Posted by
Steven Pituch on
Dec 12, 2004; 2:47pm
URL: http://elecraft.85.s1.nabble.com/SLA-Battery-charge-Level-tp372525.html
I said:
"When the battery is exactly at 13.8 volts, there would be
no current."
Bob, G3VVT said:
"In practice found over the many systems worked on professionally this is
not entirely correct.
However if one monitors the battery over a longer period after the float
charge period has started the battery will start to take a small charge that
eventually settles on the 25 to 50 mA region for small SLA's. It all depends
on the float voltage and the size of the SLA, but with a float voltage of
13.8V and a 12V SLA does definitely occur."
-----------------------------------------------
Yes, I was over-simplifying it. But a battery at 13.8 Volts will not take a
charge with a 13.8 Volt source. What happens I assume is that the battery
discharges a bit so it is lower than 13.8 Volts, and then the trickle charge
commences.
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John said:
"1) The total charging time using your method would probably be longer than
forcing 1.6 amps until the terminal voltage reached 14.2. But it might also
be healthier for the battery."
--------------------------------------------------
Yes it will take a lot longer (overnight), and not overheat the battery, but
this is how the original Powersonic recommendations were in the 1990s. I
imagine they have changed.
---------------------------------------------------
John said:
"2) If the SLA voltage got below 10.5 volts, you might initially draw more
than 1.6 amps, unless your 14.39 volt power supply is limited to
1.6 amps."
---------------------------------------------------
Yes this is true. But the powersonic web sight had recommendations for the
amount of drain a _gell_ cell would take before it was permanently damaged.
It might have been 10 or 10.5 volts. I think I chose 10.5 volts in my
design, so the batteries would not suffer from over-discharging. I also
monitored the voltage discharge during use so I would not damage the
batteries.
---------------------------------------------------
"John said:
I'm in the process of building a computer-controlled
(PIC-controlled) SLA charger to enter into my local QRP club's annual
builders' contest next Spring...."
---------------------------------------------------
This is very exciting. Please let us know about the results. If you could
leave the divice in the circuit during use you could design it to warn the
user when the voltage of the battery was getting near the danger point.
----------- --------------------------------------
I have had some requests for my circuit. Actually the ideas might help John
in his design too. I will post the info on my website soon and let the list
know.
Regards,
Steve, W2MY/5
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