Have a battery boost switch question.

[km5xa]

Had a not so much fun camping trip this past weekend.

First the blinkers on the toad were not working. Blown fuse. This has happened before so I thought to try a 7.5 amp instead of the 5. Blinkers worked when we left but fuse blew on the way to the camp site. Found wire terminal screw in the umbilical cord came out and shorted the blinker wires to the metal plug. Fixed.

Then the toilet in the front bathroom was leaking. Found the ceramic toilet bowl came loose from the base. Fixed.

We went to leave Sunday and the rig would not start. It struggled to start when we left home and I thought it was because it hadn't been started since January. Nope, bad cell. No problem, I'll use the battery boost. Nothing. Fortunately I carry a good battery charger w/ a power start. We're home and have a new battery.

So, any ideas as to where I should start looking into why the battery boost has failed? I cant find any wiring diagrams. O, the joys of motorhome ownership.

[Chuckie]

I inadvertently found my battery boost fuse blown while searching for the step fuse (glad I found it ahead of time!). For my 329DS, it's a 5 amp fuse in the battery control center box in the battery compartment. Middle fuse labeled EMS per the diagram.

[km5xa]

Originally Posted by Chuckie

I inadvertently found my battery boost fuse blown while searching for the step fuse (glad I found it ahead of time!). For my 329DS, it's a 5 amp fuse in the battery control center box in the battery compartment. Middle fuse labeled EMS per the diagram.

Attachment 211124

Thanks for the quick reply. I shall make that my starting point.

[cfo111]

were you holding in on switch while you tried crank the engine ?

[km5xa]

Originally Posted by cfo111

were you holding in on switch while you tried crank the engine ?

Yes, I was. I've checked the fuse and it is good. Accessed the back of the switch. Two wires for the switch light and two on the normal open contacts. One wire (blue) goes to battery, the other (brown) to the battery control box. Both had 12 volts. When I pull the fuse in the BCB, voltage on the brown wire at the switch was gone. So I'm not sure what is going on. But I now have a new battery for the chassis. It was the original and was almost 10 years old. I think I got my moneys wort out of it.

[mbtelguy]

km5xa, not sure if the attached schematic applies to your unit but if it does this may help.
Your test removing the BCC fuse ,which resulted in losing battery on the switch brown wire would prove continuity between BCC and switch.

A question, by any chance was the battery disconnect switch operated when you tried to start. Not sure if this affects the battery on the start switch blue wire ?

[ScottBrownstein]

Probe the battery isolation solenoid in the BCC box. It has two heavy cables, one to the house and the other to the chassis. Then there are two light gauge wires which power the solenoid when you press the boost switch and when the alternator comes on so that the house can be charged. Many coaches also fire the solenoid when the converter comes on to charge the chassis, but some do not.

If there is 12 volts across the solenoid, it is trying to fire. It may be faulty or the contacts may be burned, welded or just bad. When you push the boost switch you should hear it clunk closed.

[Mr. October]

Originally Posted by ScottBrownstein

Probe the battery isolation solenoid in the BCC box. It has two heavy cables, one to the house and the other to the chassis. Then there are two light gauge wires which power the solenoid when you press the boost switch and when the alternator comes on so that the house can be charged. Many coaches also fire the solenoid when the converter comes on to charge the chassis, but some do not.

If there is 12 volts across the solenoid, it is trying to fire. It may be faulty or the contacts may be burned, welded or just bad. When you push the boost switch you should hear it clunk closed.

I'd bet the solenoid is bad. The factory solenoids most manufacturers use aren't all that great and can go bad in a relatively short period of time.

[mbtelguy]

For more BCC information including test procedures go to the following RV Custom Products Web Site

https://rvcustomproducts.com/sdc-107a

[km5xa]

Thanks everyone. Lots of info for me to look at.

[bubbles]

As has been mentioned the interconnect solenoid energizes for, emergency start/engine alternator coach battery charging/chassis battery charging via coach converter. Therefore if there is charging voltage at the chassis battery with shore power or charging voltage at the coach battery with engine running then the solenoid is energizing. Check the voltage at either battery before applying the applicable scenario and see if there is a change at the applicable battery per the applicable scenario. At least this will let you know if the solenoid is energizing or not before tearing into the BCC.

[ScottBrownstein]

Actually the easiest is to disconnect from shore power and turn the engine off and then press the boost switch and listen for a click. If you were on shore power it may take maybe 15 seconds for the BCC to drop the solenoid. The boost switch has no time delay. You should hear the clunk every time you press it. If you don't, have someone press it and measure the voltage on the small solenoid wires which are the coil. You should see 12 volts then nothing. If that is the case and it doesn't clunk...replace it.

[bubbles]

Actually, being I can't hear mine from the cockpit and the BCC is at the battery location (no power on the coach) I would just jumper from the battery to the solenoid to see if it energizes. Many ways.