[Elecraft] K1 OT lead acid battery charging

[Wes Stewart]

The short answer is that if the battery is discharged, you
will, at least in the initial phase, be severely overcharging it and in the end
phase, be undercharging it.



At the very least, as a rule of thumb you should limit the current initially to
something under C/4, where C= AH rating = 5A.  So this is an Ohm's law
problem.  Measure the open circuit voltage, subtract that value from the
charging voltage and provide a series resistor that limits the current to that
calculated earlier.



For example, say the battery measures 12.0V.  You want to drop 13.8 - 12.0
or 1.8V across a resistor with 5 / 4 A passing through it.  So R = 1.44
Ohm. This of course isn't a common value, so if you err on the conservative
side you would want to use a higher value, thus lower initial charging current.



You can also see that as the battery charges, and its voltage rises, less and
less charge current results.  In theory, due to self-discharge, the
battery voltage never quite reaches 13.8V.  And even if it did, it's still
not fully charged; so overcharging, i.e. a higher voltage still is required to
do that.





More here:  http://www.amplepower.com/primer/full/index.html

 



--- On Mon, 5/31/10, ki4bbl at cox.net <ki4bbl at cox.net> wrote:





From: ki4bbl at cox.net <ki4bbl at cox.net>

Subject: [Elecraft] K1 OT lead acid battery charging

To: "Elecraft Reflector" <elecraft at mailman.qth.net>

Date: Monday, May 31, 2010, 8:42 AM

Ok, I have a 12vdc 5ah lead acid
battery.  I have a 15amp 13.8 volt  

power supply I use for my qrp power.  Can I charge the battery with  

that supply?  How do I know when it is fully charged, etc





Greg Doughty

Ki4bbl