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  #1  
Old Sun 28 August 2011, 13:40
Rusty Nuts
Just call me: Gary #86
 
Valley Grande, AL
United States of America
Selecting resistors for Gecko drive

I'm using Gecko 203V and the resistor listed for 4.5 amp motors is 1/4 Watt 84.6K. I checked with Radio Shack and I could only find 1/4 Watt 100k and 1/4 Watt 47k. Will I be able to use one of these sizes or will I need to order some off of the internet?

Thanks,
Gary
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  #2  
Old Sun 28 August 2011, 15:43
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Three options for you to consider: Buy one of their kits, like the 500 resistor kit 271-312 for $10, which contains 5 82k resistors - close enough.

The other option is that for resistances in series, you add them; for resistances in parallel, you average them. So, as an example, wiring four 22k in series would get you 88K; or wiring 100k and 47k in parallel would get you 147 / 2 = 73k. Add 10k in series to that and you hit 83k.

Third option is to buy potentiometers like 271-092, dial in the resistance you want using a meter when it is out of the circuit. Although this sounds attractive, I'd stay away from it; low quality pots can vary and degrade over time, and you actually don't want to have it too easy to vary the current since a mistake could destroy something.

I suggest you buy the kit; it's short money, and you'll have a bunch of resistors around to allow you to make current adjustments.
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  #3  
Old Sun 28 August 2011, 16:47
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gary,
If you want to wait for snail mail, I can mail you some on tuesday.
A small assortment even.

Last edited by domino11; Sun 28 August 2011 at 17:05..
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  #4  
Old Mon 29 August 2011, 03:02
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Brad, your averaging of resistors in parallel is faulty logic. Haven't got time now to set it right, but this had to be nipped in bud. Maybe someone else can step in while I get some work done?
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  #5  
Old Mon 29 August 2011, 03:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Resistors in parallel always give you less ohms than the lowest one in the set......
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  #6  
Old Mon 29 August 2011, 03:13
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Use the formula of 1/R = 1/R1 + 1/R2 + 1/R3 to compute resistance in parallel.

A 1000 ohm resistor in parallel with a 100 ohm resistor gives 90.9090 ohms of resistance.

1/1000 = 0.001 ohm

1/100 = 0.01 ohm

0.001 + 0.01 = 0.011

1/0.011 = 90.9090 ohms
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  #7  
Old Mon 29 August 2011, 06:27
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Ah, that's right. Thanks for the corrections.
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  #8  
Old Mon 29 August 2011, 06:33
Kobus_Joubert
Just call me: Kobus #6
 
Dalview
South Africa
Send a message via Yahoo to Kobus_Joubert Send a message via Skype™ to Kobus_Joubert
Buy a UIM ROBOT driver...amps are set on potentiometer...no resistors needed
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  #9  
Old Mon 29 August 2011, 08:43
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Thanks Mike!
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  #10  
Old Mon 29 August 2011, 20:49
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
I just love math.....it keeps me honest.
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