Fuel pump and potentiometer / resistor.

FIntruder · Post by **FIntruder** » Sun Jul 16, 2006 1:47 pm

I wanna use an MSD 2225 fuel pump on a motorcycle with only 300watt alternator. This pump can provide way more fuel than I will need so I was wonderin if I could use a resistor to slow it down some and not draw the 60watts+/- that it is rated for. Is this rating what the pump will draw all the time or only under max load?
I know that A/C blower motors use resistors or potentiometers I was just wonderin' if there is somethin' I'm overlookin'.
I picked this pump cuz it is one of the only "inline" style I could find. Is there a smaller one out there? My bike only makes about 62hp at the rear wheel, hopefully more with the larger throttle bodies. The MSD pump can support 500hp so there is room to spare. I'd really rather go with something available in the US and not some obscure 1962 Formula 1 item that many here like to try and hunt down. More power to ya, just not my bag.

jakobsladderz · Post by **jakobsladderz** » Sun Jul 16, 2006 4:19 pm

You'd definite be better getting a smaller (and probably lighter) pump. The current drawn by the fuel pump is a product of the pump's design and the pressure it is pumping. With normal MAP referenced regulators the current consumption depends on manifold pressure and will be largest at highest manifold pressure. It is relatively independant on the actual fuel consumption.
If you use too big a pump, especially on a bike with a small fuel tank (compared to a car) you will be heating your fuel considerably. Imagine sticking a 60watt lightbulk in the tank and turning it on, the fuel would boil after an hour or two. The fuelpump will do the same thing..
A resistor might not be the best solution. Fuel flow is proportional to voltage (take a bit for motor internal resistance). If you use a resistor then you'll get the lowest flowrate when the current is highest - that is, you'll have less fuel when you need more..
A constant voltage supply would be a better idea, perhaps a PWM drive that will act more like a constant voltage source.

In short you can drop the voltage to lower the power usage but the extra complexity of the setup may hurt reliability. You'd be better getting a corectly rated pump and running it of its rated voltage.

FIntruder · Post by **FIntruder** » Sun Jul 16, 2006 6:36 pm

The voltage would be constant, just less than 13.2VDC . I'm talkin' about putting a 60watt whatever Ohm resistor say on the ground wire between the pump and ground. It will only run at partial speed but should be able to keep up with my needs even at this reduced speed/volume.
I'm assuming most fuel pumps run the whole time the ignition is on with the regulator keeping the pressure where it needs to be. Lower fuel pressure when high vacumn is pulling on the regulators diaphragm at idle and cruise speeds where the voltage will also be lower cuz the rpms are lower.

jakobsladderz · Post by **jakobsladderz** » Sun Jul 16, 2006 6:58 pm

Assuming that the engine is naturally aspirated you could try this approach:

obtain an adjustable power supply of some sort fitted with an ammeter and a voltmeter.
pipe the output from the pressure regulator to a measuring vessel with the fuel pump and regulator set up as it would be on the bike.
power the pump up and adjust the voltage to give maybe 25-35% more flow than you need at full power/revs/. because the reference to the reg will be at atmospheric pressure, this will be the largest power requirement you'll need.
using the voltage/current you find, choose a suitable resistor to match that.

Whilst thinking about this I realised the archiles heel of your plan. The current consumption is proportional to the pressure being developed. If you choose a resistor to drop the voltage to the pump, you still need the same current for the same pressure. Using the resistor will reduce the amount of power being used by the pump (say from 60 watts to 30 watts) but the other 30 watts is now being dissipated by the resistor. the battery and charging system still sees a load of 60 watts, so your original aim is not met. If fuel heating was the problem this will work as the resistor will heat up, not the fuel.

A PWM driver with a flyback diode will be much more efficient so say you need to drive the pump with only 6 volts to meet your desired flow requirements, a motor current of say 5 amps at 6 volts would be an input to the regulator of around 2.5 amps at 13 volts, and the charging system would only need to provide marginally more power than the motor is using (due to some small inefficiencies in the drive).

Savvy? (sorry, too much pirates of the caribbean)

FIntruder · Post by **FIntruder** » Sat Jul 22, 2006 4:17 am

Aarrgghh......... The resistor will only dissipate some of the wattage into heat. The load would only be 30 to 35watts with some waste.
I read on another link about a Mallory 4060 pump. Is this an external inline pump? I'll try to search for it again on Ebay or speedshops but haven't found one. If it is smaller and can support 100 to 200hp then that may be what I'll need to go with.
One experience I've had with resistors was with car stereo. I have a factory Bose system in my Cadolac and the speakers sound awesome but the deck went Kaput. The speakers are 1 Ohm with amps built into the speaker box in the door. I axed Crutchfield and a few others if I could bypass the amps and run a 3 Ohm resistor in the ground wire so my new 4 channel 50watt amp would see a 4 Ohm load. Everybody said no way, it wouldn't work. I had to use an "Interface" module. I tried two different modules and after years of fiddlin' and dealing with noise I went ahead and sprung for the 50watt, 3Ohm resistor, $4 and guess what. It sounds freakin' beautiful. Some of the different responses I got from those I had asked were: "You won't hear anything, the resistor will filter the sound out", or "Thats not the way electricity works".
I really appreciate your input, I didn't think about the fuel heating issue. Does the heat come from pressurizing the fuel? Wouldn't it cool back off when the pressure is released after the regulator. Like in an air conditioner, high side is hot, low side is cool?

jsmcortina · Post by **jsmcortina** » Sat Jul 22, 2006 4:30 am

The pump is an electric motor, so if you provide it 12 volts and it draws 5 amps then depending on the efficiency a percentage of that power will end up heating the windings on the motor which are fuel cooled - hence the fuel heats up.
So if the pump is working hard to pump lots of fuel (more than you need) it will be rushing from tank->pump->rail->regulator->tank and heating up.

Using a correctly sized pump is likely to be easier and more reliable - the pumps are designed to run off full voltage so without "clever" PWM control it might not do what you expect.

However, if you want to try, you could create a simple PWM circuit with a NE556 and a VND5N07 or VB921 or similar to drive it.

James

jakobsladderz · Post by **jakobsladderz** » Sat Jul 22, 2006 4:43 am

With the speaker, it'll sound fine but the speaker will only be seeing 1/4 of the power the amp is putting in (in this case the speaker sees 12.5 of the 50 watts). It's not efficient but it will work fine..
The heat going into the fuel is partly due to resistive heating losses in the windings of the motor and partly due to friction losses in the fluid. Because fuel is essentially incompressible, it's not the same as say air heating up through a turbo.
Power flow in a fluid is pressure mutliplied by flowrate, so the pump is increasing the pressure (at a constant flowrate) and thereby doing work on the fluid. At the pressure regulator the pressure is being relieved back to a low level through the valve. The pressure power of the fuel is converted by the huge turbulence in the outlet of the pressure regulator to heat (and a bit of noise), so it actually will warm up after exiting the fuel reg. The fuel pressure regulator is the fluid flow equivalent of a resistor in an electrical circuit..

just for my own sake, fluid power calcs.. Assuming 3.3 bar (330kpa) fuel pressure and 130li/hr (~400Hp) flowrate..

130 li/hr = 3.6111e-5 m^3/s
330kPa = 3.3e5 pa

fluid power = 3.3e5 * 3.6111e-5 = 11.92 watts

this pump would probably draw ~5 amps at 13 volts to pump this amount of fuel at this pressure so electric power would be

5*13 = ~65 watts.

given that, ~53 watts are resistive/mechanical losses in the pump and ~12 watts is carried in the pressure/flow of the fuel (and either serves to push fuel into the manifold or gets lost to heat after the fuel reg). 18.5% efficiency sounds pretty bad though... hmm.

Duncan

the bubbler · Post by **the bubbler** » Sat Jul 22, 2006 5:41 am

Why don't you just get a fuel pump from a modern fuel injected bike. Plenty of them on ebay for not a lot of beans, and will only draw a couple of amps at the most.

Andy

FIntruder · Post by **FIntruder** » Sun Jul 23, 2006 4:50 am

Most if not all of the motorcycle fuel pumps I have seen are of the "in tank" variety and that is not very do-able with my plan. The bike came with carburetors stock and the tank is not very tall like the fuel pump units are. Do you know of an inline style pump that is good fer 100hp?

All pressure is is excess volume, correct? Less excess volume just means less pressure. I guess I'll be the first to know.

the bubbler · Post by **the bubbler** » Sun Jul 23, 2006 9:46 pm

Yes I'm afraid most pumps are geared towards intank fitment.

You have a couple of choices there- modify the assembly to fit your tank, or make a seperate tank for the fuel pump.

Don't forget the pressure regulator will regulate the flow according to what is required to maintain 3 bar at the injector.

Andy

ami8break · Post by **ami8break** » Wed Jun 13, 2007 11:57 am

jsmcortina wrote:... you could create a simple PWM circuit with a NE556 and a VND5N07 or VB921 or similar to drive it.

Hello James,
my local dealer isn't able to order VND5N07 (obsolete) or VB921 (not easy to get in EU). Could you tell me a replacement type for such a PWM circuit? Maybe a IRF530 (rated up to 14A) for EUR 0.86.
I found this promising circuits:
http://www.cpemma.co.uk/555pwm.html or http://www.cpemma.co.uk/pwm.html#classic . Do you think they would work to control an automotive fuel pump?
What do you recomend?

I have an inline pump (~120hp GM engine) which is much oversized (but I have also the same as spare part). I guess all 2.5bar pumps I could find on scrap yards are oversized for my poor 40hp EFI vehicle --> PWM is the way to go.

I use this pump for some years now but I hope to lower fuel consumption if the return volume could minimized (fuel vapor).
Recently I added a small hose from tank (fuel cap) to throttle body (above) similar to carcoal canister systems, but I feel much pressure losses through >5 metres (ÃƒËœ 6mm) motor bike fuel hose!

I plan to tune the lowest possible PWM with manometer in fuel line lead outside of engine bay to watch if there are drop downs when MS provides highest fuel flow. Then added a tiny "security distance" (resistor instead of the tuning pot) to provide enough fuel all the time.

Thanks
Ã‚Â»Horst