[Elecraft] Power Supply Question

[G3VVT at aol.com]

Hi Fred,
 
Your PSU has probably suffered the same fate as our local 70cm repeater PSU  
did when we floated a battery across the output for emergencies. When the PSU  
was switched off it blew the DC fuse on the output of the PSU.
 
The reason is the battery is capable of feeding enough power back into the  
PSU to exceed the current rating and rupture the output fuse which normally  
protects the PSU. The solution in our case was to fit a relay on the PSU DC  
output with it's coil powered from the AC supply. When the AC supply fails,  the 
DC output link is cut off from the PSU.
 
Not all PSU suffer this problem as we never had a problem with the 2m  
repeater with floating a large gel cell across that, but yours apparently  did!
 
Regards,
Bob, G3VVT