Weird opposite of lights dimming problem.

Post by **mr tibbs** » Tue Sep 18, 2007 3:13 pm

I noticed today on the way to my dad's house that I have an issue with the car. It seem as though instead of my lights dimming they actually get brighter when the bass notes hit. Also, my radar detector has a voltage warning indicator that says HI VOLT when the bass hits!! WTF?? I have a HO alt and I'm sure it's sensing that there is a voltage drop so it kicks the voltage up for a second, but why all of a sudden are my lights getting brighter?? Could this be a sign of a weak battery? I have been meaning to replace it, but so far it has been working so it's out of site out of mind. Any other ideas?

HoseHead · Post by **HoseHead** » Tue Sep 18, 2007 4:04 pm

Test your voltage regulator. Put a volt meter across the battery with the car off. Should read 12VDC or slightly higher if car was just running. Start the car. Measure across the battery again. It should now be reading as hgh as 13.8 VDC - Alternator/votlage regulator are now charging the battery and providing voltage for the entire car. If the "running" voltage is higher than 13.8 VDC, then your regulator is not regulating and your experiencing voltage runaway. Get back to us with your results.

Without a regulator, your alternator will charge with increasing voltage until your battery eventually blows up. With the high voltages, the battery will become quite warm to the touch, but it also very dangerous to be around one in this condition. You may also be able to hear the battery acid "boiling". You may also be able to smell "rotten eggs" with an overcharged battery. Sulphuric acid explosions are not pretty. Be careful.

Bruce

444 FED · Post by **444 FED** » Wed Sep 19, 2007 6:46 am

HoseHead wrote:Test your voltage regulator. Put a volt meter across the battery with the car off. Should read 12VDC or slightly higher if car was just running. Start the car. Measure across the battery again. It should now be reading as hgh as 13.8 VDC - Alternator/votlage regulator are now charging the battery and providing voltage for the entire car. If the "running" voltage is higher than 13.8 VDC, then your regulator is not regulating and your experiencing voltage runaway. Get back to us with your results.

Without a regulator, your alternator will charge with increasing voltage until your battery eventually blows up. With the high voltages, the battery will become quite warm to the touch, but it also very dangerous to be around one in this condition. You may also be able to hear the battery acid "boiling". You may also be able to smell "rotten eggs" with an overcharged battery. Sulphuric acid explosions are not pretty. Be careful.

Bruce

Umm, I REGULARLY measure up to 14.4 on a charging system, especially when cold. 13.8 is generally the accepted minium for a healthy charging charging system, between this and 14.4 is where you want to be.

You will have to measure actual voltage to find out what is going on. I usually use the cigarette light, for a quick connection point if I need to use a DMM to monitor while driving, not as accurate as an ignition whire or batter feed to the fuse panel, but it's quick and clean.

A weak battery could show something like this, but is unlikely the cause.

Solution, get more amos for a higher current draw, so that the voltage doesn't spike as high.

1moreamp · Post by **1moreamp** » Wed Sep 19, 2007 9:28 am

Run a cap to smooth it out

Post by **VW337** » Wed Sep 19, 2007 9:39 am

Weak battery not absorbing the initial load as it should.....

Or failing regulator over-compensating too much under load.

I would vote battery without knowing the actual design of the alt. However newer alt's have a stepping feature that is computer controlled, this way they are not creating an unneeded mechanical load when the full output capabilities are not needed, but instead increase output only as needed.