Brass Liquid Solenoid Valve - 12V - 1/2 NPS Question

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doc_gp
 
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Brass Liquid Solenoid Valve - 12V - 1/2 NPS Question

Post by doc_gp »

Quick question on this valve (http://www.adafruit.com/products/996). How LONG can it stay energized (i.e. open) before damaging the coil? These things get blisteringly hot after about 30min. Is there a limit on how long they should stay open?

Thanks in advance!

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adafruit_support_mike
 
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Re: Brass Liquid Solenoid Valve - 12V - 1/2 NPS Question

Post by adafruit_support_mike »

We don't have any figures on duty cycle, but all coils get hot under continuous power.

Try lowering the control voltage until you find the lowest that works reliably. Power increases with the square of the voltage, so a little less voltage can mean a lot less heat.

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easternstargeek
 
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Re: Brass Liquid Solenoid Valve - 12V - 1/2 NPS Question

Post by easternstargeek »

It takes significantly more power to pull in a solenoid than to keep it there. A common technique in industry is to drive the coil with a PWM signal- 100% until the plunger seats, and then throttle back the power afterwards. You can probably go as low as 50% duty cycle, but you should try some experiments. If you are driving the coil from an Arduino, you already have several pins that can provide PWM (the "Analog Output" pins).

For the record, this technique is also used to decrease the reaction time of a solenoid, whereby the supply voltage is increased beyond the coil's nominal rating, so at 100% Duty, you are hitting the coil very hard- which it can withstand for a short while. Afterwards, the duty cycle is reduced to keep the coil from overheating at the higher voltage. Even though the peak voltage is higher than the coil likes, the PWM reduces the average power dissipation to acceptable levels.

Another way to accomplish the same thing is with a PTC thermistor, which has a low cold resistance, but once current starts flowing and it self-heats, the resistance increases. The thermistor would be wired in series with the coil. That approach, while interesting to explore, is far more challenging to implement reliably.

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