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Old 03-02-2008, 01:16 PM   #1
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Add a capacitor or not

Ok, I added a subwoofer to my Safari and of course you all know that when on battery particularly, but also sometimes on shore power (converted) the water pump also tends to make the lights dim/flicker a bit.

My thought was to do one of two things or both.

Capacitors being not that expensive, my first thought was to place a .5 farad capacitor at the sub and the water pump. I also thought, perhaps it might be a good idea to place one off the converter when I do my WFCO converter/charger replacement, but a bit larger, say 1 farad, thereby covering the stereo and anything else that may take a bit startup surge hit to the DC system.

I'm really leaning toward just putting a capacitor at the sub amp and one at the pump, but the more and more I think about it, the more I'm thinking I might totally rid the lights slightly dimming, etc by doing all three.

Anyone thought or done this? Waste of money and time? Worth it to stop the lights from flickering when these units run when on battery power alone?
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Old 03-02-2008, 01:24 PM   #2
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twink

waste of effort.

1 capacitors will only help support voltage on an AC circuit. no help for the flicker.

2 wire your sub directly to the battery with a fuse of course, to take full advantage of the battery's "filter" effect.

if number 2 doesn't help the problem THEN try the capacitors, if it is a 60 cycle hum, there is ac present in your 12volt system probably due to induction by the wires laying in parallel with each other.

shielded and grounded speaker cable might be your best solution.

john
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Old 03-02-2008, 01:30 PM   #3
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The only issue I have is when the water pump comes on or the sub hits a good low, the lights slightly dim for a split second each low the sub hits or each time the water pump starts. I don't have any line noise spilling into the sound system....yet.

So you're saying that a 1/2 farad capacitor in line (next to) the pump and the sub won't have any effect on lessening the light dimming issues? This is the only reason I was considering adding some caps.
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Old 03-02-2008, 01:59 PM   #4
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John,

Many hi-end car stereos now use huge caps to prevent system overloads when the subwoofers hit those god-awful super thumper notes. You know the ones......you can feel them when the offending vehicle is 3 blocks away!!!! They do work on the DC side in this application.

Twink, I would add one to the sub, but I would check with you local car stereo shop for their recommendation on the best size for your appliction.
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Old 03-02-2008, 03:06 PM   #5
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Eric,

I see your point about when the sub hits a good low, and think a capacitor at the subwoofer could help in that circumstance.

By why mess around with a 1/2 farad capacitor? A one-farad cap, even though its overkill, would be my first choice.

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Old 03-02-2008, 03:28 PM   #6
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A monster capacitor will certainly store energy. It should be connected from the positive terminal of the subwoofer power connection to ground. That will allow the subwoofer to source its current from it (the capacitor) when the existing conductor from the battery won't supply enough current to drive the cone. But if the lights flicker when the water pump runs, there might be an issue with the battery connector(s). The capacitor will mask this problem.
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Old 03-02-2008, 03:47 PM   #7
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Silvertwinkie, I know your floor plan is not the same as mine but what size and where is the placement of your sub. Robert
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Old 03-02-2008, 04:43 PM   #8
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You have not described the problem with the sound at subwoofer if it’s a noise problem you need smaller capacitors .001 mfd or smaller larger and you will filter out the low frequency that the subwoofer is designed for.

It’s been a long time since my electronics training but as I remember you do not want a large cap across a speaker. The problem is normally the sudden voltage/current drop at the input to the stereo or noise in the stereo output.. Small capacitors are used to shunt spikes that show up as noise and large ones to filter power supplies to keep the output constant.

So you could be looking at a large capacitor say a 250 MFD 25VDC at the power connection at the stereo or a small one at the output to the speakers.


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Old 03-02-2008, 05:38 PM   #9
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As one of the younger crowd on here whose ultimate car audio system has never included an 8-track, I can tell you from experience... Go with the capacitor. It will keep the sub from driving your lights crazy.
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Old 03-02-2008, 06:01 PM   #10
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Bigger is NOT better

If someone recommends a 1F over a 0.5F capacitor, it is from not understanding the possible situation. I have seen what a 0.5F capacitor can do when it fails (it will blow the rear doors off of a 3/4 ton Ford van). Temperature accelerates this failure and most TT's sit in non-climate controled situations most of the year. Also note that a capicator that has more than 1' of wire between the load device and itself is suboptimum. I would be careful with any power caps in any vehicle. When I was getting flickering on my lights due to my water pump, I found out that my rivets holding the fuse holders were not conducting correctly causing voltage droops under a load. I replaced the fuse panel and all is good now.

-thomas
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Old 03-02-2008, 06:36 PM   #11
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From Tom to Thomas

Quote:
Originally Posted by tschat
If someone recommends a 1F over a 0.5F capacitor, it is from not understanding the possible situation. ...
Point taken.

Counterpoint:

What does Eric do if a 1 Farad capacitor is what is needed?

I had an oil-cap capacitor blow up on me once. It put on quite the show with all the noise and billowing cloud of smoke. FWIW, the capacitor was around 26 years old at the time.

Barring being hooked up incorrectly, I do not think a given NEW capacitor will blown up unexpectedly.

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Old 03-02-2008, 07:57 PM   #12
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Havn't sub-woofers been shown to cause shell separation?
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Old 03-02-2008, 08:37 PM   #13
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Well, the factory installs subwoofers as an option.

Here is a link to properly sizing capacitors.

Crutchfield Tech Support: How do I know what size capacitor to use in my system?

Here is a link to some of the logic driving these questions:

Car Audio Advice Terminology And Education | Capacitors


Now, the sub is a 100 watt powered sub, so based on what Crutchfield suggests, although higher than 1/2 farad is not required it also won't hurt anything.

Again, I'm not doing this as a line filter, I'm using it to lessen the draw down in amp, watts and volts on sudden draws that the sub does do if I hit a real low sound and the volume is up. Now keep in mind this is not sounding like one of those cars like a kid might have rolling down the street shaking windows, this is a good audophile type compliment to a factory installed system that has poor low range reproduction. At some point, I am going to replace that POS Sony and the el cheapo speakers that distort way too easily....I digress, that part is a whole different post.

Capacitors have been used successfully in DC mobile audio systems for at least 10 years. I'm not concerned with bad things happening, I think the track records for these devices is proven, when installed and sized correctly. I understand that there could be issues, but cars sit in direct sunlight over the summer months. Has anyone heard of these devices exploding regularly in cars? It was my understanding these are very commonplace in mobile high end audio systems.

To answer the question on where mine is installed, it is located under the front sofa, connected to the factory installed wiring harness in the street side armrest storage area.

There is nothing wrong with the pump. It operates as it should. However, when there is draw from the stereo, and the sub, there is a slight noticable hit to the lighting system when the pump first starts up. It's more of a cosmetic thing than anything else. The lights don't go out, nor do they dim very low, just a slight reduction in output when the pump first kicks in and/or when the sub operates under a load. I was thinking that adding a few capacitors to lessen the effects these items have to the lighting systems of the Safari if the taller draw was somehow offset. Clearly 55amps is more than enough to run almost everything in the Safari that takes DC and from what I am hearing, a capacitor will store some energy to deal with the initial demand draws. Am I hearing this correctly? I mean we're only talking somewhere around $50 on the high end for an average 1/2 farad capacitor. If these help reduce the effects of instant high demand draw, seems like a fairly straighforward issue and solution that has been dealt with by most audiophiles with mobile systems. I'm wondering if anyone else has done this with their Airstream or why this would be a bad idea to try.
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Old 03-02-2008, 09:40 PM   #14
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I've been fiddling around with electronics since I was a kid. What you are doing is perfecly OK, in my opinion. These super caps are something new to me, but the application you are proposing is legit. (I installed a 50,000 microfarad .. .00005 farad!) in one of my cars some time ago, it helped the bass response a little, and hasn't blown up to date. My suggestion is to install it as close to your subwoofer as you can. It won't screw up anything unless you hook the + to ground and - to +12 VDC.. It actually might make a spark if you hook it up hot for it will be the capacitor's charge current.
On the water pump idea.. well, why not? Same situation applies. The pump motor, when switched on demands current, and if there is an appreciable distance of wiring involved, there could be a voltage drop at the lamp filaments, causing them to dim slightly. The cap ought to supply startup current and reduce the dim....
Sorry to be so long winded. Hope this helps.
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