[Yaesu] Re: Opening Yaesu handheld battery...

Sat Jul 19 01:02:39 EDT 2008

 We seem to have wandered off the origina topic here to automobile
batteries.
A few basic things you should know when dealing with Lithium-Ion batteries...
 Their chemistry and rules for use are VERY different than the other types.
Also, the voltage varies greatly as does their state of charge, unlike
other types.
 1) Li-ion cells are 3.3 volts each. (nominally) When fully charged they
are at about 4 volts per cell, and usually end their current delivery by
around 3.2 volts.
 2) Li-ion cells cannot be allowed to drop below 3 volts per cell or they
will self-destruct.
 3) They cannot be allowed to accept (or deliver) more current than about
1C. (about their amp-hour rating, ie. a 2ah cell should not be asked to
deliver more, or accept more charge, than 2amps)
 4) They should ONLY be charged with chargers that are designed
specifically for Li-Ion cells. (PERIOD!)
 5) They are very dangerous when these rules are violated.
 When looking at Li-ion batteries for powering a 12 volt system you have
to pay close attention to current needs and voltage tolerances of the
equipment. A 3-cell system will be at roughly 11.7 volts when fully
charged. That might already be too low for a 12-volt radio. That same
pack will drop to around 9 volts before internal circuitry in the
battery pack will shut it down. If you jump to a 4-cell system you'll
be close to 16 volts at full charge, far too much for most 12-volt
radios. Fortunately, most small (HTs, FT-817, etc.) radios can
operate well in the range of a 3-cell system.
 Now for the GOOD news... Lithium Ion cells weigh only a fraction of
other chemistries for a given amp-hour rating. For example an 8ah SLA
or Nicad battery weighs over 6 pounds. An 8ah Li-ion battery weighs
1.16 pounds(!) Sure makes backpacking up a 3,000 foot mountain easier.
More good news... Li-Ion packs nearly always come with internal circuitry
that;
a) prevents excess charge current
b) prevents excess voltage being applied to cells
c) prevents excess current drain
d) cuts off the pack when per-cell voltage gets down close to 3v.
 The pack cut-off voltage is usually selected comfortably above a level
that would equal 3v per cell. Some packs come with additional circuitry
that equalizes the cell voltage allowing the pack to reach a lower
voltage before cutoff. After much research, I chose a 3-cell Li-Poly
cell with the equalization circuitry for my FT-817. It allows a cell
cut-off voltage down close to the voltage where the 817 will shut down
anyway so I'll get full use of the amp-hour capacity of the pack.
 Lithium Ion is basically the same as Lithium Polymer in terms of
characteristics. Polymer cells are flat and usually rectangular.
Somewhat less space is used for a given amp-hour capacity and at a
slight saving in weight. Most laptops use packs of round cells in
series-parallel using 18650(4/3AF) or 14500(AA) cells. Polymer cells
are used in cellphones and other specialized applications where flat
batteries are called for.
 Li-Ion packs are available commercially on the web, but for the reasons
discussed above you can't buy these packs at any walk-in battery store
or many common consumer battery web vendors, but they can be found.
 You can even buy individual Li-ion cells without the protective
circuitry and series/parallel them yourself but you DO SO AT GREAT
RISK... The cost of wired and safety packs is very slightly more than
buying the individual cells and infinitely more safe. Just be aware
that the Li-ion cells will be constantly dropping in voltage as you use
them up. This is different than what we're used to seeing in Nicads and
NiMh cells which stay fairly flat through their life of charge then fall
off the cliff rapidly. The Li-Ions will gradually drop to 3v per cell
then SHUT OFF. Another cautionary note about Li-Ion packs. They cannot
be ignored on the shelf for a few years like we sometimes do with other
batteries. If they are allowed to self-discharge below around 3v per
cell they may well be useless. So you need to charge them once in a
while.
 Nothing beats the good old Nicad for high current delivery out of small
batteries.. (and a very high cycle life). But they don't have a very
good amp-hour/volume ratio. A little 600mah nicad cell has no problem
delivering about 2 amps for a while. But you'd need about a 3000mah
Li-ion to comfortably deliver that same 2 amps. Fortunately that
3000mah cell is about as light as that 600mah nicad and you'll get gobs
more time from the battery.
 In my mind the NiMh batteries are a compromise. We stress them beyond
their design limits with these 5-watt mini-radios. They look good on
paper because of the high amp-hour ratings in small packages, but AA
sized NiMh cells shouldn't be used in these HTs unless you never use
them to transmit. They don't like rapid charging either. Yea they'll
take it for a while, but you'll get nothing close to the advertised
cycle life out of them. I prefer having two Nicad packs and rotate them
through good chargers. I don't even fast-charge Nicads unless I have
to, they're much happier at somthing around .1 to .2C. You'll get a
better depth of charge so they'll last longer between charges AND you'll
get a better cycle-life out of the cell. I've got 600mah cells here
that are 4-5 years old with well over 1000 cycles on them and still
running very close to rated capacity. But I charge them at only
50-70mah.
Hope this wasn't too punishing to wade through!!
73,
Dennis
N0SP