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  1. #11
    downunder123
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    I am almost certain that BLDC motors are used in the in-tank fuel pumps given the no ventilation situation and more importantly hazardous environment where NO SPARKS are wanted, common with brushed DC motors. Brushless motors must have electronic drivers to energize the coils at the right time and the right polarity. The driver must be packaged within our pump housing and is really the best way to control the operation of a BLDC motor. Typically reducing the voltage will reduce its speed of rotation where reducing current will decrease the torque of a motor. Applying excessive voltage for too long above rated specs is NO GOOD as it will increase the speed of rotation and generate heat. The heat is the worst enemy for motors. Applying the under spec voltage should not bother BLDC too much, it will run cooler with slower rotation until voltage drops low for motor to operate and the current will go up again.
    So I did some tests with OEM and aftermarket pumps. Bellow is the summary of measurements I took.
    Things to note:
    -I used water instead of petrol, don't think it would make huge difference on the readings with petrol
    -tests were done with approx 2 feet hoses with FPR at the end and schrader valve for my pressure gauge.
    -my bench PS was maxing out at just above 14V @ 6A with pump working under load (in the water)
    -all readings were taken with pumps under load on my workbench. The extra load and consumption of petrol by fuel injectors should be considered when engine is running.

    Aftermaket OEM
    V A psi V A psi
    14 5.9 30 14 2.09 23
    13.5 5.67 30 13.5 2.03 22.5
    13 5.49 29 13 1.98 22
    12.5 5.3 29 12.5 1.93 22
    12 4.93 28 12 1.9 22
    11.5 4.7 27 11.5 1.87 22
    11 4.5 26 11 1.85 21.5
    10.5 4.32 26 10.5 1.87 21
    10 4.1 25 10 1.92 20.5
    9.5 3.95 24 9.5
    9 3.7 24 9
    8.5 3.5 23.5 8.5
    8 3.3 23 8
    7.5 3.14 22 7.5


    The aftermarket pump @7.5V when stalled pushed the pressure to 50psi. When voltage was reduced the current went down as well and vice versa. The same happens when increasing the current ,the voltage would go up as well.
    The aftemarket pump was NOT pushing more than 30 psi above 14V up to 18 V being max V applied.
    The OEM pump behaved in the same way but the operating range was a lot smaller. Below 10V the pump's motor would stop rotating and current would go upwards.
    Temperature was not an issue and the pumps were always running cool as expected being in the water.
    For 12L of water to be moved from one to another tank it took:

    OEM: 6min 30sec (@13.5V 1.98A 22,5 psi)
    Afermarket: 5 min 40sec (@ 8.5V 3.5A 23psi)

    For the reference to the non metric people (hate those old school confusing and inaccurate imperial fractions), my Genesis I would use approx 20L per hour when I tow and have an observer on the back seat. When I solo ride at 70% throttle in calm waters my ski uses approx 12L per hour!

    It looks that aftermarket pump can be modified by either restricting the voltage or current with the same result. Reducing voltage would be easier but heat, waterproofing and physical mounting need to be worked out.


  2. #12
    This type will be good to look into is the smaller fuel pump I could find that meet the specifications.
    http://oem.fuelpumps.com/dodge-fuel-...efi-p-886.html

    The Fuel pump in the Polaris seem to come from a Dodge Ram or Dakota circa 1996!

  3. #13
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Tune by Tito View Post
    All fuel pump are rated at 12 volts nominal, however all of them are made to withstand higher voltages, the charging system can dump more than 45 volts to the battery any time.

    Also if the flow increase then increasing the load use a external fuel regulator to control the load, this system do not depend on a specific fuel pressure to function correctly, the service manual said between 20 to 30 psi, the amount of fuel injected in the chamber is determine by the stroke of the injector and the fuel maps, is a very basic Alpha Number system with a stupid complex ECU(EMM).

    So you will not loose any thing, you only will gain knowledge.
    The 45 volt system is in no way connected to the 12 volt battery, at all. The 12 volt battery circuit is separate from the 45 volt circuit. They are separate outputs from the EMM.

    The maximum voltage on the 12 volt battery during engine run/charging would be just under 15 volts.

    You are correct that the Ficht system does not require a specific fuel pressure, just decent pressure within a range. And it requires return fuel flow through the injectors.

    On a stock Polaris Ficht watercraft, we can use the measured fuel pressure to verify expected fuel pump operation.

  4. #14
    Moderator HiPeRcO's Avatar
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    Quote Originally Posted by bspanovic View Post
    I am almost certain that BLDC motors are used in the in-tank fuel pumps given the no ventilation situation and more importantly hazardous environment where NO SPARKS are wanted, common with brushed DC motors.
    You will be surprised to learn that not only are brushed motors used, but the fuel flows right through the motor (including the brushes)! This is possible because there must be a proper air/fuel ratio for a spark to cause ignition. Pure fuel does not burn, only vapor mixed with air does.

    Nice work on the pump current draw measurements! It seems that at least for the pump you have that driving it with 5V may be insufficient.

  5. #15
    martincom's Avatar
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    I did some searching for voltage regulators on Digikey. I was hoping to find something with an 8 volt output and 4.0 amps or more current capability..and in a TO-220 package. I struck out. I found one listed for 5.0 amps in a surface mount package, but it was obsolete and they had no stock.

    I'll check Mouser.

  6. #16
    Moderator HiPeRcO's Avatar
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    Quote Originally Posted by martincom View Post
    I did some searching for voltage regulators on Digikey. I was hoping to find something with an 8 volt output and 4.0 amps or more current capability..and in a TO-220 package. I struck out. I found one listed for 5.0 amps in a surface mount package, but it was obsolete and they had no stock.

    I'll check Mouser.
    Linear voltage regulators will dissipate a lot of power across them. I would focus on a search for a ruggedized DC/DC converter instead.

    EDIT: Like this: https://www.amazon.com/SMAKN-Convert.../dp/B00CXKCRME

  7. #17
    Walbro Rotary Fuel Pumps seem to work:
    Look this document the fuel pump in the middle of the PDF.
    Current: as low as 1.0 amp
    @ 300 kPa (43 psi) @ 13 volts
    http://www.walbro.com/wp-content/upl...umps_PS_EN.pdf
    But I can't find it in Walbro web page!

  8. #18
    martincom's Avatar
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    Quote Originally Posted by HiPeRcO View Post
    Linear voltage regulators will dissipate a lot of power across them. I would focus on a search for a ruggedized DC/DC converter instead.

    EDIT: Like this: https://www.amazon.com/SMAKN-Convert.../dp/B00CXKCRME
    Considering the physical size of the package, limited heatsinking, and in surface mount as well; I wouldn't think it could be too much. However, as I haven't found anything that fit the requirements, I never looked that far.

  9. #19
    Moderator HiPeRcO's Avatar
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    Quote Originally Posted by martincom View Post
    Considering the physical size of the package, limited heatsinking, and in surface mount as well; I wouldn't think it could be too much. However, as I haven't found anything that fit the requirements, I never looked that far.
    It will dissipate as much power as you apply to it in the circuit. Take the current through it and the drop across it and you have the power. For an 8V regulator (4V drop from 12V) and 3A, you'd have 12 watts (4V x 3A). That would get quite warm without proper heatsinking.

  10. #20
    downunder123
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    How much are those alternative pumps? The images on the links show the pumps are quite different physical shape to OEM. Mounting and securing them in the existing pump housing would be a real challenge and you can't be very creative with the fuel pump assembly design. At least so called aftermarket replacement units are exactly the same (shape) as OEM pumps. The aftermarket pump is about $28 + $7 for voltage converter =$35.

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