Lotus Elan

Generator or tach dying?

PostPost by: collins_dan » Sun Oct 11, 2009 7:39 pm

I have been trying to install a digital rev limiter on my S4 in a way that won't interfere with my tach. I wired into the fuse box off the position 2 of ignition (white wire input) and the tach was going crazy and the car was misfiring when highway cruising at 4000 rpm, so I disconnected everything and it seemed to run better, but I did notice the ignition light starting to come on faintly. I tried reinstalling the rev limiter again by wiring it into the fuse box in a spot running off position 4 of the ignition (white purple wire input). When driving on the highway, again I started getting misfires and then the ignition light came on very bright. Made it home, disconnected the rev limiter, but the ignition light stayed on. I tested the voltage at the generator output (brown/yellow wire) and trying both the engine and a local ground, and the voltage at 1000 rpm only reads 1, or 2 if I run it up to 3000 rpm. The other thing that seems to make my tach go crazy is if I turn on my fan, which is wired into the fuse box of the position 2 of the ignition (white wire input). I can not figure out why turning on the fan would affect the tach? I don't know if the problem is the generator, the tach, the rev limiter... or all of the above. Suggestions? Thanks. Dan
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PostPost by: Galwaylotus » Sun Oct 11, 2009 8:00 pm

I can't help at the moment but I'm having a similar problem with no electronics. My S3 is as original. I get a bit of a misfire in the upper rev range (but well before a rotor-based rev limiter would cut in) and the charging light glows faintly most of the time. Interestingly, under load, it will go out! Today I decided to do a little testing. I was only getting a couple of volts when testing the control box per the factory manual. No matter how many revs I used, I wouldn't get more volts. I took out the battery to put it on charge then started looking around and found one lead to the generator not connected. I don't know if I knocked it off when feeling around there but if so, it wasn't on very securely anyway. I squeezed the connector with pliers to tighten it up and reinstalled it. Haven't put the battery back in yet so I don't know if I've solved anything.
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PostPost by: collins_dan » Tue Oct 13, 2009 1:07 am

I re-read the factory manual on how to test the generator at the control box, and did as instructed, connected the 2 generator outputs and tested that to a couple of different ground points and got the same results, about 1 volt. When I test the battery, it reads 13 volts, so the multi-meter appears to be working, but the generator is not and that is why the ignition light is on. Can somehow explain how the ignition light works, so I can be sure that I'm not missing something simple. From the electrical drawing, it appears to always get power from the ignition and only be grounded if the generator is not working properly? Since I can start the car and the tach is working, it would seem that the ignition is working fine.

So if the generator is shot, then I am going to upgrade to an alternator from RD enterprises and change out the voltage regulator for a terminal block. Has anyone made this changeover? Is there anything unusual to be prepared for? Looks like it comes with the mounting bracket and adjustment link, and just 2 wires, same as the generator. The terminal block has the same number of terminals as the voltage regulator, so an easy swap-out it would seem. Does the ignition light work in the same fashion as it did with the generator? Sorry for the stupid questions, but having roommates in university who were engineers is about as close I've come to engineering. Thanks, Dan
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PostPost by: stugilmour » Tue Oct 13, 2009 3:03 am

Dan:

From your description of the RD alternator it sounds similar to the one I got from Bean's, although if I recall corectly, Ray's kit uses a slightly different mount. Be very careful threading the mount bolts into the Ali block; you don't have to ask how I know.

Your understanding of the ignition light is essentially correct. One side of the light is at 12v in run and start, with wire from ignition key. The other side of the light, generally light gauge brown/white is connected to alternator. It is at ground until excitation of the alternator occurs, at which point the brown/white goes to 12v from the alternator charging. As both sides of the light are then at 12v potential, no current flows through the light and it goes out. If the alternator potential goes below 12v, current flows through the key switch to the alternator, causing the lamp to illuminate.

The other bigger gauge wire from the alternator carries the charging current to the battery. It is typically wired to the solenoid positive I believe, which is the most direct route to the large cable from the trunk mounted battery. Minor exception to this if you have an ammeter in your set-up; then the alternator to solinoid wire goes through the ammeter.

With the two wire type alternator the regulator is built in, and the charging current out of the unit is already regulated. I am vague on which wires go where on the regulator because mine was already removed by the PO when I installed my two wire unit. Ray may have detailed instructions for this part; the Bean unit came with instructions and I could look around for them if you need more.

Last note. Generally if the bulb burns out, the alternator will not get excitation current to start it's charging cycle. Sounds like your bulb is OK, so no worries.

HTH
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PostPost by: JJDraper » Tue Oct 13, 2009 6:08 pm

Postscript to Stu's comment; don't get carried away with LEDs in the dash. LEDs are OK elswhere in the dash, but not in the charge light for the reason Stu mentions...

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PostPost by: collins_dan » Tue Oct 13, 2009 8:49 pm

I guess I should do a preemptive bulb change, because if the light burns out, you won't know you have a problem until the car dies, and jumping it won't get you very far. I'm guessing people carry an extra bulb.

Dan
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PostPost by: stugilmour » Wed Oct 14, 2009 12:08 am

Yes Dan, replacing the bulb and carrying spare is probably a good idea. Perhaps do it after you get the rest sorted so the job doesn't get confusing.

The other way around the problem is to wire a resistor in parallel with the bulb. This is how it is done on my '87 BMW. It was a running change on the car, indicating just a bulb alone caused some issues. I am not sure of the value of resistor to use for this purpose, but someone else may know? Anyway, it is probably a reasonably rare failure, and I think the bulb can be reached easily from below the dash, so not a giant issues. Also note you can see the failure easily because the bulb should always light up with the ignition in run but the engine not started.

Cheers!
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