About 3 years ago I purchased an alternator from a local shop and asked for a 200amp alt. The shop modified an alternator and I picked it up. When I'm driving around with the heater, headlights and fog lights on the volts are between 13.9 and 14.2. When the truck is at an idle I see 12.8 to 13.0 with everything turned on. Is this normal? And sometimes the volts will drop to 13.2 to 13.6 or so for a couple of minutes while driving with nothing turned on. Is this also normal? I added a 2 gauge wire from the alt to the passenger battery when I installed the alternator and also between both batteries.

 

perfectly normal. The alternator supplies the demand up to capacity, when the demand is lower, so is supply. It's also tied to RPM, low RPM and the alternator may not put out all the required voltage, the battery may be carrying a small load. RPM goes up, charging voltage goes up... every bodies happy.

Clean all the negative ground cables at the attachment point, battery to frame, frame to block, block to body. Small amounts of corrosion can and will hinder current flow at the attachment point... remember current flows from negative to positive. It starts at one of the negative grounding points and flows toward the negative terminal.

missing my cup of coffee in the morning always leads to a bad start for the day, I and my batteries need all the help we can get!

 

Thank you Randy! Thank you for the tips on cleaning the connections for the negative cables. I always keep the battery terminals clean but never thought of the other side of the cables. Enjoy your coffee!

 

Yeah, I never thought about that until now either. I think its cause of "out of sight out of mind". You don't see the other end of the lines connection to the frame or block.