SLA Battery charge level
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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: [hidden email] 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 |
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In a message dated 11/12/04 23:24:04 GMT Standard Time, [hidden email] writes: 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. The "absorption" charging or otherwise called "equalise charge" after the main charging cycle is complete is to equalise the voltages across the individual cells and get the maximum possible energy into the battery. With solar power systems we found that this period was better restricted to about 15 minutes when done daily to save overheating of the battery and consequently loosing electrolyte. Extended overcharging with SLA's greatly reduces their service life. When the battery is on "float" which for a small 12V SLA is commonly done at 13.8V, the current will come out at usually 25 to 50mA depending on the battery. This can be left on indefinitely as is common with fire alarm panel use, though will eventually reduce the capacity of the battery by a degree. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Dan Barker
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: [hidden email] 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 |
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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: [hidden email] [mailto:[hidden email]] 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: [hidden email] 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: [hidden email] 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 |
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In reply to this post by Dan Barker
In a message dated 12/12/04 00:35:05 GMT Standard Time, [hidden email] writes: When the battery is exactly at 13.8 volts, there would be no current. In practice found over the many systems worked on professionally this is not entirely correct. After the charging system comes out of the absorptive charge phase where the voltage has been allowed to rise above the normal bulk charge voltage for a limited time and now reverts to the float voltage, the battery indeed does not take any charge. It can even supplement the supply voltage and current for a short while after the main charge cycle. 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. Security and fire alarm technicians when carring out routine maintenance can note the current taken by SLA's in the alarm panels under float conditions as this can give an early indication of the forthcoming failure of the SLA. For critical systems under a maintenance contract they sometimes replace the SLA's at 2 to 3 year intervals to ensure system reliability under all conditions. A good source of SLA's that still have a useful life left in them if you can make contact with one of the technicians and I did! Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: SLA Battery charge level
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G3VVT wrote:
> ...alarm technicians... In the US I have found a ready supply of "alarm pulls" from Quicksilver Radio http://www.qsradio.com for 7AH SLAs when local hamfests are out of season and put one in my HF Power Pack from hfprojects.com 73, Leigh WA5ZNU _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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