Sunday, June 20, 2010

DIY Battery Backup (UPS)

I just recently talked about me starting a saltwater reef aquarium. A lot of time and money goes into starting such a device, and the rewards are great. There is one problem though with having a piece of the ocean sitting in your living room. You have to have a constant supply of electricity. (I have actually found that even on my little 20 gallon tank, that it cost about $25/month to run.) Anyway, if the power cuts off for more than 4-5 hours, it could have devastating results on the poor inhabitants. I almost feel a moral obligation to not let that happen.

I had to start thinking of what I would do in case of a power outage. The oxygen saturation in a saltwater aquarium is much less than that of a freshwater, and if the water stagnates, it can have devastating effects. I also live in a hurricane zone, so that could be a disaster. The obvious solution is to get a generator. This would work for any long term outages. But what happens when the power goes off at 8AM, and you don’t come home for 9 hours?

I thought about getting a battery backup UPS system for a computer. I quickly found that they are very expensive, and don’t contain enough energy to last very long at all. I need at least my main circulating pump to run, and I want it to run for up to 24 hours. The first thing I did was go buy a 13$ battery back up air pump that plugs into the electricity, and turns on if the power is cut. This would at least keep some of the oxygen levels up, and was a quick and cheap fix.

The next thing which I have not built yet because I don’t have the time or money is to build my own battery backup. The design of one is relatively straight forward. All you need is a marine deep cycle battery, which will allow for multiple charges and discharges. I need a trickle charger to always keep the battery topped off, and I need a power inverter. I simply plug the circulating pump into the inverter, and it will run off the battery.

Now that doesn’t make much sense. I need a way of detecting if the electricity is on or off.


All you realy need for that is a double pole double throw switching relay. You connect the coil to the electricity in the wall. If the power is on, the switch will swing one way, and if the power is off, it will swing the other way. Then you connect the “on” switch straight to the electricity. When the power is connected, the pump will be plugged in, and will get its power from the outlet. You also will connect the “off” switch to the power inverter. If the power is cut, the relay will change, and your pump will continue to run off of the battery power through the inverter. You simply buy a nice charger that will turn itself off when the battery is charged, and you now have a great DIY battery backup.

Here is a simple parts list found

-Marine 95ah deep cycle battery $45 (auto zone)
-Battery case $10 (auto zone)
-Schumaker auto trickle charger $25 (auto zone)
-Inverter- I used a really nice one that runs about $75, but you can get a 150w for about $40
-120v 3pdt relay (I found cheap 4pdt) $5 (all electronics)
-Extension cord for line in/out of the xfer box $5 (HD)
-misc. components… electrical and project boxes, ac outlet, wire, spade connectors, in-line fuse holder and connectors $20 (all electronics, radio shack)

This could also be used for a battery backup for a computer. See this great project here.

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