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machining new value's of a potentiometer

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  • machining new value's of a potentiometer

    I had to change the value's of a pot. --- great little unit with 37 detents - and two way on/off push switch built in, trouble is is this was the only one of its type at radio shack, its a 500k ohms and just started to get me into the range that I needed but not quite ---- I love my mill - never did I ever think of all the possibilities that I would end up using it for - God willing I'll never be without one...




    It was way cool to have the ohms meter right there on the mills table - take .005" off the radius of the pots resistance material and then measure the new reading - It took a couple of attempts but I got it to where I need it now.

  • #2
    Originally posted by A.K. Boomer
    It was way cool to have the ohms meter right there on the mills table - take .005" off the radius of the pots resistance material and then measure the new reading
    That's very cool AK! I never thought to modify a pot with a milling machine!
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #3
      From your description, you must need a higher value pot. You could have put a resistor in series with the pot to raise the overall value or had you needed a smaller value, you could have put a resistor in parallel with it. What value did you need?

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      • #4
        I found a way to trick my toyota's ECU, I went the oxygen sensor route for all kinds of reasons -- generally you have quite a bit or elbow room here and you also need not worry about it messing with ignition timing like a TPS or MAP sensor will, this has been a huge learning curve for me as like I stated its really not my cup of tea, and as luck would have it (murphys law 101 )
        The voltage on the OXY sensors have to go up in order for the computer to be tricked into lean, the typical proper running voltage for most O2 sensors is .45 volts with a general range from .1 to .9, if it was lower volts it would be easy, just install the proper rated potentiometer and its a done deal, but I had to come up with a stable low voltage power source -- some guys actually use a little 1.5 v batt. and just use it with a pot. along with their stock oxy sensor to create a leaner overall cond. but I dont want to have to worry about a little battery changing its values and crap, So --- I added another generator - its a box stock tercel oxy sensor I had laying around - I mounted it in the blank out boss that was on the exhaust manifold - I had to isolate the entire unit as it has two wires - a positive and a negative but even though it has a negative lead its also grounded to the sensors base which in turn is grounded to the exhaust system, So what I have now is the ability to run on my original sensor (the one thats netted me over 50mpg's) and at the push of the pots button I then utilize the two in series but can damper them down, The results on the 20 mile test drive at 2 in the morning last night have proven that I can manipulate a controlled lean condition throughout most of the range (except full throttle -- which is actually ideal)
        Not only that -- It never (so far) has tripped the computer into failsafe/rich limp mode, More testing today but so far im happy

        The top sensor is the isolated one, I used some great non-metalic exhaust gasket material, and then put it under bolts washers, the bolts are also smaller diameter for side clearance of the oxy sensors mounting holes.



        Last edited by A.K. Boomer; 06-14-2008, 01:32 PM.

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        • #5
          Originally posted by mikem
          From your description, you must need a higher value pot. You could have put a resistor in series with the pot to raise the overall value or had you needed a smaller value, you could have put a resistor in parallel with it. What value did you need?

          Mikem, Im a hack -- but, from my experience this is what I was dealing with -- I did go the route you suggested first, and it got me in my range - BUT, it then makes the pot about useless as it is no longer the "smallest valving" anotherwords - even just ramping onto the pot would put about everything onto the resistors back and then the rest of the pots travel was about useless -- Yes I needed a higher value pot, and I took the one I had that was 500k starting ohms and made it a 1750k starting ohms -- without effecting the full on position, Now i have the range of resistance I need -- all in the pot itself.

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          • #6
            Boomer,

            Hre's is couple of places besides Radio hack that should serve you well with what ever you may need in the future:

            http://www.digikey.com/
            http://www.mouser.com/
            http://www.newark.com/

            Seriously, I do this for a living. However I'll give you a thumbs up for on the spot ingenuity

            Doing what Mikem suggests is really the correct way and will tend to be less troublesome for you in the long run. The sites above (those are just three good ones I tend to use) are loaded with all kinds of gear for guys like us
            "To invent you need a good imagination and a pile of junk" Thomas Edison

            Better to have tools you don't need than to need tools you don't have

            73's KB3BFR

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            • #7
              Metalmelter, I appreciate all the info, my whole deal is once i get an obsession hell or high water wont stop me
              My bro's an electrician -- he gave me this massive "Allied" book that I can order from , its got every pot known to mankind --- For one - once I get into this mode waiting even a few hours is like torture, two, Im a hack - theres know way that I could have took a stab at what to order in the first place and been right on the money esp. with such an oddball variable like what im trying ot do, ----- this was at the very least a method to find out what ballpark I needed as I didnt even know the proper voltage of what I needed to come up with to trick the comp. - or how many milliamps the comp. was even taking out of the sensor circuit - but now that I built something to find out its also something that works so theres no need to order anything.
              Last edited by A.K. Boomer; 06-14-2008, 01:25 PM.

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              • #8
                This is where I mounted it, my right hand rests on the parking break anyways

                It has two push button modes, One is box stock with the standard position oxy sensor and Zero pot input - the other is the two oxy sensors running in series controlled by the pot.





                Edit; what you cant see is the missing radio knob that I pillaged for my new toy ;>}

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                • #9
                  That is clever. I do have several thoughts on the process.

                  First, I would have tried to find a better quality part to start with. Radio Shack parts are the cheapest of the cheap. You may have to replace it soon.

                  Second, anyone comtemplating this should be aware that the power rating of the pot will be decreased with this kind of procedure. I doubt you will have any trouble with a 12 Volt system and your resistance which is close to 2 MegOhms (P=V^2/R), but smaller value pots or higher Voltages would need careful consideration.

                  Finally, I would clean it out very carefully as any dust from the machining could get in the way of the wiper and cause erratic operation.

                  But as I said, clever idea.
                  Paul A.

                  Make it fit.
                  You can't win and there is a penalty for trying!

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                  • #10
                    Thanks Paul and Lazlo, today I went up in the mountains with it and watched the gauges like a hawk --- so far so good, slight EGT changes, was expecting a little more since I can even create a little "lean bog" with the pot fully cranked up in a fast throttle depress right off of idle, tomorrow I filler-up and start recording mileage, I'll keep you posted on the progress (if any).
                    But first - its time for a coat of wax

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