a cap is basically a battery that stores power for something...

could i say run a consistent 14v to my fuel pump by wiring it to the cap?

fuel pumps are rated on flow at a certain voltage, and mosy UDP's are alrrady robbing the car of power. i just dont see why this wouldnt be possible.

this is mainly for aaron miller....so chime in home slice

A capacitor is not a "battery" at all. Think of a capacitor as the resivoir behind a dam. Power comes into the capacitor and it "fills up" with a charge. Then it's output is regulated at a consistant voltage.

Now, when there is a higher requirement for power on the output side that is not being delivered by the input side then some of the reserve power is sent out to accomidate that need.

On the same token whenever there is a surge of power from the input side the "reservoir" absorbs the surge and still only lets a regulated voltage out to the unit you're powering.


So if you put a cap on your fuel pump it wouldn't really help much unless you're getting horrible voltage spikes or extreme underpower to the pump. I'd say don't waste your time.

the voltage drop is considerable

could a cap put out a solid 14v though? if so im definately going for it

I would think so, but you need to find a cap that runs 14v. I would call radio shack with the specs of the pump motor and see if they have a .25-.50 fared cap that would be compatible.

a car audio cap would put out 14.4v, but I think the real issue is your relay or something. You shouldn't be getting a "major voltage drop" which would require capping it.

Originally posted by a_miller_76
a car audio cap would put out 14.4v, but I think the real issue is your relay or something. You shouldn't be getting a "major voltage drop" which would require capping it.

actually we all do. Its not that uncommon to get considerable variations across the fuel pumps voltage. Its the main reason I did the fuel pump re-wire mod and even with that I can still hear a difference across the primary and Hahn pumps when i do something in the car to stress the system, ie- turn on the carputer, turn on the headlights, turn on the A/C. etc...

Originally posted by djtrickee

Originally posted by a_miller_76 a car audio cap would put out 14.4v, but I think the real issue is your relay or something. You shouldn't be getting a "major voltage drop" which would require capping it.

actually we all do. Its not that uncommon to get considerable variations across the fuel pumps voltage. Its the main reason I did the fuel pump re-wire mod and even with that I can still hear a difference across the primary and Hahn pumps when i do something in the car to stress the system, ie- turn on the carputer, turn on the headlights, turn on the A/C. etc...

I did not know that.

...:thumbsup

yea i figured this would work

got the idea from seeing the MSD fuel pump booster. i re-wired my pump too, but thats not good enough for me. i tapped the power line down at the pump, and it didnt make me very happy at idle. doesnt get enough power in my opinion.

like i said, fuel pumps are rated on flow for how many volts they run at....something to think about with a strained system like most udp driven 420a's....

The other thing to consider, Josh, is it an extended drop in power or is it a flutter? The reason is a cap will discharge rather quickly. They're only used for quick compensation (such as a bass hit in your stereo) and not really designed for keeping something at 14.4v constant for longer than a minute or two at the most. Once the reserve is gone then it's just going to flow straight from source to output, so whatever comes in goes straight out.

if you are getting any kind of voltage fluctuation, the first thing you should do is remove the ground and clean/sand it. im not sure if thats part of the re-wire or not (been a while since i read the tutorial). if you want to add a cap, a 0.5 farad should do the trick. add it inline as close to the pump as possible. the pump draws very little amperage (comparitavly) so it wouldnt take much to keep the voltage even.

just get a small motorcycle battery, put it on a solenoid off ur ignition, a charger and wire the pump to that, the pump will ahve its own independent source of power

Originally posted by VOTBLINDUB
just get a small motorcycle battery, put it on a solenoid off ur ignition, a charger and wire the pump to that, the pump will ahve its own independent source of power

I like his idea even better.
I do not believe in caps for my stereo, in fact I think they are garbage and just a cheap way for salesmen to make money... With something with a much smaller power demand though, they might do some good on a fuel pump.

Originally posted by BumpinTalon

Originally posted by VOTBLINDUB just get a small motorcycle battery, put it on a solenoid off ur ignition, a charger and wire the pump to that, the pump will ahve its own independent source of power

I like his idea even better. I do not believe in caps for my stereo, in fact I think they are garbage and just a cheap way for salesmen to make money... With something with a much smaller power demand though, they might do some good on a fuel pump.

But if that was the case then why do the pro's use them?

Because he's wrong. They do work.

lol riiiiiight. capcitors are stupid. maybe they shouldn't use them in power supplies either b/c they're just an added expense. it's not like stable power is important or anything :rolleyes

Originally posted by MCubed45
lol riiiiiight. capcitors are stupid. maybe they shouldn't use them in power supplies either b/c they're just an added expense. it's not like stable power is important or anything :rolleyes

LOL, I had to read that twice to make sure the eSarcasm was there before I went the fuck off on you LOL

Originally posted by a_miller_76

Originally posted by MCubed45 lol riiiiiight. capcitors are stupid. maybe they shouldn't use them in power supplies either b/c they're just an added expense. it's not like stable power is important or anything :rolleyes

LOL, I had to read that twice to make sure the eSarcasm was there before I went the fuck off on you LOL

haha yea i reread it after i posted it and realized that more than a few people might not catch the sarcasm. but then i thought it'd be funnier that way. :D

can the guys who dont know WTF theyre talking about just stop posting please?

no extra battery is needed :wallbash

the cap works

thankx aaron and josh :thumbsup (afterall this thread WAS to you guys)

caps do work. the thing with them is that you use a 1 farrad cap(for example, im just tossing out a number) for around 800 watt. usually 1 is enough to cover you 600-1000 watt. if you start getting into higher level amps like 2,3 4 or more thousand watt, youll have to get a 15 farrad cap, which is huge and really expensive. the caps do store a charge like a battery, they release it faster though. i am not sure how much charge can stored in a cap. a cap is only usefull for a short drain, then it need sto fill back up. using a cap for a fuel pump which will have a constant drain on power is useless. caps arent for that, caps are there to even out the current in case of drops, like when an amp hits. a battery is used for providing steady current. some use batteries instead of caps, but you will need more than one usually to help out with the current drop because batteries dont discharge as fast as a cap. in your case ur not going to have drops in current, so you want a nice steady source, which is a battery. like i said, get urself a nice bike battery, theyre small enough to be out of the way and hold enough charge to help the fuel pump. just make sure you vent it, otherwise you will run into problems with dangrous vapors leaking into the interior, you dont want that.

"using a cap for a fuel pump which will have a constant drain on power is useless. caps arent for that, caps are there to even out the current in case of drops, like when an amp hits. a battery is used for providing steady current "

no. power is dependant on both voltage and current which are twins (in a way). a regulated voltage source will provide an even current to the fuel pump. a cap WILL not only regulate voltage but also filter any unwanted a/c hitchhikers that may effect the system (be it car audio or not). an extra battery is fucking rediculous for a fuel pump, and its ability to maintain a steady voltage is no better than the current (no pun intended) battery in the car.

remember...current is a product of voltage (which fluctuates) and impedance (which is fixed for any one device). if you keep the volts even, you produce a steady stream of current. on something as small as a fuel pump, a cap could make a noticable difference. as for the audio aspect of them....im still unconvinced due to the transient nature of music, but thats a whole other thread.

Originally posted by SPL_Eclipseim still unconvinced due to the transient nature of music, but thats a whole other thread.

Exactly
I believe my amp has enough capacitance already built into it, I don't need to add an external cap. the only caps that I can imagine being useful in an audio application with a high power demand, like on a big subwoofer amp, are those gigantic ones that are 15 farads plus.

just do the fuel pump rewire and your done.

its the voltage drop due to the resistance/length of the smaller wire used that you want to get rid of. if you run a cap on the same small gauge fuel pump wire your not going to really help anything.

Originally posted by mcgyvr
just do the fuel pump rewire and your done. its the voltage drop due to the resistance/length of the smaller wire used that you want to get rid of. if you run a cap on the same small gauge fuel pump wire your not going to really help anything.

Originally posted by turbo8u
...:thumbsup yea i figured this would work got the idea from seeing the MSD fuel pump booster. i re-wired my pump too, but thats not good enough for me. i tapped the power line down at the pump, and it didnt make me very happy at idle. doesnt get enough power in my opinion. like i said, fuel pumps are rated on flow for how many volts they run at....something to think about with a strained system like most udp driven 420a's....

he already did. that's why he was asking if adding a cap would help.

actually no he tapped the line down at one point for some reason so he messed up.
if he would have done the fuel pump rewire correctly he wouldnt have this problem.

Originally posted by mcgyvr
actually no he tapped the line down at one point for some reason so he messed up. if he would have done the fuel pump rewire correctly he wouldnt have this problem.

when he said he tapped the line at the pump i think he was saying he had measured the voltage at the pump after doing the rewire and was not satisfied with the results. i could be wrong but that's how i understood his post. i guess we'll wait and see what he has to say :shrug

Your're better off running a larger gauge wire from the battery to the fuel pump, to prevent any major voltage drop issues, resulting from too much resistance in the wire run. I think i read in a post above somewhere, that the cap will "put out" 20+ volts or whatever. This is entirely not so. Just because the cap may say 24 volts on it, does not mean it can take your normal 13.6 volts(+/-), and convert it up to 24 volts. A cap isn't a transformer. The voltage it puts out, is roughly the voltage that comes into it. A cap is ONLY usefull for a instantaneos current drain situation, eg a loud bass hit(when referring to car audio). They help to keep voltage steady during this transient, because the cap can deliver the needed current, for that brief time frame, which helps support the main car battery. You will notice less voltage drop at the bass hit, and also less dimming lights, ect..

A cap for a fuel pump is pointless, let alone a waste of money. Use the right gauge wire, a proper switching relay, and fuse it at the battery, and that is all you should need. Even these high pressure, high flowing fuel pumps we use, dont draw more than 10 amps at MOST. I use a 10 gauge wire fused at the battery, going to the back of the car under the seat. From there it goes to a relay, which is switched on by the stock fuel pump power wire(blue/black i believe). Another thing that is VERY important, is the fuel pump ground! If you have a tiny gauge ground wire on the fuel pump, or if you are using the stock fuel pump ground wire, this also can produce a lot of resistance, which almost negates even doing the re-wire mod. Use the same gauge ground, as you do power. Ground it to clean, BARE metal of the chassis.

regardless of the wire guage to any electrical device in the car, there will be voltage fluctuations that could potentially be evened out with a cap. i think the main goal is to get an even power supply to the pump, not to necissarily raise the voltage. im not sure if there would be any noticable results, but this is all hypothetical anyway, lol.

ok here's another way for all of you to think of it:

he is adding a cap to his entire electrical system.

now that doesn't seem so bad, does it? but guess what? that's the same thing. if the fuel pump is already rewired and you're adding on a cap it's the same as installing a cap right next to the battery in parallel. the electrical schematic would look the same whether the cap is next to the fuel pump or in the engine bay next to the battery. for some reason you guys seem to think the cap is going to be selective and only help the fuel pump and tell the other electrical components to fuck off.

the reason for adding a cap to your audio system is not to help your sub. the purpose is to help your car's electrical system. claiming that cap's are only for audio is dumb. yes your 2000W amp is the cause of the problem, but the main benefactors of the added cap are the auxillary components which are being robbed of power (i.e. FUEL PUMP). caps are only associated with audio because high output amplifiers with exteremely large instantaneous power draws are the most common reason for needing a cap.

i'm not saying this is going to make a world of a difference but if he has measured the voltage getting to his fuel pump and found it to be dissatisfactory then i don't understand why you guys have such a hard time understanding why a cap would help to remedy this problem.

Originally posted by SPL_Eclipse
i think the main goal is to get an even power supply to the pump, not to necissarily raise the voltage. im not sure if there would be any noticable results, but this is all hypothetical anyway, lol.

exactly.

and yes, ive done the re-wire with larger gauge ground and power and still...its not that impressive. cubed understood perfectly, mcgoober confused himself just a little bit.


i talked to a few teachers at school and discovered another solution though, so its all good.