On Thu, 17 Jun 2010 02:09:18 GMT, Ross Herbert
wrote:

One possible problem I see with this simple circuit is that it has no inbuilt
hysteresis or maximum voltage charge time. A battery will charge to its preset
maximum voltage and because there is no time limit placed on the charge current
at the maximum voltage, the relay will operate and stop the charge before it has
time for the battery charge capacity to be maximised. This will lead to
"hunting" where the relay will operate and release rapidly, ad-infinitum, as the
battery voltage fluctuates above and below the preset maximum.

On Mon, 14 Jun 2010 09:00:02 -0400, default wrote:

:On Wed, 9 Jun 2010 13:13:46 +0930, "mark krawczuk"
wrote:
:
:hi, after some schematics to charge 6 volt and 12 volt sla ( sealed lead
:acid ) batteries.... basically dont need to charge them flat out , cause
:they dont get used much, something i can leave on trickle charge for a week
:or so , would be good....
:
:any body have any or know of any links ?
:
:
:
:http://electronicdesign.com/article/...gle-trans.aspx
:
:http://archive.electronicdesign.com/.../figure_01.gif

I think electronic design probably vetted the schematic before they
published.

Did you read the write-up? My only criticism might be setting turn on
point at 11.8 the way they suggest, that seems a bit low. AND it
needs an LED in there somewhere for a little glitz, or better still, a
bicolor LED.

A slight trickle could be provided around the relay contacts with a
resistor - it would also null the slight load the divider string
imposes on the battery.


Looks to me like the battery is charging while the relay is
de-energized, when the battery voltage is high enough to bias the
transistor "on," the relay energizes, at the same time the movable
contact switches VR1 out of the circuit (shorting around it) raising
the voltage on the base a little more, insuring it turns on harder,
and longer. (the hysteresis)
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