Author Topic: 12v 7AH SLA batt question  (Read 3435 times)

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rgormley

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12v 7AH SLA batt question
« on: February 27, 2006, 12:48:08 AM »
hopefully a quick and easy question?  (12v 7AH SLA)

if a batt is rated at 7amp hours does that mean it should supply 7 amps for one hour? NOW the important part of the question, what would the expected voltage be after 1 hour?? asuming the batt had been fully charged (charged and then floated at 13.8v for 2 days)
« Last Edit: February 27, 2006, 12:48:08 AM by (unknown) »

terry5732

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Re: 12v 7AH SLA batt question
« Reply #1 on: February 26, 2006, 05:54:33 PM »
These batteries aren't made for big draws and a 7 amp load will kill it quicker than one hour. But it should be fairly close to 7 hours at one amp and will certainly be 28 hours at 1/4 amp.

 Voltage doesn't really indicate charge level well on these. I've got older ones that are never better than 11.5 full but last nearly as long as newer ones. They will read 11.5 right until they drop precipitously.
« Last Edit: February 26, 2006, 05:54:33 PM by terry5732 »

nothing to lose

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Re: 12v 7AH SLA batt question
« Reply #2 on: February 26, 2006, 10:49:01 PM »
NO. At 7amps load it will take less than 1 hour to go dead probably.


Normally large deepcycle batteries are rated at a 20 hour period, C20. (I think the small ones are also) That means like 200 amps in 20 hours. That would be a 10amps per hour load. But if you hit it with a high amp load you may drop to a 105 amps of battery power (about half). T105 trojan golf cart batteries for instance. 10 amps for 20 hours so total amps 200 for a T105, but in a golf cart that is a high load in a shorter time and they are rated about 105amps total then. With a perfect 7amp battery figuring a C20 that would be a 0.35 amp load for 20 hours to get the full 7amps from it.


I think these small SLA are about the same thing as the amp ratings go as the large ones, rated for 20hours.


Battery volts often don't mean as much. I have always been told and read about voltages below a certain level means the battery is junk (when it has sat unused for days). I just had 4 7Amp 12V SLA batteries that read maybe 4-6 volts each when I tested with a meter, wired up for 24V they were showing about 13V at best. Those sat for at least a week unused after I got them. According to all normall figures those should have been junk not worth messing with.

 Geuss what, afer charging all night on the Rack Mount UPS they came in, 1750watts, the batteries actaully ran the sinwave inverter and powered a 1,500watt heat gun! Not too bad for 24V 14amp hrs battery bank. My little Leds showed full charge on the system but of course I could watch that fall fast when running the heat gun.

24V X 14 amps = 336watts, but I ran the heat gun at 1500watts several minutes before the low battery warning and turning it off.

 A 1500watt heat gun should be 62.5amps at 24V.


Basically the larger the load and faster the drain the less total amps you'll get from the batteries, smaller load and less drain the more total amps you will get.

« Last Edit: February 26, 2006, 10:49:01 PM by nothing to lose »