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Posted to uk.d-i-y
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Bathroom switch - via relay?
wrote:
You can do. FWIW though 4x AA batteries cost about the same and hold a
lot more charge. PP3s are especialy bad deals in terms of energy per
cost. And C cells are much better than AAs...
Hmm, interesting. I don't know much about batteries, so I just picked
PP3 as the kind of thing that tends to hang around long-term in smoke
alarms and the like.
Unfortunately I've now built the box with a PP3-sized space in the
lower-voltage side, so I think I'll stick with it. If I find it needs
changing too often I can always stick a holder for four D cells to the
wall next to it, like an old-fashioned doorbell.
It could. That's true anywhere mains and LV coexist. A good method to
strongly discourage it is to have the 240v come in at a position where
the wires arent long enough to reach any low voltage part, make sure
theyre cord griped on entry, and cable tie L&N together so that if one
comes off it cant move far.
I've had a bash at actually making the thing, and what I've done is to
glue a plastic partition across the box - one half 9v, one half 240v.
The relay is glued into a hole in the partition, with the 9v half in the
9v cavity and vice versa. The connections to the relay are soldered, and
have then been covered in hot-melt so that any stray metal can't make
contact. These short connections go to terminal blocks for the in and
out cables.
Then you can earth the secondary side as an added precaution.
Interesting - not sure what you mean here. Just tie one leg of the
connection to earth, on the grounds that it won't make a complete
circuit with the battery? What about the other leg - I can't connect
them both to earth or I'd be connecting them together.
Cheers,
Pete
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