Wiring power adapter to charge batteries while powering device

Thread Starter

Matthew247

Joined Sep 2, 2018
3
Hi my electronics is rusty (ne 20yrs since I studied it) so sorry for the obviosly basic question. I want some advice on how to rewrite my home radio so that the 6xAA rechargeable batteries it uses get powered by the external adapter when that is plugged in.

From reading other posts the general advice is charged >> battery >> device

Batteries are in series, connected to the device board. Currently when the power adapter is plugged in the circuit switches to get supplied from there (mechanical switch). If I get the principal, i should “hard wire” the circuit to always use batteries, and connect the external adapter to the battery pack in parallel with the circuit, and lower the amps from the adapter to a trickle voltage suitable for charging. Does that sound right? Anything else that I should consider?
 

MrChips

Joined Oct 2, 2009
20,239
Welcome to AAC!

Sounds right.
You should connect a forward biased diode between the charger and the battery so that the battery does not discharge through the charger.

Charger --->|---- battery --- radio

What type of rechargeable batteries?
Different battery chemistry require different charging strategy.
 

Thread Starter

Matthew247

Joined Sep 2, 2018
3
Welcome to AAC!
What type of rechargeable batteries?
Different battery chemistry require different charging strategy.
Thanks! I expect it’ll be the regular Nikel cadmium type AA’s, but I see there are now Litium Ion AA’s available these days so I may go for those
 

-live wire-

Joined Dec 22, 2017
907
Thanks! I expect it’ll be the regular Nikel cadmium type AA’s, but I see there are now Litium Ion AA’s available these days so I may go for those
NiCad? Those are ancient. Nothing really uses them anymore. They have extremely inferior characteristics, including when you account for cost. Also, they are pretty poisonous. So when you use batteries from the 21st century, and throw the NiCads, dispose of them properly.
 
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