question about electronics related to fuel pump and stereo system

[1986.5supra_kid]

So i have a heavy power cable (1200watt rated) for a subwoofer that goes from engine compartment threw a 40amp maxx fuse then under the carpet to trunk to a 200 watt subwoofer. I have a 400lph walbro that i was going to power from off that same 1200 watt rated cable. So i was thinking about the current drawl during the heavy bass and how this would pull power from fuel pump. so how about a walmart amp capacitor?

CLICK the PICTURE below for bigger image

Again it goes battery then 40 amp fuse(not in picture) to a junction between fuel pump and the capacitor then amp all tied to ground.

The exact power cable used in the car Scosche KPA6 1200W 6-Gauge Car Amplifier Install Kit
web link below
http://www.walmart.com/ip/Scosche-KPA6-1200W-6-Gauge-Car-Amplifier-Install-Kit/10629475

I think a 2 Farad capacitor should be PLENTY for a 200W amp
http://www.walmart.com/search/searc...pacitor&ic=16_0&Find=Find&search_constraint=0

 

[1986.5supra_kid]

Bump for information from wise and knowledgeable members

 

[supraguy@aol]

And as Supra kid knows, i'm interested in the answer to this as well.

 

[IndigoMKII]

My concern would be the amperage on the circuit itself.

The walbro 400 at 40 PSI is a 12 amp draw.

 

[SC61 MK3]

No cap needed, you need to look at the fuse on the side on the amplifier to determine its max current draw and add the current draw of the fuel pump to determine the main fuse rating. I would also suggest a distribution block with seperate fuses for the amp and pump in the trunk as close to each as possible. Save the money on the cap and make sure your alternator and battery are in tip top shape.

 

[Dan_Gyoba]

The capacitor won't hurt, but isn't really needed. The fuel pump isn't a variable load, so it won't cause problems for the amplifier. Depending on what you listen to, however, the amplifier may cause issues with the fuel pump. The pump itself may "whine" a bit, but the internal capacitance on the amp's power supply should be more than adequate to deal with it.

You will need to increase the fusing if you choose to do this, since as stated, the fuel pump draws significant current. (My system in my '89 has an 80A fuse, which I've blown once. 40A seems so tiny to me. ) I would also say that you should use a distribution block to tap the power from, and of course a relay so that the fuel pump doesn't run full-time.

Now for why this is a bad idea.

Like I said, the amplifier is going to draw a variable current based on what it needs to make the subs go thump. This means that you're subjecting the fuel pump to a fluctuating voltage. It probably won't put the pump at the point where it can't keep up to fuel pressure/flow demands, but it's not going to make things easier on it, nor on the fuel pressure regulator downstream. Also, should you blow your sound system fuse, your car will die. I don't like the idea of the sound system being tied in with the car being able to run.

You can mitigate the risk here somewhat by using a larger than necessary fuse at the battery, then using a fused distribution block with a total fuse load of less than the main. For example, an 80A fuse at the battery, then a 40A fuse at the distribution block for the amp, and a 20A fuse to the fuel pump.

Essentially, I don't recommend it at all. A 12-14AWG wire run specifically for the fuel pump is a much better idea.

 

[supraguy@aol]

I don't know if he worded it clearly, but we're talking separate fuses, fused distribution block, and cap on the amp, not the pump.
The issue is to make sure that the variable load from the amp doesn't affect the pump, not the other way around.
The only fuse that would be shared is the one next to the battery, and i wouldn't mind if this is shared, as its there to prevent the risk of short/fire, not over taxation on the system. And yes, i agree that you don't want the pump running at all times, but how would it? We're not talking about running the fuel pump relay from the battery, we're just talking about using the same piece of large gauge wire for providing the relay at the trunk, with fuel pump power, via a distribution block.

 

[SC61 MK3]

I don't know if he worded it clearly, but we're talking separate fuses, fused distribution block, and cap on the amp, not the pump.
The issue is to make sure that the variable load from the amp doesn't affect the pump, not the other way around.
The only fuse that would be shared is the one next to the battery, and i wouldn't mind if this is shared, as its there to prevent the risk of short/fire, not over taxation on the system. And yes, i agree that you don't want the pump running at all times, but how would it? We're not talking about running the fuel pump relay from the battery, we're just talking about using the same piece of large gauge wire for providing the relay at the trunk, with fuel pump power, via a distribution block.

It will not. I have done this before with much bigger amplifiers and had no issues. No cap needed. I even used a volt gauge hooked up to the rear distribution block to monitor fuel pump voltage. It was fine, just when you want to do long full boost pulls turn the stereo down to be safe

 

[supraguy@aol]

It was fine, just when you want to do long full boost pulls turn the stereo down to be safe

Lol. I can see trying to race a guy while listening to the 1812 overture, and melting the pistons during the drum climax...

 

[1986.5supra_kid]

Lolz what a climax "you know what I mean "

I guess I could run seperate 10 gauge wires for pump. Just taking the interior apart sucks.

 

[1986.5supra_kid]

Lolz what a climax "you know what I mean "

I guess I could run seperate 10 gauge wires for pump. Just taking the interior apart sucks.

 

[SC61 MK3]

Why? There is no difference, everything goes back to the battery anyways... just make sure they're fused separately

 

[91Supra313]

Fused or not the pump will run continuously. The reason the amp doesn't is because of the fancy small blue wire in the amp kit. That turns the amp on when the radio is turned on. The pump on the other hand is run straight to power.....so it will not shutoff. all ofthe fuses are a great idea, but there needs to be a kill switch in there somewhere for the fuel pump's power source. Unless you want the battery to die from the pump running 24-7

 

[SC61 MK3]

No shit, my god I hope no one would just hook a constant power up the fuel pump...

I assumed we were talking about doing a fuel pump rewire and instead of running a power wire all the way up to the battery, we were just grabbing it from a distro block shared with an amplifier.

 

[91Supra313]

I don't know if he worded it clearly, but we're talking separate fuses, fused distribution block, and cap on the amp, not the pump.
The issue is to make sure that the variable load from the amp doesn't affect the pump, not the other way around.
The only fuse that would be shared is the one next to the battery, and i wouldn't mind if this is shared, as its there to prevent the risk of short/fire, not over taxation on the system. And yes, i agree that you don't want the pump running at all times, but how would it? We're not talking about running the fuel pump relay from the battery, we're just talking about using the same piece of large gauge wire for providing the relay at the trunk, with fuel pump power, via a distribution block.

Ahhhhhhh Now I see what you are talking about now. I thought you meant power for the pump on its own. I didn't know a relay was going to be used there.

 

[1986.5supra_kid]

I should have added the relay to the picture. But I felt no one would be that ignorant to run power 24/7 to pump.

@SC61 MK3
So just split the power from the big cable to amp and relay for FP and use a 60amp fuse for subwoofer/FP at battery. the subwoofer uses a 20 amp fuse built in so I assume a 40 amp for 400lph is good. That's where I came uP with a 60amp fuse for at batt

 

[SC61 MK3]

40 amp fuse for the pump is way to big, I used a 25 amp. Most relays can only handle 30 amps anyways so I'd rather replace a fuse than a relay. And yes the easiest way is to get a "fused distribution block" with one input (from the battery) and two outputs (to the amp and FP)

 

[1986.5supra_kid]

Alright I'll search for a "fused distribution block"
BTW how do you figure out amp drawl on a fuel pump? I assume the lph and pressure have something to do with it and the 12vdc is a contrant. I'd like to know just to learn and know why.
Thank you!

 

[IJ.]

Why on earth wouldn't you run a dedicated supply?

 

[supraguy@aol]

In an effort to reduce large gauge cables passing through the car, i suppose.
If you were to run say, a 4 gauge power cable to the back, then that is essentially an extension of the battery, now located in the trunk area. Connecting there by way of a fused distribution block seems like a solid and simple method of connecting the fuel pump relay to one side, and an accessory(amp) to the other.