battery or alternator?

[Deleted User]

Joe_Horner wrote: »

With those results, don't waste money on a battery. get the alternator replaced and you'll be good to go with the battery you've got.

Deffo alternator then?

Joe_Horner

As definite as it can be without actually being there taking measurements

Strider590

12.7v is low, verging on dead.

If you start the car the alternator will start pumping everything it has into the battery, but if the battery won't take a charge you'll just see no voltage change.

You said it was unused for a year? If that's the case, then I really don't think the battery is any good.... A brand new battery can sit and hold a charge for around 6 months, a used battery much less.

Joe_Horner

Strider590 wrote: »

12.7v is low, verging on dead.

Err, no it's not. The fully charged resting voltage of a car battery is between 12.6 and 12.7 volts.

The OP charged it, then checked it after a week of standing. That gives the resting voltage. It was 12.7 volts. That is a healthy battery.

Also, if he starts the car he won't see anything from the alternator because be previously connected the battery the wrong way round. That WILL have destroyed the diode pack, so the alternator won't be working. All that was covered earlier in the thread.

[Deleted User]

Joe_Horner wrote: »

Err, no it's not. The fully charged resting voltage of a car battery is between 12.6 and 12.7 volts.

The OP charged it, then checked it after a week of standing. That gives the resting voltage. It was 12.7 volts. That is a healthy battery.

Also, if he starts the car he won't see anything from the alternator because be previously connected the battery the wrong way round. That WILL have destroyed the diode pack, so the alternator won't be working. All that was covered earlier in the thread.

Thanks Joe. :-)

colino

I don't think it's all doom and gloom on the alternator front, a lot of old, pretty basic alternators could put up with this occasional abuse (better diode packs?) but I think you might be getting misled with sound voltage on an old battery. The proof of the pudding will be in trying to start it (alternator dead or otherwise should have no effect on an old Mini). That battery voltage may flatter to deceive and you might have no current behind it.
Do a proper jump start, jump lead onto the heavy terminal on the starter motor (follow the thickest battery cable from the battery positive terminal) and put the other lead on a sound piece of metal (on an old Mini?) ideally on the bellhousing. That will basically cancel out the car battery and prevent as far as possible the donor juice trying to reenergise that, if it is now indeed just a battery shaped brick.

Joe_Horner

colino wrote: »

I don't think it's all doom and gloom on the alternator front, a lot of old, pretty basic alternators could put up with this occasional abuse (better diode packs?) but I think you might be getting misled with sound voltage on an old battery. The proof of the pudding will be in trying to start it (alternator dead or otherwise should have no effect on an old Mini). That battery voltage may flatter to deceive and you might have no current behind it.
Do a proper jump start, jump lead onto the heavy terminal on the starter motor (follow the thickest battery cable from the battery positive terminal) and put the other lead on a sound piece of metal (on an old Mini?) ideally on the bellhousing. That will basically cancel out the car battery and prevent as far as possible the donor juice trying to reenergise that, if it is now indeed just a battery shaped brick.

He's already started the car successfully twice with this battery, after leaving the lights on for 10 minutes, and with no voltage drop:

[quote=[Deleted User];65735126]Well latest tests:-

1. 10 mins with lights on still 12.7v on battery.
2. Started car - still 12.7v so I assume nothing coming from alternator?
3. Pulled plug/leads off alternator and started car. Getting 0.2v which I guess is not right either.
[/QUOTE]

So the battery is good. Maybe not as good as new, but good enough to do what a battery does!

[Deleted User]

colino wrote: »

I don't think it's all doom and gloom on the alternator front, a lot of old, pretty basic alternators could put up with this occasional abuse (better diode packs?) but I think you might be getting misled with sound voltage on an old battery. The proof of the pudding will be in trying to start it (alternator dead or otherwise should have no effect on an old Mini). That battery voltage may flatter to deceive and you might have no current behind it.
Do a proper jump start, jump lead onto the heavy terminal on the starter motor (follow the thickest battery cable from the battery positive terminal) and put the other lead on a sound piece of metal (on an old Mini?) ideally on the bellhousing. That will basically cancel out the car battery and prevent as far as possible the donor juice trying to reenergise that, if it is now indeed just a battery shaped brick.

Battery, once charged like this, does start the car.

philgr

Where in Wales are you bud?

colino

Apologies for not reading three pages to get to here. Battery is fine, speak to your local scrappy and get a replacement alternator on it and jobs done.