Adding a capacitor

oxphatxo · Post by **oxphatxo** » Wed Feb 25, 2009 2:29 pm

I'm wondering if I should add a capacitor to my power system. I notice that even with a battery bank and a standalone 250 amp alternator charging them, my voltage drops from 14.5 to sometimes 11 volts when I hit some notes. I have a digital volt gauge in my drivers cabin that tells me the voltage all the time.

I know it probably isn't a good idea to install a cap under the hood, but it sure would make things a lot easier for me. I've drawn up a schematic to explain how things work in my van for the power system. The capacitor I assume would have to be around 10 Farads? With roughly an 11000 continuous watt system? Would more Farads be a bad thing?

Suggestions please... I don't know how much the cap may or may not help with the voltage loss but I definitely wouldn't mind a cleaner power signal either way.

shaheen · Post by **shaheen** » Wed Feb 25, 2009 2:39 pm

From what I can gather off your pics, the cap is connected to the first battery , but your amps are off the battery bank.

I would suggest moving the cap to the bank as thats where your dip (power drain) comes from, not the first battery. I would also suggest 1 cap per amp if you really want to be pedantic.

I dont get the diode isolator bit. maybe thats a prob.

but I would still say caps after you split the power before the amp is the best.

oxphatxo · Post by **oxphatxo** » Wed Feb 25, 2009 3:29 pm

Actually, the sensor that is telling me what the voltage is doing is connected to the positive of the alternator under the hood. So that tells me i'm getting a voltage drop all the way up where the alternator is. The isolators are theoretically supposed to stop the voltage from travelling backwards after you've connected your batteries to the isolators' outputs. So that each battery can get a separate charge. But I guess there's still a dip. So you can understand why I am thinking under the hood. I get 13.5 volts at my amps after the charge goes through the isolators and wires I lose about a volt.

I agree each amp with it's own capacitor would be ideal, but i'm not looking to make any huge changes to my system as of yet.

oxphatxo · Post by **oxphatxo** » Wed Feb 25, 2009 3:41 pm

Here's a pic from last fall to help visualize the schematic.

Post by **Jacampb2** » Wed Feb 25, 2009 7:19 pm

I don't think the node where you are taking the voltage reading from is giving you any realistic data. According to your schematic, the battery bank is a lot further down the chain then the voltage test point. I would guess that the voltage drop at the amplifiers is far, far less than what you are seeing at the TP. I would measure voltage drop at the amps and make decisions from that point. You are seeing a voltage drop at the alternator because you are unable to supply the full current needed w/ a 250amp alternator. As long as it isn't a continuous load though, the rear battery bank should be staying fairly well charged. What is happening, is that low note puts the current draw through the roof, the alternator is supplying as much as it can at this point, and and tops out, so you get a voltage drop, however, the battery bank at the back is making up for the enormous current draw w/ whatever excess needs supplied. As long as your system is not playing test tones for hours at a time, the battery should recoup during times of lower demand. There is absolutely nothing that will fix this behavior, but to run enough alternators to supply all the current that will ever be needed, ~815 amps of alternator supply at 13.5Vdc.

In short, a capacitor will not help in this situation, it will especially not help up in the engine compartment. I also sincerely doubt that you have an actual issue. Check the Vdrop at the amps themselves.

Later,
Jason

Post by **Jacampb2** » Wed Feb 25, 2009 7:26 pm

One more thought: Is the alternator really a "1 wire" type alternator, or does it have the normal 3 or 4 wire setup and is just wired to act like a 1 wire? If it has the 3 or 4 wire regulator, one of the leads is the voltage sense lead, which provides feedback to the alternators regulator as to what the charge output needs to be. If it has a voltage sense wire, run it to the isolators input, which appears to be the closest common point to the load. This will help the alternator better regulate it's output based on what the amps/batteries are doing.

Later,
Jason

oxphatxo · Post by **oxphatxo** » Wed Feb 25, 2009 8:08 pm

Thanks for the advice, tomorrow I will check the voltage drop at the amps. Infact, I have a second digital volt gauge mounted in the driver cabin that I could easily connect to one of the amps power inputs to tell me exactly whats happening with the amps AND the other for the alternator.

The alternator is a 1 wire type. I was also thinking of routing the amp for my highs to the stock battery to help with some of the draw issues.
Thanks and i'll be back...

Post by **ttocs** » Wed Feb 25, 2009 8:20 pm

I could not imagine a cap would help with such a large system. I don't care how many farads you have in there......

oldskoolmseriesfan · Post by **oldskoolmseriesfan** » Wed Feb 25, 2009 9:20 pm

ttocs wrote:I could not imagine a cap would help with such a large system. I don't care how many farads you have in there......

please explain yourself then

Post by **stipud** » Thu Feb 26, 2009 5:59 am

oldskoolmseriesfan wrote:
ttocs wrote:I could not imagine a cap would help with such a large system. I don't care how many farads you have in there......
please explain yourself then

He's right. Alma Gates even tried capacitors in her SPL vehicle, and measured lower on the mic. With that much power, a capacitor is emptied instantly, and is then a draw on the system.

oldskoolmseriesfan · Post by **oldskoolmseriesfan** » Thu Feb 26, 2009 10:25 am

stipud wrote:
oldskoolmseriesfan wrote:
ttocs wrote:I could not imagine a cap would help with such a large system. I don't care how many farads you have in there......
please explain yourself then
He's right. Alma Gates even tried capacitors in her SPL vehicle, and measured lower on the mic. With that much power, a capacitor is emptied instantly, and is then a draw on the system.

Ya learn something new everyday, Eh!

oxphatxo · Post by **oxphatxo** » Fri Feb 27, 2009 6:05 am

Ya don't say?
So I connected my second volt gauge to the power input of one of my amps and the other volt gauge to the alternator. Here's the results... Voltage went from 14.5 volts at the alternator to about 11 volts. Voltage at the amps went from 13.8 down to under 10 volts. My gauge doesn't tell me anything lower than 10 volts, but my amps were still able to play that note very loud even at that low voltage.

I didn't think it would be this bad, especially having a battery bank. But there is no way that i'm letting this happen. It looks like i'm going to have to install another alternator somewhere under the hood. I think my only available place left for one is where the compressor is. Which sucks balls because my a/c still works. I hope that will help some.

Anybody know anything about 16 volt alts? Could I run 2 16 volt alts and get a 15 volt source at the batteries and amps without having to change anything else? Do 16 volt alts sacrifice amperage for their higher voltage?

Post by **stipud** » Fri Feb 27, 2009 7:27 am

That's an insane voltage drop considering your power distribution.

I was thinking it could be a grounding issue, but your diagram makes that a pretty distant possibility.

Not quite sure what to suggest... I have no experience in SPL systems like you are doing.

oxphatxo · Post by **oxphatxo** » Fri Feb 27, 2009 7:47 am

I'm wondering if it's my batteries. They are Alpha Gel Cell's. They are meant for backup power energy. But I got them for a real good deal

Maybe they can't handle such large instant power drains? I'm not an expert with batteries, but I know there are better ones out there. Agreed?

Post by **ttocs** » Fri Feb 27, 2009 5:22 pm

I agree that you have a bigger problem loosing that many volts from the alt to the amp. Putting another alt may help but it will only be a band-aid.

I too would start checking your grounds. I would assume with that much work done that you would have already upgraded your big 3 but I would do a general ground check and make sure they are tight.

oxphatxo · Post by **oxphatxo** » Fri Feb 27, 2009 5:44 pm

Definitely not my grounds. I'm using 0 gauge from all the amps and batteries, and 2 runs of 0000 gauge positive from the alts and a single run of 0000 gauge ground from the ground block to the alternator itself as ground. The ground block has also been welded to the frame of the vehicle. Using an electrical conducting grease smothered all over the ground block after the wires were bolted onto it. I'm thinking its the batteries, but I want some input from people about that.

Post by **Jacampb2** » Fri Feb 27, 2009 5:54 pm

Yeah, that is pretty bad...

Are you supplying the rear batteries with only the two 0g power wires? Two 0g wires is capable of supplying about 650amps. That is still quite a bit less than the amps *could* draw, even at rated power. The 815amp number I gave earlier is based on just the RMS power ratings of the amps, The draw could exceed this by 2x's or more during musical peaks. You may simply be undersized on your wiring. A ground problem could also explain this, but I agree with Stipud, it looks like the ground system was well thought out, but I would still check it thoroughly.

I would also consider temporarily taking your idolaters out of the equation. In the picture, it looks like they are just power diodes in a heat sink. Do you have any idea what diodes were used? It could be that they are your bottle neck. You could easily bypass them by removing all of the power wires from each isolator and just putting a bolt through the ring terminals and taping it up for testing.

Have you had these issues from the beginning, or is it a new development? FWIW, a voltage drop that bad is really endangering your amps. As the voltage drops, the amp tries to draw more current to make up for it. Eventually they will draw more current than the power supply mosfets can handle, and they will destroy themselves.

Good luck,
Jason

oxphatxo · Post by **oxphatxo** » Fri Feb 27, 2009 6:28 pm

That diagram I drew up was pretty much exactly to spec to what i've done. The only differences were the lengths in wire that I made not to spec since it's just an illustration for people to see. The grounds I have from the bank to the ground block are 2 runs of about 2 foot long 0 gauge wire. There are 5 batteries in the bank, 1 for each amp. The sixth is for the vehicle power. All of the grounds across the battery bank are connected together with 0 gauge. Individual positives from each battery run to each separate amp.

So yes, there is only 2 runs of 2 foot 0 gauge coming off the bank to the ground block. Then the block is welded and connected to the alternator using 0000 gauge wire. There could maybe be a chance its the ground wire from the bank to the ground block, I doubt it, but thats something I could look into.

I will try bypassing the diodes by bolting the positives together. See if that helps.. If not, i'm back to the Phoenix board.

Post by **ttocs** » Fri Feb 27, 2009 8:33 pm

now that I think about it the diode isolators could take almost 1.5v.

oxphatxo · Post by **oxphatxo** » Sat Feb 28, 2009 4:38 am

I've already accounted for the voltage loss from the diodes, the loss is 0.8 volts. The numbers I gave included all my losses from alternator to amp. It was 14.5v to 13.8v at the amps. Thats pretty good actually, since diodes can cause more then that sometimes. It's just the droop i'm trying to figure. Today is a new day, if I have time i'll get out there and start trying things...

Post by **ttocs** » Sat Feb 28, 2009 10:34 am

you could switch to a relay isolator to gain some of the .8 back.