-
12V alternator system overvolt intermittently
This has happened 2 or 3 times now, always when first starting coach I think. Most recent event I have most detail of circumstances because I installed a temporary 3 way 12v lighter plug that has a led voltmeter on the back of the feed plug. Past instances lasted few minutes and self resolved, I don’t know /remember how. In past cases I became aware of problem when inverters faulted and did not make 120 ac. I think I recall I gave up playing with buttons on inverters and drove off, was OK when I next stopped.
Scenario:
1) Coached parked at house 2 days on shore power.
2) Ready to leave to take to storage so shut off acs, unplugged coach.
3) Started coach, 12v system quickly rose to 17 volts. Shut of coach, restarted, rose back to 17. Went to inverter panels (original panels and inverters) they were in “fault” mode I presume from overvolt feed from alternator. Played with reset several times on both panels – would reset but in seconds kept reverting to fault. Played with putting some loads on inverters, refrig etc , no difference.
4) gave up, went to driver seat released parking brake to move coach. Voltage dropped to 13.x volts. Reengaged parking brake, voltage back to 17. Did this a few times to confirm it was not my imagination.
5) Don’t remember exactly what I did next, but I know I did not disengage parking brake with coach running and reset inverter, because I was on slight grade and coach started rolling when I tried that. I think I engaged park brake shut off coach, reset inverters, put some loads on, then started coach. All was fine rest of the day, even after turning off the loads.
Ideas? The thing that perplexes me most is why voltage regulation returned to normal when park brake is released. It was not a matter of fast idle dropping off when parking brake released, I tried it with and without the fast idle switch engaged, no difference.
-
4 Replies
-
David, This is just a guess, but while the 12V system is a problem, it is possible you have a separate alternator for the 12 volt system and that likely has a non-serviceable internal voltage regulator.
I think your 50DN large alternator is 24 volts and is dedicated to the chassis, and it does have an external voltage regulator.
Again, I am guessing, but you can easily verify what I am saying.
-
I believe when you release the parking brake it turns the headlights on in the driving mode, thus putting a load on the alternator. It may be a bad connection relating to the alternator not seeing the real battery voltage so the alternator thinks the battery is low and tries to bring it up.
-
Yes I I do have a separate 12-volt alternator. It is over by the fan drive. I don’t think my vintage of coach has headlights that come on in drive mode. One thing that does happen is when you release the parking brake if you have it on fast idle that will go off so there is some feedback from the parking brake to some system. A loose connection that is not providing feedback to the alternator regulator wherever it is sounds like a possibility. I will get the coach later this weekend and check that.
-
I disagree with Mikee. The way Liberty is set up on the Classic is the 50DN is the chassis alternator because Liberty equips the coaches with OTR. That is a 24V alternator and as David is describing the issue it seems the 12V house alternator is what is acting up.
The Headlights probably do come on when the coach is put in gear, but they are 12volt off the chassis batteries and not the house and thus would have no affect on inverters.
Log in to reply.