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Topic: Electrical Question (Read 2147 times) previous topic - next topic

Electrical Question

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.

Re: Electrical Question

Reply #1 –
You said your generator was running and you pushed the boost switch, if that's the
case your generator is charging your chassis battery

Re: Electrical Question

Reply #2 –
Quote from: oldguy –
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. 😂

Re: Electrical Question

Reply #3 –
Quote from: Res777 –
About 10 minutes later. Check engine light is off. Voltmeter approximately 13.8. For the next two hours. Operation normal.  My question.

Did you turn the boost switch off at this point?  If not, the generator was keeping the chassis batteries up with the house batteries.

Re: Electrical Question

Reply #4 –
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.

Re: Electrical Question

Reply #5 –
Quote from: Res777 –
I picked up a new to me 08' Nimbus from MOT.  Driving back to Dallas about 30 minutes into trip. I get a check engine light.
Code 167. Alternator voltage low. Voltage meter. Approximately 12.5.

About 10 minutes later. Check engine light is off. Voltmeter approximately 13.8. For the next two hours. Operation normal.

My question(s). I have never had an alternator go bad and come back. And why would the voltmeter immediately show 12.5?
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?

Re: Electrical Question

Reply #6 –
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.

Re: Electrical Question

Reply #7 –
Quote from: WS6_Keith –
Did you turn the boost switch off at this point?  If not, the generator was keeping the chassis batteries up with the house batteries.

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.

Re: Electrical Question

Reply #8 –
Quote from: Chuck & Jeannie –
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?

1. Daytime. Headlights off. I'm not sure if the coach has daytime running lights. I will check.
2. Approximately 13.8 volts.
3. When it went off the voltmeter was showing approximately 13.8 volts. I turned the boost switch off and the voltage stayed 13.8 for the rest of the trip. About 2 hours. About 30 minutes after turning the boost switch off I turned the dash air back on. The voltage stayed the same.

Re: Electrical Question

Reply #9 –
Quote from: Roger & Susan in Home2 –
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.

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.

Re: Electrical Question

Reply #11 –
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.
 

Re: Electrical Question

Reply #12 –
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