Battery Power - Polymer Li-Ion (Poly-Li)
Paul Sr.
Posts: 435
Has anyone ever used or have any advise regarding using this type of battery for projects - like on a BOE-BOT or home brew unit using BOE?
I have been looking at various sites and I am considering a 7.4 1050 pack (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2364) and charger(http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1230) but I would like to know if others have been successful / satisfied using these newer technology batteries.
As always, any suggestions or recommendations would be welcome and appreciated.
TIA,
Paul
I have been looking at various sites and I am considering a 7.4 1050 pack (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2364) and charger(http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1230) but I would like to know if others have been successful / satisfied using these newer technology batteries.
As always, any suggestions or recommendations would be welcome and appreciated.
TIA,
Paul
Comments
I bought the 2450mAh version
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1224
but haven't used it yet.
Kenny
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·1+1=10
Post Edited (Paul Baker) : 3/9/2006 9:09:58 PM GMT
Thanks for the feedback
I am aware that I also need to get the board - which I certainly will - interesting that they only list 1 amp or 5 amp boards - can't decide which to buy!
Decisions, decisions!
Paul
I bought a second one at a local hobby shop. For some reason, I used it about 4-5 times and it swelled up like a pregnant guppy.· I was quite disappointed as I had paid a lot for it, but the literature is quite clear about explosions from ignoring the warning signs.
So, I disposed of it and still have the one.
They look the same, but I still wonder why one went bad so quickly and the other seems fine.· From looking at the site, I do see that there are 'protector boards' which seem like the best way to protect your investment as well as yourself.
I think that I expected the same charger to work for both batteries, but it really wasn't right for the second one.
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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) : 3/10/2006 3:31:56 PM GMT
Yes. Li-Poly batters have a bad habit of doing that. It's the one thing that the designers still have not completely worked out, even for large packs. However the ones that the iPods use seem to be working. Even though they've got a lousy charge/discharge cycle. Much of this I learned from reading a large amount of good books on robotics, never actually reached the point of doing something with the gadgetry until now.
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Buck Rogers
www.gregg.levine.name
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·1+1=10
Paul, Thanks for the input. I do understand what you are saying, but my rusty old skills aren't at (or anywhere near) the level yours are at so my tendency would be to select the appropriate protection ciruit board that the vendor (batteryspace.com) lists . From what I have read, they pretty much conform to the important points you mentioned. Would you feel unsafe using theirs vs. your own brew?
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How comforting!!
Kidding...
Thanks, Paul
That's why I bought the pack with the Protection board already installed. For awhile there, they were having you sign a disclaimer saying that you know what you are doing or they wouldn't sell you the batteries. They've got so many warnings about these batteries that I was afraid to buy one
Kenny
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Yep, that's what I did.
Thanks!
I just came back from the local electronics supply, lots of single 3.7 volt lithium cells, but no protection boards. And no single cell chargers. I suppose they are just trying to cell replacement products.
But, you can get very good single, double, triple cell chargers via the R/C Electric airplane crowd. These come in adjustible outputs too. So you can handle an array of sizes.
I have a low-voltage device that was originally intended for a BEAM robot, but it seems just ideal for keeping Lithium batteries above their 2 volt per cell minimum. The BasicStamp shuts down at 4.5 volts, so the Protection Board [noparse][[/noparse]at the battery] seems like the best way to avoid trouble in multiple cells.
In a single cell appliction, you can run an SX-28 at 3.7volts with EEPROM and a lot of other logic. So, you would merely need to detect short circuits, reverse polarity [noparse][[/noparse]?]·and low voltage. It think I could do that on my own.
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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) : 3/11/2006 10:23:51 AM GMT
Any idea what I might be doing wrong? The funny theing is had never used them due to time-constraints...???
Rafael
I think they have about a 3year shelf life, even if not used.
Obviously the swelling is caused by pressure. The pressure is caused by a change from liquid to gas.
Sometimes gas is created by too high a charge rate. With lead acid, they are designed to reabsorb some degree of gas, but when you go over the limit it may not be possilbe.
The real question is whether they are full of gas in a charged state or discharged state.
If already charged, you might just use and watch them to see if the problem goes away.
Stlll, it is far safer to buy new fresh product than to use old doubtful ones. You may of bought surplus that was beyond its useful life.
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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 8:09:52 AM GMT
Sealed lead acid batteries can swell for a number of reasons, and many of these reason can be inter-related and inter-woven. One may be caused by another, or one may cause another. Unless one knows the entire battery history, and the environmental and charging conditions, it would be difficult to come up with just one answer. However, here are the general causes of SLA battery swelling in my experience:
Internal pressure too high, vents clogged - SLA cases swell or bulge when the cell vent valves maintain an internal pressure that is greater than the outer (atmospheric) pressure. These vents are designed to release the gasses formed during charging or a high rate of discharge. If/when they fail to do so successfully, case swelling will result.
Exceedingly high temperature - Extremes of temperature, caused by ambient conditions, too high a charge rate (either during regular charging or top-up maintenance), or too high a discharge rate (shorted terminals) can cause the entire contents of the SLA to over-heat and expand. Conditions like these can cause a fatal battery explosion!
Thermal runaway - Battery is continuously charged at too high a rate, which causes over-heating. Due to this over-heating the internal battery resistance will change, and may in turn cause an increase in the charge rate. This can then become self-feeding, and if/when it does, swelling of the case can and will occur, ending in the eventual destruction of the battery.
Over-extended life - Very old SLA batteries may self-destruct if they are not disposed of in an appropriate and timely fashion once they have reached their normal end-of-life. There will be a breakdown of the internal components, particulaly if the vents have become sealed over time. A seemingly DEAD battery can become quite a dangerous LIVE MESS! This is one reason why SLA batteries are usually dated in some manner.
I'm sure there are others as well, but those are the reasons with which I'm most familiar. My own extended service experience with them has been in emergency lighting, fire and security system, and UPS system applications. Other applications may differ as well.
Regards,
Bruce Bates
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Lithium batteries seem to be more forceful than most due the their higher 'energy density', but all contain caustic and toxic chemicals.
When they get fat, they should be recycled.
I posted in another thread that Lithium batteries also suffer permanent damage from just getting too hot. After that, they hold less charge. It seems directly related to the Lithium Polymer chemistry.
So you might want to use a DS1620 chip [noparse][[/noparse]from Parallax] to turn off your charger if your batteries are getting too warm during unattended charging.·[noparse][[/noparse]The surface of the chip has to touch the batteries being charged.]·Over 30 degrees Celcius is probably unneeded and should be·avoided.·Lithium certainly gets a reduced life at 40 degrees C.·I think the same thing is true for NiMh and NiCads, but they are much less expensive to replace. A good 7.4 volt Lithium battery can cost $60USD!
Vents can become clogged on old batteries by storing batterys upside down or on their side. You just never know who did what before you got it.
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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 9:52:42 AM GMT
Unattended charging LiPo batteries is really not a good idea. One overcharge can destroy the battery, and that ignores the possibility of explosion.
Like many technologies that "push the envelope", when used properly, they are safe and provide significant advantages over competing technologies. When not used properly, they will fail early in best case. In worst case, they can be dangerous.
Also note that one over-discharge below the "threshold" voltage, and the battery can/will become useless.
As indicated in other posts, the R/C aircraft world has lots of info and products available on these.
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John R.
8 + 8 = 10
I've read this thread with interest. Customers have often asked for a better (rechargable) power pack for the Boe-Bot. On Tuesday I·toured the·Sunda Battery in Zhuhai, China (http://www.zhxunda.com/). They've made an offer to make us a LiPo battery pack/charger for the Boe-Bot, designed to our specifications. Almost all of my battery experience is with lead acid except for the R/C airplanes, but the quicker LiPo charge rates offer more satisfaction for robotic products. The Boe-Bot chassis has a substantial space for a larger battery pack with more amp-hours of supply storage.
I'm interested in what you might think of this idea. A few pictures are below.
Ken Gracey
Parallax, Inc.
I'm actually more interested in a charger for·NiCd and NiMH only.· I have one that comes from China but it takes 14 hours to fully charge the batteries.· I'm thinking of building one that will take only 30 mins to an hour.
I hope I don't overcharge the battery which is why I want to use the BS2 to monitor the current and the voltage of the battery.
I'm not a boe-bot user, but have been exposed to LiPos directly via electric helicopters (These things are marginal for outdoor use in Wisconsin, unless you are really good with them). I've got one that came with a automatic "Balanced" charger, and one with a "manual" charger (the directions say "charge until warm"). I've been careful with mine, but the hobby shop is surprised I haven't ruined the battery. Based on all the other parts I've had to purchase, he said most other users would have needed two or three batteries by now because they don't monitor the battery during charge (you'd think they'd learn, wouldn't you?) He didn't have reports of any explosions, just swelled and disfunctional battery packs.
I would strongly recommend some type of "automatic" charger in order to ensure reliability (and safety).
Are there any problems running servos with 7.4 Volts (as opposed to7.2 Volts)? I've seen some newer servo specs list 7.4 volts, and realize the difference is "trivial", but am curious.
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John R.
8 + 8 = 10
I believe 9 volts DC or higher will 'kill' the electronics inside a servo.
7.2 volts is a common rechargeable battery pack voltage. This is a little 'hotter' than the 6 volt design limit -- but apparently the electronics inside most servos will handle this. The problem with this voltage is 'sparking' and heating inside the electric motor inside the servo, so its life will be reduced. By how much I don't know. I would expect 7.4 volts to have a similar effect.
The key is to use a charger designed for Li-Po use.· The only charging problems I personally have seen are when someone tries to use a NiMH or NiCad charger on Li-Pos.
I have a dual cell GWS 7.4 V 2200 mAh pack running my Boe-Bot.· It is lighter and smaller than a 4 cell AA pack, and last longer.
As for the potential problem with servos running on 7.4 V, simple fix.· Run the servos on the regulated 5 VDC.
T!
Their smallest is a 3.6V/100mAH, and it's the size of a small postage stamp.
(It'll go into a RC-blimp when I get the time to play with it and locate someone who sells Helium around here.... ) They also have a postage stamp sized charger for it.
Their 2000mAH/3.7V cell is rated at a 2C discharge and only weighs in at 36grams...
As one review states, "Two of these guys pushed 8 servos 'simultaneoustly' without even flickering'
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