# Power supply for a solenoid to open a secret compartment

I'm an avid DIYer, I don't know anything about circuits, meters, mathmatical equations etc. I have created a secret storage compartment so the door has no visible hinges, handles or locks, It's made of wood and weighs around 10 kg, it's held closed with medium strength magnets. I'm looking at using a push solenoid with a spring to return the pin back to starting position connectted to a doorbell type button via the main lighting circuit using 1.5 cable. 2 problems. Firstly can this be done, do I have to add a transformer into the mix,if so how? Secondly how will I know if the power of the solenoid will be able to detach the door from the magnets to open? Only place that sells solenoids in lamens terms is Amazon so this is where I'll be purchasing it from.

• What is "lamens terms"? Do you mean 'layman's terms'? Amazon isn't good for this type of stuff because you generally can't get the datasheets that give the detailed specification. – Transistor May 9 '18 at 21:49
• As an avid DIYer, that is how you will get through this. You have no diagram or schematic or CAD drawing or a hand sketch for us to work with. We cannot see into your head, so we need some help. – Sparky256 May 10 '18 at 1:59
• Yes I meant laymen's terms, spell check issue. I cannot supply a diagram as I only have a mobile phone, don't have access to a pc, laptop or tablet. As it's difficult for people to understand or grasp the idea I'll look somewhere else for info. Thank you for your responses. Take it easy. – Lee Christiansen May 10 '18 at 21:02

I think you may be using the wrong mechanism for the lock. Maglocks (magnetic locks) are widely used for this type of application in building security. They come in two modes: release when power off (suitable for most applications) and require power to release (prisons, etc.).

Figure 1. Maglock with magnetic poles exposed and keeper.

It seems to me that the three poles are arranged as south-north-south (or vice-versa) and that the coil is wound, pushed into the black slots and potted in position. Once the (electro) magnet hits the keeper the magnetic circuit is closed. As anyone who has played with a horseshoe magnet will know, opening the closed loop is very difficult.

Figure 2. Cross-sectional view.

Here we can see that with the lock open the exposed faces are poles of the electro-magnet. Note also that the magnetic path is twice as wide in the centre pole as on the upper and lower poles so that flux density is fairly constant. Once the lock closes the flux forms a loop through the iron core.

Some of the suggestions had ways that didn't consume power to hold it in place but still needed it to unlock it.

The "normally locked" version requires power to unlock. The coils are typically 12 or 24 V so that the controller can run with a small lead-acid battery backup. You would need to check the datasheets to learn how much current they consume and purchase a suitable power supply.

Figure 3. A compact cylindrical magnetic lock.

The locking force will probably be rated in newtons (N). You can convert this to kg-force by dividing by 10. (Actually 9.81 m/s², the acceleration due to gravity but 10 is close enough.) Remember that you want the "energise to release" type. These are not the usual types sold.

• Thanks for responses guys. I have thought about mag locks but I need the door to be physically pushed open as they are snug when shut with no where to grip the door to open it. Need at least an inch open to be able to grab the edge, also my understanding of mag locks is they need continuous power to remain closed and I'd rather not spend any more money on electricity to keep a door closed. I couldn't find any within my price bracket for the ones you mentioned that require energy to release either. – Lee Christiansen May 10 '18 at 0:41
• Product Name : Electromagnet Solenoid;Rated : DC 12V;Type : Push Pull Force & Stroke : 10mm 250g;Body Size : 40 x 26 x 20mm/1.6" x 1" x 0.8"(LWH);Plunger Bar Size : 72 x 9.4mm/2.8" x 0.36"(LD) Screw Hole Diameter : 3mm/0.12";Plunger Hole : 3mm/0.12";Wire Length : 20cm/7.8" Mounted Hole Dia : 3mm/0.12";Mounted Hole Distance : 23 x 15mm/0.9" x 0.6"(LW);Material : Metal, Electronic Parts Weight : 112g;Package Content : 1 x Electromagnet Solenoid – Lee Christiansen May 10 '18 at 0:52
• This is all the info available on the solenoid I was going to buy. I am totally clueless with this sort of technology, been told solenoids are basic useless pieces of tech that are so out dated and all are made in China so made cheap but cost a lot to buy, info provided by an electrician. I haven't bought the magnets yet as I don't know what size I need. – Lee Christiansen May 10 '18 at 1:01

Solenoids will have specs that tell you how hard they can push and how long the travel is. See if you can figure out how much pull is needed to push against the magnets to open it. (Use a string and some known weights to figure it out.) Then find a solenoid that has more push than that. Travel of a half inch or more should do it. Then once you've found the solenoid, look at what type of power it needs. If it needs like 24 volts AC, then you will need to get a transformer. If it needs DC, then you need a power supply. The solenoid will also have an amperage rating. Your transformer or power supply needs to be able to supply more than that.