lithium battery operation at 3.3 volts
LoopyByteloose
Posts: 12,537
I just returned from the local electronics supply and there are a·lot of 3.7 lithium batteries in stock.
I know that they need a special charger to avoid overcharge·and you need to avoid discharging below 2 volts, but they seem very attractive for running 3.3 volt -5.5 volt logic levels on the SXes.
After all, they are small.· They recharge quickly.· They have a lot of power in them.
The problem is that I couldn't find a 3.7volt charger anywhere in the store.· Do I have to import an expensive one, or is there an easy DIY approach?
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
I know that they need a special charger to avoid overcharge·and you need to avoid discharging below 2 volts, but they seem very attractive for running 3.3 volt -5.5 volt logic levels on the SXes.
After all, they are small.· They recharge quickly.· They have a lot of power in them.
The problem is that I couldn't find a 3.7volt charger anywhere in the store.· Do I have to import an expensive one, or is there an easy DIY approach?
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Comments
but I find it hard to believe you cant find a local source, even if it comes down to hacking a charger for a device that uses a single cell lithium battery (ipod, many cellphones, etc).
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·1+1=10
-Dan
·
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·1+1=10
If You can't find a source, try
http://h1071118.hobbyshopnow.com/products/description.asp?prod=EFLC3000
I know, shameless plug, but I work for these guys part time!
http://pdfserv.maxim-ic.com/en/ds/MAX745.pdf
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John J. Couture
San Diego Miramar College
Google research did point out that ALL lithium batteries are temperature sensitive. Heating causes permanent damage. And the Heat can either be from the ambient surroundings or from excessive rate of charge. Over 40 degress Celcius really shortens the useful life. So an additonal thermal shut down might be a very good idea if you are not going to be present during the charge cycle.
This looks like an ideal BasicStamp project -- measure temperature, sense a voltage limit, provide a charge timer, and control a current limiting charge circuit.
Sadly, the shipping for an IC probably costs as much as buying a whole charger locally.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 3/12/2006 8:14:18 AM GMT
Is there a datasheet available on the Li batteries? They might have a small circuit for charging it. The temp sensor sounds like a good idea. I seem to remember a circuit in a recent magazine with a note that "next month" they will be adding the ability to charge any voltage battery (because it has some kind of feedback loop). I can't seem to find it, but if I run across it again, I'll pass it along.
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John J. Couture
San Diego Miramar College
http://www.seattlerobotics.org/encoder/200210/lithiumion.htm
Articles and circuits on battery chargers
http://www.discovercircuits.com/B/batt-chrg.htm
THIS article looks interesting (by National Semiconductor)
Using USB port to charge your Li battery
http://www.national.com/appbriefs/files/AppBrief101.pdf
Hobby Projects site
http://www.hobbyprojects.com/B/battery_chargers.html
Pulse Chargers vs. Linear Chargers
http://www.zetex.com/3.0/appnotes/apps/an40.pdf
Google Search
"Lithium Battery Charger Circuit"
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John J. Couture
San Diego Miramar College
And the label is in Chinese. Now you know why I try to rely on engineering principles.
With Lithium cells, I have noticed voltages rated in multiples of 3.7 volts and multiples of 3.6.
Since the electrolic physics cannot change, I suspect the 3.6volt devices do have protect circuitry that is causing the voltage drop.
Yes, the more I think about it, a thermal cutoff is a very good thing and should override all other charging functions. This was very clear in what I read, higher temperatures do irreversible damage to the Lithium battery chemistry.
I will go through all you posted with great interest to see if they directly address the 'thermal problem'.
The battery protector circuits are often not clear about thermal shutdown. This concerns me.
Since the DS1620 (from Parallax) can be programed by a BasicStamp to operate independently as a thermostat, you can just connect it to a relay or other shutdown circuit. I see no one really discussing thermal shut down in their Lithium chargers, so this might even have a substantial market for R/C crowd that buys and fast recharges many Lithium batteries in the field.
The battery could sit face-to-face with the IC's surface. [noparse][[/noparse]Maybe I am going to make one of you wealthy, but there it is - a good idea with a market.]
Having bought a 7.4Volt cell for $60USD and having had it overheat after 4 or 5 charges; and then swell up to the point that I feared real bodily harm; I can see where others would want better control for their investments and safety.
There are alternatives. My Nokia just went haywire. If I feel that it is not economical to repair, I wil use its Lithium batteries for projects. And I will use the defective phone for a charger.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 3/13/2006 7:54:36 AM GMT
If you are interested in incorporating lithium ion batteries to your micro design or have the need to log gps data points to an sd card besure to check out the links below:
Storefront:
www.hbtrainer.com
Blog:
http://sdgpsdatalogger.blogspot.com/
-Dan
·
Use extreme caution when using Lithium batterys.
Jason
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He who dies with the most toys wins!
It seems that there really is little reason to fool with Lithium unless you need the absolute minmums in weight or the quick recharge or both.
It is a very interest phenomina, teh Li battery is much denser in the amounts of enery that the more conventional batteries.
That energy density is what makes it potentially unstable.
It seems the solution is to make very thin cells of retangular sizes.
This physical configuration seems to provide a package that will have a lot of room to swell rather than burst or explode.
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