Subject:
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Re: Controlling an Electromagnet (LSM)
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Sat, 24 Dec 2011 20:49:51 GMT
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Viewed:
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26756 times
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Iain,
How much power do you want for the electromagnets, and how rapidly do
you need to switch them on and off? Old-fashioned relays will give
you the least power loss, but can't be switched very quickly. They
also have a limited life (between 10 and 100 million cycles, depending
on the manufacturer and what failure rate you consider acceptable).
The usual spec is MCBF (mean cycles between failure), and you will
start getting some failures at about 0.2 MCBF.
See
http://www.digikey.com/Web Export/Supplier Content/Coto_306/PDF/Coto_Testing_Reed_Reliability.pdf
You'll also want to make sure your relay contacts are rated formore
than your DC load, as switching inductors results in large spikes.
Schottky protection diodes are often used to provide a return path to
short out the spikes. (See http://www.azatrax.com/relay-contacts.html
for example).
If you need faster switching (like for pulse-width modulation), your
best bet is to use power MOS transistors with Schottky protection
diodes. If you don't need much current (say 5 amps) but need to be
able to reverse the current through the electromagnets, you can buy
off-the-shelf H-bridge chips. There are plenty of H-bridge circuits
on the web.
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Message has 1 Reply:
 | | Re: Controlling an Electromagnet (LSM)
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| (...) Or... avoid both stock relays and chip-based switching. For a linear motor you want to trigger each electromagnet in a series, you ideally you might like a "push-pull" system, where you aren't just turning a magnet on and off, but reversing (...) (13 years ago, 31-Dec-11, to lugnet.robotics.rcx)
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Message is in Reply To:
| | Controlling an Electromagnet (LSM)
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| Hi all, It's been a while! A long while ago, while in elementary school, I used LEGO to build a manually-operated Linear Synchronous Motor (LSM) for a science fair project. I want to revisit this as an adult and built a full test track with a couple (...) (13 years ago, 24-Dec-11, to lugnet.robotics.rcx)
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