Gadet Geocache - lock not tripping

[mallaht]

Hi All,

I'm trying to build a gadget Geocache, where when you complete a puzzle it opens up the container. I've mounted six reed switches on the underside of the container and recessed six magnets into the bottom of the puzzle pieces. The switches are cabled in series with the lock and a I'm using a 9v battery as a power source.

It worked when I test fitted everything together but now I'm running into two issues. One of the reed switches failed, it got very hot and the plastic housing expanded, so I'm assuming some type of electrical failure. Also the lock does not open when the puzzle is completed, it clicks but does not open though if I apply the battery directly to the lock cables it will.

Any help or pointers would be greatly appreciated.

Many Thanks

Reed Switch Spec
Lock Spec
Wire Spec

 

[Martaine2005]

After having a quick look at the specs, The reed switches have a max switching current of 0.5A. The lock draws 1.5A.
That could be your problem.
Besides that, the lock is also 6V and you are supplying 9V.

Martin

 

[mallaht]

After having a quick look at the specs, The reed switches have a max switching current of 0.5A. The lock draws 1.5A.
That could be your problem.
Besides that, the lock is also 6V and you are supplying 9V.

Martin

Thanks, I think I have a holder for four AA batteries, that would give me the correct voltage. Do I need to add some resistors or other components to solve the amperage issues?

 

[Martaine2005]

If you lower the working current of the lock, it wont operate properly.
Probably better to get higher amperage switches or lower amperage lock.
Edit: You could try and see what the lowest current the lock will work on.

Martin

 

[mallaht]

If you lower the working current of the lock, it wont operate properly.
Probably better to get higher amperage switches or lower amperage lock.
Edit: You could try and see what the lowest current the lock will work on.

Martin

Thank you for your help so far. I've tested the lock by using 1,2,3 and then 4 AA batteries it would only open when using 4 AAs. Would 2amp switches suffice like these?

 

[VenomBallistics]

You might want to think about using the switches to feed into the gate of a MOSFET.
That would solve all your low current switch issues as well as the high current latch problem

 

[mallaht]

This is the current simple circuit, so I would add in a MOSFET before the lock?

There seem to be a number of different types of MOSFET how do I work out which type I need?

 

[VenomBallistics]

I draft these things in LT Spice, so some parts look odd (its a simulator, not an illustrator)
but your application will look a bit like this.

 

[bertus]

Hello,

@VenomBallistics , Should there not be a diode over the coil to protect the mosfet?

Bertus

 

[VenomBallistics]

Ahh yes ... that EMF thang ... make it so.

 

[mallaht]

@bertus @VenomBallistics Thank you for your help in getting the design sorted. Can you help me find the correct additional components? I think I've found the correct resistor but I don't know how to work out which MOSFET and diode would be the right one to use.

 

[VenomBallistics]

standard issue 1n4003 diode should work .... MOSFET ... IRLZ14 is my random stab at it for about a buck each.
I'm sure others have other go to N channels that'll do just as well