Measuring Reserve Capacity in Minutes Question

[mgray70]

I purchased a battery discharger that will discharge 36 or 48 volt packs and measure the minutes. My question is let's say the minute rating @75 amps is 105. Is that 105 minutes to completely dead, or 50%. This thing shuts off at 31 volts under load on 36v packs and 41 volts on a 48v pack. Any advice on this thing is appreciated. I know how to use it, just not exactly sure how to interpret the outcome.

[ThreeCW]

By definition for a 12 volt battery:

What is reserve capacity (RC) and why do battery manufacturers bother to mention it? The Battery Council International (BCI) has created a group of standardized specifications that help give consumers an apples to apples comparison from one product to the next. Cold cranking amps is one of those specifications, as is Reserve Capacity. So what is Reserve Capacity? It is a time measurement that explains how long a fully-charged battery can deliver 25 amps of current in an 80°F-environment, before the battery is discharged down to 10.5 volts.

[CCNorth]

Originally Posted by mgray70

I purchased a battery discharger that will discharge 36 or 48 volt packs and measure the minutes. My question is let's say the minute rating @75 amps is 105. Is that 105 minutes to completely dead, or 50%. This thing shuts off at 31 volts under load on 36v packs and 41 volts on a 48v pack. Any advice on this thing is appreciated. I know how to use it, just not exactly sure how to interpret the outcome.

I'll go out on this limb and suspect I'll fall off, but here goes.

The way I understand it is that the discharger will only drain the 36v batteries to a set point of 31.5 volts within the preset time of 105 minutes. So, after 105 minutes the batteries are at 31.5 volts. The battery capacity percentage is determined by how much longer or shorter time it takes to reach 31.5 volts. For example, if it only takes 92 minutes (rather than 105 minutes) then the number is written as 92/105.
92 divided by 105 equals 0.876 which is 88 percent.
88% is said to be the battery capacity. Use the manufacturer's recommendation as to when batteries should be replaced.

If it takes longer than 105 minutes then there's a problem. You have to restart the charger and measure each batter to find the problem. Readings should be 1.74 volts per cells (18 total) or 5.25 volts per battery (6 total).

As you said, the discharger can be set for 48 volt batteries. The math is the same for determining battery capacity percentage.

You can change the default settings but I will not pretend to understand under what circumstances that should be done.

Did this sort of answer your question?

[mgray70]

Originally Posted by CCNorth

I'll go out on this limb and suspect I'll fall off, but here goes.



The way I understand it is that the discharger will only drain the 36v batteries to a set point of 31.5 volts within the preset time of 105 minutes. So, after 105 minutes the batteries are at 31.5 volts. The battery capacity percentage is determined by how much longer or shorter time it takes to reach 31.5 volts. For example, if it only takes 92 minutes (rather than 105 minutes) then the number is written as 92/105.

92 divided by 105 equals 0.876 which is 88 percent.

88% is said to be the battery capacity. Use the manufacturer's recommendation as to when batteries should be replaced.



If it takes longer than 105 minutes then there's a problem. You have to restart the charger and measure each batter to find the problem. Readings should be 1.74 volts per cells (18 total) or 5.25 volts per battery (6 total).



As you said, the discharger can be set for 48 volt batteries. The math is the same for determining battery capacity percentage.



You can change the default settings but I will not pretend to understand under what circumstances that should be done.



Did this sort of answer your question?

Yes, it helps. That was kinda what I was thinking. I was wasn't completely sure. thanks!

[Sergio]

If You look at the battery spec sheet, the "Minutes @ 56amps" for 8v batteries and the "Minutes @ 75amps" for 6v batteries rating is while each cell stays above 1.75v or 31.4v (6x6v) and 42v (6x8v).

Like CCNorth said, you first fully charge the batteries and then hook up the pack to the discharge machine.

Once the machine fully discharges the batteries and shuts off, you compare the time it took with the battery rating to figure out your percentage against a new battery.

[mgray70]

Originally Posted by Sergio

If You look at the battery spec sheet, the "Minutes @ 56amps" for 8v batteries and the "Minutes @ 75amps" for 6v batteries rating is while each cell stays above 1.75v or 31.4v (6x6v) and 42v (6x8v).



Like CCNorth said, you first fully charge the batteries and then hook up the pack to the discharge machine.



Once the machine fully discharges the batteries and shuts off, you compare the time it took with the battery rating to figure out your percentage against a new battery.

Thanks Sergio! That's simple enough. It can get confusing with amp hours, , but this is understandable. I just wanted a better way of testing battery capacity other than guessing. Thanks!