battery or alternator?

[Deleted User]

Confused now. Got some people saying its been a year its deffo dead, leave it alone, and other says try a trickle charge?

[Deleted User]

Stoke wrote: »

I know someone who did this. Garage changed alternator, and battery, never thought of diode pack. Very expensive lesson there.

Diode pack - this is separate to alternator?

forgotmyname

You wont get 14 volts from an old classic mini alternator. What year is it?

Because the alternator cannot sense the battery voltage properly it wont be putting out the full power its capable of.

Remove the cars battery and run in solely on the jump pack. What voltages do you get then?

Diode pack is inside the alternator.

If its an old girl then it may even have a dynamo not an alternator.

[Deleted User]

forgotmyname wrote: »

You wont get 14 volts from an old classic mini alternator. What year is it?

Because the alternator cannot sense the battery voltage properly it wont be putting out the full power its capable of.

Remove the cars battery and run in solely on the jump pack. What voltages do you get then?

Diode pack is inside the alternator.

If its an old girl then it may even have a dynamo not an alternator.

1996 Jap import. Pretty sure its got an alernator.

You mean take battery out, connect jump pack to leads as normal and see what happens? It wont blow my jump pack or anything?

(Although I suppose when you start a car by attaching jump pack to battery its attached and recieving charge from alternator for few mins until you disconnect anyway).

Joe_Horner

forgotmyname wrote: »

[...]If its an old girl then it may even have a dynamo not an alternator.

Very good point - how classic is your classic Mini? If it's before the mid-70s then it's probably got a dynamo rather than alternator and everything changes.

Either way, 7.5v from a battery is at the extreme end of "flat". It's occasionally possible to resurrect them from that sort of level but it'll never recover fully and probably isn't worth the aggro of trying, then getting randomly stranded when it decides to quit!



eta: 1996 will be alternator.

You won't damage your jump pack by running it with that connected, but an alternator should give around 14v output with any voltage available from the battery. As soon as they starts generating they provides enough voltage to energise their own field coils, which increases output in a positive feedback until they reach the regulated output.

So, if you're not getting 14v or so out of it with the engine running then there's a fault with the charging (either alternator or alternator wiring). Note that some alternators will refuse to charge if the ignition lamp bulb is blown - does the little red light come on when you turn the key (with the jump pack connected)?

Norman_Castle

If you leave the jump pack connected does it still cut out?. Was it running well before being stored?.

AdrianC

[quote=[Deleted User];65562519]So just to clarify - with engine running, battery connected, I should be seeing 14v using multi-meter between terminals? regardless of battery state?[/QUOTE]
Yep. Think of the alternator as a pump, and the battery as a tank. Your problem is that the tank's leaky, and the pump's not pumping. If the pump was pumping, you still wouldn't be working, because the tank's not holding water.

The alternator needs to see +12v to energise the field internally, which allows it to generate electricity. That's happening when you start it, from the jumping car's battery. Once it's running, it's seeing the electricity it generates, so it should stay alive. Being such a recent Mini, it's going to be electronic injection/cat/management, just like any "normal" car. It's not a carb'n'points 850...

[Deleted User]

Norman_Castle wrote: »

If you leave the jump pack connected does it still cut out?. Was it running well before being stored?.

Was fine bfore. Well until I tried to connect the battery wrong way.

forgotmyname

Oh dear. That could have caused the diode issues.

Not that expensive to replace both anyway.

Joe_Horner

forgotmyname wrote: »

Oh dear. That [STRIKE]could[/STRIKE] will have caused the diode issues.

Fixed that for you

This is a typical schematic for a car alternator:



The diodes are the 6 "triangles with a bar at the point" for those not familiar with circuit diagrams. They allow electricity to pass (almost) as well as wire "in the direction of the arrow" (ie: with the base of the triangle +ve and the bar -ve) but block it like a switch if connected the other way.

Note that, normally, the battery +ve is connected to the "bars" so that current can't flow through them from the battery. But, connect the battery the other way, and you've got a dead short through each pair of diodes -it's like dropping a spanner across your battery terminals.

If you don't know what that's like then don't try it at home! Watch this instead...

http://www.youtube.com/watch?v=ZfFViY1-zYw