PWM fuel pump control.

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gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

PWM fuel pump control.

Post by gnutz2 »

I know this topic has been brought up here, albeit for fans but the goal is the same.

viewtopic.php?f=5&t=1121

And I've read this very informative thread over on PH forum.

http://www.pistonheads.com/gassing/topic.asp?t=916550

At the moment i have two bosch 044's on the car, the primary pump runs off the fuel pump relay and the secondary pump runs off an auxiliary at a set load.

Now i have the primary pump running off pwm on aux1 through a 40A dc/dc ssr, the pump runs great at 30% duty @ 300hz, it's barely audible and pulls only 3A load compared to the usual 11A on idle.

I have 2 problems. Firstly when i ramp up the pump duty to 100% I only see a load of 8.5A and 11v at the pump, when I measure across the ssr I see a volt drop of 3v.

Second problem is I want to control both bosch pumps ideally through one ssr but when i connect both pumps in parallel the ssr starts to overheat. Can two inductive loads be run off one ssr or would i need to run two relays and run the input in parallel.

Anyone BTDT :D

Baz.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: PWM fuel pump control.

Post by stevieturbo »

SSR usually needs a good heat sink.

There was an update to this thread recently where some people are using a PWM fan controller, seems fairly cheap used from US sources, and possibly some Euro cars might have them too ?

http://ls1tech.com/forums/forced-induct ... ems-2.html

Also, from the thread on PH...300Hz seems very very low, Max etc were suggesting well into the thousands, like 10khz for PWM control.
gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

Re: PWM fuel pump control.

Post by gnutz2 »

I have a good heat sink with heat compound on.

Thanks for the links Stevie, I'll have a look.

Found this on a basic relay tutorial site, it never entered into my head that a ssr would be so inefficient.

the voltage drop across the output terminals of an SSR when “ON” is much higher than that of the electromechanical relay, typically 1.5 – 2.0 volts

Ultimately the volt drop and corresponding drop in fuel flow could be overcome by an electromechanical relay supplying full voltage at full power. All I'm interested in is making the fucking bosch 044 pumps quiet at low engine loads, lol
Last edited by gnutz2 on Sat Oct 01, 2016 3:49 pm, edited 1 time in total.
gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

Re: PWM fuel pump control.

Post by gnutz2 »

And frequency.

I was using aux1 which is 16-400 hz and 300hz seemed to make the pump run very silent. I've just realised that aux3 does 1khz so I'll be trying that next. Even running the pump at 16hz works, the engine will run but you can hear the pump pulsing, I assume the fuel rail pressure would be all over the place too.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: PWM fuel pump control.

Post by stevieturbo »

And apparently all SSR's are not the same some are better suited to this type of thing than others, although I dont know the difference myself. I'd be surprised if the volt drop you're experiencing is considered normal or acceptable though ?

I did buy a couple of cheap ones to try, but never did get around to it. And a 2v drop is huge in terms of flow.

Although I've 2 044's on mine....never had any concerns about noise ? How are yours mounted ?

Good rubber mounts and as long as they arent inside the cabin, noise really shouldnt be a big deal ?
gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

Re: PWM fuel pump control.

Post by gnutz2 »

Mine were underneath the car fed with an8 lines from the fuel tank inside the car, on long journeys when the fuel got hot the pumps would start to cavitate at the inlet and make a horrible screaming noise, i assumed this was down to the restriction of the fuel lines and fuel filter.

So, I moved the fuel lines to the other side of the car because I thought they were picking up a lot of heat from the exhaust downpipe, then I made a surge tank and mounted both the pumps inside and added a lift pump to feed the surge tank, this removes any restrictions at the pump inlets and gives them the best possible chance of working because of the slight positive pressure inside the surge tank. To my surprise they still get noisy when run for extended periods.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: PWM fuel pump control.

Post by stevieturbo »

Depending on how you configure the swirl though, you can end up heating the fuel even more.

I've just a large tank, fuel pumps under the boot...and never really have any issues. Even driving for 4 hours non stop, no problem.
Mine only have a single -10 hose from the tank to both pumps...something I keep meaning to upgrade, but really cant be bothered removing the tank to start welding at it ! lol

Is that 1 -8 line per pump, or for both ? Short or long hose ?

I do have a cooler on the return line, but this is under the car and not really in a good spot. I only fitted it as I ended up with a spare oil cooler so decided to throw it on for that instead. I had never had any issues before I fitted it though.

Really...if there genuinely is a problem with hot fuel ( and most people who say they have...can never actually state how hot their fuel is as they dont log it )...then just fit a cooler. It's a doddle to do.
gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

Re: PWM fuel pump control.

Post by gnutz2 »

I used to have one an8 line feeding both pumps but only one pump ran full time, the secondary pump came in at half a bar of boost. The car ran fine for a year but this year the main pump started making a howling noise whenever the fuel warmed up, this was a little confusing because everything was fine the previous year so I cleaned the pre filter and the bosch pre strainer at the pump but nothing improved.

Thats when i decided to build a tank for both bos h pumps anf remove any pre pump restrictions and restore the quiet running, this was the solution with the addition of a lift pump to feed it.
Image
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Unfortunately removing all pre pump restrictions didn't resolve the noisy pump problem so I can only assume that the pump was damaged from running cavitated for a long period of time. So I decided to cut my losses with the bosch pumps and go a different route with quieter pumps that almost flow as much and I didn't like the idea of a aluminium tank of fuel inside the car.

This current setup is completely sealed in the fuel tank and almost silent.

Image
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stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: PWM fuel pump control.

Post by stevieturbo »

Make sure all that hose is suitable for being submergered in fuel...most is not.

That's a lot of pumps. Could you build a tank with a built in collector/sump at the bottom and just run a pair of pumps ?

Or even a single 340 or 450 Walbro can flow a lot of fuel, how much fuel flow do you need ?

Even a single 044 can do 650 or so depending on application. The 340's are similar or certainly 450 Walbro will do a lot more.
gnutz2
Posts: 190
Joined: Tue Jul 03, 2012 2:33 am
ECU Model: S100 Pro

Re: PWM fuel pump control.

Post by gnutz2 »

The pipe on the high pressure side came with the in tank pumps but I will keep an eye on it.

That was my old setup, I built a surge flap system with 3 sides and 3 rubber check flaps, the fuel outlet was at the rear of the tank from inside this surge box. I ran the car like this for a while and it worked better than the foam that came fitted to the tank but the pump would still get large gulps of air at around 1/3 of a tank (bearing in mind that it's only a 40l tank).

Originally I used a walbro 255 external pump and 5 x Siemens 630cc injectors, these were 100% idc at around 1.7 bar of boost. So I fitted 5 x Siemens 875cc outboard injectors and the bosch 044 pump. Now i can run the 875cc injectors up to 100% at around 2.2 bar of boost which tells me I'm using
262l/h of fuel which fits in ok with bosch pump.

Problem is that I now run a dry nitrous system which requires 15% extra fuel when activated, that takes the fuel flow to 300l/h which, on paper, is more than the bosch can do at 5.2 bar, and in the future I would like to double the nitrous shot which would then require 340l/h of fuel @5.2bar. Also remember that my fuel flow figures will be higher because of the 20% methanol in the fuel.

A single 450 walbro was my first thought and would flow enough for sure but another 450 pump would be required to fill the surge tank so I decided to try out these inexpensive 340l/h aeromotive copies.
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