It doesn't seem like it should be a very complex question, but there really IS a lot going on and a lot to explain about the phenomenon and why it happens.

Light dimming is from a fluctuation in voltage. It doesn't necessarily mean that you are pulling current from your batteries or mean that you are dropping to battery voltage, it just means your voltage is bouncing around some when playing your system and its reflected in your lights


It could be going from 14.5 to 14.0 which is very good, but you WILL see that 0.5v drop through your headlights and interior lights

Halogen or any of Filament type bulb will dim with a small amount of voltage drop. HID's are much less susceptible to dimming.

I’ll use a customer system as an example...

  • 2001 Honda Civic 1.7L with a 70-amp stock alternator and we sell a direct bolt on 200-amp model that is in the exact same housing as factory

  • The customer has a 5000-watt amplifier which pulls around 500 amps plus what the car pulls, plus an amp on the highs if he has one so let’s just call it 550 amps worth of draw total. The alternator is 200 amps so that leaves 350 amps having to come from batteries


As soon as you pull more than 200 amps you will drop to battery voltage. The higher your regulator set-point is the bigger voltage drop swing you will have. If you start at 15 and drop to 12 you will have way more dimming than starting at 13.5 and dropping to 12. It’s an ENORMOUS difference


The only way to NOT have dimming is to have more alt power than total current draw, which is almost never feasible. HID's will make a massive difference but if you are pulling more than what your alt can do, it’s going to happen

"So why does the factory one not dim?" you ask. ....


The factory alternator is only 70 amps, more than half of that is going to the car leaving little to no current left for anything else, so as soon as you turn your system on you go straight to battery voltage and stay there until you turn the system down, but actually, stay there a little longer than that while your tiny alternator tries to charge the heavily drained batteries back up. They go back up slowly, so you never notice your lights getting brighter

I'm sure I missed something to explain, so you guys let me know if you have any questions or more explanation. There is so much more that goes into it and we didn't even discuss Super-Caps, Lithium or the effect of adding more batteries....