OOOPS what damage have I done?

[tr666]

I swapped out my battery earlier today and in doing so I placed the metal hold down strap on the front of the engine. The strap came to rest on the inlet manifold and the alternator casing. On reconnecting the battery...I forget which lead I did first +ve or -v...I noticed smoke coming from the alternator internals. I remove the battery lead and the smoke ceased. What damage have I done?

[waterhouses]

I swapped out my battery earlier today and in doing so I placed the metal hold down strap on the front of the engine. The strap came to rest on the inlet manifold and the alternator casing. On reconnecting the battery...I forget which lead I did first +ve or -v...I noticed smoke coming from the alternator internals. I remove the battery lead and the smoke ceased. What damage have I done?

 

Sounds like you have shorted the alternator & in doing so cooked it, new alternator required.

[Mike Collins]

The alternator casing would be at the same potential as the manifold, ground surely?

 

Did the strap touch the alternator terminals? they should be insulated. Alt and manifold are on opposite sides of the engine to each other. Was the battery polarity correct? That could hurt the alternator electronics.

 

If you disconnect the alternator and reconnect the battery does everything apart from the charging circuit look ok?

[Eyetee]

with a bit of luck nothing.

As a rule I was told to always connect the negative terminal last and disconnect the negative terminal first, I understand that the negative terminal is where the action is.

The smoke could have been a short caused by the clamp earthing out the alternator, best reconnect, put voltmeter over the battery (should be around 12.5 volts), then run the engine and put a voltmeter over the battery again (should be around 13.5 volts). Assuming the loom is correctly tied down, this will prove battery is charging.

 

A car with an alternator has a negative earth, dynamo is positive earth, this mightnt be hard and fast but its my rule of thumb. Most of the time the terminals and plugs are different sizes.

[jean]

In my case the smoke came from the cooked diodes, was very cheap to replace at the time, But alternators are sooooo cheap these days, probably less expensive than 1 hour of labour from an electric shop