MicroSquirt.com read only forum (Jan.15,2018)

That looks like part of the solution. How would it know what the pressure is and how fast can it react? Are you sure this would work for this kinda application? Give them a call and see what they have to say. I'm sure those are available over here in the US of A, I'll search. How much is that in American $ ?

FIntruder wrote:That looks like part of the solution. How would it know what the pressure is and how fast can it react? Are you sure this would work for this kinda application? Give them a call and see what they have to say. I'm sure those are available over here in the US of A, I'll search. How much is that in American $ ?

Jaycar nitrous motor control kit.

The Jaycar US site has the same thing, $15.95 USD

Ok, we may be on to something. A PWM card/unit will do the same thing as a resistor but in a different way? Like with a Radio Controlled Car, the cheap speed controllers use a resistor but the nice expensive ones use the magic way. Do they use PWM?
The motor speed controller would not have to vary the fuel pump speed, just lower it so as to draw less current and flow less fuel. The pressure would still be controlled by the FPR and use a return line style rail.
Does anyone have a link to a nice explanation on PWM ?

PWM is a fancy way to regulate the speed of a DC motor without causing excess heating and bad regulation as you would get by using a variable resistor.

If you have a resistor, and drive a motor through that, all of the load of the motor goes through the resistor, and that resistor has a fixed voltage drop at a fixed load. Say the load changes, that will cause the current through the resistor to change which causes the voltage drop to change, thus the speed of the motor changes with load.

With PWM you are fooling the DC motor into seeing a different average voltage by the changes in duty cycle, higher duty cycle = higher average voltage, thus higher speed, and vice versa. The PWM controller drives the motor directly with a fixed duty cycle, the load can change but the speed remains relativly constant because you are maintaining that fixed duty cycle.

...and the little blue pot on that PCB will allow you to set the duty cycle to wherever you want to vary the speed/current draw of your fuel pump, just in case you were going to ask : )

Ian.

FIntruder wrote: Does anyone have a link to a nice explanation on PWM ?

PWM (Pulse Width Modulation) is a simple but brilliant scheme. You simply switch voltage on and off quickly enough that whatever you're driving effectively sees a fraction of the actual supply voltage. The effective voltage is the duty cycle('ON' time divided by total time) times the supply voltage.

For example, you may want to drive your pump at 8 volts but only have 12 available. The desired voltage is 67% of the supply, so that's the duty cycle you aim for. Say your PWM frequency is 1000 Hz(cycles per second) meaning that a cycle takes .001 seconds. You simply switch the 12v ON for .00067 seconds, then OFF for .00033 seconds. Repeat that cycle continuously and you've implemented PWM. The Pulse Width in this example is .00067 seconds. By MODULATING (varying) this Pulse Width you can create any effective voltage from 0 to 12V.

Thanks for the info and explanations. I also did a little research myself and was starting to think PWM was not the way to go but maybe it is. It seems to not work so well at lower duty cycles where the pulses can be felt and may have a detrimental effect on the motor.

Does anyone know how low a duty cycle a fuel pump could reasonably run at without any problems? When purchasing a PWM device, what specs are important besides amperage rating and probably frequency, the higher the better? Too slow of a frequency would also make pulsing evident at a higher duty cycle? Any downside to using this setup? It will also be smaller than a resistor big enough to handle 60 watts.

I don't know the answers to your specific questions regarding fuel pumps, and I imagine that each type of pump will have a different set of minimums it can handle, but a PWM circuit is not that complicated. A 555 timer circuit and a drive transistor should just about do it. There should be plenty of schematics out on the net for that.

As the FIntruder pointed out, the FP I bought for the Sporty from a Buell is some type of internal one. My bad. I thought it was external. So, I'm kinda stuck here also, unless I can figure a way to mount this thing inside a conventional gas tank, which I may have to do.

Hey Ian, as our resident Buell expert, I have some questions on that pump I have:
http://www.microsquirt.com/download.php?id=5656
The regulator is at the top, along with the out line. I assume that on the XB, this whole thing is mounted inside the tank and secured by the feed through gromet thing. Does the outlet pipe stick through the side of the tank also? Does the regulator just dump fuel out the side of it back inside the tank or does it route back somehow? I wish I could see one of these things in-situ.

If I get a separate extenal fuel pump and regulator, I kinda was thinking I could plumb it like this:

Gas tank
|
|
|-------------
Fuel pump ^
Regulator ^
|
Injectors

In other words, T the regulator return line back to the fuel pump in line from the gas tank. My thinking is that excess pressure would just feed back through the pump. Might heat the fuel a little bit, but I don't see any other reason this wouldn't work. Otherwise, I'd have to make a fitting to fit the bottom of the tank with two pipes going into it. Not impossible, but, of course, a PITA to get liquid tight, and I have a real nice Pingle valve on there now.

Or you could make a small tank and fit the pump into it and locate it lower than the gas tank. Depends how big the fuel pump is to begin with, it looks kinda small relative to some. I think this would be easier than tryin' to mod a gas tank to hold one, especially the teeny-weeny Sportster tank.

Dr.Hess wrote:As the FIntruder pointed out, the FP I bought for the Sporty from a Buell is some type of internal one. My bad. I thought it was external. So, I'm kinda stuck here also, unless I can figure a way to mount this thing inside a conventional gas tank, which I may have to do.

The regulator is at the top, along with the out line. I assume that on the XB, this whole thing is mounted inside the tank and secured by the feed through gromet thing. Does the outlet pipe stick through the side of the tank also? Does the regulator just dump fuel out the side of it back inside the tank or does it route back somehow?

I've never checked the installation of the pump you have on a Buell, but it looks to me that it's still external, except for the large round fitting going into the tank. I don't know how it would go with the fuel pressure regulator feeding back into the pump feed, I guess you could try it on the bench and see how warm/hot it gets, I've never set up a fuel system so I can't really comment.

The XB pump is totally internal, the FPR is inside so there's no return line as such, there is only one fuel line and some wires coming out of the plate that everything is mounted on. The plate is fixed by 4 screws into the end of the frame/fuel tank on the LHS above the swingarm pivot. I think it would be more difficult to use than the one you have, going by the pics in the FM.

Would it be possible to fit another Pingle fuel tap on the other side of the tank for the return? That would work well and look good, with a completely external pump/FPR.

Ian.