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Relay Delays (using relays in H-Bridges) — Parallax Forums

Relay Delays (using relays in H-Bridges)

Armored CarsArmored Cars Posts: 172
edited 2005-04-04 16:36 in General Discussion
Do solid state relays have a delay that would make them not work for H-Bridges?

Comments

  • Robert SchwartzRobert Schwartz Posts: 141
    edited 2005-03-11 01:34
    You can use a relay to control a motor (or similar load). I wouldn't suggest using PWM through them, as I don't think that they would last long being switched back and forth thousands of times a second, and I doubt if they will even switch at such a fast rate. Using one a DPDT relay as a means of controlling a motor (off, fwd, reverse) would be pretty straight forward. Just attach the leads of one side to the motor in one direction, and to the other side in an opposite direction (+ to NO and - to NC on one side, + to NC and - to NO on the other). Use a transister to power the relay, not the stamp directly though, I think that the current drawn by a relay will burn out the I/O pin. I can draw a complete schematic for you if you need. This won't be a H-Bridge though, but functionally similar.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-04-04 16:36
    The problem with using solid state relays for H-Bridges is in their configuration.· It isn't about delay.· In fact, the response should be much faster than mechanical relays.

    They are single pole, single throw.·(spst)

    That means that you would have to wire up quite a few to get an H-bridge (a minimum of four). I am not sure how you could do it.

    It seems like you could configure the four solid-state relays to work together by having half of the inputs inverted by digital logic (a 74HC14 or similar).· The delay would still be much smaller than anything mechanical.

    The usual relay setup for one motor is a double pole, double throw (dpdt) setup.·

    Also, the solid state relays really are best for driving high voltage AC from a digital logic.· There is no need to have all that isolation for DC unless there is a severe noise·problem from the DC motors [noparse][[/noparse]my guess is that usually brushes are the source and running real powerful motors the problem].· And, I am not sure that they would hold up well to all the noise.

    In hobby robotics, it seems more cost effective to use transistors and optical isolation of the inputs [noparse][[/noparse]which may not be·always necessary].

    I am curious to what you have in mind?· What DC voltage and how many amps.· I have a little board that drives up to 30 volts at 4 amps that is merely 1.5 inches by 1.5 inches.· It uses a rock-solid LM298, provides for two motors, and even has LEDs and provides some regulated 5v DC for other uses.· BUT - no isolation.


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    G. Herzog in Taiwan

    Post Edited (Kramer) : 4/4/2005 4:53:38 PM GMT
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