Alternator outputting 16V

[mike_ie]

I was watching my volt meters today while driving, and I noticed that the voltage seemed higher than usual. Once back home I cranked it up in the shed, and took the following readings:

Normal Battery Voltage (engine off): 12.92V
Engine at idle: 13.77V
Engine at 2000RPM: 16.15V!!

Basically the more you gun the engine, the higher the alternator output. So what's going on? Is the regulator on the alternator buggered? Or am I missing something??

[justinc]

Mike,

Definately a reg problem, I just had the same with a 1995 110 last week. Complained about having to add water to the battery continually, Boiled his battery almost dry within a month apparently:o

I replaced the whole unit with a Disco 100 amp one, killed 2 birds as the standard unit on Defender Tdi is only 65A.

If you DO go this way, you will have to fit another length serpentine belt if your Defender is prior to 1996, as the pulley diameter is smaller on the new ones I have been buying lately. You can change the pulleys over, but on some replacement alts the shaft size varies aswell. The belts are 1595mm long (early), and 1580mm long (later, 1996 on).

JC

[stig0000]

engine??? old or new car,

[Blknight.aus]

doesnt matter its one of the internal parts of the voltage regulator shorted out so the voltage sensor is no longer working and the only thing limiting the alternators output voltage is the amount of energy in the alternator (how many RPMS its doing) and the load applied to it.

In a nutshell theres nothing telling the alternators exciter winding to back down so its just working with the full output voltage of the alternator which means in a no load full speed situation it could push better than 400v out of the output windings (or whatever the upper voltage limit of the rectifying diodes is)

[mike_ie]

Mike,

Definately a reg problem, I just had the same with a 1995 110 last week. Complained about having to add water to the battery continually, Boiled his battery almost dry within a month apparently:o

I replaced the whole unit with a Disco 100 amp one, killed 2 birds as the standard unit on Defender Tdi is only 65A.

If you DO go this way, you will have to fit another length serpentine belt if your Defender is prior to 1996, as the pulley diameter is smaller on the new ones I have been buying lately. You can change the pulleys over, but on some replacement alts the shaft size varies aswell. The belts are 1595mm long (early), and 1580mm long (later, 1996 on).

JC

As always, thanks for the indepth information. You had mentioned before about replacing/upgrading it with a disco unit, and I was going to ring around tomorrow. Just out of curiosity, and if you don't mind me asking, how much are we talking for a 100A alternator???

[Tank]

Around $300/330, Regards Frank.

[mike_ie]

Thanks to everyone here for the replies. It was definitely the regulator - I soldered in a new 12v regulator to the regulator block and it worked fine again. Considering the recommendations I was getting, I bit the bullet and bought a Marelli 100A alternator - the Disco standard. Should be arriving today and I'm looking forward to seeing the improvements over the old one.