where can i get small powerful batterys??

[chillysalsa]

In a CMoy, the difference that anything above 10V will make may not be significant unless you are driving >300ohm headphones.

 

[Syzygies]

Quote:

Originally Posted by __redruM Most highend consumer portables now use lithium based batteries. Cell phones, camcorders, ipods. Are there regulations against charging an ipod on international flights?

True, and 3.7V prismatics are a very appealing idea. However, it's much easier to blow up a lithium battery doing something wrong, and we all make mistakes. Ever toast a DMM beyond repair? Even major brands that we know well have had recalls for fire risks on these, not something I've ever heard of for NiMH.

Remember what caused that flight to face-plant into the Florida swamp? It probably cost a thousand deaths in unnecessary traffic fatalities, by setting back budget air travel several years and pushing working class families back onto the highways.

If I were running the TSA I wouldn't want homemade lithium battery packs on board planes. I don't need to bring one on board.

 

[Frenchman]

The dangers of charging Lion or Lipo are greatly exagerated. It is most certainly possible to destroy Nimh's or Nicads, and it's just as easy as with Lithium based chemistries. The biggest difference is that STUPID stuff will destroy your Li based stuff a lot easier then Nickel based stuff. To top it all off, it's a whole lot easier to charge Lithium based packs then it is to deal with the major headaches of Nickel based chemistries.

Just go look at Maxim's website and you'll find a lot of information on charging and a lot of chargers which will do an excellent and very safe job charging your pack.

You have heard a lot about exploding Lithium packs because unlike the Nickel based chemistries, the manufacturing processes are not "common" knowledge. The exploding packs are ALL DIRECTLY RELATED TO POOR MANUFACTURING PROCESSES. These are knockoff packs made at ultra cheap prices and sold to people claiming to be original packs.

No battery is immune to damage. We use milspec sulfer based batteries (D-Cells that deliver about 7000mah) because of the high energy density. Do you know what happens when you reverse the voltage through them? Not only do they explode, they leak a very toxic gas. Does this mean they are unsafe? Heck no, they have insane ratings in every department, pressure, temperature, humidity.

I am working with a guy who just built us a charger for Lipo cells. He started off from the datasheet and followed the directions. He did kill one battery but he did it because we are charging them with a really low current and the software he wrote didn't correctly handle the extremes. Of course, this was using a more advanced charging circuit. Charging circuits for single or double cells are rediculously simple. You buy a chip, read the datasheet and set a few resistors. The whole package is very small and very easy to use. That's why people switched right over to Lithium and ditched the hassles of Nickel memory. 90% of mistakes in early Lithium design were engineers used to using Nickel trying to use the same charging steps on Lithium. That's a recipe for disaster anywhere.

So the bottom line is, if you want to use Lithium, don't be scared off by the FUD. Lithium follows different rules then Nickel but all the rules are posted, so you shouldn't have a problem.

 

[Frenchman]

By the way, what do Lithium based chemistries and their charging practices have to do with incorrectly marked oxygen canisters causing an airplane to crash?

 

[Syzygies]

Quote:

Originally Posted by Frenchman By the way, what do Lithium based chemistries and their charging practices have to do with incorrectly marked oxygen canisters causing an airplane to crash?

Lithium is often used in oxygen generators, to scrub the CO2. After "playing" with the stuff in a lab, I always imagined that this contributed to the intensity of the fire. Lithium is amazing; you really should burn some, yourself. I'd recommend the same eye protection you'd use to look at an eclipse. Oh, and try this outside, away from dry brush.

Lithium batteries are listed as low-level air hazards, along with dry ice. I was stopped from bringing dry ice onto a flight once (to keep some ice cream cold) only to borrow some from the crew. Lithium batteries are a lost cause, too common in consumer devices to keep off planes, though in India after 9/11 they actually separated my alkaline batteries as a standard practice.

Everyone's right here. Lithium batteries obviously can be made safe in practice or they wouldn't be everywhere, but they can go wrong in amateur hands. This forum is filled with pleas for help from CMoy amps that don't work, do you really want us flying with homemade lithium battery packs?

 

[__redruM]

Thanks Frenchman, I'm certainly interested in the longer life of lithiums. But I don't want to break new ground. Assuming a 12V+ pack, and a charging circut that can be protoboarded, would you be able to recomend a Cell, and a charging chip? I'm not interested in fast charge, just trickle charge, something between 50-100mah.

Syzygies, Using extreme examples is a great way to make your point, but it didn't answer my question. If... if I make this, I will be very carefull when I test... I certainly don't want a hammond scrapnel all over my workbench.

 

[tangent]

Quote:

Any suggestions on where to find Plainviews?

I haven't seen corroboration, but it's my impression that they were bought by Maha. The evidence is that plainviewbatteries.com has been offline for months now, and meanwhile Thomas Distributing has been offering a Maha 9.6V battery that looks an awful lot like the Plainview, excepting coloration and labelling.

The only thing that made them special was the 9.6V (8 cell) configuration. Most "9V" NiMHs are in fact 8.4V (7 cells) or 7.2V (6 cells).

Also, it's apropos to this thread's topic that 9.6V NiMHs do run over 10V for a substantial portion of their useful life.

Quote:

"Possibility of explosion" is a standard battery warning, it's not limited to Lithium based cells.

The danger isn't so much explosion as catching on fire.

Lithium Ion batteries have very specific charging requirements. You can't just rig up a one-resistor trickle charger. Fortunately, there are many lithium charging ICs out there, and probably a lot of good technical detail on the web. But, be careful. If you don't understand how the PPA battery board circuit works, you probably have no business rigging up a lithium ion charger.

Oh, and beware that "lithium" is a chemical element, not a battery type. There are three lithium-based battery chemistries, as I recall, and one of them isn't even rechargeable! As always, be sure you know what you're dealing with before you fire up a power circuit.

Quote:

You buy a chip, read the datasheet and set a few resistors.

Careful there, mon frere.

There are lots of people here whose eyes glaze over when you direct them to the datasheet. What's easy for initiates scares the pee-water out of a lot of newbies, and half the rest just lack the sense to be properly scared, sometimes. I'm all for turning newbies loose without much guidance on harmless projects like CMoys and such, but when it comes to power circuits, I never try to make it sound easy. People need to come to their own conclusion that it's easy, after having waded into the pool at their own pace.

 

[tcristy]

Scroll down on the linked thread below to see stats on the number of LiPoly fires just in people participating in this one RC forum (its several hundred):

http://www.rcgroups.com/forums/showthread.php?t=209187

There are also some nice videos of mischarged LiPos catching fire referenced in that thread. In this following test, the charger was set to two cells, but only one was connected. This is a fairly common mistake:
http://www.rcstuff.us/battery/lipo/images/LipoFire.mpg

Here is another one:
http://www.helihobby.com/videos/LithiumBattery.wmv

 

[Frenchman]

I certainly agree that such things should not be taken lightly. However, just as it is now considered commonplace to charge Nickel based batteries, Lithium based chemistries are similarly easy. Also, keep in mind that Lithium Ion batteries are NOT considered hazardous waste, while Nickel based chemistries are. Additionally, MSDS's yield that no battery is supposed to be overcharged, no matter the chemistry.

Now, it may very well seem very complicated. However, I assure you it is not. There seems to be some reluctance on this forum to try new things. The world has moved away from Nickel to Lithium as the chemistry of choice. Now, no one wants to design their own charger. Engineers have more important things to do. That leaves other engineers to build great chargers for you!

Take this example from Maxim.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4002/ln/

Charges a single cell from an AC adapter and also from USB. The circuit is simplicity itself. You'd be just as likely to blow up the chip as the battery. The circuit itself consists of 3 standard size capacitors and a resistor. Of course, I won't kid you, you will HAVE to deal with surface mount. If you're ready to use that, then you're more then ready to charge Lithium based chemistries.

Use a single cell with a USB powered charger and then use a Maxim based boost converter to get your 10V. Piece of cake!

 

[Frenchman]

Oh, I suppose I should address that forum post.

The operator error category is obviously out. An idiot drives his car into a wall because somebody doesn't tell him to avoid it.

The majority of the remaining are probably the result of batteries which have been severely discharged to the point where they are no longer safe to recharge. Lithium based chemistries become unstable when discharged too deeply.

The bottom line is that Lithium based chemistries are safe. This whole thread decomposes into two parts. First, be careful to follow the rules. This goes without saying and applies to ANYTHING in electronics. The rest amounts to a lot of FUD about Lithium being unsafe. If Lithium Ion was so unsafe, it would not be the primary battery of choice in millions of cell phones, millions of PDA's, MP3 players and even a large quantity of handheld instruments. Lithium Ion is now considered a safe choice for satellite battery packs. The military uses it for rechargeable applications. These are safe unless used incorrectly.

 

[Syzygies]

Technical climbing is safe, but I'm pretty fussy about who I'll climb with. I've come "unstuck" from a cliff hundreds of yards off the ground, and I was fine because we knew what we were doing. I've dived to four atmospheres and climbed to 1/3 atmosphere, backpacked at -20 F and + 110 F, all safe activities, but none to be taken lightly.

All we're trying to do here is to establish the "reading group" one should be in before fooling around with lithium ion batteries. It's indisputable that they take more care than NiMH. I wouldn't send anyone out on any of the above activities without making sure they know what they're doing, and what you board a plane with is other people's business, I'm sorry.

 

[__redruM]

Quote:

Originally Posted by Syzygies what you board a plane with is other people's business, I'm sorry.

OK, I won't charge any lithium batteries on airplanes. We're agreed

. Just curious, who said anything about airplanes?

 

[tangent]

Quote:

If Lithium Ion was so unsafe, it would not be the primary battery of choice in millions of cell phones, millions of PDA's, MP3 players and even a large quantity of handheld instruments. Lithium Ion is now considered a safe choice for satellite battery packs. The military uses it for rechargeable applications...

All things designed by Real Engineers. No one is arguing that lithium chemistries are inherently unsafe, just that it's easier to fail catastrophically with them.

Quote:

These are safe unless used incorrectly.

That's almost a tautology. "It's safe unless you do something unsafe."

Given how many times I've seen DIYer reports here where it's evident that they plugged their good headphones into a CMoy they're building without testing for DC offset first -- perhaps because they don't even have a meter! -- I'm inclined to be a little cautious about recommending some activities to just anyone.

 

[mike_d]

All of these reasons are why companies like Microchip and TI make cell monitoring and protection chips and charge controllers. These cells are perfectly safe when used within their limits - the RC crowd will build their own packs WITHOUT the monitoring circuitry to save weight. Many of these failures occur due to poorly educated RC'ers using incorrect charging circuits or specifying the wrong number of cells on a LiPo charger.

I have played around with these some and worked up a 2 chip charger/monitor board using devices from the companies I mentioned above. It works fine for one or two cells. And it hasn't exploded.

-mike

 

[Wyloch]

Quick question not worth starting a whole new thread over so I put in this related thread:

Can someone give me the straight up answer: will two 9V batteries in series indeed provide 18V? What about when they're in series? Also, which drains faster, parallel or series?