23 replies to this topic

[inyk]

Hi I have a 1995 (dec) Mini Sprite Auto...

Over time the battery will drain and the car will eventually fail to start... so we have tried the following...

1) new battery - still runs flat
2) New Alternator (45 amp) - still fails to charge
3) 2nd replacement alternator - still fails to charge
4) checked earth strap - all okay - but still no charge...

I am not technically minded so am running short on ideas as to what else it could be...!

I would be very grateful for any hints / tips or suggestions as to where I go looking next...

Shout if you need to know more and apologies if this is posted incorrectly...

[m1tch]

Hi I have a 1995 (dec) Mini Sprite Auto...

Over time the battery will drain and the car will eventually fail to start... so we have tried the following...

1) new battery - still runs flat
2) New Alternator (45 amp) - still fails to charge
3) 2nd replacement alternator - still fails to charge
4) checked earth strap - all okay - but still no charge...

I am not technically minded so am running short on ideas as to what else it could be...!

I would be very grateful for any hints / tips or suggestions as to where I go looking next...

Shout if you need to know more and apologies if this is posted incorrectly...

How tight is the belt?

[mars red mike]

Do you mean if the car is left standing for a significant amount of time then when you try to start it the battery is flat or does it go flat even if the car is used everyday

[inyk]

[
How tight is the belt?
[/quote]

The Belt is tight - just a little movement if you push it hard

[inyk]

Do you mean if the car is left standing for a significant amount of time then when you try to start it the battery is flat or does it go flat even if the car is used everyday

Sorry - should have said... it is when the car is being used.

[mars red mike]

Do you have any non standard electrical accessories fitted ie aftermarket cd player, spotlamps, anything like that?

[m1n1]

have you tested it to see if the car is actually charging with enging running???

[inyk]

the only non standard thing electrical thing on it is an aftermarket CD player - this is a sony one that caused no problems in a previous car.

With regards charging when the engine is running... we suspect not. I have had a volt meter put on it showed something like 12.5 volts.

What else can i tell you all

[SMP]

Getting somebody who knows about electrics to take a look at it. This is really easy to diagnose if you know what you're doing (sorry for stating the obvious).

Is the battery draining when the car is stood - but it takes a while for the battery to end up completely flat. Very easy to check if you've got an ammeter. Switch everything off - disconnect the earth lead at the battery and insert the ammeter. It should read almost nothing - perhaps something like 0.01 amps (sorry but I've never checked on my SPI and I suspect there will be a tiny current draw by the EEC). On a non fuel injected mini I would expect zero when doing this check unless you have a clock or alarm fitted.

Is the thick wire from the alternator to the main battery lead (I think they meet at the starter solenoid) in good order? Again this can be checked at the battery with the engine running. However you will need a much bigger ammeter and need to know what you're doing so that you don't trash the alternator by running with it disconnected.

Cheers
Steve

[inyk]

that was going to be the next port of call - was just hoping looking to sort this out myself - you know the quest of fixing something...! Easier said than done - especially when you are not an expert...

[Phaeton]

Does the RED ignition light come on when you switch on the ignition? If it doesn't come on at all, then it might be the bulb, if this is blown then the alternator won't know when to charge.

Alan...

[m1tch]

Does the RED ignition light come on when you switch on the ignition? If it doesn't come on at all, then it might be the bulb, if this is blown then the alternator won't know when to charge.

Alan...

Is the mini really wired in like that? lol thats so cool

[inyk]

Does the RED ignition light come on when you switch on the ignition? If it doesn't come on at all, then it might be the bulb, if this is blown then the alternator won't know when to charge.

Alan...

That is an interesting one...! I will have to check that one out - I can recall the Oil light - but not the ignition light... Will a blown bulb really stop the charge...?

[Phaeton]

That is an interesting one...! I will have to check that one out - I can recall the Oil light - but not the ignition light... Will a blown bulb really stop the charge...?

The alternator uses a 12v from the battery via the bulb to know if it needs to charge if the bulb is blown then it doesn't get it's 12v so doesn't know to charge. It's not strictly true as it's also down to the current draw of the bulb, but for all intense & purposes if it's blown it doesn't work. Similarly if the thin red (or is it brown) wire on the alternator gets broken it won't charge either.

Alan...

[dklawson]

It's true. With MOST Lucas alternators you have to have a functioning warning light or the alternator will not charge.

I'd like to make a few minor corrections to Phaeton's explanation. When you turn the ignition switch to the "run" position, current from the switch flows through the warning light to the field coils in the alternator. The "other side" of the field coils are connected to earth. When you turn switch, you are providing power to energize the alternator field coils. The warning light turns "on" because it has a path to earth through the field coils. Once the engine starts, the alternator starts producing electricity and the internal electronics "self energize" the field coils by providing voltage to the internal connection point where the charge warning light wire connects. When that happens (when the alternator brings the internal connection of the small spade lug up to charging system voltage) both sides of the warning light are "high" and there is no path to ground for the warning light... so it goes out.

If the warning lamp is missing or burned out, the field coils will not energize and therefore, the alternator never starts making electricity. OK... that said, there are many alternators that have some residual magnetism in the steel parts the field coils are on. SOME of those alternators will have enough magnetism that a really strong rev of the engine (like sudden burst of 4k RPM or more) can "kick in" the electronics and the alternator will start charging. This is the exception, not the rule, and you shouldn't count on it working every time. Another thing to keep in mind is that you cannot use an LED light (by itself) for the charge warning light. The LED will NOT let enough current flow through it. An LED will light up without allowing the field coils to energize.

You measured 12.5V with the engine running. Take the same measurement with the engine off. You should see about a 1.5V increase in the potential across the battery when the alternator is working. Most charged batteries will measure about 12.5V at rest so you should be looking for 14V or more across the battery for a working alternator to be charging.