On Sun, 20 Nov 2005 19:27:49 -0600, "J Shrum" wrote:

Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've not
quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the nicad
holders and put in a 12v 5AH gel cell. I modified it to charge directly from
the 13.8v power supply instead of the 18v nicad charger circuit. I charged
the battery to about 13.8v (w/ no load) by floating. If I measure the
battery while having my radio on receive, which only draws maybe 80mA's or
so, I see the battery dropping by .10's of a V in no time. The battery is
brand new.
I've noticed that the battery only draws about 30mA's while charging at any
voltage. I even added a switch so I can switch extra diodes between the
regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be fully
charged, right? Is there something going on since it is only drawing 10's of
milliamps while charging? I've read that they charge at several hundred
milli's. I'd like to use my QRP rig remotely, and at the rate its dropping,
I just don't think it will serve the purpose.

Just float charging at 13v8 isn't going to do a great lot for an SLA. Download
and read the following two docs from TI/Unitrode which will give you a fair
insight into the proper care and feeding of SLA's.

http://focus.ti.com/lit/an/slua115/slua115.pdf

http://focus.ti.com/lit/ds/symlink/uc3906.pdf

There's a lot of overlap, but good info, and that chip makes a fairly simple yet
elegant charger.