Lister Engine Forum
How to / DIY => Everything else => Topic started by: starfire on October 01, 2019, 07:22:46 AM
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For anyone interested......
Last year my lead acid batteries died, so decided to spend big on Lithium, or LiFePo to be exact, this flavour of chemistry seems the safest and most forgiving of them all. $4500 later, they arrived.
First problem was the placement. Like me, these things dont like low temperatures, we are talking minus something, so I placed them inside the hovel to keep them warm. The generator shed being 30 feet away gave voltage drop issues with the 100 or so amps charging current. This caused havoc with the alternators seeing over 18 volts at their output terminals.
I cured this by running independent sense wires, directly from the battery terminals back to the power shed, allowing the over voltage regulator to work correctly, it now reads the actual battery voltage and not the alternator output.
The maximum terminal charge voltage of the batteries is 14.7 volts, anything higher will damage the chemistry.
Here I simply designed a high voltage cutoff using a LM311 voltage comparator that switches off the alternator field current when the battery voltage reaches 14 volts... plenty, as the Lister is only used as the backup when the solar fails..
The main charging voltage comes from 800 watts of solar panels. The MPPT controller will switch of at 14.6 volts, this means the bank is full.
Here is the schematic of the car alternator control when I remember how to do this picture posting thing.....
These old car alternators are modified by removing the internal regulator and connecting one brush to ground, the other to a wire into the controller.
I then wondered about these Battery Management Systems built into these Lithium packs.
After reverse engineering one sample, I could not see how they can "balance" each cell with just a 100 milliamp draw, when each cell has a capacity of 600 amp hours..... it would have zero effect.
Firstly, I decided to establish if these Lithium cells actually do get out of whack with each other, they cannot be equalised as a lead acid bank can, this would overcook the highest cell. Is this an actual problem, or just an internet theory, steeped in myth and confusion.
I removed the BMS.
After nearly a year, the cells are within 3/10ths of a volt, highest to lowest, so unless I am extremely lucky, very unlikely, the balancing thing appears not to be the issue its made out to be. So, to simplify matters, we leave out the BMS.
It it also important not to discharge these LiFePos to less than aound 10.7 volts. This apparently causes permanent damage.
This requirement is easily met , almost all inverters will automatically disconnect at around 11 volts.
The difference with Lithium to lead acid is night and day, with a charge absorption efficiency approaching 95 percent, no sulphation or gassing..... no watering, no stress, just set and forget.
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Mr Starfire. You're back. Excellent. I was just talking about you . . .
I'm interested to hear how the lifepo's will go long-term. I just killed my (cheap, 2nd-hand) AGM by neglect and absenteeism and am mulling over replacements
Cheers
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Yes Mike,, and many thanks for the kind words......
I can honestly recommend these LiFePo batteries. I used to worry and stress over the lead acids..... how much charge I had to leave in for longevity reasons, periodic equalising, are they sulphating, much like a woman, you are never sure you are doing the right thing, and the costs of not doing so can be crippling.
Lithium are bloody expensive, but the full capacity can be used, they cannot be damaged by long periods of partial charge, in fact, they will exceed the rated 2000 full cycles if "mistreatred" like this.
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Cool. Thanks
The Bay of Plenty property where I spend a bit of time has lots of sunshine but I'm only there for the odd weekend or long weekend. To save using a noisy generator just for a few watts (lights, electric blanket - to keep that woman happy lol, small fridge - etc) I spent $300 on a panel (200W I thinK? I forget, AGM 100 A/H battery and a cheapie PWM controller & inverter.
Due to some bad planning I let it get down to about 50% and I think it's on the way out - so I need to think about replacement
The thing that bothers me with the lifepo's is the cold. I THINK it's OK for them to get cold, but not to be charged when it's cold
Will have to do some more homework
Well done on the battery upgrade :)
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Yes Mike, its the charging issue when cold is the bugaboo. Unless this is another internet myth? Anyway, cause the sun always shines on frosty mornings,making the panels active, its probably a good plan to prevent, rather than cure. Ive been lucky with lead acids, the scrap price had risen dramatically over their useful lifetime, so the scrap value almost equalled the initial purchase price, but no more unfortunately. Solar panels are about the cheapest they will be now I reckon, 1$ per watt for a quite decent panel.
Until you retire, I would wait.... Lithium is bound to get more affordable with time.
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Good advice & my thoughts too. Cheers
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A most interesting report, Starfire, thanks. The need for a BMS on lithium cells is well documented engineering, though with only 12V you only have 4 series banks of cells to worry about so it's less of an issue while cells are newish. (Parallel cells are regulated as one.) 0.3 volts variation is significant for a single cell and I would expect it to get worse over time. BMS is often ignored for low voltage strings for portable equipment where service life can be sacrificed for lower initial cost.
I agree it's interesting that just 100 ma of balancing shunt current is the typical unaided current rating of most BMS IC's. Many BMS IC's allow external power transistors to have much greater balancing current. A true BMS system will limit charge current based on IC feedback so a newly replaced, fully charged cell would cause the charge for the entire series string of cells to be limited to 100ma once that cell was full. By balancing on every charge, small balancing currents can keep cells from diverging...so perhaps with matching age and use cells, 100ma is actually useful; or, designers are cutting corners and don't want to add additional hardware for increased shunt current and the heat sinking required. If the BMS system doesn't limit total charge when the cell shunt regulators say they are maxed out, it isn't a true BMS system, and cells will drift out of sync until cell murder is achieved.
I use my own design BMS for wet lead-calcium batteries (10 batteries in a nominal 120V series string) and have up to 3 amps of balancing current available per battery before charge current is throttled. Current is then limited to whatever provides just under max shunt capability of the fastest charging battery. In actual service, charge is never limited by my regulator shunt current, as the batteries stay closely matched and while a few individual cells sag a bit over a month as seen via hygrometer, monthly equalization for 5 hrs brings them back to matching. If I could manage to the individual cell level, equalization could be eliminated.
Historically, BMS systems didn't come into play until higher voltage series strings of AGM batteries (96 volts and higher) were used for early electric cars. Equalization can't be done regularly with AGMs...so batteries were dying fast. By adding a BMS of shunt regulators with charge current limited based on regulator feedback and a shunt regulator on each 12V AGM battery in series, batteries were kept in sync, and battery life was greatly extended.
I modeled my system on these AGM designs since I was planning on a 120V series string using AGM batteries. I used Lead-Calcium batteries initially due to low cost for new hardware checkout, and found that thanks to the BMS, service life was nearly 5 years. AGM prices never came down enough to justify their use.
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Mikenash, if you haven't done it already, I suggest a careful equalization, 15.1V charge on your AGM battery, 3-4 hrs. That will recover a sulphated cell. AGM's are murdered by sulphation and also by drying out from regular overcharge. Natural death in small DOD applications is around 8+ years.
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Hi Bruce.
Yes, my legacy system is "stuck" at 12 volts. This is what I started with back in the 80s and it probably will stay that way unfortunately. All the appliances and ancillaries are 12 volt, quite a mission to change to even a 24 volt system.
The way I have understood this cell balancing is that any cell drifting high compared to its neighbours will reach the 3.65 fully charged voltage first, thereby leaving the other at a partial charge if charging stops at that point, which it must if cell damage is not to occur. Looking at the charging curve, the top most fractions of a volt represent such a very small part of the total; capacity of the cells, the loss is minimal. I have wired each battery in parallel, then ran 3 wires between cell junctions, this effectively places all cells in all batteries as one giant series parallel configuration. As you say, this limits the problem to just 3 junctions.
These are also connected to 4 of those small Chinese digital voltage displays that are taped to the battery giving a constant display of cell condition.
I have since constructed a automatic cell monitor using 2 LM339 quad comparators. One input is referenced to a seriesed and tapped resistor string across the battery, the other input referenced to each cell junction. The tapped resistor voltages rise and fall with battery voltage, but remained in a fixed relationship. The cell voltages rise and fall, but are not in a fixed relationship with each other.
This allows the comparators to monitor not the absolute voltage of each cell, but the difference between what they shuld be from the fixed resistor string, and what drift has occurred in the cells,.
By alternating between inverting and non inverting inputs, we can have a window comparator with just a few millivolt window. The open collectors are simply paralleled through one LED to indicate a fault. The remaining two comparators detect 14.6v and 10.7v respectively.
Ill post this diagram too if its useful.
To me, this has been a better way to do this.
The other BMS issue that caused me problems was its ability to turn the seriesed BMS FETs off as the battery voltage got near 14.5v, it would simply totally disconnectthe battery from the "grid", giving an open circuit to the alternator, high voltage into the house wiring and killing anything that happened to be turned on at the time. The overvoltage switch to the field works very well, and in my case, much more elegant.
The one strange thing I have noticed, the high cell is never the same one each day, it varies but so far has never exceeded 3/10ths.
To understand the balancing part of these BMS units, I removed the 100 ohm smd resistors from the dump FETs, ran wires to outboard resistor and LED combo to monitor the action. These turn on at cell voltage 3.55. Now, this is at the top of the charging curve where, at a charge rate of even a few amps, this would have little to no effect given that charging at this point is almost finished.
Still, this is my knowledge of Lithium so far.
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And Bruce, yout knowledge appears greater on this topic. I have just run the Lister for several hours and put in around 80 amps constant. The cell voltages every 30 minutes read:.
3.37, 3.34, 3.35, 3.37
3.42, 3.46, 3.41, 3.51
3.43, 3,48, 3.36. 3.57
3.52, 3.44,. 3.54, 5.55
after sitting for 10 minutes
3. 36. 3,38, 3,37, 3,38
This suggests there is some kind of self balancing happening sans BMS,?
Under charge, the chemistry is all over the place and voltage readings are invalid?
This bit I dont understand.... maybe you already know this?
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BMS with cell balancers (vampire balancers) that only allow 100mA. are not going to work well. As you suspect, charging a bank with 15A, and one cell fills up, that 0.1A is not going to do a thing to level out cell voltages.
Did the battery/BMS company explain how to perform initial balance by wiring all cells in parallel for 2 days ?
(If not, i'm not going to take the responsibility of how to explain it)
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I hear you on the 12V legacy; once you're all set up for that, no point in wrecking a good thing.
Your interconnects to parallel the cells is important in that it keeps those parallel cells matching except for minor interconnect resistance. Without those interconnects, it could get ugly as far as cell management. Because of your smart setup you only need 4 cell regulators total.
The fancy BMS IC's are really helpful for high voltage systems since so many of the darn things are needed. They typically have a fan out of 64 units, 4 or 8 cells each, all communicating back to the charge controller by a 2 wire bus.
I couldn't follow your circuit description without a schematic; but as long as you're keeping on top of cell voltages you should be fine. If you could find a way to adjust your charge voltage/current downward based on the feedback from your 4 cell shunt regulators, then you'd have a fancy first class BMS. On my regulators, I'm taking the voltage drop across the load/shunt power resistor, and sending that back as a linear signal through an opto isolator.
The old Manzanita Power system for early EV- AGM batteries used an approach you might consider. They had the battery shunt regulators be bang-bang controlled by comparator with hysterisis, with a heat sinked load resistor. They had an LED on the transistor output so you could see when it was "regulating"/shunting. As the battery reached full charge lots of LED blinking was happening. An isolated thermister was attached to each heat sink, biased by the controller and bussed together via diodes so that one voltage showed the hottest regulator, and one showed the coldest. The charge controller (a high voltage buck converter) would reduce charge current if any regulator got too hot. They do sell a lithium system now but I haven't studied it. All their new designs are microprocessor based.
My latest linear PV charge controller takes a 0-5V DC signal for 0-16 amps of charge at float, bulk or equalize voltage. (nominal 120VDC) I compute the charge current via an analog op amp integrator circuit, adjusting to keep the minimum and maximum battery regulators satisfied as loads change. The battery regulator feedback of how much current they are shunting is the driver of the whole deal. When sufficient sun or generator sourced DC charging is available the battery regulators are always just slightly regulating and the charge controller is constantly and slowly adjusting the required current to achieve that. When minimum regulator current is present and maximum regulator current is low enough for long enough, the controller kicks down to float. No microcontroller needed for this newer version which I developed for my neighbor and then rolled into my own system. Long live analog controls. The new MIcrochip nano power op amps and comparators use about 1/100th the power of the old workhorse IC's like the LM339's, and some have very impressively low offset errors.
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Mikenash, if you haven't done it already, I suggest a careful equalization, 15.1V charge on your AGM battery, 3-4 hrs. That will recover a sulphated cell. AGM's are murdered by sulphation and also by drying out from regular overcharge. Natural death in small DOD applications is around 8+ years.
Thanks Bruce. Next time I go up there I'll take the smart charger thingie from work if it has a "high" setting. But 15.1 seems very specific? I'd be interested in how the layman achieves that?
I bought the 100A/H battery, PWM cheapie, equally cheap inverter & panel all for (I think) $300 off a bloke who said it had been sitting in the garage "for a while" so history is uncertain . . . I made the mistake of leaving what turned out to be a faulty inverter attached one time I came back to find the display saying something like 10.8V and 55%. So it may be dead or it may have come back up by now. We'll see.
Cheers
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An adjustable power supply capable of at least 3 amps at 15V will do your equalization after the battery has already been charged to full via PV.
I use this:
https://www.amazon.com/gp/product/B07JCRG6G6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
It can also be used current limited, to charge any battery to a set voltage at a current rate that is safe for that battery. I use 7-15 AH sealed batteries in 12 and 6 volt for electronics development work and it's nice for those. It also works nicely on 120VDC which is handy for me. I have other 12, 24V chargers but none have equalization capability. Apparently good consumers are supposed to just buy new batteries more often. I have one AGM battery that is still in service at 12 years. It was my house/shop 12V battery, demoted at 8 yrs to House of Lister battery, which is low capacity, mostly float service, and it doesn't get annual equalization any more. It was a 110AH Universal Battery AGM, a bargain on sale.
The percent of charge shown by your controller is utterly bogus. If it's 10.8V, it's done, 0.
Being left in that state is sure to cause serious sulphation. A careful equalization charge might save it for a while.
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Starfire, I think the small variation under 80A charge may be due to variation in interconnect or internal resistance at that high current. Without a schematic I'm guessing wildly.
It would seem that due to the averaging effect of so many parallel cells, and so few cells in series (4) you may only need to balance the cells very rarely.
Cell shunt regulators would have to use bipolar transistors as the voltage per cell could be too low to operate even a logic level Mosfet, unless you want to add a transformer isolated 5V DC supplies for each regulator.
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An adjustable power supply capable of at least 3 amps at 15V will do your equalization after the battery has already been charged to full via PV.
I use this:
https://www.amazon.com/gp/product/B07JCRG6G6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
It can also be used current limited, to charge any battery to a set voltage at a current rate that is safe for that battery. I use 7-15 AH sealed batteries in 12 and 6 volt for electronics development work and it's nice for those. It also works nicely on 120VDC which is handy for me. I have other 12, 24V chargers but none have equalization capability. Apparently good consumers are supposed to just buy new batteries more often. I have one AGM battery that is still in service at 12 years. It was my house/shop 12V battery, demoted at 8 yrs to House of Lister battery, which is low capacity, mostly float service, and it doesn't get annual equalization any more. It was a 110AH Universal Battery AGM, a bargain on sale.
The percent of charge shown by your controller is utterly bogus. If it's 10.8V, it's done, 0.
Being left in that state is sure to cause serious sulphation. A careful equalization charge might save it for a while.
Hi Bruce
yes, I figured anything under an actual 12.2 was probably toast
Last time I was up there was just for a few hours, and without a multimeter so I just figured I'll worry about it later
That PWM "controller" is a piece of Chinese junk I suspect. But I bought the whole lot for not much more than the value of the panel, so what the hell. LKearning & making mistakes on some expensive "proper" stuff - that would be a mistake . . .
Cheers
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The standard minimum off grid setup here is 8 Trojan L16's (about $5000) set up as a 48V system. Newbies usually destroy the first set the first year, then wise up about power management.
I don't see anything that makes me want to switch from my lead-calcium "marine" batteries so far.
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OK, it seems this "top balancing" is a fudge. Research tells me that under high charging currents, the cell chemistry is unstable, changing cell resistance and therefore cell voltage. This settles down after charging, but then cell voltage drops, rendering these dissipative cell balancers useless. By cutting back the completed charge rate, keeping the cell voltage high, then these BMS systems have time to work. But not at the 100mA these things used originally.
So, I have modded a Chinese balancer by using the dump FETs to switch the base current of four PNP power transistors. These bang a 1 ohm resistor across that cell..... Current drain of around 3 amps differential. Now, at the time these activate, the solar controller has detected its max battery voltage at 14.6 and has shut down, supplying only the voltage required to supply the low cells and the additional shunt currents from the balancing drains. This seems to be working well, although I'm still not convinced its required, all cells are very close without. But, it will do no harm I guess. The biggest change I have noticed with lithium is the much shorter charge time , a direct result of higher chemical efficiency..... Energy not wasted producing oxygen and hydrogen gas, as you get with lead acid.
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http://nordkyndesign.com/protection-and-management-of-marine-lithium-battery-banks/
I found this useful.
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http://nordkyndesign.com/protection-and-management-of-marine-lithium-battery-banks/
I found this useful.
That's a very good article. It covers many points that destroy batteries.
I only wished it delved more into the situation that arises when the BMS or battery fails and begins to heat rapidly. Having a flame resistant container for the battery, arranged so you can quickly extract the flaming box and put it somewhere where it's not going to cause more damage, is important. I've seen the results of 2 burned shells of early Li banks and am glad I was not involved in their production.
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Most interesting... lead acid charge methods suck for Lithium. I stand corrected (and thank you); balancing during charging seems to be a poor choice. It seems you likely could do manual balancing via cell shunt load only as needed, perhaps as the cells age.
The voltage drop after the full state of charge confuses me on charge management. Since loads are variable, it's seems challenging to maintain the full state of charge. What I could not find was a chart that shows the current if a fixed voltage is maintained indefinitely.
Most cheap commercial lithium battery gear uses fixed voltage charging, so I'm missing something tonight.
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Yes, with only the terminal voltage to actually gauge battery SOC, it's not very accurate. By manually boosting each cell with a separate supply, it's possible to get them all at the same level and then let the balancer take over. It's fascinating to watch the indicator LEDs flashing as the dumps turn on and off. I will perservere with the resistor ladder network and comparator method to monitor cell voltage during a charge cycle ...this just compares each cell to the fixed ratio of a resistor network.... I know, schematics would help... I'm working on it.. Another scheme would be a sigma delta detector, ....DvDt. where the rate of voltage rise is the indicator for end of charge, and not the absolute voltage itself, this method was successful in the old fast charge NiCad days. I have noticed this effect also seems true for lithium.
It's fun learning this stuff, and Bruce, I don't envy your 120 volt system when it comes to battery management. With 600amp hours in each cell, it's very slow going to see any change occurring, and time consuming too. If my electronics gets any more complicated, it may be better to just have dpdt relays between cells to force parallel connection of all cells occasionally?
I'm still wondering if I'm over thinking this.
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Oh, and Bruce, the fixed constant voltage once batteries are full apparently is a no no..... something about the lithium actually electroplating the separator? There seems to be a very defined upper voltage plateau where charging must end completely. Now, this really can't happen with an off grid situation, the battery is also being discharged concurrently. There really is no way of knowing if the current in is exceeding the current out at the milliwatt levels alluded to when full charge is reached. I guess the easy way here is simply lower the terminal charging cutoff voltage at some safe level and forego a few ah of capacity.
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OK tried registrating myself on the image gallery to send it schematics, not happening.???? Im a total failure.
I used the LEF2017 thing as a global password.... is that correct to do that.?
Anyhow it didnt work, if some kind soul can walk me through?
'
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Lithium sure is an interesting battery to care for. I enjoy a chance to learn something new and greatly appreciate your sharing your project, Starfire.
Your stated full cell voltages are on the low side, so I suspect that is the solution your lithium battery vendor has chosen. Then you can have a fixed "full" voltage, low enough that it won't cause damage. Some loss of capacity but simple and good battery life, so a good trade off for an off grid home power bank. With a microcontroller and coulomb counting via load and charge shunts, it would be possible to regulate charge for higher capacity while having variable loads and variable charge (PV) rate, but it would be a heck of a project. Fixed (lower) voltage charge regulation is a much more attractive solution given that it also extends lithium battery life.
For an off grid lithium bank, cell balancing might be best done at night (switched on by low PV voltage), by very modest shunt loads switched to slowly discharge high cells - comparing to the average cell voltage (divided total) with some hysteresis to allow modest variation. Readily doable in analog or via any small microcontroller. Overvoltage monitoring on charging would then be for insurance only, with charge disconnect and latched warning piezo buzzer. It should never happen unless there is a serious failure.
Alas, I can't help on the image posting, it always works for me.
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schematics in the gallery
Car alternator cutout simply latches a relay and applies field current until Vsense reaches 14 volts.
cell monitor is a series of differential comparators detecting cell voltage variations compared to the fixed relationship from the left hand resistor network. Absolute voltages are ignored. Outputs ORed to give indication of an error. Additional 100 ohm resistors in that network give a few mV offset to prevent mindless chattering of outputs.
modded BMS is simply additional sinking capability added to an existing Chinese BMS balancing PCB, section with minimal count fan controller.
A bonus that someone may find useful, a diesel autostart control i recently designed for remote water pumping.... easily adapted to any diesel generator.
The "float switch" when grounded initiates a 10 second delay then cranks engine. Oil pressure rises activating fuel solenoid. Engine starts and runs until float switch opens, shutting down engine.
Oil pressure loss causes instant shutdown. After 10 seconds, engine will crank and attempt a start, if still no oil pressure, engine latches in a permanent fault condition and cannot be started until reset.
Low fuel causes permanent shutdown until reset.
maximum cranking time 10 seconds, if no start, permanent shutdown.
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Your cell monitor is interesting...always good to learn how someone else solves a problem. 12V does make cell monitoring much simpler than with a 350V system (Tesla).
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The real killer i found with lead acid is that final 20 percent or so charge, where the battery will only accept a fraction of the bulk charging current,without excess bubbling so this finishing charge takes many many hours to complete.
In real life, the bank is being continuously cycled, charging and discharging at the same time, the final top up never quite happens.... so the things will eventually sulphate regardless..... i know, pessimism right there.
.Forcing wont work, bubbles and fizzing is what sheds plate material. This i think is lithium's big advantage. over lead acid..... or at least they promise this.
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The lithium capability of operating happily without a full state of charge would be a marvelous thing. I can hardly imagine it as my own PV/battery system was designed for lead acid's need for being fully charged, and when I think about batteries, I immediately think of how to keep them topped off to extend life!
For wet lead-acid, the true deep cycle batteries are a horror show of inefficiency. For good life they must be fully charged, but charge efficiency for the last 10% is near or below 50%, and they eat power like crazy even when full. The self discharge rate is terrible. The floor polisher battery (6V) I got recently for my welder sucks 2 amps continuously when topped off, and this is within the manufacturer's specs. I was shocked.
A much better lead acid technology is the AGM batteries, which don't continue to eat power when full, and have high charge efficiency. They are what I designed for. The cheap semi-deep cycle, lead-calcium batteries I'm using don't have performance as good as AGM, but vastly better than wet deep cycle lead acid in that the charging cycle current does taper to nearly nothing (50ma). Lightly loaded and charged at moderate currents, the Lead-calcium batteries are a decent value. By using 120V instead of 12V, keeping actual battery loads to a few amps, and DOD down to 15% on average it's a different situation. My batteries are fully charged every day long before noon, but I don't have to wait for that, I have enough excess PV power during the morning for big loads. In fall, my batteries are nearly full but not in float by 10AM. Direct DC use and propane refrigerator/freezer is a big plus, there is zero load at night when I turn off my lights and computer. The inverter is only on when needed, though it only draws 15W when idling. A house heating cycle draws 20 Watts for about 4 hours from my 12V AGM battery for the circ pump, daily in near zero F weather, every other day for most of the winter due to thermal mass and super insulation. Yes, I am a fiend about low power design.
If/when lithium ever gets down in price to compete with my lead-calcium batteries for ongoing replacement cost, I'll have quite a project to design a new BMS for a 120V series string of cells. It's good to learn that I can do cell balancing slowly at night, as I'd need nearly 40 cell regulators instead of your 4.
Thanks for sharing your pioneering project on lithium batteries!
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Fascinating stuff Bruce & Starfire
Much of what you postulate is completely out of the realm of possibility for me. Where possible I like to keep the tech as simple as I can - that's why I have old Toyota Camrys and why my last diesel truck was a non-turbo, pre-common-rail and why my last four motorcycles all had carburettors. If possible, I like to run things I can understand in operation
I still have a few years to retirement (if there is such a thing) and I hope you guys will have sorted out all the potential wrinkles in any decision-making I need to do at that time
As I have no need for a water pump, have solid-fuel heating, and a gas hob plus direct solar or wetback water heating (and, more importantly, as any women up at my shed are visitors rather than residents) my electricity needs are modest and I still lean towards a keep-it-simple-stupid approach to power generation: 12VDC + solar + AGM batteries (although I could be talked into 24 or 48VDC if the case for the benefits was strong enough to outweigh what i see as the advantage of being able to use cheap automotive stuff in the system . . .)
Keep it up. I am being both entertained and educated here. Thanks
On a semi-related note, current wisdom says the LIFEPOs will intantly evaporate into a mist of expensive, radioactive steam if charging current is applied at sub-zero temperatures. I wonder how the Teslas et al do in Canada/Alaska? I figure they are "charging" with regenerative braking while being driven? Perhaps they are "smart" enough to have a work-around
Cheers
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There's no battery that does well at sub zero F temps. Here it's not so tough- moderate insulation will suffice to keep them above 32F, 0C, even with a little bit of ventilation in the battery box. The large thermal mass of the batteries helps. Much easier to insulate the batteries with lithium, they are smaller, lighter, no venting, no regular access needed for watering.
My neighbor is on his 5th year with his $1000 bank of 10 Walmart marine batteries. He say's they are still looking good on the hygrometer, very little variation in cells between monthly equalization. He waters twice a year (I only do once/yr.) . I designed his wall of batteries to make it very easy to service. The batteries are all raised to accessible height, longwise to the wall, so easy to see into each cell without pulling them out a bit as I must do. A large access panel seals it off, his 10 battery regulators with LED indicators are just above it, as is the charge controller board and PV regulator. He blew his battery funds on fencing for his milk goats, so I hope he gets to six years. My current set, on the same hardware, is only 3 years old.