# converting C/8 to C/20 rate

Solar Expert Posts: 5,183 ✭✭✭✭
I am looking into some newer AGMs. The only rate I can find in Exide's literature is the C/8 rate, but I would like to translate that number to C/20 for comparison to my old battery.

the battery is an Absolyte GX 2000 C/8 is 2000Ah @ 1.75 V @ 25* C
http://www.ieeco.net/Documents/Batteries/ExideAbsolyteGX.pdf page 3

they also provide 24 hr, 12 Hr , 10 hr and 8 hr discharge data @ 1.75 V @ 25* C as follows:

Time....24hr ...... 12hr ...... 10hr ..... 8hr
Amps ...96 ........ 178 ........208 .......250

then a qualifier, bottom page 5,
"Note: To obtain amps for each GX system — multiply the amps/positive value from
table by the number of positive plates "

System .............. GX2000 GX3000 GX4000 GX5000 GX6000
# of Positive Plates 12 .........18 .......24 .......30 ..... 36

This last part makes no sense to me as 8hr x 250A = 2000Ah, and 12 hr x 178A = 2136 Ah and 24 hr x 96 = 2304 yet
96A x 12 ( from table) = 1152A

???Am I correct in saying the (C/20) Ahr rating for the GX2000 is ~ =2248Ahr??

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep

• Solar Expert Posts: 3,738 ✭✭✭✭
Re: converting C/8 to C/20 rate

Westbranch, If you use the charts, just multiply the amps by the hours to get amphours.

If you use the graphs, the numbers shown are per plate and you would need to multiply them by 12 (for the gx2000) to get something that makes sense.

For example, the graph on the bottom of page 6:
The 8 hour line intersects the 1.75 volt/cell line at about 167 amphours per positive plate. 12 plates X 167 amphour per plate = 2000 amphours

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 5,183 ✭✭✭✭
Re: converting C/8 to C/20 rate

Thanks VT, I was doing things right then. I just am not sure of how to interpolate between 12 and 24 hr rates.
The 2248Ah is straight line interpolation, which I know is close...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep