12 volt problems

[rsw1943]

I have a 1997 Bounder, (ford 460 chassis). When I disconnect the 12 volt engine battery, why does the engine still start????? With the 12 volt battery disconnected, everything still works. BUT if the 12 volt battery is dead, I can't start the engine... HELP

[subford]

Sounds like someone has miss wired the battery.
Could also be a stuck closed parallel solenoid or its switch on the dash.
Here is a diagram below of the starter wiring:

[Iangolf]

Are you sure you are not disconnecting the coach battery and not the chassis battery?

[rsw1943]

I disconnected the 12 volt chassis battery. Not to 2, 6 volt coach batteries

[Scarab0088]

From your brief explaination, it would seem that both battery banks are wired together.

With a dead battery in the circuit, the other battery would not have enough power to back charge the dead battery and start the engine, but pull the dead battery and the engine can be started.

Connections between the chassis battery, house battery, alternator, converter/charger and inverter are usually managed by a cross over switch, but your RV might just be all wired together or the switch is stuck in the all connected position.

You will want to replace the chassis battery. And if everything is connected, be careful to avoid discharging all batteries overnight or you will be stuck and unable to start the engine and/or the generator (if so equipped).

Like Bills post shows, to fix the cross over switch or system is involved and would require electrical service experience.

Best of luck

[Coaster1]

Perhaps the emergency start solenoid is stuck.

[georgetown350]

Sounds like the disconnect is not working. Doubt that it is the isolator solenoid as the power would still be stopped at the disconnect switch.

[subford]

Originally Posted by rsw1943

I disconnected the 12 volt chassis battery. Not to 2, 6 volt coach batteries

Can you post photos or email them to me of the battery Box and the solenoids and wiring. If you send them to me I will post them in this thread.

That might help.
My email address is at the bottom of this post.

[justimagination]

We have basically the same model year, just a different design. My HOUSE battery(two 6v) is wired to my main CHASSIS battery, therefore rendering 12 v to the house battery to keep them charged.
If your coach is wired like mine, buy you a new chassis battery and hopefully problem is solved. Mine unit just turned 40k miles, and has never been changed or tampered with. JMHO, good luck, and buy a good battery. As a side note, if your coach has a Solar charger on the roof mounted front a/c, make sure the two small wires are connected to your chassis battery when you change it.
david g.

[Old Bounder]

If you are plugged into shore power, the BCC will have the isolator/aux start/charge solenoid energized with power from the converter. This would allow the engine to start from the house batteries.

If you are NOT plugged into shore power, then your isolator solenoid contacts are welded closed or someone has purposely connected the batteries together.

[TQ60]

There are diagrams on this thread, please study them.

Get a volt meter and start making measurements as that will tell you what is wrong.

Check everything in the diagram, "divide and defeat", pick some spot in the middle or start at one end, verify if the measurement is correct, then determine why incorrect readings are what they are and do not buy any parts until they are confirmed bad instead of bad wiring.

We learned on a Fleetwood that the battery controls are powered by the coach batteries.

If boon docking and you run your coach batteries down, you cannot engage the starting battery, you are dead in the water...unless you have a helper that can hold down the boost switch to connect the starting battery to the house batteries so you can activate the starting batteries.

That one took a little troubleshooting to determine, not much, only a couple measurements, but determining if normal, that took awhile...

[Old Bounder]

Originally Posted by TQ60

There are diagrams on this thread, please study them.

Get a volt meter and start making measurements as that will tell you what is wrong.

Check everything in the diagram, "divide and defeat", pick some spot in the middle or start at one end, verify if the measurement is correct, then determine why incorrect readings are what they are and do not buy any parts until they are confirmed bad instead of bad wiring.

We learned on a Fleetwood that the battery controls are powered by the coach batteries.

If boon docking and you run your coach batteries down, you cannot engage the starting battery, you are dead in the water...unless you have a helper that can hold down the boost switch to connect the starting battery to the house batteries so you can activate the starting batteries.

That one took a little troubleshooting to determine, not much, only a couple measurements, but determining if normal, that took awhile...

I'm not sure HOW or WHEN you learned this, (or just what you think you learned) but it's not true. RV-Custom Products, who designed the BCC circuit board used in Fleetwood coaches, added dual battery power to the disconnect switchs as their very first modification back in about 1990. Check page one of this document. CB-200 Rev B.

[YC1]

Your description is a bit confusing and does not add up but it is a simple system.

With the engine battery disconnected and you turn the key it is bringing your house batteries in to play and hence you start the engine via that bank of batteries. That should answer your first question. But then you add "if the 12 volt battery is dead" why doesn't it start.

What battery do you mean.

Your system should be very simple. Two battery systems. One for the rv, one for the engine. If the rv batteries die, your engine should start via the engine battery. If the engine battery dies you should be able to start because a solenoid brings the rv batteries online when you turn the key. Sort the two batteries out and replace the bad one or ones. If over a couple of years just change the batteries and stop fussing about.

[TQ60]

This is a 1993 model, the power lead for the ckt board is attached to the coach battery, and there did not seem to be any active connection to the starting battery.

It is possible that this unit is not in original condition, or something could be wrong with it.

But this unit with low voltage on the coach batteries will not engage either battery system if they are both turned off with a low voltage condition on the coach system.

The relays need a minimum amount to pull the contactor in.