[Fourlanders] Questions about portable power and solar

Ted Wood ted at k4k.pw
Tue Jun 23 16:57:37 EDT 2020


Fourlanders,

Field Day has me thinking about batteries and solar. I've wanted to 
retrofit my shack out with solar power for a long time and I was 
thinking a good starting point would be powering just the radio "stuff" 
first, upgrading until eventually everything is running off of it. I 
have started off very small scale with a PWM charge controller for the 
battery with the thinking that I could run the controller off of my 
shack DC power supply until I was ready to make the switch to a single 
PV panel. In this way, I had hoped I could run off battery easily and 
have a fairly robust and seamless charging experience and battery backup 
solution for the shack. Unfortunately, it would seem I did not do enough 
homework. DC power supplies are not appropriate power sources for a PWM 
charge controller. According to many online forums, due to the 
controller expecting a current limited source such as a PV cell, (and 
the DC supply is expecting the inverse) you have a situation where 
there's no current limiting and the controller will draw whatever it 
can, potentially damaging either the controller or the power supply.

Bearing this in mind, here's my goal. I'd like to have something that 
can take advantage of solar power, when it is available, to charge a 
bank of batteries but that can switch to charging via commercial power, 
by way of a DC supply like the one running my radio gear, either until I 
have panels installed or, once panels are installed, on a cloudy day. I 
know I can charge the gel cell battery just fine off a standard 12v 
supply but I'd like to use something that can float the battery instead 
of overcharging it and shortening it's lifespan (so something that can 
cut off the charging current when the battery reaches a voltage threshold).

Ideally the setup would look something like this fully time, the battery 
acting almost like a giant uninterruptible power supply.

Solar/Power Supply -> Battery bank -> Radio

What sort of device am I looking for? Do you have any resources that 
might help me understand these topics more? How do you do it?

-- 
73
Ted
K4KPW


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