Rapidly changing the polarity of a 55 volt DC Circuit

Discussion in 'General Electronics Chat' started by Pyro62, Jan 4, 2016.

  1. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Hi Guys, and have searched the forum for answer to my question but I can not seem to find the exact answer/scenario I am trying to achieve. I am trying to build an electrical circuit to pulse a fuel injector off of a Evinrude E TEC outboard motor. It's different than any other fuel injector out there. First of all it operates on a 55 volt dc signal. The voltage is flipped to open and close the injector. So 55 volts positive to open the injector and then 55 volts negative to close the injector. What I was thinking was a 12 Vdc to 55 volt transformer to an H Bridge ( to flip the polarity) to the fuel injector. I am not sure what I need to control the h bridge to rapidly reverse the polarity. Can somebody please help? Or if you have another idea please share.
     
  2. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Furthermore, if somebody wants to build the above for me, I will gladly pay you to do so.
     
  3. ifixit

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    Nov 20, 2008
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    Post a spec for the injector.
    Do you know how Evinrude drives it?

    A boost converter from 12 to 55V then an H bridge sounds like a good start. Where does the timing come from in your case? More info about your application would be good.

    Ifixit
     
  4. crutschow

    Expert

    Mar 14, 2008
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    What are the characteristics of the signal that would operate this circuit?
     
  5. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Yes Evinrude Drives it creates the 55 volts from the the flywheel of the engine spinning over the stator. Then the EMM (engine management module) controls this voltage to the injector. I should have also stated why I am trying to accomplish this. I want to remove the injector from the motor, submerse in an ultrasonic cleaner and pulse the injector while in the ultrasonic cleaner for a few minutes to clean it. Here is a video of what I am trying to accomplish, I just can't see what he is using to fire the injector with.

     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Did you call the number at the end of the video to see how much he charges?
     
  7. Pyro62

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    Jan 4, 2016
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    Yes I sure did and it's very reasonable, only $44.00. The issue is I am in The Bahamas and he is in the USA. The cost of shipping the parts to and fro, coupled with the Bahamian import duties do make it economically viable. I also know there is going to be an issue shipping used fuel components into the USA through CBP.
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Are you sure about how it works?
    http://www.evinrudenation.com/owner-zone/understanding-the-e-tec-fuel-injector-by-bill-grannis/
     
  9. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    I am 100% sure of how it works. That article is for the laymen and does not even mention the 55V circuit. I am an Evinrude Master Tech and know the system in and out. It hits the injector with the 55v positive charge and the injector opens. The EMM keeps the injector open with this positive charge for as long as it needs too. Then it reverses the charge/polarity to close the injector for as long as needed.
     
  10. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Ah yes, I see now the flywheel is the power supply.
    You could probably use a 48 volt power supply (higher voltage ones are harder to find) and the build what is called an H Bridge to reverse the polarity.
    Can you measure the coil resistance so we will know the current?
     
  11. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Yes, I was thinking about using a 48 volt power supply. In fact when diagnosing the engines, and testing the 55 volt circuit it's more like 52 volts on my fluke. I will measure the coil resistance tomorrow and revert. Thanks for the help.
     
  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Many industrial power supplies have output voltage adjustments. +/-10% is a very common adjustment range, which would get you almost to 53 V. If you need 1 A and the supply makes 2 A, then operating at the higher voltage will not be a problem.

    ak
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Many power supplies have output voltage adjustments with at least +/-10% range. This would bring the output to almost 53 V. If the load requires 1 A and the supply is rated for at least 1.5 A, it should be fine at this output.

    ak
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    How long do you need to keep the injector open to clean it? Most injectors are open for only a few mS per cycle in normal use. High voltage is used to help overcome the injector coil's inductance and so speed up the opening, but prolonged high voltage (and hence current) would cause over-heating. Injector drivers normally allow for a high opening current followed by a lower sustaining current while the injector is open, to keep power dissipation down. Would you need to provide a similar current profile before the reverse voltage is applied to shut the injector?
    Injector inductance is key. Do you have a figure for that?
     
  15. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Hi Alec, the injector cycle is 2-5 mS depending on engine speed. Once we can rapidly open and close the injector I think we are fine. To my knowledge there is no other voltage being introduced.
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Agreed. Another site lists the coil resistance at 2.7 ohms (I hope he had zeroed his meter and he didn't measure "in circuit"). If true, we don't want hundreds of watts going through that injector constantly as we pull it open and push it closed. It only needs to be popped in each direction and possibly a small hold current before it is slammed into to inject into the cylinder.

    These injectors are actually multipurpose devices. They are essentially a peristaltic pump that pulls in a specific amount of fuel as the engine rotates and then bangs the fuel into the cylinder sometime during the intake or power stroke. Pressurized fuel rails are the big fuel-saving/energy giving technology in the past few years. The fuel in injected at the last possible instant before the spark so there is no time for pre-ignition (pinging) which is essentially combustion caused by the diesel effect (compressive heating) before the spark plug fires.

    In the end, these things are fuel injectors, but also pumps and metering devices. Each of the six fuel injectors are measured for volume delivered vs. response before assembly and that response info is entered as firmware into each individual engine's management system.

    At 1200 Rpm (idle), these things are firing 10 times per second on a four stroke engine (I think these are two stroke so 20 times per second). Of that 1/20th second (0.05 seconds), assume we get a half rotation of the engine to fire the contents. That is 0.025 seconds. Since we cannot maintain 20 amps of current in each direction, then hopefully there is enough inductive reactance to limit current at 20 Hz. The trouble is, now we need an inductance measurement of the coil and some info about saturation of the coil and how the metering system works in these little pumps/injectors. Is it based in time at full voltage or based on analog voltage?
     
  17. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    Hey Gopher T, I measured the coil resistance of the injector and it bounced between 2.8-2.9 ohms. You have gone above my head when talking about the "inductance measurement of the coil and some info about saturation of the coil and how the metering system works in these little pumps/injectors. Is it based in time at full voltage or based on analog voltage?" I can do more tests on the coil etc...
     
  18. Alec_t

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    That reverse voltage is to close the injector as quickly as possible in the engine application. For your cleaning application I don't see the need for rapid closure; in fact that would be a disadvantage. Hence uni-polarity pulsing of the injector would be my choice and would simplify the circuit needed. You might consider using a control chip such as the LM1949 to provide the peak-and-hold current profile to minimise power consumption and heating.

    Edit: If I recall correctly, coil inductance of a typical injector is around 2mH. Can you post a link to your injector's datasheet/spec?
     
  19. Pyro62

    Thread Starter New Member

    Jan 4, 2016
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    HI Alec_t. Unfortunately I do not and can not find the fuel injector data/spec sheet.
     
  20. BillB3857

    Senior Member

    Feb 28, 2009
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    An AC source with a bipolar cap would allow reversing polarity to the injector. Properly sizing the cap would allow for open/close/off timing.
     
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