power fluctuating / headlights dimming problem

[gunlak]

Hi,

I noticed that my headlights dim a bit when the fan kicks in and if you switch the defogger on.. it will only dim momentarily and can be counteracted by giving it a little gas.

Also when the AC is on full blast, you'd hear the blower get less power when you turn on the lights, defogger, and other electical stuff..

Any solutions to this? I already have a grounding kit installed to the chassis, engine mounts, and the alternator.

[91cavgt]

Basically what you are experiencing when the fan kicks on when the headlights are on is a sudden increase in power demand. The alternator can not respond immediately so it take a second or two for the alternator output to increase to meet the new demand on power. Until the alternator can match the power output to the demand, the voltage will drop and you will see the momentary dimming of the lights. This is normal on vehicles with small electrical systems and there's not much you can do to prevent it short of installing a huge battery and a massive alternator.

When you have almost all of the electrical devices in the car turned on all at the same time, if the car is at idle it is normal for the voltage to drop to the low 13, high 12 volt area. This is also normal. If you were to raise the rpms of the engine, or drive at just about any speed that raises the rpms up above idle then the slowing of the blower motor and the dimming of the headlights will go away and they will work like normal. What you are experiencing here is the alternator is already putting out as much power as it can at that rpm (alternators always put out more power once you raise the rpms). So when the power consumption at that time exceeds power production the alternator is capable of making at that rpm you end up with voltage that drops, and the extra power is then taken from the battery.

There are a couple of ways to stop this from occuring.

1. Install an alternator that puts out more power at low rpms (some higher amperage alternators actually put out less power at idle than the stock alternator, so bigger is not always better).

2. Over drive the stock alternator. This involves changing out the pulleys to increase the rpm the alternator spins at while at idle. But, you run the risk of over spinning the alternator if you ever take your car up to redline. For example, most cars spin the alternator at approximately 2 times the engine speed. This means at idle, the alternator is actually spinning at approximately 1700 rpm. So this means at redline, the alternator is spinning at about 12,000 rpm. If you over drive the alternator by a 3:1 rate instead of a 2:1 rate then at redline the alternator would be spinning at about 18,000 rpm. See how this could end badly?

3. Don't turn all of the accessories on when the car is at idle. If you do have everything on and you slow down to a stop, turn the blower fan speed down, decrease the rate of your windshield wipers wiping, turn your radio off, and turn your fog lights off.

[grsupercity]

Couldn't he install a capacitor? That would store the extra juice and can be used when needed correct?

[cyclopathic]

Couldn't he install a capacitor? That would store the extra juice and can be used when needed correct?

That and LED headlight bulbs.

[91cavgt]

Couldn't he install a capacitor? That would store the extra juice and can be used when needed correct?

A standard capacitor does not store enough energy to make a difference. If you went with some of the super huge capacity capacitors then it still would not work and here is why.


The lights dim because the voltage drops from 14.3 volts (roughly) down to about 13 volts. The capacitors can't supply enough current at 14.3 volts to make a difference. If you were to add another battery, or just a larger battery then the lights would still dim just as much because the battery alone is only good for 12.8 volts. Anything above that is supplied by the alternator. So the only way to help stop the dimming is to decrease your load (LED lights would be a start) or change the alternator out to one that produces more power at idle.

[laceygirl]

I love my LED headlights, I am also replacing the tail lights to full led's too... They are expensive as they are a whole unit, and if you were to just replace the globes on the tail lights, you'd need load resistors on EVERY globe in order to tell the car its pulling the required amount of power....

[91cavgt]

I love my LED headlights, I am also replacing the tail lights to full led's too... They are expensive as they are a whole unit, and if you were to just replace the globes on the tail lights, you'd need load resistors on EVERY globe in order to tell the car its pulling the required amount of power....

The resistors defeat the purpose of installing LED lights, unless you are swapping to LED lights just for the look.


The purpose of installing resistors along with LED lights is because LED lights pull so much less current than a standard bulb that in some cars it will cause a light to illuminate on the dash letting you know you have a light out. The resistor makes the LED bulb pull AS MUCH CURRENT as a standard bulb so you would not be using any less current than with a standard bulb.


I replaced the license plate lights, dome lights, front parking lights, and my fog lights with standard non-resistor LED lights and I have seen no change in the lights dimming.

[laceygirl]

^^ Exactly...

I did the same thing with all my lights, I'm saving for the tail lights that are Canbus Error Free...I didn't bother doing my front indicators but my side indicators are LED's....

[gunlak]

I see. Great insights guys. So i guess its normal then. I really dont have much of a probkem with it as long as the alt is charging and wont die down while driving.

So changing all the T10's and P21 and 5w wont do much for the halogen h4?

[inuvik]

I see. Great insights guys. So i guess its normal then. I really dont have much of a probkem with it as long as the alt is charging and wont die down while driving.

So changing all the T10's and P21 and 5w wont do much for the halogen h4?

I think changing the headlights with LED's is probably about the most effective move. You should be able to reduce your electrical load by at least 80 watts, which is about 6 amps.