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Forum Index : Microcontroller and PC projects : cheap lithium cells
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palcal Guru  Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
For those in Oz, I found this site Lithium Cells I bought 10 to see what I get. I'm a bit wary of Lithium-Ion cells, They are good in one way but I never leave them unattended when charging and use all the protection possible. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
Very wary of Lithium. I tolerate the 40kWh battery parked in the garage. I do most of my other charging in the shed, not the house. On the todo list is a steel cabinet for housing the ever growing collection of power tool chargers. Also fitting a timer to limit the charging time to 2-3 hours. This will save going back to the shed so often. Jim VK7JH MMedit MMBasic Help |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
I've never really liked them because of the way they have to be charged, but great capacity to weight. I wish they would hurry up and bring something else on to the market. I read about some new type of battery quite often, but when. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| al18 Senior Member  Joined: 06/07/2019 Location: United StatesPosts: 175 |
NiMH batteries are proven technology, but at a lower power level than Lithium Ion batteries. Price seems reasonable also Amazon Basics 2000 mah AA batteries are $12.41 for an 8 pack |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5742 |
You have to put things into perspective. There are a vast number of lithium cells in existence - almost an unimaginable number. The media jump on every one they can find that catches fire (it makes impressive news), and they still don't reach 100 per week when tens of thousands per day are being produced. Most of the time it's not the fault of the cells. It's the result of mechanical damage (sometimes the result of poor mechanical fixing), excessive heat due to poor electrical contact at the terminals (poor mechanical design again) or electrical damage caused by very cheap chargers built without safety systems such as cut-off timers or temperature monitoring. Phones and laptops too thin, e-bikes too light and with poorly designed mechanical support for the battery, e-scooters are even worse as the battery is often where it will get hit by kerbs etc., manufacturers not selling chargers at sensible prices - leading people to buy very cheap copies, using unprotected cells to keep costs down to a minimum. It results in the technology getting very poor press. . Edited 2024-04-26 17:24 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
@ Mixtel90, yes I agree, the media love dramatic stories like the E-Scooter that burnt the house down. But when you think about it there would be millions of these batteries/cells around so the percentage of failure is probably extremely small. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
I believe in the expression "Prudent avoidance" It will cost me nothing more than a few hours work to change the shelf in the shed to a metal cabinet for the charging rack so why not do it. It takes a few minutes to walk to the shed when I want to charge the drone battery. It does get hot in use so the time walking gives it a chance to cool down before charging. Having the charging rack on a timer will be peace of mind and probably save a few dollars in power over the years. In most cases, it is minimal effort to reduce the risk so why not? I really do like to see the recycling of battery packs but I don't know what their quality control is like so I would be extra cautious. Jim VK7JH MMedit MMBasic Help |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 389 |
I think there are some chargers that are basically unsafe. I would not use any charger that "balances" cells within a lithium battery. Once a lithium cell is charged, pushing more charge through damages it irretrievably. And if a cell is self-discharging significantly faster than the others in a pack, it should not be used at all. A safe charger has to check for problem cells each time, most chargers don't do that. Which leaves the question, how do you tell is a lithium cell is good ? I guess you can discharge the individual cell to the stated end point, then slowly charge it at a safe rate, measure the output as it discharges and see if it provides the rated capacity. Then a pack can be made using the smallest-capacity cell as a guide for charging times and rates. But what happens when, down the track, one cell wears out/fails before the others ? My guess is, dodgy chargers simply attempt to push extra charge through, and the dud cell does into chemical/thermal runaway. Edited 2024-04-27 09:14 by zeitfest |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 1799 |
The battery packs for major name brand devices have built-in electronics to monitor each cell. On charge they bypass the charge current around each cell as it reaches the max. safe voltage so the weaker cells don't get overcharged. They also disconnect the battery if it gets to the max. safe temp. On discharge all cell voltages are monitored and the whole battery is switched off if any drop below the set minimum and again disconnect the battery if it gets gets to the max. safe temp. |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
I am watching this with interest as one job I have in mind for them is an electric fence charger connected to a small inverter and the lithium battery there for power. A small 12 volt 300 watt inverter will run the charger and lets say 175 watt solar panel for the charge. The standard method is just use a 40AH sealed battery which at best only last a year or so mainly due to using cheap off the shelf chargers. So yes a BMS has to be added and whether one is made or lets see with ali can throw up a they sell completed stuff cheaper than we can make. As lithium has been around for ages there should be some real cheap BMS's to get. Regards Bryan |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 389 |
One DIY charger project I saw would charge cells to the set voltage (4.2 v I think), which is fine, and then left it at that voltage with a small current going in. A very small current compared to the cell rating, but then it was left on indefinitely. Perhaps they were thinking of a "trickle" charge idea. That is a concern because some lithium cells slowly self-damage at the top voltage, it implies to me that the very small current is actually current associated with the damage as it occurs. Obviously task requirements and circumstances change a lot but in general I would not charge above 90-95% capacity, certainly not leave it connected to standby/trickle charge like water-based cells. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2290 |
the fundamental 'problem' with Li-Ion cells is that if damaged they are quite capable of converting all the chemical energy contained therein into heat at a rate unheard of with previous battery chemistries. but provided they are not ever physically damaged, on the whole everything is very satisfactory and pleasant (ie, hunky dory). i'd wager that if fires due to physical damage could be factored out, then Li-Ion cells would not have such a bad reputation. however, once you start putting hundreds of cells together in close proximity (ie, in an EV), the probability of a single cell being physically damaged (be it during cell manufacture, battery assembly, or some random impact to the whole EV in-the-field) becomes significant. and when one cell goes rogue, then its neighbors tend to join the party. what we really need for EVs (and e-scooters et al) is a battery technology that has a lower deliverable discharge current. i agree 100%. for months i've been looking for a charger design that can charge multiple cells in series in a safe and reliable way. on the whole, these simply do not exist. single-cell charger circuits (such as the TP4056) actually do an ok job once the maximum charging current is set to a sensible rate (C/4 is my choice), but lack the versatility to set a reduced voltage limit (fixed at 4.2v, i'd prefer 4.1v) and termination current (fixed at 1/10th max charging current, i'd be happier with 1/4). to date i've found no readilly available device that allows these parameters to be set. but even then, for an N cell battery pack you still need N charging circuits and N isolated 5v power supplies - one of each for every cell. the 'balancing' circuits that are used in place of multiple individual chargers are, in my view, not a satisfactory solution. cheers, rob :-) Edited 2024-04-27 13:45 by robert.rozee |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
Well wouldn't you know it go to cut firewood for the first time this season and the ute wouldn't start and the tractor battery was dead. So went in for a look and even $100 + plus chargers looked like crap so went to the 12 volt shop and asked for a charger. Well Victron do make chargers and I went for the 7 amp one for charging N70 batteries. Well this unit does have Li-lon as an option so I did go for a look thru the menu and one can set all parameters. Got it for $150 too as the day before I took that 100/30 MTTP back to swap it for a 100/50. Now after about an hour on charge the ute started and about an hour after that the tractor started. Now the tractor had a dead flat battery so with 2 hours charge not bad. So by leaving just a charger to do all the work until runaway wouldn't just a thermister on each string would catch any runaway and stop that runaway before it can start. Regards Bryan |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5742 |
You should choose the battery technology to suit the job. Trying to do otherwise isn't likely to work well. e.g. there is a reason why lead-acid batteries are used for most standby power systems that have to run for any length of time. The amount of current drawn isn't huge and there is plenty of charging time available. Additionally, lead-acid is ideal for "float" charging, where the voltage is kept up by using a very low continuous current. Lead-acid batteries will take a lot of abuse and will usually recover pretty well most of the time. They are also cheap to produce and are remarkably recyclable at end of life. Ordinary alkaline batteries, although non-rechargeable, are often the best choice for test equipment, single point emergency lights or for emergency torches. You do have to keep an eye out for corrosion though. Not great at low temperatures as the electrolyte is water-based and can freeze. Lithium technology cells have a much better power density. They are the choice for where you need a lot of power in a small space. They are virtually useless at low and high temperatures. Their maximum temperature range is about -20C to +60C as their capacity falls quickly and they suffer permanent damage. They are also unsuitable for float charging. Their terminal voltage falls very slowly off-load so it is difficult to get a charger that will automatically keep them topped up. The most efficient way to use these if you need over 20V or so is probably to use less cells and use their high current capacity to drive an inverter (or several) to get the voltage(s) you need. This simplifies their charging requirements. Because the internal resistance is so low the charging conditions are very important. A technology that seems to have gone out of fashion now is NiFe. They have a big advantage in that it's almost impossible to damage them by running them completely flat or by overcharging them. They are bulky, heavy, expensive and don't have a good energy density though. An almost perfect choice for emergency power systems. IIRC the old GPO used to use them in the exchanges as they also have a long life. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
Just had a look around that battery site and found these. So with 8S6P 600 AH for $1150 with shipping and local returns for bad one's. Man I have run my house on a 600AH forklift battery since '10. Now try go buying the same lead acid battery today for that price. Off memory the 100/50 does have a Li-lon option too so the 1.5Kw can handle that as the 1.9Kw does fit for the house. I do want to setup a separate power system so I can get my woodwork shop out of eternal retirement as it's going to be needed. So what do you think guy's those cells do have hefty connections a fitter can wire up so can the fun start. Regards Bryan : EDIT This may mean a full service of my ol'95 Unbreakable to drive from Adelaide to QLD to pick them up and eh why not bring close to a ton back home. If Bruce is still kicking we can finally visit. Thinking now about the dangers of thermal run away on how can we use old cells to create heat to liquidify metal and control the toxic element. I mean just putting around some 1860 cells around a crucible and see how it takes to heat the metal. This can be done in controlled environment so just how many cells would it take to melt metal. Regards Bryan Edited 2024-04-27 18:56 by Bryan1 |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2290 |
while alkaline batteries used to be great for test equipment, these days they are somewhat of a disaster. it is almost impossible to find a brand that does not leak after a random time, and a great deal of rather expensive test equipment has been wrecked as a result. i've had several fluke handhelds damaged. for discussion, see: https://www.eevblog.com/forum/blog/eevblog-1274-long-term-alkaline-battery-leakage-testing and: https://www.eevblog.com/forum/testgear/rechargeable-9v-batterries-for-dmm-or-alkaline-only where they can be fitted, modern Li-Ion cells are actually a pretty good bet; the self-discharge is low enough that you will get several years of standby before needing to remove and charge, and the old problem of limited lifespan from date of manufacture seems to have been resolved. cheers, rob :-) |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
I bought a couple of these modules  three years ago, then got worried about the cut-off voltage of 2.4v which seemed a bit low for longevity of LiPo cells. They have just three active chips: TP4056 - Charger IC for Li ion. ML8205A - Dual mosfet, switches low side. DW01A - Battery protection IC, cuts load at 2.4v. Somewhere I read that the DW01A cutoff was a bit low for battery (18650) longevity and a better chip might be the FS312F which cuts load at 2.9v. I bought some of them then tried to change one. That wasn't a goer unfortunately (ham fingers) but the original module seems to work OK for one battery so I gave up. Any comments about the usefulness of changing these, or should I just bin them. Greg Edited 2024-04-28 16:16 by paceman |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5742 |
Bear in mind that the DW01A disconnects the battery at 2V4 - but that is an on-load voltage. At that point the battery is unable to supply significant current as its internal resistance has increased. Once the load has been disconnected the terminal voltage of the battery actually increases to about 3V, but there is no current drawn as it's been disconnected. The load will remain disconnected until the voltage will reliably remain above 3V. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Ah ha, thanks Mick - that's something that didn't occur to me. It's a bit surprising that that point is not highlighted more in discussions about cutoff but then maybe I've just half ignored any 'under load' qualification. I won't in future!  |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5742 |
It's not very obvious, maybe that's why. When you think about it it makes sense though - the terminal voltage can only ever be read under some sort of load, even if it's only that of the measuring device! The *true* terminal voltage can never be read, only approximated by using a very high resistance device. The DW01A alone could be drawing as much as 6uA. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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