RogerN wrote:
> "Ed Cregger" <ecregger@[EMAIL PROTECTED]
> wrote in message
> news:gcm39s$sdv$1@[EMAIL PROTECTED]
>> I agree with Chris.
>>
>> You are literally playing with fire when trying to charge packs in
>> parallel. If it were that simple, you wouldn't see so many different
sizes
>> of packs available.
>>
>> Ed Cregger
>
> Yeah, but you can buy packs already wired in parallel. The key should
be to
> have them at the same voltage level before connecting the leads.
Another
> RCer told me that they connected a 4.2V cell and a 3.8V cell and only
had 5A
> flow between them and it diminished quickly. Alghough I don't recommend
any
> connection that would cause cause more than 1C current to flow into a
cell,
> I don't think paralleling equal voltage cells would be any more
dangerous
> than charging LiPo's is. However, if one pack would go bad, it may be
> relying on the fuses to protect the other packs.
>
> I think I'd be better off with a multiple (4 or 5) ****t charger that has
> 250W power like the Hyperion 0610i does. I wouldn't have to match the
cell
> voltages before connecting. Just trying to come up with an easier way
to
> handle multiple packs without lugging around multiple chargers.
>
> RogerN
>
>
Yup. The thing here is that as long as the packs are of the same
chemistry/construction style and from the same manufacturer, *even if
the cells are of differing capacity* you can connect two packs in
parallel *once you are sure they are at an equal state of charge*.
If you are not sure, don't risk it.
Now once they ARE in parallel, you can charge and discharge as a single
pack.
But the moment you use them independently you MUST go through the above
procedure all over again to make sure the state of charge is the same.
The reason for this is that *as long as the cells are identical
chemistry and construction style*, there is a completely unique
relation****p between voltage and charge state. So they will distribute
charge and current correctly, and stay in balance. This is of course how
large capacity packs are made up: From identical cells in parallel..
What is distinctly dangerous, in order of increasing insanity, is
mixing cells of different quality - say 15C packs versus 25C cells -
from the same manufacturer, mixing cells from different manufacturers,
or connecting cells in parallel when at a different state of charge.
You MAY be lucky. Do you feel lucky today?
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