Cap for headlight dimming?

[IHaveAHorse]

I have a 250W RMS A/B amp for my mid range speakers and 1000W RMS Class D for a sub in my 2012 Impreza, so at max power draw probably 1750W going into the amps.

I have an issue where the headlights will dim for a fraction of a second when the sub hits hard, but they almost instantly go back up to full brightness. I know a lot of people say caps are useless, but I've also heard that's because most people had no idea what they were supposed to be used for and just slapped them onto setups that didn't need them.

I'm guessing the reason my headlights dim for a fraction of a second when the sub hits (even if it's an ongoing bass note) is because the alternator takes time to catch up to increased power demand. I'm almost positive I can actually feel the alternator being loaded and unloaded repeatedly if I'm driving at a low speed and the sub is hitting hard intermittently. It makes the entire car jerk slightly like I'm tapping the brakes a tiny bit.

From what I understand, that's exactly the only valid use case for a capacitor, right? It's supposed to bridge that gap to prevent major voltage drop for a fraction of a second while the charging system ramps up.


For what it's worth, when the sub hits the charging voltage on the car when parked/idle only drops from 14.4v to 14.3v on my multimeter. The multimeter isn't fast enough to catch the initial super short voltage drop when the sub hits though.



So... cap: yes, no?

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[nwood1976]

A cap is really a band aid in this situation. If your amperage needs are exceeded by your accessories, the fix is a higher amperage alternator that will meet your requirements. When I bumped into this year's ago I used ohms law to figure out that I needed about 10 more amps than the stock alternator was putting out. I used these guys to get a new alternator with higher amperage.
https://www.maniacelectricmotors.com/

[802-303]

Caps are outdated.
Big 3 upgrade! It's cheap and effective. I'm running more draw then your setup, and it fixed my drop.

Big three consists of,
Upgrading the power wire from alternator to battery.
Upgrading the ground wire between battery ground and engine ground.
Upgrading the ground wire between battery ground and chassis ground.

Whatever gauge power wires you add off your battery need to be upgraded for the big 3. I.E you ran 4ga to your amps, add 4ga wire between the three points listed.

[802-303]

Double post for double power!

[IHaveAHorse]

Originally Posted by 802-303

Caps are outdated.
Big 3 upgrade! It's cheap and effective. I'm running more draw then your setup, and it fixed my drop.

Big three consists of,
Upgrading the power wire from alternator to battery.
Upgrading the ground wire between battery ground and engine ground.
Upgrading the ground wire between battery ground and chassis ground.

Whatever gauge power wires you add off your battery need to be upgraded for the big 3. I.E you ran 4ga to your amps, add 4ga wire between the three points listed.

Already did the big 3, didn't help at all.

[19std]

I think yout at the alternator now man, i have seen some big power set ups that run a whole second deep cycle marine battery. Then when all that fails, caps.

[nwood1976]

If your wattage info is correct, ohms law shows your peak use current draw as 125amps. 1750W/14V=125 amps.
From what I could find on a quick search, your car has a 110amp alternator. Thicker gauge wire or large capacitors won't "fix" your issue.

[nwood1976]

That is just your audio we're talking about. You still need the required amperage the car requires to run correctly.

[IHaveAHorse]

Originally Posted by nwood1976

If your wattage info is correct, ohms law shows your peak use current draw as 125amps. 1750W/14V=125 amps.
From what I could find on a quick search, your car has a 110amp alternator. Thicker gauge wire or large capacitors won't "fix" your issue.

If the alternator were unable to keep up with the power draw of the amp, the voltage wouldn't be staying above 14v when the sub is playing at full volume as far as I know? Which it does. I didn't think the amp would be able to keep up with it, but like I said the headlights only dim for a fraction of a second initially, which I assume is the "smart charging" system taking some time to react to increased power draw. Not sure what to make of things here

I was looking at a high output alternator at one point, but I don't know who to trust. I'd rather get the stock one rewound if that's still a thing, but I was unable to find any services like that, and unsure if it'd be cheaper than just buying a good HO alternator. "power bastards" has a drop in one supposedly, but everyone says they're an absolute garbage company.

[NutBucket]

Originally Posted by nwood1976

If your wattage info is correct, ohms law shows your peak use current draw as 125amps. 1750W/14V=125 amps.

From what I could find on a quick search, your car has a 110amp alternator. Thicker gauge wire or large capacitors won't "fix" your issue.

If you are actually drawing that much power you'll likely be deaf. You'd be surprised how little power it takes to get a lot of volume...assuming you're not doing some crazy spl competition thing.

Anyway, does sound like an upgraded alternator is in your future. Does it happen when you're driving or just at idle?