Alternator charging advice

[ram250098]

I have been having a charging issue. I have underdrive pulleys on the car and at idle I was getting 10.5 volts and when running the car it would go up to 13.5 volts. Problem is I couldn't drive at night with the lights on while at a stop light.
I changed the alt pulley from a 3 1/2 to a 2 1/2 and now at idle it is 12.5 volts and when I rev the engine it jumps to 16 volts and higher. I really can't afford to change all the pulleys if that is my problem.
Any advice. I have checked the alt and voltage reg and both are good.
Thanks
AL

 

[cudajim]

It should never jump to 16 volts under any condition regardless of size of the pulley. You're not regulating properly and/or you may have bad grounds causing this condition. Check the ground connection at the regulator and the back of the engine to firewall. You should never be reading over 14.2 volts DC if the system is working properly.

 

[ram250098]

Thanks for the reply Jim. I had another old alternator in the garage, was not sure if it worked or not...but I swapped it out anyway to try it.... My readings are now 12.5 at idle and with the engine reving it does not go above 14 volts but holds above 12.5 with lights on.
When the shop changed the pulleys could they have damaged something inside the alternator? Maybe I will have them check it again.
Thanks
AL