TC Projects: Lead-Acid Battery Backup

May 01, 2020

For the last decade, my mom has actually worked from home. And about a year and a half ago, she and my dad moved to the country, surrounded by farmland about a two-hour drive from Chicago. Her most recent work setup includes a RAP, which essentially creates a dedicated, wired VPN connection over the Internet, so as far as her computer and desk phone know, she's still in an office in Chicago. He occasionally travels to the office, but for the most part he works here. Now, in the last few months, for some reason the electrical service at her house has become a little unpredictable.

They have never been without power for more than a day, and usually less than 8 hours, but in the last month there have been two power outages. And they have happened during her work hours. Which sucks. Actually, it really sucks, because depending on the circumstances of the day, you might have to get in the car and drive two hours to work in the blink of an eye. So today I'm going to fix that for her. Now before she suggests it, they have a portable generator. But the generator lives in a shed and takes time to install; Plus, it's cumbersome and too heavy for my mom to move alone.

More Interesting Facts About,

tc projects lead acid battery backup...

And anyway, her generator produces really dirty and noisy power output, which some electronic devices really don't like. Since all of this equipment belongs to her company, she is very cautious about plugging it into the generator. And I don't blame her. We know from experience with the generator and a small uninterruptible power supply that... well, the UPS did not find the generator output to be safe enough and would not pass its power. And after that it never worked properly. So what we're going to do is use a deep cycle

lead

acid

battery

as a temporary power source. A pure sine wave inverter on

battery

will produce a clean output that hopefully won't bother your setup.

And to recharge the battery, we will simply use an automatic car battery charger, since after all, a 12V

lead

acid

battery is practically universal in the way it is charged. But that doesn't mean all lead-acid batteries are the same; no, they are not. I will explain it shortly. I want to add here that this process was done keeping convenience in mind. My mom decided to buy this inverter on Amazon and deliver it to her overnight, and that day we would pick up a battery at Menards (she had to visit them). The inverter is excellent, no qualms about that, but the battery is not ideal.

This is a deep cycle marine battery. As far as batteries you can buy at a hardware store, this is the closest to the best type. But it probably won't last too many charge cycles. Here, let's explain a little about the chemistry of lead-acid batteries. Wait, if you're new to the channel and just looking for how to do this, go ahead and jump to this moment. On this channel I like to explain a lot about how things work and I totally understand if that's not why you're here. Lead-acid batteries are incredibly simple. They are the oldest type of rechargeable battery, invented in 1859 by French physicist Gaston Plante.

Its construction is quite basic: two plates, one of lead and one of lead dioxide, are immersed in a bath of sulfuric acid that serves as an electrolyte. When fully charged, the acidity of the electrolyte solution is very high, so there are many positively charged hydrogen ions floating around, as well as negatively charged sulfate ions. Now I won't go into the chemical details (I'll save that for another video), but the battery's energy comes primarily from the acid. Sulfate ions will react with the negative and positive plates to form lead sulfate, and hydrogen ions will react on the positive plate with oxygen atoms to form water.

The more concentrated the acid is, the more charged the battery will be. On the contrary, the more lead sulfate appears on the plates, the more discharged the battery becomes. And this is where we get into the nitty-gritty of battery types. There are two basic categories of lead-acid batteries; deep cycle and SLI which stands for Starting, Lighting and Ignition. Essentially, an SLI battery is a car battery, and these are absolutely terrible at deep cycling. If you simply buy a car battery for

backup

power, you'll be lucky if it lasts a dozen cycles before dying. And that's because of how they are designed and built.

Car batteries must be able to produce a huge surge of current for the starter motor. To get more current, you need a large surface area on the battery plates. And with limited space, this surface is created by making the dishes small, numerous and somewhat sponge-like. These spongy plates are great for producing tons of current, but they limit the battery's ability to discharge and recharge. As the battery discharges, the plates not only become coated with lead sulfate. They are converted to lead sulfate, just as a piece of rusty metal is not covered in rust: the metal has oxidized.

And lead sulfate is not a good conductor. If you let a car battery discharge too much, the spongy plates can become clogged with lead sulfate. The more this happens, the less current can pass and then it cannot be recharged to reform the lead and lead oxide. Another common occurrence is called shedding. Again, due to the spongy nature of the plates, expansion and contraction as the lead plate is converted to lead sulfate and converted back to lead by recharging can cause pieces of the plate to fall off, which It limits not only the current passing capacity but also the capacity. .

But normally, a car battery will stay almost fully charged all the time. The starter will only run for a few seconds and then once the engine is running the alternator will quickly replenish that charge. Typically, the battery is barely cycled and very little lead sulfate forms anywhere in the battery. Therefore, it is typical for a car battery to last 5 years or more, but may only survive a few episodes if the headlights are left on. Deep cycle batteries, on the other hand, have large, thick, solid plates. With limited surface area, they cannot produce monstrous surge currents, but they can tolerate much larger lead sulfate buildup without damaging the battery.

They are less susceptible to shedding due to the non-porous nature of their plates and are generally more specialized and slightly more expensive. Due to their inability to create surge currents, they are not used as a car battery, but for things like golf carts,

backup

battery solutions, and some of the first electric cars used them as their main source of propulsion power. For this project, we used a compromise battery. There is a subset of batteries called marine batteries, and within that subset there is a subset called marine deep cycle. That's what this is. These batteries have thicker, stronger plates than those in a regular car, but can still provide a generous boost in current.

I chose this battery because it was A) readily available and B) cheap. A whopping $89, however, a $7 base charge was added because I didn't have a used battery to return. Speaking of which, did you know that lead-acid batteries are among the most recycled things in the world? Everything here can be easily recycled and purified, making it impossible to recover only the paper separators between plates. Because of that core charging, people are incentivized not to throw their batteries into landfills, and battery manufacturers have a steady supply of used batteries to condense them into their constituent parts and make new batteries again.

This battery was almost certainly once many other batteries, and the materials jumped from car to car and ship to ship. Look at that, society comes together to solve a problem and no one complains about it. Great job. So first we want to determine what our needs are. And I was making a budget. This setup uses a laptop in a docking station and two 20-inch monitors, but there is also a power supply for the RAP, your phone, the Google WiFi router (although it could be turned off if necessary), and the actual DSL modem . So while the computer and monitor are probably the biggest part of everything, there are a lot of small loads that can add up.

I basically assumed 100 watts would be enough, and let's go with that. Annoyingly, this type of battery is usually not labeled with a useful figure like amp-hours or watt-hours. Instead, it has a stat called reserve capacity. Now I just chose the largest battery they had from this selection and I still didn't know what RC meant. So after some googling I discovered that the reserve capacity of a battery is the time in minutes that it can sustain a discharge rate of 25 amps before dropping to 10.5 volts, which is pretty dead. The reserve capacity of this battery is 170, so 25 amps for 170 minutes is about 70 amp hours, and since this is a 12 volt battery, that means it has a capacity of about 850 watt hours.

This was good, as I had estimated that your setup would use around 100 watts, and should barely get you through an 8-hour day. But another fun feature of lead-acid battery chemistry is that its capacity will increase the slower you discharge it. So while this battery may only have 850 watt hours at a 300 watt load, reducing that load by a third could increase the capacity into the kilowatt hour range. If we're really lucky, with a slow drain, we could get 1.1 or 1.2 kilowatt hours out of this thing. So, we have a battery. But now we need a way to convert the 12V DC to the 120V AC that your material uses.

That's what investors are for! These devices will step up the voltage and continuously reverse the phase up and down to create A/C current from a DC source. If you use electronics, you will definitely want a pure sine wave inverter. This will replicate the sine wave pattern as seen in the actual A/C power. Cheaper inverters will simply spike up and down, which many modern power supplies can tolerate, but probably aren't good for everything. When choosing an investor we went extraordinarily overboard. I basically checked my mom's reviews on Amazon, and while there was a much cheaper inverter that would have worked, it had some mediocre reviews that indicated it could overheat, so we went with this huge beast.

You never know, it might come in handy one day. And we also need a way to charge this battery. For this we will use an automatic car battery charger that my parents already had. This is a relatively slow charger, only putting out 6 amps, but that's 72 watts and will be enough to recharge this empty battery in about 16 hours. If there was a prolonged power outage, the charger could run from the generator overnight. But having a slow charger is probably a good thing. Look, you have to worry about hydrogen production when charging the battery. Normally very little hydrogen is produced;

In fact, ideally, almost nothing would be produced and most of the hydrogen would come from an overcharged battery, which this automatic charger should avoid. But even if the battery were overcharged, the amount of hydrogen generated depends directly on the amount of current input into the battery. I ran the numbers and determined that for the hydrogen to reach dangerous levels in this room with 6 amps of charging current, it would take about a month of overcharging. Clearly, that's not a concern. However, I changed course for safety: I was planning to put the battery in a small cart, but its partially closed top could trap hydrogen and potentially create a small explosion risk.

So I got to work getting things ready. This battery has threaded studs for mounting cables in addition to the standard terminals. We'll use the studs with the wires supplied by the inverter, but I added a large fuse for short circuit protection. In theory, the inverter could draw 125 amps continuously (although the battery couldn't sustain that for long), so I looked for a fuse above that rating. Now, I only add this to protect against a short circuit. The inverter has its own built-in protections, but in case something metal gets stuck behind the inverter, or some other stupid thing causes a short circuit, those 600+ cranking amps need something to stop them.

But then I added this little guy. This is a battery level monitor and voltage indicator. This is really cool, it can support different voltages and battery chemistries, but it comes pre-configured for a 12V lead-acid battery. It now displays that percentage based on the battery voltage reading. This will give you a relatively good indication of theload, but it means that if there is a load on the battery, causing its voltage to drop, the reading also drops. Additionally, every time the battery is charged, the reading will jump to 100%, as the charger gives the battery a higher voltage during charging.

However, it will still be a useful indicator, as after its initial drop, that percentage will steadily decrease as it discharges. Best of all, pressing the button turns on the backlight and pressing it again will switch to an actual voltage reading. The specs on this thing indicate that it draws 112 microamps when idle. This is practically insignificant and may cause the battery to lose 1% charge in a few months. You will also notice that this is connected directly to the battery. It would be wise to fuse this as well, however it's quite likely that there is a fuse somewhere on your circuit board (even if it's just a resistor or something that's "supposed" to not be a fuse) and even if there isn't First, these thin wires would melt quickly in a very short scenario.

Therefore, I am not worried. Now, this setup is practically finished. After running the charger long enough for it to switch to float charging mode, I charged the battery and inverter to its workstation. Finally I also used a switch to determine the actual consumption of your workstation. Hopefully it will be 100 watts or less. Surprisingly, everything here only consumes between 52 and 55 watts! It occasionally reaches 70 watts, but even if we take that as the worst figure (plus, this will account for 10 to 15% loss in the inverter conversion), this battery will now easily spend 12 hours of backup time, and with an average of 4 and a half to 5 amps drawn from the battery, it may be even more.

This extra capacity also means that the battery won't cycle as hard in a day, prolonging its life. Using this is really simple. Everything is already connected to a small uninterruptible power supply, but it's really small and can realistically only provide 20 minutes of power, maybe an hour if we're really lucky. However, this means that in the event of a power outage, everything will work perfectly. If the power goes out, everything in your settings will stay on. To switch to the large backup supply, all you need to do is unplug the UPS power cord from the wall and plug it into one of the inverter's power outlets.

After turning on the inverter, the UPS will say "hey, that power seems fine" and will return to what it thinks is normal AC power. At this point, the entire setup runs solely on the large battery. This should provide at least a full working day of backup power, and possibly 2 if the slow drain increases the battery capacity up to 1.2 kilowatt hours. When the power comes back on, simply turn off the inverter. The UPS will work again briefly, but after plugging it into the wall, it will once again receive real AC power. Then just grab your car battery charger, plug it in, and after an overnight charge, your battery will be full again.

If there is a prolonged power outage, the battery charger could, in theory, become an indirect power source for the inverter, using the battery itself as a large buffer or ballast. The dirty power coming from the generator will be converted to DC power, and when the inverter changes it back to AC, it will be clean as a whistle. This charger might even be enough, since 6 amps equals 72 watts. It would be pretty close though. A larger battery charger may be necessary for this purpose. But using this with a generator isn't really the point. If that were the point, then a smarter investment would be a generator with a built-in inverter, which can safely power electronic devices.

Rather, the goal of this setup is to provide immediate, easy, and convenient backup power that will last at least a day. For most power outages, this battery will be all you'll need to get my mom through them. One last thing before we sign off: this brass terminal on the inverter must be grounded. Right now, when running on battery power, none of these pieces of equipment are grounded. This is not necessarily a terribly dangerous scenario, but to be safe a ground wire should be connected here. We could connect a wire to the ground wire inside this electrical box, or we could use an adapter like this one.

Whichever you choose, make sure it has a good ground connection. Thanks for watching, I hope you enjoyed the video! Lead-acid battery technology may be very old, but it has some compelling applications like this. But remember, this battery will not last many cycles. It's not necessary as it will probably only be discharged a few times a year, but if you want to regularly charge and discharge a lead-acid battery to store energy, you should choose a better battery. Golf cart batteries, which are typically 6 volts and therefore require a pair to be connected in series to get 12 V, are a good start.

The solar energy community seems to favor Trojan batteries for their longevity. I'm planning to make some videos looking at the costs and lifespan of deep-cycle lead-acid batteries versus lithium-ion for stationary energy storage, because the winner may be less obvious than it seems. But for now, thanks to everyone who supports this channel on Patreon, especially the great people who have been scrolling through your screen. With the incredible support of people like you, I've been able to turn Technology Connections from an odd hobby to my full-time job. And there are great