Li-Ion packs

[Jerry Budd]

Hi Verne,

There is an indicator light but it operates a bit differently than 
what most people are used to.

It appears that the charger is a constant voltage charger, which 
means that the amount of current flow into the battery pack is 
proportional (but not linearly proportional) to the difference 
between the voltage level of the battery pack vs the set (more likely 
requlated) voltage put out by the charger.  The greater the voltage 
difference, the greater the current flow into the battery pack. 
Initially there is a relatively high current flowing into the battery 
which decreases as the voltage of the pack increases.  Eventually 
(about 2 hours for a fully discharged pack) the voltage of the pack 
(given the pack is healthy) rises to the same voltage output level of 
the charger, at which point there is ZERO current flow into the pack, 
and you are done.

As far as how to tell when the pack is fully charged?  If you connect 
a pack that has had some amount of usage, the indicator light (really 
a diode) on the charger will glow red.  As the pack voltage comes up, 
the current flow tapers off somewhat, and the indicator light changes 
to a red-yellow hue, then to a yellow color, then to a yellow-green 
hue, and then finally it goes completely green (indicating no current 
is flowing and a fully charged battery pack).

The only flaw in the system is that when the charger is connected to 
a 12v power source, the light glows green, whether a battery pack IS 
CONNECTED OR NOT!  Why?  There's no current flowing through the diode 
to make it change color.  Obviously this creates a concern as to how 
can you tell that you actually have a good connection between the 
charger and the battery pack.  What I do is make sure that I see the 
diode change color when I connect the charger to the charge jack.  If 
I don't see a color change, I either have a battery which is still 
fully charged (not likely - check it with a digital voltmeter with a 
0.5 to 1 amp load), or I don't have a good connection.  If I see the 
diode change color as described above I know it's charging.

Now, can you leave the charger hooked up to the battery pack 
indefinitely?  In theory, yes.  In practice, maybe (you still need to 
exercise the pack once in a while).  Bern suggests NOT to leave it 
hooked up.  I have left mine on for as much as a week or more with no 
effect (as far as I can tell).  Your mileage may vary.

The cool part of all this is that the charger is essentually a fast 
charger in that it initially puts out a lot of current at the 
beginning, and then tapers off to a trickle, without any really fancy 
circuitry involved.  This is a good thing as simpler directly 
translates into increased reliability (assuming reasonably high 
quality components are used).  The drawback is that if you have a 
"bad" battery pack, the voltage of the battery pack MAY NOT come up, 
causing the current flow to remain high, and you could "cook" a set 
of batteries (and maybe an airplane).  I think this type of failure 
mode is extremely unlikely.  A more likely scenario is that the 
(compromised) pack never does quite reach peak voltage, the charger 
continues to put out a small amount of current (which probably 
doesn't cause much of anything to happen), and you (hopefully) notice 
that the charge light never quite reaches a full green color (which 
tells you something is not right).  You then check the pack voltage 
with that 1 amp load VOM I mentioned, and realize the pack is maybe 
not doing so well.  I think that's a pretty graceful failure mode, 
and it's certainly one I can live with.

I know that the DuraLight folks are putting some circuitry into their 
battery packs to eliminate overcharging as an issue.  However, that 
extra circuitry introduces additional failure modes, which may be 
what we are starting to hear about on this (and other) lists.  I 
personally don't think it's really necessary, and in fact it may 
actually cause more problems than it solves.

Jerry


>Jerry,
>Is his charger of the type that has a light that tells you when it's done
>charging?
>
>Verne
>
>
>----- Original Message -----
>From: "Jerry Budd" <jbudd at QNET.COM>
>To: <discussion at nsrca.org>
>Sent: Friday, September 06, 2002 2:00 PM
>Subject: RE: Li-Ion packs
>
>
>>  >Thanks Jim.
>>  >
>>  >Ive been curious what a discharge curve looks like for
>>  >these batteries, anyone seen one?
>>
>>  My experience is that it's pretty constant (but not level), similar
>>  to a lead-acid battery (which makes it very predictable).  As far as
>>  I can tell (and I've run my Li-ion packs from Bern Furgang at
>>  http://www.superbatterypacks.com down to slightly less than 6.6v) it
>>  stays pretty linear with no discernable change in slope.
>>
>>  I eMailed Bern about this and he replied with, "I would not go below
>>  the 6V threshold as you could loose the pack.  7.2V is a very safe
>>  low end.  If you are at 6.6V you are OK."
>>
>>  Before I purchased the Li-ion pack/charger I consulted with Jim
>>  Oddino as he had some experience with them.  He indicated that he was
>>  favorably impressed.  I purchased the bx & charger in late June, and
>>  at this point, I am too.
>>
>>  Jerry
>>
>>  --
>>  ___________
>>  Jerry Budd
>>  mailto:jbudd at qnet.com
>>  =====================================
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>>
>>
>
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-- 
___________
Jerry Budd
mailto:jbudd at qnet.com
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