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Alternator only starts charging when taken over 3000rpm
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wildbits
New User
May 11, 2013, 4:10 AM
Post #1 of 7
(2275 views)
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Alternator only starts charging when taken over 3000rpm
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Anyone understand alternators and their control systems?
I have a Peugeot 306 LX Auto 1600cc reg 2000 approx 75k miles. It failed while driving at night - all the electrics failed slowly until it wouldn't run. Clearly it wasn't charging and just went until the battery died.
RAC man tested the battery and declared it to be fine (though now flat). He jump started it and then metered the output and it was not charging. Next he put a wire between one terminal of the alternator and... another point, don't know where, could have been the battery? When this extra wire was connected it started charging.
Next he took off the extra wire, turned the engine off, restarted it, REVVED IT TO approx 3000RPM and it started charging AND KEPT CHARGING EVEN WHEN IDLING.
This is how I've been running it for about 4 months. Every time I start the engine I blip the throttle to a good 3000rpm - at this point THE BATTERY WARNING LIGHT COMES ON which now indicates it's charging. It stays charging until the engine is turned off. I've tested this many times with the meter, it works every time, NOT INTERMITTENT, and it's been fine for 4 months. The battery has never been charged other than by the alternator.
So what's the problem? Well I don't want to keep revving it hard from cold, and I don't like driving with a red warning light permanently on. I'd like to fix it rather than just get round it.
My local garage insist that I need a new alternator and/or battery. I don't see this when the battery behaves perfectly and the alternator consistently puts out 14.5v - when it's told to. The bit I need help with is how to instruct the alternator to start charging other than revving the engine.
My impression is that there's a broken connection somewhere between the alternator and the battery warning light - but where?
Thanks for reading this far! Got any ideas?
Cheers
IanB
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HT
User
May 11, 2013, 4:46 AM
Post #2 of 7
(2266 views)
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Re: Alternator only starts charging when taken over 3000rpm
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My best guess is the alternator has a bad diode and probably should be replaced.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 11, 2013, 5:14 AM
Post #3 of 7
(2257 views)
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Re: Alternator only starts charging when taken over 3000rpm
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#1, not sure but have witnessed that. Dependably a car (more than one) wouldn't charge until revved up and fine after that for ages. Swapping one out did fix that and I think (just can't be sure) that brushes were sticky somehow and the rev up just made them connect.
Those were easy ones. Long time ago and think a slight whack with something like a plastic hammer could make them snap to working. Most people wouldn't put up with that so I did not just take them apart in attempt to fix them just replace and it was done,
T
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Discretesignals
Ultimate Carjunky
/ Moderator
May 11, 2013, 11:39 AM
Post #4 of 7
(2221 views)
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Re: Alternator only starts charging when taken over 3000rpm
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The alternator doesn't appear to be excited which accounts for the engine having to be revved for the alternator to start functioning. Most alternators need external power from the lamp circuit to get the alternator excited, so it can start charging. If there is lamp voltage at the regulator, more than likely the regulator is the problem.
You could remove the alternator and have it bench tested.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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wildbits
New User
May 12, 2013, 3:21 AM
Post #5 of 7
(2202 views)
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Re: Alternator only starts charging when taken over 3000rpm
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Ah! Thanks, that's a useful explanation. I'll get the meter out again and see what I can learn.
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wildbits
New User
May 19, 2013, 11:00 AM
Post #6 of 7
(2144 views)
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Re: Alternator only starts charging when taken over 3000rpm
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Okay, don't know whether to feel embarrassed, vindicated or just happy, but I seem to have fixed it!
I metered it again and it was charging perfectly within range, just not being excited on starting. And so...
even though I was sure I checked all the fuses before, I checked again and found a blown 15A fuse. I replaced this and, sure enough, it's working just fine. Doh!
Not sure exactly what this fuse does as none of the 3 possible versions shown in the manual bear any obvious relation to the one actually in the vehicle. Also the clock and the electric windows are now working, so apparently part of the same circuit. Don't know what caused it to blow in the first place either, as all seems to be well now.
Anyway, thanks all for your input - if nothing else it encouraged me to go and get my hands dirty rather than just believe the guys garage who had a look and told me I definitely needed a new alternator - sounds like that would have been an expensive way not to solve the problem!
I'll keep an eye on it just in case some kind of alternator issue caused the blown fuse in the first place, but I'm seeing 14.5v at fast idle, dropping to about 14.3 with all the lights and A/C on - that's about right isn't it? That's from cold this morning and it's about 12C here.
Cheers
IanB
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 19, 2013, 11:37 AM
Post #7 of 7
(2140 views)
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Re: Alternator only starts charging when taken over 3000rpm
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Your voltages are now good, consider this solved unless it continues to blow that exact fuse. It's just being a French car to you
Why is it wired that way - who the heck knows? I should consider this problem solved and lock the thread but will wait to see how long this good find lasts,
T
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