How To Make a Power Back-Up Unit from a UPS and a battery

  • Get the NEW AquariaCentral iOS app --> // Android version will be out soon!


AC Members
May 2, 2006
Cedar Rapids, Iowa USA
I seen this on the net and thought WOW, I'm going to do this.
Between thunder storms and what ever may cause power outages here in Iowa, my power went out 5 times last year. Best of all I have a huge UPS that powered 4 servers, and the battery has died. I've just been to lazy to take it to the lanfill.

All too often the power can go out for many reasons, and at any time. To protect yourself from the possible loss of animals in your aquarium during this type of emergency situation, you can keep some basic but vital pieces of aquarium equipment running by taking an old UPS (Uninterrupted Power Supply) and a 12 volt (Marine Deep Cycle preferred) battery to put together your own power back-up unit. This simple project only takes a few dollars to make and little time to assemble.

Difficulty: Easy

Time Required: 15 Minutes
Here's How:

1. Locate an old or used UPS that is functioning properly. These are commonly used by people with computers to protect their systems in case of power interruptions, and to filter power dips and spikes. When the battery wears out, most people throw their UPS away because it is obsolete and they cannot obtain a replacement battery, or they may just want to get a more powerful unit.

2. Check the voltage of the UPS battery to make sure that it is a 12 volt battery.

3. Check the wattage of the equipment that you want to keep running in the case of a power outage. Check the maximum wattage output rating of the UPS. This is the the most wattage that the UPS will handle in the case of a power outage. The UPS will not handle any more wattage than it is rated for.

4. Purchase a 12 volt battery. You can usually find a fairly good quality battery on sale for under $50 which will serve your purposes. Generally speaking, the higher the "Cold Cranking Amps" an automotive battery is rated at, the better the battery will serve you. Automotive batteries will work well for fairly low wattage demands and short periods of usage, however a marine quality deep cycle battery will work best for higher wattages and longer periods of time.

5. Check the connector type on the UPS battery. Most of these connectors are the spade (flat) female type connectors. Purchase 2 connectors which will fit in the connectors from the UPS. If possible, take the old UPS battery with you when you purchase the connectors. This way, you can make sure that you are buying the right connectors.

6. Purchase 2 metal hose clamps. These will be used to clamp the wires from the UPS to the battery terminals. If the battery you bought has the screw type terminals, you won't need these clamps.

7. Cut 2 pieces of 12 gauge wire of sufficient length to go from the battery to the UPS.

8. Measure how much bare wire will be needed for the UPS connector and battery terminals and strip the insulation from the ends of the 2 wires to fit.

9. Attach the ends of each wire to each of the wire connectors.

10. Clamp the other ends of the wires to each of the battery terminals. If your 12 volt battery has the screw type terminals, wrap the stripped wire ends around the screws and tighten the screws.

11. Attach the battery terminal wires to the UPS battery wires. Black is negative, red is positive.

12. Plug the UPS cord into your 110 volt house outlet.

13. Turn the UPS on. The UPS should indicate that it is running normally.

14. Plug a lamp into the UPS "Power Protected" outlet. The light should come on.

15. Unplug the UPS from the wall outlet. The lamp should stay on. Most UPS units will emit a beep or give some other indication that it is running on the battery and not the house current.


1. Check the UPS wiring diagram to make sure that you are connecting the UPS battery wires to the battery correctly.
2. A wire stripping tool, such as can be purchased at an auto parts store, works very well for stripping the wire ends and clinching the connectors.
3. If you have multiple lights on your tank, you can stretch the battery life by plugging only one light and other essential equipment into the "Power Protected" outlet of the UPS. Plug the other light and all other nonessential equipment into the unprotected outlet.
4. If you have only one protected outlet in your UPS, use a power strip to attach more equipment.
5. Once your UPS is set up with all of the equipment on and running through it, unplug the UPS from the wall outlet to make sure that everything keeps running as you planned.

What You Need:

* 12 volt battery (Marine Deep Cycle battery is preferred)
* 2 wire connectors
* 12 gauge wire
* Wire stripping and connector clinching tool. (Optional)

Article source


AC Members
Feb 27, 2007
You can get a replacement battery for less than you would spend on a deep cycle marine battery. Do not use a starting battery as you will kill it quickly by deep discharging it.

However runtime from a UPS operating pumps and heaters is going to be low. You need to add up the wattage to find a UPS rated for what you want. A 1000VA UPS only handles approx 600 watts. Thats not much if you have a 200 watt heater and pump running. Granted the heater is not running the entire time.

Using a bigger battery like stated above will give you a longer runtime, at the cost of a longer recharge cycle, and more heat buildup. Most of these units are not meant for that kind of duty cycle. They were designed to protect the machine during sags and provide the computer with power until it can be safely shutdown or a generator can be started and power transfered over.

Heres a quote from another forum

"Lots of UPSes (namely, APC BackUPS models) don't use "heat sinks" inside for their main switching transistors, they use "heat slugs".. basically large blocks or thick sheets of metal bolted to the transistors, which are designed to absorb (not dissipate) the heat from the transistors by heating up slowly.

The "slugs" are large enough so that the transistors won't overheat because the battery designed into the UPS will go dead first. But this obviously won't happen if you use a big battery, and the UPS will probably overheat and die."

An alternative, although not automatic, would be to buy a deep cycle marine battery, an inverter, and a battery charger. Inverters are meant to handle their load rating for extended periods of time and have built in fans to cool the unit. Hook up the charger and inverter permanently to the battery. It will trickle charge when the power is on, when the power fails just switch on the inverter and plug the tank into it.

Look to spend around 130-180 dollars for the above setup. You can get a Xantrex 700 watt inverter for 50 dollars, a charger for around 30, and a battery for 50-100. I have a couple Xantrex inverter's an they haven't let me down yet. One is in my Jeep which I take off roading on the weekend. Its subjected to dust, dirt, vibrations, banging, etc and it never skips a beat. Also a plus is that the fan only runs when needed, instead of running the entire time the inverter is switched on.