Regulation circuitry in LiIons

[Fallingwater]

Where is the regulation circuitry in LiIon cells?
Or, to put it better: at which end do I have to peel the plastic off in order to access the regulation circuitry?
Thanks

 

[SilverFox]

Hello Fallingwater,

The protection circuit is physically located at the negative end of the cell.

Tom

 

[Fallingwater]

Thank you.
Now I can order regulated 3v RCR2s from DX for spare change, rip the regulation off and have plain 3.6v cells.

 

[NotEnoughLight]

Just curious, why not just get the 3.6V cells?

 

[Fallingwater]

I'm looking for tiny rechargeables in 3.6v voltage. If I don't want to use prismatic lithium-polymer cells, the CR2 format is the smallest there is for LiIon.
I can find RCR2s in 3v format on sites like DX for about two bucks, but if I want a 3.6v one I have to pay several times that price to get it here on CPF.

Since paying more to get less is not my idea of a wise investment, I've decided to order the 3v ones from DX and chop off the regulator. They'll have less juice than true 3.6v RCR2s because of the space taken by the chip, but at two bucks a pop who cares?

 

[mdocod]

what about a 10440 or 14430?
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=740

 

[Fallingwater]

Way too large.
The cells I need have to be TINY. AAA or 4/5AA cells just won't do.
Besides, I'm not in the USA, and batteryspace have stupidly high international shipping rates.

Thanks anyway

 

[rgbphil]

Hi Fallingwater,
I've just gone through the process of selecting a lion battery for a design, and have a few things I've found.

Firstly don't chop off the regulation circuitry, it's better described as protection circuitry.

You're average phone or prismatic battery will have over/under voltage protection. You charge it with too high a voltage and the protection circuitry will cut off the power to the lion cell. You discharge the battery too low, and it will again cut off power to the application. Same with over/under current, over/under temperature.
This is all very important. Too much voltage/current in or out and the battery will catch fire. Charge it at too high a temp and it will catch fire, to low a temp and it will be damaged. Too much discharge and the chemical structure of the battery will be damaged, it will either fail and not work again, or it's life will be reduced. You can't guarantee there won't be some stray fault in wiring,

Also if you want to sell your application commercially, you'll be up against some regulations.

So keep the protection circuitry, unless you're providing you're own in the circuit. I know RC people use raw lion cells, but they invariably take special precautions like having a charging dish to take care of any problems, and usually don't stick their RC model down their pants pockets..

Having said that you can get small prismatic/cylinder units from places like sparkfun with inbuilt protection circuitry which might do it. Alternatively (but more expensively in small quantities, cheaper in high qtys) try some place like Maxcell and you can get any number of custom shapes and sizes and capacities.

Newer nanophosphate batteries with less susceptibility to catch fire are coming onto the market....maybe a while before they'll be accessible to the average punter though.

Phil

 

[mdocod]

rgbphil

I think you are a bit confused about what the type of cell fallingwater is planning on modifying...

There are in fact cells that contain voltage regulation circuits, that's how they come up with "3.0V" lithium-ion rechargable cells.... So while there are cells with protection like you are describing, there are ALSO cells with voltage regulators, in the case of the cells with both voltage regulators and protection, the actual cell within is quite a bit smaller than the overall package, that is the cell he is trying to get at.

 

[DM51]

If you want the smallest Li-Ion you can get, AFAIK that would be a 10180. ~5mm shorter and ~4mm smaller diameter than an RCR2.

 

[Fallingwater]

Firstly don't chop off the regulation circuitry, it's better described as protection circuitry

No, it's actually regulation circuitry.
There are cells that are just protected and not regulated, but the RCR2s from DealExtreme are not that type.
Their regulator might include protection too, but its main purpose is to drop the voltage from 3.6/4.2 volts to 3.2/3.6. Which is precisely what I don't want, so it has to go.

You're average phone or prismatic battery will have over/under voltage protection. You charge it with too high a voltage and the protection circuitry will cut off the power to the lion cell. You discharge the battery too low, and it will again cut off power to the application. Same with over/under current, over/under temperature.
This is all very important. Too much voltage/current in or out and the battery will catch fire. Charge it at too high a temp and it will catch fire, to low a temp and it will be damaged. Too much discharge and the chemical structure of the battery will be damaged, it will either fail and not work again, or it's life will be reduced

I am familiar with the workings of lithium cells, and I know the potential risks I take by running unprotected cells.
Charging is not a problem, as I have a dedicated LiIon charger that knows when to stop to avoid barbecuing the cells.
Deep discharge shouldn't be a problem either, because the LEDs I'll be running will probably be so dim by the time the cell reaches its lowest safe voltage I'll want to recharge it much sooner.
Let's just hope I manage to avoid shorting it while building the thing...

Also if you want to sell your application commercially, you'll be up against some regulations.

Nah. The first one I make (provided it all goes ok) will be for my use.
I might consider making others if I see the prototype comes out right, but I'd only ever sell them on eBay as homemade with no warranty whatsoever.

I know RC people use raw lion cells, but they invariably take special precautions like having a charging dish to take care of any problems, and usually don't stick their RC model down their pants pockets

Being a RC person myself, I have a deep respect for bare lithium-polymer cells... especially since a pack puffed up on me for no apparent reason just the other day, argh!

Having said that you can get small prismatic/cylinder units from places like sparkfun

Thanks for that, I didn't know sparkfun. Their shipping is quite cheap for small items, I'll probably be buying some stuff from them in the near future.

DM51: thanks, but I've no idea where to get them from. Google isn't helping either...

 

[DM51]

AW does 10180s and other sizes - see post #2 here:
http://www.candlepowerforums.com/vb/showthread.php?t=140362

He has both protected and unprotected cells, although 10180s will not be protected as they don't make protection circuits small enough to fit 10mm diameter cells. He ships worldwide, and his service is good and quick.

 

[Fallingwater]

AW's 10180 = $4.50 without international shipping
DX RCR2 = $2.45 shipped

Note that in no way I want to imply that AW's products aren't good or worth the price. I have no doubts that if so many people swear by him his cells must be of very high quality, and I myself might buy from him in the future should I need any.
They just aren't what I'm looking for right now. The application I intend to use the cell in doesn't need a good quality cell, it just needs something that can deliver a trickle of power for a decent time, be rechargeable, small, and as cheap as possible.

I ordered the cells from DX, with any luck they'll be here soon and I can start my hacking.

 

[DM51]

What you are doing sounds interesting (whatever it is, lol). I thought you might rule those out on price, but it was worth mentioning because you said small size was important too. Anyway, for future reference, if you need high-quality cells, AW's are very good.

 

[rgbphil]

re regulation v protection.....thanks for the info guys, I didn't know there were regulated batteries out there. I should have looked at the links the others provided.

Sorry about the 'scare' tactics, like I said I've just gone through the process of selection for lion batteries for a commercial product and the first thing that you see out there are the horror stories, plus rules/regs for shipping and qualification. But if it's for your own use...no problems.

Incidentally....what application are these regulated batteries for? Seems a bit strange, but I'm sure theres a good reason for them.

Also am I correct in assuming the non-rechargable lithium 'button' cells have a slightly different chemistry to rechargables...and so you get 3V out of them but 3.2V rechargables? Seems like they're too small to have regulation circuitry inbuilt into a button cell.

Phil

 

[Fallingwater]

What you are doing sounds interesting (whatever it is, lol)

Oh, it's just... shall we say, optimization of a product that has really failed to meet my expectations in stock form don't get your hopes too high or you'll probably be disappointed
Hell, for all I know I might not even be able to rebuild the thing, so the project might die an early death. Let's hope it doesn't

Sorry about the 'scare' tactics, like I said I've just gone through the process of selection for lion batteries for a commercial product and the first thing that you see out there are the horror stories

You want horror stories, try reading this

Incidentally....what application are these regulated batteries for? Seems a bit strange, but I'm sure theres a good reason for them.

Flashlights that work on 3v non-rechargeable CR123 cells but that would burn out on 3.6v RCR123 (aka LIR123) ones. Mostly direct-drive incandescents, as regulated LED lights are often compatible with both 3.6v and 3v cells.

Regulated cells work, but they need to be loaded to get the voltage down to about 3.2. Unloaded voltage is about 3.6 to 3.8 volts even for regulated cells, and there are some flashlights whose circuitry will burn out before it manages to put any significant load on them. Such lights can only be operated on primary non-rechargeable cells.

Also am I correct in assuming the non-rechargable lithium 'button' cells have a slightly different chemistry to rechargables...and so you get 3V out of them but 3.2V rechargables? Seems like they're too small to have regulation circuitry inbuilt into a button cell.

You are correct. Primary cells have a chemistry that outputs about 3 volts with no need for regulation.
There are some primary lithiums that output 3.6v, but I don't know whether they do it with a regulator/boost circuit or if they have a slightly different chemistry.
They are rare and I've yet to see them used in anything.

There exist also rechargeable LiIon button cells. As far as I'm aware the smallest form factor is LIR2032, which have the same size as CR2032 but output 3.6v (they are way too small for any kind of regulation).

 

[cy]

falling water... click on link in signature. it may be worth a read.

 

[Fallingwater]

I always monitor the voltage of the cells that come out of my cheapo charger, and it never exceeds 4.2. Actually it most often stops charging at 4.15-4.18.
I think I'm pretty safe.
But I've taken to charging LiIons in the same small metal pot I use to charge my RC-grade LiPos, so even if it should overcharge and the cell vents it won't set fire to anything.

Thanks anyway