slow305

iTrader: (2)

I've been searching here and can't come up with anything that will solve my problem.

Car is a '90 Formula with an LB9. Went to drive it last night and noticed the voltage was just above the red zone when the car wasn't moving. 5-10 seconds after I got up to speed, the volt meter moved to the normal position, and every light on the car got brighter. When I came to a stop, the volts dropped back down, and everything got dimmer. I drove the car home, did some searching here and figured it was the alternator.

Bought a re-manned alternator from Advanced, and I still have a problem with low voltage. I tested the voltage off the battery with the car off, and it was 12.16, and it was about the same reading with the car running. Off the connection on the alternator directly from the battery, and it was a little over 12, too. On the connection at the top of the alternator, the larger pin was 12, too.

During all this fiddling, I noticed that my fans don't run anymore. When I bought the car, the fans were hooked up to run full time, even when you click the ignition to just accessories. I even unhooked the fans and started the car, and the volts were still low. Is there some fusible link somewhere I should check? (The diagrams in my Helms manual make my head hurt.) Help me keep from paying $60/hour to have some gimp monkey on it!

Pat

cronsformula350

theres a fuse in the fuse box called "fans" check that, if that fuse is gone, your fans won't run, and the alternator won't get a signal to the field wires, which tell the alternator to charge. So basically, your car is running off the battery. Check that fuse, then come back with more info.

Danno

First, charge the battery. At 12.1 volts it's technically in a state of discharge. Any testing you do is moot with a discharged or defective battery. The fact that the lights got brighter does indicate the old generator was working somewhat. On the top plug, one wire should read 12 volts all the time, the other will read a little lower and is key controlled. That wire is the "sense" wire the previous post referred to. It is used to turn the gen on and off. After you fix the problem wire the fans back to stock. They will cause premature failure of the generator if left running all the time. The generator is simply not capable of running the car and all accessories with both fans on all the time. It causes failure of the rectifier bridge and overheating of the alt. One question, is it worse with the new gen? Remember to always disconnect the battery before changing the alt. The gen can be damaged by false biasing if it is changed with the battery hooked up. Also, there is a fusible link between the gen back post and the battery. Average charging battery voltage on cold start up should be between 13.5-15.0 volts.

cronsformula350

That fusible link hardly ever pops, I bet its the fuse in the fuse box. Oh yeah we don't have generators anymore, there alternators. Generators made dc current, and had no rectifier to convert the current, as in an alternator, the current made is "alternating, or AC" like house current, so the rectifier bridge converts the voltage back to dc, this also makes the alternator more efficient. The fact that his lights were getting brighter, tells me, that his regulator is more sensitive even without the sensory field wires telling the alternator to charge the battery. He's running off the battery right now. Some batteries put out up to 13.8 volts without a load also, so you know the cars using power.

slow305

iTrader: (2)

It was the fuse. Or what was left of it. Checked the fuse panel tonight, and the "Fan" fuse wasn't there. Peered a little closer, and it looked like the old fuse had just melted away. I pulled out a couple metal fragments, cut away a bit of melted plastic, put in a 20 amp fuse and turned the key. Immediately there was a small flash from the fuse area. Turned the key off and crawled into the footwell again -- everything appeared OK, but when I pulled the fuse out of the "fan" slot, it was blown.

Soooo, I popped in a 30 amp fuse from the "Lid" slot (it looks like every fuse is over the recommended amp ), clicked the key -- no spark -- and fired the car up. Wa-la! The voltage meter on the dash climbed to 15 or so. I let it run for a few minutes, and everything appeared to be OK.

Now I'm just wondering when the old fuse blew and why I didn't smell burning plastic.

I guess next step is to figure out how the fans are wired so they don't run all the time, or at least disconnect one (it would be nice to have them run all the time while autocrossing, though, especially considering a friend of mine will be co-driving with me).

Thanks for the help, guys!

Pat

cronsformula350

See I know what I'm talking about, I had a similar problem on my 89 formula, and I consulted the archives, and thats how I fixed myne. Except I put a new regulator in my alternator, because everything else appeared to be fine. You can have both fans running, but only for a short period of time, or the fuse will continue to blow. I have my passenger side fan running all the time, with underdrive pulleys, 51% crank, and 23% alternator, and I never had problems with voltage, except at idle, so basically you don't let the car idle forever, and your fine. If I were you, set up a relay off the battery, and use a fuse right off the battery, and run a switch into the car, and then you can turn on the a/c fan whenever you need to.

Danno

Pat there is still a problem, there is no reason for that panel fuse to melt. Perhaps the guy wired the fans right off that circuit-that would do it. That fuse feed the fan relay coils and the generator, it rarely if ever fails. The fan motors normally get thier power from the contact side of the relays which gets power directly from the battery thru a fuse link. I have seen all sorts of hack jobs, you need to check it out. The generator need very little current to run it, in some applications the 12 volts actually is fed thru a simple bulb circuit. Generally cavity fuses if they are run very close to thier rated value will get hot and eventually fail. I would eventually do some more investigating before you wind up with a more serious problem.