Power Bank From Old UPS Batteries

A recent, several day long power failure had me rigging up lights and scrounging for batteries. Sure, I have a good supply of headlamps, camping lanterns and regular flashlights, but these are not great for extended use. Since this happened in January, in Oregon, it got dark around 4pm, and we needed useful light for working, cooking and household chores. I had some sealed lead acid (SLA) batteries on the shelf, left over from some computer UPS that had died. I found some 12-volt LED lights among my project supplies and managed to assemble some serviceable lights. For phones and tablets I have some small power banks I use for traveling and they lasted a few hours. Again, among my project supplies I found some parts that allowed me to get 5 volts from the 12-volt batteries and I recharged the power banks from that. Some of the "fun" involved making connections without the aid of a soldering iron. Alligator clips and some creative crimping managed to hold things together. We survived with sanity intact. We had lights, our cell phones were charged, a backup cell phone provided a Wi-Fi hotspot, and the battery pulled from one of the cars kept a laptop running. Once we had power back, I resolved to make a power bank using the SLA batteries, and be better prepared for the next power failure.

Sources

Here are some sources for the parts I used:

Sealed Lead Acid (SLA) batteries - BatteriesPlus

SLA Battery Charger - .75 Amp - BatteriesPlus

16 AWG hookup wire, spade terminals, automotive fuses - local car parts store

Fukuai 10Ah (5.6 actual) LiFePO4 Battery - Amazon

Eco-Worthy 10Ah (9.5 actual) LiFePO4 battery - Amazon

LiFePO4 Battery Charger - 4 Amp - Amazon

5.5 x 2.5mm charging socket - Amazon This matches one of the charging cables that come with the LiFePO4 charger.

For battery testing I use the Atorch DL24 tester from AliExpress YouTube is the best source for learning how to use it. One of many videos available is here.

SPDT switch - AliExpress

Anderson Power Pole style connectors - Amazon Most of these on Amazon are clones. If you want the real deal, order from here.

Battery Protection Module - Amazon I set the cutoff at 11.8 volts and turn back on at 12.2 volts

LED Lamp voltage and current regulator - Amazon For the recycled lamps I set these to 3.7 volts and 1.5 amps

Automotive USB Plug - Amazon These come with integrated volt meter display that I use as a power-on indicator, and it gives me some idea of remaining battery capacity.

COB Led - Amazon

Files for the 3D-printed parts are available upon request.

There are lots of power banks and solar generators available of-the-shelf. However, I wanted to use my existing batteries and limit myself to using as many items I have on hand as possible. A lifetime of tinkering results in a significant accumulation of "stuff" and my current project goals focus on minimizing buying new stuff.

The basic component for this project is the battery. How can I make the best use of it? It's not big enough to power an inverter, so I'm going to be limited to 12 volts and below. To be useful for the next power failure, or other off-grid experience, this power bank needs to provide for lights and phone charging.

In addition to the battery I would need:

• An on/off switch
• Wiring and connectors
• Some way to connect phones and lights
• Some way to make a package out of it, a sort of battery "cap"

The switch, wiring and connectors were easy - I have plenty of those.

For most of my 12-volt and automotive electronics I use 15/30/45 amp Anderson Power Pole connectors so I use those for connecting to any lamps. The battery cap has two sets of plugs.

For the USB power outputs an automotive USB charging adapter works.

I do want to avoid running my battery down too much and thereby ruining it, so some sort of limiter, or battery management system (BMS) is included.

A 3D-printed battery cap provides the packaging. The printed parts consist of the cap, with necessary openings, handle, and a universal lamp mount. Well, universal for me, since it's based on an articulating lamp design that has provided me with many lamps for workbenches, power tools, and other uses.

A side note about my favorite glues... I use PLA for most of my 3D printing, and it tends to have a slightly oily finish that generally doesn't glue well. I discovered that if you "roughen" the surfaces to be glued with acetone, most cyanoacrylate adhesives will work. The Gorilla Glue version is good for shock resistance and space filling. I use it to attach the handles and lamp mount. The E6000, also sold as "Household Goop" is a type of rubber cement that sticks to almost everything. Again, I prepare the PLA surfaces with acetone. One of the features of the E6000 is that while it provides a good bond, it is still removable. I use the E6000 glue to hold circuit boards in place and around the switch and USB adapter.

The second picture shows a simplified connection diagram. It describes two options, one with BMS and one without. The sealed lead acid batteries I started with do not come with integrated charge and discharge control circuitry so that needs to be included. Later, I built a version for LiFePO4 lithium batteries, and they come with a BMS built in, so I do not need to include one in the caps I make for them.

I set the cut-off voltage for the SLA BMS at 11.8 volts. I researched this a bit and found recommendations that ranged from 11 volts to 12 volts. The majority were closer to 12 volts, so I settled on 11.8.

The third picture shows all the parts wired together, and then mounted in the cap, along with a 7.5 amp in-line fuse. The fuse is a standard automotive fuse and I use two 0.25-inch female spade terminals to connect it. The usual in-line fuse holders are too big to fit inside the battery cap. And, finally, everything is assembled and ready to mount onto the battery with some hook-and-loop straps.

My initial lamps consisted of some recycled LED lamps from a rechargeable lantern whose recharging circuitry got fried. Fortunately, it was put together with screws and therefore easy to dismantle. 3D-printed enclosures contain a step-down voltage and current limiting circuit board, plug, and switch. These lamps are OK, but the beams are too narrow for general illumination. I made another lamp from automotive COB LED strips, and mounted it with some articulating lamp parts.

One thing I discovered is that by aiming the bright LED lamps at the ceiling, it diffuses the light and can provide fairly good general lighting for use in the kitchen, bathroom, and at my desk. The COB LED provides diffuse light works best sitting on a high shelf or atop the kitchen cabinets.

When I took apart the original burnt-out lantern, I discovered it was powered by a pair of 18650 lithium cells. My new lights, using the same lamps, are now powered by much larger batteries, and the whole assembly is only a bit larger, if considerably heavier. The handle makes them convenient to use as lanterns, and the tilt-able lamps are an additional advantage over the original lantern.

Battery Straps

The first battery cap I made used a single hook-and-loop strap for fastening it to the battery. This is strong enough but the strap in the middle of the battery results in it rocking back and forth. I adjusted the design to accommodate two straps. You can see the two versions in the picture at the beginning of the article.

Recharging

Initially, I assumed that during a power failure I would use these until the battery was used up and then switch out batteries and continue. After power was restored, I would recharge the batteries and set them on the shelf. Then, I realized that I was using these new lamps a lot, particularly the one with the COB LED! The heavy, yet portable base and bright light was great at illuminating work spaces, such as under a sink or in the trunk of a car. The articulating arm let me direct the light as needed. I will be using this light a lot and don't want to be dismantling it every time I need to charge it. Therefore, I integrated a charging port and changed the switch so that in one position it would connect the battery to the charging port, and in the other connect it to the lamp and USB electronics.

Battery Capacity

A disappointment in working with these batteries is in the capacity rating. I use name-brand, supposedly high-quality, AGM lead-acid batteries. The labeled ratings are for the total charge, however they are only supposed to be discharged to 50%, essentially halving the useful capacity. Using a battery tester, I got 3.6Ah from my 7Ah-rated Duracell, provided I drew less than 1 amp. Something similar happened with the 50Ah AGM car battery I was using to run the laptop. (I have a car adapter for running laptops.) Later testing of the battery revealed that it could only provide 25 useful Ah. This was all new information to me.

That lead me to trying a LiFePO4 battery. They are supposed to have higher capacity, be lighter and allow for many more charge/discharge cycles. I bought a medium-priced 10Ah-rated one on Amazon and tried it out. Supposedly they can be discharged to 10% of their rated capacity without harm. Imagine my disappointment when the built-in BMS quit at 5.6Ah.

Later I was able to test a similarly-priced, but different brand of LiFePO4 battery and it came in at 9.5Ah. And that was at the 11.8-volt shutoff I set on the battery tester. Some LiFePO4 BMS actually allow drawing the battery down to 10 volts. I didn't test for that. The key bit of information here is the varying quality of batteries.

Of course, like any good tinkerer, I took the batteries apart to see what might explain the difference. The first picture shows the inside of the 5.6Ah Fukuai brand. It consists of 20 18650-sized cells. From my use of these cells in flashlights I know there is a wide range in quality and capacity in these cells.

The 9.5Ah Eco-Worthy brand is made up of 8 what look like 26650-size cells. I noticed there is even a temperature sensor connected to the BMS. I still need to test if this is a high or low temperature cutoff sensor. (LiFePO4 batteries shouldn't be charged if they are below freezing.)

Hot Lamps

The COB LED lights are designed for automotive 12-volt systems and do not include a voltage regulator, unlike my recycled lamps. When I used the COB LEDs with a freshly charged LiFePO4 battery they got warm enough to warp the 3D-printed parts that used PLA. I made two adjustments. I remade the plastic parts with ABS, which has a higher softening temperature, and I inserted a diode into the connecting cable to get a 1-volt voltage drop in the circuit. Most diodes have a .7 volt drop but I found one high-current version that had a 1-volt drop. The voltage drop resulted in a cooler lamp. I use the COB LED with the lithium battery which has a very flat discharge curve. There is little noticeable dimming of the light as the battery drains.

What I thought would be a simple project turned into a significant learning experience. I never thought much about the care and feeding of lead acid and lithium batteries. This project lead me to do a lot of reading and experimenting. I did meet my original goal of making power banks from my excess SLA batteries. And, I now look forward to working more with lithium batteries, particularly the LiFePO4 types. (These are the ones that don't burst into flames if you puncture them!).

Have fun making - I know I will.

- Jürgen