We bought a Mini three months ago, a 1991 998cc. After a while the battery died so we bought a new one which was fine for a week or so, got progressively slower turning the starter then was flat. Check for anything that could be draining, removed interior light bulb. Gave it a good trickle charge and in the interim fitted a battery isolator switch which has been used every time the car has been left.
A week on it has got flatter and now is too flat to start the car.
I suspect the alternator or wiring even though the red warning light doesn't come on while driving and it is working. Is it correct to assume that if I put a volt meter across the battery terminals with the car running and get a reading of 13.5 ish volts the alternator is charging ok or is it not that simple?
Thanks,
Stuart
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Oops, should of course read FLAT!!!
easily amended PU
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Assuming your voltage measurement is accurate..
13.5 volts "charging" isn't enough IMHO.
It aught to be mid 14's at this sort of temperature.
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Well you ought to be getting a bit more than 13.5 volts when the engine is running, as this is at the low end of the scale for an alternator output voltage, but given what you have done to try to eliminate this problem it does sound like a weak alternator or a dodgy connection somewhere.
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Put the h/lights on as well-should still hold more than 14v. at engine speeds above idle.
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If you switch everything on with engine running,it should tell you in minutes if the alternator is causing the problem.
wipers will slow down, so will heater motor, then lights will start to dim
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Favourite troublespot on these old Minis is a poor engine to body earth strap.It is a good idea to fit an extra lead to reduce any volt drop.hth
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1991 Mini 1.0 ... Regulated Voltage ... 13.6 to 14.4 Volts ...
Alt output at eng speed ... A/V/RPM ... 45/14/6000 ...
Battery Drain Test ...
Charge the battery (Warning; explosive gases) and use a small bulb (a sidelight bulb holder?) connected across the disconnected earth terminal and the earth battery post to test for a drain.
If you find one; (the bulb lights) sequentially remove every fuse until the bulb goes out. Remember to make sure that everything, including the interior light, is turned off.
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i44.photobucket.com/albums/f11/scotmech/Mini.jpg
For some reason its only linking to Photobucket's Home Page - PU"
{Sorted. The "IMG" commands at the start and end of the post were preventing it from opening - DD}
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Thanks for all the advice so far!
Have just bought a digital multimeter!
The Mini JUST about started and on a fast ish idle the reading at the battery is only 9.72 volts. Could this be because the battery was almost flat or would this not matter? Many Thanks,
Stuart
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Take a reading without the engine running, sounds like the Alternator to me, is the ign. light coming on when you first turn the key ?
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That doesn't matter, the problem thus appears to be that your alternator is not charging at all.
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I was wondering whether the "charging light" wasn't working at all....IYKWIM
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I know the charge light is ok as it comes on with the ignition and doesnt illumate or even flicker when the car is running. With the engine off the battery voltage is still only 9.8 volts.
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With the engine off the battery will still only be 9.8 volts because it is in a partially discharged state. I would be surprised if it will be able to start the car again.
The problem is that your charging system is not working. Either the alternator is u/s or there is a problem with the wiring. Forget the fact that the alternator warning light on the dash is acting normal, you have a charging system fault regardless.
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I know the charge light is ok as it comes on with the ignition and doesnt illumate or even flicker when the car is running. With the engine off the battery voltage is still only 9.8 volts.
Check your new meter by measuring the battery voltage on another (good) car.
If that's a sensible value ( around the 13 volt mark, engine not running, 14.something engine running )
check the voltage between the engine and the bodywork of your mini with the engine running - if you can get it to start again. You should only measure a small fraction of a volt between these two places - any more and, as mentioned previously, you have a poor earth strap connection between the gearbox and bodywork.
I have faint memories of the speedo cable, or was it the choke cable, glowing like an electic fire on a (very old) Mini due to earthing problems.
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Grateful thanks to all those who have offered advice so far today.
Update: I have replaced the alternator with one from a spare engine which is untested. On idle the reading across the battery terminals has now progressed to around 12.6 volts. The reading between the engine and earth is zero volts and I notice a new-ish looking earth cable has been fitted in addition to the bare braided one.......an attempt to address whatever this problem is by the previous owner maybe???
I'm beginning to think it maybe a wiring issue as two duff alternators seems too much of a coincidence to me.
I have even earthed the engine by connecting a long jump lead between the battery and the engine block but still no good : o (
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Well look at the bright side, its fixable by a reasonably competent mechanic without resorting to blinking diagnostics and replacing a failed ECU.
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Pugugly I agree entirely! I've just remove the head from my Mondeo 2 litre and have seen enough pipes and wires to last me a lifetime...........and the car is 10 years old!!!! The Mini is oh so simple but frustrating at the moment! Just need to get busy with the test meter and find out what the problem is!
I have just had it running for an hour. Still only putting out about 12 volts. Switch the lights, heater HRW on etc and it drops down to 9 volts across the battery.
Turned off engine. Went to restart.........not enough welly in the battery to start the car......... Doh!!!!!
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Have you replaced the Battery leads X 2 ?
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minis dont you just love them
you say alternater light is working but these work off a different circuit in the alternator anyway so is fools gold if you understand me
sound like a known good third alternator is required to me
old minis with low oil pressure used to have the dynamo and oil light swapped on the dash prior to going to auction ;-0
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Just a thought, presumably one of the terminals on the back of the alternator sends the current to charge the battery back to the boot? Can I find out if the signal is 'full strength' at this point and work my way backwards?
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Thanks Bellboy!
Update!!!!!
I am getting a reading which is the same from all three terminals (one small and two large) at approx 12.4 volts which is the same as the reading at the battery. (The fan belt is very worn and needs replacing but its not slipping)
Have I just got two bad alternators?
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as somebody else said with all the extras turned on your alternator should be kicking out at least 14 volts to supply the load and replenish the battery
so yes
i tink alty no nating
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Thanks mate. I'll take it to my local recon man and get it swapped for a good one. I'm pleased it seems to be a 'bolt on' part rather than a nightmare to find wiring issue somewhere.........
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