Overvoltage. Replace Alternator?

[Jason Weinstein]

With the engine running, once it hits high idle speed, the voltage meter on the driver console shows 16volts. The Heart Interface with show 15.5v and sometimes go into fault due to the over voltage. I take it that the alternator regulator has gone bad or there is a problem with the alternator sensing the voltage of the chassis batteries. Is there anything else I should check? From reading through the boards, it sounds like the regulator is part of the alternator and therefore the alternator needs to be rebuilt or replaced. How difficult is it to remove the alternator myself? I've done so on a couple cars, but this big diesel engine, and the complex wiring of a motorhome, is new to me as of a few months ago.

And, as a possibly unrelated question, there is a white wire connected to the negative terminal of the chassis batteries. If this is not connected, the engine will not start, it will not even turn over. I find it odd that something needs to connect directly to the negative terminal versus the grounded chassis. What is this wire? Does it have something to do with the alternator sensing?

Thanks so much. This is my first post.

[Gerald Farris]

Jason,
You are right about the possible causes for the engine alternator producing excess voltage, and it should be corrected before driving the coach. Your alternator is easy to remove for service, but be sure that your sense wire is good and has good connections before removing the alternator for service. There are two 1/2 inch bolts (3/4 inch wrench) that hold the alternator on and four wires, two small wires and two large ones. The large ones are for alternator output and ground, and one of the small wires is for ignition power (hot with ignition on) and the other small one is the sense wire (hot at all times) that lets the voltage regulator know the output voltage at the chassis batteries. If there is 16 volts at the sense wire terminal with the engine running, you need a voltage regulator.

The sense wire goes to the positive battery terminal, and the alternator output wire (cable) goes to the battery isolator center terminal with the chassis battery positive cable on one of the end terminals and the house battery positive cable on the other end.

The alternator wiring described above pertains to the DUVAC charging systems that were used on all Beavers up to the very early Monaco built coaches, but not the latter Monaco built coaches that have a "BIRD" system.   

As for the wire on your negative battery terminal, it has nothing to do with the alternator. It is possibly a ground for the ECM or starter solenoid.

Gerald

[Bruce Sieloff]

As a safeguard I would check the connections on the battery isolator, mine is blue anodized, looks like a finned heat sink and was located in the battery compartment and has three terminals. You may have four. I had a loose connection at the isolator that gave me a high voltage issue intermittently and then constantly when the connection finally failed. I chased that connection all over the engine bay. In my case I replaced the isolator because of a failed teminal but the effect was the same. In any case it's an easy check for reassurance. Isolators are cheap, less than $100 if you need a new one.

[Jason Weinstein]

Thank you to both of your responses. I had a RV repair tech come by and he said the problem is that my house batteries have gone partially dry (oops...another new RV owner learning moment). He stated that I should replace all four. I'm trialing using a concentrated magnesium sulfate solution to see if that can help give me some more life from my batteries.

I'm going to check my isolator anyway.

[Mike Stuart]

I'm having a similar problem and the information on this post is helpful.  But my indications are different.

With the engine running, the silverleaf shows 12.6 volts on the Chassis batteries.  The gauge on the instrument panel reads the same.  The CMP monitor shows 16.6 volts on the house batteries and the inverter shuts down showing "Fault" and "Warning" indicators flashing.  Shutting down the engine returns the inverter to working and the house batteries to normal voltage indications.  Starting the engine up shows high voltage indications on the inverter then the inverter shuts down with the Fault and Warning indicators flashing.  Connecting shore power or generator power has no effect (obviously but I thought I would include this).  Adding more load to the chassis with lights, a/c, etc, decreases the alternator voltage also.  So it is apparent to me that the alternator is pumping maximum voltage out (to the house batteries).
Also, I have a Magnum Smart Battery Combiner and it will not connect with the engine running.  Disconnecting it from the system by pulling both fuses has no effect.  (Additionally, I have 6 deep cycle house batteries.)

My situation is different than the one mentioned in Jason's post because the silverleaf is showing 12.6v and the house are 16.6v.  In his situation the chassis and house were showing the same voltage.  Is this a voltage regulator issue or perhaps a bad house battery or batteries?

Thank you in advance...

[Gerald Farris]

Mike,
To answer your question, you are going to do a little troubleshooting. On your coach the alternator output is connected to the center terminal on the battery isolator, and the alternator gets its voltage reference thru a sense wire that is usually connected to the chassis batteries. So if the battery isolator failed and no longer lets the alternator charge the chassis batteries or if there is a bad connection between the chassis batteries and the alternator, you could get the symptoms that you described.

First, you need to check the continuity between the battery isolator and the alternator. Then check the sense wire voltage at the alternator voltage regulator. If the sense wire is reading chassis battery voltage check for continuity between the chassis batteries and the battery isolator. If everything checks OK, check the battery isolator.

If the above instructions confuse you, and you need a little help in troubleshooting the issue, just call me. 713-254-4156

Gerald         

[Mike Stuart]

I did the trouble shooting and discovered:
1.  The alternator has a good connection to the isolator
2.  The alternator is reading the chassis voltage
3.  All connections of batteries are good both chassis and house
4.  I then checked the isolator and sure enough it is only distributing power to the house batteries; not the chassis batteries.  So while the alternator is reading chassis battery voltage and the voltage is low, it is increasing voltage to try to charge the batteries but that is only going to the house batteries hence giving me the overvoltage on the house batteries.

So I'm off to locate a replacement isolator which should cure my problem.

Thanks to Gerald for the assistance.  I couldn't have done this without his help!

[john brunson]

It appears we are on the  same path.....  where did you source your new isolator??

thanks

john

[Bill Lampkin]

Here's a link to Leece Nevell website with good info on alternators. (for my 2005 Beaver Patriot) I took the part # from my build sheet and did a search [urlhttp://www.prestolite.com/pgs_products/specs.php?item_detail_id=821&item=LBP2180&product=ALTERNATOR][/url]

[Gerald Farris]

Bill,
The coaches that are being discussed in this thread all have a battery isolator that requires the use of a Duvac alternator with a sense wire to regulate the charging rate. Therefore, your coach's alternator will not fit any of them because your coach uses a "Bird" system instead of a battery isolator so the output terminal of the alternator has a direct contact to the chassis batteries at all times, and does not use a sense wire. The "Bird system allows the use of a very readily available standard HD truck alternator instead of the more uncommon, and usually a little more expensive Duvac design. 

Gerald

[Bill Lampkin]

Thanks Gerald. Good to know about earlier rigs using the isolator vs Bird.

Here 's a link on how to 'convert' a HD alt to 'Duvac'. I guess my post was to say that the Prestolite/Leece Neville site has tons of info on all there alternators, including Duvac. I was surprised at how much support info is available.

http://www.prestolite.com/pgs_support/duvac.php