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Need help picking out resistors

Discussion in 'General Electronics Discussion' started by ladybridgeport, Oct 16, 2012.

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  1. ladybridgeport


    Oct 16, 2012
    I am integrating my HVAC heater controls from my car to a mini itx computer that I installed in my trunk. Mt heater controller is digital with vacuum lines. So far I connected my blower motor using switching relays via a fusion brain from website. So basically when I press the touchscreen monitor in my dash, the fusion brain sends signals to the relays to turn whatever relay I want on so my blower motors switches on.

    For my heat and cold, it has a slide switch using resistance. I metered it's output and got these readings on various positions, I am not sure what resistors or if I have to double up on resistors to get the ohms I want. I see the beige 1/4 watt type and mohm type resistors on the controller board. Can someone let me know what type resistors to buy to get the following resistance??

    The following are the ohm readings for my slide switch:

    Hot: 10.01-10.08 k ohm 10.03
    1: k ohm 9.72
    2: k ohm 9.15
    3: k ohm 8.47
    4: k ohm 7.95
    5: k ohm 7.35
    6: k ohm 6.77
    7: k ohm 6.17
    8: k ohm 5.58
    9: k ohm 4.97
    10: k ohm 4.41
    11" k ohm 3.78
    12: k ohm 3.188
    13: k ohm 2.604
    14: k ohm 2.006
    15: k ohm 1.416
    16: k ohm .815
    17: ohm 234.4
    Cold: ohm 40.1
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    How precisely do you want to approximate the characteristic you measured?
    Using resistors from the E96 series you can easily realize this seqence:

    E96 resistor accumulated resistance
    280 10000
    569 9720
    680 9151
    523 8471
    597 7948
    583 7351
    597 6768
    590 6171
    612 5581
    560 4969
    626 4409
    597 3783
    583 3186
    597 2603
    590 2006
    604 1416
    576 812
    196 236
    40,2 40,2
    Pretty close to your measurements, isn't ist? But with a more relaxed attitude towards the precision you can use these values:

    E96 resistor accumulated resistance
    300 10000
    590 9700
    590 9110
    590 8520
    590 7930
    590 7340
    590 6750
    590 6160
    590 5570
    590 4980
    590 4390
    590 3800
    590 3210
    590 2620
    590 2030
    590 1440
    590 850
    220 260
    40,2 40,2

    With the exception of three resistors all others are 590 Ohm - much easier logistically and still not too far away from your measurements. I'd guess that's even much nearer to what the original controller containes.

    Use the same size/wattage as on the original controller board.
  3. ladybridgeport


    Oct 16, 2012
    I measured it with my TPI Scope Plus 440. I just used my oscope to read the ohms at different positions of my heater control. I see 5% tolerance resistors on the board. So if I want to get a reading of 9270 ohm, how would I get that reading from 590 ohm resistor? I'm new to finding resistance.
  4. CocaCola


    Apr 7, 2012
    If it was me, I would just get a 20 lot of multi turn pots and dial them in to the appropriate values... With how cheap they can be had from China it's hardly costly to do it this way and allows a single component to cover all possibilities... Once each one is dialed in hit it with a dab of glue to lock the dial in place and you will be golden...

    Something like this 10 pcs lot for $1.90 delivered or $3.80 delivered for two lots that will do your entire job...

    To use them as a variable resistor, you tie the middle leg to one of the outer legs and presto you have a variable resistor...

    The 3296W series is 1/2 Watt no issues there...
    Last edited: Oct 17, 2012
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    It is meant in this form:
    You stack the resistors in the sequence given by the left column of my list. From each tap to ground the resistance accumulates to the values in the right column.
    For setting the HVAC this should be precise enough. CocaCola's sugggestion using trimmers can be nearer to your measurements, but surely is more expensive and a lot of work to trim all the pots.

    Attached Files:

  6. ladybridgeport


    Oct 16, 2012
    That sounds like a good idea, but there is going to be a lot of vibration in the vehicle. How would I do it with regular resistors?

  7. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The solution with regular resistors I have shown in my answer. If unclear: what or how can I clarify?
  8. ladybridgeport


    Oct 16, 2012
    ok thanks
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