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Need help picking out resistors

ladybridgeport

Oct 16, 2012
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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 mp3car.com 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
 

Harald Kapp

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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.
 

ladybridgeport

Oct 16, 2012
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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.
 

CocaCola

Apr 7, 2012
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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...

http://www.ebay.com/itm/10pcs-3296W...460?pt=LH_DefaultDomain_0&hash=item4d05dbf6e4

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:

Harald Kapp

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It is meant in this form:
attachment.php

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.
 

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ladybridgeport

Oct 16, 2012
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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?

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...

http://www.ebay.com/itm/10pcs-3296W...460?pt=LH_DefaultDomain_0&hash=item4d05dbf6e4

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...
 

Harald Kapp

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The solution with regular resistors I have shown in my answer. If unclear: what or how can I clarify?
 
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