Generator Failure?

[seatkid]

Ahem........don't try to do resistance measurements on the main supply, I will not be held responsible for fried swedish meatballs! :rolleyes:

 

Ola needs to....

 

1. disconnect battery and discard.

 

2.Remove fuse box, inspect cables and their connections to fuse box for damage and condition (along entire length), clean connections thoroughly..if they are badly burnt get new cables/connections.

 

3. Install new fuse box ensure connections are made up tight and sound.

 

4. Install new battery, connect positive terminal only temporarily while keeping an eye on the fuse box. If there is evidence of a large current drain, or the fuse box gets hot, remove battery connection immediately, disconnect alternator and try again. (I doubt this will be necessary)

 

5. Connect a VOLTMETER to the battery, start the car and check the battery voltage - should be between 14 volts and 14.6 volts. A lot more and the alternator could be faulty. A lot less and you probably have an electrical problem in the wiring.

 

Don't drive away until you're happy everything is OK.

[Smilge]

Ahem........don't try to do resistance measurements on the main supply, I will not be held responsible for fried swedish meatballs! :rolleyes:

 

Never mind Ahem ....... battery should be disconnected anyway and what your suggesting when everything's connected back up .... by the time the new fusebox has started to emit smoke its too late. Might be worth finding where the short is first before connecting everything up thats why I suggested testing the alternator feed to earth first. Seen it ...done it.

[mumof4]

all depending if there is a short in the alternator..WE dont know yet if there is a problem with the alt.

 

It may be that all that is needed is a new box and cable..oh and battery...def replace the cable...dingo has had this happen to him as have i.

 

if when all connected up every thing looks fine..you should keep checking it to see if it is overheating again....the drop of water trick is good.

[ola]

I took my multimeter and measured the impedance between the

junction melted away and the chassis and it was an open circuit.

Meaning that there is no short between the connection to the

alternator and the chassis. I suspect a faulty alternator - open circuit

in this must mean a destroyed winding, am I right?

[seatkid]

I took my multimeter and measured the impedance between the

junction melted away and the chassis and it was an open circuit.

Meaning that there is no short between the connection to the

alternator and the chassis. I suspect a faulty alternator - open circuit

in this must mean a destroyed winding, am I right?

No.

 

For the technically minded among our readers..... the output of an alternator is via 6 diodes arranged in a star 3 phase configuration. Therefore to get a short between the output and ground you would require two of the diodes on opposite side of the bridge to fail short circuit. This is highly unlikely. Measuring with an ohmeter would, depending on the meter show open circuit in one direction and medium "resistance" to open circuit in the other direction - this depends on the meter and the voltage it uses to measure "resistance".

 

Translation for plebs.... "You can't measure an alternators health with an ohmeter..." :rolleyes:

 

There are two common electrical failure modes for alternators, both as a result of the inbuilt regulator failing. Depending on which slip ring brush wears out first.

In one instance, it fails so you get little or no output from the alternator. In the other, and a remote possibilty here, is it fails so that the alternator loses regulation and wacks out maxiumum output current all the time, you will know this is the case when all your lights get very bright and the battery gets very hot and starts to boil, possibly leading to thermal runaway, a disastrous situation where the battery will literally explode. :D

 

OLA - measure the disconnected battery voltage (after the battery has been stood a while) - if it is less than 11.0 volts, one of the cells has failed (probably short circuit). This will have led to overheating of the poorly assembled fusebox connections as the alternator attempted to charge it up with 120amps. BTW the fuse link is rated at 150amps, in practice it will pass 300 amps for several seconds before popping. Those connections should not get hot even at 300 amps.....its a manufacturing defect, either the crimps are poorly executed or the bolts were not tight enough. Probably the crimps are faulty if you ask me, so you may need new leads to avoid this happening again.

[ola]

Perfect explanation, thanks.

[ola]

A photo of the fuse box for the interested...

[ola]

and the photo...

[insider]

The same Service station can

[mumof4]

Your pic is sooo familiar ola...........i really do hope that you get it sorted out.

[ola]

Battery disconnected and charged, now 12,72V

 

Fuse box replaced and all connections properly cleaned and reconnected.

 

Battery connected, Ignition key turned to first position - battery lamp on and then turned off.

 

Ignition on - engine started, voltage over battery 13,84V regardless to load.

 

Cable to alternator gets warm after a couple of minutes, so warm that I can

[insider]

<* Sigh *> why on earth is the cable warm?

Too much current going through it. You need to find out where the extra current is going to isolate the fault.

[mumof4]

Did you replace the cable or is it still the original one?

[ola]

It

[ola]

My dear Ford Service Station don

[insider]

It

[mumof4]

It was recommended to replace the cable aswell....I know when my cable was replaced the mechanic made one up...You could do this your self..if you show the garage the cable you are on about and tell them you want it replaceing..they should do it...new cable and new connections and all should be well.

As insider has said..the cable is the problem and needs to be replaced

[seatkid]

The cable may be in poor condition, but with no electricals (lights etc) on, it shouldstill not get hot.

 

The alternator is pumping out max amps but not managing to reach the correct terminal voltage which is about 14.5 volts.

 

Your battery is dead, on charge it should easily rise to 14+ volts. 12.72 indicates a shorted cell.

 

You need a new battery.

[mumof4]

But he said the cable got warm with the ignition on..so there were electricals on.

I still reckon its the cable.

[seatkid]

Believe me.....I'm a doctor........ :P

[insider]

The way ola's post reads, the battery voltage was 12.72v disconnected. This rose to 13.84v while the alternator was running. If 14.5v is expected, a faulty cable could easily be dropping the 0.66v voltage difference across it (14.5 - 13.84). Therefore, I think he should eliminate the cable first by replacing it with new then assess the situation with the battery afterwards.

[caiss4]

Been following this thread.

 

I noted that ola said that when he turned on the ignition the battery (ignition) light came on and then went off; it shouldn't do that, it should remain on until the engine is started and there is a charging voltage on the battery (which there clearly is as when the engine is running he has 13.7V across the battery)

 

The question I have is what is the battery terminal voltage when the ignition is switched on but the engine not started? The fact that the ignition light goes out suggests a major current drain from the battery lowering the battery voltage - hence the light goes out (although this would be extreme as experience says the light dims before it goes out altogether)

 

The battery voltages he's measured seem to be OK but the 12.72V is without load - measuring the voltage with ignition on should introduce some load but the reading shouldn't drop below 12V. The engine running voltage is a little lower than you'd expect (no load I'd look for about 14v at idle) and so insider could be correct, there's a voltage drop in the cable possibly made worse by a defective battery as seatkid suggests.

 

Looks like replace the cable anyway and replace the battery - can you borrow one to test?

[Smilge]

Having had a little break from this post I'm really confused now ......

 

For the technically minded among our readers..... the output of an alternator is via 6 diodes arranged in a star 3 phase configuration. Therefore to get a short between the output and ground you would require two of the diodes on opposite side of the bridge to fail short circuit. This is highly unlikely. Measuring with an ohmeter would, depending on the meter show open circuit in one direction and medium "resistance" to open circuit in the other direction - this depends on the meter and the voltage it uses to measure "resistance".

 

Agree .....

 

Translation for plebs.... "You can't measure an alternators health with an ohmeter..."

 

Oh yes you can ......

 

Those connections should not get hot even at 300 amps

 

So they're super conductors then?

 

Battery disconnected and charged, now 12,72V

 

Sounds good!

 

Ignition on - engine started, voltage over battery 13,84V regardless to load

 

Sounds good too!

 

Too much current going through it. You need to find out where the extra current is going to isolate the fault.

 

Agree ..where is it going?

 

connections, etc. will increase proportionately with resistance. Power dissipation = heat.

 

Yep agree with that too.

 

The alternator is pumping out max amps but not managing to reach the correct terminal voltage which is about 14.5 volts.

 

If that was the case then the voltage regulator's knackered ....... No more than 14 Volts ...... 13.8 is Good.

 

Your battery is dead, on charge it should easily rise to 14+ volts. 12.72 indicates a shorted cell.

 

12.72 with the battery disconnected ........ OK

 

there's a voltage drop in the cable possibly made worse by a defective battery as seatkid suggests.

 

Bingo!!!! ...arr but short circuit battery cell ...no voltage drop.

 

Captain we have a cell in the battery gone short circuit allowing maximum current flow through the dilethium crystals ...... too much current !!! ..... she cannee take it! Arrrgghhhh! The heat produced has melted the cable and fuse box! ........ Change the cable too Scotty! Aye Aye captain!

 

Oh missed this bit ..........

 

noted that ola said that when he turned on the ignition the battery (ignition) light came on and then went off; it shouldn't do that, it should remain on until the engine is started and there is a charging voltage on the battery (which there clearly is as when the engine is running he has 13.7V across the battery)

 

The reason the light comes on is to indicate the excitation voltage thats being sent to the alternator to get it going ...... once it receives it, it self excites once rotating, and the light goes off. This is part of the voltage regulator circuit and will indicate a charging fault whilst the alternator is being driven.

Edited August 14, 2007 by Bleeno

[ola]

caiss4, you

[Smilge]

caiss4, you