SAVE Your PRINT When the Power Goes Out! Longterm Battery Backup

Introduction: SAVE Your PRINT When the Power Goes Out! Longterm Battery Backup

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Have you ever been 18 hours into a 20 hour print and had your power go off? Frustrating and wasteful, isn't it? What if I told you I had a way to keep your printer up and running for a couple hours, or longer? One of the drawbacks to conventional battery backups is they simply do not have the storage capacity needed to handle the initial surge of power necessary to keep the printer from fading when the main power supply cuts out. A car battery size backup like my design will power a medium sized 3D printer for around 4 hours(my Taz stays running for just under 4 hours, but a smaller desktop printer could stay running for much longer). This is especially useful if you live in an area, like mine where people seem to be fond of cutting tree limbs over your cities power lines. Sometimes that four hours is just enough time to finish that 20 hour print you started yesterday. More often than not it allows your printer to stay up and running even through brief brown outs that usually takes your printer offline. With some relatively cheap, easy to obtain pieces, you can save yourself a ton of time and money in failed prints.

Step 1: Supplies and Tools


  • Battery Storage Box to fit the battery you have
  • Battery - car, truck, other large vehicle battery
  • Battery Backup
  • Battery Cables
  • Pure Baking Soda
  • Two Splicer Reducers - large enough to fit the battery cables
  • Red and Green Zip Ties
  • Electrical Tape


  • Drill
  • Bit Set
  • Crescent Wrench
  • Pliers
  • Heavy-Duty Wire Cutters
  • Wire Cutters or Scissors
  • Lashing Strap
  • Utility Knife
  • Soldering Iron - Optional

Step 2: Step 1: Prepping the Battery Backup

Remove the small inner battery from the battery backup and unscrew the cover. Drill two smaller holes through the cover where shown, these will be for the battery backup's cables to come thru the cover. Then drill two larger holes, equal to the size of battery cables you have. It's better to start with a smaller bit and gradually increase the size of the hole to prevent the plastic cover from cracking.

Step 3: Step 2: Prepping the Battery Backup Cont.

In order to join the wiring that was in place for the small battery with our new larger battery, you need to cut the plugs off of the wires, like shown.

Optional: battery backups have this obnoxious little screeching alarm that goes off every time your power goes off, and so far I haven't found a way to turn it off for longer than about 10 minutes by pushing any of the buttons on the outside. However, you can unsolder this little black canister from the board inside the battery backup for sweet, sweet relief from a shrill reminder your power is off.

Step 4: Step 3: Marking the Wiring

One of the most important things working with any type of wiring is making sure you keep all of the wires marked correctly. I like to mark with the traditional green and red, green for ground, red for hot. Insert the ends of the battery cables through the holes drilled in the battery backup cover. You can use the zip ties to mark inside and outside of the cover to make sure you connect the correct wires to each other.

Step 5: Step 4: Connectors

With the thinner wires you can use conventional wire strippers, but with the battery cables, I found it was easier to use a utility knife to cut through the outer casing. Twist the ends of the wiring together and insert both the hot wires into each end of the connector, same with the ground. Once you have the connectors tightened, it's important to wrap each connected and any exposed wire with tape so there isn't any shorting.

Step 6: Step 5: Battery Storage and Final Assembly

I didn't get a picture of this step, but before you put the battery down in the battery storage case, you want to put some baking soda down in the bottom, so in case the battery would ever start leaking, the baking soda will help contain any adverse reaction.

My dad, who taught me everything I know about working on cars, always told me to connect the ground side first so you only have one point to worry about(the hot side) instead of two points. Make sure the cables are tightened down and secure. Once you have the cover closed up, set the battery backup on top the case and fasten both together with the lashing strap. You can use the left over part of the strap to secure any extra cable length.

Your battery backup will take a little while to charge the car battery back to full. Once it's fully charged your battery backup is ready to roll.



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    11 Discussions

    Great I-able, But one fair warning, from someone who has built similar, as a portable supply for running a computer. Make sure the UPS can handle the draw, and One suggestion, making additional ventilation and adding a cooling fan to the UPS. This is, internally, an inverter that kicks in when the power goes out, and an oscillator is driving power transistors. The higher the load, the hotter the power transistors will get! I had a 300W UPS catch-fire (Literally melted the case, and suddenly flames!).. Even a 1500W strains under heavy draw. a STRONG cooling fan keeps mine from doing another melt-down. (quiet fans are NOT enough! The faster the CFM, the better. Noise should be irrelevant!)

    1 reply

    Agreed, I did something similar to this project using two of the batteries it's designed for, and while it will happily keep my router alive by itself for 8 hours, if the fan dies (or is blocked) it can't run very long. I have a 120mm computer fan wired parallel into the inverter circuit so it comes on as soon as the switchover happens.

    I have thought about doing this in the past, now I am inspired to move forward with it. Thanks.

    Does the UPS model matter? I notice you're using an APC 500. Would a smaller one function the same?

    1 reply

    You need to go bigger, most just to be sure the internal components are heavy-duty enough to handle the charge. Additionally the smaller units have a built in thermal shut off that keeps them from running for very long. The 500 is mostly just cause that's what my local store carries, but I would recommend bigger. Thanks for commenting, I never thought about this!

    This is a must with this weather.


    What are the pigtails with wire connectors on the outside of the battery box??

    2 replies

    They're for connecting additional power to lights, charging, etc.. I've seen the cables used on Riding lawnmowers, and farm tractors. (though, odd seeing one on the "-" side?) the main (larger) usually goes to the starter, and the smaller to everything else, Including the ignition/starter switch..

    I'm not exactly sure what they are for, but I left them on to be able to check the battery charge even when the storage box cover is closed. You can just stick a multimeter in the plugs and easily check whether the battery is holding charge.

    Great instructable. This could be used for so much more than 3d printers too. However, I think a deep cycle battery would perform a bit better than a car battery in this application. You'd get longer run times and more charge cycles too.

    1 reply

    Thanks for the comment, the battery I used is actually a deep cycle car battery. I do agree that you'd get a much longer lifespan from a deep cycle, but they are more expensive. A conventional car battery will work just fine for most things it will have a slightly shorter charge span depending on the type of draw, but it will likely be just fine for most applications. I actually have several of these scattered throughout my house. One keeps my security cameras(dvr & 16 cameras) up and running for nearly 40 hours. Thanks for the comment!