Alternator Shaft Speed

[petert 586]

After fitting a new logging dash and having the ability to accurately monitor battery voltage, I've discovered it's not charging very well at race speeds. It starts off the day with a constant 13.8V after a night on the charger. It's happy as Larry idling or driving around the pits. As the days goes on however, the voltage slowly drops. At the end of 5-6 slaps, it's typically putting out 13.1V and harder to restart later.

 

I'd assumed the battery was slowly dying, but some googling suggests the maximum alternator shaft speed should be 16000rpm max. Some calcs suggest I'm typically 13500 to 17800.

 

Has anyone else experienced this?

[j_turnell 137 3 Cars]

Had similar issues on a Caterham RST, was running a Mountune lump x2 1000cc bike heads on a custom bottom end making it a v8. Was revving to around 10k and the alternator couldn't handle it, ended up fitting a Brise alternator IIRC and was fine after that.

 

Pug1off make a 30mm reduced bottom pulley for the RS lump to help reduce alternator rpm.

[welshpug 1,657]

Must be why Sandy's engines tend to have a Satchell pulley kit

 

http://www.ebay.co.uk/itm/106-GTI-SAXO-AX-16V-MOTORSPORT-ALLOY-CRANK-PULLEY-KIT-/121078735027

 

or just the alternator pulley.

 

http://www.ebay.co.uk/itm/68MM-RACE-RALLY-LIGHTWEIGHT-ALLOY-ALTERNATOR-PULLEY-/121078735024