1999 Beaver Marquis Alternator burn out

[mgrovesjai]

I had the alternator in my 1999 Beaver Marquis rebuilt on April 1st 2014. Once installed along with 2 new chassis batteries the voltage reading at the batteries was 14.6V. No reading was taken at the alternator output. After approximately 4000 miles, at the beginning of June or so, while on a cross country trip, my Silverleaf system alerted me that the chassis batteries were no longer charging. While in Idaho Falls, ID, I again had the alternator rebuilt. This time the techs noticed that while the "bench" output was in spec at 14.2V for the Leece Neville alternator, once installed on the Marquis the output was about 15.6V with about 14.6 at the batteries. They figured that the prior rebuild had burned out due to the out of spec voltage coming from the alternator but didn't understand why the bench versus installed voltages were different. Since they were not familiar with the total charging system, they simply wired a patch which limited the alternator output to its spec of 14.2V. So, that the voltage at the chassis batteries was now 12.8 to 13.2 (approximately 1 volt less still than the alternator output). I thanked them for pointing out the issue, and said I would check with other coach owners to try to find out what is creating such a resistance in the circuit that the alternator decides to generate the nearly 15.6V output. My question to the forum audience is: If you have a similar coach, what is the voltage at the output terminals on your Leece Neville Alternator? If it too is in the 15.6 to 16V range then I would say we both have an identical problem, but if its 14.2V then I'd appreciate any insight on where I might look to discover a part that is obviously not working properly. Thanks, Mike

Moved to Tech Issues forum from DIY.

[MEXICOWANDERER]

The LN 79000 series voltage regulator has a voltage adjustment pot which is hidden until the regulator is removed from the plastic brush holder plate.

When you have the rectifier based BATTERY ISOLATOR removed. Save it. I need to disembowel it and can use the heat sink. I'll pay you for postage to Chula Vista CA. Contact me through private messages on the top of the page. Direct connection between alternator and battery positive and do not forget to check the "other" post on the back of the alternator. On the right side, is the + post which is 5/16" diameter. On the left is the - negative post 1/4" diameter. Make durned sure that negative wire is in excellent condition, and has clean and tight connections, especially where the - wire connected to the engine block or frame.

A 200 ampere rated BI-DIRECTIONAL

(Continued After An Internet Outage)

relay, would be ideal here. But wire the alternator directly to the HOUSE batteries and then connect the house battery bank to the engine starting battery with the Bi-Directional relay and appropriately sized wire. That way the relay endures perhaps 70 - 90 amperes of load most of the time. Not 130 amperes.

[Golden_HVAC]

I agree that you probably have a diode style battery isolator, and they are no good. If they open the circuit for even a couple of seconds, the alternator can spike in voltage to well above 25 volts and melt the diodes inside the expensive alternator.

By replacing the diode type isolator with a relay, you will have much more reliability, and will not disconnect from the chassis battery ever. The relay is energized while the engine is running, and disconnects from the chassis battery when the engine is off. The huge advantage is you can now install a dash switch, that once activated (usually a momitary switch that you hold down for a few seconds) you can activate it and while starting the engine be able to use both the engine and coach battery to start the engine.

In my motorhome, I used the radio +12 from under the dash to power my coach battery to chassis battery relay. So if I put the RV in ACC or start it, either one will energize the relay and charge the coach battery from the alternator, or if parked will allow the coach charger to charge the engine battery.

The relay is Grainger part #6C017

http://www.grainger.com/product/WHITE-RODGERS-DC-Power-Solenoid-6C017?s_pp=false

While rated at 100 amps, that is the forklift rating. So it is rated to go on and off with 100 amp loads 12 hours a day for 100,000 cycles. You can actually run about 125 amps through the relay for a short time or 100 amps for hours at a time.

You probably have #4 wire or #2 wire from the alternator to the old diode splitter. Your voltage is probably 15.6 at the alternator to this location, then drops by 1.2 volts across the diode, then will have a wire #2 or so to the engine battery and another #2 wire to the coach battery bank.

What needs to be done is connect the engine battery directly to the alternator (you can use the input terminal of your old diode if you like to mate the two wires together). Then run a wire from the alternator to the new relay, then to the battery bank with #2 wire rated at around 110 amps. The new relay will offer a voltage drop of only about 0.1 volts - so 14.2 volts from your alternator to the battery bank will reach it at 14.1 volts at upwards of 100 amps.

Fred.

[ScottG]

It sounds like it is going through a diode based isolater that has perhaps failed. Do you know if you have one of those?

If so then I would remove it from the circuit and replace it with a 100% duty cycle solenoid relay. It will last forever and there's no voltage drop across diodes.