burosky said:
I'm just wondering if the LM1458 of ac current detector from Bowden's
Hobby Circuit doesn't need any supply at all. Since its pin # 8 & 4 are
not stated on the schematic diagram. Will it be possible to precisely
set any desired current setting to activate relay (i.e 4 amps). What's
the 1st op-amp used? Is it TL061/62? With regards to the pick-up coil,
are there any wounding procedures? Will it be right if I just wound it
continuously w/o putting anything between layers?
Hope you can help me with this.
As mentioned in the other posts, the LM1458 is an 8-pin dual op amp.
Even though the drawing shows two separate op amps, it's all one IC,
and all eight pin connections are there.
As mentioned at the bottom of the circuit description
http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif
the circuit is set to have the second op amp (which is used as a
comparator) turn on the transistor with a current of about 1/4 amp AC.
Also, as he mentions in the writeup, you can increase the sensitivity
by increasing the number of turns. You can also decrease the
sensitivity by decreasing the number of turns. They're not directly
proportional, though.
You should hook up a line cord to 4 ea. 100W bulbs, and reduce the
number of turns until it just doesn't turn on. You will then have
fairly reliable turn on at about 4 amps (or 480 watts at 120VAC). I
would guess something around half the number of turns on the U-bolt
would be a good start.
Magnet wire has a very thin enamel insulation, which is easily
scratched. It isn't necessary to provide insulation between layers.
However, it is very necessary to avoid winding over the threads of the
U-bolt. The sharp edges of the threads will short out the insulation,
and ruin your work. Make sure you use an iron U-bolt.
For a "real world" current detector, tape one end of a 6' zip cord to
the U-bolt, then solder the ends of the wound magnet wire to the
dressed leads of the zip cord. Also, be sure to at least tape the ends
of the magnet wire down. Once you've got it working, a layer of tape
all around might not be a bad idea. Copper wire of this diameter will
break out of spite if you even look at it wrong. And for hobbyist
stuff like this, electrical tape can be your friend.
Mr. Bowden's circuit is versatile, and can also be used to give a
fairly accurate reading of peak AC current (by measuring the voltage
across the second 10uF cap).
Good luck. Feel free to post again if you have any other questions or
problems, or to let us know how it works.
Chris
