Electric gate lock woes.... (Fotek SSR relays, Power over CAT6 etc)

[Simon Still]

I'm beyond my practical electronics knowledge/experience on something and need a few tips. 

So I've got a gate with a Viro V06 electric lock. You feed it 12V AC and it makes that familiar buzzing sound and the lock releases. Except its' not doing it reliably. The transformer is located a long distance from the lock. Most of the link is made with a length of CAT6 cable (4 cores for each side), then a short length of 0.5mm stranded cable. It's linked to my Loxone.

I (wrongly) assumed that the electric release would be a low power thing so just ran a couple of CAT6 cables from my Loxone cabinet to the gate.  One for a 1 Wire reader, the other for the gate release.  I figured using all cores I wouldn't have an issue.

http://www.viro.it/EN/5.ELECTRIC_LOCKS_AND_STRIKES/116-117.Spare_parts_and_accessorie/COIL_ABSORPTION.asp  

However, the magnets actually need 15W with the standard 12vAC coil.  As I half expected there's a significant voltage drop over this distance - 14.9v at the 12v transformer(!) is just under 10V at the lock. It worked fine for a few months but as it's got a little stiffer it's now unreliable. 

I tried running 24V over the cable and it seemed to work without any loss so I bought a 24V coil and a 0.63A 24V power supply and swapped them out.  That's actually running worse than before - the voltage drops to about 11V under load and there's not enough power.  

Connecting to the 1.5A power supply that's running the rest of Loxone sees the voltage drop to 18V (which isn't great for my Loxone kit).

The resistance of the cable loop measures about 1 ohm on my multimeter. 

It seems I've got a few options - need a bit of advice on whether any of them will work or whether I need something else. 

1) Get a more powerful 24V power supply just for the gate.  What's going on with the one I've got? Why do i get less drop in voltage with a more powerful supply?

2) Relocate either the 12VAC or 24V DC power supply to be closer to the lock. There will still be a length of CAT6 cable in the circuit (it would be very difficult to replace that now) but it will be a lot lot shorter.  It would be a bit of fiddling about and won't look as neat but can be done.  

I'd then need to control it with a relay over the other lenght of CAT6.  I've got some Fotek Solid State Relays *but* the output side of them is rated 24-380VAC so 12V is below spec. I've tested it with a multimeter on the bench and it seems to work (though the voltage drops about 0.5v against the transformer output).  Alternatively I could use the SSR relay to switch the power to the power supply (but I'd assumed that power supplies are not designed to be switched on/off frequently or rapidly.  

Any other suggestions?

[Simon Still]

Ok

The 24V coil they've sent isn't the one I ordered - it's the 2000mA one not hte 460mA, which is why it's causing the voltage to drop so much on the power supply.....

UK distributor says that's the only one they have.

[Duncan]

your new low current 24v coil may well work with your existing cable, however if its not reliable i would suggest to locate a separate power supply closer to the lock and use a relay or ssr - however the AC SSR cannot switch dc to your lock coil - you have to use a DC specific ssr - there are plenty available

you could use your ac ssr to switch the mains to your new power supply from a loxone digital / low voltage output or to switch the 24v ac from a local power supply to the lock - probably better simply switching mains for the local power supply on/off

[Simon Still]

On Wednesday, 19 July 2017 18:11:23 UTC+1, Duncan wrote:

your new low current 24v coil may well work with your existing cable, however if its not reliable i would suggest to locate a separate power supply closer to the lock and use a relay or ssr - however the AC SSR cannot switch dc to your lock coil - you have to use a DC specific ssr - there are plenty available

 

I think I've worked out what was going on.  The 2000mA 24V coil was drawing 1.6A and the power supplies were dropping their voltage as a result under load.  

Manufacturer has said they'll send me a 460mA coil direct so I'll try it again with that.  Do you have any idea why they might have both a high current/low impedence 24V DC coil AND a low current/high impedence  24V DC coil?  When would you spec the high current one?

 

you could use your ac ssr to switch the mains to your new power supply from a loxone digital / low voltage output or to switch the 24v ac from a local power supply to the lock - probably better simply switching mains for the local power supply on/off

As above - are there any issues with repeatedly powering up a switch mode DC power supply for <1 second rather than leaving it running continuously?  I've looked at my capability to fit a local power supply and I've worked out how to do it with the cables I've got installed but it's more work and more awkward than I'd like.  I'd probably go back to the 12v AC coil though    

 

[Duncan]

personally i wouldnt have any concerns about switching the local psu on /off - if you are using the 12v ac coil, then presumably you will use a local 12vac power supply as well, switched on/off by the ac ssr - in which case a very simple ac psu will be a transformer inside and probably no electronics at all. your door isnt going to be constantly going on/off all day so the total power cycles will be fairly low.