chrismore

Ok, Here is the story. I am building an FC race car and I completely stripped out the entire car and rewired the entire car manually. Everything has gone as planned except one part: My alternator is charging very strangely.

This is what I'm seeing:

1) Before I start the car, battery volts is at about 12.1 volts per my multimeter

2) I start the car and the volts drop down to about 11.8 volts and do not increase much past 12 volts.

3) If I rev up to about 2,000 rpms and back down to idle, the volts jumps up dramatically. a) at the alternator post it is 15.3 volts. b) at battery it is 14.8-14.9 volts c) at the switch panel on the dash it is 14.9 volts.

What I don't understand:

* Why I am not seeing 14.7 volts anywhere in the system at idle.
* Why it jumps up above 15 volts as soon as I rev it up and back down to idle.

How do I have it wired?

* + battery to alternator post
* S plug lead to 12 v ignition
* L plug lead to nothing

What have I tested?

* I've replaced the alternator (both tested fine at store)
* I've checked voltage drop on the positive and negative circuits and both are only .1 volts.
* I've run as a test jumper cables to the battery to the alt post on both the positive and negative side to eliminate any grounding issues.

The only thing I can think of is that this is perfectly normal, but below 14 volts at idle initially and above 15 volts after a rev scares me with all of the electronics.

Any ideas?

Any help is appreciated!

misterstyx69

iTrader: (142)

what wiring do you have in the car now?
Which ALTERNATOR is on the car now?

chrismore

I've rewired the car manually with only the circuits that I need for the race car. I used the factory wiring manual to do all of the wiring. The alternator wiring is about the easiest to do, but I did eliminate pretty much everything in the car. I am pretty sure there is no other voltage regulation outside of the one inside of the alternator, but it is possible since I deleted everything on the car.

I have an S5 alternator in the car and I have an S5 alternator in the car before.

Japan2LA

iTrader: (256)

What pulley is on the alternator?

chrismore

Stock pulleys on both alternators. No other engine mods.

chrismore

I tried another battery and the same problem! I don't know why an alternator would work fine off the car as soon as I put it on the car that it causes these issues! This doesn't make sense. Anyone have any ideas?

schaft

iTrader: (1)

Hmm I may have a thought on this, but first what's the volts it tested out of car?

chrismore

I brought the alternator to the parts store and it passed all three tests and was putting out 14.7 volts. The second alternator also tested out fine, but again did not work in my car. It has to be something with my custom wiring in the car. This is a race car so most of the circuits are deleted and I'm only using the main relay and some fuses/breakers. Overall, the wiring is pretty simple.

Thanks in advance.

schaft

iTrader: (1)

Its late where Im at so if this doesn't make sense ill check back in the morning, when a place test an alternator its ran at a certain resistance and that resistance helps put the voltage in the correct range. By you simplifing the wires you may have lowered the resistance and therefore increased the volts. Or the part store is hooking it up wrong which is very possible. Also try and tripple check ur voltage regulator, or switch to am external unit..

schaft

iTrader: (1)

Ill probly know ur issue in the morning.

chrismore

That's possible, but that is also assuming that the voltage regulator in alternator does not actively regulate voltage, but instead of set to assume a specific amount of resistance from the OEM set up. It also would require that when you bring your alternator to the store to get tested that their machine can simulate the same resistance from an the OEM wiring harness, but that seems unlikely.

I could run an external voltage regulator, but does that explain why the alternator doesn't do any charging until you hit the throttle one time?

Couldn't other people test their voltage from their alternator post without any hooked up to see how many volts it is putting out?

satch

iTrader: (1)

Look in the FAQ section for a diagram of the S5 alternator and you'll see the L terminal you left out when wiring.

chrismore

I left the L terminal out on purpose, because it serves no purposes for a race car. From what I understand, it is only for the dash warning light. I only have the S terminal hooked up to a 12 v ignition source.

I've read other people saying that I don't need the L terminal hooked up, is that not true?

chrismore

This is what people have said about the L terminal:

https://www.rx7club.com/showthread.p...27#post4965227

I don't see how wiring up L will do anything unless I'm missing something.

chrismore

Also, the L terminal (W/B wire) goes to the warnings and auto clock unit in the center of the dash, which I no longer have. I am only running the stock dash cluster and nothing else.

http://www.flickr.com/photos/chrismo...in/photostream

GregW

You need to rectify via the W/B wire aka, terminal L. Its your "exciter" wire. With out that your alternator will not "turn on" till you give it a rev.

Normaly a diode/light in the dash does this, light comes on when you turn on the key, draws a current, then you start the car and your alternator is doing its job dynamicaly, you need to find a way arround that. Look it up on the internets, you got lots of options.

Easy way out:
Either hook it directly to the +side of the battery or use a diode so current can only flow to the alternator. NOTE: If you hook it directly to the +terminal your battery will drain. If you use a diode your battery will not drain when the car is off. This may or may not be a problem if you have a discon switch

Get it?

chrismore

Wow, this is exactly it! I though the dash wire was just for a light and it didn't have have anything to do with the exciter, but that makes complete sense.

I will do it tonight and I bet this is exactly the problem. I will just hook it up to positive cable after the disconnect switch so that it doesn't draw on the battery. Can't I just hook up the L and S wires to the same 12v + ignition source?

Thanks a bunch!

chrismore

Question about the wiring of the L terminal on an S5. A lot of the other documentation was either not correct or related to an S4. Can I run the L terminal to a 12v supply from the same source that I am getting 12v from for the S terminal (voltage regulator wire)?

I tried to run both L & S over the same wire to a common 12v source, but it didn't work and I am going to try to separate wires to see if it is better. Should I run L terminal to an ignition source or one that turns on with the kill switch?

HAILERS2

S wire gets connected to the EGI fuse on a series five car and that is constant power 24/7.

L wire should go to a switched source of power and also install a diode inbetween. Heck I'd install a 500 ohm resistor inbetween similar to a series four car. Inbetween meaning b/t the switched source of power and the L terminal at the alternator.


All wires connected to a series four or five alternator should result in approx 3vdc on the L wire at the alternator (see manual). That's with key ON engine OFF.

And yes, a lot of what has been mentioned about the L wire in the past has been wrong as can be. IT is excitaiton voltage.

Earlier when the output was 12 or less when the engine was idling.........and then you rev'd to over a couple grand and returned to idle and saw higher voltage....................that was the alternator SELF EXCITIING itself through residual magnatism in the alt rotor etc doing the job of getting the alt all excited. and putting out.

And yes, I was one of those idiots in a thread you attached waaay above that more or less said on a series five car the L wire was idiot light sensitive only........but at that time I also mentioned I owned a series four and not series five car. And in endless series four threads, I've mentioned the role of the L wire in exciting the alternator and also mentioned why reving the engine causes an alt to put out.

chrismore

Ok, just to clarify. So for the L wire to have 3vdc with key on and engine off, the 500ohm resistor is what is going to knock it down from 12v? Since this is a race car, I have none of the OEM stuff so 12v is flowing through the entire car and there isn't even a central fuse box anymore.

I will run a second wire to my ignition switch for the L terminal and install a 500ohm resistor between the ignition switch and L terminal.

I will update this thread soon if it worked.

Thanks a ton!

chrismore

Ok, this didn't work either. I ran two wires.

S > 12v battery

L > 12v ignition with 500ohm resistor inline (unless I need to use something to knock this down to 3vdc)

The alternator is still not exciting at start up.

Since this is a race car, wouldn't this be 1000% times easier if I just put on an external voltage regulator and just let the alternator self-excite itself?

HAILERS2

Hmm. Sounds to me like the regulator inside the alternator is shot if it's seeing voltage on the L terminal when the key is put to ON.

I'd just buy another stk internal regulator for ??? 25-30 bucks and solder it in and try again. I've been there done that before. Bought the regulator on/off EBay.

chrismore

Ok, I'm still having no luck with another alternator that was just tested today to be fine. I wired up an LED idiot light on the dash to match the wiring diagram of the OEM unit. The problem is that I'm only getting .6 of a volt on L terminal now instead of the 1-3v for the alternator to excite.

Do you think I should try a non-LED idiot light and a few different sizes? I'm really guessing at this point and very close to scrapping it all and go to a GM single wire alternator.

I'm so tired of this and hopefully someone can give some a direction on where to go now.

HAILERS2

************************************************** ****************
When you had the 500 ohm resistor in line with the L wire, and all connectors on the alternator with key ON, engine off, what does the L wire read with a meter? Like backprobing the L connector under those conditions and the meter reads???? how many volts?

The L and S connector being connected to the alt when you read the meter is what I mean.

Are you SURE you don't have the L and S wires switched around on the alternator??????

chrismore

Before I go double check the voltages, I drew up a wiring diagram of how I have it wired now. This is a simplified diagram, but not much different from reality given it has almost no OEM parts.

Can you double check how I have it wired up?

http://www.flickr.com/photos/chrismo...n/photostream/