10 replies to this topic

[Bock]

Model:MINI 1000 City E
Year: 1984
Hi,
Been driving this mini almost a year now. Driven to shop once a week, driven most weekends and then long journeys ~once a month (~120 miles).
We've had electrical issues since the beginning but initially it was a faulty alternator. Having replaced it with one from my other mini. alternator definitely charging, >12.5V with revs. No mods, apart from radio which I disconnected since we've had problems. Checked the current, no current loss when ignition off. When key turned to position II there is a ~3.5A drain with nothing on (starter not engaged). When battery fully charged everything runs as normal.

Observations:
1. When battery low, starting the car reduces voltage in battery to ~11.3V and then the voltage very slowly comes back up (if left overnight will start but only once).
2. Having fully charged the battery, drove 70 miles, towards end of journey lights dimmed to basically off and the engine started struggling, had to go up hills in first gear (only for last 5 mins of drive). Charged the battery for 3 hours during the meal and for the 20 mile journey to another home no problems, lights completely fine.
Only noticeable difference was that it was raining in the first journey.

Question:
1.Could rain really have caused my battery to drain to 11.3V from full in a 70 mile journey whilst the alternator was working.
2. is it more likely that I have a temperamental short, that coincidentally happens whilst it rains.
3. If it is the rain, do I just need to waterproof the distributor or do I need a full on shield?

Thank you very much for reading and potential help.

Olly




no non-standard parts. (radio disconnected)

[Yoda]

I think your Alternator is not charging as well as you think. It should show around 14.6 volts with the engine running. Or you battery is completely shot or dry.

[tommy13]

A battery draining whilst driving is usually a sign that the alternator if failing. Although you say it is putting out a charge of more than 12.5 volts with revs, the figure should be in the 13.6 to 14.4volt region. I think the rain is only incidental in your argument because you would have been using the wipers and heater and flattened the battery more quickly than in the following journey which was also shorter.
I have read on here that it is common to find a bad connection where the altermator wire connects to the starter solenoid. Also check all solenoid, battery and engine earth connections, even the alternator body to engine block can be effected with corroded alternator bodies.
It is possible , but unlikley that the alternator could be effected by ingress of rainwater, but if all connections chech out OK I would consider changing it.
Almost forgot, the most common cause of charging problems, and the simplest to fix is the fan belt slipping.(can be worse when wet)

Edited by tommy13, 16 May 2010 - 11:26 AM.

[il-barba]

does the battery light come on when you switch the ignition to position two? and while driving? 12.5 is definitely a low voltage output

[Bock]

Hi,
thank you all for your quick replies.
Went out and checked the voltages again. Was going to check the earths but is started raining.

Battery:
Before starting the engine the reading was 12.3 V.
Once started that dropped to 11.94V
a touch of revs brings us up to 11.97V
relatively high revs 13.86V
and foot to the floor 13.92V

as soon as engine was cut the voltage dropped to 12.90V
then dropped slowly down to 12.70V didn't look like it was going to stop.
will probably drop back down to the initial 12.3V.

Did check the fan belt, does look like it could do with a tighten but I don't think it's the sole cause.

Thank you very much,
Olly

Edited by Bock, 16 May 2010 - 03:59 PM.

[Bock]

I think your Alternator is not charging as well as you think. It should show around 14.6 volts with the engine running. Or you battery is completely shot or dry.

Hi customcart,
thanks for your reply.
I don't think the battery is dry as the elements in each of the 6 cells is still submerged in fluid. When you say running, should it read 14.6V when idling, because if it does I'm way off.

Idling, 11.94V just after start of engine.
then 13.92V when I rev hard and then when I cut the engine 12.9V, dropping steadily probably back down to 12.3V. (it started raining)

thanks for your help,
Olly

[Bock]

does the battery light come on when you switch the ignition to position two? and while driving? 12.5 is definitely a low voltage output

Hi il-barba,
thank you for you reply.

The light comes on in position two but turns off as soon as the engine starts.

Thank you,
Olly

[Bock]

A battery draining whilst driving is usually a sign that the alternator if failing. Although you say it is putting out a charge of more than 12.5 volts with revs, the figure should be in the 13.6 to 14.4volt region. I think the rain is only incidental in your argument because you would have been using the wipers and heater and flattened the battery more quickly than in the following journey which was also shorter.
I have read on here that it is common to find a bad connection where the altermator wire connects to the starter solenoid. Also check all solenoid, battery and engine earth connections, even the alternator body to engine block can be effected with corroded alternator bodies.
It is possible , but unlikley that the alternator could be effected by ingress of rainwater, but if all connections chech out OK I would consider changing it.
Almost forgot, the most common cause of charging problems, and the simplest to fix is the fan belt slipping.(can be worse when wet)

Hi Tommy,
thanks for your reply.

I've written down the voltages I got in the post. Checked belt and think it could do with some tightening but I don't think it's the only cause to my problems.

thank you,
Olly

[cambiker71]

Hi,
thank you all for your quick replies.
Went out and checked the voltages again. Was going to check the earths but is started raining.

Battery:
Before starting the engine the reading was 12.3 V.
Once started that dropped to 11.94V
a touch of revs brings us up to 11.97V
relatively high revs 13.86V
and foot to the floor 13.92V

as soon as engine was cut the voltage dropped to 12.90V
then dropped slowly down to 12.70V didn't look like it was going to stop.
will probably drop back down to the initial 12.3V.

Did check the fan belt, does look like it could do with a tighten but I don't think it's the sole cause.

Thank you very much,
Olly

The alternator looks like it's not charging, check the voltage at the back of the alternator with the engine running and see if the voltage is higher, should be around 13v at idle speed higher if revved, if so you either have a connection problem somewhere or a bad engine to body earth or body to negative terminal cable problem.

[Bock]

Hi all,
reckon I'm going to get a new alternator. Which one do I get? do I realy need 80Amp? speakers relatively big but not excessive.

Thank you,

Olly

[il-barba]

did you check the earthing points as well as the alternator belt? might be something much simple. also some workshops have the capability to test alternators to see if they are faulty