mike30841 Posted November 27, 2015 Share Posted November 27, 2015 May I pick your collective brains re my Bedford OX? Whilst my son was driving last weekend, the ignition light came on and stayed on, and the ammeter sits steadfastly at zero. I tested the dynamo as per the manual, and got a reading fluctuating between 0-4 volts, manual says 15 point something. I therefore concluded that the dynamo was at fault, and ordered a reconditioned one from Chris Morter. Having fitted the new one today, the problem remains, except from the new dynamo I get a steady reading of 0.5 volts. The ignition light still stays on and the ammeter is rock-solid at zero. With auto-electrics not being my strong point, I am now baffled - it is distinctly possible that the replacement dynamo is faulty, but before I send it back, am I missing something? Could a different fault give the symptoms of a non-charging dynamo? Any ideas gratefully received. Mike Quote Link to comment Share on other sites More sharing options...
arcot1751 Posted November 27, 2015 Share Posted November 27, 2015 Regulator box ? Quote Link to comment Share on other sites More sharing options...
rampant rivet Posted November 27, 2015 Share Posted November 27, 2015 Polarity of generator / dynamo ??? Quote Link to comment Share on other sites More sharing options...
Tony B Posted November 27, 2015 Share Posted November 27, 2015 If you did polarise the Dynamo, one was it the right way, two , was the regulator box still connected? If the regulator box was on when polarised, you may have blown the box. http://www.dynamoregulatorconversions.com/polarising-a-dynamo.php But DO NOT connect regulator. If you don't polarise you won't get charge. Other obvoius one, is the belt tensioning correctly, check earth line. Quote Link to comment Share on other sites More sharing options...
mike30841 Posted November 28, 2015 Author Share Posted November 28, 2015 Thanks for your input, guys. To update - oops, had forgotten to polarise the dynamo (in my defence, I have only ever changed one dynamo, and that was around 30 years ago!). I have now done this, but it has not made a difference. Ignition light stays on with engine running at around 1000 - 1200 revs, ammeter sits on zero (it does show a discharge if I put the headlights on), and testing the dynamo output as per the manual, it still shows an output of around 0.5 - 0.6 volts. Strangely, so far the battery does not seem to be going flat. I have checked the dynamo earth with a continuity tester, and this seems ok. I am still tempted to think that the replacement dynamo is faulty, but obviously there are other possibilities. I can't get in to the regulator to inspect visually, as the vacuum tank for the wipers is in the way and it's now raining, so I have given up for now. Does anyone know how to test the regulator, by the way, as the manual seems rather reticent on this point? As far as I know, however, it I extremely unusual for a regulator to develop a fault. I would welcome your thoughts. Mike Quote Link to comment Share on other sites More sharing options...
arcot1751 Posted November 28, 2015 Share Posted November 28, 2015 If you test the voltage at the battery ignition off, then start the truck at test again at fast idle is there any difference in voltage + - ? Increase revs does ANYTHING happen to readings ? Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted November 28, 2015 Share Posted November 28, 2015 As far as I know, however, it I extremely unusual for a regulator to develop a fault. I would welcome your thoughts. Mike Hi Mike, These CAV regulators can give problems, related to age and its construction. I have even had nos ones give problems. The electrician who did my work found a way of substituting a more modern Lucas regulator internal workings into the CAV box, and with it set up on his test rig with the dynamo, performed perfectly. Had quite a number of them done successfully. regards, Richard Quote Link to comment Share on other sites More sharing options...
Tony B Posted November 28, 2015 Share Posted November 28, 2015 Don't rely on a tester for the earth, take it off clean well and use toothed washers to rescure. I've had many problems over the years , that all came down to a simple clean, even where to examin and check the earth looked good. Quote Link to comment Share on other sites More sharing options...
thedawnpatrol Posted November 28, 2015 Share Posted November 28, 2015 First thing I would check is the fuse in the regulator box, you say you can't get to it ? That's your first job, if the fuse wire is ok, pull out the fuse and clean the contacts, had a similar problem with my MW, just needed the contacts cleaned. Regards Jules Thanks for your input, guys. To update - oops, had forgotten to polarise the dynamo (in my defence, I have only ever changed one dynamo, and that was around 30 years ago!). I have now done this, but it has not made a difference. Ignition light stays on with engine running at around 1000 - 1200 revs, ammeter sits on zero (it does show a discharge if I put the headlights on), and testing the dynamo output as per the manual, it still shows an output of around 0.5 - 0.6 volts. Strangely, so far the battery does not seem to be going flat. I have checked the dynamo earth with a continuity tester, and this seems ok. I am still tempted to think that the replacement dynamo is faulty, but obviously there are other possibilities. I can't get in to the regulator to inspect visually, as the vacuum tank for the wipers is in the way and it's now raining, so I have given up for now. Does anyone know how to test the regulator, by the way, as the manual seems rather reticent on this point? As far as I know, however, it I extremely unusual for a regulator to develop a fault. I would welcome your thoughts. Mike Quote Link to comment Share on other sites More sharing options...
mike30841 Posted December 16, 2015 Author Share Posted December 16, 2015 Still no further forward with this, mainly due to lousy weather. Have polarised dynamo as per instructions, but still only getting around 0.5 volts output at dynamo terminals, with or without dynamo fuse in place. I am beginning to suspect that the dynamo still isn't correctly polarised. I note that the instructions in the link are for a Lucas dynamo, and I wonder if the CAV unit fitted to the OX is wired differently? I cannot find instructions for polarising a CAV dynamo on the internet, and all three Bedford manuals I possess omit this procedure. Does anyone know the correct procedure? Do I simply try reversing the polarity to the earth and F terminals or is this likely to damage the dynamo? Any help would be appreciated. Mike. Quote Link to comment Share on other sites More sharing options...
MatchFuzee Posted December 16, 2015 Share Posted December 16, 2015 You may find these are useful reading. http://pub25.bravenet.com/forum/static/show.php?usernum=2099944454&frmid=5&msgid=980490&cmd=show There are a number of articles in the Electrical and Ignition section:- http://www.austin7.org/Technical%20Articles/#Electrical Quote Link to comment Share on other sites More sharing options...
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