I am guessing that someone else has tried this.

I have a stock alternator in my race car for now (upgrading to new 1-wire later). Relay board and entire harness is gone.

I know that I need the external voltage regulator, so I decided I better figure out how to wire it up...
It turns out that the plug from the Alt that goes to the relay board is exactly the same connector & pinout of the Voltage Regulator!

So it can just plug right in... not so fast.

For the alternator to startup/charge, it needs the voltage that is fed from the Alt light in the combo gauge.

SO, can I just wire in a bulb from +12V and splice it into the D+ lead on that connector where it goes into the VR plug?

Then the system should work exactly as before....??
Is the stock Alt bulb a special wattage?

Stu

Yup

Nope.

i just plugged my VR in and moved on to the next task. all tho, i use super brite LEDS for my idiot lights so i did have to wire a little incandescent bulb for the alternator. the led didnt pull enuff load by itself.

Thanks for the responses so quick!



That is funny! I didnt want to complicate the question by asking: Ok, now, can I use a 12V LED instead of the stock idiot light ;-)

How did you determine it would not work?
I figured if it didnt work, I would just add a resistor across the LED to give it more current.

Anyone know how much current the Alt field winding needs to work?

Stu

i just soldered 2 wires to the stock bulb and used it.

Stock bulb is 2W

What's "upgrade" have to do with a single wire alternator?

The Cap'n

Cap'n

"upgrade" in the sense: use a more modern alternator that I can find at any FLAPS ( like the delco 35 amp).

1-wire: just to simplify the system and not need an external regulator.

I want to see if I can use the Delco 10-SI because a lot of the other racers use them and chances are there will always be one at the track.

I am still debating 1 vs 3 wire as I dont mind the idea of the idiot light.

Stu

The lamp is required for 2 way current/voltage flow. That is why a LED (Diode) will not work. It is not a load issue. When the engine is OFF, the alternator is the ground, lamp on. When the engine is running, the alternator is 12V+, to turn off the lamp.

kg6dxn,

It is not an issue that the idiot light is a diode.
The issue is that the diode lets such a small amount of current flow (it is very efficient) that is does not provide enough current to energize the field winding.

Based on McMarks comment above , that means that the stock setup allows ~170mA of current to flow through the stock bulb and through the field winding when the alt starts up.

But you do not need 2-way current flow.
You need current flow into the field winding to start it.
Once the alternator is generating it's own voltage, it feeds the field winding itself.
This makes zero volts across the idiot light (or my LED) and no current flows any longer (light is off).

I will just put a 70 Ohm resistor across my Diode and that will be enough to kickstart the Alternator.

Stu

Fr a race car, invest in a new lightweight alternator...
Summit sells them.

Rich

stu, when you find a resistor that works, will you post up what you used? i wouldnt mind getting rid of the lamp im using behind the dash.

Well it works.

I used a 70 Ohm resistor ( actually 2X 140 Ohm in parallel since high power 70 Ohm must be ordered) in parallel with the LED indicator light.

The light turns on when you turn on the ignition and goes off when the engine starts.
Read 12.4 V before start and ~13 after, but havent got the car to driving on the street yet, so I have limited info.
Since this "fix" only applies to alternator startup, I think we have it.

You could run with just the 70 Ohm resistor and no indicator if you want.
If you leave the ignition ON and the engine not running, the resistor will get hot, but not much more than the bulb (use high watt resistors).

Stu