Everything I Don’t Know About Lithium Batteries
And a few things I do.
Lithium batteries are everywhere and you probably have some. I know I do. Seems like, though, the more I learn about them, the more I know I need to learn. Isn’t that usually the case? I have an archaeology project like that, right now.
We know they are lightweight and pack a punch for their size. They are way better than the old NiCads they used to put in tools. From the news we learn that some kinds, like the ones in hoverboards, e-cigs and Teslas can seemingly spontaneously combust. Also, we know that our portable power tools don’t slow down, they just quit when the battery gets low.
Understand that “Lithium” is not an all encompassing term. There are many variants, but we will break them down into the common Li, or Lithium Ion variety or the LFP/LiFePo Lithium Iron Phosphate variety. The quick take is the Li has a higher energey density, but they can burn. LFP is slightly less dense, but they don’t burn. I don’t know about you, but there’s a factor there that might influence my choice.
There has been a lot of bad press about flaming Teslas and, just this week, a flaming laptop that caused an airliner to make a precautionary landing. Exciting times! There are ways to prevent this and some manufactureres have gone overboard. I recently bought a Greenworks 48v electric chainsaw that uses two 24v batteries. It is a nice saw for light duty, but it is so aggravating to charge. The batteries get hot when actually cutting a tree. At some point they will claim to be discharged when they are simply hot. Then, if you put them in the charger it will refuse to charge them. You may come back later to collect the recharged batteries, only to learn they are taking the afternoon off. Even when they do charge, they go very slowly at the task. It is pretty clear that Greenworks does not want to get sued over batteries burning down the house.
While Greenworks has gone overboard with caution, some aftermarket batteries and cheap imports take no precautions at all. Canon, for example, warns you to use their $80 camera battery because the ebay $10 battery might burn your $5000 camera. Okay, that’s certainly something to consider.
Most packaged batteries, as in tools or laptops, have a Battery Management System or BMS. Some are tiny enough to fit inside a camera battery and some are pretty substantial. What the BMS does is to limit the charge or discharge current to safe levels, keep the temperature under control and prevent over or under charging. Some of this functionality can be had in a solar power system by tuning up the specs on the charge controller and inverter. My thoughts are for having a dedicated BMS in place. Not all of my charge controllers are state of the art.
Lithium batteries of all flavors are lighter than lead acid and more energy dense. They also have their peculiarities that can be a real advantage in a solar power system, but this comes at a cost. Set everything up right and the batteries might outlast you, especially if you are my age or older.
I read in the boating forums about guys who have had a lithium or lead acid battery system in place for years and others who have to replace the batteries every year. Boats you can live on are essentially off grid homes and most seem to include solar, these days. Clearly, some of these skippers have done something right and some are oft gang agley, as Robert Burns might say.
Lead acid batteries should not be drained below the halfway mark to maintain a reasonable life. I have two banks of lead batteries on my main system. The sealed telecom batteries are getting some age on them now, but are holding up well. The forklift flooded batteries are from 2015-2016, I think, and are also doing well, though they are horribly ugly with their rusty containers. I will switch to the grid or exercise the generator if there is a danger of dropping below 50% during a cloudy spell or if the batteries need freshening with an equalization and desulphation charge. Seems unfair to own all those amp-hours, but can’t use them for fear of damaging the batteries. If you habitually undercharge lead batteries they will get gunked up internally and lose capacity.
This is where lithium really shines in home power. You are best off if you don’t top up that last 10% of battery capacity and you can run them down to 10-20% without hurting them. With care, you can get 6000 or more cycles out of them, which translates to a lot of years. Best of all, you never really have to fully charge them. It’s like if you are one of those people who just buy $20 worth of gas at a time (It was a dollar when I was a kid) instead of a fill up. The car’s fine as long as there is SOME gas in it, right? That is a huge advantage on a day like today.
It rained, yeesterday, and I flipped to grid while the wife ran the dryer. It is raining today and the HVAC is switched to the wood furnace to avoid the load of the heat pump. I’m not charging the electric farm vehicles, either, but then I am not driving around in the rain. None of these would be a concern if I could safely use 80% of the 100+ kilowatt-hours I can stash away.
Though lithium batteries are more expensive for a given size, the combination of greater capacity and longer life are beginning to make them look like a good deal.
Now, let me tell you about some concerns. What happens when the BMS decides it is time to rest?
My handy Home Depot impact driver just suddenly quits when it is done. No problem. I keep a spare battery in the tool kit and those batteries charge quickly. What if the BMS on your home system says good night, leaving you sitting in the dark? Isn’t keeping the lights on one of the reasons you went solar? I wonder about the BMS characteristics of the electric airplane that is allegedly coming to my place. It has been on order for two years, but so far battery life has not been an issue. The only large-ish lithium battery at my house is in the ZERO FX electric motorcycle in my motorpool. It clearly goes further when driven slowly, but what’s the fun in that? I have made a couple of forays that have really tested the range, though, once leaving me to wonder if it was going to leave me pushing it the last mile home. In that case, I was pleased to see that it slowed down and let me make it home. I don’t know if it was the programming of the BMS or a lack of BMS that let me crawl back to the shed.
I seem to have an upcoming need for a new vehicle bank. One of the farm vehicles is losing range. I could replace the bank with lithium, or do my usual thing of handing down the batteries from Sun King, the solar launch, and then replacing the boat batteries with lithium. Here we get into BMS questions. There are special batteries for golf cars that would work in the farm trucks presumably they are optimized for the way things work. My buggy has a 600 amp controller in it, though that rating is quickly lowered in actual use. Many BMS units are only rated for 100 or 200 amps. That’s a lot of power, but do you want to stomp the pedal and feel the surge of acceleration, only to have it roll to a stop until the BMS resets? Or not be able to pull a trailer?
On the other hand, the boat has a very gentle charge rate and draw of around 25 amps in normal cruise. The motor can take a lot more, but is fused at 5o amps. No problem. The only issue might be the galley. Mr. Coffee can draw 40 amps, as can the microwave.. Running both while underway would require the bigger BMS. Still, I am leaning toward going with lithium in the boat if I can get some additional ballast in place. The lead batteries are down low and heavy while the solar panels are up high and heavy. If all the heavy is up high there could be stability issues. Same thing with the solar yacht projects. I pulled 1200 lbs. of lead from one of the hulls, thinking the weight would be replaced with batteries. Always something to consider.
Well, now the time has come to put up or shut up. My friend Courtney has been working toward building battery systems. He has sold a few, but they weren’t pretty. These days, you gotta have pretty. He’s awaiting some pretty system components now and sold off some of his other stuff to defray costs. I ended up with 16 LFP cells rated at 32o ah and two Daly BMS boards. It was an accident, I swear. I didn’t really mean to spend all that money, but might as well make the best of it.
There is a new generation of battery systems coming that I am hoping to get Sun to sell. Pricing may even be better than the a la cart stuff I bought. In the meantime, what I have here will be very educational and useful even when I move to packaged systems.
My solar yachts will be 48v, but I usually practice new stuff on Sun King, my solar expedition launch. Sun King runs on 24v, so I am making two batteries of 8 cells each. I could go with one battery and come pretty close to my current lead acid capacity, which comes from 6X 8 volt golf car batteries. I like total power redundancy to get me home when I am far away. The two batteries will give me more than 3x the useful capacity I have now. This is good because since my 2000 mile trip in 2015, I cut the number of solar panels in half to 810 watts. That’s good on short or leisurely trips, but when crossing bays or the Gulf of Mexico I want the ability to run through the night. Sun King does not do well in rough water and things are often more calm at night.
There will be a Part 2 (or even more) to this saga, but lets start with the basics. Each 24v battery will be made of 8 cells at a bit over 3v each. Over or undercharging can immediately ruin the expensive cells, so they are used with a Battery Management System board. This prevents damage from too-high charge or discharge rates, high temperature, low and sometimes high voltages. There are drop-in lithium batteries for car, motorcycle or boat that have all of this integrated into the familiar form of a battery. We are looking at the guts and basics of lithium, so bear with me if you like the nuts and bolts.
Prismatic lithium cells, the blocky ones and not the cylinders, tend to swell when charged, so you have to lock them together. Courtney delivered my cells in blocks of 4 with steel strapping and metal end plates. I was going to use threaded rods to pull it all together, but he saved me a step. Between each cell there is an insulating space, in case the metal cell case should be hot to one terminal or the other. Apparently that can happen as the spacers are something I did not see in the past.
My boat can be a wet place and I want to keep my batteries out of salt water, so I want them in a protective case. I have not yet measured, but it looks like 4 cells will fit within a standard plastic battery box and the boxes will fit in the battery compartments. I will measure to avoid disappointment and unnecessary profanity later. The BMS should fit inside the lid of one of the boxes. The fat blue cable will go to the negative battery cell and the fat black wire will go to boat negative. Balancing lines go from the BMS to each cell to keep them all the same. Finally, there are gadgets that plug into the BMS. One is the temperature sensor, which is very important. There is a voltmeter that can be handy. There are two communications gizmos, on for Bluetooth and another USB so you can get all the details of your battery on your phone or laptop. These are also used for setting the operating parameters.
A criticism I have of Daly before even powering up is the documentation. There is a bar code you can scan to get to a video on your cell setup. The documentation that came with the board is not even Chinglish. I know from hearsay that there are apps, but just try to find it on their website. I have a little Windows netbook I designated as my battery monitor and finally found the software in a rar package on a user web page. I had to find a rar unzipper to use the file, but looks like all loaded up. The Google Play Store had the phone app.
Now I am ready to go out to the shop an build a battery.
To be continued….–Neal