Alternator Failure, Voltage Spike. Beyond Economical Repair?

[JohnWest]

My dad was driving along when his dash lit up like a Christmas tree. He pulled over and switched off, except it took a few presses of the button for it to switch off. He then tried to switch it back on, but nothing. It was dead - no lights, no sound, nothing.

Being totally dead, he suspected the battery was flat and called a friend and him to bring some jump leads. The leads were hooked up and left for about 10 mins, he tried to start again and still nothing. He got the car towed home, a mechanic neighbour friend took a look, put a multimeter across the battery and saw a reading of the square root of jack. At this point they thought it only required a new battery so a new one was bought and fitted, tried to fire it up and nothing happened.

It got recovered to a (non-Ford) main dealer (where neighbour works), they've spent a few hours on it and this is their findings:

- With terminals connected to battery, voltage drops to zero
- All fuses/connectors removed in engine bay, one by one, no power returned
- Terminals from alternator and starter motor disconnected, very small amount of power returned
- All fuses removed from internal fuse box one by one, still no power returned
- Removed 3 main connectors on right hand side of fusebox, full power returned
- Suspect issues with alternator and fault in wiring harness to internal fusebox

They think the alternator is the root cause, the electrical system has spiked and has caused these issues. Not having the Ford specific equipment and wiring diagrams, they can't take this any further. The local Ford workshop are full until middle of January.

The opinion of the mechanic was that it's probably beyond economic repair.

The car is a 2010 Focus TItanium, 1.6 tdci. It's done 92k miles and last year had new cambelt and water pump and a full service last month. Looking at similar cars on AT, a fully working one seems to be worth around £2.5k.

Does anyone have any experience of a repair of this nature and can comment on rough cost? This information will help decide the next step:

i) Fix the car
ii) Break the car
iii) Sell as a non runner
iv) Call the scrap man

Thanks for reading, any help much appreciated.

[Krikkit]

Get an alternator and used battery on eBay/scrap yard, which will be a hundred quid total, fit and see what's what.

[LimSlip]

JohnWest said:

- With terminals connected to battery, voltage drops to zero

Where is the voltage being measured where it drops to zero? It can't be at the battery terminals unless the new battery is also dead. Zero volts on a good battery means there would be smoke and flames.

[Limpet]

I would be looking for a good independent automotive electrician, if it were my car. You should be able to get a rough diagnosis for the cost of an hour's labour (£80-£100), and then be able to have an informed discussion around options for repair.

Without knowledge and the right kit, you are relying on pot luck to find the problem. You might get lucky throwing secondhand parts at it, but it's unlikely.

In my experience, a main dealer will relieve you of £150 to tell you it needs £3,000 spending to repair it. Sister-in-law had it with her Corsa after a similar experience. They quoted £3k for a new ECU, various sensors and other parts. A local automotive electrician looked at it properly and found a broken wire in the engine loom. £80 repair.

Edited by Limpet on Friday 18th December 10:03

[inkyhands]

Had a similar issue last year with my focus and it was the instrument cluster, the immobilizer is built into the cluster, and they suffer from dry joints that need re soldering.

Try clearing the codes and also banging the top of the instrument cluster.

Mine cost around £100 to have re soldered.

Might not be your problem, but it's a known fault.

[Tankrizzo]

Surely if the battery is new and fully charged then it can't be the alternator? This sounds like a VERY obvious question, but they've checked all the main engine bay fuses?

[JohnWest]

Thanks for all the replies. I think it's probably worth looking for an automotive electrician going by these experiences, if anyone can recommend one in the north Wales area I'm all ears.

LimSlip said:

Where is the voltage being measured where it drops to zero? It can't be at the battery terminals unless the new battery is also dead. Zero volts on a good battery means there would be smoke and flames.

Tankrizzo said:

Surely if the battery is new and fully charged then it can't be the alternator? This sounds like a VERY obvious question, but they've checked all the main engine bay fuses?

I'm not sure where they measured between sorry, where they measured across wasn't in their report. Though when I had a quick chat to the mechanic neighbour yesterday he suspects the new battery may also be toast now as it was connected up when he suspected the original battery to be at fault.

The report reads like all the fuses were checked though it's not explicitly stated.

inkyhands said:

Had a similar issue last year with my focus and it was the instrument cluster, the immobilizer is built into the cluster, and they suffer from dry joints that need re soldering.

Try clearing the codes and also banging the top of the instrument cluster.

Mine cost around £100 to have re soldered.

Might not be your problem, but it's a known fault.

That's good to know, thank you. When I find an auto electrician I'll mention that to him/her.

If the car can be repaired then maybe this wretched year won't get any worse, though who knows! Thanks again for the replies and suggestions.

[anonymous-user]

If the battery is connected, and it's output voltage drops to ZERO, then there is a HARD short between the positive 12v side and chassis ground! A car battery, well a decently charged one in good condition, can put out the best part of 1000 amps if shorted, and that current has to be going somewhere. Normally there is a main fuse on the +ve battery terminal that blows in this case (normally caused in a serious crash when the cable to the starter motor gets crushed by the engine and shorts to chassis...)


Now, there is pretty much only one thing that can shunt 1000 amps to ground without itself immediately going POP and that is the alternator, or more precisely, the rectification diodes in the alternator. If these fail short then they will effectively clamp the +12v to chassis ground, causing the symptoms you describe.

So:

1) remove the large +ve lead from the alternator, and measure using a multimeter set on "diode test" mode, between where that connection comes out the back of the alternator and the alternator body (chassis earth) i suspect you will find it measures 0 volts, ie a dead short....... Fix is a new alternator.


2) Disconnect as much of the fuse box as your can, ie remove fuses and connections, and ideally using a current limited power supply (rather than the battery that will evapourate anything it can) slowly reconnect and repower the car harness bit by bit

Hopefully, if it was just the alternator diodes failing short then this will actually have prevented damage to other more sensitive electrics/electronics, and the car will pop back to life :-)

[anonymous-user]

BTW, should have added that the alternator diodes can be "killed" by an initial gross short somewhere in the system, pulling too much current from the alternator, which is driven by the engine so won't stop spinning. That short however will be somewhere fairly "high up" ie towards the battery / main fuse box, because it must be low enough resistance to pull enough current to damage those diodes, ie hundreds of amps.


Modern main fuse boxes include all sorts of trickery, including relays, TVS diodes, fuses and lots of power distribution "Bus bars" etc. It's not un-heard of for the actual fuse box to fail short.

You mention that there are three main power connectors, and removing these (and the alternator feed) stops the short, so you need to identify which of those three is the problem one, and to what it connects, and by a process of elimination work out where the short lies.

Again i cannot stress enough the importance of not doing this with the car's battery supplying power, as it is powerful enough to cause endless further problems if shorted across electrical / electronic items! The alternator going short has SAVED these other items, please don't now blow them all up by reconnecting the battery willy-nilly!!!

[JohnWest]

Max_Torque said:

If the battery is connected, and it's output voltage drops to ZERO, then there is a HARD short between the positive 12v side and chassis ground! A car battery, well a decently charged one in good condition, can put out the best part of 1000 amps if shorted, and that current has to be going somewhere. Normally there is a main fuse on the +ve battery terminal that blows in this case (normally caused in a serious crash when the cable to the starter motor gets crushed by the engine and shorts to chassis...)


Now, there is pretty much only one thing that can shunt 1000 amps to ground without itself immediately going POP and that is the alternator, or more precisely, the rectification diodes in the alternator. If these fail short then they will effectively clamp the +12v to chassis ground, causing the symptoms you describe.

So:

1) remove the large +ve lead from the alternator, and measure using a multimeter set on "diode test" mode, between where that connection comes out the back of the alternator and the alternator body (chassis earth) i suspect you will find it measures 0 volts, ie a dead short....... Fix is a new alternator.


2) Disconnect as much of the fuse box as your can, ie remove fuses and connections, and ideally using a current limited power supply (rather than the battery that will evapourate anything it can) slowly reconnect and repower the car harness bit by bit

Hopefully, if it was just the alternator diodes failing short then this will actually have prevented damage to other more sensitive electrics/electronics, and the car will pop back to life :-)

Thank you for this information. My spannering skills are practically zero, the car is still stricken in the main dealer workshop. While it's there I may ask them to change the alternator and see what happens. If it works, then I owe you a beer. If not, then at least the alternator can be ruled out.

Thanks again for this reply and all other replies.

[JohnWest]

Max_Torque said:

BTW, should have added that the alternator diodes can be "killed" by an initial gross short somewhere in the system, pulling too much current from the alternator, which is driven by the engine so won't stop spinning. That short however will be somewhere fairly "high up" ie towards the battery / main fuse box, because it must be low enough resistance to pull enough current to damage those diodes, ie hundreds of amps.


Modern main fuse boxes include all sorts of trickery, including relays, TVS diodes, fuses and lots of power distribution "Bus bars" etc. It's not un-heard of for the actual fuse box to fail short.

You mention that there are three main power connectors, and removing these (and the alternator feed) stops the short, so you need to identify which of those three is the problem one, and to what it connects, and by a process of elimination work out where the short lies.

Again i cannot stress enough the importance of not doing this with the car's battery supplying power, as it is powerful enough to cause endless further problems if shorted across electrical / electronic items! The alternator going short has SAVED these other items, please don't now blow them all up by reconnecting the battery willy-nilly!!!

With this new information, perhaps I'll get the car back and get the auto electrician to swap the alternator and do this detective work. Armed with this info hopefully it'll be a good starting place for them. Thanks again.

[powerstroke]

JohnWest said:

With this new information, perhaps I'll get the car back and get the auto electrician to swap the alternator and do this detective work. Armed with this info hopefully it'll be a good starting place for them. Thanks again.

Shouldn’t need the alternator connected for a test run
Try the fuses on the battery connection , generally
You have a direct un fused lead to the starter,
Then a alternator fuse , a main fuse that goes to the fuse
Box ..

[andy43]

You can buy diode packs for older cars rather than a complete alternator.
Auto electrician is best bet as alreaqdy suggested.

[Cestrian]

inkyhands said:

Had a similar issue last year with my focus and it was the instrument cluster, the immobilizer is built into the cluster, and they suffer from dry joints that need re soldering.

Try clearing the codes and also banging the top of the instrument cluster.

Mine cost around £100 to have re soldered.

Might not be your problem, but it's a known fault.

+ 1 for the instrument cluster. Very well known and common problem on this age of Focus.

[BUG4LIFE]

I currently have a dead alternator in my Jaguar STR.

Bit different to you OP, as the car is worth a bit more, but I'm trying to decide what replacement option to go with...

- New OEM, which is a chunk of cash. Add labour and I'm looking at a grand.

- Used OEM and hope it lasts a good number of years [used item would come from my Jag specialists contact and comes with 3 month warranty]. Cost is roughly 50% of new, including labour.

- Have my broke alternator repaired [by an auto electrician] and hope they do a good job. I think my Jag guy has had some bad experiences with re-furbed parts though, as this was his least preferred option

I guess you'd have the same options OP. Would a used item not be a good option considering the worth of the car?

Edited by BUG4LIFE on Friday 18th December 13:54

Edited by BUG4LIFE on Friday 18th December 13:54

[Krikkit]

I'd always take a refurb over extortionate OE/aftermarket alternators. A lot of the aftermarket ones are refurb anyway!

If budget or time is tight then used is a good short term alternative.

[Penelope Stopit]

Max_Torque said:

If the battery is connected, and it's output voltage drops to ZERO, then there is a HARD short between the positive 12v side and chassis ground! A car battery, well a decently charged one in good condition, can put out the best part of 1000 amps if shorted, and that current has to be going somewhere

There is no way anyone could apply a dead short across a good battery without noticing it, first of all there would be lots of sparks at the battery/cable terminals, welding would commence and the cables would go into meltdown if someone managed to not notice sparks flying and managed to get the cables battery terminals connected and tightened without burning their hands off

Applying a short circuit across a good battery couldn't possibly drop its voltage to zero, yes the voltage would certainly drop and by how much would be governed by the size of cables with a short circuit, the voltage would then start to rise as the cables slowly burnt out

Max_Torque said:

Now, there is pretty much only one thing that can shunt 1000 amps to ground without itself immediately going POP and that is the alternator, or more precisely, the rectification diodes in the alternator. If these fail short then they will effectively clamp the +12v to chassis ground, causing the symptoms you describe

The diodes in an alternator if going short circuit will then go into meltdown and burn themselves out of the circuit or the whole rectifier pack will melt and possibly apply a dead short from alternator negative to alternator positive which would cause the alternator fuse to blow or if unfused would rapidly get to work on burning out the main alternator positive supply

A Ford Focus Alternator rectifier couldn't possibly handle 1000 Amps, the diodes would have burnt out long before reaching anything close to that much current, the cable supplying the alternator couldn't handle anything close to 1000 Amps and the internal rectifier connections would also fail long before 1000 Amps

[Penelope Stopit]

LimSlip said:

Where is the voltage being measured where it drops to zero? It can't be at the battery terminals unless the new battery is also dead. Zero volts on a good battery means there would be smoke and flames.

As above

Replacement battery is flat or faulty

[paintman]

BUG4LIFE said:

I currently have a dead alternator in my Jaguar STR.

Bit different to you OP, as the car is worth a bit more, but I'm trying to decide what replacement option to go with...

- New OEM, which is a chunk of cash. Add labour and I'm looking at a grand.

- Used OEM and hope it lasts a good number of years [used item would come from my Jag specialists contact and comes with 3 month warranty]. Cost is roughly 50% of new, including labour.

- Have my broke alternator repaired [by an auto electrician] and hope they do a good job. I think my Jag guy has had some bad experiences with re-furbed parts though, as this was his least preferred option

I guess you'd have the same options OP. Would a used item not be a good option considering the worth of the car?

Good quality refurb.
Probably not a lot of help to you due to the distance, but for anybody in the Leicester area have had alternators & starter motors done by Green's of Leicester for our own cars. Sensible prices & never had subsequent issues.
https://leicester.cylex-uk.co.uk/company/greens-12...

[anonymous-user]

Penelope Stopit said:

Max_Torque said:

If the battery is connected, and it's output voltage drops to ZERO, then there is a HARD short between the positive 12v side and chassis ground! A car battery, well a decently charged one in good condition, can put out the best part of 1000 amps if shorted, and that current has to be going somewhere

There is no way anyone could apply a dead short across a good battery without noticing it, first of all there would be lots of sparks at the battery/cable terminals, welding would commence and the cables would go into meltdown if someone managed to not notice sparks flying and managed to get the cables battery terminals connected and tightened without burning their hands off

Applying a short circuit across a good battery couldn't possibly drop its voltage to zero, yes the voltage would certainly drop and by how much would be governed by the size of cables with a short circuit, the voltage would then start to rise as the cables slowly burnt out

Max_Torque said:

Now, there is pretty much only one thing that can shunt 1000 amps to ground without itself immediately going POP and that is the alternator, or more precisely, the rectification diodes in the alternator. If these fail short then they will effectively clamp the +12v to chassis ground, causing the symptoms you describe

The diodes in an alternator if going short circuit will then go into meltdown and burn themselves out of the circuit or the whole rectifier pack will melt and possibly apply a dead short from alternator negative to alternator positive which would cause the alternator fuse to blow or if unfused would rapidly get to work on burning out the main alternator positive supply

A Ford Focus Alternator rectifier couldn't possibly handle 1000 Amps, the diodes would have burnt out long before reaching anything close to that much current, the cable supplying the alternator couldn't handle anything close to 1000 Amps and the internal rectifier connections would also fail long before 1000 Amps

You are missing one important point, that it is POWER and not Current that damages things. Short a car battery into a low impedance load, and the power is actually very low, because the output voltage of the battery is low. The majority of the power is actually disipated in the internal resistance of the battery itself, which for a wet lead acid battery is actually quite high. And because a wet lead acid battery is about 20 kg of material, it can withstand that power disspation for a significant period of time. I've spent a fair bit of time shorting car batteries across various loads as part of a project to develop a 12v electrical boosting system that needed to pul about 3kW of power from a std car battery!

The alternators diodes can easily "withstand" that current because they are not dropping any power, being shorted!

But yes, there would almost certainly be sparks at the terminals, but a lead on lead or lead on brass terminal is actually quite spark and "weld" resistant.

What i would expect to happen however is for the main battey "fuse" (generally a fuseable link) to blow at some point, as it should be rated to blow under exactly this condition!