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Switching ON a 35A mains power relay?

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cupoftea

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Hi,
Regarding this 35A 277VAC power relay (12V coil)
https://www.panasonic-electric-works.com/cps/rde/xbcr/pew_eu_en/ds_hes_en.pdf

Is the best way to switch it on as follows…
a…Wait for mains zero crossing…
b…apply sudden step of 12V to the coil, so that current builds up as quickly as possible in the coil and reduces bouncing time as much as possible.
c….Wait x seconds, then reduce current to the holding current.

…or should the initial coil voltage applied be say 18V, in order to reduce bounce time even further? (and thence reduce the chance of contact welding?)
Is it worth waiting for the mains zero cross?....i mean, its going to bounce over the mains half cycle interval anyway?....(strange that the datasheet doesnt give the bounce time?)
 
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Hi,

a)
waiting for mains zero cross is useless. It has no influence on coil behaviour. And the contact timing is not that accurate and precise to switch at mains zero cross. (operate time is specified to be 30ms max. but there is no min specification)
.. so it could be 20ms (zero cross @50Hz) or 25ms (peak at 50Hz) ... plus contact bouncing

b)
Bouncing is not specified at all.

c)
Reducing current is just for saving power and reduce coil heating. I don´t think it has influence on contact bouncing.

Mind:
Reduced coil current will make the contact bouncing more prone to mechanical vabration. In worst case the contact will OPEN and stay OPEN.
So it´s not recommended for high vibration environment.

Klaus
 
Thanks, what about appying 150% of niominal coil voltage to start off with (switch relay ON)?
 

Hi,

as with a couple of "inductive" applications.... you may apply a constant current. If you do this within the rated 157mA, there should be no problem for the relay. You may apply 100V ... the magnetism will build up, and the same way the current will build up (or vice versa)... at a certain current (magnetism) the contact will start to move.
And the voltage will automatically drop down.

This will speed up operation time. While it will not overheat the coil.
(for sure there is a voltage limit because of coil wire isolation)

Klaus
 
Don't think that reduced holding voltage has an effect on contact bouncing, because the voltage will be reduced long after make. Holding voltage can be reduced in almost any application, perhaps except those with extreme mechanical vibrations exposed to the relay.

As stated, it's impossible to predict contact closure time better than 5 or 10 ms, even with higher coil voltage. I won't be sure that higher coil voltage reduces bounce time, it may have an opposite effect as well.

Just use the relays like everyone else.
 

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