Probably a dumb question

[GaRRy]

The various pro and cons of battery types and best place to locate them etc that I have seen on few posts on here has got me thinking.

I believe im right in saying that our batteries are made up of a series of small batteries linked together and contained in a case. ?.

So why dont we have the equivalent of a set of AA, AAA, C, D Batteries in the case ?

This to me would be a big step forward as it would mean the manufacturers could put the batteries any where they want and irrespectve of the location the actual batteries could be common across all bikes making them cheaper and easier to source.

It would also mean could easily replace them once worn out just like any other battery powered device, and also could easily swap them out for more powerful versions as they arrive (I think current rechargable AA's are over 4 times more powerful then ones a few years ago)

Im sure someone will tell me why this is not technically possible but seems a good idea to me and maybe a few of the manufacturers should get together to come up with a standard ?

 

[Scimitar]

I believe im right in saying that our batteries are made up of a series of small batteries linked together and contained in a case. ?.

So why dont we have the equivalent of a set of AA, AAA, C, D Batteries in the case ?

Essentially, that's all they are. The major difference is that every cell is spot-welded to its neighbours in series/parallel configuration. To have cells that are easily individually replaceable wouldn't really be feasible as they'd be rotten with bad connections and prone to shorts - something you don't want with lithium chemistry.
There's really nothing much to breaking open and stripping down a battery and replacing dud cells, either one at a time or the whole lot, it's just expertise and you get that by burning your fingers once or twice.

 

[neptune]

Interesting idea. There are snags as always. It is the nature of commerce that it is not about the common good, more about me, me, me. Another problem is that due to the high current draw, cells have to be soldered or spot welded into the circuit, unlike say, a radio, where just spring contacts are used.
As new types of battery chemistry hit the market, other things change, such as the voltage of each cell . So a new battery management system , and charger are needed. Of course if you build your own batteries, like Jerry Simon, then your design philosophy can be much as you describe.

O

 

[flecc]

A single cell is not a battery, despite the common incorrect usage. The word battery implies many, it's original meaning being a battery of guns.

The reason cells are not simply plug-in like a torch is that the current used by e-bikes is sometimes far beyond what can be reliably passed through an end to end pressure contact, the connections must be soldered or welded.

Failed cells can be individually replaced, but it can be a risky thing since any imbalance in cell performance can result in the whole pack being destroyed. As for replacing all the cells, it's rarely worth it since they are almost all the battery value, the case being only a very minor part of the cost. In addition progress with cells means that replacements may not match the old BMS electronics.

 

[GaRRy]

See I knew it would all be explained to me

so not impossible just not currently practical

 

[jerrysimon]

Exactly how mine are though not a standard size.

My DIY batteries have a smaller overall capacity and do not require a Battery Management System (BMS) "built in" to balance them, though I do it manually every few months or so.

Easy to brake apart and swap out a dud cell.

This pack is 30 months old, 700 charge cycles and 3500 miles with one replace cell after 12 months when I was abusing it basically by running it flat before recharging.


As stated though some care is required as these cells will discharge at VERY high currents in this case 128Amps peak!

In terms of configuration these are in two packs of 6s1p (six series one parallel) and then each of the two 6s1p packs is connected together to form one 12s1p pack. Standard commercial ebike batteries tend to be of a larger capacity and more cells in parallel.

Regards

Jerry

 

[alfazzr]

Hi Jerry,

Those batteries look really interesting. Have you ever posted a thread on how to make them and why a BMS is not required etc ? I cannot believe you have not, but I have not been able to locate such a thread. Do they work out cheaper than the packs that one can buy ? Was it a typo to say that two 6s1p make a 12s1p - by my reckoning a cell has gone missing somewhere? Can you (or anyone else) explain the relative merits of the numbers of batteries in series and parallel please?

Many thanks
Alfazzr

 

[jerrysimon]

Have you ever posted a thread on how to make them and why a BMS is not required etc ? I cannot believe you have not, but I have not been able to locate such a thread. Do they work out cheaper than the packs that one can buy ? Was it a typo to say that two 6s1p make a 12s1p - by my reckoning a cell has gone missing somewhere? Can you (or anyone else) explain the relative merits of the numbers of batteries in series and parallel please?

See here

No mistake. Two packs of 6s1p are connected in series to make a 12s1p pack. If connected in parallel they would be 6s2p but the voltage would be insufficient in our application here, unless you then connected that parallel pack in series with another 6s2p to give you 12s2p

The reason I keep them in 6s1p packs is to make it easier to balance them, 6s balancers being readily available in the RC hobby arena.

All your questions should be answered in the thread linked above. I would recommend you read the whole thread, as you can now buy the 6s1p packs ready made up for the same cost near enough as it would to buy individual cells and build them.

Please note though the larger pack is only 2.3Ah compared to many stock batteries supplied with bikes which would be 10Ah or more. Mine is good for about 10 miles on the flat.

The other alternative is to use RC Lipo packs, but there are even more rigorous safety issues to consider with those, another reason why I prefer these that have a safer chemistry.

Regards

Jerry

 

[GaRRy]

Anotherh dumb idea. Acceptng that spring connections are not suitable then why not use threaded connections ?

 

[flecc]

Anotherh dumb idea. Acceptng that spring connections are not suitable then why not use threaded connections ?

Cost would be a big factor, but once again the resistance could be potentially higher than a welded connection. We're speaking of up to 30 amps at times, so even a slightly poor connection could cause problems. Cells are delicate things, so tightening a pole end connector could cause breakages, anyway many use soft pack cells. And then there's the cell to BMS mismatch problem I've already mentioned. All battery design is continuously work in progress, one I know of which looks identical has been through five different cell and BMS upgrades in just three years. Imagine the potential problems of knowing what to use for recelling.

Cells and BMS circuits sold separately as pack replacements would of necessity be more expensive than those used in the battery in the first instance due to the difficulties of stocking all the varations. Since the battery case is probably only a fraction of the cost anyway, the recelling cost could exceed the original battery cost.

Basically the manufacturer is producing a battery, an item which has always been accepted to be a consumable. That it's expensive isn't relevant, despite what a customer might feel.
.

 

[Biker44]

So why dont we have the equivalent of a set of AA, AAA, C, D Batteries in the case ?

Yes, it would be possible to push the cells into the kind of carrier sometimes seen in torches (or into the kind of arrangement that's internal to a torch). Held under enough pressure at the top and bottom (so you need a strong, accurately made carrier) and you could almost certainly get a top-quality contact (plating and spring-steel must be very high-quality, of course) capable of lasting the full lifespan of the cell. (Even under the potentially severe vibration/impact conditions imposed by a bicycle).

However, the whole battery case would have to be sealed against water and corrosion, since any contact failure would lead to disastrous heating, potentially setting the whole thing on fire.

This to me would be a big step forward as it would mean the manufacturers could put the batteries any where they want and irrespectve of the location the actual batteries could be common across all bikes making them cheaper and easier to source. It would also mean could easily replace them once worn out just like any other battery powered device, and also could easily swap them out for more powerful versions as they arrive (I think current rechargable AA's are over 4 times more powerful then ones a few years ago) Im sure someone will tell me why this is not technically possible but seems a good idea to me and maybe a few of the manufacturers should get together to come up with a standard ?

Manufacturers guard their niche-markets and never get together like this. Ask Colonel Whitworth what a ****** it was to get the sensible people in the home of the Industrial Revolution to all use one kind of thread! Even then, some other people invented American Fine (A/F) and screwed it up, while Napoleon screwed us up again with his metric system even after he was dead! I may be thinking of Colonel Whitbread, however, and that's another tale.

 

[benjy_a]

Anotherh dumb idea. Acceptng that spring connections are not suitable then why not use threaded connections ?

Not a dumb idea at all! Threaded connections are absolutely possible and already offered by Headway batteries in the U.S. I very nearly bought one.

http://stores.headway-headquarters.com/-strse-DIY-BATTERY-KITS/Categories.bok

These would be very simple to repair...just unbolt one cell and replace. These batteries are used by many on the endless sphere forum....obviously you can build as big as you want, at whatever voltage you want. All you need is the corect BMS and charger.

Ben

 

[alfazzr]

Or, from the UK, and on offer too:

Headway LifePo4 38140S 12AH

also sell BMS and Chargers, joining plats and neat little stacking pieces.

 

[benjy_a]

Or, from the UK, and on offer too:

Headway LifePo4 38140S 12AH

also sell BMS and Chargers, joining plats and neat little stacking pieces.

Cool! Good to know.

 

[NRG]

Beat me to it, was going to mention Headway, many of the guys on ES uses them...only downside is size and bulk, but easy maintenance...

Edit: 4.7Kg just for the cells alone in a 12Ah / 36v pack

 

[muckymits]

Excellent as I was just about to order a set

 

[jerrysimon]

I am not sure how well they perform/how long they last but I guess as NRG highlights if you need a decent sized DIY/Fixable battery these make for a good buy even though you could get a similar multi celled lithium battery for the same cost.

Also as NRG says probably a bit heavier than many normal lithium batteries. If I had a larger bike and needed the range I would probably go for these and buy a couple of spare cells to hopefully cover me in the event of any failures. There is someone on the forum that uses them with out a BMS (many prefer not to risk a BMS failure that destroys the cells) and then checks them regularly and balances them manually.

Regards

Jerry

 

[alfazzr]

Are these a good buy for someone perhaps? 4.2V 4000 mAh, free shipping $8.39 each for orders over 10.

L 26650 4.2V 4000mAh Rechargeable Lithium Battery (Blue) - EB304L at US$ 9.88

Probably insufficient current supply - I cannot find it stated?

Better deal here perhaps? but again not enough current I guess.

http://www.ebay.co.uk/itm/6-x-18650-4000mAh-Rechargeable-Battery-Li-ion-Protected-/180902252794?pt=UK_ConsumerElectronics_Batteries_SM&hash=item2a1e9d50fa

6 times 3.7 volt 4000mAh for £13 delivered.

 

[jerrysimon]

Discharge capacity not specified anywhere. I like the idea of the built in protector.

With ebike cells it is essential that they can discharge at the required current, without significant voltage sag.

I suspect they would not be any good.

Regards

Jerry

 

[Scimitar]

6 x 18650 4000mAh Rechargeable Battery Li-ion Protected | eBay

6 times 3.7 volt 4000mAh for £13 delivered.

Far too cheap - they'll be repackaged used laptop cells with a very dodgy chance of setting your house on fire.