[Elecraft] KX3 UPS - Battery charger AKA PowerGate

[Acbross via Elecraft]

I've been using that circuit for years, the double diode Schottky circuit, because the company I worked for at the time used that same circuit to keep the backup SLA batteries charged in their repeaters. It' a very simple circuit and you always have a charged battery when power fails. I believe this is the best way to go as you always have the DC batteries on trickle charge while the AC power supply is running the rig and supplying the trickling. So all my main radios are run from their own 100AH (sealed lead acid) batteries with a PowerGate type circuit keeping them charged. We don't have a lot of power failure where we live in AZ but during the monsoon rains we can get some power bumps. I like using this type of circuit because it isolates the radios from any of the power bumps and brownouts we sometimes get. Essentially all my radios are running off batteries. The changeover from AC to Battery is instantaneous with no hiccups no matter how many times the power bumps. I still use UPSs for my computers because their primary power source is AC.

I have used this simple circuit to power scanners and 2m radios during power outages. I used some smaller rated diodes then the ones called out because I had them. (15 and 20 amp) I had some 7AH batteries out of my UPSs and a 58 AH for my 2m radio kicking around. As long as the current draw does not exceed the rating of the diodes you're OK. I even heard of one person who was going to use diodes out of an alternator. Don't know if he did. I build my smaller circuits on a screw type terminal strip with a clip on heat sink on the diode and attach the strip right to the top of the battery with double stick tape. My scanner is run off a 12v wall wart and a 7AH SLA instead of a PS and works just fine.

Because of the drop through the diodes, you may have to turn up your voltage from the PS to compensate.

Been running several these circuits for several years with no mishaps. (always fuse power circuits)

Art - KC7GF