battery gauge

[fordboy]

Hi guys. My mother has a 1996 Honda Accord. A few years ago, the battery went dead on us in town. The battery light never came on, So we had no warning. Whats it for if it dont tell us its low? No matter if the battery is low, the light dont work.
If they don't work, whats the point in having the thing?
Keep in mind that it is a battery LIGHT. Not a GAUGE. (IF that helps)

What's wrong with it?

 

[AlanRebod]

Bulb burned out? Does the light flash when you first start the car along with the other lights?

 

[Donald]

OK, its not a battery light, its a alternator light. There are a few ways an alternator can fail and not all of them turn on the the light (according to the rebuild guy who told me).

Your post says it went DEAD in town. Should I assume you drove into town and a few hours latter the battery was DEAD. I would first charge the battery with an AC charger and load test the battery.

 

[Chris Meutsch]

Doesn't the charging light only come on when the charging system isn't working (i.e. the alternator)? That's my experience with multiple cars. Battery bad, no light. Alternator bad, light on.

 

[bepperb]

Even though it looks like a battery, it really only tells you if the charging system is operating at the correct voltage, or not.

As posted earlier, a battery can short and a battery can operate correctly but not have enough cranking amps to start a car... both of which would be considered "battery failures" but neither would trigger the light.

Probably nothing wrong with the light. Did you have the battery checked? Replaced?

Is it a [censored] system? Maybe. But every car these days have the same thing. Very few cars have a voltmeter or ammeter. To get what you want, you'd need both and I've never seen a car come with both from any factory.

 

[meep]

I've come across 2 different types of battery lights. The normal is the one that lights up when the alternator stops producing power. Light on = alternator circuit bad.

Then there's chrysler. Learned the hard way that the light was not directly tied to the alternator circuits. Light on = LOW Voltage. hmm. discovered this because the lhs kept throwing the serp belt, but it would be a while before the battery light would pop up. My mechanic (was fed up w/ the car and had someone else do the work) said those cars were voltage-triggered for the lamp.

M

 

[kgb007stb]

The charging light only lights up if and only if your alternator has one specific failure, the excitement coil is not energized while the alternator is operating. This can only happen if all the brushes are fine, there is no damage to the coil, so that it can conduct electricity.

When turning on the key, charging light lights up as electricity flows through the alternator excitement coil to the battery, upon start the flow reverses, so it is like attaching two positives or two negative leads to your light bulb, it will not light up.

But what happens when the coil is shot, one or both of the brushes are not fully contacted for what ever reason, (be they worn, failed springs, or other failed connections) the diodes go bad, or the individual charging winding circuits go bad that’s right no light what so ever to warn you.

 

[brianl703]

The charging light will also light up if the key is on and the alternator isn't turning due to a broken belt (or the engine not being started). But that's not really an alternator failure.

 

[brianl703]

This suggests that the light will come on if the battery voltage is higher than the output of the alternator:

http://www.alternatorparts.com/understanding_alternators.htm

I have seen this behavior before, and I wasn't sure what was causing it. It happened while jumpstarting a GM from a Ford. The alternator light in the Ford came on as soon as the GM started. I know that GM alternators have a higher output voltage setting than do Ford alternators, so maybe that's what caused it.