Might be more than the blog owner wants to spend for what is just a fun hobby project.
There are some 3U rackmount size nominal 48vdc 50Ah lifepo4 (approx 4.8kWh capacity) with built in bms and LVD you can get from china now.
edit: I pasted my comment (prefaced with "context = lead-acid batteries") into ChatGPT and got this answer, maybe someone who knows could, instead of having to explain it all to me, just confirm GPT-4 got it right, or if not the correct it / add detail?
> If a lead-acid battery is allowed to go below 40% state of charge (SOC), it can cause some issues, but the effects are not necessarily immediate or catastrophic. The depth of discharge (DoD) and frequency of these deep discharges can impact the battery's overall lifespan and performance.
> 1. Brief dip to high 30s: If the battery's SOC occasionally dips into the high 30s, it may not cause significant harm. However, consistently discharging to that level can gradually decrease the battery's overall lifespan.
> 2. Discharge to 0%: If a lead-acid battery is allowed to discharge to 0%, it can cause more serious damage. Repeatedly discharging the battery to this level will dramatically shorten its lifespan and could potentially cause it to fail prematurely.
> The relationship between DoD and battery life is not linear. For example, discharging a battery to 50% DoD might give you around 1,000 to 1,200 cycles, while discharging it to 80% DoD might give you only 300 to 500 cycles. It is generally recommended to keep lead-acid batteries at a higher state of charge to maximize their lifespan and maintain optimal performance.
> In summary, allowing a lead-acid battery to occasionally dip below 40% SOC may not cause immediate damage, but consistently doing so can reduce its lifespan. Discharging the battery to 0% can cause even more significant harm, especially if done repeatedly. It is best to keep lead-acid batteries at a higher state of charge to ensure their longevity and maintain optimal performance.
One thing that we can all agree on though is that you must never ever use car batteries. Lead acid need to be the deep cycle kind.
> please provide an example data to show non-linar relationship between DoD and lifespan in 5% increments.
Depth of Discharge (DoD) Approximate Number of Cycles 05% 3,500 - 4,000 10% 3,000 - 3,500 15% 2,500 - 3,000 20% 2,000 - 2,500 25% 1,800 - 2,200 30% 1,600 - 2,000 35% 1,400 - 1,800 40% 1,200 - 1,600 45% 1,100 - 1,400 50% 1,000 - 1,200 55% 900 - 1,100 60% 800 - 1,000 65% 700 - 900 70% 600 - 800 75% 500 - 700 80% 300 - 500 85% 200 - 400 90% 100 - 300
> thinking through the following steps please create an asci bar chart for this table, dod given in 5% increments:
1. Calculate the number of cycles for the first increment 2. Extract the maximum number 3. Calculate the number of stars with 1 start = 500 cycles 4. Put number of starts into a table 5. iterate over the table
Once the table has been completed create the asci bar chart plotting DoD vs Cycles
Example: 1. 5% DoD = 3,500 - 4,000 2. 4000 3. 8 stars
DoD Cycles
05% ********
10% *******
15% ******
20% *****
25% ****
30% ****
35% ***
40% ***
45% **
50% **
55% **
60% **
65% *
70% *
75% *
80% *
85% *
90% *
Lol, the way this came out to sit perfectly with OP's intuition. Even down to the drop from 2-stars to 1-star!
For instance, telling a brand name cell from a fake cell can be extremely hard, but your vendor knows exactly where they bought them. I buy cells from nkon.nl, who are a high rep local vendor and I've yet to be disappointed but buying a pack that is sealed from a low rep vendor may well incur a lot of risk. You'd almost have to split open the shrink wrap to make sure you got what you paid for. One quick and dirty way to check is to weigh the pack and to compare the weight to the manufacturers spec for the cells. It's obviously not perfect but many fake cells have weights that are wildly different from the cells they pretend to copy (usually due to much lower actual capacity).
If your has equalization, try to discharge & equalize charge it 2-3 times first.
If you can actually get access to the cells, measuring cell resistance is not expensive. Anomolies will show themselves very quickly. Everything should be pretty clumped together in internal-cell-resistance. If you have a pack equalizer, it can be used to help you read this out. My <$100 charger has a cell resistance test mode.
Yes, that can't be stressed enough. And depending on the fault and how the BMS handles it a more dangerous condition could easily develop. For instance an undetected short would cause the other batteries to be overcharged to the point where they are much more likely to die themselves, and some of those may do so in pretty violent ways.
Cheap / missing BMS are a serious problem with cheap Lithium-Ion packs, they are the first line of defense and bad cells can even happen when supplied by good brands (but the chances are a lot higher with no-name stuff).
Another good test: charge the pack, balance it, measure the pack voltage and the individual cell voltages, then let it rest for a day or two and measure again. Any kind of deviation between cells is a sure sign something is not working well and is the earliest warning sign for trouble you can get. The rate of self discharge should be the same for all cells and it should be very low, too low to measure (and make sure you disable the balancer after the initial charge!). After a month or so it would be fine to see the pack drop a little bit, but not a lot.
Yet another quick test: use an IR camera to look at the pack both during charging and at rest. Any cells that are warmer than those around them are suspect.
They may work for the the initial phases of charging but not for “float” I.e keeping the battery as close to 100% charge over a longer period.
I set us up here, totally off grid, three years ago, using a bank of OPzS cells, giving us 42kWh of usable storage. I rarely take them below 70%. Their performance has barely budged since installation, and with the condenser caps, they have required zero maintenance - I check the specific gravity of the acid once a year, and go “yup”, and that’s it.
LiFePo4 I am considering for a booster bank at our cabin, which is 500m from our power shed, as the cable limits us to ~2.5kW here before we see significant voltage drop - it’s either that or step-up/step-down at either end, but transformers are surprisingly expensive. Main reason I’m leaning towards them for this application is mass, as our only access is either by foot or an aerial cableway - our lead bank weighs about 2000kg, equivalent LiFePo4 is about 450kg.
So - LiFePo4 is a decent choice, but depending on your application, a pile of big lead acid cells can be better. See, for instance, storage at various solar projects - it’s virtually all OPzS cells, as the amortised cost is still favourable.
I think they will be at 80% after a decade, thus not trash.
> if you’re sealed, and if you get something like OPzS cells and treat them well, you will get 20 years of life from them.
If you have the space, 6V or even 2V OPzS cells can be huge.
So if for example, you need 1600 AH, you would spend $1500 for a 2000 AH lLiFe02 bank, plus 150 for a decent BMS, so $1800 US including shipping. (Just bought our 5th and 6th banks)
For the OPzS, you would need to buy 5714 AH to get the same cycle life and longevity, plus you have to write off 38 percent of your charging energy due to voltage and discharge rate discrepancies vs about 10 percent for the LiFeO2.
I seriously doubt you could obtain 5700 AH, shipped to your location, for less than $1800.. and then the size, maintenance, and corrosion issues (some of that goes away with the considerably more expensive sealed designs) also add to the headache.
If the battery magazine will be subject to below freezing temperatures, both types incur additional risks and energy costs for the lithium, you must heat it prior to charging. For the lead, you will need to add another 40 to 50 percent capacity to meet your target power capacity.
For home brewers, measuring specific gravity at the start and end of your brew process is the simplest way to know how much alcohol is in your creation. For this you'd use a hydrometer: https://en.wikipedia.org/wiki/Hydrometer
https://en.wikipedia.org/wiki/Hydrometer
>Battery hydrometer
The state of charge of a lead-acid battery can be estimated from the density of the sulfuric acid solution used as electrolyte. A hydrometer calibrated to read specific gravity relative to water at 60 °F (16 °C) is a standard tool for servicing automobile batteries.
See also here:
I'd personally not want a lead-acid battery burping flammable gas inside an apartment. They're supposed to be installed in ventilated spaces with drainage holes for any acid that spills out.
You could of course also use some of the charge from the battery itself to heat it up.
[1]: https://relionbattery.com/blog/lithium-battery-cold-weather
I have a small solar powered device (Pi Zero controlling an antenna switch) in my backyard that I use a little mechanical temperature switch to turn on and off a teeny tiny mat heater attached to the battery. It's all in an enclosure that's water tight, so I doubt it got below 0 during the day in there in the first place. We didn't get temperatures below 0C this winter in the NE USA (which is not ordinary), and even with some dips below 0 the battery seems fine.
I'm trying to respond to some comments, but since this is not my thread, I'm rate-limited.
> Let's talk about the battery. I've chosen to use a large used lead-acid battery even though Lithium (LiFePO4) batteries beat lead-acid in every metric. I bought the battery second-hand for €100 so that's not a significant investment for a battery. Although it's a bit worn-down and the capacity is reduced, it is still good enough for me to run my computer setup for 10 hours after a full charge. The lead-acid battery also serves another purpose: is a relatively cheap option for me to validate my setup. If it works as intended, I might opt to upgrade to lithium (LiFePO4) at some point."
I'm asking because I'm creating a similar setup to OP to control the climate in my glider's trailer.
Lead acid also have their own set of problems. Some types can produce hydrogen gas while charging, which can be an explosion hazard in an poorly ventilated room. Also, all types of battery are energy storage, and in case of a short circuit, they will release a lot of it as heat, and even if the battery itself can handle it, it can ignite flammable material in the vicinity.
Au contraire, lead-acid batteries work pretty well at temperature extremes, needing only changes in charging (e:) voltage and being limited by discharge current.
I have a summer cabin with a solar panel and a couple 12 V lead acid batteries. It would be great to be able to install some lithium type batteries instead, so long as I know they will survive winter.
Not necessarily lying but rather there are heating pads that use some of the energy to bring the battery up to safe operating temperature based on BMS readings. There are some LiFePo4 battery breakdowns on Will's YouTube channel that show the various heating pads used by each vendor. [1] So probably better to say they leave out some details that will affect capacity at lower temperatures. He has a HN account so maybe he will also comment.
For off-grid buildings lead/AGM is fine especially if not depending on solar and perhaps instead keeping a charge from a water turbine from a river or stream. AGM have significantly less charge cycles than LiFePo4 and the disparity is growing more every year. China went both Sodium and LifePo4 due to logistical and shipping issues with some of the materials required in Li-ion. Li-ion batteries also have heating pads. I can't see AGM being viable in solar farms due to the low charge cycle ratings. Either that or whoever the manufacture is will be very happy as those batteries will have to be cycled out quickly.
I have 4 AGM batteries for a few of my inverters that need higher surge capacity in a smaller space and the UPS driver remembers me for it. Now they make me get the batteries out of their truck. Since I keep the AGM's fully charged with commercial power the charge cycles are less of an issue for me and thus the TCO/ROI is acceptable. LiFePo4 current ratings are catching up though. Now I can get one that has a 200+ Amp discharge rating and I am told there will be one with a 300AH/320 Amp discharge rating soon.
I am most curious about what comes next. The 3D printed solid state batteries look very interesting. 50% of the weight for the same capacity, higher C rating, significantly safer. Mass production is just starting for those so time will tell I guess.
The killer feature of lead acid designs is cost and availability. In many applications, they are significantly cheaper. The chance cycle issue is real and i’m glad you brought that up. For some applications, they make sense. One is a low power draw solar-powered website. Lead acid batteries also outlast most lithium chemistries by several years. These batteries have been around for decades now are are absolutely everywhere and the voltages are standardized. that alone is a significant advantage.
Case in point - i run a UPS using my old 12 V car battery. Granted, i cannot keep this indoors but it works well.
Similar to what you said - off-grid or backup power is the mainstay of lead acid designs. almost every electrical substation out there uses lead acid for backup power.
> Operation below freezing ambient temperatures requires a heater and heaters need energy.
No. Charging requires a heater, discharging does not. It's really not reasonable to say "operation" requires a heater. While you're discharging, you're worried about the capacity and duration, and running a heater is a huge problem. The slower your discharge, the more of an issue it is to run a heater.
While you're charging, it usually isn't. You're already losing plenty of power to the charger inefficiency, it just takes a little more power to keep it above ambient. If you're plugged in it's irrelevant.
Also, i’m not sure plenty of power is lost to charging inefficiency. most industrial inverters operate at nearly 90% efficiency. Besides, above ambient isn’t a good metric - lithium chemistries do well around 10-25 C. If ambient is - 5 C, a delta of +5 C doesn’t change my core point.
Even if you are plugged in, lithium batteries aren’t dissipating heat. Not sure what the charger inefficiency has to do with this because that heat often isn’t the batteries themselves.
But it isn't a loss of capacity (although there is also a loss of capacity due to cold, in any chemistry). The capacity is the same, it just takes more energy to put the same amount of energy in. If you are putting energy in, you usually have an oversupply, and heating the battery is not an issue.
> If ambient is - 5 C, a delta of +5 C doesn’t change my core point.
I used the phrase "above ambient" specifically because the battery does not need to be warm unless you need to charge it quickly. If it's above 0 Celsius, it can charge. The warmer you make it the faster you can charge it. If the wasted energy is an issue you can charge slower.
> most industrial inverters operate at nearly 90% efficiency.
An inverter is significantly simpler than a battery charger. FePO4 charging can start as low as 2.5 volts and go past 3.6 volts. Making a converter with a 50% swing in voltage is not particularly easy. This higher-end charger picked at random[1] drops to <75% efficiency at the end of charge.
[1]: https://www.analog.com/media/en/technical-documentation/data...
I wonder whether there is some off-the-shelf controller that can do something clever like run a heater instead of charging battery till it gets up to temperature
There are some specialty ones that allow lower temps but that comes back to cost again
Or, you know, you get limitless amounts of 24Ah 12V SLABs free for the hauling away because they test at a bawhair under factory spec after five years of having an easy life.
LiFePO4 age by elapsed time more than cycle count, so after 10 years they will be reaching the end of their useful life regardless of how much you have used them. Lead-acid age by cycle count more than elapsed time, so you could have a battery last well longer than 10 years if you treat it well.
I'd note that lead-acid batteries are divided into deep-cycle batteries that have are designed for longevity and basic batteries that are optimised for peak supply current (for vehicle starter motors). Use a deep-cycle battery, otherwise yes it will die very quickly.
I'd argue that if you're in a part of the world that has unreliable sunlight, such that you want to store say 4 days of energy but rarely actually use it all, then lead-acid is a perfect fit, because you just buy lots of storage at a cheaper price than LiFePO4, and that regime automatically treats the batteries well.
If you're in a part of the world where sunlight is reliably every day and you only want to buy enough battery to last a single night, then I can see that LiFePO4 may be a better option. But I'd still be inclined to buy several days of lead-acid instead. If you want to charge your batteries from cheap early morning grid power and effectively cycle twice a day, then LiFePO4 is definitely the better option.
The other thing that is nice about lead-acid batteries is the recycling rate - they are very easily recyclable and very highly recycled. I don't think we're there with LiFePO4 yet.
Batteries are going to improve rapidly over the next decade, and the battery you replace your current LiFePO4 with at end of life is likely to be much better when that time comes.
One good point that was made is that lead acid starts to behave terribly after losing 20% of its capacity, to the point that they fail outright and can no longer hold a charge. Lithium can usually keep working way longer than that, just with a reduced runtime.
Those cycle life numbers look great, but lead acid batteries in practical applications tend not to last the lifespan advertised on brochures. We can gauge that by how confident the manufacturers are:
* The Trojan SIND 06 610 has a 2 year warranty.
* The NSB100FT - 3 years.
* The Battleborn BB10012: 10 years
The Trojan battery weights a whopping 220lbs and holds 600amp hours. It's not even in the same category as the other two. You need a minimum of two as they output 6v. The price for the amount of storage they provide is pretty good though.
> Lead-acid age by cycle count more than elapsed time, so you could have a battery last well longer than 10 years if you treat it well.
Have you ever seen a lead acid battery last this long? Was it able to hold a meaningful amount of charge?
Lead acid batteries may be cheaper but they are unlikely to survive for as long as claimed.
That said - if you want a battery backup that you basically never use, there is a chance that you'll get a good return on investment on deep cycle lead acid (specifically those industrial ones) – if they don't fail for whatever reason and are properly maintained. For the same amount of money you can buy a ridiculous amount of storage for a real emergency.
Good point about the recycle rate. Lithium is theoretically just as recyclable as lead acid, but the logistics are not there yet (but how will that look like in 10 years?).
Do test the cells individually with an acid tester, a simple hydrometer one is easy to take along when you go shopping. One important thing to keep in mind when buying any kind of battery is that for some batteries there are pretty strict requirements as to how they can be installed, what kind of physical isolation you have to use and how you need to vent any gases that they produce. These rules can easily disqualify some battery chemistries or configurations from consideration.
tl;dr if you are starting a solar battery project, LiFePo4 is the clear choice by far, unless you're going for the absolute cheapest possible build due to immediate budget constraints.
https://www.canbat.com/a-detailed-comparison-of-lead-acid-ba...
https://www.power-sonic.com/blog/lithium-vs-lead-acid-batter...