Batteries draining while driving

[ardbark]

Originally Posted by dennis45

As I mentioned in another dead battery post, you have a serpentine belt with a tensioner. If the belt is loose or broke, the first thing you will see is high engine temperature. Concentrate on diagnosing the alternator. When you replace the alternator, install a new belt and you're good for another 50K

So if I was a fuse for the Exciter Terminal what would I call myself so nice people could find me inside the fuse box?

[Monacoach]

As a general practice it is bad to leave dead house batteries for the alternator to replenish. Better to boost the generator and run it before starting the engine.

[ardbark]

Originally Posted by dennis45

As I mentioned in another dead battery post, you have a serpentine belt with a tensioner. If the belt is loose or broke, the first thing you will see is high engine temperature. Concentrate on diagnosing the alternator. When you replace the alternator, install a new belt and you're good for another 50K

disconnect from shore and measured battery array at 12.7v and each individual battery at 6.4v-ish. Turned on house lights etc, drug the batteries down to 12.34v. Fired up the engine and let it sit on fast idle for a few minutes and measured while running - about 12.3 volts (and dropping).

Alternator doesn't seem to be talking to the batteries. Looked for fuse that might have anything to do with the Exciter terminal but couldn't find anything labeled remotely close. Also can't find terminal on alternator, must be hidden on other side.

I guess its off to repairland tomorrow. It was a good couple of months

[mel s]

Originally Posted by ardbark

CAT 330 and yes, the alt is driven by a serpentine. Funny, a slipping belt was the very first thing that came to my mind and at times I have thought I've heard some "chirping" back there. But a fellow camper who had the same rig as mine mentioned that our tension pulleys are spring loaded and self adjusting. I have no idea if he is right or not.
Actually, the alternator on this rig is not bad to get to, it's right behind the air filter. I just grabbed the belt and have about 2" of play (1" either direction) between the alt and the component below it (which I can't see), which is a span of no more than 12" between the pullies. That seems a bit loose to me but having never played with one of these belts I can't be sure.
Bad belt certainly fits the bill though, and this coach did sit for quite a few years before I bought it last summer - 27k miles on an '03.
Recommended belt deflection between two pullies no more than 12" apart?

ardbark
I don't know the "feel" of a loose belt.

However, I do know that when I had a similar charging problem, (in '05, at 76,000 miles), my spring loaded belt tensioner had failed...(the bearing in the tensioner pulley went BAD and the spring was WEAK).
A new tensioner, (Cat P/N 1352151), AND a new belt fixed my alternator charging problem.

Mel
'96 Safari 250 hp Cat, 138k miles

[Johndale]

Before I would remove anything do a load test on the batteries because one may have a bad strap inside of it. Goto any auto parts place they have them and will check them for free.


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[ecurb74]

I had similar problem. After having the alternator rebuilt I still had no voltage. By chance I happened across a resetting circuit breaker for the sensing (exciter) wire that was hot only on one side. $3.99 part from auto parts store and I had 14 volts. It was mounted on the bulkhead next to the battery isolator.

[tiredvet]

If you have a ground fuse on your coach I would check it.I cured my non-charging issue by replacing this fuse at a cost of $8.95.

[Gary RVRoamer]

Be aware that you can have proper voltage from the alternator but still almost no amps, so that the battery discharges from normal loads even though the voltage looks good. That is a symptom of a failed diode in the alternator.

Are you making voltage checks at house batteries or chassis batteries? Or both? In your Discovery, the BCC (Battery Control Center) generally won't apply alternator charging to the house batteries until the chassis batteries reach about 13.3v.

[mel s]

Originally Posted by ecurb74

I had similar problem. After having the alternator rebuilt I still had no voltage. By chance I happened across a resetting circuit breaker for the sensing (exciter) wire that was hot only on one side. $3.99 part from auto parts store and I had 14 volts. It was mounted on the bulkhead next to the battery isolator.

ecurb74
Was that bad resetting circuit breaker in the "sense wire" or the "excite wire" for the alternator?
What was the amp rating of that breaker?
Wondering.
Mel
'96 Safari

[ecurb74]

Originally Posted by mel s

ecurb74
Was that bad resetting circuit breaker in the "sense wire" or the "excite wire" for the alternator?
What was the amp rating of that breaker?
Wondering.
Mel
'96 Safari

Mel,

My coach isn't here right now but I believe it was a 15 amp. I broke out the schematics and it appears that it was the voltage sensing wire, not the exciter wire from the alternator. The sensing wire is one of the two smaller wires coming off the alternator. Edit (Just went out and looked at my spare and it is a 15amp)

My coach has been rewired due to 4 large solar panels and to charge both banks of batteries from the inverter/charger so I'm not real sure on the schematics. If someone else is up to speed on this please correct me, I wish I was more knowledgable on the electrical system.

Ardbark,
I would check with an alternator shop that rebuilds alternators instead of Wally World. Mine did the same thing, I was driving off the batteries and the alternator wasn't recharging the batteries but when I plugged in it would charge them and run fine for a while until the batteries got low, I had three cranking batteries so it took a while to run down. My voltage gauge in the dash would read what my batteries were at so when I started I was at 12 plus volts and it would gradually decrease.

[ardbark]

Tuesday update
We took the coach to RV Renovators in Phoenix yesterday afternoon. Thanks to everyone who have offered tips and advice but between my limited ability to work under the basement doors (getting old sucks), limited tools and even more limited knowledge of where all these suspect relays/CBs/fuses/etc are physically located so I could check them, we decided this is a job for the pros.

I only hope now that if the whole thing ends up being just a faulty relay or $2 fuse or whatever, they tell me. I hate being cynical but honesty is not as easy to find as it once was.

Anywho, I'll let you know what it ends up being, might help someone else who runs into a similar situation.

[ardbark]

turned out to be combination of a bad alternator and a hung EMS/BCC. One new alternator, a hard reset on the controller and 4 days in the shop and we are good to go.

Thanks for all the suggestions, tips, etc. We're back on the road and I learned a few things along the way. That's all you can ask for.