Connect with us

Help with circuit

Discussion in 'Electronic Basics' started by JimDFB, Mar 6, 2006.

Scroll to continue with content
  1. JimDFB

    JimDFB Guest

    I would appreciate help with this question.

    I have a magnetic lock which I need to provide backup power supply to
    (in case power goes down, it needs to function for as long as

    The lock has an adaptor plug (which converts 120-240V 0.3 A mains power
    to 12v 1.0 A output).

    What I have done is to buy a computer UPS unit (Trust 600 UPS), plug
    the UPS to the mans and the mag lock into it. Works BUT, if the power
    goes down, it seems to only provide 20 minutes of power and then the
    lock opens.

    Now, can I use a car battery? I have a 12V car battery 60Ah 450A and
    also a car batter charger (which trickle charges and stops
    automatically to prevent over charging etc).

    I am hoping this will provide me with longer life... however I am not
    exactly sure:

    1. If I can connect the lock directly to the battery. Do I need to put
    in a fuse? Should I buy an inverter to change the 12 v to 220 and then
    back to 12 v?
    2. Assuming I can connect the lock directly to the battery, can the
    battery be hooked up to the charger at the same time? Ideally, I want
    the keep the battery hooked up so that it is always full... I realise
    it should be run down once in a while

    Your help would be greatly appreciated... needless to say, I didn't
    want to create a fire hazard or damage the lock.

  2. Rich Grise

    Rich Grise Guest

    You've got your lock installed backwards. It should be set up so that
    you apply power only when you want to open the door, like the buzzer at

    Good Luck!
  3. John Fields

    John Fields Guest

    So if there's a fire or something which knocks the power out
    everyone is guaranteed to be locked inside?

    "Grise"... is that German?

    You obviously missed that the lock fails open:

    "it seems to only provide 20 minutes of power and then the lock

    and that until power fails, control of the lock depends on
    whatever's controlling the lock. After that the lock opens.
  4. redbelly

    redbelly Guest

    John, that is not a problem for two reasons:

    Any lock SHOULD have a mechanical means of controlling it from the
    inside, to overide any electronics failure.

    Any body who uses a lock without such an overide SHOULD burn to death
    in a fire and remove their genes from the human pool.



    p.s. Aplogies to anyone who finds my post unduly harsh or Allisonian.
  5. Chris

    Chris Guest

    Hi, Jim. Sorry for your troubles.

    If you look on the Trust website, you'll see that the Trust 600 User
    Manual specifies it has a a 12V, 7Ah battery. That means that, if
    you're running the battery at a 1 amp load, it will take 7 hours to
    discharge. If you're running 1/2A, it will take 14 hours, and so on.
    Amp-hours capacity = number of amps load times number of hours.

    Also, you should know that an unregulated wall wart is kind of a
    squirrely load for a UPS, because it only draws current during the
    positive and negative peaks of the AC waveform. Most computer power
    supplies are made to draw power more evenly through the AC cycle.

    Given those two things, it's possible but not very likely that your 12
    watt load would only be powered for 20 minutes (4 watt-hours) with a
    UPS through a battery that has a capacity of 84 watt hours. If you
    bought your UPS used, you may want to try replacing the battery.

    I'm sure the direct hookup of the battery would be OK, at least for a
    while. But a 12 watt load is like leaving your running lights on when
    you park your car -- it will run down the battery in a day or so.

    A car battery in use is being constantly trickle-charged by the
    alternator when it's lightly loaded. It does this by regulating the
    alternator voltage to 13.8 - 14.2VDC. That's not enough to force the
    battery to overcharge, unless you never load it down. Your trickle
    charger works like your alternator. So, your battery with trickle
    charger hooked up should work OK for your lock circuit, as long as the
    trickle charger can crank at least 1 amp (nearly all of them can).
    Here's the plan (you'll need a meter to do this):

    1) While the lock is energized, use your meter to check the DC voltage
    that's being supplied by your wall wart. Let's assume for the sake of
    discussion that your meter reads 12.9VDC.

    2) Now, set up your battery and trickle charger. Leave it on for a
    while, then read the voltage present on the battery. Let's assume for
    the sake of discussion it's 14.2VDC.

    Now, figure out the difference between the two voltages (1.3V here).
    If the wall wart has the same or a higher voltage, you can just connect
    the battery/trickle charger directly in place of the wall wart (be sure
    to watch polarity -- don't hook it up backwards or you'll let the smoke
    out). If the battery/trickle charger voltage is greater, do some sums:

    * less than 0.7V greater = 1 diode
    * less than 1.4V greater = 2 diodes
    * less than 2.1V greater = 3 diodes
    * less than 2.8V greater = 4 diodes

    and so on. Then hook up your battery/charger to the lock circuit with
    some 1N5401 diodes in series as shown (view in fixed font or M$

    | Charger Lock Ckt
    | .-------. 1A .--------.
    | | | _ | |
    | | +o----o->|-->|---o-\_/o--o+ |
    | | | | | |
    | | | +| | |
    | | | ---12VDC | |
    | | | - Battery | |
    | | | | | |
    | | | | | |
    | | -o----o------------ --o- |
    | '-------' '--------'
    (created by AACircuit v1.28.5 beta 02/06/05

    This example shows two 1N5401 diodes because the example difference was
    1.3V -- put as many or as few in series as you need per above. You
    should fuse the line running from the battery to the lock circuit for
    electrical and fire safety, and to protect the diodes. You can use a
    standard automotive fuse if it's available, or a regular fuse is OK.

    I hope this has been of help. Feel free to post back if it isn't
    clear, or you have further questions.

    By the way, the fuse is NOT optional. Make sure to enclose the battery
    and fix it in place (but leave vent holes to prevent buildup of
    explosive hydrogen gas), and be sure to put insulators over the battery
    posts to prevent accidental shorting and explosive failure of the
    battery. When it's in use, periodically turn off and disconnect the
    charger for a shift to help the battery along by doing a partial
    discharge. And periodically touch the battery case to see if it's
    heating up -- always a bad sign. It should be cool during normal
    usage. Be safe.

    Good luck with your project
  6. JimDFB

    JimDFB Guest

    Thanks Chris... very much appreciated. I do not understand why the UPS
    does not last long... I bought it new. I did the measurement as
    suggested and the voltage dfference is about 1.4v. I need to get hold
    of some diodes. Again, thanks!
  7. John Fields

    John Fields Guest

    Wouldn't hurt, but you'll need to put something pretty big in there
    in order to make sure that unless it's a catastrophe the lock stays
    where it's supposed to. 5 amp slow blow would probably be a pretty
    good choice.

    No, no, no, a thousand times NO!
    Yes. Hook up your stuff like this:

    +---------+ +---------+
    MAINS>----|~ +12|---[1N5822>]--+---|+ |
    | ADAPTER | | | LOCK |
    MAINS>----|~ -|---+----------|---|- |
    +---------+ | |K +---------+
    | [1N5822]
    | |
    | [FUSE]
    | |
    +---------+ | | +---------+
    MAINS>----|~ +12|---|----------+---|+ |
    | CHARGER | | | BATTERY |
    MAINS>----|~ -|---+--------------|- |
    +---------+ +---------+
  8. JimDFB

    JimDFB Guest

  9. Hmm, feeling the need to add one remark: Make sure the voltage provided by
    the battery is lower then the voltage from the adapter (both measured on the
    lock-connections). Otherwise the battery may go halfway empty before the
    adapter takes over.

    petrus bitbyter
  10. JimDFB

    JimDFB Guest

    thanks John
  11. Chris

    Chris Guest

    Hi, Jim. Wishful thinking. It says it has "dual voltage". That means
    there's a connection for 12V, and a connection for 24V. This doesn't
    sound like you can put up to 24V on the 12V terminal. Probably a split

    | 24V
    | o-----.
    | |
    | C|
    | C|
    | C|
    | 12V |
    | o-----o
    | |
    | C|
    | C|
    | C|
    | COM |
    | o-----'
    (created by AACircuit v1.28.6 beta 04/19/05

    There's also the question of the voltage requirement for whatever's
    controlling the lock.

    If you try to duplicate your existing power supply as closely as
    possible with your battery/trickle charger, it _should_ be OK. You
    were asking specifically about replacing a wall wart. I can't tell you
    about how your security system is wired, or what else is connected.

    Good luck
  12. JimDFB

    JimDFB Guest

    Hi, Jim. Wishful thinking

    Yes, it was rather. I appreciate everyone's help. I have ordered the
    diodes and will get it all sorted soon. Regards
  13. Chris

    Chris Guest

    One more thing, Jim. Sorry, but the thought just occurred to me now.

    I'm guessing your wall wart is an unregulated 12VDC, since it's being
    used to drive a solenoid. If it's not, any other circuitry may be
    relying on a regulated supply, and you might end up with big problems

    An easy way to check is to measure the wall wart voltage with the
    solenoid off, then with it on. If the output voltage goes down by more
    than 50mV or so, it's unregulated, and all the advice above is OK. If
    the output voltage stays the same, post again -- you'll need another

  14. JimDFB

    JimDFB Guest

    Hi Chris. The only other circutry is a controller It
    says: Installation and set-up are simple. The AP-4 operates on 12-24
    volts, ac or dc. It can be powered directly from the radio power output
    of most gate operators. Installation and set-up are simple. Power
    Input: low voltage plug in transformer or power from access device
    12-24 .
  15. JimDFB

    JimDFB Guest

    sorry didn't complete the posting before posting it:

    Hi Chris. The only other circutry is a controller It
    says: Installation and set-up are simple. The AP-4 operates on 12-24
    volts, ac or dc. It can be powered directly from the radio power output

    of most gate operators. Installation and set-up are simple. Power
    Input: low voltage plug in transformer or power from access device
    12-24 volts AC/DC.

    Does this answer the question? Regads
  16. JimDFB

    JimDFB Guest

    12.07 v on and 12.13 v off... regards
  17. Chris

    Chris Guest

    You're good to go, Jim

    Good luck
  18. John Fields

    John Fields Guest

  19. John Fields

    John Fields Guest

    You're welcome, but due to Petrus' input it's back to the drawing

    This _will_ work:

    .. +---------+
    .. MAINS>--|~ +12|-----+----+
    .. | ADAPTER | | | O----->To lock +12V
    .. MAINS>--|~ -|--+ | [COIL] - -|
    .. +---------+ | | | O--> |<--O
    .. +--|----+ |NO NC|
    .. | +-------+ |
    .. | +------+
    .. | |
    .. +------------|-------->To lock GND/0V
    .. | |
    .. +---------+ | | +---------+
    .. MAINS>--|~ +12|--|------------+--|+ |
    .. | CHARGER | | | BATTERY |
    .. MAINS>--|~ -|--+ --------------|- |
    .. +---------+ +---------+

    Where the relay is any small 12V coil relay capable of hot-switching
    an amp and a half.

    Or, if the additional load from the relay coil is too great for the
    adapter to bear, you could get a 120VAC coil relay and run it off
    the mains, like this:

    .. +---------+ NO NC
    .. MAINS>-+---|~ +12|------O--> |<--O
    .. | | ADAPTER | [COIL] | |
    .. MAINS>-|-+-|~ -|--+ | | O-------->To lock +12V
    .. | | +---------+ | | | |
    .. | | | | | |
    .. +-|--------------|--+ | |
    .. | +--------------|-----+ |
    .. | | | |
    .. | | +------------|---->To lock GND/0V
    .. | | | |
    .. | | +---------+ | | +---------+
    .. +-|-|~ +12|--|------------+--|+ |
    .. | | CHARGER | | | BATTERY |
    .. +-|~ -|--+---------------|- |
    .. ++---------+ +---------+

    This will get you complete isolation between the adapter and the
    battery/charger, which is a good thing.
  20. JimDFB

    JimDFB Guest

    Many thanks for the combined mains adapter and charger option but I am
    not sure if I gain anything by having both the battery (hooked up to
    the charger) AND the mains adapter at the same time. Seems to me
    charger+battery only covers all needs, or am I missing something?

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day