I am new to electronics and am trying to build a fun project that needs a solenoid strong enough to push/pull the latch open of a masterlock (thats open or combo has already been entered) Im not sure how strong my solenoid would need to be or what I should use for a power source. Any tips or place to start would be great!

I have found this one: http://www.digikey.com/product-detail/en/F0462A/527-1021-ND/668306 is it enough? overkill? and what kind of power supply would I need?

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    \$\begingroup\$ This is either a shopping question or about mechanical design. \$\endgroup\$ – Olin Lathrop Jan 27 '15 at 20:59
  • \$\begingroup\$ @OlinLathrop oh sorry, I was told to come here :/ \$\endgroup\$ – BluGeni Jan 27 '15 at 21:01
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    \$\begingroup\$ Get a spring scale.. or grab a spring and calibrate it yourself. Then pull on the latch and see how much force you need. The solenoids will list a stroke /force table. (Do they make solenoids that both push and pull?) \$\endgroup\$ – George Herold Jan 27 '15 at 21:06
  • \$\begingroup\$ You might try Googling (or Amazon), "car door lock actuator" \$\endgroup\$ – Tut Jan 27 '15 at 21:18

I would guess that a 48W solenoid would do it. I'm not sure that anyone is going to know the actual force required to open it in order to compare it with the force generated by the solenoid. That one is rated at 48W / 12V = 4A.

At $23, I would hesitate and reconsider using a linear actuator instead.

-Essentially constant force (they are basically screw-driven)

-0.1 - 40.0 inches of travel distance vs. solenoid maximum somewhere around an inch.

-Can push and pull

Edit: Home-made linear actuator

Essentially, weld/affix a nut to the lock and thread a bolt through it (~$1). Turn the bolt with a regular DC motor (~$5?). Reverse the polarity to the motor to reverse the direction the nut travels along the bolt; up for close, down for open.


A large hobby servo with the correct horn on top could probably supply enough force to open a padlock, as well.

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That's an old way, but I have some experience in magnetic old door latch modification.

Usually the spring that used in latch it it has a presure of around 10 Kgr to compress it around 7mm. However double the preasure force it is a guaranteed way.

So what you need it a solenoid with frame (to help the return of magnetic lines) with a force of 20 Kgr (~200Nt) at 6mm (1/4") strock.

In practice mains voltage used, thouse the coil size keeps relativelly small. A 10,000 Ampere Turns can do the job.

If you are use 110V, you can make the plunger by yourself using a coil form with length of 11.5 cm and a core of iron 1.9 mm diameter and same depth of winding with AWG23 wire.

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