My controller's LVD is 11.5V and won't turn the load on again until 12.6V, which does give the battery a chance to recover I think.
The sensing at the moment is simply done by the coil of the first relay across the 12V supply: if the 12V supply is on then the mains power is shut off.
You're right that if I make my voltage sensor more sophisticated then something like 12V off and 13V on (ie with decent hysteresis) might be good, and I could even bypass the controller and connect straight to the battery if I wanted. The relay I've specified only uses ~140mW, ie 12mA or ~0.25Ah per day!
Steady power draw should be about 25W or less (I hope); I get the laptop next week with luck.
Rgds
Damon[ Parent ]
I suspect you'll need a comparitor circuit with adjustable on and off points to prevent this.
Also, I think you'll only need 1 double pole single throw relay to do the switching. Use one pole to switch the positive side of the input to the DC-DC convertor. The negative can stay connected. The other pole can switch the "hot" side of the AC input to the computer charger. The 3rd relay you show at the output of the DC-DC convertor can be replaced by using 2 diodes (one from each charging source) to prevent backfeeding.[ Parent ]
Even if I use Schottky diodes, I think that I'd be wasting ~1W (0.5V forward voltage times a couple of Amps) out of a total power budget of ~25W or less. I did think about diodes, but I'm trying to be very energy efficient here.
And you're probably right that I could avoid DP relays, but I get a warm feeling inside totally isolating the unwanted supply, and the DPDT relays didn't seem (more) expensive... B^>
But, yes, thanks for the observations: they're spot on!
Here is the fun of DIY... B^>
Thanks for the prompting!
