Saturday, April 19, 2014

RV Alternator troubleshoot/replacement

NOTE:  Reposting this.  After posted first time accidentally deleted it.  Was able to go back in history to find, PHEW!

About a month ago, sometime after I left Yuma, AZ on my way to Pecos, TX, noticed that the voltage needle was fully pegged to the right side instead of staying steady'ish in the middle..  Knew this wasn't good so I immediately turned on everything I could, just to draw more power to reduce the voltage.  Pulled into the first place I could find (a Love's truck stop), and looked at the battery.  It boiled over.  They were able to test voltage and the younger person there said the battery was bad..  I was like, yup, kinda new that..  He also measured the alternator voltage, and while don't know the readings, he said it was "charging fine", even though volt meter on the dash showed it over charging.

So, went off to find a Walmart and replace the battery, this was a fairly easy process and didn't upload a picture of that.  They had almost the same battery, a 12 Volt RV/Marine Deep Cycle battery.  Almost even the same CCA (Cold Cranking Amps).

After a new battery it still didn't fix the issue, so spent night in the general area and continue trip to Pecos, then to San Marcos, Austin, and back to San Marcos, TX.  In the meantime fried another battery and just replaced it.

Troubleshooting alternator:

There's a remote sense terminal on the alternator.  What this does is make sure that there's about fourteen (14) volts sent to the battery, so the auto sense wire goes to the battery to measure the voltage.  Am assuming this allows the voltage regulator to adjust voltage appropriately.  This document describes process of testing, and bypassing, this function.

What I did was take off the wire, check it's serviceability, cleaned it little with WD-40 (not that that cleans things, but what had on hand), and put the wire back on.

Ground wire on left, power on bottom
Another step, which was the first one I did, was to check all the wires.  As can be seen here, the ground wires is on the left hand side (in back of alternator), while the power wire can barely see at the bottom right.  Can see the power wires (actually two of them) better in above photo.  There was a plastic shroud around them (help to prevent shorting?) that didn't "survive" the transplant.

I also asked around at the forum.  There's a thread there where all sorts of great people came together to help me answer my question.

Another person came up with this alternator diagram that shows all the parts which make up the alternator.  If the voltage regulator was bad (and think it was in the beginning), looks like it would've been fairly easy to replace that one piece.

Since I ran the alternator so long in it's overcharging state, truly think that this caused the whole alternator to go bad.  As can be seen in the thread, the alternator stopped charging totally and was warm to the touch (with engine off all day).  So pretty sure that there is a short in there someplace.

Testing "spare" alternator

When I bought the RV it came with a bunch of spare parts, and one of those was a spare alternator.  When first noticed it I looked at it and said "really"...  turns out it was there for a reason..  Now I hope don't need all the other spare things.

The testing piece was interesting too.  Brought it to the local AutoZone, and to their credit, they went above and beyond to get this tested.  Took them about an hour to do, in between other things, but they never gave up!

The main problem they had in testing is their testing rig is from a different manufacturer, and so requires the manufacturers part number.  Things is, for this alternator, the manufacturer didn't have anything comparable.

After quite some time they found something that worked, though the amp rating was lower (100 amps instead of 160), but they got it to work.

Turns out the alternator is perfectly fine.  Spoke with someone from the forum (owns a repair shop) and he said that sometimes alternators that have sat around for awhile are flaky and might work for a week, month, year, or a lifetime, and there is no rhyme or reason to how long they last, and he wasn't sure why.  So for now am living in the lap of luxury!

Test results:

Lamp/Diode Trio PASSED
Regulator Test PASSED
Rectifier Test PASSED
Rated Amps: 100

Date: 4/15/2014
Time: 12:55:02

Battery volts 14.20 14.44 16.00
Ripple volts 0.00 0.40 2.00
Lamp On volts 0.00 1.97 9.00
Lamp Off volts 11.00 14.52 0.00
Rated Amps: 100

Unsure what the three sets of numbers mean, but this is what it was rated at.  Looks OK to me.

Replacement of Alternator

Engine, under bed

This part was a little easier than I thought.  Went to a Vocational - Technical high school, which allowed us to learn a trade for half of the school year, and took normal high school classes the other half (in three week blocks).  As a freshman, we went through one week of each of the nine different shops, and one of them was Diesel shop.  Forget what we actually did, but we worked on engines, got greasy and smelly, and it was actually somewhat fun.

"front" of the engine
Watched couple video's on youtube prior to doing this, all for the same diesel engine, but not in an RV.  According to the videos it is a fairly easy and simple process.  The hard part here (initially) is that, as can see in the photo's, there isn't a lot of room to see where the belt goes.

In this picture can see the actual part which was rumored to exist but couldn't really see it.  Turns out was in front of me the whole time without me realizing it (story of my life there).  It is the tensioner for the serpentine belt.  As the engine is running this applies pressure on the belt to prevent it from falling off, while still allowing "play" and room for normal loosening through wear and tear.

If look closely at what I call the tensioner can see there's a square "hole" in there.  This is where something like a breaker bar goes, to lift it up and out of the way.  According to the youtube video I watched, believe he said it was 1/2 inch.  Turns out that in this instance it was 3/8 inch, so used my ratchet (better to use a breaker bar or something without fine gears).  It worked fine, though was a little rough as couldn't really brace it all that much while removing belt from the alternator (another pair of hands would've been great).  Just push the ratchet (or breaker bar), it will move the whole thing just enough to remove tension on the belt, then slide belt off of alternator.  I found it best to not move it too far off the alternator, basically slide it off and down a little.  This is to help avoid having to reroute the whole belt through all the wheels...  That would've been not so fun.

Removing wires
This is VERY IMPORTANT...  Prior to removing alternator wires, fully disconnect the battery which starts the engine.  Bad things happen when there's power in the line.

Here can see where I start to remove the wires.  Hard part here was getting a wrench down there to loosen the bolts, especially for the ground wire.  Can see, at top of the picture, the ground wire is removed.  Also, mostly removed is the two "live" wires, the ones which carry the "juice".  Not sure why there's two, but there is.

Of course, the next part is to actually remove the alternator.  At this point, have done the following:  Removed serpentine belt, removed the two wires at bottom of the alternator, removed the ground wire, and removed the power wire.
Top mounting bolt

Removing alternator is a fairly simple process.  With this one, there are two nuts and bolts to remove.  A long one on the top, as seen here, and then a smaller one at the bottom, which is just out of the picture.  On the top it's a longer one to presumably help with stress of the serpentine belt (only a guess).

Alternator at the bottom
Next step is to get the beast out of there.  Didn't have enough room to pull it up into the RV itself, so decided to drop it down.  Worked out better than expected, but can't tell that from this picture.  Had to work a little to wrangle it around and out the bottom.  Went closer to the radiator and twisted it around until it slid down and out.

It's out, and made in USA!!!
After it was out, fairly simple process to lift the new one up and into place.  After had it up there, put the bottom bolt in place (to hold it in, and tightened a little with ratchet, just so wouldn't fall out.  Doing this backfired on me a little.

Couldn't get it on
After crawled out from underneath, went back to the top of the engine and tried wrangling around the alternator.  Just couldn't get it on, as seen in this picture.  Had to go back underneath, loosen the bolt a little (wasn't tight to begin with), and that gave me some slack to move it around from the top.

Almost there....
After doing that it slid into place almost effortleslly, until another issue came up.  While looked like was in the proper place, the long bolt wouldn't slide in.  Was able to find out (thanks to phone) the reason for this.  While looked like it was close enough to allow, it wasn't close enough.  Can see in the picture that it's slightly off center.

To correct this tried using breaker bars, wrenches, etc, and none of them seemed to work.  Would always lift it up a little, not enough, and then go back down.  Suddenly had a spark of consciousness..  Used an allen wrench that I had, a bigger one, that slid into the hole and was able to move it around enough to allow the bolt to slide in.  This picture, only for illustrative purposes, shows the allen wrench on one side, bolt on the other.

Bolt on left, allen wrench on right
Got one side of the bolt in, then while it was there, used allen wrench on other side to make the bolt go all the way through.

It was then a simple matter matter of tightening up the bolts, lifting up the tensioner and sliding the belt on (make sure it's FULLY seated, another important thing).  Double check everything again and then fire up the engine.

Engine running, have only done for a minute so far.  The voltage meter showed right around 13.5 - 14.0 volts, which is right where it should be.  Revved engine a little and no problems.  Will be updating this as appropriate.

Alternatives to fixing

While this would have to be fixed for the long run, the owner of repair shop mentioned something and thought worth noting here, as never know if it'll help someone.

RV's have two sets of batteries, a pair for the house to provide electricity to lights, fans, refrigerator, etc., and one for the starter engine.  These are typically seperated and the house (lights, fans) battery is not charged when engine is running.  The reverse is also true in that if plugged into the power grid (120V), the engine batteries are not charged.

So, what could have done, is started the generator.  This would have the effect of charging the house batteries (as well as providing 120V power).  Since the house batteries are charging, could run a wire (jumper wires in a pinch) between the house batteries and the engine batteries.  This would keep the engine battery charged.

Couple caveats can think of is that this would use more fuel (engine and generator).  It could also wear down the house batteries a little (in terms of longevity) as they're meant to draw down slow.  If have headlights on this would tend to draw battery down faster.

However, it would get me down the road with minimum of fuss.  The repair shop owner said someone went 500+ miles like this, just enough to get where he was going before getting it properly fixed.

If I was to do this with my overcharging problem, think it would have been best if removed the positive battery from the alternator, and wrapping the end in electrical tape, then hooking up the jumper cables to the two batteries and go down the road.

This would only be a last ditch effort and not something want to do as a common practice.


  1. That's quite an impressive account on how to fix and replace alternators. Many people would rather leave it to the pros, but it never hurts to know how these things work, so you'd know what to buy in case something breaks down. If someone doesn't know what part is in need of repairs, they might waste their money by buying the wrong or unnecessary parts. Thanks for sharing!

    Kathryn Weber @ Global Parts, Inc

  2. Is it common that only one battery will die at a time? We’ve just purchased an RV and I am hoping to be prepared as possible for situations like these. Also, would you suggest having a spare alternator on hand? Thank you for sharing your experiences. Your recount is very informative and helpful. Thank you for sharing this.

  3. Put on new alternator, checked ground wires and still not charging enough on gage.