We were traveling with friends recently that have a '98 U295 when he noticed high voltage ( 17-20) on the voltmeter. The next morning the engine would not turn over and both engine batteries were completely dead showing about 1 volt. We attempted to recharge the batteries with little success and because of their age elected to replace them. After replacement the engine started right up with no problem. However, the voltmeter was following the engine RPM and was going right up to the max on the gauge. We disconnected the alternator and they made their way home with out further incident and running the generator to keep the batteries up. Three questions: 1. What happened ? 2. Is it really necessary to run the generator all the time if you have the alternator disconnected? and 3. Is there a better way to handle this.
Falconguy,
Since none of our more learned folks have chimed in here is my guess.
1. -- Voltage regulator. Remove alternator and replace yourself or have trusted alternator shop do the work. For $75 to $100 you can have new bearings and brushes while your at it.
2. -- I certainly would run the gen. All dash electrical equipment runs off the engine start battery so dash lights, running lights and dash HVAC (if on) would pull the start battery down. The gen likes to run so I would have mine on as I do much of the time anyway.
3. -- As to LANDING the right procedure to handle this situation, I think you have GREASED IT ON with the nose wheel right on the center line. Good job.
Could be something as simple as a broken sense wire.
Start by checking out all the connections between alternator, isolator and if external, the regulator.
And, with a non-functioning alternator, yes you can keep up the batteries by: Running generator which powers the charger section of the inverter/charger, which charges the house battery bank. Since most are NOT wired for the inverter/charger to charge the chassis battery, in most cases, you will need to use the BOOST SWITCH to allow the inverter/charger to charge the chassis battery.
Very easy to tell if your inverter/charger charges your chassis battery directly, or if you need the boost switch. With alternator not outputting, main engine running, note voltage on the dash gauge. Turn on the boost switch. If voltage goes up, you need to leave the boost switch ON.
Now, a caution. If the alternator is functioning (i.e. all other wires are in place) and you just disconnect the large B+ output wire and run the engine, you will blow the diodes in the alternator. It MAY BE (check with your alternator manufacturer) that disconnecting both B+ and sense wire and/or external regulator would not harm the alternator-- I have no idea. Were it mine, I would diagnose the problem and fix it.
I had a similar problem on our 91 GV. It turned out to be the regulator (which is built into the alternator). The stock alternator was a 105 amp Leese Neville which is no longer available. I replaced it with a 160 amp Leese Neville which fit right in. The newer alternators are self excited and do not require the external excitation wire that my old one had. I just left it disconnected and taped off. Have a great day ---- Fritz
Note-- if you have a diode-based isolator, you really need an alternator/regulator with external sense wire and that wire needs to be on the OUT side of the isolator. Diode-based isolators drop voltage about .6 VDC. The other option is if the new one has an adjustable regulator and you adjust alternator output higher by .6 VDC to account for the loss across the isolator.
A third option would be to ditch the diode-based isolator in favor of a simple switch to combine batteries or solenoid-based isolator.
Brett
Thanks for all the input. I just talked to our friends and they en route to MOT for repairs. I passed along everyone's comments and I will post the findings when they pick up their coach.