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Have 5.19V DC and want 5.00V DC ... need help please

  1. Jan 23, 2017 #1
    hey All,
    i have an old wall charger that is 120v AC input, 5V DC output @1 amp. when i put meter on output i get 5.19v dc. i need 5.00v dc.

    How can i get to 5.00v?

    I'm making a throttle position sensor test tool. manual is asking for 5.0v +,- 0.01

    i plug power in to wall, plug in TPS, use meter to probe common negative to supply 5.0v to confirm start setting then probe TPS out to negative and set TPS to 4.0 or 4.20.

    thank you in advance for any help
     
  2. jcsd
  3. Jan 23, 2017 #2

    berkeman

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    Just use it as is. You should be fine.
     
  4. Jan 23, 2017 #3
    You are probably at the limits of your meters accuracy ... put two or three meters across the supply and you'll be surprised at the variation in readings ..

    Also this is the voltage at no load you are reading .. it will drop once current is drawn ... also probably as mains voltage fluctuates this will effect voltage .....

    If you're really sure you need such an accurate supply you can find many cheap voltage regulators on ebay you can adjust the voltage yourself , but you will need to feed it 7v or more ... make sure to buy a few meters and take the average of the readings to get an accurate output ...

    I find it hard to believe you need such a precise supply ... Is there no way of trying the supply you have and seeing if it works ?
     
  5. Jan 24, 2017 #4

    f95toli

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    I would suggest looking for 5.0V voltage references instead of a regulator; most sensors want an accurate voltage but won't draw much current (1% 5V refrences are dirt cheap).
    But yes, you will probably need a 7.0V or so supply,
     
  6. Jan 24, 2017 #5

    sophiecentaur

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    You have to ask what is 'special' about the 5V requirement? If it's required as a supply for some circuit then, unless the circuit is really poorly designed, it should be more than capable of dealing with power supply variations. (Read the detailed spec).
    If you need 5V as a reference then a wall wart is not the way to do it.
     
  7. Jan 24, 2017 #6
    I need 5.0 v as a reference. I don't see the need for any current. Once I have the 5.0 reference then I move pos probe to tps output to read a value. Then lock the tps down.

    If the tps is at true 3.9 v the snowmobile will bog off idle and accelerate sluggish.
    If the tps is set at true 4.3v then detonation sets in and you rebuild the motor.

    The sweet spot is @4.25-4.28 BUT I need a perfect 5.0 input or the output is skewed.



    Could I "assume" that if I input 0.2 over value the I could adjust output by same to reach the "difference" in voltage that the book is calling for?
     
  8. Jan 24, 2017 #7

    sophiecentaur

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    Have I missed something here? If the system you are developing is to work on a snowmobile then shouldn't you be deriving all your circuit power (references too) from the 6 or 12V battery?
     
  9. Jan 24, 2017 #8

    Averagesupernova

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    Automotive sensors typically use a 5 volt supply from the computer.
     
  10. Jan 24, 2017 #9
    The tps needs to be set to tell the CDI where the throttle plates are in relation to rpm so the CDI can trigger spark at correct moment. This is all happening at 8000+ events per minute!

    A slight clocking (degree) of the tps makes a huge difference.

    I'm making a tool to set the clocking of the tps when sled is NOT running.
     
  11. Jan 24, 2017 #10

    sophiecentaur

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    That makes sense. So, clearly the sensor needs the '5V' from the on board computer. That will clearly be appropriate for the system as it's designed that way.
     
  12. Jan 24, 2017 #11
    I need to supply the 5.0v there is no on board supply to use when setting the TPS hence the reason I'm here asking if there is a way to reduce my 5.19v "wall wart" to supply 5.0v when setting the TPS?

    How can I get a 5.00v DC output from a wall plug vs using a 9 volt battery? (They are always low or dead when needed) I would only be in garage and never out and about so 120v AC will be avalible.
     
  13. Jan 24, 2017 #12

    sophiecentaur

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    I still don't understand where the TPS gets its supply from and why you can't use the same source. Alternatively, get hold of a higher voltage wall plug (9 or 12V) and use a 5V regulator. People are always throwing out these things. Ask around. Alternatively, get hold of a rechargeable battery and a charger (also available all over the place). You have a problem if you want this all to be done for free but you're already spending some money. Perhaps you just need to come to terms with spending on something you thought you could get for free.
     
  14. Jan 24, 2017 #13

    NascentOxygen

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    Probably if you connect a resistor across it the 5.19V will drop a little. Try 47kΩ, or 33kΩ, or 22kΩ, or some resistance that's higher or lower, and watch your meter. But as others are indicating, no sooner will you have got it right then the fridge or something will cut in and your 120V drops a bit and takes all the unregulated wall warts with it.

    It seems you are needing it to be 5.00V only for a few seconds, so this might work out if you're patient.
     
  15. Jan 25, 2017 #14
    I don't mind spending some money. I'm over my head with circuits. I have wall plugs with 9v DC out. I will buy a 5v regulator.

    Could someone post a simple circuit for me to wire this together? Will there be other parts needed?
     
  16. Jan 25, 2017 #15

    CWatters

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    That's an accuracy of 0.2%. It will be very hard to find or make a 5V supply that accurate. Things like temperature changes might effect the voltage more than that.

    How accurate is the multi meter you will use to check the voltage? Some multi meters are less accurate than the number of digits they display might suggest. Typical handheld meters can be accurate to about 0.5% (say +/- 0.025V at 5V). Bench meters can be better at around 0.01%(+/-0.0005V).

    I suggest you post data on the throttle position sensor and info on what would constitute a pass/fail on test.
     
  17. Jan 25, 2017 #16

    CWatters

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    PS I suspect the data for the TPS only says +/-0.01V to ensure they can claim it's output is accurate to some specific % without a built in regulator. In practice most systems won't need the output of the TPS to be as accurate as claimed in the specification so a lower accuracy power supply is acceptable.
     
  18. Jan 26, 2017 #17
    That kind of accuracy is voltage reference range, not supply range. It'll be hard to do this as 'supply', and I think it would require some kind of 4w feedback from the sensor.

    As reference, it can be done with some kind of boost DC-DC converter (bring up the voltage to ~7V), lot of filtering (DC-DC makes a lot of noise) and a 5V reference.

    But: I don't think that you really need that accuracy. I think it would be enough if that source you have can supply a stable voltage.
     
  19. Jan 26, 2017 #18
    A simple Voltage Inverter can make 5.0 V DC no matter whether the input voltage is more or less:

    Inverter.jpg
     
    Last edited: Jan 26, 2017
  20. Jan 26, 2017 #19
    If that accuracy is really needed, then you don't wanna' do this with direct DC-DC, nor you wanna' mess up the grounding just like that...
     
  21. Jan 26, 2017 #20
    As for the ground, we can modify it like this (the switches are simultaneous),
    Inverter.jpg
    ― physically, it's a simple "buck" regulator with an n-channel MOSFET and a diode added.
     
    Last edited: Jan 26, 2017
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