Amp hour Conversion

[RobNCD2]

Can anyone tell me how to convert battery amp hour ratings?  I have a VRLA 6 volt battery rated at 1000Ahr @ 10 hrs and 960Ahr @ 8 hrs.  What would be the 20 Ahr rating?

Thanks for any help

[AbyssUnderground]

The 20hr rate won't be much higher than the 10hr rate I wouldn't think. I don't think there is any direct conversion you can do. The battery capacity should be written on it and that is usually the 20hr rate.

If you can try and find a datasheet for the battery as that should have discharge rates on it in a nice table.

[RobNCD2]

This is all the info I can find.  It is a Lucent battery so most info is long gone.  I would just like to get a conversion so I know how it will compare to my old battery bank, which are rated at the 20Ahr rate.

[SamoaPower]

I have to disagree with Abyss on this. It will be substantially higher at half the discharge rate. Perhaps 25%, but that's a guess.

Google "Peukert's exponent" or "Peukert's equation" and calculate it from that.

[ghurd]

Agreed.  The hours go up faster than the amps go down.

The charts before they changed to PDFs were far better.

This is for alkaline batteries.  The concept still applies.

http://data.energizer.com/PDFs/528.pdf

G-

[WindChopper]

Try Google'n "VLRA Batteries" and grab any curves that you can find to give you a "Typical" set of curves that are readable.

Take a look at   http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_VRLA_LC-R1233P.pdf  

At 12v/33aHr it is not even close to the battery that you are asking about, but does have one of the clearer set of curves that I came across.

What it does show is a general relationship between 20hr, 10hr, 5hr, ..... down to what looks like 7min @ 105A load.   Note that the load currents used to generate the curve are all 1/2 or x2 the adjacent point.

You can use the information from the curve as a "general" predictor for your battery.

IMHO .... If the battery is not new stock, even original curves are only a wild guess, as your battery will probably only exhibit a limited part of their published original total capacity.

The best way to curve them yourself using "your typical" load.   That way you have reading on "your" new batteries.    

But that is another conversation, as it requires a reliable Low Voltage Cutoff Switch ( Pic/Picaxe circuit ), reasonable "Typical for your use" fixed load, and a Timer.   If your Inverter has a LV Cuttoff and the battery voltage matches the Inverter input ( I assume you are a 12v system and that you have x2 the 6volt battery that you mention ), you can use that to measure "time to cutoff" which is what you are really interested in.

Published curves are nice, but the real issue is how does "this" battery compare to "my other" batteries under "my" load conditions.

Russ