Monostable NE555 control of Solenoid

Thread Starter

graham.hepworth

Joined Jul 5, 2021
4
Hi everyone.
I am after some help on controlling a 24V solenoid valve in the creation of a firing mechanism for a paper rocket launcher for a school project, similar to this one https://bathastronomers.org.uk/2018/01/14/paper-rocket-launcher-how-to/
I have been reading up and believe that using an NE555 and MOSFET will possibly work (or use a relay?). I would like to ideally adjust the pulse time between say 0.01s and 0.1s (can I use a variable resistor for this?). I am happy to have 2 power supplies (12v for the circuit and 24v for the solenoid) unless there is an alternative?
The pulse will be triggered on the press of a button (I presume the circuit timing re-sets when the button is then released?).
Can someone pull together a circuit diagram for me at all and perhaps identify some of the main components required? There seem to be so many different ones available out there.
Based in the UK so RS components would be ideal.

Thanks so much, Graham
 

Alec_t

Joined Sep 17, 2013
12,321
Welcome to AAC!
There are plenty of 555-based monostable circuits on the net and in manufacturers' datasheets/application notes. A quick google should find some suitable candidates.
24V is too high for a 555, so use the 12V supply for that.
 

LowQCab

Joined Nov 6, 2012
1,372
I would skip all the electronics and just use a
Push-Button-Switch, a Resistor, and and several Large-ish Capacitors.
With this type of setup, you can use very small Batteries, and they will still last forever.

How much Current does your 24-V Solenoid-Valve require ?
This will determine how Large the Capacitor(s) need(s) to be to
get your pulse-length dialed-in exactly how You want it.
.
.
.
Air-Rocket Launcher FLAT .png
 

Thread Starter

graham.hepworth

Joined Jul 5, 2021
4
I would skip all the electronics and just use a
Push-Button-Switch, a Resistor, and and several Large-ish Capacitors.
With this type of setup, you can use very small Batteries, and they will still last forever.

How much Current does your 24-V Solenoid-Valve require ?
This will determine how Large the Capacitor(s) need(s) to be to
get your pulse-length dialed-in exactly how You want it.
.
.
.
View attachment 242743
Thanks LowQCab, this looks like it could be an ideal solution. I believe the solenoid will draw a peak of about 2A, but continuous is less than 1A.
The coil on the solenoid is rated at 24V, will putting 40V to it not cause damage? You are right that I want it to open quickly, though the documentation states that at 24V this will be 30ms.
The reason for questioning 40V is that I already have a 24V supply available.
What would be suitable capacitors for this?

Thanks again
 

MrChips

Joined Oct 2, 2009
24,651
If you stick to launching paper rockets this should be ok.
With all types of projectile launching experiments proper safety procedures must be in place and enforced.
 

MrChips

Joined Oct 2, 2009
24,651
I don't see anything unusual about that capacitor.
We need to see a circuit diagram in order to judge its suitability.

btw, are you the instructor or supervisor for this school project?
 

LowQCab

Joined Nov 6, 2012
1,372
Those Capacitors are the exact item, get 10 of them.
Now, for Power .......
A Solenoid-Coil has Inductance,
this tends to slow-down its opening when applying its rated continuous Voltage.
Twice the rated Voltage will make the Solenoid Coil eventually over-heat,
but you will only be applying a higher Voltage for ~50ms or less,
so there's not enough time for any Heat to build-up at all.
You could probably benefit (very slightly) from going as far as a ~100-Volt spike,
but the advantages don't out-weight the more dangerous Voltages.
Even ~40-Volts can BITE You, so be careful.

A ~40-Volt spike will not hurt the Solenoid in any way.

Going with the Batteries, (or any source of ~40 to ~50-Volts DC), is definitely worth it.
It's a one-time purchase, you will never run them dead, even with tiny Triple-A-Cells.

Alternatively,
you could get a cheap Chinese Boost-Converter that can
easily double your 24-Volt Supply to 48-Volts.
It will have to supply very little Current, so the smallest one you can find will work great,
as long as it's rated for 24V Input and ~50V Output, any Amperage or Wattage-rating is fine.

If you want to build your own,
a Capacitor-Coupled-Voltage-Doubler is a really easy project.

For long-term storage,
simply remove any one of the batteries to break the continuity of the Charging-Circuit,
then press the Button once to discharge the Capacitors.
When it comes time to use it again,
just replace the one Battery, and in ~20-Seconds you're ready to launch !!!
.
.
.
 

Thread Starter

graham.hepworth

Joined Jul 5, 2021
4
I don't see anything unusual about that capacitor.
We need to see a circuit diagram in order to judge its suitability.

btw, are you the instructor or supervisor for this school project?
I have run this for the past 2 years with the kids (I am instructing) but previous control of the solenoid has just been through a manual switch which then dumps all of the air in the chamber rather than a short pulse. Hopefully this will be a great addition.
 

Dodgydave

Joined Jun 22, 2012
10,095
Here's a circuit to generate a pulse from 10 to 100 milliseconds with a 100k potentiomer, using a 555 timer chip which can run on 6 to 12V, the solenoid is driven by a Mosfet .

20210706_114617.jpg
 
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