By Dave Solberg
Dear Dave,
How can I test the emergency start switch and then troubleshoot/trace an issue? I used it once several years ago and it operated as intended. I needed to use it again a few months ago and it didn’t operate. Thanks so much! —Grant, 2008 Fourwinds Windsport 35B
Dear Grant,
The “emergency start switch,” as you call it, is actually a battery isolation manager (BIM) solenoid that is connected between the chassis and house battery or batteries. When you are traveling down the road, the engine charging system provides a charge to the chassis battery and then through the cable to the BIM and ultimately the house batteries, so it is basically a free charge.
The BIM has a spring-loaded switch that, when depressed, provides voltage from the house batteries through the BIM back to the engine battery. That is the emergency start function you are referring to.
Most newer BIM solenoids will also allow voltage to trickle to the chassis battery when your rig is plugged into shoreline power. That way the engine battery stays fully charged. It will also isolate the batteries to prevent discharging or overcharging them.
How and what to test
I am not sure what function you want to test; however, I would assume it is the “jump start” of the chassis battery from the house battery.
First, verify your house batteries have 12.6 volts, which is the fully charged state. Make sure the battery disconnect feature is not activated; no voltage will go from the house batteries to any 12-volt function. Depress the switch on the dash. You should hear a click at the solenoid, which is typically located in the battery compartment, but not always. I’ve learned to never say always or never say never when it comes to how RV manufacturers build or design things!
Use a multimeter and, with the switch depressed, test the chassis battery voltage. If it was low to begin with, it should read the same as the house battery you just tested. You can check the switch by testing for 12-volt power from the switch to the ground terminal on the solenoid. If there is 12 volt at the switch but the solenoid does not click or provide power, the solenoid is defective. Otherwise, it is the switch.
Test the solenoid for other functions
You can also test the solenoid for the other functions by starting the engine and using a multimeter to check voltage at the house battery. If it goes up when the engine is started, the solenoid is allowing a charge to go from the engine charging system through the BIM and to the house batteries.
Plug in the shoreline power cord and use a multimeter to test the voltage at the house batteries. It should be at least 13.2 volts and may be as high as 13.6 volts if the battery is low, as the converter will be in charge mode. Then test the engine battery and you should see the same voltage as present at the house battery.
Years ago, I was sent this by my technician contact at Winnebago on a little more specific testing.
MORE FROM DAVE ON BATTERIES
- Do deep cycle batteries have to be trickle charged individually?
- How can I charge my engine battery when connected to shore power?
- RV batteries aren’t charging while driving. What should I look for?
- Why aren’t my solar panels charging the house batteries?
- Why won’t RV’s converter charge the battery unless reset button is pushed?
- Follow-up to post on RV converter not charging battery
Read more from Dave here.
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Our coach was professionally converted to lithium and solar by the prior owner. Double-tapping the battery boost switch is supposed to activate the Victron Cyrix Li-ct device, but I’ve never noticed a change in engine battery voltage when doing that. The Cyrix is a clever device that keeps the engine batteries charged when the lithiums are near their fully charged state by temporarily interconnecting both battery systems. After starting the generator or plugging into shore power, which will charge the lithiums via the inverter/charger, the engine battery voltage rapidly increases via the Cyrix. That seems to make the battery boost switch essentially superfluous.