Your station is likely to shut down LONG before you get to 1.75V per cell. That's 10.5V battery voltage, and most all 12V ham gear I've seen is specced at 13.8V +/- 15%, so the low end is around 11.73V. Even if the radios do keep running, they may (at best) act squirrely, not put out full power, or just not put out anything at all. At worst, they may start generating garbage all over the band(s) as various circuits start operating outside their design parameters, or resetting the microprocessor and losing your settings, or even potentially damage themselves. (I've seen forum posts on a few highly microprocessor-controlled rigs that can wipe service settings in hidden menus that effectively leave the unit useless when the power drops too low.)
Also keep in mind, the voltage will sag some when you start pulling current. The larger your current draw is a percentage of the battery's total AH rating, the larger that sag will be. Different chemistries and designs will also affect that.
So I'd suggest you at least size up the battery so you don't fall below 11.7V or so (or be optimistic and go with 11.5V) for the desired "outage duration" you want to target.
Each person is different, of course, with differing motivations, but in my case I figured just getting a "backup battery" to standby on float all the time would be rather boring... I rarely have power outage, even short ones. And I wanted to be able to continue operating at full capacity even during an outage, so I just installed a solar system capable of doing that and am now off-grid full-time for the ham bench. I sized my battery bank primarily to handle the refrigerator as well during an outage, but that just means I draw it down even less during normal times. Or I can opt to run something else off of it "just because"! :) [ Parent ]
Just thinking outside the battery box for a second here... would it maybe make sense that rather than boosting my 13.8V battery bank (currently a bank of one) up to where I don't ever go below 12V, instead I add an appropriate 6V battery in series to create an 18V (or 20.7V) source and put in a heavy enough 12V regulator to run everything? Wouldn't that give me a lot more run time before it dropped below 12V? Or would I lose too much in the regulator to make it worth it?
Either way, I'm even more convinced that I need to increase my solar output.[ Parent ]
PowerSteam makes an off the shelf solution. Input shown as 9 to 14V. Output of 13.8V. ~90% efficient. Starting at $120. There is a note about ham radio use at the bottom. http://www.powerstream.com/dc2.htm
It may be a non issue. Like Bob said, I would not run the batteries below about 12.2V if there was a way around it. The fancy charger on a generator, a $10 handyman generator, long jumper cables to an idling car... G-[ Parent ]
