Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: metaphysics1221 on May 17, 2009, 09:31:50 PM
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I need to build a control circuit for an underwater robot. I've been trying to use MOSFETs in an H-bridge, and my circuits work...occasionally. I would like to try relay control.
My questions:
1. When a relay is labeled something like "5V, 12A" what is what? It doesn't require 12A to trip the coil? Is it 12V to turn it on, then the internal switch is rated 12A?
2. How much current do these draw, just as a guess? Is it at all possible I could directly wire this to an Arduino microcontroller?
3. Anything else I should know about relays? My knowledge of electronics is limited, so any comments you have are welcome!
Thanks!
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Answers:
1. The voltage is typically the turn on voltage of the coil.
2. Expect to need a transistor. The max output for the Arduino is 40mA. There are lots of tutorials for how to hook this up using bipolar transistors.
3. Relays have a limited life since they are mechanical devices. You get what you pay for.
Unless you need lots of power consider some of the many off the shelf H bridge units on the market.
Best Wishes
Kirk
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Hi,
1. When a relay is labeled something like "5V, 12A" what is what?
Coil is for 5V and the relay contacts can handle up to 12A (non inductive current typically).
2. How much current do these draw, just as a guess?
Somewhere between 50mA and 150mA would be a guess. Probably in the upper half of that range, given the contact rating.
Is it at all possible I could directly wire this to an Arduino microcontroller?
Not really, besides the drive current, you also have to consider spikes from the relay, as they might not be properly dampened by the conventional diode protection.
3. Anything else I should know about relays?
You should allways mount a diode (or two, depending on the configuration) to protect against inductive spikes.
It should be the fastest diodes that you have, which is able to handle the spike energy.
And of course, a simple transistor driver, to go in between the controller and the relay.
My knowledge of electronics is limited, so any comments you have are welcome!
With that comment, I'd advise against trying to complete an underwater robot - better start with something simpler.
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You still need MOSFETs when using relays, so you're just over complicating things . . . why do you want relays?
With that comment, I'd advise against trying to complete an underwater robot - better start with something simpler.
Hey, no discouraging comments! :-X
My attitude is a beginner can do anything, as long as he does his google search homework first :P
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Hi,
Hey, no discouraging comments! :-X
My attitude is a beginner can do anything, as long as he does his google search homework first :P
Wasn't ment to discourage, merely to say: Crawl before walking (running) - building experience in a way that doesn't disappoint so much that you give up this fun hobby completely.