Author Topic: '03 patriot thunder-DC chassis voltage-20 volts DC  (Read 5531 times)

Richard Turner

  • Guest
'03 patriot thunder-DC chassis voltage-20 volts DC
« on: January 20, 2010, 03:28:16 AM »
DC chassis voltage reading 18 to 20 volts with engine running.  Alternator bench tested at 13.5 volts.  Batteries at 13 volts with engine off.  Battery isolator has been replaced same issue.  Voltage measured at dash, alladin, isolator etc. Any suggestions for next checks for problem and resolution.  Any help appreciated
« Last Edit: January 20, 2010, 03:54:23 AM by 193 »

Gerald Farris

  • Guest
Re: '03 patriot thunder-DC chassis voltage-20 volts DC
« Reply #1 on: January 20, 2010, 03:22:51 PM »
Richard,
There are several bits of information that I need to help you.
1 Year and model of coach
2 Are you pluged into shore power
3 Is the generator running
4 What kind of voltmeter (how accurate) are you measuring the voltage with
5 Charge state and condition of house and chassis batteries

If you would like to talk over the problem, call me. (I am the Region 4 V.P.)

Gerald
« Last Edit: January 22, 2011, 04:35:57 PM by 14 »

Edward Buker

  • Guest
Re: '03 patriot thunder-DC chassis voltage-20 volts DC
« Reply #2 on: January 21, 2010, 04:37:44 AM »
Just a couple of thoughts on this one. The isolator is O.K. because the voltage output of the alternator is being seen on the output side of the isolator as measured elsewhere, dash etc. I'll asume that both diode sets in the isolator are good and that both house and chassis batteries see charging voltage levels of 13+ volts. The bench test of the alternator indicated that the regulator was working because the voltage was held at 13.5v while the output current was tested at rated output I will assume, approaching 165amps or so.  There are several smaller leads typically on these alternators, like the Leece Neville configuration, that are used to remote sense the voltage levels and then regulate the field current to adjust the alternator output. Your voltage levels are very high indicating that the field current is turned fully on most likely due to a false low voltage condition being sensed on these leads. If the regulator was O.K. and the sensing voltage was right the output could never climb to 18 to 20V because the field current would be adjusted by the regulator to maintain around 14v under various current loads. The root cause can be an open circuit breaker, a bad diode in series, a broken wire, or an open ground wire as part of the sensing circuit. I would measure each of the smaller external wire voltages with the ignition on and off just to see that some voltage is present. If you have a friend with a similar coach they may be able to provide useful voltage information or an alternator shop may be able to give you the proper expected voltage range at these terminals. Hope this helps...

Bruce Benson

  • Guest
Re: '03 patriot thunder-DC chassis voltage-20 volts DC
« Reply #3 on: January 21, 2010, 04:27:41 PM »
Ed is on the right track.  You should be able to read voltage on one of the two small wire terminals on the alternator with the ignition switch off.  The other small wire terminal should have voltage only with the ignition switch on.  Check this first with the engine not running.  Then check it with the engine running.  You should see 14.5 volts or less on the sensing terminal.  

If you show more than 14.5 volts on the sensing terminal you need to find a new alternator shop.

I suspect that one of the terminals will show no voltage with ignition off or on.  This would indicate an open in the sensing wire to the positive terminal chassis batteries.  You would need to run this wire down to find the open or perhaps easier, run a new wire.  

The alternator cannot "see" the chassis battery the way a car alternator does because of the battery isolator that allows for the charging of both the house and the chassis batteries by the engine alternator.  The sensing wire is what allows the alternator to "see" the batteries and thus regulate the voltage.

Bruce