Water Solenoids

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Re: Water Solenoids

Post by adafruit_support_bill »

Ah, the capacitor is in parallel, not in series. That makes more sense - and may help with boosting the speed of the solenoid actuation.

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hgmm
 
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Re: Water Solenoids

Post by hgmm »

Thanks Bill, so should i work on the first diagram or second one with the 68 ohm resistor.
Also what size capacity should I use?

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Re: Water Solenoids

Post by adafruit_support_bill »

I'd go with the first diagram. The PWM is taking the place of the resistor in the second diagram.
The capacitor size is not so critical. Bigger is generally better. 4700mF is probably a good place to start.

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Re: Water Solenoids

Post by hgmm »

Thanks Bill, before I saw your note today morning, I tried both options and documenting for future audience.

You are right adding a resistor any larger than 5 ohms and the solenoid will not open.
So i removed the solenoid completely and it is not a good option.

Adding the capacitor helped very much and got the solenoid to operate consistently in less than 1 sec and even with voltage as low as 9 volts.
When running on 9 volts it did not work a few times, just to note.

However, now I have bigger problem, the mosfet is getting very very hot and I risk failure.

Documenting the scenario's :-

Before adding the capacitor, the mosfet would get very hot for the duration of 100% duty cycle which in my case was for 20 seconds.
The current consumption would 1.4 Amps, as I reduced the duty cycle to 25% the mosfet will cool down really quick and both the mosfet and solenoid will be running cold
and working perfectly for next 30 mins. This is normal operation and current consumption full down .04 Amps. I only tested for 30mins but it could go for as long as the battery lasts. So the main issue here is the solenoid actuation takes more than 20 seconds at times and does not work every now and then.

After adding the capacitor, solves the problem of solenoid taking time to actuate and gets it down to 1 second. Tried several times and there was no failed actuation.However to my surprise, the mosfet continues to heat up and does not cool down when the duty cycle is lowered from 100% to 20%. which means this would fail sooner or later.

Appreciate any suggestions.
Thank you!
HG

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Re: Water Solenoids

Post by adafruit_support_bill »

A discharged capacitor is going to look like a zero-ohm load to the MOSFET, so the current draw will be pretty high during the 25% of the PWM cycle where the MOSFET is on. When it is off, the cap will be discharging that energy back through the solenoid. You can probably back off the duty cycle further so that the average energy input is similar to the no-capacitor circuit.

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Re: Water Solenoids

Post by hgmm »

Hi Bill,

I tried all combination, analogWrite(PWM_PIN,38) is lowest i can go and my initial setting was analogWrite(PWM_PIN,40).
Any lower the valve shuts down, Is there any modification I can do the resistance on the mosfet gate?
or try to do a valtage booster circuit? Is there anything on Adafruit store that I could use.

Thanks for your help.
HG

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Re: Water Solenoids

Post by adafruit_support_bill »

If you are using the N-channel power MOSFET from the store, you should not need a resistor on the gate.

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Re: Water Solenoids

Post by hgmm »

Thanks - I do have the power mosfet from the adafruit store.
I wanted if removing the extra resistor from the gate will have any impact on the Mosfet heating?

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Re: Water Solenoids

Post by adafruit_support_bill »

The resistor value should not affect the MOSFET heating. You could try using a smaller capacitor. You can also bolt a heat-sink to the tab on the MOSFET.

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hgmm
 
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Re: Water Solenoids

Post by hgmm »

Thanks Bill and if running into issues with low capacitor, i would switch to a 11.3 volts Lithium battery.
That way i would not need to capacitor at all.

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Re: Water Solenoids

Post by hgmm »

https://www.adafruit.com/products/996
Just some final thoughts on the brass solenoid.
The capacitor did not help much, I changed the PWM_PIN to 10 on the Pro-Mini,which I believe has higher frequency.
That helped greatly with the solenoid actuation time, less than few seconds.
Once actuated was able to get this operate down to PWM 38 which is less than 15% duty cycle, power consumption on run time was .03 Amps.
Power Consumption during actuation was 1.25 Amps. This solenoid is really good as there is no minimum pressure requirement and development is easy as don't have to connect it to water at all.
Pain points - Even the best AA batteries cannot get this to actuate consistently. Consider a different power source, a wall adapter or 11.3 volts lithium ion battery pack.

https://www.adafruit.com/products/997
I got my replacement of the plastic solenoid, this time I managed to get his to work and keep every thing "cold".
You have to run it at 50% duty cyle, PWM 127 with about 50 PSI water pressure and this will work great.
I have NOT measured the energy consumption, I will do that when I get to it and will post back results.
My guess would about around 150 milliamps run time and about the same to actuate.

Bills - Thanks for you support and help, please feel free to correct if I have misstated anything as I am learning and not an expert.

Thanks
HG - An Adafruit fan!!

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Re: Water Solenoids

Post by adafruit_support_bill »

Thanks for posting your results.

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