need help with resistor math ;) - Electronic Circuits Projects Diagrams Free

strokedmaro · 15th June 2008, 09:17 AM

I have 2 solenoids that are read by a computer. Each solenoid has about 25 ohms and has 12 vdc applied all the time...solenoids are controlled by a ground supplied from a computer. I currently use two 25ohm, 5 watt resistors to "fool" the computer into seeing the solenoids and want to try and use just 1. How would I figure that out. Basically two grounded computer pins connected to a single resistor, connected to 12vdc. Any help appreciated. THANKS!

Mikebits · 15th June 2008, 09:47 AM

So, if I understand your correctly, you want some sort of relay simulator, that is something that has the same I draw as your relays. Using ohms law I=E/R 12v/25

hm: = .48 amp Using ohms law again P = IxE 12 x .48 = 5.76W
But now you want to simulate two relay (In parallel I presume) so two 25 ohm resistors in parallel equals halve the value of two equal resistors, in this case 25

hm: = 12.5

hm: So I think you want a 12.5

hm: resistor rated @ 12W or better.

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15th June 2008, 09:17 AM	(permalink)
strokedmaro	need help with resistor math ;) I have 2 solenoids that are read by a computer. Each solenoid has about 25 ohms and has 12 vdc applied all the time...solenoids are controlled by a ground supplied from a computer. I currently use two 25ohm, 5 watt resistors to "fool" the computer into seeing the solenoids and want to try and use just 1. How would I figure that out. Basically two grounded computer pins connected to a single resistor, connected to 12vdc. Any help appreciated. THANKS!

15th June 2008, 09:47 AM	(permalink)
Mikebits	So, if I understand your correctly, you want some sort of relay simulator, that is something that has the same I draw as your relays. Using ohms law I=E/R 12v/25hm: = .48 amp Using ohms law again P = IxE 12 x .48 = 5.76W But now you want to simulate two relay (In parallel I presume) so two 25 ohm resistors in parallel equals halve the value of two equal resistors, in this case 25hm: = 12.5hm: So I think you want a 12.5hm: resistor rated @ 12W or better.