building adjustable dc supply 10-200v

Discussion in 'The Projects Forum' started by scampo77, Jun 24, 2011.

  1. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    its my first post and im excited to be here!!!

    i am auto mechanic and i need a way to test diesel injectors. the problem is that different manufacturers use different voltages to fire injectors. i need to make a variable dc power supply that has a range from 12-200v dc and be capable of around 1-3 amp. i thought i could just de construct a cheap multimeter for the display. as for the supply i can only find designs for 0-12v dc and nothing that goes as over about 60dcv. i need it to be 114dcv minimum and i thought higher voltages are probably just around the corner so better be safe and get it to reach to 200dcv.

    any advice or ideas of where i can get this question answered would be appreciated.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    You may need more than one device. 200 volts at 3 amps is 600W !! That's a lot for a DIY power supply. And, I don't think you'll get much support for such a dangerous thing. Safety first.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  4. #12

    Expert

    Nov 30, 2010
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    Not a problem. @$500 for a fuel pump, he can afford it.
     
  5. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    i was thinking that i need 3A at the very extremes but ya those numbers add up quickly dont they. these injectors are around 10 watt maybe a little more but not much. the biggest volatage i need right now is around 110dcv at 50 watt
     
  6. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    right now i am just building a proto type to see if i can fire the injector and capture all the diesel. if i can get it to work i dont have much of a problem buying that super power supply. i just need to find out if it will work first.
     
  7. #12

    Expert

    Nov 30, 2010
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    The question in my mind is: how you gonna fire them?
    You can't just connect a hundred volts and see if they spray. The actuator coils will melt in less than a second.

    Do you have something to pulse the power?
     
  8. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    that will be the next step after i figure out the power i have a range of 300uS at idle to 2400uS under full load. i was hoping to accomplish this with 555 timers

    as it sits right now i am just putting 12v to a 110v coil and it works i can see if it sprays left right or straight. its not accurate or reliable but atleast i can test the nozzle and as well the pump and pressure system. its very "hillbilly" right now cause i have a black and a red wire that i just strike together.

    also the wires going to the injector are 18-22 gauge so im not dealing with very much power i hope this helps
     
  9. someonesdad

    Senior Member

    Jul 7, 2009
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    I suggest you get a scope and take some pictures of the waveforms you're dealing with (both the current and the voltage), as that will help you design the stuff you need. You'll likely be able to do the switching with an appropriate MOSFET. If you have a function or pulse generator handy, that will help you get precise pulses. Of course, you can also build a 555-based circuit as you alluded to.

    I know this is picky , but I saw your "300 uS" and wondered what the hell a diesel mechanic was worried about measuring conductivity. :p The capital S is the unit for siemens, not seconds (the Asians almost always make this mistake in their documentation). Normally, it's easy to figure things out from context, but it's also a good habit to use the correct SI form of the unit, which is the lower case 's'. <picayune mode off>
     
  10. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    my spelling aside do you have any idea where i can find diagrams to make a 10-200v power supply?

    the timer i can figure out after
     
  11. #12

    Expert

    Nov 30, 2010
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    Last edited: Jun 25, 2011
  12. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    thank you very much but this seems to be a link to a service manual. i was hoping to build one.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    AWG-22 stranded wire is typically used in aircraft for circuits of up to 5A, so I'm not quite agreeing with your estimation of "low current".

    Marlin P. Jones & Associates, one of my favorite suppliers, has an 0v-120v 3A variable power supply for sale for $265.95:
    http://www.mpja.com/prodinfo.asp?number=9313+PS
    I'll suggest that this supply may meet your existing needs without having to build a supply.

    They have a 0v-120v 1A variable supply for $129:
    http://www.mpja.com/prodinfo.asp?number=9312+PS
    However, its' output may trip (turn off) with your injector loads; I simply don't know what your actual current requirements are.

    Your requirement for a 10vdc to 200vdc supply would be very difficult for a novice to build, and would likely cost a good bit not only in parts, but your time as well. I'll suggest that this unit is a comparative bargain. You are much better to use commercially available off-the-shelf equipment wherever possible; particularly if you are going to use it for a business.

    As far as getting reasonably accurate timing for the actuation of the injectors; a couple of 555 timers won't be very accurate. You might get "in the ballpark", but it'll be imprecise at best. A microcontroller could provide accurate, repeatable results - but programming one would be a challenge for a newcomer.

    Whatever solution you use for triggering the injector; it will need its' own low-voltage supply. Microcontrollers generally use around 5v. 555 timers can use from around 5v to ~16v.
     
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