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Topic: 3 wire solenoid (Read 7 times) previous topic - next topic


Hey guys,

I made the circuit as was shown here (via fritzing) but the resistors burn.

what Watt should I use? I used 0.5 watt (smd resistors) but I think I got too much current and burned them and the pnp.



That Sir is what I was trying to tell you. 1. 1 solenoid only per controller 2. the transistors must be capable of 20A surge current for about 50 uS I used 2 different ones a D44H11 PNP and a PN222 Mosfet I found surplus somewhere. It wasn't the best part but it was OK for the design And the surplus guy had about 5K of them that He'd be happy to get $0.05 Ea for.. So I used the Rdson to damp the solenoid by keeping the gate high (or base low) this kept the 4700 uF cap connected until all the ringing stopped, 100 mS worked well.
I used a 100 ohm resistor in series with the cap and the battery to make it the capacitor the only source of current... A battery dies after a while and it does so generally by loosing current capacity, the capacitor means that as long as the battery/solar panel can keep the cap charged all will work as it should even with a battery reduced to 100 mAH capacity.  I was using 1.2 AH Yuasa 12 V SLA batteries. The charging was processor controlled and temp compensated charge rates were applied to avoid battery damage due to overcharging.
Controlling a bi-polar solenoid is easy but it takes some seriously wide PCB tracks and a serious driver transistor, a very serious driver. Probably the easiest for you would be an H-Bridge based on an L298 H bridge motor driver, 2 pulses Forward (open) and Go (momentarily apply power) and 2 more for the Reverse (close) and Go. The shields are 6 to 12 dollars each and ready for your application assuming that your original spec's were right.
You could charge a capacitor and "dump" it into a coil with the H-Bridge.

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The h-bridge was perfect, although it needs only 1 pulse, 100ms with 12v battery, also the 4700 capacitor you offered is working perfectly.

thanks a bunch for all of the help.


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