The alternator from hell - if you can solve this there's a pint in it for you!!!!

Discussion in 'American RV's' started by paulmj, Mar 17, 2008.

  1. paulmj

    paulmj Deleted User

    Hello all.

    I've been wrestling with this alternator problem for ages. I've been looking for advice on, ahem, another site and here is the gen:

    My initial post....

    "Hello all.

    I haven’t been active on here for a while as once more I have been off on a tour of nasty places courtesy of her Maj! And a great time I had too…….

    Now I’m back and the weather is improving it is time to get the RV out a gain. However, as always I’m after your learned advice.

    Just before it came off the road for winter (ie the last time I managed to use it properly before I disappeared off……) the alternator went. What a pain. I spoke to Duncan who did some digging and discovered that he would have to get one from the states at about £400 – 500 and it would take quite a long time to arrive. So I sent it off to an alternator rebuilder that I had used in the past and who always did an excellent job, to see if they could do something with it.

    They could. They replaced regulator and bench tested the alternator and all seemed good. When I first fitted it all seemed good too. But after an hour or so it was clear that it was over charging….. all they way up to 19v.

    So it went back and they discovered that the regulator was dead.

    Basically, the connections on the alternator are as follows:

    1. A big fat high current connection that goes from a connection on the main body of the alternator to the battery.
    2. On the regulator there are three connections:
    a. A direct connection to the battery that the regulator uses to sense the battery voltage.
    b. The link to the alternator warning light and then up to the battery.
    c. A tacho link that on this vehicle is linked to the last connection on the alternator….
    3. A single spade terminal on the main body of the alternator that is connected to the tacho output from the regulator – no one seems to know what this is for. But the connection is there and is good.

    And the failure mode was that the voltage sensing connection (2b) was shorted to the alternator body. Hence, when ever the alternator was plugged in it was linking the battery to earth. Luckily there was some resistance in this so all it did was flatten the battery after about 24 hours.

    So, after the alternator went back for a new regulator it came back and after fitting it I had the same problem. At this point I am suspecting a problem with the electrics on the vehicle. However, they were working fine before the alternator originally went. But there are only three main wires:

    The main battery feed which goes to the battery – OK.
    The regulator sensing wire, which goes to the battery – OK.
    The alternator warning light wire – OK, in that when you put the ignition on and short the wire to earth the light comes on and when the alternator is running it goes off.
    The tacho output remains connected to that other terminal on the alternator (disconnecting it makes no difference) and the alternator guys tell me it is irrelevant anyway.

    The alternator will be back again with a new regulator in the next couple of days having been bench tested for an hour and proven to be fully working. I expect that the problem will still be there.

    Can anyone see what I might be missing or what I am testing incorrectly? Is there a diode issue somewhere? Basically, why is the regulator being killed so quickly and not regulating, or is the fact that the battery is being over charged killing the regulator – if so what is causing the over charging/fooling of the regulator?

    Arrgh! Can any one please help? This is driving me mad!

    Many thanks in anticipation………


    Some extra info after a couple of questions.....

    "Perhaps I should have added the following two nuggets of info:

    1. This is still the same alternator that originally went boobs up, so the pulley size is the same as it's the same pulley. I should have made that clearer.
    2. This isn't the original alternator as fitted by Ford. Ford fit a standard 75A job to this engine, but HR upgrade it to a 110A job in their factory (thanks to Dunc for that info). It has had this alternator all of its life.

    From the above, I'm pretty sure that alternator should be able to handle any load applied from the vehicle. And in any case, the alternator can only supply up to the rating of the regulator, I thought?

    I will make sure I disconnect the leisure batteries before starting though (had thought of that but haven't yet tried). Both the leisure batteries and the vehicle battery are in good condition. Although I will run the generator for a few hours before start up to make sure they have a good level of charge in.

    I will also check the connections on the starter and the main engine earth, although I have checked continuity and all seems good - it starts fine too."

    There were some really useful comments and after acting on the advice, here is my latest situation......

    "Ok, here's the latest......

    Firstly, anyone got a pot of sleeping tablets handy??? I have now lost the will to live.....

    Right. Got the alternator back and refitted it after checking that the new regulator wasn't down to earth as the old ones had been on removal. All seemed ok. I then ran in a new engine to chassis earth and ran one from a bolt just below the alternator directly back to the battery. I also put in a second main charge cable from the stud on the alternator directly back to the battery. I also ran in a second wire from the battery through a fuse to the sensing connection on the alternator. So I now know that the earth for the engine and alternator are definitely good and that the connection from alternator to battery is good. I also know that the sensing connection on the regulator has a good connection to the battery and is sensing the correct voltage. I also cleaned up the actual battery connection clamps.

    On starting the engine all appeared good. Regulating at spot on 14.8 volts and steady as a rock. Gradual increase in revs and still steady as a rock. Left it for a while, still 14.8 volts. Hurrah, I though.... sorted! But no!

    If I blip the throttle quickly so that the revs rise suddenly the damn thing puts out 19 volts and the warning light comes on. When I release the throttle it drops back to 14.8 volts. If I open the throttle gently and allow the engine to get to quite high revs it stays at 14.8 volts. It seems to be the speed of engine revs increase that is now the problem. Speed the engine up quickly, even a little bit, and the alternator starts producing 19 volts. Speed it up slowly, to high revs, and it stays fine at 14.8 volts.

    I've even tried another battery. No change. All of this has been done with the leisure batteries out of the vehicle and the leisure circuit isolated.

    The new regulator HASN'T blown this time and hasn't gone down to earth.

    Any thoughts? I'm getting desperate! Please.....

    My thoughts are as follows.....

    I think that I did have a connection problem which is why I have been blowing new regulators (thanks for the suggestions, guys!). This seems new. The guys who have been rebuilding the alternator have told me that they aren't sure why the tacho output from the regulator has a connection back onto a pin on the alternator body. Connecting and disconnecting that link makes no difference to anything, by the way. So, is it possible that this alternator has a secondary regulator system which senses revs? Could that be why there is a feed back from the regulator into the alternator from the tacho connection? Could that secondary system be what is now knackared? Can anyone think of anything else? I think I need to bite the time/cost bullet and get a new alternator in from the states. The wiring and battery are definitely good.

    It is really odd, as it seems to be regulating correctly now until I blip the throttle quickly.

    Guys I'd be really grateful for any more ideas.

    In desperation,

    Paul M-J"

    So that is where I am.

    If anyone can help it would be most appreciated.

    In the mean time I'll be whipping it off again first thing in the morning to send photos etc to Linda from Stateside as I am assuming that the only way forward is a new alternator.........

    Any thoughts?

    Many thanks all!

  2. Geo

    Geo Trader - Funster

    Jul 29, 2007
    Likes Received:
    I would question from reading your post, if you really do have a problem at all??
    given the high reading only appears when the engine speed is rapidly increased, a phenomenon that wouldn't happen in normal use to the same degree, is it mearly a time lag in the voltage reg/stabilizer, as you say it returns to normal reading, I have seen stranger things operate normally but on such tests as you describe act weired, only to go on and perform within parameters
  3. NEV3

    NEV3 Read Only Funster

    Feb 11, 2008
    Likes Received:
    North East Wales
    The alternator from hell

    Hi Paul,
    my heart goes out to you. I had an almost identical problem on my Sun Voyager about 6-7 years back. I don't have the same technical knowhow that you appear to have so all my "repairs" were carried out at a local truck servicing garage.
    My van was giving me identical symptoms to yours and the garage sent the alternator off for refurb/replacement. Never was too sure which it was in the end. Anyway to cut a long story short.... two weeks later and about a thousand quid out of pocket, they admitted defeat and said they had no idea what was causing the problem. I took the van away almost in tears (of frustration) and took it away for the weekend. While away the symptoms disappeared and never returned. The garage told me it was most likely a bad earth return to the battery/alternator. Who knows?
    I sold it on to a dealer about two years later and bought a Holiday Rambler Vacationer. Hope I don't have the same problems again with this. It's coming up to about the same age (five years)

    I wish you luck

  4. American Dream

    American Dream Read Only Funster

    Aug 20, 2007
    Likes Received:
    I totally agree with what Geo has said here.If the increase to 19v is merely a "blip" when revving the engine quickly, it sounds like it's the response time of the regulator electronics. However, if the voltage does NOT stabilise at approx 14.5-14.8 volts then you do have a problem.

    You seem to have tackled and addressed all the issues that may cause charging problems.

    Personally I believe you don't have a problem now, but, If there's not one fitted, for my own peace of mind, I would fit a voltmeter (and Ammeter) on the Dashboard and keep an eye on it.

    Have you cleaned the battery terminals and earth lead.The battery would normally tend to "float" across the output when tne engine is running, tending to smooth out blips in voltage.

    What do the headlights do when this blip occurs.?Are they relatively steady in light output, or do they become much more intense?
    Last edited: Mar 18, 2008
  5. paulmj

    paulmj Deleted User

    Geo, AD,

    That's what I thought at first, so I took it for a short drive.

    Sadly, by blip I don't mean much of a blip. Opening the throttle at the normal rate you would when pulling out of a junction causes it to hit 19v - it then stays there until you let the engine go back to tick over - I should have mentioned that before, sorry! It doesn't always do it though, it comes and goes.

    As there are only 3 wires to the alternator (main charge feed, ignition light, sensing feed) and that odd short loop from the regulator back into the body and they all seem good it must be an alternator issue of some sort. I'm sure (God, it must be!) the wiring is good.

    Here's a photo of the acursed beast!

    I'm getting to the stage where shooting it with a high powered rifle would be most satisfying.....




    Attached Files:

  6. American Dream

    American Dream Read Only Funster

    Aug 20, 2007
    Likes Received:
    Have you got the manufacturer/model number of the alternator please?

    Can you scan the relevant wiring diagram from the workshop manual?
    Last edited: Mar 18, 2008
  7. paulmj

    paulmj Deleted User


    It's a Ford Motorcraft item. All the markings on it are as follows:

    On the front of one of the mounting lugs the figure "5" is cast.
    On the rear the usual Ford monica of "Motorcraft" is cast.
    On the rear, on what appears to be a shaft end cover the figures "P4" are printed along with something illegible.
    On the regulator "785/6" is moulded into the plastic as are the connection markers "A", "S" and "I".
    Printed on the regulator is "CARGO 136230"
    On the side of the regulator "your-F786H G23576" is also printed.

    I don't have a wiring diagram, but it is the usual type:

    1 x main high current feed which goes directly to the battery.
    1 x sensing feed which goes from the relevant connection on the regulator straight back to the battery positive.
    1 x wire which goes from the regulator to the warning light and up to the positive side of the battery (via a diode, I suppose).
    And..... the odd one which is a loop from the centre pin on the regulator (tacho output) straight back to another terminal on the alternator.
    It is body earthed.

    Does that spark off any thoughts?


  8. Lindy-C

    Lindy-C Deleted User

    Paul, we have just got the power back on if you'd like to send the pics through that you mentioned to James :Wink:
  9. paulmj

    paulmj Deleted User


    Sent them this morning.

    Just sent them again, to make sure.

    Many thanks.

  10. kands

    kands Read Only Funster

    Jul 20, 2007
    Likes Received:
    Hi Paul
    Firstly welcome aboard matey :thumb: I thought you had been ignoring my attempts to talk to you, but glad that you are back safely from those "nasty" places :thumb:
    Have you got a split charge relay on your bus? Is there a switch that connects the leisure batteries to the engine batteries for starting? If so is it working?
    Is it possible to connect the alternator to a seperate battery and just connect up the relevant wires, run the engine and test the voltages on the new battery terminals? This will eliminate all the wiring on the coach. Not to sure about this loop that you have, I think I would be inclined to disconnect it as it seems to be a tacho output and your problem seems to be speed (tacho) related????
    Good luck matey and please let us know the outcome of any tests.

  11. paulmj

    paulmj Deleted User

    Hello again Keith!

    Hope all is good. Nah, not ignoring you, just never at home. Just been 'busy' again since your post.

    Yeah, I have got a seperate split charger. I've tried every test I can think of and I've now basically rewired the alternator wiring on the bus to ensure that the wiring is good. Even using this new wiring and a different battery I get the same symptom.

    I've tried running with and without the short 'loop' on the alternator and it makes no difference to anything. On the basic principal that it must be there to do something.......... the alternator must be knackered. I think.



  12. ruffingitsmoothly

    ruffingitsmoothly Read Only Funster

    Jan 2, 2008
    Likes Received:
    West of Southampton edge
    Just a thought have you ever run the RV whilst still hooked up?

    I have heard that this will effect/knacker the alternator why I don't know?

    Regards pat
  13. Lindy-C

    Lindy-C Deleted User

    Paul, you have PM.
  14. paulmj

    paulmj Deleted User

    Hi all,

    Just got back from another overseas jaunt. Sooner or later I'll actually get round to using the RV this year....


    Did you get my e-mails ref bring it over for a look?


  15. Lindy-C

    Lindy-C Deleted User

    Sorry Paul, no I didn't.........which Email addy did you use?

    Reference coming over, probably best to give James a call first band have a chat - we are working at Newbury this weekend but anytime Tuesday onwards would work.
  16. paulmj

    paulmj Deleted User


    Really I was just thinking that the best bet would be for me to bring the RV over so that James can have a look at the vehicle with it on. That would also allow him to get eyes on the alternator itself if he agrees that is up the creek!

    The complicating factor is that the RV's MOT has expired, so the question is: are you an MOT garage? If not, do you have one nearby that we could book it into to a) keep things legal b) get it MOT'd which it needs in any case.

    Grateful for your thoughts and suggestions on a good time over then next few weeks - I'm fairly flexible.


  17. Lindy-C

    Lindy-C Deleted User

    Hi Paul

    We are not an MOT station nor do we work on RVs, with the Porsche/VW engineering shop and RV parts businesses there are simply not enough hours in a day (there's only two of us) which is why I suggested that you speak to James first to see whether of not he could fit you in between engine building and shows.

    As for an MOT station, we have always used a place in Honeybourne near Evesham. A fair old hike from your neck of the woods.
  18. itexuk

    itexuk Read Only Funster

    Apr 3, 2008
    Likes Received:
    Taunton Somerset
    This might help. about half way down
    split charge

    one warning, unless the regulator is made to protect against this.. if the new voltage sensing wire ever becomes detached from the battery positive terminal, the alternator will see no volts, and think the battery is totally dead, and pump out maximum current and voltage to try and compensate, this will of course boil the battery pretty quickly, and bugger up some of the more voltage sensitive items in your van, check this scenario out with the person who modifies the alternator for you, it may be the case that the regulator is intelligent enough to shut down output if the voltage detected is lower than a certain voltage, but most machine sensed alternators won't have a need for this feature as the internal link between the volt sense input on the regulator and the output terminal is unlikely to ever fail.. but it happens sometimes, i've seen a few burnt out iveco's in scrap yards where the fires started at the alternator area of the van, it was known that the voltage regulators on certain alternators could fail, and when they did maximum voltage and current gets sent up the wires to the battery, this melts the wire and starts a fire.. and usually the driver didn't have a fire extinguisher with him, or if he did it was one of those silly little 1 kilo jobbies that don't last long enough to surprises a high current electrical fire, so the van gets lost for the sake of a few pennies worth of silicone inside the alternator.
    Last edited: May 17, 2008
  19. shortcircuit

    shortcircuit Read Only Funster

    Sep 13, 2007
    Likes Received:
    You have no idea how much this post has helped me although on a slightly different subject.

    For a number of years now I have been rebuilding a kit car (Burlington, based on Spitfire). I have at last got it in a position for an MOT and was going to give it a quick blast on the road. Although it appeared to be running satisfactorily previously it started to misfire and eventually would not run. I traced this to a brand new coil having failed. I have a voltage meter fitted and did note the voltage was a bit high at nearly 15volts. As it was an old instrument I unfortunately discounted the reading.

    The Triumph engine is fitted with a Lucas alternator with two heavy red outputs which go directly to battery +ve. The 3rd connection is blue and I had left dangling. From your description that is my problem and I will need to connect to the battery. I may have confused the matter by using a wiring loom out of and old Seirra. I have not obtained a new coil as yet and will measure the output with the blue wire connected.

    Should I have a ballast resistor fitted to the coil?

    Sorry to have highjacked this post as I have been searching the web and this really came through as somebody that new what they are talking about.
  20. pappajohn

    pappajohn Funster Life Member

    Aug 26, 2007
    Likes Received:
    YO11 2BD

    have a look <<here>>. ok its for a ford but they all do the same thing...


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