Welcome to the North American Subaru Impreza Owners Club Thursday July 18, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC General > Car Audio, Video & Security

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 06-07-2023, 09:01 PM   #1
IHaveAHorse
Scooby Newbie
 
Member#: 507873
Join Date: Oct 2019
Default Cap for headlight dimming?

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?
* Registered users of the site do not see these ads.
IHaveAHorse is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 06-08-2023, 12:23 AM   #2
nwood1976
Scooby Newbie
 
Member#: 103273
Join Date: Dec 2005
Chapter/Region: SWIC
Location: AZ
Vehicle:
2002 WRX 2.15 18gxtr
Sedona Red Wagon

Default

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/
nwood1976 is offline   Reply With Quote
Old 06-09-2023, 11:34 AM   #3
802-303
Scooby Newbie
 
Member#: 283194
Join Date: May 2011
Chapter/Region: RMIC
Location: Colorado
Vehicle:
2017 STi and '05 WRX
WRB and PSM

Default

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 is offline   Reply With Quote
Old 06-09-2023, 11:34 AM   #4
802-303
Scooby Newbie
 
Member#: 283194
Join Date: May 2011
Chapter/Region: RMIC
Location: Colorado
Vehicle:
2017 STi and '05 WRX
WRB and PSM

Default

Double post for double power!
802-303 is offline   Reply With Quote
Old 06-10-2023, 12:07 PM   #5
IHaveAHorse
Scooby Newbie
 
Member#: 507873
Join Date: Oct 2019
Default

Quote:
Originally Posted by 802-303 View Post
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.
IHaveAHorse is offline   Reply With Quote
Old 06-10-2023, 05:21 PM   #6
19std
Scooby Specialist
 
Member#: 510366
Join Date: Jan 2020
Default

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.
19std is offline   Reply With Quote
Old 06-10-2023, 08:08 PM   #7
nwood1976
Scooby Newbie
 
Member#: 103273
Join Date: Dec 2005
Chapter/Region: SWIC
Location: AZ
Vehicle:
2002 WRX 2.15 18gxtr
Sedona Red Wagon

Default

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 is offline   Reply With Quote
Old 06-10-2023, 08:10 PM   #8
nwood1976
Scooby Newbie
 
Member#: 103273
Join Date: Dec 2005
Chapter/Region: SWIC
Location: AZ
Vehicle:
2002 WRX 2.15 18gxtr
Sedona Red Wagon

Default

That is just your audio we're talking about. You still need the required amperage the car requires to run correctly.
nwood1976 is offline   Reply With Quote
Old 06-11-2023, 04:42 PM   #9
IHaveAHorse
Scooby Newbie
 
Member#: 507873
Join Date: Oct 2019
Default

Quote:
Originally Posted by nwood1976 View Post
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.

Last edited by IHaveAHorse; 06-11-2023 at 04:47 PM.
IHaveAHorse is offline   Reply With Quote
Old 07-06-2023, 09:07 PM   #10
NutBucket
Scooby Specialist
 
Member#: 90804
Join Date: Jul 2005
Chapter/Region: SCIC
Location: SFV
Vehicle:
2021 Ascent
2012 Accord

Default

Quote:
Originally Posted by nwood1976 View Post
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?
NutBucket is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 03:29 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.