Lights are dimming on my car. does ohms make a difference? 4 or 2?


Bronze Member
Username: Followyoursole

Post Number: 43
Registered: Sep-04
I noticed the lights have been dimming on my car(interior lights and headlights) lately since ive been using my amp for a 2 ohm load. Does using 2 ohms on a amp put more strain on battery rather then 4 ohms? i was pushing 300 at 4 ohms to a 12 but now im pushing out 420 at 2 ohms to one 12 (dvc 4 ohm in parallel. And what will help? A capacitor?

Danny Pickens
Unregistered guest
sounds like you shoul get a new alternator with higher amps, it's better than getting a capacitator.

Bronze Member
Username: Ctx

Post Number: 83
Registered: Jun-04
yea it does effect it,the amp is pulling out more power from the alternator to make the extra 120 watts. If its a regulated amp like the jl slash series it wouldnt make a difernce

Silver Member
Username: Zacdavis~

Post Number: 173
Registered: Sep-04
get a new battery first, buy the highest reserve capacity and cca battery you can fit in the tray, some batteries just get old. you arent drawing very many amps with that little amp, so i'd say an alternator might be a little overkill.
and yes...if your lights only dimm when the bass hits a capacitor can help with this problem. its just that people mistakenly try using caps to give their system more amperage but all they end up doing is adding another component for the alternator to charge. but in your case its different, your not drawing more than what your factory alternator can handle, so after replacing your more than likely tired battery, keep an eye on your voltage gage and if it only does little drops when the bass hits, then can you'll be able to further resolve your voltage issue with a cap. i guarantee it
btw, yes the lower your impedance, the less resistance, thus the more flow of current.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5028
Registered: Dec-03
the battery won't do squat for you if this is happening when the car is running.
dimming lights mean sagging voltage rails from the alternator, and if this is happening, your battery isn't getting charged either.

you need to go back to a 4 ohm load, or put in a larger alternator.
I've seen a 200 watt amp cause a car to stall due to current demands exceding the capabilities of the car's charging system. Thank companies like Honda who use a 60A alternator in a car with power everything.. the alternator has little to no reserve capabilities.

as for why 2 or 4 ohms makes a difference..
the lower the load, the more power the amp produces.
the more power the amp puts out, the more current it has to draw to do so.


how do you know how many amps your amp is pulling off your alternator?? lets just say its a 1200.1 class d mono

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5051
Registered: Dec-03
at peak output, the JBL bp1200.1 draws 115A of current.
It's in the product specs, but I can show ya the calculation easily enough:

class D amp = 80% efficient (1.2x multiplier)
1200wRMS / 12 (volts) = 100A
100A * 1.2 (effiency factor) = 120A current draw.
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