battery or alternator?

[Deleted User]

Got an old classic mini. Not been used in about a year.



Anyway, had to jump start and it runs ok. Runs for about 10 mins and then dies.



Voltage on battery is reading 7.5v so I guess this is why. Should it charge just idling or best to start it and then take it for drive?



Got sneaky suspicion its alternator not charging (I connected battery wrong way once). How do I confirm this?



Or could it be the fuel in there now - gone a bit manky?

wildincrawley

"Got sneaky suspicion its alternator not charging (I connected battery wrong way once). How do I confirm this?"

Does the ignition light on the dashboard go out when it is running? If so, it's making some charge, at least.

With a healthy battery and alternator, I would expect it to be fully charged after 20 minutes (steady running, not slow idling - I believe alternators reach maximum charge around 1200 rpm. I have increased idle speed to help cars charge while idling before, but you would have to be VERY confident in the cooling system - not recommended).

I suspect you have at least 2 different issues there.

My first guess would be that if the battery has been flat for a year, it will not now hold charge properly. Do you have a healthy battery you could swap in to check if that fixes some of the problems? Or take the battery off the car, check the fluid level, and trickle charge overnight, to see if it will hold charge?

Paradigm

[quote=[Deleted User];discussion/4973407]
Voltage on battery is reading 7.5v so I guess this is why. Should it charge just idling or best to start it and then take it for drive?
[/QUOTE]

7.5v from a 12v battery that's stood for a year....it's dead!

I doubt any amount/type of charging will help.

The old fuel will be well past it's best too. If there's a lot in the tank I'd drain it, if there's only a little fill it with fresh.

Quentin

If you can get it to a garage/battery place they will put the tester on and see if it's battery or alternator at no cost

Iceweasel

I agree - that battery will NEVER recover - no matter what you do to it.

AdrianC

Whether the battery's alive or dead shouldn't stop it running after ten minutes or so. Once it's jumped and running, the alternator should provide more than enough to keep the ignition going.

Have you put a multimeter across the battery with the engine running?

If, once it dies, you immediately jump it again - what happens?

I wouldn't worry too much about year-old fuel, tbh.

System

we had this issue years ago ,we changed both the battery and the alternator only to find it was the belt that was at fault . expensive lesson learnt!

Paradigm

AdrianC wrote: »

I wouldn't worry too much about year-old fuel, tbh.

Year old fuel stored in the cars tank is way, way past it's best... especially if it's an ethanol blend (all modern petrol I believe)

The cars tank isn't airtight & ethanol attracts water... could be why it's cutting out (faulty alternator aside)

Robisere

A battery that has been idle for a reasonably long period of time begins to "Sulphate" - sediment builds up from the plates and its efficiency is very much reduced. It will never recover full charge. If you did connect the battery the wrong way round, you reversed the polarity, which may well have destroyed the diode pack in the alternator, so you may have two problems, as has been said.

If you check the battery with a multimeter, take the caps off the battery cells, but DO NOT lean over the battery whilst you do so (fumes which are potentially explosive - no sparks please!) Note the reading, then remove the tester and look at the cells. Are they gassing? (Bubbles coming up through the electrolyte) If so, there is enough life remaining in the battery to pass sufficient starting current. Is the level of electrolyte in the cells low? If so, get some distilled water from a parts shop/garage and top it up, but only to the level shown in the battery. Don't forget to replace the battery caps!

If you have access to any "jump Leads" you can ask a friend with a car to run them from his battery (whilst his engine is running) to yours, then after a few minutes, try to start the Mini. Fortunately the old Mini was uncomplicated, without so many of the modern electronics that can cause problems.

Good Luck!

[Deleted User]

Paradigm wrote: »

7.5v from a 12v battery that's stood for a year....it's dead!

I doubt any amount/type of charging will help.

The old fuel will be well past it's best too. If there's a lot in the tank I'd drain it, if there's only a little fill it with fresh.

I did take it out and charge a month or so ago.

[Deleted User]

AdrianC wrote: »

Whether the battery's alive or dead shouldn't stop it running after ten minutes or so. Once it's jumped and running, the alternator should provide more than enough to keep the ignition going.

Have you put a multimeter across the battery with the engine running?

If, once it dies, you immediately jump it again - what happens?

I wouldn't worry too much about year-old fuel, tbh.

7.5v no more when running.

Can jump it again - same thing runs for few mins.