1214Re: 11.7 Volts from Lithium Ion Cells?
- Jun 3, 2007Most of the major manufacturers of lithium ion cells prevent their
distributors from selling individual cells, because of risks and
liability issues. Lithium ion cells can store and deliver enough
energy to cause fires and injury, if they're not managed correctly.
Some of the cells available at various battery sellers on the internet
may come from lesser manufacturers overseas, and they may carry more
risks than the cells from the big guys. Be sure you use a protection
circuit for any pack you build.
There are several suppliers of lithium polymer (LiPO) packs on the
internet, and most of these are sold for R/C (model radio control)
hobbies. These batteries have great specs and are favored for
competitive R/C applications like high-performance airplanes. They are
way better than what you need for a QRP rig, and the prices are
reasonable for the smaller packs. Be sure you use a charger designed
to charge whatever battery you use. Lithium packs must not be
overcharged, over-discharged, reversed, or discharged at too high a
rate. Read the fine print and don't cheat. Always charge in a safe
place, away from flammable material, with a safe charger. Think about
what might happen if the power goes off during charge with no one
around; will the battery dump into your charger and burn something up?
Don't even think about using clip leads or open wires connected to a
lithium pack - it's too easy to have a short-circuit accident.
Polyswitches can prevent a lot of trouble.
When we take radios to the field, more problems happen - connectors get
stressed, radios misbehave, matching circuits don't match, we sometimes
forget to connect the antenna, the antenna falls down, we plug in the
wrong plug in the wrong hole, clip leads somehow get reversed, etc.
Please be sure to protect your radio from accidents - the one or two
tenths of a volt that a polyswitch takes when the key is down will
never be missed, but good batteries can take out your finals and even
the traces on your pcb if there's no protection.
Many of the accidents that have happened with lithium ion cells have
occurred when people were building or rebuilding battery packs. Think
about how easy it is to have a short circuit with perhaps 100 amps
flowing, just because you slipped with a soldering iron and bridged a
couple of points in the cramped space of a battery pack. What if you
goof in the part of the wiring that's not protected? If you choose to
do this, read up on it first, and use discipline so you leave little to
chance. Most of what you read will be full of warnings and
disclaimers. It's probably just as dangerous to work on a lithium ion
pack as it is to work on your house wiring.
Please be careful...
--- In AT_Sprint@yahoogroups.com, Richard McKee <QRP_1@...> wrote:
> Anyone know of a good source for individual lithium ion cells for
> rebuilding battery packs ?
> Rick McKee, KC8AON, Ohio - www.angelfire.com/electronic2/qrp
> Monthly QRP Field Day Group - http://groups.yahoo.com/group/MQFD/
> With God all things are possible <><
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