From: ekblaw@vnet.ibm.com   
      
   Louis Ohland wrote:   
   > Rick, what would be the minimum rated Watt-Hour for the battery pack?   
   > 180W over 10 seconds?   
   >   
   > Assuming a 12v battery pack...   
   Louis, your battery engineer is just going to shake his head sadly at   
   you, as the watt-hour rating for this battery pack is going to be   
   irrelevant because you're not looking for it to provide continuous power   
   for even a minute, much less an hour.  Since you want to assume a 12V   
   pack instead of my suggested 24V, to get to 180W you need 15A of current   
   coming out of that pack for the 10 or 11 seconds required -- actually a   
   bit more because you will have some losses involved inverting the DC   
   power output into AC to back-feed the PSU -- unless the battery backup   
   is just used to feed the DC section of the PSU, which might be the way   
   IBM did it.   
      
   As I think about it, feeding the DC section of the PSU is more likely   
   than doing the AC inversion.  Since the highest output voltage is 12V, a   
   12V battery pack would be just fine.  But you said the charger is rated   
   for 26V, so that would suggest a 24V battery pack.  It's all getting   
   complicated, for sure.  But if you pressed your battery engineer for a   
   watt-hour rating for this hypothetical battery pack, it would probably   
   be in the high single digits, maybe as much as 10 -- certainly nowhere   
   close to the 100+ rating of the 1290 12V SLA battery pack.   
      
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