From: no@never.com
On Sun, 14 Apr 2013 04:22:23 +0000 (UTC), danny burstein
wrote:
>Hoping somenone can give a pointer to a device
>which I'd have thought would be readily available,
>but I'm only finding Big Expensive Fullscale setups.
>
>We've got a sump pump in the basement. I'd simply
>like to know when it turns on (there's a "float" switch).
Get an inexpensive current transformer, say, 50:1. Pass one motor lead
through it. Digikey/Mouser has 'em. Measure what the inrush of the
pump motor is. Let's say it's 20 amps. 20 / 50 = 400 ma on the
secondary. Pick a burden resistor that would produce say 10 volts at
that current. 25 ohms 5 watts will do.
from the burden resistor, place another resistor and zener (with back
diode) to give you the voltage you need to operate a small lamp or
LED. The zener will keep the lamp from flashing too brightly and
shortening its life on inrush.
zener
+-----------/\/\/\----+----------+----------/\/\/\/-----
| | |
| back diode --- ---
/ \ / / \ zener To lamp \
burden --- --- or zener
/ resistor | |
\ | |
+----------------------+----------+----------------
from CT
Shouldn't cost you over $15.
If you want to buy something already made, look at TimeMark's current
switch. First product on this page
http://www.time-mark.com/SearchResults.aspx?categoryID=3
Their stuff is very inexpensive. I'd guess about $30 for that unit.
Maybe twice that for a high mark-up vendor like Granger.
John
John DeArmond
http://www.neon-john.com
http://www.fluxeon.com
Tellico Plains, Occupied TN
See website for email address
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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