Electronics > Beginners
How to improve Solenoids open/close response time ?
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Albatroon:

--- Quote from: soldar on March 16, 2019, 07:37:03 pm ---If you have many valves in a complex system you wight want to consider having two rails (+V, 0, -V) so you can first connect between +V and -V and then switch to half voltage.

--- End quote ---
Thank you for your suggestion.


--- Quote from: Zero999 on March 16, 2019, 08:08:26 pm ---The bootstrapping idea is a good one. Note that each transistor should have its own base resistor, which has been omitted from the schematic.

To improve the turn off speed, a zener diode can be added in reverse parallel with Q2.

Yes, the main drawback with that circuit is it takes awhile for C1 to charge, via R1which will limit the repetition rate. R1 can be replaced with a current source or better still, another transistor. THe Hfe of Q3 will determine the charging current, so there's a bit of "Hfe suicide" here, but it should be fine.

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Is the inductor Necessary ? What it do in this circuit ?
ebastler:
@Albatroon, I have two questions:

* You have not really told us about your application. What switching speeds are you targeting? Beyond spped, how many switching cycles (per hour, per day, over the lifetime of the product) do you need? Are relays the right solution, or should you look at solid-state switches?
* Who the heck is Bob? ;) You start referring to "Bob's design" mid-thread, but I could not find a reference for that?
Albatroon:

--- Quote from: ebastler on March 16, 2019, 10:19:29 pm ---@Albatroon, I have two questions:

* You have not really told us about your application. What switching speeds are you targeting? Beyond spped, how many switching cycles (per hour, per day, over the lifetime of the product) do you need? Are relays the right solution, or should you look at solid-state switches?
* Who the heck is Bob? ;) You start referring to "Bob's design" mid-thread, but I could not find a reference for that?
--- End quote ---

I posted my project on Replay #16.. Here's my replay:

--- Quote from: Albatroon on March 13, 2019, 11:09:10 am ---By the way, I am driving about 200 solenoids, many times per second.
I started this project back in 2012, I Built this https://youtu.be/YtlYc2bzUEs?t=10.
Now I am trying to build a new one with batter valves, better performance & a Bigger size !

--- End quote ---
And about Bob's design.. It took awhile for me too to find what "rstofer" mean on replay #8.

--- Quote from: rstofer on March 11, 2019, 09:17:46 pm ---
The fastest it will run is with no diodes but that isn't possible because there is a body diode in the MOSFET.

There is a possibility of some kind of capacitive discharge circuit that forcibly opens the solenoid by driving a reverse current through the inductor.  No, I don't now how to do it and I didn't find much on Google.

Here's a circuit that is interesting but it only works on pull-in:

https://www.electronicdesign.com/analog/what-s-all-solenoid-driver-stuff-anyhow

Basically, you have a lot of stored energy in the inductance and all the time it is discharging, there is current flow through the solenoid.

Here's an idea:  Use Bob's circuit above to pull the solenoid in and then reduce the current to some lower value for hold-in. Now when it comes time to drop out, you have less current flow so less stored energy and the release is faster.  Couple that with the Zener approach and maybe you'll have something.

--- End quote ---
Bob's design is here https://www.electronicdesign.com/analog/what-s-all-solenoid-driver-stuff-anyhow

Thank you
Zero999:

--- Quote from: Albatroon on March 16, 2019, 10:13:05 pm ---
--- Quote from: soldar on March 16, 2019, 07:37:03 pm ---If you have many valves in a complex system you wight want to consider having two rails (+V, 0, -V) so you can first connect between +V and -V and then switch to half voltage.

--- End quote ---
Thank you for your suggestion.


--- Quote from: Zero999 on March 16, 2019, 08:08:26 pm ---The bootstrapping idea is a good one. Note that each transistor should have its own base resistor, which has been omitted from the schematic.

To improve the turn off speed, a zener diode can be added in reverse parallel with Q2.

Yes, the main drawback with that circuit is it takes awhile for C1 to charge, via R1which will limit the repetition rate. R1 can be replaced with a current source or better still, another transistor. THe Hfe of Q3 will determine the charging current, so there's a bit of "Hfe suicide" here, but it should be fine.

--- End quote ---
Is the inductor Necessary ? What it do in this circuit ?

--- End quote ---
The inductor represents the solenoid of course.
ebastler:

--- Quote from: Albatroon on March 16, 2019, 10:26:33 pm ---
--- Quote from: ebastler on March 16, 2019, 10:19:29 pm ---You have not really told us about your application. What switching speeds are you targeting? Beyond spped, how many switching cycles (per hour, per day, over the lifetime of the product) do you need? Are relays the right solution, or should you look at solid-state switches? [/li][/list]

--- End quote ---

I posted my project on Replay #16.. Here's my replay:

--- Quote from: Albatroon on March 13, 2019, 11:09:10 am ---By the way, I am driving about 200 solenoids, many times per second.
I started this project back in 2012, I Built this https://youtu.be/YtlYc2bzUEs?t=10.
Now I am trying to build a new one with batter valves, better performance & a Bigger size !

--- End quote ---

--- End quote ---

Oh, thank you -- and my apologies for overlooking that information in your earlier post.
That is a pretty cool project indeed!

Obviously, solid-state water valves are hard to come by, so solenoids it is...  ;)
How long do they typically last in this application?
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