I picked up a new to me 08' Nimbus from MOT. My first MH. Driving back to Dallas about 30 minutes into trip. I get a check engine light. Hmm. Coolant temp. Good. Oil pressure. Good. Look at the engine monitor. Code 167. Alternator voltage low. Voltage meter. Approximately 12.5. No good place to pull over. Generator is running so I select the boost switch. Should get me to Henderson okay. I'll check it there. About 10 minutes later. Check engine light is off. Voltmeter approximately 13.8. For the next two hours. Operation normal. My question. I have never had an alternator go bad and come back. And why would the voltmeter immediately show 12.5? It makes me wonder about the health of my chassis batteries.
You said your generator was running and you pushed the boost switch, if that's the
case your generator is charging your chassis battery
I understand that. Selecting the boost switch ties the two battery banks together. I was attempting to keep the chassis batteries from going dead. The interesting part was selecting boost barely raised the voltage on the voltmeter. I also turned off the dash air thinking this was off the chassis batteries. A big complicated electrical beast. 😂
Did you turn the boost switch off at this point? If not, the generator was keeping the chassis batteries up with the house batteries.
For clarity, as others have done: One can drive for weeks with dead alternator, if generator is on to power house battery charger and boost solenoid is powered to also charge start batteries.
Firstly, you performed the correct "emergency procedure" by turning on the boost switch with generator running. You obviously know enough about the electrical system on your coach to realize that this will keep both battery banks charged indefinitely. As said above, you can drive cross country in this condition - no problem.
Your questions are:
1. What happened to the alternator?
2. Why did dash voltmeter immediately show 12.5?
More info would be helpful.
1. Were you driving during the day or night? Headlights on?
2. What was the voltmeter reading
before the check engine light came on?
3. When check engine light went off, and voltmeter was reading 13.8, did you leave the boost switch on or did you turn it off?
Alternator is suspect. Make sure excite wire and sense wires are in good shape. Connectors at the ends are a common failure point. Make sure all connections at alterntor and isolator and at the batteries are clean and tight.
Isolator could be failing to.
Yes. When I saw that the voltage returned to normal I turned the boost switch off to see if the alternator was working. The voltmeter stayed at approximately 13.8 volts for the rest of the trip. About 2 hours. I just thought it was strange for the alternator to quit charging and then start again. I was thinking maybe a loose connection somewhere.
I was going to check the connections from the alternator to isolator to battery. I am assuming since the house batteries are in the belly of this beast. That the chassis batteries are as well. Unfortunately that's a question I forgot to ask on the checkout. Any recommendations on the best isolator. I may go ahead and change that preemptively. Hopefully it's not the alternator.
Thanks.
Test your isolator: How To Test A Battery Isolator | RV Lifestyle (https://rvlifestyle.com/how-to-test-a-battery-isolator/) If you have to change it, take a photo of the wiring and make sure they are clearly labeled in the photo.
Pierce
I would suggest taking some voltage measurements with a multimeter directly (not the dash meter) before guessing and replacing parts.
With engine idling, everything off (inverter, headlights, fans, etc) measure...
1-voltage at alternator B+ (big) post (~14.5v -15v)
2-voltage at chassis battery + post (~13.5v-14v)
3-voltage at house battery + post (~13.5v-14v)
Now add some load on the alternator - i.e. headlights on, dash fan on high)
Repeat measurements 1,2,3 and post results.
Sense circuit must be working or alternator won't seek to adjust voltage. Much cheaper to test these items rather than change hoping for results. Congratulations on your new coach
Scott