Alt-BEAM Archive
Message #10560
To: beam@sgiblab.sgi.com
From: "Sathe Dilip" sathe_dilip@bah.com
Date: Sun, 20 Feb 2000 22:49:02 -0500
Subject: [alt-beam] Re: Breadboarded solenoids
Did you get a chance to measure the current requirement of your
solenoid? I think the culprit may be that it requires a lot of current
(in Amps - instead of miliamps as with using a BEAMish motor). When you
are using a transistor as a switch, the transistor needs enough base
drive to saturate at the required load current. If the drive is
insufficient, the transistor goes into linear operating region & drops
most of the voltage across itself. This in effect does not produce the
required result; which is to give (almost) the full available power to
the load.
A solution would be to use a quality mosfet (low operating voltages, low
ON resistance, sufficient current rating etc) to drive the solenoid. A
low gate current SCR might work (again if it does not drop a lot of
voltage across itself in ON condition and I am hoping the solenoid
drains the capacitor enough to drop the current below the SCR's holding
current for commutation).
Measure the coil resistance & post to the list so that those who have
been in similar situations (driving/switching relatively high current
loads at low supply voltages) can recommend suitable components. An
indication as to which circuit configuration you are using (a reference
to related web page or something) will also help.
Note: One experiment you can try to see if the capacitor can provide you
with enough oomph is to charge the capacitor to 5 volts or so & then
connect the solenoid directly across it. This is the most power you are
likely to get even with the best of switching device. If you are not
satisfied with the kick of the armature, you will have to increase the
capacitor size as well.
Dilip
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BUDSCOTT@aol.com wrote:
>
> well, i breadboarded (or protoboarded, whatever) the solenoid photovore that
> i've been working on. now i swear i saw the solenoids triggier once, but then
> i couldn't get them to trigger. i've got the circuit all hooked up correctly
> as well as the solenoids. i've got two 4700uF caps hooked in parrallel, 1381L
> (3.0-3.3v), and a large 5.5v solar panel, but the piece of #$%& still won't
> work! i realize that transistors limit the current somewhat from the current
> going to the base, but i still think that it would trigger the #$%&
> solenoids. Patients is a virtue, or an asset, i cant remember which, any
> insight? Thanks o ton for help!
>
> -Spencer
--
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The early bird may get the worm, but the second mouse gets the cheese.
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10561 Mon, 21 Feb 2000 16:44:28 +1300 [alt-beam] Re: walker - a bit better "Seamus Allan" Umm, just wondering, are you sure you put them in *Parallel*?? You should
put them in series to increase voltage, not parallel.
>. Im suspecting battery trouble. They're 2 no name
> generic lithium batteries, each 3V, put in parallel for 6V total. What do
> you think?
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