 # Furniture with extras (solenoid, motors, LED strip)

I’m helping my brother with creating a furniture piece that has doors that open and colourful LED strips.
(The problem is that I only know how to program but have to read up all electronics related things.)

At the moment, I’m stuck on the following decisions:
Q1. Which power source should I use for the solenoid.
(Q2. Can I power the Arduino and the LED strip both with the same 5V@10A power supply.)

I have two power sources:
A) 5V for Arduino (because of the LED strip: 5V@10A)
B) 24V@1A (we have a sponsor how gives us specialised motors for opening cupboards, therefore the constraint of using a 24V power supply.)

Now, both power supplies have more than enough power for a small solenoid, but I’m worried about how to reduce the power in the circuit to avoid too much power at the solenoid. (I am aiming at 8W power at the solenoid.)
A) I would buy a 6V@1A (HS-0530B; DC 6V 1A) solenoid. I guess that running it with only 5V will only reduce the power of the solenoid?
If I understand it correctly, the solenoid will pull more current if available. Therefore, I would add a resistor to keep the current low enough?
(see schematics attached)

B) If I use the 24V power supply, I match the specifications of a 24V solenoid (JF-0530B 24V 300mA), but again, I think I need to add a resistor to limit the power at the solenoid. On the other hand, I read that at 24V the solenoids are less powerful. I want to use 3m of WS2812B with 60LEDs/m. According to the seller that needs 18W/m, hence 54W. I will reduce the brightness a bit (or shorten it) to stay below 45W. The remaining 5V@1A should be sufficient to run the other devices and the Arduino. steffenpl: ... If I understand it correctly, the solenoid will pull more current if available. ...

Sorry, but i think this is the point where you fall ... current is totally depending from voltage AND resistance ... if a load have a resistance of (example) 10 ohm, and you power it with (example) 5V, there is no way that it can pull more than 500mA (Ohm law, I = V / R), also if your power supply can give 100A, the load still draw its own 500mA and no more (until you don't increase the voltage ofcourse)

powering it with 5V instead of 6, simply DECREASE the nominal current (and you have to check if at 5V it still have enough force, cause ofcourse also that is decreased a bit)

The only thing you need to take in consideration is the fact that being an inductive load, it store energy that release at turn-off ... so, usually is always used a diode in antiparallel (K on +, A on -) on every inductive load, especially if used with logics (included your relay)

About solenoid forces, they depend from mechanic construction, better or worse use of magnetic flux in them, used materials ... nothing say that a 24V solenoid have to be less strong than a 5V one ...

Thank you very much! Yes, I definitely lack basics, thanks for your explanation, that helps me a lot!

Sorry, but i think this is the point where you fall … current is totally depending from voltage AND resistance … if a load have a resistance of (example) 10 ohm, and you power it with (example) 5V, there is no way that it can pull more than 500mA (Ohm law, I = V / R), also if your power supply can give 100A, the load still draw its own 500mA and no more (until you don’t increase the voltage ofcourse)

I get how I was wrong. What I don’t understand now how solenoids are regulated?

The datasheets often show plots of force/displacement for different levels of power (i.e. 4W, 8W, 16W etc).
They state that a higher power level is only allowed if the duty cycle is low enough.

I have a solenoid with 6V and rated current 300mA => 1.8W (and R ~ 20Ω).
If want to use it with 3.6W, then the way to archive this would be to use a “6*sqrt(2) V” power source? Since then P = U²/R = 12 / 20 W = 3.6W. Is that correct?
Somehow, I imagined that it would be easier if solenoids have less resistance but instead one would limit the current to control how strong they push. steffenpl:
I get how I was wrong. What I don’t understand now how solenoids are regulated?

The datasheets often show plots of force/displacement for different levels of power (i.e. 4W, 8W, 16W etc).
They state that a higher power level is only allowed if the duty cycle is low enough.

You can vary the power level by varying the voltage supplied to the solenoid. The solenoid has a fixed (DC) resistance, so more voltage will translate to more current and thus greater power. The caveat is that greater power will also cause greater heat rise within the coil, and if this is excessive it will destroy the coil. This is where duty cycle comes into the equation. Also, you cannot supply just any arbitrarily chosen higher voltage, because at some point you will cause breakdown of the wire insulation… with unfortunate results.
S.

Sounds good! I think I know what to do now. Thanks for your help!