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MSGulfCoast · 04-24-2016, 07:09 PM

I have a Leece Neville 4884JB 200 AMP alternator which is a rebuild. Previous one had the fluctuating tach/low voltage symptoms. On a short trip this weekend the dash voltmeter suddenly was showing 16 volts!

Checked the voltage at the batteries and it indeed was 16 volts.

Now before I put the previous alternator (now rebuilt) back on what should else should I check? The batteries seem ok but could a bad battery cause the alternator to put out 16 volts? I've shut off the big switches on the side of electrical panel in the engine compartment and disconnected shore power to let the batteries "rest" and will check again tomorrow. I thought turning those switches off would stop the batteries from being charged but it seemed I was wrong as they were still charging.

This may be totally normal as I don't normally have my head in the engine compartment but there was a clicking sound coming from either the Lambert or the big isolator??? Connections seem fine on all these components but I have not checked the connections at the alternator yet as I didn't crawl under the coach.

I've read as many threads as I could find but just wasn't getting a "warm & fuzzy" feeling about what to do. I've also seen all the posts on switching to the Delco 28SI but don't want to go that route.

Would appreciate any words of advice to proceed. Thanks.

ScottyBye · 04-25-2016, 12:54 AM

I had a similar problem on a 1800cc Honda Goldwing, and it ended up being a faulty Voltage Regulator.
Not sure if a MH is the same but worth a try

Keep in mind that newer in vehicles the ECM should trigger a fault code on an overcharge condition...it should be able to turn the alternator off too.

Also having a bad battery could indeed cause the alternator to stay in charge mode longer or even full time. May want to also LOAD TEST the batteries individually

DtBt · 04-25-2016, 06:18 PM

Since you have a "JB" alternator aka DUVAC, it has a remote sensing wire. If that is not connected correctly or the isolation diode is bad the alternator may go to MAX output trying to charge a battery not conducting through the isolation diode. The battery isolator in rear run bay is perhaps a cutler hammer 48160. It has fins and three large terminals and consists of two big diodes internally. The center terminal goes to the alternator output and the other sides go to the chassis battery and the house batteries. Use a meter with the engine running to measure the voltage on each terminal. The center terminal will be 13.8-14.3 volts and each of the other terminal should read about 0.2 volts less than the center alternator terminal. THe DUVAC or remote sensing wire is usually connected to the chassis battery side of the battery isolator.
If all that checks out then you need a new alternator internal regulator.

twinboat · 04-25-2016, 07:19 PM

Putting on the original may cure your problem.

Most rebuilders don't know what a DUVAC alternator is and may have done something wrong when rebuilding it.

Even if you go with a Delco, you need the external sense for the regulator.

Your MH uses a diode based regulator. The diodes only let power flow away from the alternator. With that, there is no feedback voltage to the alternators internal regulator.

The remote sense wire from your chassis battery supplies that feedback. Make sure it has power at all times.

Newer MHs use mechanical controls to combine the battery banks and the alternator output wire has battery voltage on it..

There is a lot of info about DUVAC regulators on line. Google will lead you there.

MSGulfCoast · 04-26-2016, 11:26 AM

I know exactly what & where the battery isolator is but wasn't sure what I was supposed to see when checking it. So to be clear I should find a chassis ground then check with positive probe on each of the three terminals on the isolator correct? I'm pretty sure I'm going to see 16+ volts as I did at the batteries themselves. I now know how to test the isolator itself which I will do at the same time. I'm assuming the Lambert battery maintainer wouldn't have anything to do with the dash voltmeter reading 16+ volts!

Quote:

Originally Posted by DtBt

Since you have a "JB" alternator aka DUVAC, it has a remote sensing wire. If that is not connected correctly or the isolation diode is bad the alternator may go to MAX output trying to charge a battery not conducting through the isolation diode. The battery isolator in rear run bay is perhaps a cutler hammer 48160. It has fins and three large terminals and consists of two big diodes internally. The center terminal goes to the alternator output and the other sides go to the chassis battery and the house batteries. Use a meter with the engine running to measure the voltage on each terminal. The center terminal will be 13.8-14.3 volts and each of the other terminal should read about 0.2 volts less than the center alternator terminal. THe DUVAC or remote sensing wire is usually connected to the chassis battery side of the battery isolator.
If all that checks out then you need a new alternator internal regulator.

MSGulfCoast · 04-26-2016, 11:38 AM

Good point about the rebuild but this one has been on a couple of years now. I'm just worried there might be something downline from the alternator which is really the problem and might fry the "new" one.

I've actually got 4 wires connected to my alternator: B+, I, S & something else which I am not sure about! The first three I understand what they are and what they do. The fourth is connected to one of the 3 bolts in the diode bank (don't know what you call that part). I have a picture at home I can post so maybe somebody could educate me on that 4th wire.

Funny thing is that every time something happens I get a little more educated about the MH systems through good folks on here and internet sleuthing. Still have A LOT to learn though.

Thanks.

Quote:

Originally Posted by twinboat

Putting on the original may cure your problem.

Most rebuilders don't know what a DUVAC alternator is and may have done something wrong when rebuilding it.

Even if you go with a Delco, you need the external sense for the regulator.

Your MH uses a diode based regulator. The diodes only let power flow away from the alternator. With that, there is no feedback voltage to the alternators internal regulator.

The remote sense wire from your chassis battery supplies that feedback. Make sure it has power at all times.

Newer MHs use mechanical controls to combine the battery banks and the alternator output wire has battery voltage on it..

There is a lot of info about DUVAC regulators on line. Google will lead you there.

twinboat · 04-26-2016, 11:46 AM

Have you looked for a smaller wire on the diode isolator "chassis battery" post. That should go back to the alt.
Some isolators have a smaller, 4th post, for the alt sense.

Otherwise, have you had any battery cables off ? Could one have been left off or put on the wrong post ?

Always look where the last guy worked.

DtBt · 04-26-2016, 04:33 PM

The fourth wire, often gray, connected to one of the alt diodes is the "ALT Fail" connection. The diodes form a 3 phase rectifier bridge of the ac voltage produced by the stator as the rotor revolves. The tap on the ac is connected to the coil of a 6v ac bosch type relay. If the ac is present the " ALT Fail" light on dash is turned off by the 6v relay being energized.

MSGulfCoast · 04-26-2016, 04:34 PM

Here are my alternator connections. The second one from the right has me stumped. I just put it back on the way it was when I put this one on a couple of years ago.

DMTTRANSPORT · 04-26-2016, 04:43 PM

Alt over charging...replace it, most likely an internal reg.

MSGulfCoast · 04-26-2016, 05:08 PM

Wow you must have posted while I was trying to put up the pic. Thanks for that info. Definitely more complicated than I ever imagined. Does it matter which "lug" it is attached to?

Quote:

Originally Posted by DtBt

The fourth wire, often gray, connected to one of the alt diodes is the "ALT Fail" connection. The diodes form a 3 phase rectifier bridge of the ac voltage produced by the stator as the rotor revolves. The tap on the ac is connected to the coil of a 6v ac bosch type relay. If the ac is present the " ALT Fail" light on dash is turned off by the 6v relay being energized.