side of the isolation, Trombetta, relay. Thus when our cranking battery was dead, 4.5 volts, we were unable to pick up, energize the isolation relay which ties the house and cranking batteries together.
I posted a pic in another thread. I'll try to find it.
On our coach power for the crossover solenoid used by the emergency start switch is powered by both batteries (through two diodes so that they aren't physically connected until you hit the switch). I've verified this by disconnecting either battery and the emergency start switch still works.

(Our coach is an older one without the BIRD & Trombetta)
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Old 12-01-2016, 02:51 AM   #6
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Originally Posted by SuperD View Post
My first question would be were the house batteries charged? The emergency start switch ties in house to chassis batteries, if they're dead the switch won't work.
Yes, the house batteries were fully charged (having been on shore power)
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Old 12-01-2016, 02:54 AM   #7
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Originally Posted by scrubjaysnest View Post
This is a way to test it; but you also need to see how the BIRD or BCC, which ever system you have is wired. On ours the power that feeds the BIRD and the Aux or emergency start switch was on the cranking side of the isolation, Trombetta, relay. Thus when our cranking battery was dead, 4.5 volts, we were unable to pick up, energize the isolation relay which ties the house and cranking batteries together.
I posted a pic in another thread. I'll try to find it.
So, if the chassis battery is dead, then the emergency start will not work? There were no dash lights, no indicators, nothing
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Old 12-01-2016, 03:01 AM   #8
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Originally Posted by JamieGeek View Post
On our coach power for the crossover solenoid used by the emergency start switch is powered by both batteries (through two diodes so that they aren't physically connected until you hit the switch). I've verified this by disconnecting either battery and the emergency start switch still works.

(Our coach is an older one without the BIRD & Trombetta)
We have the BIRD and trombetta system on ours. Figure I will throw some jumper cables into storage just to be on the safe side, but hate to have to use this since this was one of the selling points of the MH.

We are planning on doing quite a bit of boondocking, so hate not to have a way to use coach batteries to start the truck
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Old 12-01-2016, 10:01 AM   #9
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Had the same problem, here's what Thor said

I had the same problem happen to me. I contacted Thor and they had me hold in the emergency start switch down for like 1-2 min then try to start...nothing. They told me that if the chassis battery was completely drained (not just low), the coach batteries would not start the engine. I'm not sure why this is the case. It seems that it would just use the coach battery but apparently that's not what its doing. It seems to being trying to "recharge" the chassis battery which doesn't work if the chassis battery has drained too low. I charged the chassis battery and everything was fine and it has not happened since. I guess the emergency start will only work in the case where the battery is borderline low.

From this I decided to get a charger/jumper that can be charged up and/or connected to shore power just in case it happens again. I have not had to use it yet and I'm keeping my fingers crossed that I never will .
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Old 12-01-2016, 10:04 AM   #10
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The coach battery has to have enough juice to operate the trombetta (solenoid) that ties the batteries together.
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Old 12-01-2016, 12:29 PM   #11
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You can easily check if the emergency start switch works without disconnecting anything. If you have the BIRD/ Trombetta setup, test the voltage at the two poles of the Trombetta. On mine the right pole is the chassis battery. The voltages should be different. Now have someone push the emergency start and measure the voltage on the chassis battery again. If the emergency start button is working, the voltage will increase (if the chassis battery is below the charge of the house) batteries. The emergency switch is hooking the two battery systems together. If you do not have the BIRD/Trombetta setup, you can do the same thing by measuring the voltage at the chassis batter and coach batteries, have someone push the emergency start switch and see if the voltage on the house battery increases (again, if the chassis battery is below the charge of the house batteries.
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Old 12-01-2016, 12:33 PM   #12
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If SuperD is correct that the house battery or coach battery must be above a certain voltage to open the Trombetta. However, I believe that the way the system is wired, the Trombetta does not have to open for the emergency start switch to work. It makes a direct connection between the house and chassis batteries.
Just because the emergency start is working does not guarantee that the vehicle will start. As theTraveler indicated, the chassis battery is the one that starts the RV. It must be at a high enough voltage to start the vehicle. That's also a safety thing. I once started a car with a battery charger and immediately disconnected it. The voltage on the chassis battery was high enough to start the car with the charger connected, but when I disconnected it, the charge was not high enough to run the car computer. It blew up the computer and it cost me a lot to replace it. Lesson learned for me. I always check the charge on the chassis battery before I put a charger on it and attempt to start the car. Expensive lesson.
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Old 12-01-2016, 12:38 PM   #13
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Originally Posted by Mo_Mike View Post
So, if the chassis battery is dead, then the emergency start will not work? There were no dash lights, no indicators, nothing
Yes that was the case but only because the power feed was on the cranking battery and not on the house batteries where the electrical drawings show it to be if you have the BIRD/Trombetta system.
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Old 12-01-2016, 12:51 PM   #14
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Yes that was the case but only because the power feed was on the cranking battery and not on the house batteries where the electrical drawings show it to be if you have the BIRD/Trombetta system.
If that is true, then the house battery would be connected to the house battery and not the chassis battery and the emergency start switch would never work. That does not seem to be the case. The emergency start switch does work in most RVs, so it must connect the house and chassis battery unless it is miswired. Which certainly could be true. My BIRD was miswired at the factory.
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Old 12-01-2016, 12:52 PM   #15
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The Trombetta ties the house batteries together under 3 conditions when the BIRD and emergency switch are powered correctly from the house batteries.
1. The motor is running and alternator output is above ~13.2 volts.
2. Any time the motor is off and the house batteries go above ~13.2 volts
A. Shore power will do this.
B. Running the generator will do this.
C. A solar system will do this.
In the above cases there is a time delay before the Trombetta is "closed";
this is a normally open isolation relay until you put power to it.

3. If you press and hold the emergency start button this will also put power to the Trombetta. No time delay.

Eds write up on this is very clear, the wiring diagrams that I hand verified, also agree with this.

Mine did not work this way until I moved the yellow wire from the cranking side, chassis, of the Trombetta to house side per the drawings.


In all our years of RVing the house and cranking batteries were not tied together until an isolation relay between the two was powered up. Might be the ignition switch turned to on or some system like the BIRD.
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Old 12-01-2016, 01:06 PM   #16
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The problem with your explanation is that the emergency start switch works without the coach being on shore power or generator or the engine running. If that is so, the voltage in the chassis battery is below 13.2v so it cannot open the Trombetta. You must be on shore power/generator or the engine must be running for the batteries to be above 13.2v necessary to open the Trombetta. The emergency start switch works at below 13.2v so it must tie the two battery systems together directly. I don't see any other way no matter what the Thor diagrams say.
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