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 possible).
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:
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?
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.
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 apartments.
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$ Notepad):
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.
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!
--
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.
The lock has a rating of 12-24 voltage... does this mean that I would be OK with the 14.2 V the charger sends out or do I need to reduce the voltage with the diodes? Thanks and regards. The lock details are here
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.
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 coil:
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.
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 here.
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 solution.
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 .
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:
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?
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