Community Forums

DJJ · 10-29-2014, 08:10 AM

I think the alternator is going bad but want to make sure I am not missing something with the BIRD system.

Plugged into shore power and motor running 13.6v at alternator and helm.

Unplugged, motor running 12.7v at alt, 12.5v at helm.

Turn on head lights, motor running 12.6v at alt, 11.8v helm.

Using Scangage D for front voltage and volt meter on Alt for the other reading. So it seems to me the alternator is not putting out enough voltage.

I just replaced two 12v deep cycle bat's with four 6v Interstate golf cart bats for the coach. They are fully charged and have been in for a couple of weeks with RV on shore power. And, as I understand, the BIRD system is suppose to favor the chassis batteries if motor is running.

Is their something in the BIRD system I don't understand that would cause this? Just want to check before I pull the Leece Neville LN2824LC alternator.

Thanks

"007" · 10-29-2014, 12:00 PM

Do not pull anything looks to me everything is OK.
Your alternator may only output the voltage you are reading of it as is.
Since 2003 chassis makers have install larger output alternators so yours maybe all you will get out of it for charging voltage.
The Bird System favors the house batteries than will switch over to the chassis batteries when on shore power, when your driving system works in reverse and alternator will charge the chassis batteries than the house.

12v BATTERY SYSTEM----12V WIRING AND FUSES

Iron Man · 10-29-2014, 12:48 PM

Have alternator checked. 12.6 volts at the alternator means it is not charging. Checking the voltage at the alternator eliminates the BIRD system.

DJJ · 10-29-2014, 12:50 PM

Thanks. I was wondering if the voltage regulator dropped the output so as not to over charge the chassis battery.

Since we got home a couple of weeks from a 5 month trip I've done a lot of maintenance to the coach and decided to go fill the fuel tank and get everything warmed up and make sure all was good when I noticed the voltage gage was under 13v. It is usually at or above. I just unplugged from shore power so the batteries were fully charged. I started the generator while driving and there was no change. I think I have seen the gage less then 13v in the past.

If the alternator fails will the BIRD system let the generator charge the chassis batteries while driving ?

I always thought if you added an additional load like headlights and the voltage dropped, motor running, the alternator was the problem. One of the diodes has gone bad.

Jeff

GaryKD · 10-29-2014, 02:34 PM

Hi DJJ,
The generator will charge the chassis batteries while driving.

dennis45 · 10-30-2014, 09:05 AM

Just went through this issue.
If you are seeing 13.6V when on shore power or generator running, the BIRD relay is functioning. With the engine running and shore power unplugged, you should see output to the batteries of 14.2V. If you see less, chances are the alternator is not working.
Before you replace the alternator, check the Alt Fuse in the rear fuse block. You don't say which coach you have but on mine it is located in the passenger side electrical bay just ahead of the batteries.
This fuse is the one that supplies power to the alternator exciter. No power, no output. Photo shows the fuse block with the cover removed.
New alt will cost about $420. Some like to say a rebuild is cheaper and just as good but I beg to differ. A new one will take you another 10 years of trouble free while a rebuild maybe half that if you're lucky.

DJJ · 10-30-2014, 02:27 PM

Talked to the field rep from Leece Neville today he said if I have 12+v on the ignition terminal and on the duvac terminal with motor running the alternator should put out 14.1v, if not alternator is bad. One thing that screwed me up was I read some place the output post on the alternator should not have voltage with key off, with key on you will read battery voltage and once started read what the alternator is producing. Mine has voltage on the alternator with the key off. The rep agreed I should not have voltage with the key off and that I had a bad relay or diode block somewhere. But he still thought it was a bad alternator , and that was a different problem. Called Freightliner and they said it was normal to have voltage at alternator with key off and they also said the alternator was bad. Removed and took to NAPA to test, they did not know how to test one that had duvac. So, went ahead and ordered the same one through Amazon from a company called Rare electrical $333.75 delivered, brand new 1 year warranty. NAPA wanted over $600 for a new one but I think it was a different brand.

It's a good thing I have an impact wrench, that's the only way I could get the top bolt loose.

Thanks to all who gave input.

Jeff