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ardbark · 03-15-2015, 11:43 AM

Background: 2003 Discovery 39L, batteries new in April 2012

Everything was fine until one fateful night of boondocking at Wallyworld in Del Rio Texas in low 30's weather with the house heaters running. This is when that cold snap went through Texas a few weeks back. Next morning the batteries were low (duh) so went to fire the genny. No luck, not enough juice. Fine, got the engine started and headed out figuring the alternator would slowly charge things back up. Not 30 miles down the road the dash Battery light came on and both sets of batteries read in the low 10's on the panel. We've been fighting it ever since.

Soon as I hit shore power they charge right back to the mid 13's but now I can't drive more than 100 miles without the light coming on. I can actually watch the Volt meter on the dash slowly creep to the left and if I hit the throttle hard the needle will immediately drop even further. Doesn't matter if I have the Inverter on or off while driving.

Yes, I've checked the water level, it's fine, and I had a guy check the alternator (at the battery) and he said it's cranking out juice (although I don't if i trust him or not).

Any troubleshooting tips would be appreciated. If worse comes to worse does anyone know a real RV mechanic in the Phoenix area? I know there is a Camping World in here but... arghhhh... anywhere but there

oh no · 03-15-2015, 11:56 AM

Does your generator charge the system back?Battery cable clean an tight?

**TonyDi** · 03-15-2015, 01:02 PM

If you have a volt meter check to see what you are showing at the batteries. I'd recheck the alternator as well as all connections. Some one else may have another suggestion.
Good luck!

BoA36 · 03-15-2015, 01:09 PM

Dollars to donuts a connection issue. Be sure the cables are tight on batteries. Doesn't take much play in the clamps to make the alternator ineffective on the road. I know from experience.

frizzen · 03-15-2015, 01:12 PM

If the alternator was checked without taking it out of the vehicle you may have gotten a false reading. I've had that happen to me.

D Lindy · 03-15-2015, 01:17 PM

When you had the alternator checked, you weren't by chance still hooked to shore power were you? If so he was reading the voltage from the inverter/charger not the motors alternator.

dennis45 · 03-15-2015, 02:04 PM

Unplugged from shore power, check the battery voltage. Then start the engine and set to high idle at about 1000 RPM. Check battery voltage again after a couple minutes.
You should see about 14+ VDC at the batteries. If not, you have an alternator issue which could be anything from a blown fuse on the exciter circuit for the alternator, faulty BIRD (or whatever coach/chassis system you have), poor connection at the alternator or battery etc etc.
If you are limited in your capability in this area, I would search out a shop such as an RV shop that does chassis work or at least can recommend one for you. Also might look at a HD Truck shop that does not mind working on RV's

ardbark · 03-15-2015, 03:29 PM

Quote:

Originally Posted by BoA36

Dollars to donuts a connection issue. Be sure the cables are tight on batteries. Doesn't take much play in the clamps to make the alternator ineffective on the road. I know from experience.

I checked the cables and they all seem good, except for one ring lug which does "bend" kind of easy, easier than the others anyhow.

I'll check that one closer, it is one of the gang grounds, but doesn't it make sense that if it was a loose or corroded cable the batteries wouldn't take a charge from anywhere? As it is now they charge on shore but not the alternator.

I'll run the alt test as Dennis45 suggests here in a bit (after it cools down, it's 90 degrees on that side of the coach right now :-) and see what that tells us.

thanks much....

dennis45 · 03-15-2015, 03:55 PM

Quote:

Originally Posted by ardbark

I checked the cables and they all seem good, except for one ring lug which does "bend" kind of easy, easier than the others anyhow.

I'll check that one closer, it is one of the gang grounds, but doesn't it make sense that if it was a loose or corroded cable the batteries wouldn't take a charge from anywhere? As it is now they charge on shore but not the alternator.

I'll run the alt test as Dennis45 suggests here in a bit (after it cools down, it's 90 degrees on that side of the coach right now :-) and see what that tells us.

thanks much....

I suspect your alternator has gone south on you but if all the connections are good (no signs of corrosion or loose connections) and the voltage test does not show 14+ VDC, the next thing is to locate the Exciter Terminal on the alternator. The alternator does its thing based on how much voltage is fed to this terminal on the back of the alternator. The higher the voltage, the less the alternator puts out. That is, when the battery is charged to capacity, the alternator reduces its output. As the battery voltage drops, the alternator output increases.
On the back of the alternator, you will see two large terminals and one or two smaller ones. One of these is the exciter. You need to see voltage here with the ign on.
So, before you condemn the alternator, be sure it is getting voltage to this terminal. Exactly how much is not important as long as it's in the realm of 12 volts. The voltage is supplied when the ignition is on. No voltage, no charge. There will be a fuse somewhere for this circuit that could be blown.
If you have voltage to the exciter and the charge voltage at the batteries is under 14 VDC with the engine running, you need to go shopping for a new alternator.
Word of caution, if you are going to change the alternator yourself, it can be a challenge. These things ride in the worst of conditions and rusted/seized fasteners are the order of the day. Be sure you are prepared or find a good truck shop. My son and I changed mine in a campground. We are both mechanics and carry lots of tools and it turned out to be a @&$87(?!.
Good luck....

twinboat · 03-15-2015, 04:02 PM

Wow, a classic sign of loose belts is charging at idle and not when you increase the RPMs . Has anybody looked at your belts yet.

Most people don`t know what a properly adjusted belt, feels like.

The faster the alt. turns, the more it tries to put out, increasing the effort needed to turn it.

Good luck

Deny · 03-15-2015, 04:10 PM

Yes, I think belt slip is the issue.

If you can push the pulley around by pushing your thumb on the cooling fins (if it has them)
it is too loose.

mel s · 03-15-2015, 04:18 PM

Quote:

Originally Posted by twinboat

Wow, a classic sign of loose belts is charging at idle and not when you increase the RPMs . Has anybody looked at your belts yet.
Most people don`t know what a properly adjusted belt, feels like.
The faster the alt. turns, the more it tries to put out, increasing the effort needed to turn it.
Good luck

twinboat
Good point

.
BTW, if the alternator is "serpentine belt driven" a failing, a or bad, "belt tensioner" can allow the belt to slip at higher RPMs, (highway speed).
Mel
'96 Safari

ardbark · 03-15-2015, 05:37 PM

Quote:

Originally Posted by mel s

twinboat
Good point

.
BTW, if the alternator is "serpentine belt driven" a failing, a or bad, "belt tensioner" can allow the belt to slip at higher RPMs, (highway speed).
Mel
'96 Safari

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?

dennis45 · 03-15-2015, 05:51 PM

Quote:

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?

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