Mailbox Open Indicator

thingiverse

This is a 40% scale model of a mailbox with a solenoid inside that is operated by a 12V 1A (or more) power supply, and the Dakota Alert RE-4K-Plus receivers relay. This project is used in conjunction with this project: https://www.thingiverse.com/thing:4719705 video of indicator in operation:https://youtu.be/s7ywz5HACO8 I used this solenoid: https://www.amazon.com/gp/product/B07F1S3JNL/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 From the listed specs, one would think you could hook it directly to the 12V output of the RE-4K-Plus since it can output 400 mA, but the specs are very misleading. The 300mA specification is the continuous current that this solenoid can handle. It can't actually operate at this current. It might stay extended if it is already extended at this current, but that is it. The resistance of the copy I got of this solenoid is 12 Ohms, so it will draw 1A at 12V DC. I was able to find this data sheet for this solenoid: https://www.hobbytronics.co.za/Content/external/1274/D2512640695.pdf As you can see from the graphs it can never achieve the claimed 5N of force. It does produce enough force for this application. To make this work, I used a 12V 2A supply, and plan to hook the two wires (seen in the video) to the NO contacts of one of the RE-4K-Plus solenoids. To prevent burning out the relay, one must connect a reverse biased diode in parallel with the solenoid so that the energy in the activated solenoid can be safely dumped when the relay opens, and does not cause arcing on the relay contacts. The size of this mailbox can be adjusted my changing the "Scale" value in the spreadsheet. I'm using M2 cap screws in 4mm, 6mm, and 18mm lengths to mimic the rivets on the actual mailbox. If you deviate too far from the 40% scale, you will have to change the screw sizes in the design. It would not take too much editing to remove the Solenoid mount and the wall mounting brackets if you did not want them, and just wanted a scale model of a mailbox. Completed unit demo: https://youtu.be/q8vB0lY_oyQ I used this counter: https://www.amazon.com/gp/product/B00CB9ZXBO/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1