PDA

View Full Version : What is the difference between 3V and 3.6V CR123 Li-ion?



XNOR
08-31-2006, 06:10 AM
Greetings,

I am thinking about building a small robot base and am looking at what batteries to use.
From looking at the Parallax Penguin project, it looks like two CR123 batteries in series
(for a total of ~6V) would be a nice size.

While looking for rechargeble CR123's, I found two different types of CR123 Li-ion batteries:

www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1641 (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1641)

and

www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1387 (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1387)

It seems that the batteries and their respective chargers are not compatible or interchangeble.
Why is that? Are these different Li-ion chemistries? Which type should one use? http://forums.parallax.com/images/smilies/confused.gif

Thanks for any insight. http://forums.parallax.com/images/smilies/smile.gif

P.S.: If anyone has any other ideas for powering a small robot (Penguin sized),
please feel free to throw in your 2 cents. http://forums.parallax.com/images/smilies/wink.gif

metron9
08-31-2006, 06:54 AM
Answer 0.6 volts, they are smaller in physical size, charging a 3V with a 3.6volt charger is not good, when batteries are in series the 0.6 volt difference adds up to over voltage for devices that are designed to use 3V batteries in series.

I think that's about it.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think outside the BOX!

RDL2004
08-31-2006, 10:33 AM
Something doesn't sound right about that to me. I thought cell voltage was chemistry dependent. I don't know that much about batteries, but isn't that like making a 0.6 volt NiCad? I'm wondering if the magic is in their "special charger"?


They said...
Warning

* Peak voltage of 3.0V Li-Ion will be 3.9 V after fully charged. Once loaded, cell's voltage will drap to 3.6 - 3.2V
* No PCB built in the cell. Please never overdischarge battery below 2.6V/cell, and always charging the battery immediately after use via a smart charger.
* Must use 3.0V RCR123A battery charger included to charge these batteries, please do not use other charger, include any 3.6V Li-Ion bttery charger, which can not make 3.0V Li-Ion battery fully charged

Loopy Byteloose
08-31-2006, 07:02 PM
I agree with you RDL2004, battery voltage is generally chemistry dependent.
Nonetheless, we see a range of Lithium Ion batteries from 3.0v to 3.6v.

My guess is that in some cases[but not all], on-board charge monitoring and regulation accounts for the voltage difference. Some manufacturers actually include a charge protection board in the battary case. This seems an attempt to avoid what Song/Apple/Dell are going through.

Metron9 is intuitively right, but heat rather than mere voltage is the real destroyer and the higher voltage increases the rate of charge. thus the heat accumulation [which translates into a chemical reaction] is destructive.

Also, it seems all batteries prefer to stay at their top end for longer life. With Lithium, the bottom line is 2.6 volts,; with lead acid, it is 50% of the rated voltage.

Here, I suspect that the chemical difference are due to what makes the 'ion' in the Lithium Ion. The vendors are not telling us all, but calcium is one common additive.· In fact, they may both be 3.6volts, but have a different power curve and different charge rate requirement [My guess is that the 3.0v would require a slower charger].

So you have quite a design dilemma, two 3.0 volt batteries might allow you to avoid a voltage regulator, but certainly have less useful life. Two 3.6volt batteries provide more useful life, but the voltage regulator will burn up 20-30% of that extended life. If the figures are about the same, I would probably go with the 3.6 batteries as they are possibly more durible.

A much better solution -- forget Lithium and forget button cells.
We are recently seeing NiMh batteries with 'lithium-similar' power capacities. A few years ago I was buying 900ma/h AA cells. Now you can get 3000ma/h AA cells and the 1.2 volts allows you more choices of design. Instead of 3.0, 3.6, 6.0, & 7.2; you have 3.6, 4.8, 6.0, 7.2. I suspect that 4.8volts is optimal.

About the only significant advantage the Lithium offers is quick recharge. The prices are sky high!· I use them in my cell phone and PDA. My charging turn around is a few hours rather than the 10 hours with NiMh. But if you are using AA cells, you can easily swap sets and charge one set while another is in operation.
I know the CR123 are not button cells, but at 650ma/h they fall short in total payload. And $23USD for a battery makes me queasy.

Button cells are really not good choice for robotics. While smallest, robots may consume most of their power in a few minutes of operation [due to motors]. They really are meant for hearing aids, small calculators, and small clocks. Everything electro-mechanical is a function of available power and unless you have found a way to beat gravity and friction, you need more power reserves.

The Penguin pushes the limits of smallness and that is its purpose, but as you can see there are other design factors that may really make for considering·a·broader set·of design criteria.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan


Post Edited (Kramer) : 8/31/2006 11:17:23 AM GMT

Gadgetman
08-31-2006, 08:00 PM
I recently got hold of a 3-motor RC Helium blimp(the 'flying saucer' model) and I intend to replace the battery in it with THIS 100mA (http://www.sparkfun.com/commerce/product_info.php?products_id=731) cell from Sparkfun. (and add a Propeller and an ultrasonic sensor or two, and possibly even a compass chip)

But This, 860mA (http://www.sparkfun.com/commerce/product_info.php?products_id=341) one, at $6.95, isn't too bad, either...

And with a $14.95 (http://www.sparkfun.com/commerce/product_info.php?products_id=726) charger, you're all set...

They do have cheap 2000mA batteries, too...
(Can't be bothered to add more links... )

Now I just need to track down a supplier of Helium...

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Don't visit my new website...

XNOR
09-02-2006, 01:31 AM
Thank you for all the info and suggestions.

I wanted to use a standard battery size,
so that's why I was thinking of using CR123's.
Initially I thought 4 AAA's would work, but that's
a little too big (and heavy).

From reading Kramer's reply, MiMH does sound like
the better solution. I'm thinking maybe 2/3 or 1/3
size AAA's would do the trick.
(I haven't yet found a place to get those.)

Thanks again.

(edited)

Actually, a 9V battery would be the ideal size.
How wasteful would it be to use a voltage regulator to bring it down to 5V?
For the small motors it might even have to go down to 4V (I'm guessing).

Post Edited (mprobo) : 9/1/2006 6:53:11 PM GMT

Loopy Byteloose
09-02-2006, 03:32 AM
It is tough to get much smaller than the AA size with reasonable output.
That is possibly why the Penguin used the CR123.
Still, I have seen AAAs @ 900ma/h vs. thev CR123's 650ma/h.
Much of it is the choice of servo motors defining the design.

I spent a lot of time thinking about smaller batteries [like the AAA] and found that the only way to
really do it is to go to a microcomputer that allows a 5.5 volt maximum and 3.3volt minimum system without a voltage regulator. You could do that with the SX28 chip, have a Tidlen H-bridge [6 transistors glued together and wired in a small block], and some tiny gearhead motors [try www.solarbotics.com].

The device would run the SX-28 from 4.5 to brownout at 3.3.
The motors would be happy in that range too.
You could program in SX/B if Assemby is too difficulty.

The 9 volt battery is one of the least optimal small batteries. You dump 30% of the power through the voltage regulators.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan


Post Edited (Kramer) : 9/3/2006 12:40:44 PM GMT