help with battery datasheet  - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: October 20, 2013, 03:22:19 am
content: i just bought this battery and it seems to be working ok however usually Lead Acid batteries are rated at12v - 7Ah12v - 9Ah12v - 12AhI want to know how many amps does this battery give as an output, but if you see their datasheet you can see thathttp://www.csb-battery.com/upfiles/dow01375845369.pdfits rated at 12v - 34wso im now confused, i know P=IV so i can make thisI=P/VI=34(6 cells)/127 = 1.60so it does not make any sense, the guy that sold me these said these are 12v - 9A but i want to confirm this otherwise i will return them could anyone help me out to understand the datasheet?

author: auto_218
author_rank: Newbie
timestamp: October 20, 2013, 04:29:31 am
content: It sounds like to me that the guy you bought the battery from didn't know or was confused. The 9A he was probably talking about was the Ah rating. The current you calculated is a little off. I am not sure where the 127 came from. But it looks like you multiplied the 34W times the 5 cells, which doesn't need to be done. The whole rating for the batt is 34W. So 34/12 = 2.83A. How many amps are you going to be pulling?Sent from my iPhone using Tapatalk -now Free

author: Lightages
author_rank: Unknown
timestamp: October 20, 2013, 04:35:50 am
content: Batteries are rated at how much energy they can produce when at a discharge rate or current draw that takes them to what is considered their full discharge voltage at 20 hours. That is the industry standard. This data sheet assumes a constant power discharge rate in their specs so it will all look different.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 20, 2013, 05:03:37 am
content: Quote from: auto_218 on October 20, 2013, 04:29:31 amAccording to my meassures i got this table for my PC, (see pic) according to it when my pc is at full load after being disconected from the wall it would pull (in the US) 300W/120Vac = 2.5Aac. From the _batteries_ (wired in series for sure) 300W/(2*12V) = 12.5A, and that does not include the losses from the electronics doing the conversion from DC to AC. From the tables in the datasheet, you are looking at 20min of runtime @300W, neglecting losses.however i still dont get if the batteries i got are 7Ah or 9Ah since the actually cost twice the price

author: IanB
author_rank: Super Contributor
timestamp: October 20, 2013, 05:26:28 am
content: Quote from: GoatZero on October 20, 2013, 03:22:19 amThe data sheet tells you what the battery can do in the tables at the foot of page 1, the constant current and constant power discharge tables.Now you say you want to know how many amps this battery gives as an output, but the answer is "as many as you want" up to about 130 A. That is at the top of the data sheet, "Maximum discharge current: 130 A (5 sec)".When a battery says it is "12 V 9 Ah" that number is not 9 amps, it is the storage capacity, the total amount of charge stored. The battery can release that stored charge fast or slowly, and that is what the tables at the foot of page 1 tell you.This particular battery can supply 34 W per cell (204 W total) at constant power discharge down to 1.67 V/cell (10 V total) at the 15 minute rate. In other words if you start out fully charged and draw 204 W from the battery it will be discharged in 15 minutes.If you discharge the battery at constant current, it can supply 17.4 A down to 1.67 V per cell at the 15 minute rate. At a slower discharge rate it can supply 5.61 A for 1 hour down to 1.67 V/cell.The capacity of the battery therefore appears to be about 6 Ah.

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2013, 05:38:29 am
content: So for this one it can deliver 34W per cell to a low voltage cutout of 1.67V per cell for 15 minutes. Thus it is for a UPS, and will in your case for 2 batteries in series deliver the 300W load for 15 minutes before low voltage shutdown. This gives a rough capacity of 6Ah for the battery, but it likely is a 7Ah unit if discharged at a lower rate. Capacity is really a function of the discharge current, and is set by the cut off voltage per cell, which will be lowered as the current increases because the cell internal resistance does increase as it discharges which reduces terminal voltage.Not going to be good for many cycles at that loading, probably will only do about 10 cycles before the battery dies, or will last about 2 years at float charging in a nice hot UPS casing.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 20, 2013, 05:54:57 am
content: though I think 10 cycles is a bit pessimistic as the mfgr lists discharge times down to !2min! I think those cells are pretty rugged.Load at 300 watts at full load which does not happen when power goes out, its usually 177Watts almost half, howeverI can't 100% say for sure. I know from the 90 min discharge data that they are at least 6Ahr. (4A*1.5). If you extrapolate out to 20Hrs is the discharge going to be > 7AH? probably yes.I note going through the mfgr's product selector, they do not seem to sell a 12V 9AH battery in any family, they do have a 7.2AH though.BUT, the battery seems to be optimized for high discharge rates (and is of a different family than the aforementioned 7.2Ah battery), (that battery family does not seem to be rated for AH @ 20hrs).Now i doubt it could hit 9AHr @ 20Hrs.Now according to all this... a 9AH battery might not deliver longer endurance at the high discharge rates i need? in spite of having more capacity at a lower discharge rate.?

author: IanB
author_rank: Super Contributor
timestamp: October 20, 2013, 06:11:42 am
content: In the data sheet they claim you can get 200 cycles of full discharge until the capacity is down to 60%. That seems pretty impressive for a lead acid battery.If the battery can meet your estimated load and run time requirements and is recommended by the manufacturer for the intended purpose you should stick with it. Usually higher capacity in a battery comes at the cost of other desirable things such as shorter lifetime, lesser endurance, lower power output, etc.

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2013, 10:00:03 am
content: Discharge capacity, lifetime, cost. Choose one, the others will be constrained by the one you choose.

author: G7PSK
author_rank: Super Contributor
timestamp: October 20, 2013, 03:21:36 pm
content: The data sheet says that the battery is good for at least 260 cycles full discharge at the top of the page,HRL 1234W is specially designed for high efficient dischargeapplication. Its characteristics are high energy density, smallfootprint and high discharge efficiency. It can be used for morethan 260 cycles at 100% discharge in cycle service, up to 8years in standby service.