Author Topic: Snubber for relay  (Read 1228 times)

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Offline iXodTopic starter

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Snubber for relay
« on: September 13, 2019, 05:44:02 am »
I want to use a simple RC snubber on a relay that provides 230vac to a small controller board (low voltage inputs and outputs).

The relay NO contacts switch one leg of the 230v. The input of the controller PCB consists of a 10w TDK-Lambda PS brick.

The snubber will be a simple series 0.01uF cap and 220 ohm resistor—unless anyone has other values to suggest.

But my question is really this: do I place the snubber across the relay contacts or across the AC input terminals of the PCB?

Thanks.
« Last Edit: September 13, 2019, 06:16:23 am by iXod »
 

Online Zero999

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Re: Snubber for relay
« Reply #1 on: September 13, 2019, 08:42:33 am »
What are you trying to achieve?

A relay snubber can help by reducing arcing when switching inductive loads, but a switched mode power supply is not an inductive load. It's capacitive, so a snubber will do nothing. If you want to increase the contact life of the relay, then limiting the inrush current to the switched mode power supply will do a lot more than a snubber.
 

Offline Le_Bassiste

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Re: Snubber for relay
« Reply #2 on: September 13, 2019, 01:46:47 pm »
as for the question where to put the snubber, you would put it across the load's contacts, not across the relay contacts, because you want to avoid any leakage currents into the load while the relay contacts are open.
and, as zero999 already stated, such a snubber protects the contacts from inductive loads, it won't help on capacitive loads.
however, if your power brick contains a (either active or passive style) PFC front-end, having a snubber is not a bad idea at all (in addition to an inrush limiter).
An assertion ending with a question mark is a brain fart.
 

Offline iXodTopic starter

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Re: Snubber for relay
« Reply #3 on: September 13, 2019, 03:40:42 pm »
Can’t tell if this PS has PFC front end:

https://www.us.tdk-lambda.com/ftp/Specs/kw.pdf

Datasheet says inrush is limited to 30A for this model (10w) with nominal 200v input.

I’d like to further limit inrush when the relay contacts switch on.

Thanks.
 


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