[Elecraft] KBT-2 out of radio battery charging

[W3FPR - Don Wilhelm]

Vic,

Thanks for adding that - in my haste, I forgot to say that indeed for a
Smartcharger, the current must be set with consideration for the battery.
OTOH, I believe the thing that is usually adjusted is the 'bulk current'
which is the high current part of the 3 stage charging cycle.

Reviewing the UC3906 3 stage controller chip, I found that Stage 1 was the
bulk current stage - where the resistance can be changed to limit the
maximum current.  When the terminal voltage reaches 95% (13.7v) of the full
charge voltage, stage 2 is triggered which increases the voltage (to 14.4
volts for a 12 volt SLA), and the charging continues until the current drops
to a small value - then stage 3 begins which limits the voltage to 13.8
volts (trickle charge value).


73,
Don W3FPR

> -----Original Message-----
>
> W3FPR - Don Wilhelm wrote:
>
> > Of course, an even better system is to use a 3 stage charge controller
> > specifically designed for SLA batteries - something like the A & A
> > Smartcharger would do a fantastic job.
>
> Keep in mind that the Smartcharger (and most likely other 3-stage
> chargers) has an adjustment for the amount of trickle current.  If the
> charger is designed for an automobile battery this will be too much for
> a small gel cell and will destroy it.
>
> How do I know?  Because I have a Smartcharger and I made an error in
> arithmetic when I selected the value of the resistor that controls the
> trickle current, and the rest -- including my 4ah gel cell -- was history.
>
> --
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
> --
>
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