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Bosch Alternators, Excitation

PostPosted: Wed Apr 06, 2016 1:29 pm
by DougB
I have a Bosch 120 amp Alternator, model BXU12121a that I want to regulate using a SAR V3. The standard internal regulator can be replaced by a Bosch brush holder with DF terminal suit for use with external regulars.
I understand this and most that Bosch alternators are not self exciting and excitation is achieved via the power applied to to D+ terminal via connection with 2 watt lamp to ignition .
The wiring diagram of the SAR V3 only shows 3 connections required from the alternator I.e. -
Alt B+ to battery positive
Alt Ground to battery negative
Alt D Field terminal to SAR V3

My questions are -
1. Are you aware if any other alternator modifications are required other than swapping to a simple brush holder?
2. Can you confirm Ample SAR instructions for only connection to the alternator as shown above and that no additional wiring is required wrt to initial excitation of the alternator and D+ is left unused etc.
3. I expect full load output cause belt slip. Is it satisfactory to de-rate the output semipermanently using the SAR until I fitted serpentine pulley arrangement .
Thank you.

Re: Bosch Alternators, Excitation

PostPosted: Wed Apr 06, 2016 4:18 pm
by Coulomb
The D+ wire to the charge lamp is not used.

As long as you ground one end of the field and connect the other end to the regulator, it will work.

You can set current limiting on the regulator to what ever you want. With a good belt, good wrap around the alternator sheave we wouldn't think you'd have slip.