Alternator failure…Nov. 2006

Many times over the last 2 years I’ve tested the voltage across the batteries with the engine running. It’s always measured 13.8 Volts. This is fine and indicated a correctly functioning alternator. But on the recent trip between Fort Stockton, Texas, and Hondo Texas, the voltage meter on the dash rose to a very high value. Still indicating ‘OK’ but higher then normal. After an hour of that, it suddenly plunged to ‘discharging’ on the meter. Hmmm. I kind of expected the alternator to fail sooner so I just assumed it was bad and did what I could to conserve battery energy while I continued on to Hondo, a mere 3 hours distant. Firstly, I turned off the stereo radio, it’s large speakers draw a lot of power while playing, secondly the headlights, no need for them in the daytime. I have nothing else to turn off. And the meter, although it’s now higher then when I started, is still in the discharge zone. The diesel engine doesn’t use any electricity while running so the power draw must be the control circuits for the refer and the LP and CO alarms and some other 12V parasitic draws like the radio clock and such. Not a big deal but I didn’t want the battery (starting battery – a single ‘Deep Cycle’ 12Volt) to be discharged to deeply since that can ruin it.

So I stopped the rig, kept it running, and jumped my little trickle chargers 12 Volt lamp load out of circuit so the ‘House’ batteries (two deep cycle 6 Volt wired in series) would trickle current into the starting battery. Of course this would eventually exhaust the house batteries and if they were too deeply discharged could be ruined too.

I make it to Hondo Texas OK and hook to 120 Vac which charges the 6 Volt batteries, and the starting battery too (with my trickle charger installed-not standard equipment in many RV’s).

The next day I move to a RV park closer to town, also closer to the towns services, and start calling around for tech help. I could do the job myself but don’t really want to. After calling a local shop, which doesn’t do that kind of RV work, I get a tech’s number but he had been burned on a Class A RV job recently so he doesn’t even show up like he said he would. He didn’t share details so I suspect he was the problem, not the RV’er. Well, Hondo is kind of small, so I leave the next day for McAllen, Texas. A much larger city with lots of service support if I get in trouble changing it myself. I limp down there with my genset running the whole time to use the converter to charge the batteries. Takes around 6 hours to get to McAllen.

I get lucky that afternoon and find a nice RV park that has room for our small, informal caravan with all the services nearby or at the spaces. Once hooked up, I get to work trying to find out what type and size of alternator I need. Read the books and then call Freightliner. They tell me the style, 21SI, and the output, 100 amp. So I call around to auto parts stores and find a Delco alternator, get to work and 6 hours later, I have the old alternator out. Not fun, not fun at all. It’s all dirty under there and I wipe grime out of my ears for a couple days while I rest and watch the weekends football games.

Old alternator, it’s really grimy too:


Saturday, I get a ride downtown and buy a rebuilt 100 Amp alternator. Costs $142. Plus $10 for the shop guy to take my old pulley off and place on the new one. Just easier for me. Run back to the rig and drop it in place, climb under the rig and don’t notice that I’ve got it wedged in wrong so it’s bending the bracket. Well, one thing leads to another and soon I’ve bent the shaft on the dang thing so it won’t turn.

Monday we return it and I buy another one. They’re out of the 100 Amp units so I get a 135 Amp. Costs another $143. With a promise from the desk that they will submit my warranty claim…I don’t expect much from that but I’ve already saved over $100 in labor costs…so now I’m committed to finishing the job myself. If I get a refund, great, if not, I’m not that unhappy, I’ll just pretend I had to buy it from Cummins or Freightliner. By the way, I called and Freightliner wants $470 just for the alternator. Labor would have been $90 an hour if I’d had them replace it.

We also run around trying to find a new connector that supplies the field voltage to the alternator, mine is all corroded and stuff, and they’re suppose to be available ‘everywhere’. NOT. We found it at one auto parts store out of the five we went to.

On Tuesday morning, armed with the new alternator, the new connector and the knowledge I didn’t have on Saturday, I rewire the new connector, clean all the other connectors, and slide the new alternator in place, making sure I don’t bend the bracket again. It takes a bunch of reefing and hammering on stuff but I get it installed and wired up.

The engine starts right up and I see the voltmeter jump up into the green, means the alternator is wired correctly and operating. Whew. So I go out and get everything picked up, do some strapping of cables and such and finally finish. Just in time to go take a shower before the women in our group arrive.

Here’s a shot of the engine compartment and the hole where the alternator goes:


Now with the new alternator installed:


And another view:


Some thoughts on replacing the alternator:

1) Don’t ever use a floor jack to push up on the pulley, see what’s blocking it, if anything, I stupidly did that and it cost me a new alternator;
2) I tried to loosen the belt idler adjusting component but it seems to be siezed up, I didn’t want to break it so I had to install the alternator onto the belt using as much care as possible and by wedging the alternator in the right place against belt tension then hammering in the bolt. Then the lower bolt required more wedging with a crow bar. By dropping the alternator in wrong the first time, it wedged in against the lower bracket wrong, so I bent it, and consequently, bent the alternator shaft;
3) It’s filthy under there and if I had to do it over, I’d spray wash the engine, bottom and top first;
4) I checked the belt before reinstalling the alternator to be sure it was still good, plus I have a spare belt;
5) Changing the small connector carrying the field voltage to the alternator is a good idea if your unit is older, they get a lot of crud on them and corrode easily. I cut the old wires back 3-4″ to avoid any old corrosion that may have creeped up the wires and reattached new wires with terminals for the new connector;
6) After starting the engine and checking the voltage meter, go back and check the alternator to be sure the belt is running true.

Good luck! Don’t be a dummy like me!


Flakey behavior – 2008

I had replaced the alternator a couple years ago, and then when I’d had the bearing go bad, I let the tech convince me that I needed another new one because of a squealing belt, (I didn’t, it was a bad chassis battery), but now, occasionally, I’d get a flakey behavior that was observable on the dash gauge. I could see the needle jumping up and down occasionally. Sometimes dropping to ‘Discharge’ and staying there for a minute or two. Especially after starting. It would smooth out eventually, but it was worrying none-the-less.

There’s several things that could cause an indeterminate charging issue, a bad alternator of course, bad belt, bad battery, bad wiring. Over the months, I’d occasionally check each of those things or eliminate them as a possibility based on symptoms. I did have a weak starting (chassis) battery but I wasn’t willing to replace it at this time so I limped along with it. It wasn’t shorted or anything, just weak and wouldn’t hold a charge very well and was hard to recharge after starting. My workaround was to hold in the AUX start switch to parallel the house batteries. Then I’d hold it in while driving along or while letting the engine warm up until the auto sensing circuit saw that the house batteries were fully charged and switch over to the chassis battery.

But, there was an issue, so one time I stopped and settled in at an RV park I was determined to track it down. I was pretty sure that problem was with the Field voltage going to the alternator. Checking the chassis schematic I’d gotten from Freightliner as a PDF and printed out, I discovered this system has a blocking diode between the dash, and the alternator’s field terminal. This voltage is provided as sort of a fault tolerant system check of the dash electricals. It comes all the way from the chassis battery in the back of the rig, up to the dash, goes to the ignition switch, then works it’s way around under there and goes all the way back to the alternator Field terminal after passing through a blocking diode.

OK, where was that diode? I wanted to check it out. It took days of leisurely checking to find it, eventually, within 4 feet of the alternator. If I’d thought about it at the beginning, I’d have checked there first as that’s the most logical place to put it. Anyway, it was under the rig, soldered inline with the Field voltage wire going up to the top of the engine and connecting to the alternator ‘F’ terminal.

Found that the wire on either side of the diode was corroded 2-3 inches up along the copper, and that the diode, although still good, was really grungy with road grime. And the tubing it was in was all cracked due to heat aging. I replaced the diode with a new one, cleaned up the connections, cut out the corroded wire areas, added heat shrink tubing for protection, etc. Even rerouted the wire so it wouldn’t get all grimy anymore.

After all that, I’ve not had any evidence of that kind of flakey operation of the alternator since. So I think that took care of it.