Community Forums

ArkansasRomr · 08-07-2019, 05:03 PM

Hello, all you do it yourself smart guys/gals,

Here’s the deal:
*New inverter and new chassis batteries 09/18
*I always turn off both house/chassis batteries after use
*House batteries hold over 13 volts always
*Chassis batteries drop to 7-8 volts even with shore power
*Battery boost not working, suspect bad relay. Btw whats replacement part #
*Ive been starting by using cables and jumping from house to chassis

What could be draining chassis power even with switch turned off?
I know I need to replace boost relay but need part number. I’ve found some that I think might be it but it costs $350 to $405.

I’m barely competent with mechanical but shite with electrical.

Thanks before hand to all my friends and fellow forum members!

legrandnorm · 08-07-2019, 05:22 PM

There must be a bad solenoid switch that does not cut-off the chassis batteries.
Find a competent rv service center... (not a Camping World)

RVPioneer · 08-07-2019, 05:24 PM

Why aren’t your chassis batteries charging while on shore power?

doublechevy · 08-07-2019, 08:07 PM

On my coach 2008 Knight when connected to shore power chassis batteries will only charge after house batteries are fully charged . this is accomplished thru the boost solenoid. if boost solenoid is not working then it cannot connect the chassis batteries to the charging circuit. I found the same problem and disassembled boost solenoid cleaned boost solenoid contacts reassembled cured my problem

twinboat · 08-07-2019, 09:25 PM

You may have a seperate charger back by your Big Boy solenoid. Take a few pictures and post them.

Have you tried leaving the chassis battery switch ON, to see if it charges while plugged in. The battery disconnect switch is for storage without power.

The house battery bank disconnect doesn't matter because the inverter/charger is connected directly to the batteries.

Your unit is a 2001, newer units may have different systems. What fixed theirs may not fix yours.

rschreifels · 08-07-2019, 09:29 PM

I check our "one year new to us" 2005 Cayman PDQ solenoid and found it was not working. I forgot $150+ brand it was (but not a high dollar BigBoy) but I replaced it with a Cole Hersee 24059-BP 12V Insulated SPST Continuous Duty Solenoid for $20. All of the expensive solenoids appear to not last very long, so I'm trying a cheap one!

ArkansasRomr · 08-07-2019, 09:33 PM

I will that a go and thanks!

ArkansasRomr · 08-07-2019, 09:33 PM

I’m with you on the camping world!

ArkansasRomr · 08-07-2019, 09:36 PM

I don’t know RVpioneer, that’s what has stumped me. I think doublechevy May be on to something. I’m gonna try to take my boost solenoid apart and clean it.

ArkansasRomr · 08-07-2019, 09:43 PM

Twinboat,

Trying a $20 part can’t hurt even if it fries. And thanks for the part number.

Thanks again

twinboat · 08-07-2019, 09:56 PM

Quote:

Originally Posted by ArkansasRomr

Twinboat,

Trying a $20 part can’t hurt even if it fries. And thanks for the part number.

Thanks again

It wasn't me suggesting a $20 solenoid.

I suggested that your older system may not use that or any solenoid to charge the chassis battery.
It may fix the boost, if its the solenoid and not the switch or wiring.

rschreifels · 08-07-2019, 10:04 PM

You can test the solenoid by turning on the boost switch and testing to see if there is 12v across the solenoid coil terminals. Also, if the battery banks are at a different voltage, there would be a voltage difference across the two main posts with the solenoid turned on, if the switch was bad.

rschreifels · 08-07-2019, 10:08 PM

If you do change out the solenoid, undo the battery bank GROUND wire from both banks before swapping out the solenoid out. Then reconnect after the swap. And be sure the shore power is not connected.

RVPioneer · 08-07-2019, 10:38 PM

Quote:

Originally Posted by ArkansasRomr

I don’t know RVpioneer, that’s what has stumped me. I think doublechevy May be on to something. I’m gonna try to take my boost solenoid apart and clean it.

Have you tried charging the chassis batteries with a separate charger?

Not sure how yours is wired. The big brain that engineered mine decided it would be a good idea for the chassis batteries to control the “big boy relay”. Guess what happens when the voltage gets low on the chassis batteries? The relay won’t close to combine the batteries and the “boost switch” becomes useless.

7-8 volts isn’t good for the batteries. Bringing them up to full voltage may solve the problem. It may also be possible that the batteries won’t charge with the disconnect switch in the “off” position.