DC (via PSU) switching to battery

Hi Ron @zander and Richard @rsalvage,

  Maybe more 18650s have been made than any other size, particularly in the earlier production days?

And they may have been the easiest size to buy and subject to trauma to find out how they fail?

I am not aware this cell size is especially different or more susceptible than any other shape. If you look at cell construction, which is reminiscent of a Swiss roll, it is the 'natural shape', Rectangular cells are either thin and flat, probably just one sandwich thick, or folded like a blanket, which may make 'stress points' more likely.

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  18650 LiFePO4 certainly seem to exist .. I have never bought any.

The now apparently defunct A123 Systems had them a fair number of years ago, so they are not 'novel', though I don't think they sold many on the retail market.

https://en.wikipedia.org/wiki/A123_Systems

  I have recently seen them on AliExpress, but I can understand any doubts about such sources .... though I expect at least some will be LiFePO4 , as the voltage will confirm/deny. As for their quality, or the reliability of any particlar supplier,you must decide yourself.

 RS (large UK components distributor with many decades of history) are offering "ENIX" product

https://uk.rs-online.com/web/p/speciality-size-rechargeable-batteries/8183005

I would hope they would have established some form of providence to maintain their reputation.

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My  incomplete understanding is that there are several aspects of 'protection' to consider with all 18650s (all chemistry versions) . There is some overlap, as to who does what.

I assume, without evidence, much of this list applies to all cylindrical cell sizes.

Cuboid shape batteries often contain more than one cell, and may have at least a partial BMS built-in.

The following is just a summary of what I suspect ...please check and verify ... I am not responsible for any errors.

• charger .... obviously has to be appropriate voltage and current flow rating for the type of cell. Should also monitor temperature and stop charging if not in range ... and I think that should include too cold as well as too hot, if it is likely to encounter temperatures below about 0 deg C (32 F). In some cases, BMS might monitor temperature, and disconnect  the cells if the temperature goes out of the safe range.
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• discharge ... short circuit protection .. some cells include a small current limit circuit, probably just below the positive terminal, which limits current to a 'few' amps. I have a feeling, this is omitted for cells destined for the vape market, but this feeling maybe 100% wrong! It is not obvious which cells include it.
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• over discharge protection ... discharging below certain voltage is hazardous. I don't think 18650s (and other basic cylindrical cells) are likely to protect against this .. I think they expect an external BMS to be employed for this purpose
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• cell balancing .. even when multiple cells are in a simple series only configuration, one (or more) will reach minimum charge point before the others. This can result in a cell being over discharged, The balancing aims to keep them all 'in step'. There are different schemes, the better ones, being more complex (and expensive) , help to minimise the loss of capacity, by transfering charge between the cells, .. I think the simpler ones, simply discharge the'stronger cells down to the level of the weakest cell. Cell balancing is also normally part of the overall BMS scheme .. not built into an individual cell.
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• Under temperature discharge - I am even less clear about this - maybe only applies at even lower temperatures than for charge, so only required for colder climes. Again I would expect the BMS to be involved, if required.
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• cell heating .. in applications such as cars, subject to low temperatures ..sometimes the battery is used to heat itself .. again the BMS plus resistor heating strip

As I say, the above is just a list of things to check on .. some may not be relevant in some cases, and I may be mistaken in what I suggest.

I have used BMS (Battery Management System) as a broad term to cover every function I could think of,  outside of the cell itself. It may be a 'practical' BMS consists of two or more different units,  if you buy 'off the shelf' management boxes, where each unit is responsible for certain aspects.

In addition, as Ron (and others) has discovered, the design of insulation on some cylindrical cells can allow shorts to happen. So far I have escaped this fate, so I am not clear about the circumstances .. maybe some cell holders have a bare metal strip to bring the negative terminal to the top of the cell,  to enable the cells to be connected in series? Perhaps, Ron you can enlighten us please?

 Hope this is useful .. please point out any errors.

Best wishes, Dave

@davee In my case, the cell exterior was negative so the physical distance between + and - was a couple mm. Yes, some cells are made with tabs (both + and - I think) that are welded together to make a battery. My Battleborn 100AH are made that way. I have seen the 18650 advertised with as much as 9,900AH. I accidently purchased some 5,500AH. I will be testing them but I am 99% sure they are fake. To the best of my knowledge the bulk of 18650's come in chemistries that produce between 2300 and 3600 mAh. There do appear to be some LiFePO4 but the capacity is under 1,400mAh, as low as 1,250mAh but typical is 1,350mAh.

Hi Ron @zander ,

The RS/Enix cell I pointed to claims 1.8AHr, which is probably reasonable if 2.3AHr is 'easily doable' with one of the cobalt variants.

I think some trading between maximum sustained current flow (charge and discharge), lifetime, and total capacity is possible, so I wouldn't be surprised if cells claiming 3.6AHr have reduced performance in other directions, ... or of course, just boasting more than they can achieve, maybe a bit of both.

I would definately agree, more than 3.6 AHr is most likely fiction ... On AliExpress, one supplier site that had broad selection of 'plausible cells'. also had a 'PP3' (the ubiquitous small 9V battery) lithium claiming 9.9 AHr ..  I wasn't sure whether to smile or wonder what planet the website maintainer was on.... caveat emptor indeed!

Best wishes, Dave

@davee Here is a picture of the 5000mAh 18650. It claims to be protected as well. It does have the little nipple associated with protected cells, but my 'good' cells that are proper specs and proper BMS has an almost flat top. One thing to note, this 5000 battery actually can not short out as the plastic wrap keeps the -ve side covered enough so as to not short.

Hi Ron @zander,

 I have two different types, two came in a headlight, the other two I bought at the same time, to get free delivery from Amazon! 

Minehave different colours and markings from yours, though UltraFire also appears on the spare set. They all have wrap around sleeving, and pips, so I wasn't clear how you had a problem.

Mine have 2200 mAH and the Ultrafire 3000 mAh markings... do I believe either ... probably not, but prior to Covid, I did make good use of the headlight pair, in spite of being rather heavy and the headlight is Dalek like. (Since, then, I have been lazy and hiding from the bug!)

I am not sure if the pip does mean protected ... I am not saying that they are not protected .. just don't rely on it unless you have verified the fumctionality .. a pip shaped piece of metal probably costs the same a flat bit, if you buy a million at at time!

Best wishes, Dave

@davee There is a project that keeps trying to get attention in all this talk, a battery capacity meter. Who has the best design? How I define best is the ability to test many kinds of batteries not just 18650.

@zander

Posted by: @zander

[snip]

One thing to note, this 5000 battery actually can not short out as the plastic wrap keeps the -ve side covered enough so as to not short.

 [snip]

I don't trust these things as far as I can throw em...
I wouldn't be surprised if it can cause an "UltraFire"!

Cheers

Hi @frogandtoad ,

 I empathise with your feelings.. trouble is, whenever we buy a laptop or phone or battery power tool or .... , we acquire some more batteries whose provenance is unknown.

We may hope that if the outer box has a well known label, then what goes inside is safe and reliable ... but usually a quick check of the small print on the label suggests it all comes from the same part of the world, whose visbility is very limited.

In reality, many of the products with different labelling probably come from the same place ... only the outer plastic sleeve is different.

So where do we draw the line ... I don't know.

Do I care? .. yes,   Can I do much about it? Probably not.

Best wishes and good, safe luck. Dave

@davee 

Posted by: @davee

Hi @frogandtoad ,

 I empathise with your feelings.. trouble is, whenever we buy a laptop or phone or battery power tool or .... , we acquire some more batteries whose provenance is unknown.

We may hope that if the outer box has a well known label, then what goes inside is safe and reliable ... but usually a quick check of the small print on the label suggests it all comes from the same part of the world, whose visbility is very limited.

You're not talking about "Chyna" are you? 😉

Posted by: @davee

n reality, many of the products with different labelling probably come from the same place ... only the outer plastic sleeve is different.

So where do we draw the line ... I don't know.

Yeah: "Chyna" 😉

Posted by: @davee

Do I care? .. yes,   Can I do much about it? Probably not.

Absolutely you should, actually... you can do a lot if you constitutionally educate yourself, Dave!
Stand up for your god given constitutional rights Dave across the ditch!

We Australians are relying on people like you around the world, to do the right thing!

Take care!

Hi @frogandtoad,

   I think we may be heading down a dangerous rabbit hole ... not that I necessarily disagree with your sentiments ... just don't want to upset our exceptionally kind host.

So, I'll just quietly note that the UK doesn't have a constitution .. well not a written one, anyway .. excepting maybe the Magna Carta, which is probably nearing its Best Before Date  ...

Best wishes my friend,

Dave

@davee

Posted by: @davee

Hi @frogandtoad,

   I think we may be heading down a dangerous rabbit hole ... not that I necessarily disagree with your sentiments ... just don't want to upset our exceptionally kind host.

So, I'll just quietly note that the UK doesn't have a constitution .. well not a written one, anyway .. excepting maybe the Magna Carta, which is probably nearing its Best Before Date  ...

Best wishes my friend,

Dave

Hi Dave,

We are still clinging to our 1900UK constitution, Magna Carta and 1868 Bill of Rights, although every government is trying to userp it since their inception.

Anyway, I hope you weren't offended, as my comments were meant to be "tongue-in-cheek" 🙂

PS: - Did you know that king Klaus and team are looking into consuming human meat, i.e: -cannibalism?

Not a topic for here, that's for sure!

Take care!

Hi @frogandtoad,

I didn't even consider taking offence ... more like worried my reply could degenerate into 'pub-style' rant about various individuals and groups around the world, including but by no means limited to those in the UK. And luckily, I haven't heard of K Klaus ...

Take care and best wishes, Dave

@davee 

If you haven't heard of "King Klaus"... well... I have no words for you!

Cheers and look after your yourself!

Hi @frogandtoad,

  Well I tried Googling it ... and most of the first page discussed an Aussie race horse ..... though I did notice some 'fandom' thing at the bottom?  Neither feature on my radar ... 😀 

Hi Ron @zander,

re: There is a project that keeps trying to get attention in all this talk, a battery capacity meter. Who has the best design? How I define best is the ability to test many kinds of batteries not just 18650.

Sorry, I saw this question when you posted it, and thought I'll reply a little later ... then my grey cell forgot about it until now ...

As this is 'off-original-topic', and if it is to be continued, will need more contributors, etc., so you might want to start a new topic, but for now ...

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There are products on the usual bazaars ... in addition to numerous in-line USB meters, which are probably not applicable or even adaptable, there are some more 'general' devices ... I haven't looked, but this one found my screen ... I am not recommending or castigating it ... just thought it gave a starting point for a little thought and discussion.

https://www.aliexpress.com/item/1005001712924193.html

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Particularly, if you are thinking of a 'home brew' project, but even if an 'off the shelf' solution is what you are considering, I think the first thing you need is a rough spec, as your question is of the 'How long is a piece of string?' type.

The following is a quick list of the type of points that need to be considered ... I am sure there are more, so please add the ones I have forgotten. Equally, some points may be 'over the top' for your requirements and aspirations, so feel free to comment appropriately. I take the view, that the stupidest points and questions, are the ones that DIDN'T get considered and asked!

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• 1 cell (multi-shape & multi-capacity, I assume from your question) or include battery (of cells)
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• Depending upon above point, what connection methods are needed?
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• Do you want to monitor BOTH charging and discharging?
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• If charging is included, does it need to incorporate charging circuitry?
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• If includes batteries, what cell monitoring and cell balancing is envisaged?
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• Smallest and largest capacity (how many amp-hours)
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• Lowest & highest current flow ... and with current flow, is that short time, maybe a few seconds peak or sustained for minutes/hours? (Maybe both, but different current values)
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• If including battery ..  highest voltage and highest power to dissipate .. short term and sustained (I realise this is the product of the previous two, but sometimes it is easier to think in terms of power as a 'separate' parameter, then rationalise the overall spec later)
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• How do you want data recorded/presented? Just a few summary values, or ability to plot graphs, etc.
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• General portability/usage/physical form ... 'lab style instrument' or 'quick and dirty' .. only used in 'clean and safe' conditions or something for yard/garage usage?
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• How much construction & design do you want to do?
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• budget

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Hope that is helpful. best wishes, Dave