DIYbanter - View Single Post - A wall-wart alternative

wrote:
Bill_M wrote:

Of course you don't have enough current for the audible device so your smoke
detector should sit quietly by while you toast!

No. That current would come from the 9 V trickle-charged battery.

We might replace it every 6 years or so, if the alarm
fails to shriek with the test button.

Nick

But youve then got a battery alarm, not a mains/battery one. Whats the
point of running a mains supply to it if it wont work off the mains
supply.

I always wondered about using miniature audio transformers for mini
psus, get it ringing at eg 500Hz with a series cap. Wont have enough
insulation to be touch safe though. But maybe custom tfs could work.
But not worth it, as the bigger 50Hz transformer would be cheaper than
the cap.

NT