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Most of the digital caps I have seen just place the voltmeter on top of a normal cap in parallel. The problem with this is all the current that flows into and out of the capacitor has to also flow through a dinky little voltmeter piece. That is not what you're looking for.
I remember a particular RF cap that we pulled apart at work because my boss told me this and I didn't believe him. Sure enough there it was, you could pull the voltmeter piece right off and there was a normal cap. I don't think they are all like this but it's tough to figure it out without some disassembly.

 
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whats the 'side effect' of having the voltage going through the meter first?

 
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It's not the voltage that is a concern. The voltage should be the same at all points from the top of the capacitor to the bottom. The problem is you are pulling all of the current through this little voltage meter which isn't designed to pass tons of current, just to calculate voltage.
A better design would be to have the meter leads connected at the bottom of the capacitor so the current doesn't pass directly through it.

The main issue is the very thin contacts on the voltmeter can't pass the amounts of current the cap is capable of containing/distributing.
Again, I've only seen this in a Rockford cap but it might be more common.

 
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okay, see your blue one going from the battery to the engine? right where it hooks to the engine, there's a braided metal "strap." that's 1 of the "Big 3". replace that so you have a 4ga going from engine to chassis. don't run it back to the battery as you have it now. it really won't hurt anything, just unneeded.

i can't see behind the battery, but it looks as though you still have the stock cable on there. where the battery cable runs left in this pic, follow that down to the chassis just under the relay box. that's the main battery to chassis cable. that's the one you want to be at least 4ga, if not 2ga or 0ga depending on how big you make your system later on. with the stock setup, this cable is crimped into a bracket and then continues down and right to the tranny. that is the third cable in the big 3. i don't have my camera until tomorrow or i'd take pics of mine to show you.

 
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parallel is fine. series would create the problem you describe. i've never seen one that's in series though. with parallel, you have multiple paths for current flow so the massive currents will flow through the cap and large guage wires. you have 12+ coming in to the + terminal and then on to the amp. the - terminal goes to ground. the digital readout just sits there connected to both terminals, but virtually no current goes through it. by design, most voltmeters are going to have extremely high resistance so they have very little current flow. you're talking 500K ohms or more for most DVM's. i don't know what the resistance specs are on the digital caps, but it would have to be high to prevent damage to the LED readouts. if all the current flowed through the LED readout, then if you took it off, the cap would be junk. that's not the case though. you remove the meter and the cap still works. that's why you can buy readouts and install them on caps that don't have them.

 
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The problem is the current flows into the + terminal of the cap, directly through the volt meter contacts, and then into the capacitor. When the amp draws power from the cap it must go through those contacts before it can go on to the amp. All current which flows into and out of the cap must go through these thin contacts.

Series vs. parallel has nothing to do with it because you can't put a voltmeter in series (but you already knew that, and voltage drop testing is excluded).

Again, if the connections for the voltmeter were at the bottom instead of the top with the terminals there would be no issue.

 
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if the power has to go through the meter before it can get to the cap, then that's series. no other way about it. i've never seen one like that before. if you take the meter off, the cap still works right? if so then it's parallel and the cap operation and current flow is not dependant on the contact of the meter.

 
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A voltmeter will only work in parallel, right?

 
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yes, that's my point. the way your describing is a series situation. with parallel, the size of the contacts on the meter don't matter because they're not going to have much current going through them. all the current for the cap will be going through the binding posts.

 
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The way I'm describing is the only way it could possibly work. A voltmeter won't work in series.

But the problem is all the current ever held in the cap went through it.

 
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you got a closeup pic of what you're talking about? we may be thinking the same things, but saying them differently.

 
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If I get around to it I'll draw up a circuit diagram that explains it.

 
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all the caps i've seen have the big binding post that the cables connect to. the binding posts go down into the cap. the meter has a ring terminal or something clamped in the binding post that feeds it. with this setup, there's no current limiting properties by the meter.

 
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The RF I'm referring to literally had the meter resting directly above the terminals on the cap. We knew there was an issue because the bolts spun like crazy and weren't nearly as tight as they should have been.

 
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did it come from RF like that or was this already in someone's car?

 
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Nope they were shipped like that. My boss even opened one up to explain it to me because I thought he was on crack. But sure enough he was right, that was about a year ago though. I haven't seen any caps in a while since they pulled me out of the stores so they may have redesigned.

 
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interesting. maybe they changed it when they found out it's flawed? i haven't seen any that would be limited the way you describe. the meter usually taps off the main + binding post, but the meter connection is not the main path for current. makes me wonder what other kind of crap that RF is putting out there that people don't realize?

 
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RF's quality has moved slowly but surely down in the last ten years.

I'm going to see if I can find an example of this cap. I'll be in a shop tomorrow morning interestingly enough so I might just open one up and see. The guy who showed this to me was a MECP Master and the most electrically knowledgeable person I've ever met. He opened it right up and could show the voltmeter part just resting on top of the terminals. It was about an inch and a half or so thick and used much longer bolts than needed if you weren't using it. In fact the cap worked just fine if you took it off. The design may have been restricted to RF. I'm doodling some diagrams that might explain a little better what I'm getting at but I'll try to get a pic.

Basically my point is if you want a cap for the benefits of having one (stabilization of voltage supplied to amps, ability to release large currents faster than the car's electrical system) it sucks if you get the 'best' one but the design isn't all that well thought out. It looks cool but doesn't work as well as it should. Again, not saying all caps are like this at all. Just be on the lookout.

 
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cool man. let me know what you find out.

 
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I was too busy dealing with the car I was looking at today to check anything out but I'll be there again next week.

 
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bump

 
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what are you bumping for? what other info are you looking for?

 
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^the discussion about the caps is not done and i want to know which one should i get.

 
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do u think a 1 fahrad cap would be enough for both of the amps hooked up to it or do i need a larger cap?