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    • CommentAuthorSimon Still
    • CommentTimeJul 5th 2017 edited
     
    Asking on here as I know there are some people with some good practical electronics experience.

    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 Home Automation system and intercom...

    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.

    A few options - need a bit of advice on whether any of them will work or whether I need something else.

    1) Feed the lock with 24V DC. This would be simplest. The locks will run with either 12V AC or DC supposedly - am I going to damage the lock by feeding it a higher voltage? They make the lock in a 24v version as an option and it supposedly has different coils.

    2) Relocate the 12V transformer to be closer to the lock. I always thought i might need the power supply closer so there is somewhere I could intercept the CAT6 cable, mount and power the 12V transformer. Then use the CAT6 back to the Home Automation hub to switch a relay linked to the 12v output.

    This is quite a bit more work and won't look as neat. It's probably £20 for a good quality Din Rail enclosure to hold the transformer (the really cheap ones i bought are crap).

    Also, need to find a relay. 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). So, how's the SSR likely to behave over time?

    3) I could get a 24V coil for the lock and swap it out. However, Italian made lock - will likely take a long time to get a replacement and with shipping and spares markup likely to cost almost as much as the lock did originally.

    Also, am I likely to get the same problem with voltage drop at 24v?

    [edit - tested this. No voltage drop but the draw of the lock is enough that it messes with other stuff the 24V supply is powering, so I'd need an extra 24v power supply]

    Any other suggestions?
    • CommentAuthorCWatters
    • CommentTimeJul 5th 2017
     
    Do you know how much current the lock draws? Can the lock be stalled causing high current draw?

    If it works on DC one option might be to use an adjustable DC voltage regulator to produce the exact voltage needed at the gate end. These days they are pretty cheap..

    http://www.ebay.co.uk/itm/MP1584-Adjustable-3A-DC-DC-Converter-Step-Down-Voltage-Regulator-/263005321438?hash=item3d3c56b8de:g:G6sAAOSw1WJZKIcE

    but it's only rated for 3A and may need a heat sink. Say it's 90% efficient then 10% of 36W = 3.6W of heat to be dissipated.

    Another option would be to put a 12V lead acid battery at the gate end. At the house end feed it whatever DC voltage is needed to produce 13.5-13.8V at the battery to keep it float charged. Then use a relay to switch the 12V to the lock. Means using one of the CAT cores to control it.
  1.  
    Cat 6 cable is a data cable (?) correct me if I am wrong. You say you have 10v at the gate, is that 10v standing or 10v whilst the solenoid is energised and the gate is trying to open?

    The fact that the lock worked OK at first and now fails to open sometimes to me implies that it is borderline on the supply voltage.

    Can you get a decent thickness cable (1.5mm2 or preferably 2.5mm2) to do a temp hook up to see if that solves the problem?

    I wouldn't run the lock on 24v, you will significantly shorten its life.
    •  
      CommentAuthordjh
    • CommentTimeJul 5th 2017
     
    You don't say what current the lock draws, which will affect things somewhat. Cat6 can supply 600 mA per "mode" (pair of pairs).

    The simplest, although not necessarily the cheapest solution is perhaps to get an adjustable power supply and adjust it so it produces exactly 12 V at the lock.

    Other possibilities include pushing a higher voltage AC down the wire, to reduce current draw and losses, and then transform it down to 12 V just before the lock.
  2.  
    Posted By: djhCat6 can supply 600 mA per "mode" (pair of pairs).

    Which gives about 7W.
    I would be very surprised if the lock solenoid was anything even close to as low as 7W

    Posted By: djhOther possibilities include pushing a higher voltage AC down the wire, to reduce current draw and losses, and then transform it down to 12 V just before the lock.

    Or just install a thicker cable!
    •  
      CommentAuthordjh
    • CommentTimeJul 6th 2017
     
    Posted By: Peter_in_HungaryWhich gives about 7W.

    Well, 14.4 W actually since Simon said he's using all 8 cores.

    But pushing say 48 V down the cable and then using a 4:1 transformer at the far end would allow over 50 W.

    Or just install a thicker cable!

    I've been presuming that is difficult for some reason, since it's such an obvious cure, but perhaps it's best to wait for Simon to confirm more details.
  3.  
    The lock coil specs are here - http://www.viro.it/EN/5.ELECTRIC_LOCKS_AND_STRIKES/116-117.Spare_parts_and_accessorie/COIL_ABSORPTION.asp

    Looks like the standard coil is 15W so I'm just over the limit of Cat6 (but surely since the load is momentary - say half a second) that isn't going to be an issue?

    I'm thinking I should order the 24V 460mA coil and it will be fine?

    Cables were put in about 2 years before the gate and long before it was designed or specced. I didn't look into it too much at the time - with the local power supply/relay being the fallback if it didn't work as I've now installed it.

    10V is the voltage at the cable ends at the lock when the power supply is in circuit (and is the same if the wires are connected to the lock or not)
  4.  
    Posted By: Simon Still10V is the voltage at the cable ends at the lock when the power supply is in circuit (and is the same if the wires are connected to the lock or not)

    I am surprised that the voltage is the same between load and no load. Generally speaking if the cable is at its limit then I would expect a (significant) drop in the voltage when the lock is energised as against the no load voltage

    Posted By: Simon StillI'm thinking I should order the 24V 460mA coil and it will be fine?

    The 24v coil quoted as 460mA is 24v DC, I thought we were talking about AC coils in which case the 24v AC coil is 1000mA which is still over spec for the cable but half (as you would expect) of the amps required for the 12v AC coil, but given that the 24V AC coil is still over spec for the cable there is no guarantee that the 24v coil will solve all the problems..

    Can you run a temporary thicker cable to test / prove that it is an inadequate cable causing the problem? And how easy would it be to replace the existing cable?
  5.  
    Posted By: Simon Still(but surely since the load is momentary - say half a second) that isn't going to be an issue?

    Oh and the half a second or so overload won't be a problem for the cable, an over loaded cable will heat up and eventually burn out but probably not in this situation. But that is not the problem, the problem is that the cable can not deliver enough power to operate the device, that shortfall is the same regardless of the time the cable is carrying the current. (ignoring resistance changes due to heating which won't be relevant for the short periods in question here)
  6.  
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>But that is not the problem, the problem is that the cable can not deliver enough power to operate the device, that shortfall is the same regardless of the time the cable is carrying the current.</blockquote>

    Ok, but 460mA at 24V should be fine?

    It's been working fine again for the last 24 hours (I gave the inside a spray with silicon before I put it back together to give it a bit of help).
    • CommentAuthordpmiller
    • CommentTimeJul 7th 2017
     
    I'm guessing the power and current quoted is steady-state, but what is the inrush current?
    • CommentAuthorSimon Still
    • CommentTimeJul 7th 2017 edited
     
    Posted By: Peter_in_Hungary

    I am surprised that the voltage is the same between load and no load. Generally speaking if the cable is at its limit then I would expect a (significant) drop in the voltage when the lock is energised as against the no load voltage

    Posted By: Simon StillI'm thinking I should order the 24V 460mA coil and it will be fine?

    The 24v coil quoted as 460mA is 24v DC, I thought we were talking about AC coils

    Can you run a temporary thicker cable to test / prove that it is an inadequate cable causing the problem? And how easy would it be to replace the existing cable?


    I set the HA system to sent 12V to the lock for 10 seconds or so to get a reading. My multimeter was reading a stable 9.8v whether the coils were connected or not. Maybe there's a lot of headroom built into the coil spec - actually the load is not as high as documented?

    There are AC and DC coils available. Using AC gives the loud characteristic buzz when active. That's often a useful signifier to a user that the lock has released and to push the gate. In my case it's just annoying (the gate part opens when the lock releases) so DC is preferable.

    (replacing cable isnt' an option)
  7.  
    Posted By: dpmillerI'm guessing the power and current quoted is steady-state, but what is the inrush current?


    How do i measure it? Why is it important?

    Is a 0,.63A 24V power supply and the 460mA 24V DC coil likely to work (or am I likely to need a more powerful P/S)
  8.  
    0,.63A I presume is 0.6A = 630mA power supply. The coil at 460mA would be running at 73% of the power supplys capability so it should be OK. I am assuming here that the power supply output is DC and that the output of 630mA is the DC rated output.
    •  
      CommentAuthordjh
    • CommentTimeJul 10th 2017 edited
     
    Posted By: Simon StillHow do i measure it? Why is it important?

    It's moderately difficult to measure and not terribly important in this application I suspect.

    I suspect the lack of difference between load and no-load voltage is a fat finger problem. Do NOT connect the coil when measuring the no-load voltage.

    It seems likely that it is marginal voltage/power that is causing the lock not to work, and lubricating it has reduced the power necessary for the moment. In which case, substituting a 24 V power supply and coil should improve things; only time will tell whether it improves things enough that you tolerate whatever lubrication regime is implied. An adjustable power supply, adjusted to provide 24 V at the lock, would be even better.
    • CommentAuthorsnyggapa
    • CommentTimeJul 10th 2017
     
    try an 18v transformer so that at the lock it gets "about 12" after losses?

    (or an adjustable one as others have mentioned - just twiddle the pot until you get 12v at the far end)
  9.  
    Posted By: Peter_in_Hungary0,.63A I presume is 0.6A = 630mA power supply. The coil at 460mA would be running at 73% of the power supplys capability so it should be OK. I am assuming here that the power supply output is DC and that the output of 630mA is the DC rated output.


    Yes, that's right - I was just thrown by the 'inrush current' question - whether this application would need more headroom.



    Posted By: djhIt seems likely that it is marginal voltage/power that is causing the lock not to work, and lubricating it has reduced the power necessary for the moment. In which case, substituting a 24 V power supply and coil should improve things; only time will tell whether it improves things enough that you tolerate whatever lubrication regime is implied. An adjustable power supply, adjusted to provide 24 V at the lock, would be even better.


    Either the lubrication, or more likely disconnecting and remaking each of the cable connections has reduced the resistance slightly (either better connections or now un-corroded) but either way likely a temporary fix.

    Connecting the 24V power supply that the rest of the HA system runs off delivered 24V at the lock without load but I think I'll get one just for this purpose. They're usually adjustable as well.

    Thanks all.
    • CommentAuthorSimon Still
    • CommentTimeJul 19th 2017 edited
     
    Damn.

    So, new lock coil and power supply fitted and it's worse than before which is dissapointing. There's no Voltage drop when no load but connect the coil and when activated the voltage drops to <10v (12V if I crank the power supply up to 28V)

    If I connect to the larger 1.5A power supply (which is running various other things) then the voltage only drops to 18V but that's running other things and dropping the voltage for that's not great.

    What's going on? Do I just need to accept the losses in my cabling and get a meatier power supply?


    So, despite the power supply theoretically being able to deliver enough power the length of the cable must still be the issue. Resistance of it is measuring 1 Ohm.
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2017
     
    As previously, use an adjustable supply and set it so it delivers 12 V under load. Or use double or quadruple the voltage and then bring it back to 12 V with a step-down transformer just before the lock.
  10.  
    <blockquote><cite>Posted By: djh</cite>As previously, use an adjustable supply and set it so it delivers 12 V under load. Or use double or quadruple the voltage and then bring it back to 12 V with a step-down transformer just before the lock.</blockquote>

    Sorry, changed my post above before you posted. I've now got a 24V DC coil on there. Trying to fit all this in existing cabinets as well to complicate matters further.

    Next options are
    1) a meatier 24V power supply (£15) or
    2) locating the power supply closer to the Lock (messier and more work - £15+ for a decent metalclad din rail box plus a relay). Is a shorter length of CAT6 cable still going to fail to deliver the power?
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2017
     
    You need 24 V at the lock and 460 mA according to your lock specs, yes?

    You can push 1.2 A down Cat6 cable using all 8 wires. So that shouldn't be a restriction.

    When you run the 1.5 A supply and the voltage is 18 V at the lock, is the voltage still 24 V at the power supply? I think it should be unless you're drawing over an amp for other things. And is the lock drawing 345 mA approximately (3/4 of its rated 460 mA)?

    If so, then the problem is simply the voltage drop along the cable. If you fit a 32 V power supply, that should produce 24 V at the lock.
    • CommentAuthorsam_cat
    • CommentTimeJul 19th 2017
     
    Get a more appropriate thickness figure 8 cable and do a test run.. Cheap test.

    As for local regulation, one of these works for me (for other uses)
    https://www.amazon.co.uk/gp/product/B00GY01UMC
    • CommentAuthorSimon Still
    • CommentTimeJul 19th 2017 edited
     
    <blockquote><cite>Posted By: djh</cite>When you run the 1.5 A supply and the voltage is 18 V at the lock, is the voltage still 24 V at the power supply? I think it should be unless you're drawing over an amp for other things. And is the lock drawing 345 mA approximately (3/4 of its rated 460 mA)?</blockquote>

    I've measured voltages across the power supply terminals and at the lock. The drop is about the same. With nothing else connected I get about 22V at the lock (so can probably turn up the power supply to get 24V)

    However, the current is reading 1.6A !!@! which makes me think they've sent me the wrong 24V coil. They'd packaged it by taping the coil to a piece of cardboard. The packing tape tore then label off the coil and wasn't readable....
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2017 edited
     
    Posted By: Simon StillI've measured voltages across the power supply terminals and at the lock. The drop is about the same. With nothing else connected I get about 22V at the lock (so can probably turn up the power supply to get 24V)

    I don't quite understand that. What do you mean by "The drop is about the same."? Also what is the voltage at the power supply when everything is connected?

    However, the current is reading 1.6A !!@! which makes me think they've sent me the wrong 24V coil. They'd packaged it by taping the coil to a piece of cardboard. The packing tape tore then label off the coil and wasn't readable....

    Certainly sounds like something is wrong. Maybe they sent another 12 V coil? Call them and ask them how to identify the coil, either visually or by electrical measurements.

    PS if you edit your posts and select Html formatting, the quoting will work.
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2017
     
    Posted By: sam_catAs for local regulation, one of these works for me (for other uses)
    https://www.amazon.co.uk/gp/product/B00GY01UMC

    One of those might well work, mounted near the lock, once you're sure you've got the right coil and aren't overloading the power supply.
    • CommentAuthorSimon Still
    • CommentTimeJul 19th 2017 edited
     
    Posted By: djhI don't quite understand that. What do you mean by "The drop is about the same."? Also what is the voltage at the power supply when everything is connected?


    Power supply voltage with everything connected (but gate draw not active) 24V. When gate coil is active it drops. I get near enough the same reading across the power supply terminals as across the lock coil terminals.


    Posted By: djhCall them and ask them how to identify the coil, either visually or by electrical measurements.

    The UK distributor have sent me the 2000mA coil not the one I asked for. That's the only one they have and they say it's what they get sent when they order 24V DC. They obviously didn't pay any attention to the detail of my order that did specify the other. Wasn't helped by them ripping the label off the coil with packing tape.

    Have contacted the Italian manf to see if they can help.

    Posted By: djhPS if you edit your posts and select Html formatting, the quoting will work.


    Yes, I know. For some reason it won't on the post above now. And if you select HTML links don't work unless you type full html around them.
  11.  
    I think I'm going to have to go back to the 12v coil and install it closer to the gate, messy as that will be.

    The 2A the 24V coil i've got needs takes it beyond the cable rating based on what you've written above.

    Damn Damn Damn. Can't believe how long I've wasted on this now.
  12.  
    Ok, so the Italian manufacturer is going to send me the right coil direct. I wonder if there is some other drawback to the low current coil that I've not spotted yet. Why would they have both a 500mA/50Ohm and a 2000mA/12ohm version?

    I've refitted the 12VAC in the meantime.
    • CommentAuthorCWatters
    • CommentTimeJul 19th 2017
     
    Lots of the numbers seem inconsistent with each other. For example if the lock draws 1.6A when operating and the cable resistance measures 1 Ohm then the voltage drop should only be 1.6V yet you report ten times that (28V-12V = 16V).

    If the lock is trying to draw 2A from a 1.5A power supply the power supply might be shutting down to protect itself. That would explain the inconsistency and is probably why djh asked what the voltage was at the power supply end with the lock operating.
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2017
     
    Simon, the only reason I can think of for two current ratings would be to comply with some standard or other, but I can't see why they would both use 24 V.

    Colin, yes there's still some confusion in my mind about what the exact situation is, and the power supply being taken out of spec might be part of the explanation. Hopefully if Colin gets the correct coil he'll be able to make it work. If it doesn't work straight out of the box then using a DC supply together with the DC-DC converter that Sam suggested will make a workable system.
   
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