SparkFun Forums

[chromatech]

Hello,

I'm trying to run a project using a Cell battery.
I can't figure them out though.
the CR2032 is about 200mAh, but it says Max Cont Discharge current is 4mAh. Does that mean I can't draw more than 4mAh at a time?
I don't get what this Max Cont Discharge current means.


I need to draw about 30mAh or so.
I don't care if it doesn't last very long. A few hours is good enough for me.

Any advice?

[SOI_Sentinel]

Ok, I found a different datasheet. Anyway....

The lithium coin cells are meant for backup and really low power draw applications. The datasheet I dragged up...
http://www.codix.hu/nagyker/products/li ... cr2032.pdf
Mentions max recommended draw at 4mA, pulsed (aka intermittent) at 12mA.

This isn't uncommon. Most batteries will show much lower lifespans as the current draw increases. However, most rechargeables are by chemistry high discharge rates. This doesn't work with your common coin cell. There's even a possibility that the cell (if you chose to run your app off a CR2032 still) will rupture and ruin your project due to the high discharge rate. I haven't tried anything of that high a current off a coincell, so I can't say how long it will last in a practical matter.

If that current rate is constant, you're looking at needing to parallel 8 coins to match it. Hearing aid batteries are no better (Zinc-air). You're probably going to have to look at camera style lithium batteries or just break down and use a pair of AAA's.

[chromatech]

all I have to say is:


well that sucks

What am I supposed to do now?
I need to use a small battery. I guess I will break and use AAA's.

I have to talk to my advisor about this.

Thanks for the notice.

[Philba]

how small does the battery have to be (or should I say, what's the largest you can tolerate).

Anyway, there are N batteries which are stubby AAs. You can get some pretty interesting shapes of Li-Ions.

also, you might want to go back and sharpen your pencil on power requirements. lots of tricks to cut the fat out.

[chromatech]

Well to cut the fat out, I don't think its really possible.
I'm using the nRF which requires at least 10mAh. I'm using a PIC which is only 350uA. Also an analog circuit along it takes about 16mAh, which I could reduce, but it still won't work on a regular Cell Li.

But I will look into the N batteries.

[roach]

You could try a cell-phone battery. They're typically 3.3 - 3.7V, with 800 - 1400mAh. I've used a nokia replacement battery BL-4C in previous projects. Very slim, 720 mAh. I don't know what the max. continuous discharge is, though...

You can get one here

[leon_heller]

You could try a cell-phone battery. They're typically 3.3 - 3.7V, with 800 - 1400mAh. I've used a nokia replacement battery BL-4C in previous projects. Very slim, 720 mAh. I don't know what the max. continuous discharge is, though...

You can get one here

A similar battery is used in a little hand-held radio transceiver I've got. It's probably delivering over 1 A when transmitting at the maximum power level.

Leon

[chromatech]

that would be a good idea.
However 3.7V (from the old cell phones that I have) is too small for the voltage regulator. It need a little more than that produce a stable 3.3V

I think I'll settle for a 3 AAA's.

[roach]

I've sucessfuly used 3.7 volt supplies with 3.3v components int he past. How sensitive are your components? You might not even need a regulator.

[SOI_Sentinel]

Chromatech, ever considered something like this?

http://www.microchip.com/stellent/idcpl ... e=en010593

You'll still need AAA's, N's. or a LION cell, but this will take care of stabilizing and keeping your voltage level from start to finish. I've seen single use larger LION cells (photo, IPASS, computer backup battery, have a Radioshack where you live?) that MAY be able to give you your power requirements without need to charge. They're quite a bit more expensive, so be warned.

[RonnyM]

I work in a watch repair place for my real job. I have gotten to play with just about every coin cell/button cell there is. If you need some current, look at the Eveready 357s. They can be stacked, and easily supply you with 10 mils continuously. There are other Lithiums which will supply the current, but they are larger in size. the CR 2450 comes to mind. You will find them in Pharmacies for medical device use. Not cheap. If you use a Lithium Ion @ 3.7 volts, put a schottky in series. It will drop it about .25 volts without much fuss. The Zinc/Air batteries are very cool with a huge capacity, but the current draw is not great, and you actually need a fresh air supply for them to operate (a pin hole in the batt compartment will do it.) DO NOT SOLDER TO ANY OF THE ABOVE!!! Your better off sitting by a campfire with a sealed can of cream corn in the coals. Yes, I've done both, but in all fairness I didn't know about the corn!
BTW N cells are becoming scarce.

[wheeler]

Just get creative! If you use a CR2032 with a big cap (say 22uF - you can get one in a 1206 surface-mount package from Digikey) and transmit in short bursts you can do it. Either cut the analog circuitry's current requirements (look at the Microchip MCP6041 - 0.6uA quiescent draw) or just put a FET in line with all of the analog components (so the PIC can disconnect it from VCC) and never use the analog circuitry and transmitter at the same time.

I have a project right now that will operate off of one CR2032 for over two years and uses an ATmega48 and an IA4220 to transmit (it draws ~11mA with everything on, which is practically never, but does happen).

If you went with something bigger such as a CR2450 it would be even easier.