Charge Light Removal

[Boaty]

Grr!

 

I have found so far like 20 different answers to the same question!!!

 

I am going to be removing the charge light from the stock 510 instrument panel.

Well that is going to cause the atlernator not to charge until 3K RPM or so... not ideal.

 

The guages that are replacing everything in my dime have indicator lights but are part of the guage, not external (Speedhut Revolution).

 

So, I need to install a resistor in the circuit to maintain a charge @ idle+.

 

What resistance do I need to pick up?

 

So far, I've seen everything from 2.5k Ohms to 510k Ohms.. even a few Datsun sites have results, ranging from 10k ohms to 200k ohms..

 

I'm hoping somebody here has done this in the past and might remember... I give up for the night.

 

Happy Cinco de Mayo! Err... Ses de Mayo!

[68Datsun510]

Measure resistance of the charge bulb.done.???

[DanielC]

The easiest would be to just hook up a charge light, and hide it. The resistance of a light bulb changes as it gets hot, so measuring the cold resistance of the bulb will give you the wrong number.

 

Measuring the current flowing through the bulb, and using that number to divide the voltage applied to the bulb will give you the resistance when the bulb is hot, and glowing, will get you the actual resistance of the bulb.

 

The nominal wattage of the bulb is 1.7 watts. This is from a 521 factory service manual.

 

Dividing the power, in Watts by the Voltage applied to the bulb will give you a calculated current flow.

1.7 (Watts)/14 (nominal voltage) = .1214(Amps) The bulb should draw around 121 milliamps.

 

Dividing the voltage applied by the current actually flowing will give you the resistance.

14 (nominal voltage) / .1214 (Amps) = about 115 ohms.

 

The truth is the resistance is really not that critical. The field coil pole pieces in the alternator have enough residual magnetism to "boot up" the alternator if the alternator is spun fast enough. A resistance the same as the removed charge lamp should make the alternator function just as if the charge lamp was there. A too high resistance will tend to make the alternator act as if the charge light is disconnected, or blown out.

 

If you leave your car sitting without the engine running, with the key on, you will need to be concerned about the power being dissipated by the replacement resistor. The resistor could get hot. When the engine is started, this problem goes away, the charge lamp is off.

 

Here is another thing to consider. I am assuming that you are going to monitor the voltage, or the amp output of the alternator with the new gauges. However, if your fan belt breaks, a charge light comes on immediately, telling you something is wrong. This is the same fan belt that runs the water pump, and the radiator fan. You potentially become aware of the problem faster with a charge light, than you would without it.

[kelowg]

I used 200 or 300ohm on my setup. Thats with saturn alt. Higher ohms raises regulated voltage, mines at 14.5 @ 800 rpms. But as mentioned above, with key on egine off it gets HOT.

[Boaty]

I can set the warning light ON the gauge (and I can buy an external light that plugs INTO the gauge). But, it doesn't eliminate my problem with the alternator.

 

If I have to I'll just bring the alternator down and have it modded so it doesn't even use the charge light, like my Saturn alt.

If I can't read a 2 5/8" guage 2 feet away with a bright LED whenever it drops <12v, we have issues anyways lol.

[bonvo]

just leave the stock one hooked up it has its on seperate pig tail to make it work leave it connected and stuff it behind the dash no need to guess what the resistance is and you will just have a light bulb that no one will see

[Boaty]

I'm going to get a push-in bulb and just drill a hole in the instrument cluster to mount it, or remote-mount it next to the volt meter somehow.

 

Anybody know if an LED will provide the required resistance??

[ggzilla]

510 ohms is most appropriate. Current only flows through it with key ON engine OFF.

[Boaty]

510 or 510K?

 

I've heard so many different numbers, I just want one that works! Or else I'm going to just run a bulb under the dash somewhere I don't see it and just forget that it's there.

[Uber Deaf One]

510 or 510K?

 

I've heard so many different numbers, I just want one that works! Or else I'm going to just run a bulb under the dash somewhere I don't see it and just forget that it's there.

 

Why do you want to get rid of or hide the charge light anyway? I think it's a handy thing to be able to see a light and know your alt isn't charging ;)

[Boaty]

Because, there is no place to put it at the moment, that's why. Lol.

[ggzilla]

I've heard so many different numbers, I just want one that works!

 

They all work.

[izzo]

Boaty,

 

An LED should work fine. I replaced all the dash lights in my 71 510 smagoon with leds from superbrightleds.com and my Autometer voltmeter read the same when car was off or running. (If it makes any difference, it was just a standard wedge LED). The sight does provide specs on it I believe...

 

Link -- You can browse the sight and find something else that might work as well....

 

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fspecs%2FWLED-x.htm

[datsunaholic]

Actually, an LED won't pull enough current AND it's a 1-way circuit. A lot of folks have had problems with using them as a charge light. An LED in parallel with a 70Ω, 3Watt resistor would work.

[ggzilla]

Some LED-replacement lights have a higher resistance to make things like the turn signal work. And the ALT. But other LEDs do not.