Li-Polymer batteries for headphone use?

[Dougigs]

My mobile-phone company sends me and my wife a new phone each August, and every year the batteries get smaller and more powerful.

This year's is 3.6 v, 900mAh. It measures 4.8cm x 3.4cm x 5mm thick (1.75" x 1.3" x 3/16") -- it's a Sony Ericsson BST-37 battery (from their K750i phone).

You could fit at least 4 of these into a mint tin with circuits (see pic)... or a lot more into a slightly larger case with the necessary smart-charging circuits.

Has anyone played with these? I have 2 batteries from last year's phones (3.6v @ 770mAh, 6cm x 3.5cm x 5mm) that I might use for experimentation; is it easy to obtain or to work with charging and power-management chips for these?

These would seem to beat the pants off conventional rechargables in terms of bang per surface area, if we could just harness them... I'm very new to battery power-supplies, though, so perhaps there's something obvious I'm missing. Let me know if you folks have already tried these things and dismissed them out of hand...

Below is the battery 3.6v 900mAh battery next to a MINT amp and some other familiar items for scale:

 

[Dougigs]

Ok, there was a thread on this topic in March, which left the topic a bit incomplete (link below).... Several designers pointed out the challenges of lithium-based cells, which are fairly well known -- i.e., you need a "smart" charging system to prevent overcharge and discharge conditions, and perhaps to initiate a full discharge before charging begins. This is not terribly exotic -- I note that Elektor has published several good circuits and sells a couple PCBs for charging and managing power on these cells... I can't remember if they're designed with higher-voltage series-connected applications in mind.

The tiny, 8-pin ISL6294 chip, which is the standard phone-battery management chip, is designed for single cells, and would probably not help us much.

Much cooler for headphone amps would be the ISL6253, designed for charging up to 4 li-polymer cells in series for laptops and PDAs... this is not a chip for the faint-of-heart, though -- a hefty VLSI monster. But it's a pretty cool device, and one does dream of jamming it into a little Hammond case with a string of mobile cells, and charging the whole rig with a 16v laptop adapter...



Original thread:

http://www6.head-fi.org/forums/showt...ght=li-polymer

Elektor charging PCB:

http://www.elektor-electronics.co.uk...d=28&art=50216

Elektor tiny LiPo charger:

http://www.elektor-electronics.co.uk...d=28&art=52826

Datasheet for chip: http://www.intersil.com/data/fn/fn9117.pdf

 

[guzzler]

Li-Poly would be great, there's not especially widely available just now. The HeadAmp AE-1 uses those batteries. The Elektor circuits are usually fairly bomb-proof as well, although series circuits are a little trickier. Maxim tend to have a lot of battery management chips in stock, well worth a look there

 

[Dougigs]

Interesting about the headamp -- it claims an output swing of 6.5v in each direction, which would indicate a fair stack of cells.

I've just noticed that Farnell here in the UK has started carrying li-polymer cells...

This is the datasheet for the 3.7v, 1000mAh cell (13 pounds 30 pence -- i.e. $25):

http://www.farnell.com/datasheets/59954.pdf

and here for the amazing 3.7v, 2000 mAh (a very unfunny 24 pounds each):

http://www.farnell.com/datasheets/59953.pdf

So I think I'll play with used mobile-phone batteries until I've got the technology really nailed -- that's some serious money! However, these things do seem to have absolutely perfect specs for low quiescent drain, high current availability, fast recharging, long life and of course small size...

 

[guzzler]

I got a letter from a Varta battery rep a few months ago in the middle of my exam period. Obviously I had more important things on my mind, so I completely forgot about it. They were offering an evaluation pack with 5 batteries and a charger for free; gutted I didn't accept with those prices

I'm back at uni in about a month, so can't really get involved in any sort of development until next summer. Keep us informed though

 

[morsel]

Lithium polymer batteries are almost at dangerous as lithium ion batteries. They are little bombs, waiting to blow up in the hands of unqualified hobbyists. They are not suitable for DIY projects.

Lithium battery explosion:

http://rcstuff.us/battery/lipo/images/LipoFire.wmv (4.5MB)
http://rcstuff.us/battery/lipo/images/LipoFire.mpg (3.3MB)

Photos:

http://rcstuff.us/battery/lipo/lipo_DNA.html

For further information:

http://www.google.com/search?q=lithium+battery+explode

 

[Dougigs]

Yes, well there is that. Perhaps best sticking to evaluation boards and pre-designed circuits with these things. Heaven knows I've blown up a great many lesser components in even simpler circuits....

(He said, slinking back to the the comparatively safe world of line-powered amps with kludge-wired 600-volt DC supplies driving red-hot glass cylinders. Fewer surprises there.)

 

[Born2bwire]

Gotta defer to Morsel on this one. I've worked with Lithium Polymer batteries on a research project. In addition to the higher costs, the Li-Poly are not as resilient as Li-Ion. They are very easy to over discharge, overcharge, and other problems. You would need to make a very concrete charging and power monitoring circuit. Probably the most annoying thing about working with them is the fact that if you discharge them below a nominal voltage, the batteries are worthless. On the 12 V packs we were working with, a discharge below 10 V would destroy the batteries. If I recall correctly (and if my coworkers were correctly informed), the danger arises because hydrogen gas will be released during the discharging of the battery. If they are discharged improperly (like below the minimum voltage) a lot of the hydrogen will be released and will be unable to be reabsorbed by the battery. The battery packs got puffy and bloated from all the gases. A plus though is that we were able to use lithium ion charging chips for the charging boards we designed. So it appears that the lithium polymer batteries have some of the same charging characteristics and requirements as lithium ion.

 

[guzzler]

The new charging supervision chips are very reliable, as you'd expect. Designing a system that cuts out the battery when the level drops below a certain voltage isn't too hard either. The picture sequence on that links is a VERY extreme example as well; charging a fully charged battey at one amp with no control mechanism. I'd be surprised if a NiMH didn't show a bit of damage after that amount of punishment, even if it doesn't explode.

I don't think they should be excluded on the basis that there are possible dangers and difficulties involved in using them. A lot of reading and careful design would be needed, but by no means out with the ability of some

 

[tangent]

Quote:

Originally Posted by guzzler The new charging supervision chips are very reliable

Yes, but the batteries aren't always so reliable. Look at how many cell phone and laptop battery recalls have happened in the past year. If Dell, Apple and Nokia can all be stung by lithium battery problems, what makes you think you'll be immune?

 

[Dougigs]

The issue of shelf life does concern me. I've never had a laptop battery pack last longer than a year (i.e., after a year its charging life drops in half, and I have to spend $200 of my company's money for a new one, or get a new laptop). Now, NiMh batteries only have a useful life of about a year (if you use them regularly), but the sums involved are much, much smaller... if I'm spending the eqivalent of US$200 on batteries for a headphone amp, they'd better last longer than a year.

(p.s., speaking of battery life, regular alkalines actually recharge quite nicely -- if you use them in an NiMH 'smart' charger, they'll recharge almost as many times as bona fide rechargables, i.e. for almost a year. The performance drops off more dramatically, but it's dropping from a might higher MaH point to start with, so it's not a bad tradeoff. Yeah, there's a greater leakage risk, but not a huge problem if you make sure your batteries are located very separately from your circuitry, and you occasionally peek in to make sure there's no goo. I've got a pair of copper-top 9v in the charger right now).

 

[setmenu]

Quote:

Originally Posted by Dougigs , NiMh batteries only have a useful life of about a year (if you use them regularly),

Really?
I thought their life was determined by the number of cycles they endure before a significant reduction in capacity occurs?
The above of course dependent on how the are treated regards correct
charging/discharging.
Usual quoted figs for number of useful cycles seems to be in the region of 4-500.


.

 

[Frenchman]

I admire the protective spirit you guys have, but it does become a bit tiresome.

You speak of recalls. These recalls have been because companies like Apple buy their batteries from distributers. These companies then buy cheap batteries from second rate manufacturers and claim they are good ones. They charge Apple the same amount but make more because they bought cheaper batteries. Unless you plan on buying thousands of them, you won't deal with these companies. The world is switching to Lithium based rechargeable chemistries, so a few spotted cases with highly non-typical circumstances don't really lend a lot of weight to the idea they're "dangerous."

If you plan on using these batteries for a headphone amplifer or something, then these batteries are ideal. Plug them in every night and you'll have batteries that will last you forever. Many small discharges are very good on these batteries, so it should work well.

These batteries don't require especially special charging circuits either. Perhaps back when these batteries first came out it was something to worry about. Now, you can get chargers that do all the work for you. Provide a DC supply to the charger and away it goes. About the only downside from the hobbiest point of view is that these chargers are usually surface mount chips. Quite annoying. But if you can stand the surface mount, you can easily implement these designs.

Now, the BEST part about morsels post: his google search. Let's look at this. First result, batteries that won't explode. Next, a product safety datasheet.... for a NON-RECHARGABLE BATTERY. Next, don't recharge non-rechargable batteries. Next, another instance of substandard batteries exploding. Next, don't recharge non-rechargables. Blah blah blah on that same thing until the end. My favorite is the last result on the last page. I'll extract my favorite lines...

Lithium batteries have earned a reputation for being dangerous.

"we have not been able to get any of our Li-Poly batteries to explode"

Yes, quite a good google search for how rediculous these hypes of danger are. Thanks for helping people realize there isn't much to using these batteries. I am currently using 4 high discharge Lipo packs, each delivering 7 amps for 20 minutes. I charge them all the time with NO problems. We are also using Lithium Ion and Lithium poly batteries for several systems using both commercial chargers and chargers we have made ourselves. We are hobbiests for the most part. We haven't had any problems. Additionally, charge protection circuits are also small and VERY easy to use.

Don't be scared by these people. Why they have a unnatural fear of these batteries is quite beyond me. Tangent says "Look at the big guys. They're been stung!" Yes, look at how many batteries are affected out of their total amount of product. Now, I've also heard about electrolytic capacitors having problems on major manufacturers motherboards. I believe this means electrolytic capacitors are unsuitable for hobbiests! Well, we all know this is rediculous.

Time to step out of the dark ages.

 

[morsel]

Frenchman, you may be competent (although that remains to be seen) but this forum is full of people without the engineering background or common sense to work with hazardous technology. Many have never seen an oscilloscope in real life. Those who know they know what they are doing will do as they please. I rest my case.

Oh, and nice job of selectively screening the google search results you reported on... not.

 

[Nisbeth]

FWIW, I agree with Morsel. If you have the skills to handle Li-Ion batteries properly they are a great idea, but if you don't, you could get a few nasty surprises. IMHO your examples are no better than Morsel's, because just because it is possible to run a Li-Ion in "way out of spec"-conditions for extended periods of time, doesn't mean it's safe (in fact, unless you have extensive test results to back you up, you could just be considered very luck

) Also, asking a battery manufacturer directly if they have serious quality issues with their products might not generate a totally honest reply...

You would most likely get the same sort of reply if you asked about designing an off-line SMPS (= Don't!) Does that mean off-line switchers are difficult and dangerous? No, not if you know what you are doing, but if you are having trouble assembling a headphone amp kit, you shouldn't do mains wiring in the first place (and besides, breadboarding a functioning SMPS is easy enough, but designing and building an SMPS that is safety- and EMI-approved is not)

(EDIT: I'm not implying that you do not have the necessary qualifications, but like Morsel wrote, many in here do not)

I'm not trying to derail the discussion further, but prudent advice to be careful shouldn't be dismissed that easily. Depending on your confidence in your own abilities you may of course choose to ignore said advice, but I must remind you that overconfidence in your own abilities is a very common cause of death

/U.