Lithium cells: Too many in series? - Electronic Circuits Projects Diagrams Free

DigiTan · 28th March 2007, 05:15 AM

I need a circuit built into a very compact casing. It needs to operate for short periods on time on 12, 18, or 24 Volts, depending on how initial design testing goes.

Because of the small space, I need to use Lithium coin cells in place of the 12V "security/alarm" cells I typically use. Before I do anything, I need to know the max number of these button cells I can link in series before something dangerous happens. Anyone have an idea of what the upper limit is?

Specifically, these are CR1220...
Voltage: 3V
Continuous Drain: 0.1mA

As an alternative, I could take some other battery type.

[edit] A mod can delete this duplicate topic. The forum gave me some "Invalid form" jive when I tried to post the first one.

**Nigel Goodwin** · 28th March 2007, 09:12 AM

I don't see any problems with putting as many in series as you like.

justDIY · 28th March 2007, 01:36 PM

at 100uA perhaps internal resistance is not a problem... but those tiny cells do have quite a lot of resistance, even though they're lithium based.

Sceadwian · 28th March 2007, 01:49 PM

The voltage is going to be very unstable if the load varries a lot. Nothing harmful will come of it, but you'll have to try it to make sure it works they way you want.

justDIY · 28th March 2007, 03:22 PM

how about using a single 'beefier' 1.5 or 3v battery and a boost converter? Maxim makes some very compact switching regulators, which for 100uA would require only tiny components. a single 4mm smt pot would let you dial any voltage you desire, toss in a few ceramic caps and a low profile inductor and you're set, probably consume less space than a big stack of little batteries.

ikalogic · 28th March 2007, 03:46 PM

Quote:

Originally Posted by justDIY

how about using a single 'beefier' 1.5 or 3v battery and a boost converter? Maxim makes some very compact switching regulators, which for 100uA would require only tiny components. a single 4mm smt pot would let you dial any voltage you desire, toss in a few ceramic caps and a low profile inductor and you're set, probably consume less space than a big stack of little batteries.

yes i think it's the best idea, because if you have many batteries in series.. if one of them is empty before the others, no current will flow at all...

Hero999 · 28th March 2007, 07:24 PM

The continuous current specification doesn't change by putting more cells in series and neither does the short circuit current because the impedance also increases.

DigiTan · 28th March 2007, 07:53 PM

Quote:

Originally Posted by justDIY

how about using a single 'beefier' 1.5 or 3v battery and a boost converter?

That's one of the options I'm weighting. It will really depend on the resistance of this device I'm trying to drive. (I might even be looking a buck conversion if the current demand is too great). I don't actually have the load device at the moment, so I'm just collecting ideas for now.

So with these boost converter ICs...do have I have to supply an AC signal in addition to the DC supply, or is the AC signal provided internally (preferred)?

justDIY · 28th March 2007, 08:23 PM

as I understand the terminology:

boost converter = monolithic solution, contains everything you need, except usually the blocking diode is left out.

boost (or smps) controller = just regulation, feedback and switch driver circuits, you supply the switch(es) and blocking diode

there's no AC involved, unless you're looking at some sort of off-line configuration

check out the TPS61040 from Texas Instruments. It's a monolithic switcher that is very small (sot23-5)

ikalogic · 28th March 2007, 09:11 PM

Quote:

Originally Posted by DigiTan

That's one of the options I'm weighting. It will really depend on the resistance of this device I'm trying to drive. (I might even be looking a buck conversion if the current demand is too great). I don't actually have the load device at the moment, so I'm just collecting ideas for now.

So with these boost converter ICs...do have I have to supply an AC signal in addition to the DC supply, or is the AC signal provided internally (preferred)?

it's provided internally.

Sceadwian · 29th March 2007, 01:33 AM

Considering how much extra weight and wasted space the casing of the coin cells make it'd probably be more space and energy efficient to use a single AA (Or maybe 1/3 or 1/4AA) and a boost converter. You could probably build it in the same maybe slightly larger size than the coin cells but dramatically increase battery life.

justDIY · 29th March 2007, 01:38 AM

hey, thats a good idea ya got there :P

Sceadwian · 29th March 2007, 01:50 AM

Ikalogic, if one cell runs out the entire pack will still source current the voltage will just drop, cells don't suddenly become non-conductive when they run out of chemical energy. That's what I meant when I said the voltage will be unstable. You'll also get significant loading effects. If the load has lots of peaks your voltage is going to be all over the place and likley effect the circuit it's powering. Basically if drawing 100ua from a single coin cell will drop the voltage by .2 volts then you're going to drop 1.2 volts from the same current on the 24 volt scenario. I don't know the voltage drop at those currents though so it could be much worse than .2 volts drop per cell.

Oznog · 29th March 2007, 05:04 AM

Just what are you trying to run here?
How much current do you need?

One suggestion, are you SURE you need 12V/18V/24V? You can't run on 3.3v or 5v?

Many of the common loads that come to mind that might require higher voltages may require too much current for a series of coin cells as well. For example, a relay, 12v bulbs, etc.

CR1220 are fairly expensive unless you buy in bulk. This could be expensive.

There's also a small "alarm battery"- ok I don't recall any numbers for it- that is less than half the length of a AA and a bit narrower. It's like 12V, or maybe I think I saw 22V. Not many amp-hrs or a low resistance.

As has been said, maybe just a boost converter.

DigiTan · 29th March 2007, 05:27 AM

For this project a AA, or even N an cell would be too large. But I'm up for using larger coin cells. I'll some tests on the load and go from there.

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28th March 2007, 05:15 AM	(permalink)
DigiTan	Lithium cells: Too many in series? I need a circuit built into a very compact casing. It needs to operate for short periods on time on 12, 18, or 24 Volts, depending on how initial design testing goes. Because of the small space, I need to use Lithium coin cells in place of the 12V "security/alarm" cells I typically use. Before I do anything, I need to know the max number of these button cells I can link in series before something dangerous happens. Anyone have an idea of what the upper limit is? Specifically, these are CR1220... Voltage: 3V Continuous Drain: 0.1mA As an alternative, I could take some other battery type. [edit] A mod can delete this duplicate topic. The forum gave me some "Invalid form" jive when I tried to post the first one. __________________ The most-hated young engineer in America. * AVR Projects * Robot War: TI * About

28th March 2007, 09:12 AM	(permalink)
Nigel Goodwin	I don't see any problems with putting as many in series as you like. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

28th March 2007, 01:36 PM	(permalink)
justDIY	at 100uA perhaps internal resistance is not a problem... but those tiny cells do have quite a lot of resistance, even though they're lithium based. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

28th March 2007, 01:49 PM	(permalink)
Sceadwian	The voltage is going to be very unstable if the load varries a lot. Nothing harmful will come of it, but you'll have to try it to make sure it works they way you want. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

28th March 2007, 03:22 PM	(permalink)
justDIY	how about using a single 'beefier' 1.5 or 3v battery and a boost converter? Maxim makes some very compact switching regulators, which for 100uA would require only tiny components. a single 4mm smt pot would let you dial any voltage you desire, toss in a few ceramic caps and a low profile inductor and you're set, probably consume less space than a big stack of little batteries. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

28th March 2007, 07:24 PM	(permalink)
Hero999	The continuous current specification doesn't change by putting more cells in series and neither does the short circuit current because the impedance also increases. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

28th March 2007, 08:23 PM	(permalink)
justDIY	as I understand the terminology: boost converter = monolithic solution, contains everything you need, except usually the blocking diode is left out. boost (or smps) controller = just regulation, feedback and switch driver circuits, you supply the switch(es) and blocking diode there's no AC involved, unless you're looking at some sort of off-line configuration check out the TPS61040 from Texas Instruments. It's a monolithic switcher that is very small (sot23-5) __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

29th March 2007, 01:33 AM	(permalink)
Sceadwian	Considering how much extra weight and wasted space the casing of the coin cells make it'd probably be more space and energy efficient to use a single AA (Or maybe 1/3 or 1/4AA) and a boost converter. You could probably build it in the same maybe slightly larger size than the coin cells but dramatically increase battery life. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

29th March 2007, 01:38 AM	(permalink)
justDIY	hey, thats a good idea ya got there :P __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

29th March 2007, 01:50 AM	(permalink)
Sceadwian	Ikalogic, if one cell runs out the entire pack will still source current the voltage will just drop, cells don't suddenly become non-conductive when they run out of chemical energy. That's what I meant when I said the voltage will be unstable. You'll also get significant loading effects. If the load has lots of peaks your voltage is going to be all over the place and likley effect the circuit it's powering. Basically if drawing 100ua from a single coin cell will drop the voltage by .2 volts then you're going to drop 1.2 volts from the same current on the 24 volt scenario. I don't know the voltage drop at those currents though so it could be much worse than .2 volts drop per cell. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 29th March 2007 at 01:53 AM.

29th March 2007, 05:04 AM	(permalink)
Oznog	Just what are you trying to run here? How much current do you need? One suggestion, are you SURE you need 12V/18V/24V? You can't run on 3.3v or 5v? Many of the common loads that come to mind that might require higher voltages may require too much current for a series of coin cells as well. For example, a relay, 12v bulbs, etc. CR1220 are fairly expensive unless you buy in bulk. This could be expensive. There's also a small "alarm battery"- ok I don't recall any numbers for it- that is less than half the length of a AA and a bit narrower. It's like 12V, or maybe I think I saw 22V. Not many amp-hrs or a low resistance. As has been said, maybe just a boost converter. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

29th March 2007, 05:27 AM	(permalink)
DigiTan	For this project a AA, or even N an cell would be too large. But I'm up for using larger coin cells. I'll some tests on the load and go from there. __________________ The most-hated young engineer in America. * AVR Projects * Robot War: TI * About