OT - Strange Battery Markings on UPS Battery

[The Other Mike]

No mention at all of of ampere hours, just a manufacturer specific part number and this: "12v 36W/cell 15 min" The dimensions indicate something around 7Ah although the battery bay also contained a dummy battery of the same size.

The UPS was allegedly rated at 650VA (for how many seconds?) and had been in service for about 10 years. It easily held the PC up during numerous relatively short mains voltage dips until it had to cope with an extended power loss that didn't auto shutdown the PC.

But at least I could remove the battery without an angle grinder/axe/chainsaw as fortunately the UPS wasn't made by APC.

[Lobster]

Does that mean what I think it means (he says, having bought an APC UPS a couple of weeks ago :( )

[harry]

They are giving up on ampere hours to size a battery as it is meaningless anyway. It says it will deliver 36 watts per cell for 15 minutes. Iif it's 12 volts it will have six cells. So that's 432 watts for 15minutes.

15 minutes so divide by four = 106 watthours Divide by 12 volts= just over 10 ampere hours.

[Andy Burns]

Uh-huh ...

So with a bit of multiplication and division, you convert their number into the "meaningless" amp hours figure anyway?

[The Other Mike]

Who is they?

When I said it was "something around 7Ah" that wasn't a wild guess, it was based on the dimensions and the very comprehensive datasheet and application guide of a major battery supplier who don't mention W *anywhere* with the exception of Energy Density in Wh.L.20hr and Specific Energy in Wh.kg.20hr.

[Mike Tomlinson]

En el artículo , Lobster escribió:

They're well known for overcharging and cooking their batteries.

[Ian Jackson]

In message , harry writes

The amp-hour duration falls as the current is increased. I'm more familiar with 'so many amp-hours at a such-and-such a current'. Sometimes two or more AH ratings are given, for different currents.

However, why do they use 'watts per cell for so many minutes'? Although it's sometimes nice to know, the actual number of cells is rarely of any interest whatsoever to the normal user. I would have thought that '432 watts for 15 minutes' would be simpler, and more logical.

[Andy Champ]

36W at 2V = 18 amps, so if it will do that for 15 minutes that's 4.5AH. Odd... OK, what's 6 * 36?

Andy

[harry]

It's meaningless because the power output depends on volts as well as amps.

The time is specified because the total amount of electrical power available from the battery falls as the current is increased, more power is lost as heat within the battery.

[harry]

Just so you can compare the two systems.

[harry]

36 watts per cell. If it's 12 volts there will be six cells assuming lead acid/gell cell technology.

[Andy Burns]

Visited an occasional customer today, they'd had an aircon failure (actually I suspect they had one ages ago and didn't notice until the second one failed).

Ambient temperature in the room 42 degrees, servers all shut off automatically, internal temperature of APC SU10000RT 57 degrees, I don't suppose that's done much for the battery pack's longevity :-)

The account that should have received an email alert had been deleted!