[Elecraft] RE; How well does the K3 work with lower power supply voltage . . .

[John Kountz]

Doug,
Like the Monte Python joke, 
Observer: My dog has no nose
Question: How does it smell?
Observer: Horrible!
I have two K3 transceivers and have attempted to use them on several Field Days with limited joy and unlimited disappointment.  I've attempted to use one or the other with 120 Watt solar cells and 100 
AH GelCel and/or Lead Acid batteries which had been charged beforehand.  As long as there is healthy sunlight and you have a duty cycle of between 10 and 15 percent transmission with 85 to 90
 percent monitoring you'll have a functioning station.  But, when the sun goes down or you get into a run you'll find yourself out of order.as the battery drops below a nominal 13 VDC..  Operation after  twilight, forget it.  Again, it's the 13 VDC cutoff.   I've used 40 amp boost converters supporting a 13.6 VDC out for a range of input voltages with success, but you can end up frying a battery as the converter struggle to suck 13.6 VDC out of a battery dipping below 10.5 VDC on transmissions.  Although I've not tried it, I suspect a Yamaha or Honda 1 KW generator would keep the K3 running, but you're in another category.
Have fun and 73,
John Kountz WO1S