alternator idiot light LED?

[aaalbedo]

I recently converted all lights (except headlights) to LEDs, even the dash indicator lights. But in preparing to install my AR 95 amp alternator, I see that the indicator is an integral part of the regulatory system and I'm wondering if the LED might mess it up. Any opinions?

Sometime in the past I found a parts list that someone at Superbright had put together, and they do list an LED for this service but note that "Use of LED Bulb negates full diagnostic value of ALT light". Which would indicate that it won't do any harm, but will be inferior to a filament bulb.

So I'll probably revert to filament, but don't relish the idea of yet another visit inside the dash right away... maybe I'll just wire one up under the hood for the time being.

Thanks for any insight.

Larry

[baltobernie]

... I see that the indicator is an integral part of the regulatory system and I'm wondering if the LED might mess it up. ...

Depends on the electrical system of the car. Some designs use the filament resistance to energize the alternator. Others measure differently, and illuminate the indicator with a relay. I'd ask Auto Ricambi.

[nelsonj]

Keeping the original is a safe bet, but I don't see any harm in trying the LED and seeing if it works. Personally, I'd keep (and did keep) the filament bulb both for the certainty the circuit would work properly and to save $$$ because that light should rarely be on.

Got and picture of "before and after"? I posted a bunch of stuff here when I did the project about 6 months back.

Peace.
Out.

[aaalbedo]

Ramzi at AR indicates that there will be issues with the LED since these systems use the resistance in the bulb as part of the circuit. I'm not certain though what those issues will be... with my original probably 65 amp alternator still installed and the new LED in the dash, the alternator is definitely not charging at idle, and battery voltage is not enough to flash my rear LED turn signals (front ones and dash indicator all flash, but the rears are only putting out maybe 1%; I can barely see them flash with the board out of the housing). 1500 RPM brings those rear LEDs back to full output. The dash alternator indicator LED lights up before cranking, and stays lit after starting, but if I rev it far enough that the light goes out, it stays out when I go back to idle.

I was thinking that I have an extra LED so maybe I can measure the resistance on that and compare to the filament version, then add a series resistor to make up the difference and trick the alternator into thinking there's a filament in place. But that would drop voltage at the LED and prevent it from working. So it looks like I'll have to go back to a filament.

lw

[Jon124]

Your LED bulb is going to have a much higher resistance than the incandescent, thus it has a lower current draw. To match the old bulbs resistance you would need to add a parallel resistor rather than series, and this wouldn't affect the voltage to the LED.

[baltobernie]

Just put the incandescent bulb back in and be done with it.

[RRoller123]

+1. I don't see the value in this?

[spider2081]

I think one of the big differences between an alternator and a generator is, generators use a permanent magnetic for its magnetic field and an alternator uses an electromagnetic. The electromagnetic needs to have current flow through it to produce a magnetic field. This path for current is through the battery warning light. This is what excites the alternators electromagnet so it can start to produce an output once it is spinning. When the alternators RPM reaches something in the area of 1000 RPM its own output keeps the electromagnet powered through the voltage regulator. At this point the "battery warning light" has voltage applied to both sides of the light bulb.
To my knowledge there is no practical way to by pass an LED "battery warning light" with a stock alternator.
There are some aftermarket alternators called "single wire alternators" that do not depend on external excitation. These are used on some hot rods. I don't know if any of our regular vendors supply this type of alternator. Also I don't know if they have a "battery warning light" output.

[aaalbedo]

Thanks for the comments, especially Jon's on the resistance. I'll try the parallel resistor but don't expect it to be the final version.

I'll go back to a filament, but for now there is "value" in avoiding removing the dash once more...

The white instrument illumination LEDs are a big improvement (and not too bright with my flaky dimmer bypassed) but the colored indicators are brighter than they need to be.

Lw

[baltobernie]

Removing four thumbscrews will get you to the offending lamp. You might even be able to access it from underneath without removing anything.

Getting this circuit right is a lot easier and cheaper than replacing a fried regulator, a cooked battery, over or -under powered bulbs, or a ride in a tow truck.

[aaalbedo]

It's a bit more involved than the four thumbscrews on my '84; I do seem to recall that it was just that simple on my '80, but that was 30 years ago so my memory may not be reliable. On the '84 I have to remove the wheel, loosen bolts to lower the column, and remove the Speedo cable from the transmission to get enough slack. And it usually takes about three tries to get the dash back in place without dislodging a bulb or two. But enough whining; I'm back to incandescent for the alternator indicator and charging as well as my tired stock alternator can. As soon as I find the harness I'll install the new 95 amp.

I also found the LEDs too bright for both headlight indicators (low and high beam). They were reflecting off the windshield right in my line of sight. So those are back to incandescent, too.

I think this is the first time I've ever had a fully functional, properly illuminated dash. Very nice.

Lw

[nelsonj]

I'm very happy after I did the upgrade to LEDs. Driving at night is a lot more fun...


Full Dash Before:

Full Dash After: