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Another battery question
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Tech Guy
What type of battery is the safest? There have been several fires from e bikes lately in the news. You can have a fire with anything. I used to take care a few hundred APC ups units, some in data centers that were multiple rack cabinets of large batteries. Lead is heavy but I never had a fire. Bioenno seems popular but any horror stories about different lithium types ? 73 John N4HNO |
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N2MS
The safest lithium chemistry battery is a Lithium Iron Nanophosphate battery LiFePo4. That is what Bioenno sells. This type os also replacing the Lead Gel Cell batteries in wheelchairs and scooters. Stay away form Lithium Ion and Lithium Polymer batteries.
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The e-bike batteries are no-name brands people are buying and charging with unauthorized chargers. As a rule I only charge my batteries when I am present, no unattended charging. Mike N2MS On 11/23/2022 7:53 PM Tech Guy <tech48055@...> wrote: |
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AndyH
John,
All chemical storage cells can cause fires and/or contribute to explosive situations when mishandled. Proper wiring, fuses, etc. apply for all. Lead acid gives off hydrogen when being balanced (a controlled overcharge to bring all cells to the same state of charge), or when abused (wrong charger, out of control voltage regulator, etc.). Adding a hot wire or spark can quickly lead to a bad day. In the lithium ion family, the most used consumer cell type is a lithium cobalt oxide chemistry. These can exotherm, liberate metallic cobalt, and ignite when abused or improperly charged. These are the cells involved in burning laptops, air freight shipping restrictions, and toasty ebikes. The safe lithium chemistries are lithium ion/ferrous phosphate and lithium manganese types. These are being used more often in electric vehicles because they won't exotherm during charging, and won't ignite when punctured. (In a previous life I tested cells; and made custom lithium battery packs for ebikes, motorcycles, and electric lawn mowers; and designed and installed analogue management systems.) 73, Andy |
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Jerry Gaffke
LiFePO4 is safer than Lithium Ion, but either can be plenty safe.
All the cell phones and laptops I have owned the last couple decades have been Lithium Ion, and have had zero trouble with them bursting into flames. I am more concerned with driving around in a car with 15 gallons of gasoline, or breaking my neck in the shower. The whole idea of a battery is to pack lots of power into a small space, and that can be dangerous when products compete for maximum energy density and the fastest possible charge times. On any battery, if worried about safety, avoid charging or discharging at or above the maximum specified rate and you should be fine. In particular, be careful not to short it out. Speaking of fast discharging, it is amazing how well the new breed of auto jump start batteries work. I have a Gooloo 2000 which I rather like. In addition to being able to jump start an F250 diesel, it has a 15V 10Amp port out the side to run a small transceiver. It charges slowly through a USB-C port. Fast discharge is not possible unless you plug the jump start cable into the side of the pack. Includes a flashlight and several USB power out ports. Weighs 3 lbs. Walmart sells it for $78. Might save your bacon if you leave the headlights on while working Parks-On-The-Air. Using the battery off a shop tool also makes good sense to me. Why buy an extra battery for ham gear when you can make use of a battery that is used for other purposes? A high volume consumer product is often cheaper than a niche product. Jump starting truck with a 3 pound Lithium Ion battery seems an extreme case, but I see very few web reports of this resulting disaster. Mostly just a few reports from 2015 for one particular product. Your mileage may vary. Jerry, KE7ER |
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AndyH
Mike,
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Every cell chemistry in the lithium family is "lithium ion" and "lithium polymer". They all use a polymerized electrolyte, and all rely on lithium ions for charge transfer within a cell. What many think are 'lithium ion' are lithium cobalt oxide cells. These are the cells used in RC aircraft, electric razors, laptops, and most other consumer devices because they have a high energy density. They're also used by Tesla in the US. They're safe to use ad long as they're charged correctly and not abused. FMI: https://batteryuniversity.com/article/bu-205-types-of-lithium-ion 73, Andy, KG5RKP On Wed, Nov 23, 2022 at 07:06 PM, N2MS wrote:
The safest lithium chemistry battery is a Lithium Iron Nanophosphate battery LiFePo4. (snip) Stay away form Lithium Ion and Lithium Polymer batteries. |
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Jerry Gaffke
You are correct, though some of them don't have much cobalt these days.
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A web search for "lithium ion vs lifepo4" shows that common usage is to just say lithium-ion if it isn't LiFePO4. Metal cylinder construction such as 18650's is generally safer than pouch cells. If you want safe, buy a well regarded product that includes over-charge, over-discharge, and over-current protection. That should include most consumer products these days. Get something that has been out for a year or two, and read the reviews to see if it has had trouble. Jerry, KE7ER On Wed, Nov 23, 2022 at 06:11 PM, AndyH wrote: What many think are 'lithium ion' are lithium cobalt oxide cells. |
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AndyH
Yes, cobalt levels in some LiCoO variants are decreasing. The relative safety standings remain, however.
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'Common usage' isn't a useful metric. Folks interested in selecting a product within a family benefit from understanding when a disk ceramic doesn't replace an electrolytic, or why NP0 matters, right? Have you heard that nobody makes their own radios these days? hihi Metal cased cells are 'safer' only if one is working with individual cells and not a properly constructed battery. Anodes and cathodes need to be held together during charging and discharging. It's part of that 'safe if not abused or mishandled' thing. Look at how Tesla makes their reduced cobalt LiCoO batteries. Even though they start with metal cased cylindrical cells, they still have to encase them in fire retardant adhesives. In a crash they can still burn furiously and the fire can be difficult to extinguish. (Sandy Munroe also shows how pouch cells are packaged into a proper battery.) https://youtu.be/4JiDZVO9NdM https://youtu.be/3loFX_QId6Q Battery management chips are cheap these days, and one can purchase small battery management modules that provide cell balancing, charge and discharge current control, and cell-level high- and low-voltage protection while reporting battery health via low-power Bluetooth. Fun times to DIY batteries. 73, Andy On Wed, Nov 23, 2022 at 08:39 PM, Jerry Gaffke wrote:
You are correct, though some of them don't have much cobalt these days. |
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Jerry Gaffke
Andy,
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No real argument, I agree with most of what you say. 'Common usage' is a useful thing to be aware of, as this is how most other people describe what they are doing, and even how manufacturers describe what they are selling. In the world of lithium ion batteries, LiFePO4 chemistry is different enough that it is necessary to call that out. In particular, voltage per cell is different. Everything else often gets lumped together under the more generic term of lithium ion. Some 15 years ago I bought a few raw pouch cells because they were cheap. Big mistake. If building a small battery pack, go with cylindrical cells like 18650's. The pouch cells rupture easily and need far more physical protection. You definitely want appropriate electrical protection circuitry. If figuring all that out does not sound fun, then buy a successful battery pack of some sort and use the charging device that comes with it. Could be borrowed from a shop tool, an auto jump start device with a well protected low current port, or one of the excellent Bioenno LiFePO4 batteries. If building a big battery pack and you are interested in an educational project, I can recommend the prisimatic LiFePO4 bricks from http://www.powerwholesale.net/ Shipped from China, so may be tough to get if they go into lockdown again. These have likely been passed over by electric vehicle manufacturers for having specs somewhat out-of-family, but are relatively cheap. Lots of even cheaper vendors on alibaba, but be careful as many are selling used or damaged cells. Good info on https://diysolarforum.com Being offgrid, there's a bank of 32 EVE LF280K cells in the basement powering this conversation, configured as 2P16S, 29 kWh total, along with a JBD 200A BMS. Jerry, KE7ER On Thu, Nov 24, 2022 at 03:32 AM, AndyH wrote: Yes, cobalt levels in some LiCoO variants are decreasing. The relative safety standings remain, however. |
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ajparent1/kb1gmx
I've used LICC (carbon cobalt) those are some of my oldest 18650 cells (most are 1800mah).
I have an abundance of Lipo 18650 form most are the 2200 and 2800mah size. I also have Lipo pouch cells, flat form factor. in the 3000 to 5600mah sizes. Also some large 12Ah, 24Ah and 100Ah Batteries that happen to be LIFePO4. All have built in or have added to them BMS/BPP board to assure safe charge and some form of extreme short protection. Generally that is needed to keep Oops factor and abuses to safe levels. I have some NiCd 150Ah and smaller 2Ah batteires and the most important thing is short circuit protection. The larger 150Ah battery can easily supply 3000A, and the smaller 2Ah has supplied 10A (bursts) . I have used BMS on smaller NiCds (they make them for multicell NiCd and like NiMh as well batteries) to keep the cells from improper charge and reversal. The care and feeding of NiCd is required for bet life. All the bad things that Lipo can do like explode and fires have been seen with NiCds, Lead acid and most any other battery tech that can and will put out large amounts of power. SO: The hazard with Li tech is that they can easily supply very high currents usually more than enough to melt wires. The other is improper charging (too high current and excessive end state voltage). When not antagonized the last very long periods of time, have excellent shelf life, and generally give back the most power for the power put in. The entire cordless tool industry was NiCd, the NiMh and now all are Lithium based. My experience with cordless drills (Ryobi, Makita, Dewalt) from the days of NiCD to current is the lithium batteries are superior by a factor or 5 to 10 for lifespan alone. Oldest Li battery is the Ryobi ONE+ that replaced the 18V NiMH for the drill and is now nearly 10 years old and outlived 4 of the older NiMh 10:1. Why the 150AH NiCd, got them for free and flooded cells are the most durable battery known. THey stand overcharge and deep discharge without issues. For my use they have performed longer and better than any prior lead for powering the station using Solar/Battery 13V bus. Are the as efficient as Li, hard no. Thats not a problem as I have excess solar to make it though New England winters. At the time I got them (for free) over 10 years ago lithium in that size was about 2400$ new. If any of the NiCd cells fail that battery will be retired for lithium but based on the vendor Info they could outlive me. Likely a second lithium based system with solar will be put in place and used for house power. FYI the 100Ah lithium (talentcell 4170) has its own 100W panel and controller for portable use and its proven to be very good. Also handy as the battery has Voltage display, 5V(USB) and cigar lighter socket for powering those odd things as well as terminal posts for higher current loads. Allison ------------------ Please use the forum, offline and private will go to bit bucket. |
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Jerry Gaffke
The 2P16S bank of EVE LF280K LiFePO4 prisimatic cells here replaced a
6 year old bank of eight Trojan L16RE-B 370AH 6v flooded lead acid batteries. Those L16RE-B's were quite good for lead acid, the chart in the datasheet at https://www.trojanbattery.com/pdf/datasheets/L16REB_TrojanRE_Data_Sheets.pdf shows them to be good for 4000 cycles to 20% discharge, and 1000 cycles to 80% discharge. So really doesn't matter how deep you discharge an L16RE-B, you get the same amount of energy storage over the life of the battery. I worked the L16RE-B's hard during dark winter weeks, got more life out of them than I had reason to expect. One reason to avoid deep discharge of lead acid batteries is that without a BMS (battery management system) monitoring each cell, eventually a weaker cell will develop that discharges completely (or even goes negative) before the voltage of the entire bank falls 15% down from nominal. The over-discharge will damage that weak cell even further, and then the entire bank fails. So conventional wisdom is to only discharge lead acid down to about 50%. When charging, flooded lead acid will self balance nicely since any cells that reach the full charge state first will consume the extra power by breaking down water in the electrolyte. Be sure to check occasionally if water must be added. An automotive lead acid starter battery is designed only for high starting currents. You might get a dozen deep discharge cycles from such a battery before it fails. The primary thing to look out for when transitioning from lead acid to lithium is that lithium needs some other strategy to balance the charge state of all the cells. Once a cell reaches a fully charged state, any additional power will damage it. For this reason we need a BMS that detects when any cell exceeds it's maximum rated voltage (or minimum voltage on discharge) and disconnects the battery from the rest of the system to prevent battery damage. The BMS on a lithium battery also has a mechanism to weakly discharge any cells that are reaching maximum voltage before any other cells when charging. The lithium cells then "top balance", and should reach full charge simultaneously. One issue to consider when transitioning from lead acid to lithium is what happens if the BMS detects an overcharged cell and disconnects from the charging device. This never happens with lead acid cells, they tolerate overcharging rather well. A lithium battery disconnect when being charged may cause momentary voltage transients depending on the design of the charging device, high enough to damage any electronics involved. In my case, I monitor my BMS closely to ensure it is keeping the cells reasonably balanced, and have the charger programmed to stop charging at a reasonably low system voltage. A BMS shutdown due to high cell voltage will hopefully never occur, and with luck the transients would not be excessive. The L16RE-B's were good, but my new LiFePO4 cells are cheaper per kWh and should give roughly 5 times the number of full discharge cycles. They will last for a couple decades, at which time I expect household fusion reactors to be cheaply available. ;-) Jerry, KE7ER |
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AndyH
Lost a reply on the phone...let's try this again on the laptop...
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With respect, Jerry, "common usage" depends on the group being surveyed. For the general public, I agree that "lithium ion", "Lithium polymer", and LiCoO are used interchangeably. It's like saying all capacitors are electrolytic. In the marine world, lithium ion specifically means LFP/LiFePO4. In research and transportation, lithium Ion means the family and one has to identify the chemistry being discussed. Even within specific chemistries, there can be 'power cells' or 'energy cells', and some LFP are doped with yttrium or other elements. While the operational voltage per cell can vary between about 2.4 and 3.8, the family still has a max of 4.2 and a minimum of about 2V per cell. https://marinehowto.com/lifepo4-batteries-on-boats/ https://www.researchgate.net/publication/277963083_Effects_of_yttrium_ion_doping_on_electrochemical_performance_of_LiFePO4C_cathodes_for_lithium-ion_battery I've not used powerwholesale. I used to import 10 Ah cylindrical cells from PSI in Taiwan. I've used A123 cylindricals; Headway, PSI, Thundersky (thundersag...), CALB, and other prismatic LFPs. I've also used plenty of LCO pouches from Hobby King, both for RC and portable radios. NiCd and NiMH before that. My 5KW electric scooter/motorcycle was my primary vehicle and BMS test bed when I was building batteries. It had a 21S pack of 60 Ah Thundersky LiFeYPO4 cells. I have had good results from Docan Power and their Houston, TX warehouse. They stock grade A and B cells from CALB, CATL (supplies VW), and EVE. DIYSolar and DIYElectricCar both have too much bad info. I prefer the signal to noise ratio of the Endless Sphere forum - more engineers and fewer "youtube influencers". I appreciate your comments about your off grid battery. While my battery business was tailored to ebikes, electric motorcycles, and the occasional plug-in Prius conversion, my personal goal was off-grid. I'm a huge fan of the passive solar Earthship and have a complete solar and wind package (minus battery) for a future building. While the energy demands for a passive solar building are about an order of magnitude lower than a conventional US single family house, my needs now that I'm living aboard a sailboat are down another order of magnitude. My PV needs dropped from 3KW for the Earthship to 100W. My current house battery is the battery I made for portable radio use - 2P4S 25 Ah LFP cells, a 100 A JBD BMS, and a 10A Genasun MPPT charge controller, all in a plastic 50 Cal ammo can. I would have preferred to use a Stewart Pittaway DIYBMS, but didn't get it integrated in time before I put my lab into storage before the move. If one is a DIY type, it's really hard to beat the DIYBMS, especially if they use Victron balance of systems equipment. https://www.youtube.com/@StuartPittaway/videos https://github.com/stuartpittaway/diyBMSv4 Best, Andy KG5RKP/MM On Thu, Nov 24, 2022 at 09:05 AM, Jerry Gaffke wrote:
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Andy, I looked at your bio on QRZ.COM... Very impressive and thought inspiring and it encourages imagination. Thanks. Bob KK5R
On Thursday, November 24, 2022 at 04:06:46 PM EST, AndyH <awhecker@...> wrote:
Lost a reply on the phone...let's try this again on the laptop... With respect, Jerry, "common usage" depends on the group being surveyed. For the general public, I agree that "lithium ion", "Lithium polymer", and LiCoO are used interchangeably. It's like saying all capacitors are electrolytic. In the marine world, lithium ion specifically means LFP/LiFePO4. In research and transportation, lithium Ion means the family and one has to identify the chemistry being discussed. Even within specific chemistries, there can be 'power cells' or 'energy cells', and some LFP are doped with yttrium or other elements. While the operational voltage per cell can vary between about 2.4 and 3.8, the family still has a max of 4.2 and a minimum of about 2V per cell. https://marinehowto.com/lifepo4-batteries-on-boats/ https://www.researchgate.net/publication/277963083_Effects_of_yttrium_ion_doping_on_electrochemical_performance_of_LiFePO4C_cathodes_for_lithium-ion_battery I've not used powerwholesale. I used to import 10 Ah cylindrical cells from PSI in Taiwan. I've used A123 cylindricals; Headway, PSI, Thundersky (thundersag...), CALB, and other prismatic LFPs. I've also used plenty of LCO pouches from Hobby King, both for RC and portable radios. NiCd and NiMH before that. My 5KW electric scooter/motorcycle was my primary vehicle and BMS test bed when I was building batteries. It had a 21S pack of 60 Ah Thundersky LiFeYPO4 cells. I have had good results from Docan Power and their Houston, TX warehouse. They stock grade A and B cells from CALB, CATL (supplies VW), and EVE. DIYSolar and DIYElectricCar both have too much bad info. I prefer the signal to noise ratio of the Endless Sphere forum - more engineers and fewer "youtube influencers". I appreciate your comments about your off grid battery. While my battery business was tailored to ebikes, electric motorcycles, and the occasional plug-in Prius conversion, my personal goal was off-grid. I'm a huge fan of the passive solar Earthship and have a complete solar and wind package (minus battery) for a future building. While the energy demands for a passive solar building are about an order of magnitude lower than a conventional US single family house, my needs now that I'm living aboard a sailboat are down another order of magnitude. My PV needs dropped from 3KW for the Earthship to 100W. My current house battery is the battery I made for portable radio use - 2P4S 25 Ah LFP cells, a 100 A JBD BMS, and a 10A Genasun MPPT charge controller, all in a plastic 50 Cal ammo can. I would have preferred to use a Stewart Pittaway DIYBMS, but didn't get it integrated in time before I put my lab into storage before the move. If one is a DIY type, it's really hard to beat the DIYBMS, especially if they use Victron balance of systems equipment. https://www.youtube.com/@StuartPittaway/videos https://github.com/stuartpittaway/diyBMSv4 Best, Andy KG5RKP/MM On Thu, Nov 24, 2022 at 09:05 AM, Jerry Gaffke wrote:
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Jerry Gaffke
Curious, we wound up at the same vendor.
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From http://www.powerwholesale.net/about_us.html "About Us Docan Technology (Shenzhen) Co., Limited is a famous OEM battery factory with providing battery solution for customers, located in Shenzhen, Guangdong Province of China." Was no longer in a hurry when getting the second set of 16, so had those shipped from China, those took about a month before being dropped off by UPS and the price was significantly less. All cells were pristine, extremely well packaged, and worked well. Both buys were made through the same Docan rep, and payment for both was made through alibaba, paypal, and my credit card company. A bit scary to buy that way, but I read enough favorable reviews of Docan to buy with confidence. Jerry, KE7ER On Thu, Nov 24, 2022 at 01:06 PM, AndyH wrote:
I've not used powerwholesale. .... I have had good results from Docan Power and their Houston, TX warehouse. |
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Jerry Gaffke
Also, note that when clicking on "Battery" in the upper left of http://www.powerwholesale.net/,
you are presented with the following choice: Category Battery Li-ion battery
LiFePo4 Battery
Ni-MH Battery
Ni-cd battery
They wouldn't sell as many if they made it too complicated. ;-) Jerry, KE7ER On Thu, Nov 24, 2022 at 05:00 PM, Jerry Gaffke wrote: Curious, we wound up at the same vendor. |
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The common brick lithium battery packs are the least safe because they are very vulnerable to abuse. That is: over-charging, over-discharging, shorting, puncturing, and failure to balance the cells. These are the battery packs that have a main power lead and a balancing connector:
 They have no built-in protection. Cordless power tool lithium battery packs are among the safest because they are encased in hard plastic and have built-in short circuit, over charging, and over discharging protection. Also, you can't forget to balance the cells because balancing is also internal. Cheers, Don |
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ajparent1/kb1gmx
What needs to be respected is written on the label...
Lithium tech allow a significantly greater amount of energy to be in a far smaller and lighter package. And if not managed they can deliver it all in short order, such as short circuits. 25C and 50C that means the nominal discharge current times either as a maximum. So we are talking in excess of 50A and as high as 500A, things melt if not adequately fused or otherwise protected. That can include the battery itself. That means for a lot of uses its safe if not abused, that includes both mechanical and electrical abuses. Specifically do not bend, fold, spindle, mutilate, peirce, overheat, charge while too hot or too cold. All kidding aside how many of those abuses are perpetrated by the average Ebiike or Hoverboard user? That's a 148WH battery, if pushed to the limit easily delivers 7400wh for maybe a minute. That is a lot of energy. For that level of power we are talking the equivilent of a 10Hp engine!! Its also enough power to run a 100W radio (about 240W DC input) for maybe hours depending on TX and RX time. While being able to supply the needed 18-20A on 100W TX. This is why power tools and other safe batteries are max current protected for discharge. Most all have a matching charge system. For example I have a built up 18650 11AH 3S4P pack with BMB selected for a current cutoff of 8A. Since its only running a FT817 that is more than needed but enough to protect the battery from a short. If I were to attempt to charge with more than 13.1V the board cuts off the battery and rendered it safe. If any cell in the pack goes under 2V or over 4.2 it also cuts off. It uses a specific charger I made for it. That is basic protection. Another pack with BMS does both that and has a charging port that has the needed current and voltage control for charging with uncontrolled voltage source, again for safety. It also does charge leveling plus all the BMB safety functions. But the BMS value is it allows for a simple wall wart charger with enough output voltage as all the management is on the board. So if I were to use that pouch pack battery it would be placed in a heavy wall plastic case with BMS added and suitable connectors for field and other uses. Or I'd just buy a battery with all that is in a nice hard plastic case with standard tab or wire connectors. FYI most of the 7-9ah Lithium tech (usually Lipo or Lifepo4 families) replacement for gell cell 12V batteries do all that as well. However if you buy a quality battery with protection it will outlast most other alkaline (NiCd, Nimh) and lead acid tech but a wide margin making their cost actually economical. Allison ------------------ Please use the forum, offline and private will go to bit bucket. |
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AndyH
Don,
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RC batteries aren't unsafe because they don't have an i ternal BMS. In RC use, management is split between the charger on the ground (charges, controls voltage and current, and balances). In the air, the speed controller monitors battery voltage and disconnects the load. The only weakness is cell level low voltage isn't monitored (though the low voltage disconnect is conservative for that reason). (An example, not a recommendation) https://www.amazon.com/gp/aw/d/B0B5LLVSRK My bench battery for the past 12 or so years was a 'naked' 4S 10 Ah LiFePO4 pack made from PSI cells. I didn't worry about low voltage monitoring because I seldom discharged to 50%. I connected to an analogue BMS when charging with my bench PSU. I use LiCo pouches the same way. Without automation, we become the management system - the battery is as dangerous as we are. https://endless-sphere.com/forums/viewtopic.php?t=26554 If their bulk works for the mission, tool packs do make things easy, tho - and using them definitely reduces the need to not touch batteries until after coffee! Best, Andy On Fri, Nov 25, 2022 at 09:11 AM, Don LeRoi wrote: The common brick lithium battery packs are the least safe because they are very vulnerable to abuse. That is: over-charging, over-discharging, shorting, puncturing, and failure to balance the cells. |
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Jerry Gaffke
Andy,
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Sounds like you have made a career in offgrid power, something I have only dabbled with. The earthship must have been a major project and a big learning experience, I was looking hard at that before going with strawbale infill on our post-and-beam house, has a Faswall basement and is positioned for passive solar. Had 2.2 kW of PV till a couple years ago, now at 4.4 kW and will probably double that soon so we can get through dark NE Oregon December weeks without running a generator. Most winter heat is currently from windfall ponderosa pine, as I get older and less inclined to swing a chainsaw we may pivot to a large well insulated hot water reservoir in the basement heated by excess PV on occasional sunny winter days to keep the hydronic floors warm in bad weather. Wind and micro-hydro are vague possibilities here, but enough PV for cloudy weather at $0.50 per Watt is hard to beat. When we first bought, got by with a 20 foot yurt and 45W worth of PV from Harbor Freight and a couple used golf cart batteries. Most of that power went to a Sundanzer DCR225 fridge, cooling it off during the day and coasting through the night. Have power lines to the property, but was quoted $15k to get power to our building site if I dug the ditch. Was happy to hear that, as I was inclined to go offgrid anyway (we all need hobbies!). With 4.4 kW of PV and 29 kWh of LiFePO4, we pretty much never use the generator and my partner Liz need not think about my hobby when using the 26 cuft front loading fridge/freezer, 3 chest freezers, and dishwasher with superheater. I've given up complaining when and empty rooms are left with the very efficient LED lights left on. Being remote, power to the area occasionally goes out, and I rather enjoy telling the neighbors "no" when they ask if our power went out too. The JBD 200A BMS has a rather wimpy passive balancing scheme, discharging any cells with excessive voltage at maybe 250mA. This is proving adequate for the 2P16S pack of relatively well behaved LF280K cells from Docan, though I found it necessary to disable balancing at anything under about 3.41 Volts as the charge curve for the various cells differed enough below that value that the wrong cells were getting discharged. I'd guess this is because any cells with tighter specs were cherry picked for use in EV's. A minor nit of which I am sure you are aware, but seems worth pointing out to the forum: > "While the operational voltage per cell can vary between about 2.4 and 3.8, the family still has a max of 4.2 and a minimum of about 2V per cell." The LiFePO4 cells should never be charged much above 3.6 Volts, they would definitely be damaged if held at at 4.2 Volts. Pretty much all the other Lithium Ion chemisties are good to around 4.1 or 4.2 Volts as stated. I charge my battery to a max of 54.8 Volts (3.425 Volts per cell) and shut things down when it falls below 48.0 Volts (3.0 Volts per cell). This is using my Magnum PT100 charger, which was designed for lead acid and so is not aware of individual cell voltages. That range gives me something close to 99% of the available capacity and allows fast charging when only occasional sun is available, but avoids extreme highs and lows where top balancing (at the high end) and matched capacities (at the low end) become critical. As these cells diverge with age, I may need to program those high and low voltages to something more conservative. Ideally, I would instead figure out how to tell the PT100 to stop charging (without the possible voltage transients of letting the BMS take care of this) when any single cell exceeds 3.6 Volts. Letting the BMS relay cut out the battery when any single cell falls below 2.5 Volts is probably just fine. Looking forward to having an electric vehicle, especially if it can be cabled up to the house during a week of foul weather to make good use of that 70 kWh battery. Will check out Endless Sphere. When a difficult technical issue is raised on diysolar there can be ten different answers, and I might find eight of them to be misinformed. Jerry, KE7ER On Thu, Nov 24, 2022 at 01:06 PM, AndyH wrote:
I appreciate your comments about your off grid battery. While my battery business was tailored to ebikes, electric motorcycles, and the occasional plug-in Prius conversion, my personal goal was off-grid. I'm a huge fan of the passive solar Earthship and have a complete solar and wind package (minus battery) for a future building. While the energy demands for a passive solar building are about an order of magnitude lower than a conventional US single family house, my needs now that I'm living aboard a sailboat are down another order of magnitude. My PV needs dropped from 3KW for the Earthship to 100W. My current house battery is the battery I made for portable radio use - 2P4S 25 Ah LFP cells, a 100 A JBD BMS, and a 10A Genasun MPPT charge controller, all in a plastic 50 Cal ammo can. I would have preferred to use a Stewart Pittaway DIYBMS, but didn't get it integrated in time before I put my lab into storage before the move. If one is a DIY type, it's really hard to beat the DIYBMS, especially if they use Victron balance of systems equipment. |
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AndyH
Very cool, Jerry! It sounds lime you've a good handle on things there! I agree that commercial and most DIY BMS have wimpy shunts. I expect you already know that you likely don't need to shunt often, especially with your very conservative voltage settings. (For yet another tangent, the Smart ev and my current Outlander PHEV both have similar 250 mA-ish shunts. It takes a couple of cycles, or a day plugged in, but the battery will eventually balance. I seldom care, tho, as that extra 1/10 of a mile range isn't usually an issue hihi).
You're right that there's no point to charging cells to 100% - especially the ones like LFP that carry most of their energy at a lower voltage. It'll definitely reduce the cycle life. (From Thundersky-Winston, for example - operational voltage is 3.8, though charge/discharge tests run to 4.0 V. I used to set shunts to 3.65 and charge to 3.6. Shunts didn't activate until a cell got weak. https://en.winston-battery.com/static/upload/image/20210516/1621135112165001.jpg Ok, the wind is back - time to sail. 73 all Andy |
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Jerry Gaffke
Don,
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That Lumenier is a 10 Amp-hour battery, nominally 14.8 Volts. Rated for 25C, which means a maximum current of (10 Amp-hour) * 25C = 250 Amps, where the 25C has the rather odd units of Amps per Amp-Hour. So it can fully discharge that battery in (60 minutes)/25 = 2.4 minutes, with a power of 250 Amps * 14.8 Volts = 3700 Watts. A 3700 Watt appliance would blow fuses at 120 VAC, you would need a 240 VAC outlet. If you insist on moving that much power in and out of such a package weighing 0.845 kilo, that is inherently dangerous. But that's what the RC aircraft guys feel they need. When an aircraft is taking off it needs a burst of power, much more than when cruising along in even flight. The battery has to be as light as possible. And when they land with a depleted battery, they want to recharge it as quickly as possible (in this case around 2.4 minutes, assuming the max charge rate is the same as the discharge rate of 25C) That way they can get it back up in the air again for more fun. So they really are wanting to move 3700 Watts in and out of that battery. That's inherently unsafe, and why vendors also sell a "Lipo Safe Bag" to hold the somewhat expected explosion when charging at 3700 Watts. However, if you take that same product and charge/discharge at 10 Amps, and have an appropriate BMS hooked up when charging, there is very little danger of an explosion. Just make sure you don't short out those two roughly 1 cm diameter copper cables. Same applies to the starting battery in your car, not far from all that gasoline. Jerry, KE7ER On Fri, Nov 25, 2022 at 07:11 AM, Don LeRoi wrote: The common brick lithium battery packs are the least safe because they are very vulnerable to abuse. That is: over-charging, over-discharging, shorting, puncturing, and failure to balance the cells. These are the battery packs that have a main power lead and a balancing connector: |
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