Confused - VRLA batt - Capacity
quid_non
Solar Expert Posts: 48 ✭
I'm confused - been looking at a "deal" on several 12V VRLA batts - they only state the wattage - 390W not the capacity. These are likely UPS batteries.
Since they are 390W @12V does that equate 32amps. How do I determine the AH capacity?
The batt is EATON PWHR12390W4fr
Thanks for any help!
Wayne
Since they are 390W @12V does that equate 32amps. How do I determine the AH capacity?
The batt is EATON PWHR12390W4fr
Thanks for any help!
Wayne
Comments
From this data sheet:
Eaton 12V 390W Battery
There is a table... Taking 1.8 volts per cell (near dead), 90 minutes, it will supply 88 watts--My guess:
88 watts * 1/12 volts nominal * 1.5 hours = 11 Amp*Hours at a 1.5 hour rate
If you are using a 20 hour discharge rate--the Amp*Hour capacity should be significantly higher.
-Bill
PS: that 390 watts would only be for 15 minutes--so:
390 watts * 1/12v * 1/4 hours = 8 Amp*Hours
Thanks Bill -
Since this batt has six independent cells, would the total capacity be 6cells*8aH/Cell = 48aH??
This batt weighs 75lbs... way too much to be omly 8aH capacity. I have a 7aH batt that is a fraction of this weight....
Cells in series, adds voltage, 6x2.1V = 12.6V
By weight alone and knowing the voltage, I'd guess at about 180AH capacity.
I've never seen a battery rated in watts
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
The battery is almost rated like a "starting" battery... 800 amps max for 5 seconds or 100% discharge in 15 minutes--perhaps that is why the Amp*Hour rating is so low--could be much higher at 20 hour rate???
High current would seem to indicate thin plates--would not give great life for a deep cycle application it would seem.
-Bill
It really does look to be a UPS battery, rather than an SLI.
Someone would have to calculate the Peukert exponent for the batteries to get a C/20 rating. Based on the maximum discharge and charge rate, they are probably good for solar applications. Based on the rated life cycles to 100% DOD, I'd pass on them.
And to answer the questions, they are 105AH batteries at C/20, based on a Peukert exponent of 1.20, which was calculated from the discharge data from Eaton.
And to derail this thread,
Hello Tallgirl, nice to C U here ! Vic
Ruh roh...it seems we've confused vBulletin...it thinks "tallgirl" is a "New Guy".
EDIT: Or...does the system know something we don't? o_O
Isn't it amazing how whenever a woman walks into the room the men all start making fools of themselves?
This is really straying from topic. Sorry. Terminal sense of humour.
It's one of my amazing super powers. When I was younger I made men walk into walls. Now I just turn them into blubbering idiots. And then they walk into walls.
Oh, hey, Vic, Crewzer, boB.
Where's Tim? Anyone else from the Outback forum here?
Hi Julie
Ralph Day from OB forum, and Greenpowertalk.org too. Good to see you here...it'll add another dimension to the discussions.
Ralph
tallgirl,
welcome to the forum. personally, i don't need a woman to do that as i can make a fool out of myself without help.
Well, just wait until I get REALLY technical. Some of the OB regulars will tell you that I'm no slouch on the electrical nitty-gritty.
And I've been meaning to show up for a while, but never seemed to make it ....
Sry to not be on topic, Hi Julie and all the other OB`ers
Have a good one
Tim
Hey, Tim -- I have some really great software that does everything BUT calculate Peukert exponents. Should I mention it here
This is a much more interesting forum than the OB one. I should have shown up sooner.
Julie,
There is certainly more traffic on this forum than on OB. OB seems to be a little more restricted to OB products (although some other products are mentioned sometimes:p) More varied topics as well.
Ralph
Thanks for the help - this is useful. Looks like the "deal" is one to pass on based on your estimated capacity. I'm positive I have no idea what in the world a "Puekert Exponent" is, but thanks for your expert advice...
and btw...
Welcome!
Best
Wayne
The Puekert calculation just helps the battery gauge to better know the actual capacity of the bank when it is discharged at higher rates than normal....
Normal, being maybe, C/20 or something like that.
boB
Peukert calculations assume a constant current of 1A, rather than a C/xx rate.
It's mostly useful for sizing battery banks based on expected runtime or load. For example, my "typical" load is an average of 500 watts -- that's without any power savings. No turning things off, just what I use. To 50% DoD that's about 24 hours, assuming I don't do anything and the sun stops shining. So, for me (hand waving), my discharge rate is "C/48" (48 hours to 100% DoD), rather than C/20. Except that the slower the rate of discharge, the higher the capacity. Setting the DC current to 12A, which would normally be C/43 (552AH @ C/20), I find that I have 668AH of capacity, or 28 hours of runtime.
re: "By weight alone" - figure 22 watt hours per pound for lead acid batteries. a 75# battery would have a 1650 watt hour capacity or about 135 AH at 12v.
AGM are so low resistance, the wires and connector terminals become a major current steering factor, and you will have a hard time keeping the banks balanced.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,