I make a hobby out of improving my gas mileage wherever possible and safe. I have an Optima Yellow Top D34 battery and a 6 month old alternator if that matters. One thing I have been experimenting with is disabling the alternator with a switch when accelerating and cruising with no accessories, and enabling the alternator when coasting in gear in decel fuel cut off or when braking. I can actually noticeably improve my gas mileage from reduced drag, My question is will this damage the alternator? The battery is deep cycle so it should not be damaged. I am mainly concerned about the alternator wearing out from being enabled and disabled so much. Thanks in advance!

 

No you don't. Do not do that. What car do you drive? Example. The 1996 Honda Civic has a built in voltage sensor in the fusebox. During normal highway driving, the alternator fields itself low, producing like 11.5 Volts opposed to 13.5 Volts during warm up. See, Honda already thought of this and when your battery is charged back up, it does this electronically. By doing it yourself you risk causing wider electrical problems, Ive not tested it but I would guess the sparking might damage the alternator, ecu, any corodded terminal and possibly your expensive new battery. All 2000+ Hondas have some varient of variable alternator output, the newer cars having a more variable version of this. Trust me if this would give more power and up 2mpg, Honda would have already done it if it were safe.

 

The honda alternator already runs in a low output mode to save gas when accessories aren't on. No need to do anything else. You just don't notice it cause manuals don't run in low output at idle so you can't really check it unless you use a cigarette lighter voltage tester.

http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1011&context=auto_pres

 

Thank you for the reply. I have a 2005 Civic and I am well aware that it has an ELD. But I do not think that it is working because the voltage always stays between 14.1 and 14.4 volts on the highway with all accs off, according to my Scangauge 2. When should the voltage be dropping? Does it only do that at a certain speed or something? Thanks again.

 

did you click on that link yet ?

"vehicle speed between 10-45 mph or at idle while in drive"

you can pick up a cigarette lighter plug voltage tester, plug it in and watch it while you drive around after the car is warmed up

 

Thank you, I did not even notice the link lol.