John, I did exactly the same thing many years ago. I looked up the Powersonic information on their web site.
Lets assume the battery is to be charged with the 1.6 amps when the voltage is down to 10.5 Volts, also that the current must be 80 milliAmps when the charge gets to 14.2 Volts like you said. Using V/A=R we can figure out the voltage and resistance to do this. For the initail charge rate and V/A=R, where R is the dropping resistor, and V is the regulated voltage: (V-10.5)/1.6 = R For the final state: (V-14.2)/.080 = R Since R is the same (V-10.5)/1.6 = (V-14.2)/.080 Therefore V = 14.49 Volts Substitute V back into one of the original equations and you find the ballast resistor is 2.43 Ohms. Therefore using a voltage regulator at 14.39 V with the resistor of 2.43 Ohms will charge the battery at 1.6 Amps when the battery is at 10.5 Volts, and the charge will taper to 80 milliamps when the voltage reaches 14.2 Volts. This is exactly what Powersonic advises. Next you use a 25 cent op amp to make a voltage comparator and turn off the circuit when the voltage reaches 14.2 volts. Next you use a little relay to switch to a 13.8 volt regulated supply. The battery will stay on this supply indefinitely jusy taking enough current to keep it charged. When the battery is exactly at 13.8 volts, there would be no current. I wrote an article for QRP Quarterly years ago describing this. My original charger is still working without any adjustments needed. It does everything needed without using a CPU or an IC. You can get all the parts at Radio Shack. Steve, W2MY -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John R. Lonigro Sent: Saturday, December 11, 2004 6:32 PM Cc: Elecraft Subject: Re: [Elecraft] SLA Battery charge level Dan: According to the PowerSonic instruction sheet, after "bulk" charging (< 1.6 Amps for my 8 Amp Hr SLA), you are supposed to switch to about 14.2 volts for "absorption" charging. Once the current gets down to 80 ma, you can switch to a 13.8 volt "float" charge indefinitely if you wish. Since you are drawing 80 ma at just 13.8 volts, my guess is the battery is still charging. It should slowly drop to quite a bit less than that, maybe 30 ma or less when totally charged. Leaving the charger on longer shouldn't harm anything. It just might take longer to charge if you are only using 13.8 volts for all 3 types of charging. At least that's my understanding of the matter. Perhaps others can enlighten me if I'm way off base here. 73's, John AA0VE Dan Barker wrote: >When is a 12v SLA full? > >I'm charging at 13.8v and the current is slowly falling. Currently (har >har) at 0.080 A. > >Dan / WG4S / K2 #2456 > > > > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com --- Incoming mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.806 / Virus Database: 548 - Release Date: 12/5/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.806 / Virus Database: 548 - Release Date: 12/5/2004 _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
