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another thread about an alternator, pulsing lights?

4xcrazy

4xcrazy

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Anyone know what causes the lights on vehicles to pulsate slightly at times when running? I had always assumed it was something in the alternator causing the pulsing. Figured something in the regulator pack or something.

This is on the '05 Avalanche, 5.3. Is there something I can do on this style of alternator to replace, rebuild or whatnot?

Of course whenever you take them to have them tested, they always show in good working order, yeah, sure it's pushing out the correct voltage, which it is, and never has any issues with a dead battery or starting. i do notice a few times the volt gauge reads at varying levels, I just figured it's times when charging is needed to replenish the battery power or whatever.
 
Only time I've seen this is on a low battery when I was running my stereo at high volume with lots of bass and a huge fosgate amp running. The alternator was too weak to keep up with the power I was taking from the battery and would pulse with the bass. I'm thinking your alternator is dying or battery is getting weak and not taking a charge. Could also be bad grounds. The lights will get a weak signal and dim out also. Check battery after sitting not running for a few hours. Should be above 12. Turn truck on. Should be charging above 13 vdc. If the amperage back to the battery is fluctuating the regulator rectifier is going out inside the alternator. Should charge between 13-14.5 volts. But should stay fairly constant after the battery is fully charged. Only takes about a minute or two to get it back after you start it up.
 
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This will do it all night long, a consistent pattern of pulsing, never changes in pulse pattern like it wold with a big stereo system, I have that deal in my Burb with the big amps as well.

Some days it will not do it, most of the time lately it does. I took a trip to SoCal a few months back and it did it all the way there, was a rough night, hypnotizing me all the way. It's not just the headlights, it's the whole electrical system, dome lights, dash lights, everything.

I already have plans on changing out the alternator, but just thought I'd ask if it would be something easier I could change, maybe less expensive to replace.

just fishing for ideas. :D
 
My guess is it could be the altenator's diodes ,there are more than one and if one croaks it can do this,yet still charge fairly well..might cause the battery to discharde when sitting idle eventually too..another possible cause is a rotor winding hitting ground while spinning ("flying ground") and that may not happen all the time..regulator could be going koo-koo too..

Also overloads like a direct short somewhere will make it "strobe" ,so can poor grounds ...altenators are actually 3 phase AC ,thats converted to DC by the rectifier,if something gets damaged in the rotor winfings or feild coils it will pulse like that..
 
Yeah, could be one of the 3 rectifiers is bad. You should see the pulse rate change with engine RPM, though. If the pulsing frequency seems unrelated to engine speed, then something must be pulling current like that. Has it ever done it without the engine running?
 
no, it doesn't do it with the engine off, the pulsing does change a small bit the faster it goes, but it's not like it turns into a strobe light. It'll speed up, but only to a certain speed, not much faster than idle.

Best guess I can give of the pulse rate by visual and rough estimate of time is about 5 pulses per second. It doesn't completely kill the lights, just a slight dimming like you'd see with stereo bass hitting at loud volume.

I tried to take video of it last night, but the camera I was using wouldn't focus real well, couldn't get a decent shot of it and I don't think it was doing it as bad as it does at other times.
 
On the caps it would have helped and I was sixteen and wanted to bounce quarters on my roof of my car. Lol. Now I want to hear the engine more than the music. I'd say its got To be your alt in my opinion. If something in there goes it can cause a lot if weird issues. I got a a alt from kragen once that they built with a diode backwards. It would charge but would keep the circuit open from the battery to the ignition so it would kill the battery once you shut it off. It sucks To Have to buy parts but I think this is where you are needing to go with this.
 
The wifes 99 Lumina does this every now and then. Car is 100% stock, so I'm gonna say a big stereo is not the cause. It may not be helping it though. When it first started happening I thought it may be a ground issue. Being the battery is in a horrible spot, I just let it be. I'm not ruling out the alternator or battery (coming up on 6+ years old), but I'm going to wait till something dies before I start tossing money at it. Car still starts up fine after sitting all night, even when she leaves the dome light on all night.
 
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