Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - How to Install an alternator cut-off ("kill") switch on a 1998 Honda Civic

OneOfFew · 05-24-2012, 10:06 PM

Today I thought I had it figured out.

I verified again today that if you disconnect the Alternator fuse while the engine is running the alternator voltage will drop into the 12v range. Because of this I wired my circuit to switch power to the fuse and installed a new circuit for all the engine sensors that are also powered by the alternator fuse. Not too difficult, just some rewiring. After I finished this I tested the circuit and... ...it didn't work. I unplugged the fuse completely removing power from the alternator circuit and it still didn't stop the alternator from making 14.2v. I was baffled for about 30 mins. I could not understand, I tested it just an hour before, removing the fuse kills charge voltage.

Then it hit me. To verify my hypothesis I tested the voltage on the blk/yel wire going to the alternator, it had 3v! The alternator was putting 3v back on the line the only difference now was the engine sensors were not there to eat the power. I grounded the wire with 3v on it (fused of course) and bam, charge voltage dropped to the 12v range! It appeared to be unstable though. It was jumping up and down by about a volt. I think by doing this it makes the regulator go crazy. Even though it seemed to functionally kill the alternator I decided it was too unstable to use. I don't want to kill the regulator prematurely.

tomorrow I will be trying a 4pdt relay to switch all 4 plug wires. If this fails I have a 70a 1" cube relay I can tie into the power out.

I guess the only reason I'm telling anyone what's not working for me is so it's not repeated by future readers.

05-24-2012, 10:06 PM	#47 (permalink)
OneOfFew EcoModding Lurker Join Date: Jul 2011 Location: Greensboro, MD Posts: 17 Civic HX - '96 Honda Civic HX 90 day: 40.05 mpg (US) Thanks: 4 Thanked 12 Times in 6 Posts	Today I thought I had it figured out. I verified again today that if you disconnect the Alternator fuse while the engine is running the alternator voltage will drop into the 12v range. Because of this I wired my circuit to switch power to the fuse and installed a new circuit for all the engine sensors that are also powered by the alternator fuse. Not too difficult, just some rewiring. After I finished this I tested the circuit and... ...it didn't work. I unplugged the fuse completely removing power from the alternator circuit and it still didn't stop the alternator from making 14.2v. I was baffled for about 30 mins. I could not understand, I tested it just an hour before, removing the fuse kills charge voltage. Then it hit me. To verify my hypothesis I tested the voltage on the blk/yel wire going to the alternator, it had 3v! The alternator was putting 3v back on the line the only difference now was the engine sensors were not there to eat the power. I grounded the wire with 3v on it (fused of course) and bam, charge voltage dropped to the 12v range! It appeared to be unstable though. It was jumping up and down by about a volt. I think by doing this it makes the regulator go crazy. Even though it seemed to functionally kill the alternator I decided it was too unstable to use. I don't want to kill the regulator prematurely. tomorrow I will be trying a 4pdt relay to switch all 4 plug wires. If this fails I have a 70a 1" cube relay I can tie into the power out. I guess the only reason I'm telling anyone what's not working for me is so it's not repeated by future readers.