solenoid problem

hi all,

i am familiar with arduino and have coding skills yet I greatly lack electronic knowledge. i am trying to drive a solenoid through the arduino, and strangely it works for a while then it stops working. here is my schematic. i am using TIP120, 1K res, and 1n4004 diode just as in the schematic. as the solenoid, i have a push solenoid that is branded as "IDI DAYTON OH 9810 12 VDC" on the sellers website. and on the solenoid it says "IDI DAYTON OH 0237 381814-044A 3964-7706a". and i am using two 9V batteries serially connected as an external power source. i am sure i have connected the circuit properly, i have also made a fellow friend from microelectronics test all the connections and currents with a multimeter while it was connected to the arduino with the simple blink uploaded. the funny thing is the solenoid first starts off working properly but then it dies off. power of the pushes gets degraded after a few pushes then it comes to a halt. nothing is burned or damaged, everything is intact and if you let the solenoid rest for some time, and then connect again, it works again. by working i mean just about 3-6 proper pushes and then it dies off. i am so very frustrated, as i can't figure out what the problem is. if anyone has any ideas or insights, it would be very very appreciated.

thanks s.

if anyone has any ideas or insights, it would be very very appreciated.

I suggest two changes:

  1. This one isn’t causing the problem but the best place for the diode is to wire right across the coil terminals, best at the solenoid, not on the board as you wish to clamp the transients as close to the source of the collapsing magnetic field rather then on the board.

  2. The problem is most likely the choice of battery power you are using. Standard 9 volt batteries are only rated to supply a few tens milliamps continuously and have too high an internal resistance to supply the current for most solenoids. Take a multimeter (if you don’t own one, buy or borrow one, they are essential for working with hardware) and measure the resistance of the solenoid coil. Then calculate the current if will draw with your ‘18 volt’ battery. current = 18/ohms. If think you will find it needs 100ma or more depending on your specific solenoid. 9 volt batteries probably have the worst mah hour rating per dollar costs. Lots of AA rechargeable batteries wired in series would be a better choice if you have to have portability, if not a 12volt wall transformer rated at a amp or more would be better.

Lefty

thank you both very much.. i will retest according to your suggestions.. i will be posting here the end result.

edit: i have done what you said and as expected it worked. i should have asked days ago rather than being stubborn but anyways :) thank you very much

s.