How? I can't see it. Not unless there's another relay controlling the main charging/load-switching relay.

It would be a repeat cycle timer that would momentarily open the relay coil circuit, either by switching off a semiconductor device or by opening a contact in series with the relay coil. If it were an actual semi device then the power source connection would require careful evaluation to avoid a crossed circuit condition.

 

Hear is a modified circuit to get around the problem the sghioto spotted in post #59

It involves adding a second relay that disconnects the load from the battery if there is an output from the charger

Les.

 

With that configuration K2 is activated by the battery when the charger is OFF.
I think like this:

 

That's why I loved picture books as a kid. That I can see. I don't recall if I mentioned a second relay or not. I'll have to look back and see. But yes, this solution would work nicely. And it doesn't have to be once every 5 minutes, it could be every 2 minutes. That would reduce the amount of discharge from the battery through the latched relay. (just a suggested tweak to the timing)

 

I agree that K2 will be activated via the back feed through K1 NO contact until the next 1 second pulse causes K1 to open. This will mean that the TS has to wait up to 5 minutes after the charger is switched off before the radio comes on. I think your idea of monitoring the battery voltage to decide when the charger is on would be better. If it was an old style (Transformer and rectifier.)charge detecting 100 (or 120) hz ripple on the battery voltage may work. If it is a modern switch mode charger then there probably would not be any 100/120 hz ripple. (I have never looked at the output of a modern switch mode charger to see if there is any noticable ripple (Either mains or PWM frequency.))

Les.

 

TS has to wait up to 5 minutes after the charger is switched off before the radio comes on

I drew a radio to show what I have in my shop (sort of). The TS has Aqua LED's for a load. It appears to me that the LED lights may be a night light of some size that is charged during the day and illuminated during the night. But yeah, I hear you.