doncarlosalbatros
Full Member level 2
I need to control eight solenoid-valves for water drainage outdoors remotely and simultaneously. The valves are normally closed (NC) type which I guess in that context means they open and let the water drain only when they receive ON signal at their input.
Here is the exact model and the datasheet for the solenoid valves. The datasheet says the relay is 4.5W and I guess passes around max 400mA in steady state. Since I don't know the the inductance of the coils, I thought it wouldn't be more than 10uH.
The idea is to keep the 12V power supply and the controller(Arduino in this case) indoors and send the power and the control signal 25m far away to the optocoupler and then to a MOSFET which drives the solenoids.
Here is what I came up with so far:
Since I don't want false triggering I decided to use an optocoupler 4n25 at the far end. This both isolates the ground of the 12V power supply and prevents coupling noise.
If I use a coaxial cable, it has like 80pF/m. So for worst case I assumed the total parasitic capacitance of the cable Cp all the way down is around 10 nF. I also assumed Arduino rising and falling edges as 100ns.
Zener and the flyback diodes are for taking care of inductive kicks fast. This is based in what I saw in some examples.
I found the MOSFET **broken link removed**suitable for such application current and powerwise.
And here is simulation results for power current and the voltage for the MOSFET:
According to the datasheet Maximum Power Dissipation is given as 88W at 25°C. The peak in my simulation shows max 10W.
And here is the zoomed view of the power during a switch transition:
There is parameter called Maximum Safe Operating Area but I don't know how to relate it to this scenario and plots.
I have made many assumptions such as Arduino digital output rise fall time 100ns; total cable capacitance as 10nF; solenoid LR as 10uH and 30 Ohm.
If these assumptions are reasonable can we say that this MOSFET can handle this application? Is there any fundamental issue with this schematics?
Here is the exact model and the datasheet for the solenoid valves. The datasheet says the relay is 4.5W and I guess passes around max 400mA in steady state. Since I don't know the the inductance of the coils, I thought it wouldn't be more than 10uH.
The idea is to keep the 12V power supply and the controller(Arduino in this case) indoors and send the power and the control signal 25m far away to the optocoupler and then to a MOSFET which drives the solenoids.
Here is what I came up with so far:
Since I don't want false triggering I decided to use an optocoupler 4n25 at the far end. This both isolates the ground of the 12V power supply and prevents coupling noise.
If I use a coaxial cable, it has like 80pF/m. So for worst case I assumed the total parasitic capacitance of the cable Cp all the way down is around 10 nF. I also assumed Arduino rising and falling edges as 100ns.
Zener and the flyback diodes are for taking care of inductive kicks fast. This is based in what I saw in some examples.
I found the MOSFET **broken link removed**suitable for such application current and powerwise.
And here is simulation results for power current and the voltage for the MOSFET:
According to the datasheet Maximum Power Dissipation is given as 88W at 25°C. The peak in my simulation shows max 10W.
And here is the zoomed view of the power during a switch transition:
There is parameter called Maximum Safe Operating Area but I don't know how to relate it to this scenario and plots.
I have made many assumptions such as Arduino digital output rise fall time 100ns; total cable capacitance as 10nF; solenoid LR as 10uH and 30 Ohm.
If these assumptions are reasonable can we say that this MOSFET can handle this application? Is there any fundamental issue with this schematics?