View Full Version : Selecting resistors for Gecko drive

Rusty Nuts
Sun 28 August 2011, 12:40
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?


Sun 28 August 2011, 14:43
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.

Sun 28 August 2011, 15:47
If you want to wait for snail mail, I can mail you some on tuesday. :)
A small assortment even. :eek:

Gerald D
Mon 29 August 2011, 02:02
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?

Gerald D
Mon 29 August 2011, 02:03
Resistors in parallel always give you less ohms than the lowest one in the set......

Mon 29 August 2011, 02:13
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

Mon 29 August 2011, 05:27
Ah, that's right. Thanks for the corrections.

Mon 29 August 2011, 05:33
Buy a UIM ROBOT driver...amps are set on potentiometer...no resistors needed :D

Gerald D
Mon 29 August 2011, 07:43
Thanks Mike!

Mon 29 August 2011, 19:49
I just love math.....it keeps me honest.