DP Charging Problem

If you have to replace the alternator, and it is a leece neville unit, the Delco 28 SI will probably replace it. I did this on my 2000 Freightliner (now sold), and it worked well and cheaper than the leece neville.

The delco web site has the wiring diagrams for hookup.

There is more info in my post on IRV2 linked below:
alternator conversion

If you really want to get into troubleshooting, the following website has the steps for the leece neville alternator.

alternator troubleshooting

Fred

While driving with generator on, house batteries being charged with chassis batteries in parallel; the combined battery voltage slowly drained from 13 to 11.75 over a 2 hour period. After getting home I disconnected the parallel setup, allowed all batteries to be charged with house charger. Battery voltage came up to normal charged value.

Lewis,

If combining the batteries while driving (but generator OFF) kept the chassis battery at 13.5+ VDC, most likely suspect is your BATTERY ISOLATOR.

That is because the house batteries ARE receiving a charge from the alternator, so it is OK.

Now, if the generator was running as well, above does not apply as house batteries would be charged by your converter or inverter/charger.

Thanks railtrailers, sounds like the same problem, except that my voltage dropped down to about 9v after several hours on the road. I stopped and connecter the house batteries in parallel so the house charger would hold the voltage up until I got home.

Have checked all connection except on the Alternator at this point, removed batteries and checked them as well. Been busy but my next job is to look under the bed. I replaced the air filter once but had a hard time sealing off the engine compartment so fumes didn't come in while driving. Don't look forward to getting back in there.

We had a very much the same problem with our 2001 Dutchstar, Freightliner, CAT engine. Cruising up hill, voltage drops to perhaps 12.4 volts, down hill voltage rises to perhaps 13.6 volts. Could not find anything wrong with batteries, wires or wire connections. Solved the problem this past spring by replacing the Leece Neville alternator with a new one from AJ-Electric via Amazon for about $260.00. Now voltage stays rock steady at about 14.1 volts.

I theorize that the difference between up hill versus down hill was due to vibration of the hard mounted alternator being driven by the engine power strokes when powering up the hill versus coasting down the hill. Perhaps one of the brushes was hanging up in its bore.

I purchased a replacement voltage regulator and brushes for the old alternator. Burnished the slip rings where the brushes ride and now it appears to work quite well on the test stand so it rides along as a spare in case ever needed.

Really heavy alternator to pull and replace solo, but I got it done. Getting the air intake plumbing in and out was a task also. (Be sure to cover the intake to turbo to be sure that nothing goes down the hole.) Needed to replace some of the air intake hose clamps as they did not want to loosen and also did the air cleaner while I was in there.

My installation does not use a diode isolator, it uses a BIRD and a Fat Boy relay to accomplish the function of the diode isolator without the voltage drop (0.6 volts) that the diodes would impose.

To get to the back of the alternator where the connections are, access from INSIDE. Under bed/closet, etc.

Then follow the large-gauge cable (usually red) from alternator B+ to locate the battery isolator.

Thanks for the info from all. Will check the sense line and other connections to alternator if I can reach them. Can see the alternator from rear door but can barely reach ; not sure how I will check the connections but will try. I know where the sense line connects to battery. Have a diagram of the isolator relay but not sure where it is. Diagram says "Rear Electrical Center". Don't believe its the electrical where AC power comes in?

Battery is not the problem. It charges from coach charger when engine is off, then cranks engine ok.

If there's a diode based isolator present, it's more than likely the cause.
I would by-pass it by placing all battery leads on the same terminal and see if all the batteries charge.
I bet they will!

The way it is running I would be popping a new alternator on.
Original 2001? 16 years is good service.

Sounds like you suspect it could be batteries. My first guess would be batteries with that in mind. How old are they?