FW: [Elecraft] Lithium Polymer batteries

[Dan Barker]

Per cell Vmax is 4.2. 3.7 under load. Pulling 7A out of full cells, they
drop all the way down to 3.65V! You could mount an automotive-style
cigarrette lighter in your KX1 if:
 a) You needed one, and
 b) You could figure out how to fit it it!

Amps are NOT going to be your problem.

WARNING: If the manual doesn't mention Lithium batteries, don't try it. Most
chargers are constant current. LiPo demands constant voltage (Actually, peak
voltage AND peak current - Current limited to 0.5C until 4.2V/cell is
reached, then voltage limited as the current falls off until you get bored
of watching the meters. The batteries don't even get slightly warm doing
this.

Dan

-----Original Message-----
From: Phil Wheeler [mailto:w7ox@socal.rr.com]
Sent: Friday, November 28, 2003 2:02 PM
To: Dan Barker
Subject: Re: [Elecraft] Lithium Polymer batteries


So I guess you are the charge control microprocessor, Dan ;-)

I have a pretty versatile charger (Maha C-777 Plus) which pretty much does
everything well.  The manual does not mention Li Poly cells, but likely that
is because they are new.  I will check the Maha website and see if that is
true.

What is the "per cell" voltage of these critters, Dan -- and over what range
of voltage is a cell useful?  Seems like they are around 3.7 V nominal so
three in series would produce around 11 V.  And if they are 4.2 V at full
charge, the max V would still be well in the range for a KX1.

Intriguing possibilities here!  Thanks for the heads up.

73, Phil

Dan Barker wrote:

I don't have one. But, I have a bench power supply with both voltage and
current limiting. So, I set volts to 8.4, and current to 2. When the current
limiting switches over to voltage limiting, it's nearly charged. When the
current drops below .5A, I call it done (whether it is or not). It won't
hurt a thing to float it at 8.4, and probably current would eventually fall
below .1A

Dan / WG4S / K2 #2456

<snip>
What charger do you use with these batteries?
</snip>