Alternator packed up

[jonamacg83]

Our Cerbera has just ran out of juice near Winchester, as the alternator has given up. I was planning to go down tomorrow with a couple of spare batteries, and try to get the car back up to Leicestershire (140 miles or so) by running it till it dies, then swapping in the next battery. Hopefully if I do this in the day it will do a decent distance before it runs out.

My questions is, how far should I expect to get with no alternator? Obviously I need to get a few batteries but want to know how many I should get before I attempt this!

Thanks

[TDFPELTD]

Mine managed 90 miles on a big red top before it started misfiring including 20 mins in traffic at the Dartford crossing with the rad fans going.

We're halfway between Northants and Cambs just off the A14 if you need a stop for coffee/battery change etc.

[vroom]

Have you checked the big fuse at the back of the alternator - not uncommon to disintegrate / pop?

May be worth a look before driving back.

I guess with no lights or heater etc you'll be drawing about 10A ECU including coil pulses. Hazzard a guess at 1A for the instruments etc.

So 5 hours tops on a fully charged 60Ah battery.

All very approximate of course - but doable

[Gazzab]

Per above - how do you know alternator has gone?
Did you have electrics funnies for a while eg rev counter playing up?
Could be big fuse.

[jonamacg83]

Thanks for the info guys - I have no idea as I wasn't driving the car, I just got the 'rescue me' phonecall! The RAC chap came out and diagnosed a dead alternator - though quite how he did that if the car was running I do not know.

What kind of fuse is it - may well be worth picking one of these up too whilst I am getting the battery etc.

Thanks

Jonny

[Gazzab]

Do a search on big fuse or look at the recent thread on fuse holder.
It is under the windscreen , behind the engine.

[Steve_T]

jonamacg83 said:

Thanks for the info guys - I have no idea as I wasn't driving the car, I just got the 'rescue me' phonecall! The RAC chap came out and diagnosed a dead alternator - though quite how he did that if the car was running I do not know.

What kind of fuse is it - may well be worth picking one of these up too whilst I am getting the battery etc.

Thanks

Jonny

He'll be measuring the voltage at the battery and possibly the current delivered by the alternator with a clamp meter.

[jonamacg83]

Steve_T said:

jonamacg83 said:

Thanks for the info guys - I have no idea as I wasn't driving the car, I just got the 'rescue me' phonecall! The RAC chap came out and diagnosed a dead alternator - though quite how he did that if the car was running I do not know.

What kind of fuse is it - may well be worth picking one of these up too whilst I am getting the battery etc.

Thanks

Jonny

He'll be measuring the voltage at the battery and possibly the current delivered by the alternator with a clamp meter.

But if the car isn't running because the battery is dead, he won't be able to do that. I am not sure if he jumped the car or charged the battery sufficiently to get it running and then do the check. I think this would be the only way to do that.

[vroom]

I guess he would have started it via another batt.

Float charge should have been around 13.8V, so if he didn't see that across the batt (i.e. just 12V), he would have automatically assumed a dead alternator.

[Steve_T]

jonamacg83 said:

Steve_T said:

jonamacg83 said:

Thanks for the info guys - I have no idea as I wasn't driving the car, I just got the 'rescue me' phonecall! The RAC chap came out and diagnosed a dead alternator - though quite how he did that if the car was running I do not know.

What kind of fuse is it - may well be worth picking one of these up too whilst I am getting the battery etc.

Thanks

Jonny

He'll be measuring the voltage at the battery and possibly the current delivered by the alternator with a clamp meter.

But if the car isn't running because the battery is dead, he won't be able to do that. I am not sure if he jumped the car or charged the battery sufficiently to get it running and then do the check. I think this would be the only way to do that.

Agreed, he'd have to start it to test in this way.

[Steve_T]

vroom said:

I guess he would have started it via another batt.

Float charge should have been around 13.8V, so if he didn't see that across the batt (i.e. just 12V), he would have automatically assumed a dead alternator.

Doesn't work on a Cerb because the sensors for the alarm are permanently connected to the battery and hence there is always a small drain that prevents a float from building up.

[vroom]

Steve_T said:

vroom said:

I guess he would have started it via another batt.

Float charge should have been around 13.8V, so if he didn't see that across the batt (i.e. just 12V), he would have automatically assumed a dead alternator.

Doesn't work on a Cerb because the sensors for the alarm are permanently connected to the battery and hence there is always a small drain that prevents a float from building up.

Don't agree

With a trickle charger possibly, but with a paralleled battery no

[Robscim]

My money is on the big fuse - as said above!!

They fracture and look fine, but they're usually not! The tacho not working is the clear sign, so jump start it first and see. 10 minute job to change the fuse!

Best of luck! Fingers crossed!

Rob

[greenm]

Yep big fuse mine did the same showed no charge starting dying. Was hard to see fuse looked fine but when I ran a test over it no continuity it had cracked in the middle all was fine after!!

[Mad Mark]

Just out of interest whats the alternator from?

[TDFPELTD]

Range Rover 3.9 V8 if memory serves.

Here's the kaput one from mine showing part no etc. :



It's not a hard job to change it, here's mine in pieces.