Alternator putting out 12.9v, how bad is this?

In reply to Dr. Hess:

He had the stock alt swapped for a unit meant for a Mazda Protege and the new alt is overcharging the system. I think you missed a reply of his.

spitfirebill wrote: You sure are hard to please Goldilocks. Too high, too low... I got nothing else.

Henceforth and forevermore, Gameboy shall be known and referred to as "Goldilocks"

The light is merely an indicator. It is on when getting voltage from the battery only.

when the alternator output equals or exceeds that , no current flow , the light goes out.

The bulb is the resister.

iceracer wrote: The bulb is the resister.

Right, and from what I understand the problem is that the Samurai's bilb doesn't have enough resistance - it's an LED from the factory.

Are you sure the resistance is too low, and not too high, which would cause more voltage drop in the circuit?

Seems like there's more to it than the bulb. The light isn't even on when charging, but I suppose it could be part of a feedback circuit.

If you want to try the resistor route, you can use simple math to figure out a place to start.

If you know the watt bulb in dash then the resistance is:

Watts / (Amps X Amps) = Resistance

And

Watts / Volts = amps

So if you know the wattage, you can calculate resistance (for when it's on, when the bulb is off the resistance should be lower).

I think this guy has the best explanation of the problem:

http://www.pirate4x4.com/forum/suzuki/326620-suzuki-alternator.html

OK, my brain's about to explode from trying to wrap my head around all this analog electrical stuff, but I think I've figured out that the resistor I need to add is going to act as a pull-up resistor between the reference connector on the alternator and some positive source that would be used by the warning light circuit (this is the next part i have to figure out). This increases the reference voltage which should reduce the output voltage. It looks like a 100ohm 1 watt resistor should do the job of simulating the load of a small bulb.

Again. the light has no effect on alternator output.

Resistor? You sure this is wired right?

With a internally regulated alternator you generally have three wires.

The main charge wire straight to the battery + post, fused at the alternators max output.

The "field" wire, goes to a key on 12 volt source, your idiot light is spliced into this wire(in series), the bulb plays no factor in how it charges, unless it should burn out, then you may get no charging(some alternators self excite and the light is solely a trouble light).

The "sense" wire, goes straight to the battery + post, though you can generally cheat and jumper this right on the back of the alternator if you only have one battery.

High voltage is a bad sense connection. Low voltage is either a bad alternator, or a really bad connection/undersized wire on the charge wire.

Right, from what I understand the "sense" connection (which goes to the idiot light) has too low of a voltage on it for a GM-style alternator, so I need to use a pull-up resistor to increase the voltage there.

iceracer wrote: Again. the light has no effect on alternator output.

That is incorrect, in many vehicles if the bulb is burnt out or there is an open circuit between the Bulb and the alternator the alternator output goes away.

That sounds unusual that the Sammy would use an LED for the charge indicator lights. can a regular incandescent bulb be swapped out in place of the LED? If not a resistor would probably need to be in parallel circuit with the led to make the system work.

I have to admit though, I'm not quite sure how not having the proper resistance would make it over charge.

That

In reply to Kenny_McCormic:

I like the idea of running the sense (the VFR "monitor" wire I discussed on page 1) straight to the high-amp output cable on the back of the alternator with a jumper and seeing what happens.

In reply to GameboyRMH:

The sense connection does not go to the idiot light, the sense wire goes directly to the battery. If it is not putting out the correct voltage wired as I describe, the regulator is bad.

pres589 wrote: In reply to Kenny_McCormic: I like the idea of running the sense (the VFR "monitor" wire I discussed on page 1) straight to the high-amp output cable on the back of the alternator with a jumper and seeing what happens.

That would be a good test.

Maybe this will clear things up. Taken from my Bosch electrics book.

Generator warning lamp is in the pre-excitation circuit and acts as a resistor when the ignition is switched on. During cranking, with sufficient current flowing through the lamp, the pre-excitation causes a strong enough magnetic field to the necessary self excitation. As a result of the potential difference between the alternator and the battery, the pre excitation current flows from the battery via the generator warning lamp to the positive pole of the alternator. As long as the lamp lights up, no current is flowing in the excitation circuit, the lamp goes out as soon as self excitation is initiated and the generator is feeding the vehicle electrical system. When the alternator is in operation no external power source is required.

Normal rating for the bulb is 2W

Now is everyone confused ?

Oh, alternators are self exciting.

Here's a much simpler way to fix this. Go to a junk yard or the junk drawer in the garage find a 1156 bulb and socket. wire that inline with your dash warning light sure the bulb will burn out over time but if you wire it somewhere you can see the glow you'll know it.

Update on this?

iceracer wrote: Again. the light has no effect on alternator output.

It sounds like Suzuki did something really bizarre like running the field current and voltage sense through the alternator light circuit, so they need to take the voltage drop across the resistance of the bulb into account.

But this makes no sense unless the Mazda alternator was also designed like this, and was tuned for the incandescent voltage drop but with the lack of drop by the LED the resulting voltage is higher.

Ugh, I hate charging systems...