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What this motor type?

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perieanuo:
Relays are expensive,slow,not reliable.And big.
Put a relay if you want.I'll prefer always triacs or ssr-s
Regards,pierre


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Zero999:

--- Quote from: perieanuo on November 15, 2018, 04:19:12 pm ---Relays are expensive,slow,not reliable.And big.
Put a relay if you want.I'll prefer always triacs or ssr-s
Regards,pierre


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--- End quote ---
I don't think I've ever seen TRIACs used for changing the direction of a universal motor, simple on off or speed control yes, but not directional. There would need to be four to make an h-bridge. I can't see how it would be cheaper or less reliable than a relay, since it won't be switched very often. TRIACs also are more sensitive to current surges, over-voltage and false triggering, compared to relays.

perieanuo:

--- Quote from: Hero999 on November 16, 2018, 02:52:39 pm ---
--- Quote from: perieanuo on November 15, 2018, 04:19:12 pm ---Relays are expensive,slow,not reliable.And big.
Put a relay if you want.I'll prefer always triacs or ssr-s
Regards,pierre


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--- End quote ---
I don't think I've ever seen TRIACs used for changing the direction of a universal motor, simple on off or speed control yes, but not directional. There would need to be four to make an h-bridge. I can't see how it would be cheaper or less reliable than a relay, since it won't be switched very often. TRIACs also are more sensitive to current surges, over-voltage and false triggering, compared to relays.

--- End quote ---
Over voltage my a..ss,current BTA's have 600-800 Volts,over current if you have a shortcircuit both relay and triac dies.
If it's not often put an inversion switch like in drilling machines.
I like cause it's elegant.you put like you said a h-bridge of s202-s12 like ssd's and you're good.triacs are cheap for the currents they commute,relays not.false triggering never happens if you do your job right in command circuit.
Anyway false command may happen with CW-ccw from microcontroller.
I have one last argument :nobody uses mechanical relays anymore if you can do this with ssd's.even for slow commutation devices like valves and motors.
His demand to invert rotation on a classical motor is not usual thoe.
Anyway, I think I'm free to consider triac a better alternative, with respect others don't :)
Regards,pierre


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james_s:
Relays are more reliable than triacs generally speaking. There's a reason that even most modern iron transformer type xray machines have a mechanical relay for the secondary control. A triac or back to back SCRs handles the exposure timing but the relay is tested to verify it is open and then closes immediately prior to the exposure and opens once finished. Solid state devices usually fail shorted, adequately rated relays very rarely do.

perieanuo:

--- Quote from: james_s on November 16, 2018, 04:59:28 pm ---Relays are more reliable than triacs generally speaking. There's a reason that even most modern iron transformer type xray machines have a mechanical relay for the secondary control. A triac or back to back SCRs handles the exposure timing but the relay is tested to verify it is open and then closes immediately prior to the exposure and opens once finished. Solid state devices usually fail shorted, adequately rated relays very rarely do.

--- End quote ---
No they are not.In terms of reliability electronics beats mechanics.
If you don't know how to handle it it's another business.
If some machine use mechanical relay,ok,I can enumerate many others that don't.
Your example does't state a rule.It's just a simplier solution to securise an automation where hasard in commuting is disastrous.
In the OP case, doesn't seems to be (in fact, it's not mentioned if direction reversal is critical).
I will continue tu use ssr (just checked an 8amps 600 volts triac costs 0.3 euros in France from mouser).and if I need to deal with commutational hasard I'll just put electronical commutation verifications on triac involved.The protection will be much faster than mechanics.I saw already half a relay blocked (yes, welded contact) and the other relay contact who did his job.in this case, you're f..ed if you don't have hazard protection in place.
I'm speaking from some years of research and dev in medical and general electronics where security matters and cost you patient's life.
Pierre


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