Auto electrician, anyone here?
Submitted: Wednesday, Jul 12, 2006 at 00:53
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V8 Troopie
Had a curious problem with the alternator in my troopie. Its a Bosch 85A unit and it has been working fine since Brunswick installed it with the 6.2 V8 diesel.
Anyway, I noticed a faint high pitch whistle coming from somewhere under the bonnet. A bit like the whistle some older TV's make. Engine was switched off. I started disconnecting things to see where it comes from and found the alternator was the culprit.
The annoying bit is that the whistle also caused a 0.9A current draw from the battery.
So I took the alternator out and had a good look at it. Also unscrewed the brush/ regulator holder and checked it for shorts with the multimeter - nothing obvious.
One of the brushes was a little shorter than the other but there appeared to be enough wear life left in it.
Put it all back in the car and, lo and behold, the whistle had gone. Also the 0.9A current draw. The regulator is working, putting out 14V.
But I really really would like to know what could have possible caused it and if I should replace something lest it comes back. The idea of a flat battery does not appeal to me. The whistle could not be heard unless the bonnet was open and one listened carefully, luckily my hearing is still good.
So, if anyboody could bust that mystery for me, I would be most grateful.
Klaus
Reply By: hl - Wednesday, Jul 12, 2006 at 06:40
Wednesday, Jul 12, 2006 at 06:40
Hi,
The regulator in some alternators is actually a switch mode type controller and that could be the noise you heard. Somehow it was oscillatiing when it should not have been. Maybe a poor ground connection somewhere.
Cheers
AnswerID:
183090
Follow Up By: Mike Harding - Wednesday, Jul 12, 2006 at 08:16
Wednesday, Jul 12, 2006 at 08:16
Most (all?) switch mode supplies oscillate above human hearing and I would be surprised if the OP can hear anything over 15KHz - I can't hear anything over about 10KHz these days :( But I agree it does sound like a switch mode supply doing _something_? What worries me is that I don't think it should be oscillating at such low frequencies and that makes me wonder if something may be in the process of failing?
If you are planning to do any significant bush trips in the near future I would consider carrying a spare alternator or regulator pack (if available) for, at least, the next few months. Failing that some other method of charging the battery (small gen?) so you can at least drive a bit – charge the battery – drive a bit etc….
Mike Harding
FollowupID:
439594
Follow Up By: hl - Wednesday, Jul 12, 2006 at 08:58
Wednesday, Jul 12, 2006 at 08:58
Hi,
TV line oscillators in older sets were quite audible and they operate at 15khz. What you hear are sub harmonics by some mechanical parts i.e. windings that are vibrating.
Also, it is likely that the oscillator starts working as soon as you turn the ignition on.
I had a
Tarago once that would create all sorts of noises on HF from the regulator which I could never totally eliminate.
Cheers
FollowupID:
439599
Follow Up By: Mike Harding - Wednesday, Jul 12, 2006 at 09:59
Wednesday, Jul 12, 2006 at 09:59
Depends on your hearing but I suspect _very_ few people over 40 years of age would be able to hear 15.625KHz and, these days, given the extensive use of music systems with headphones for the past 20 years I doubt many over 25 would either!
Your comment relating to sub harmonics is possible but, I think, in this case unlikely. It would need an interaction of multiple sub harmonics which, in the first place, were causing mechanical surfaces to resonate at some frequency above audio and then for those vibrations to produce a difference signal in the audio range and given the power losses in harmonics I have doubts.
I agree it will probably work at ign. on and will certainly put rubbish out on the HF frequencies - part of the reason I haven't bothered to install HF in my vehicle :)
My money is still on a possible upcoming failure – of course it could simply be a design flaw which, under certain power removal conditions, causes the switching chip to go into an odd mode and do silly things? Wouldn’t be the first time I have seen similar.
Mike Harding
FollowupID:
439616
Follow Up By: Richard Kovac - Thursday, Jul 13, 2006 at 00:50
Thursday, Jul 13, 2006 at 00:50
Mike
I love It
FollowupID:
439781
Reply By: Member - Crazie (VIC) - Wednesday, Jul 12, 2006 at 08:22
Wednesday, Jul 12, 2006 at 08:22
Klaus
I can't help you with any suggestion, but am wondering how you measured the current draw of 0.9A. Just trying to learn. My understanding is you need a shunt to measure the amps? I have also seen V/ohms=Amps?
Would love to know how to measure amps on the run.
thanks
Ads
AnswerID:
183095
Follow Up By: Mike Harding - Wednesday, Jul 12, 2006 at 10:04
Wednesday, Jul 12, 2006 at 10:04
With DC current the only? ways are either with a shunt of known resistance value across which the voltage is measured and the formula I = V / R applied to calculate the current or by measuring the Hall Voltage (hall effect) which can be done by clamping a probe around the wire - it's a, sort of, magnetic measurement.
en.wikipedia.org/wiki/Hall_effect
Mike Harding
FollowupID:
439620
Follow Up By: Member - JohnR (Vic)&Moses - Wednesday, Jul 12, 2006 at 10:53
Wednesday, Jul 12, 2006 at 10:53
Hi Ads, talked to our local (very good and
bright) autolec about his amp meter/multimeter arrangement. Mike is talking about the inductive type with the clamp above which are very good for higher ampeges but there are many different multimeter arrangements.
The one Gary has locally cost him about $500 ten years ago and is the Roller of multimeters, branded Fluke. It measures current draw to 10 amps and is fuse protected. I guess some may say Fluke isn't the Roller, but it was the best he could get at the time. Gary has inductive ones too but not so good at the lower amperages.
FollowupID:
439636
Follow Up By: hl - Wednesday, Jul 12, 2006 at 11:54
Wednesday, Jul 12, 2006 at 11:54
Hi,
The Jaycar QM1562 is a clamp-on meter and works
well. It will measure DC current under 1 amp without breaking the wire!
Cheers
FollowupID:
439655
Follow Up By: Member - Mike DID - Wednesday, Jul 12, 2006 at 12:22
Wednesday, Jul 12, 2006 at 12:22
The Jaycar QM1564 is even cheaper at $99.
Site Link
Mike
FollowupID:
439661
Follow Up By: Member - Crazie (VIC) - Wednesday, Jul 12, 2006 at 12:33
Wednesday, Jul 12, 2006 at 12:33
Hi Guys
Thanks for your help.
100mA is only 1 amp isn't it? Would meassuring 1 amp help. Just general 4wd gear running?
So would i need for something to meassure about 10amps?
Thanks
Adam
FollowupID:
439667
Follow Up By: Member - Mike DID - Wednesday, Jul 12, 2006 at 12:47
Wednesday, Jul 12, 2006 at 12:47
100mA is 100/1000th of an Amp i.e. 1/10th amp.
These Clampmeters will measure up to 200 amps and can detect currents as small as 1/100th amp.
Mike
FollowupID:
439674
Follow Up By: Member - Phil G (SA) - Wednesday, Jul 12, 2006 at 15:48
Wednesday, Jul 12, 2006 at 15:48
Given that this measurement was done with the motor off, whats wrong with using a common garden DMM set on the 10amps setting, and disconnecting the battery earth to make the measurement?
FollowupID:
439701
Follow Up By: V8 Troopie - Wednesday, Jul 12, 2006 at 23:13
Wednesday, Jul 12, 2006 at 23:13
Phil G that's exactly how the measurement was done.
Well guessed!
FollowupID:
439772
Reply By: GUPatrol - Wednesday, Jul 12, 2006 at 16:26
Wednesday, Jul 12, 2006 at 16:26
Klaus,
Your problem is a faulty (leaking) rectifier. Basically a bad diode in the output rectifier bank.
If it is a BOSCH alternator, it is easy to repair, you can get the parts from any bosch dealer such as autopro or alternativelly from Ingram.
You need to have a good soldering iron and need to know how to solder properly. Too little heat and you won't weld the connections, too much heat or too long and you will damage the new rectifier.
Will
AnswerID:
183166
Follow Up By: Mike Harding - Wednesday, Jul 12, 2006 at 16:32
Wednesday, Jul 12, 2006 at 16:32
Sounds reasonable to me. The only thing which confuses me is that Klaus says the 900mA current leakage stopped after he removed the alternator, if a diode was breaking down I would expect it to leak all the time?
Mike Harding
FollowupID:
439704
Follow Up By: GUPatrol - Wednesday, Jul 12, 2006 at 17:04
Wednesday, Jul 12, 2006 at 17:04
Mike,
Fair question.
The answer is that diodes as all electronic components measure different at different temperatures and loads.
He will find that when he puts it back in it may even work fine and one day (specially under load) it will open again and leak or even short circuit.
Will
FollowupID:
439712
Follow Up By: V8 Troopie - Wednesday, Jul 12, 2006 at 23:27
Wednesday, Jul 12, 2006 at 23:27
Thanks to all for the replies, lots of ideas to ponder now. I will investigate the temperature thing, though when I noticed the whistle first the engine was cold as I just had installed a new radiator.
The next day I took the car for a drive, it was hard to start initially, like a low battery, which prompted me to investigate further after I got back home with a warmed up engine.
As I said, the whistle and current drain has disappeared now, the car started fine this morning even though we had a rather cold night.
I would back up Mike H with the assumption that diodes usually do not come good once faulty, at least that has been my experience with general diodes rather than alternator diodes of which I have no experience.
I'm more inclined it was a faulty earth as suggested above, one of the brush holder screws does provide an earth connection to the regulator block. I will experiment with loosening that and see if the symptoms reappear.
The suggestion of getting a spare regulator assembly is a good one and I will do so. Its easily exchanged and can be done in situ without having to take all the bits off that prevent a quick removal of the whole alternator.
Klaus
FollowupID:
439773