Lights brightness fluctuation with subwoofer on..problem? (1 Viewer)

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super50

super50

Joined
May 12, 2008
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Northern California
All my lights dim briefly when the subwoofer is on and putting out loud bass...is this an indication of a battery problem or a bad install?

Everything else seems OK, and the battery is only 1 year old. Charging system seems fine as well. My son thinks its cool, but I don't want to get stranded on a camping trip! I never run the music when the truck is off.

TIA!
 
Are you running only one battery? If so your battery may not have enough power to run your cruiser and the sub-woofer/stereo. You are going to have to run an extra battery or if you can go to a bigger alternator.
 
I would make sure the sub amp is wired straight to the battery and is grounded solid. Dimming of the lights would be normal with the engine off but shouldn't be that noticeable with it running. if you don't play music with the truck off I doubt it could leave you stranded.
 
Last edited:
Yes I have only the standard single battery configuration. Its a walmart battery but with the OEM replacement specs. And the sub is wired directly to the battery.

Would a larger/higher capacity battery be a cheaper alternative to a second battery set-up for my purposes?
 
super50 said:
All my lights dim briefly when the subwoofer is on and putting out loud bass...is this an indication of a battery problem or a bad install?

Everything else seems OK, and the battery is only 1 year old. Charging system seems fine as well. My son thinks its cool, but I don't want to get stranded on a camping trip! I never run the music when the truck is off.

TIA!
Click to expand...

What sub/amp are you using? And are you using the stock battery?
 


You need a capacitor. That's the silver thing. It fits nicely under the seat.
 
Hold on before you go recommending a cap. Give us the details of your system, the amp specs and how the wiring was done. It would have to be a pretty bad amp to legitimately require a cap. Also, upgrading the "big 3" would also help out.

Here's a good article from crutchfield, although I'd argue heavily to upgrade the big 3 before deciding you need a cap.

http://www.crutchfield.com/S-2QJYqOHLLul/learn/learningcenter/car/stereo_power_ups.html
 
Thank you - useful article. I wouldn't call my light dimming bothersome, maybe they dim 10% so its noticeable for sure. My battery is aftermarket, OEM spec.
I will query the stereo installer about the capacitor.

My stereo configuration:
Kenwood Excelon 7" head unit
Kenwood Excelon X500 500watt monoblock amp
JL Audio 8" sub
Audison 8-gauge powerflow cables
 
A 500W amp pushing a single 8 should not cause lights to dim or flicker and necessitate a capacitor.

A cap would likely fix the problem, but upgrading your other wiring, double checking the ground and amp wiring would be my first step.

Also, that amp is a 500W amp but has max output of 1000W. I would've used 4# power and ground. Where's the amp located and how approx. how long is the run?

http://circuitwizard.bluesea.com/

or

http://www.crutchfield.com/S-uX8pH4YtabB/learn/learningcenter/car/cable_gauge_chart.html
 
fireball said:
A 500W amp pushing a single 8 should not cause lights to dim or flicker and necessitate a capacitor.

A cap would likely fix the problem, but upgrading your other wiring, double checking the ground and amp wiring would be my first step.

Also, that amp is a 500W amp but has max output of 1000W. I would've used 4# power and ground. Where's the amp located and how approx. how long is the run?

http://circuitwizard.bluesea.com/

or

http://www.crutchfield.com/S-uX8pH4YtabB/learn/learningcenter/car/cable_gauge_chart.html
Click to expand...

My amp is bolted on the subwoofer box. The entire assembly is portable and sits in the rear, behind the second row. I remove it when hauling stuff for the space. The wires run from the engine bay and the head unit to behind the 2nd row seats...6 feet maybe?
 
X-whatever, you need a capacitor....
 
Your total wire run is way longer than 6'. From the battery at the front of the engine bay, snaked along the wire trough and back behind 2nd row seats I'd guess total length of 15-18'.

A straight shot from the battery to just behind second row is 10'. That doesn't account for any twists turns or bends. When calculcating total length you need to include the ground as well so that's how I arrived at 15-18'. Also given that it's removable I'd check all the wiring connections/plug/disconnect/whatever they used.

I bet you a 12 pack that with 4# wire and proper grounds and wiring connections you won't have dimming lights with a 500W amp powering a little 8" sub!!!!!!!!
 
^^ l agree with fireball. At that length you should be running 4awg wire.

But, that won't make any difference with the dimming problem. Your dimming is from high amp draw...Turn your volume down and you will see no more dimming. Turn it back up and it will return. A capacitor will support the peak amp draws when needed, getting rid of your problem or reducing it.
 
2001 LX...850+ watts from 2 amps...no dimming. IMO a cap is simply a masking fix. I personally would start looking at battery connections to make sure its getting full voltage from the alternator...and/or check the alternator itself is putting out full voltage...

**EDIT**
Okay, retested and on some songs(decaf chopped/screwed bass tracks) I do have a small amount of dimming. Have to get out and stare at the light pattern on the garage wall to notice... But I stand by my previous comments simply because depending on if your running an 8w3@4 ohms or a 8w7@3 ohms, you only talking about either 300-400 watts from that amp depending on the sub. Unless that Kenwood is the most inefficient Class D amp every created, I just don't think you should have dimming issues with healthy stock electrical... But, I'm not an expert, just an enthusiast, so take my opinion with a grain of salt...
 
Last edited:
A cheap battery, plus a decent run of wires...no matter what the gauge will dim the lights a little bit. I was running a 10" sub with a 1000 watt amp off a cheap Wal-Mart battery and my lights would dim very noticiable in my last Chevy truck. I added a 1/2 farad capacitor and it helped alot. A cap works kinds like a surge protector/battery backup device. It is the easiest fix and can be wired up right next to your amp to keep it all portable still.
 
Get a real battery first and then upgrade the big 3, going after the ground first. A cap is only going to mask the real problem. Use 4awg for the run from the battery to behind the rear seat for sure.
 
Thanks for the suggestions. I will look in the battery threads and get the biggest battery I can get to fit in that space. Any recommendations?
 
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