Re: [DMCForum] Original locking module: Really that bad?

[Martin Gutkowski <martin@xxxxxxxxxxxxxx>]

Hi Ryan

Ever turned a light switch off slowly? You know how you can get that 
ZzZZZing noise in the switch making the light go dim? Will, that's what 
happens _every_ time the relays that power the solenoids switch off. 
This is a really bad bit of design - the relays are powered from a 
charged capacitor which discharges through the relay's coil, meaning the 
relay gets fed a decaying voltage - not a snappy "on/off".

Each itty bitty relay powers both solenoids in parallel (one is unlock, 
the other is lock). They're pretty hefty devices, and are also what's 
known as "inductive" - that is, electromagnetic. Inductive devices 
generate massive voltage spikes when turned off - this is how an 
ignition coil works. And this massive voltage generates a spark across 
the contact being opened - the relay - which in the case of the lock 
module, also happens to be open to the air.... and is underrated for the 
task. The result will be relays which weld themselves shut, burning out 
the solenoids and locking you in/out.

One simple solution is to replace the relays with hermetically sealed 
ones - they are sealed in an inert gas (argon?) which removes the 
sparking. A better solution is to redesign the board complately, as in 
the LockZilla, and our own replacements which both get rid of relays 
altogether and use solid state devices (fets in our case)

Martin
DMUK

ryanpwright wrote:

> 
> For the fun of it I took the lock module apart. Folks, this is a very
> simple circuit. A few wires, couple of diodes and relays, not much
> else. What's the problem with the circuit? Are we sure this is a
> problem with the locking module and not simply the age of the
> solenoids themselves? When they fail, they will short right back into
> the lock module and cause problems. Seems to me that rewinding the
> solenoids will restore them to new and prevent this problem from ever
> occuring.
> 
> Is there something I'm missing?
>

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