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I have an electric sliding gate, with a motor powered by 220V.

The problem with this kind of solution is that, when we have a power supply failure, we must remove a screw and open it manually. It is annoying and problematic when my mother (65 years old) must open it alone.

I would like to connect the main power to batteries (using a convertor AC/DC) and the motor to batteries. The problem is that i know that these motors require a high spike of energy to start it up and i would need a kind of capacitors, but i'm not quite sure, if there is already something in the market or if anybody did it already and has some directions for me.

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What type of gate (sliding, swing)? A quick search shows that battery backup is basically a standard feature on new gate motors - it may be cheaper/simpler just to buy a new motor rather than try to rig something up to what you have now. –  gregmac Dec 14 '11 at 21:57
    
@gregmac it is a sliding one. i did update my question, thanks –  VP. Dec 15 '11 at 0:29
    
Is a backup generator out of the question? It could be used to keep other vital systems online as well. –  Tester101 Dec 15 '11 at 11:58
    
Many gate systems have their own build in backup circuitry, you just need to add batteries, they usually are not included because they cost allot –  ppumkin Dec 15 '11 at 13:16
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1 Answer

up vote 3 down vote accepted

Basically, what you want is a UPS (Uninterruptible Power Supply); it's a combination surge protector and battery backup. These are usually spec'ed for computer systems (server rooms, uptime-critical workstations like for call centers, etc) but as long as you keep the actual unit inside some weatherproof area like a garage, it should be just fine for powering outdoor equipment like your gate. Be aware that U.S. 220V UPSes are hard to find; most 220-240V supplies are designed for use with ordinary European single-phase circuits, which run on double the voltage but half the amperage as U.S. 120V circuits. You want it to work with a two-phase U.S. circuit, which is double the voltage AND at least 15A. That will make most 220V UPSes cry uncle.

The UPSes that will do the job are going to cost a bit of money (this one from MultiStar is marginal for the amperage draw you'll need, and it's $535: MultiStar 3000VA 220-240V 60Hz UPS). You will have to ask yourself whether it's cheaper just to buy a gate system that has its own battery backup specially designed for the gate.

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There's several factors that you need to take into account in addition to this. The startup draw of a motor is generally 6-7 times the full load draw, which means you need a much higher rated UPS just to handle the startup. Many UPSes, especially cheaper ones, put out a modified square wave (instead of a true sine wave) and this may not work or may even damage the motor. –  gregmac Dec 15 '11 at 0:26
    
@gregmac nice point –  VP. Dec 15 '11 at 0:32
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