@JohnW2, or anyone else educate me please, regarding your earlier comment a few questions
Sparkymarka earlier suggested an IN4001 diode as do google, but you both implied IN4004 was fine and I got the impression my IN4004 would be fine but the PIV of 400V was a bit over the top, can you elaborate on that please.
In case i come across this situation again, I have some more IN4004 diodes , but should i stock up on IN4001.
We sometimes only have to to check the mains power supply to maglocks, but if we can solve the other non mains issues, like this case thats a bonus.
Therefore Is there a diode size that would likely cover the range from small to medium locks both 12V and 24V, I do not know off hand current ratings but can likely find out.
But seems they all are about 500ma. or less
Also it does appear that most locks have something built in, therefore is it a problem if a Diode is still added, I assume its not a problem.
Anyway I fitted it within the maglock casing and all appears fine, apparently over 4 years and over 6 people have looked at this lock and not solved the issue, so the Manager was well happy.
A bit of background on the job, its a pub external yard gate that leads to the beer garden, but the buttons in the pub, therefore to get from the button to the gate was a 2 man job, now he can hit the button and walk to the gate within the delay and still get in.
One final question though, I fitted it by using the indicator Marking on the casing, I therefore assume it is the right way round and feel that if it was the wrong way round, i would be right to think it would have Dead shorted the power supply.
It amazes me how something so small can do what it does, so therefore a final query, does the diode get hot and is its lifespan limited.
Thanks for all your help EVERYONE, i have learnt more here, as usual than I ever did on my C+G Electronic servicing course about 10 years ago
As usual things are easy when you know, pre maglock days we used to change a lot of the Solenoid deadlocks and my friend at RS used to always bang on about there Emf and Diodes, I should have paid more attention.