Negative earth....... or not.

[MikeBee]

hi, in haste I recently connected the battery the wrong way round! only for a second or two. The only evidence seems to be that the ignition light is permanently on now - even with the key out. It goes out when the engine starts but it doesn't seem that the alternator is charging now.
What should I consider doing to recify my error?
Thanks.
ps it's a 1973 Pus 2 S 130/5 in long term restoration.

[Hawksfield]

Hi Mike

You have probably damaged the surge diode or the main diode's on the alternator

Unplug the alternator and seem what difference there is, trial and error.

[TimMullen1]

Which ground is the car - negative or positive ground?
Alternator or Generator.

If it's a generator, I seem to recall a procedure to "set the grounding" of the generator. Something about running power through the generator in the proper direction to get things "started". Maybe you need to re-initialize the generator.

Or course none of this has anything to do with an alternator equipped car.

[c42]

That's unfortunate but nothing an exchange alternator will not solve.

Regards
john

[ricarbo]

I'm not sure what a surge diode is in this context, so far as I know there isn't one. But reverse connection is a classic way to destroy the electronics in an alternator. It will allow the unrestricted current from the battery to flow through the alternator to earth. and this will blow the diodes which are in the alternator to rectify the alternating current to a direct current of the appropriate polarity. The remedy is to replace the blown diodes. Depending on the alternator make and model, a new diode pack may be available, but the voltage and current regulator electronics may also be destroyed. It may well be that an exchange alternator is the cheapest option, depending on the price and availability of the electronics packs for the particular alternator.
regards
richard

[englishmaninwales]

Hmmmm.. looks like I was lucky as I did the very same thing last week, but all seems to be OK!
Malcolm

[Craven]

Hi,
Lucas ACR range of alternators incorporate a surge protection device, an avalanche diode.
Arranged to protect the transistors in the regulator circuit from the high transient voltages that can occur by faulty connections or removal of a battery lead when the alternator is running.
This device is of no help in your reverse battery polarity situation.
Ron.

[Chancer]

It will most likely be the regulator that is damaged.

Reversing the polarity will not destroy a diode, their sole function is to allow voltage to pass in one direction and not the other, however any unprotected transistor in the regulator circuit will die immediately if reverse biased.

A diode failure usually manifests itself with the battery rapidly discharging through the alternator windings when the engine is switched off.

[MikeBee]

Thanks for all of the comments.

I think that a replacement alternator is the most effective way out of this and have ordered one.
It should be a reasonably quick fix and at least I'll know it shouldn't need any attention for a good long time!

Regards.