Backup power
Backup power (the following is a documentation of what I HAD done and NOT what will work; please read it as a reference and make sure you have some basic electrical knowledge before attempting projects dealing with electricity. Don't blame me if you set anything on fire! :) )
(April 17, 2002) The original concept goes to Playfair and Odenwell on Reef Central. Thanks to their help (and others on the reef bulletin board), I made my backup power with a few of my own modifications. The backup power unit works just like a computer UPS system. Main difference is a standard UPS will only provide about 8 mins of runtime for a computer...let alone a reef tank. Taking apart an old UPS, replacing the original battery with a flood cell is not an option. The charger inside an UPS ultilizes a different charging method, and may cause damage to flood cell batteries. When true seal battery (such as the ones found in UPS) are used, the overall cost of this project will skyrocket making it not feasible to DIY to being with.
This backup unit will run my Dolphin Ampmaster pump for at about 5 hours in case the AC power goes out. If I add my heaters to it, I think I'll get about 4.5- 5 hours off it still (since heater is not ON all the time). Also a good UPS cost about $200-300 for 8 min of run time. This DIY unit is half the cost, but will run 5 hours. The circuit is powered with AC normally. When AC power goes out, the relay will turn on the inverter and supply power to the circuit to run the connected devices. The 120V light on the outlet box indicates power to the outlet. The light should be lit regardless of running on AC or battery.
The entire unit consist of:
KEST KR205N Quad pole Double throw; 120V relay; 10A @ 120V ($4) - All Electronics
Relay holder ($5) - All Electronics
Project box ($3) - All Electronics
Mis. wire/ plugs/ outlet box/ etc. ($10) - left from other projects
Glass type fuse 10A and holder ($5) - All Electronics
120V red indicator light ($1) - All Electronics
12V 300W inverter ($35) - Harbor Frieght
12V auto float charger 750ma ($30) -
12V marine deep cycle battery 115ah ($60) - Costco
Total: $153
Several issues worthy of concern in design and making the unit:
1.) Regular 12V flood cell battery as used in this design will give off hydrogen gas when charged regardless of amperage of charger. A charger outputing under 1A will produce very little hydrogen to be of concern. Hydrogen gas is highly explosive, odor-less, and colorless, so that should be taken into account. The other option is an AGM battery. It is totally sealed and even less gas during charge cycle will be produced. However, it cost three times as much and has half the capacity of a flood cell.
2.) Out of the four poles on the relay, only three were used. First for AC plug, second for plug from Inverter power; third for a serial connection on the inverter switch. The third pole controls the ON/OFF of the inverter when AC is available or not. At first I the made the connection at the input wire of the inverter. This was a big mistake!! 300W inverter/ 12V= 25A. Since the relay is only rated at 10A, the relay contacts melted within seconds and smoke was coming out....whew... To solve this problem, I change the connection to the ON/OFF switch in the inverter (opened it and connected on the at the ON/OFF switch of the inverter). Now it is at 300W/ 120V= 2.5A. Well under the relay's max capacity.
3.) Depending on the circuitry design of the inverter, some designs require the power switch to be turned on and off before the inverter will switch on. For the particular inverter I used, I had to resolder the switch connection to make it turn on as long as 12V power is supplied. Without this modification, the automactic backup system will not work.
Updates: (April 23,2002) Now I'm running a total of 452W off the backup system. One Ampmaster pump (112W), two Ebo Jager 150W heaters (312W), small AC fan for cooling sump (20W), and two electronic temp controllers (8W). The equipment wattage listed above were measurements taken using an ammeter and averaged from several tests. The original glass fuse used was 3A. 3A x 120V = 360W. This proofed to be insufficient and the fuse blew after 5 min (or when the heaters came on). Now a 10A fuse is used. I have not put the whole system under "backup test" yet, to see how long would the battery really last. Also with the additional load, I am now using a 600W inverter instead of the original 300W. When you size inverter, make sure you consider the PEAK output of the inverter. Typically, pumps demand 2-3 times more wattage when they first start up. As for the Ampmaster....it runs continous at 112W. But at start up, it requires 286W. That's an additional 174W!
Updates: (Mar 1, 2003) Two months ago, after the power resumes from a power outage, the pump DID NOT restart! Needless to say, wet carpet all over.... About 8-10 gallons were on the floor. Everyone whom has had an over-flow experience will know 8-10 gallons is pure nightmare. After the cleanup of two plus hours, I finally had the chance to figure out what went wrong. The culprit was a faulty relay. A $4 part caused all this headache and forced me to update the design quick....
Just add two relays.... :) It is the same circuit as before. Now there are two relays to complement each other and switch the circuit from A/C to backup power. One relay failing...maybe....but two at the same time....I'll say highly unlikely..... I just have to remember to check once a month on their operation to make sure both are working.
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