About a mechanical relay

Comments

• Phil Pilgrim (PhiPi) Posts: 23,514

  2014-10-21 20:23 edited 2014-10-21 20:23

  The voltage rating has more to do with insulation integrity and arc prevention when the contacts are open than with current when the contacts are closed. So, no, I would never use a 120V-rated relay in a 220V circuit.
  
  -Phil
• LoopyByteloose Posts: 12,537

  2014-10-21 20:24 edited 2014-10-21 20:24

  While you are not exceeding the current limitation of 3 amps, and you are not exceeding the power limitation; being over the voltage limitation may cause insulation problems.
• stamptrol Posts: 1,731

  2014-10-22 04:51 edited 2014-10-22 04:51

  As has been noted, its probably wise not to knowingly exceed the manufacturers rating.
  
  That particular relay likely has a replacement that has a 220 volt rating if you wanted to change them out.
  However, there might be a serious problem with the spacing or current capability of the circuit board traces.
  
  In the circumstances it would make sense to use the existing relay to switch an external relay, either solid state or electro-mechanical, which has suitable ratings and can be mounted in a safe enclosure.
  
  Cheers,
• Paul Posts: 263

  2014-10-22 07:41 edited 2014-10-22 07:41

  According to the datasheet the contacts are rated for 1A at 250VAC (TUV). I have no idea what the "TUV" stands for.
  
  Link:[URL=" http://www.tianbo-relay.com/bigimg/15.pdf"] http://www.tianbo-relay.com/bigimg/15.pdf[/URL]
• Publison Posts: 12,366

  2014-10-22 08:04 edited 2014-10-22 08:04

  Paul wrote: »

  According to the datasheet the contacts are rated for 1A at 250VAC (TUV). I have no idea what the "TUV" stands for.
  
  Link: http://www.tianbo-relay.com/bigimg/15.pdf

  
  TUV is a testing and certification company, like UL listing:
  
  http://www.tuv-sud-america.com/us-en/tuev-sued-america/about-tuev-sued-america
  
  One amp at 220 volts is a maximum rating. That would be too close for comfort for me. I tend to double the ratings so I don't have to make service calls.
• Paul Posts: 263

  2014-10-22 09:03 edited 2014-10-22 09:03

  Thanks for the "TUV" info. I learned something today.
  
  Also, I agree it's best to stay below maximum ratings. Always give yourself a cushion. The 250VAC rating should be okay but the 1A is just too close for comfort.
• stamptrol Posts: 1,731

  2014-10-23 07:30 edited 2014-10-23 07:30

  The pic that the original poster used clearly shows the relay ratings as determined by UL for both Canada and the US. A datasheet rating is likely an "absolute maximum", not a rating to be used blindly in a consumer application.
  
  Also, without information about the circuit board ( trace dimensions, spacing and board substrate material ) that the relays are mounted on, they may in fact only be rated at a fraction of those values by the time you connect to the terminal screws.
  
  Cheers,
• LoopyByteloose Posts: 12,537

  2014-10-23 08:58 edited 2014-10-23 08:58

  I would not go toward 'absolute maximum' ratings for mechanical relays. It is a loosing bet if you desire reliable performance. Mechanical relays have long had a system of de-rating for specific uses to optimize longevity.
  
  What you need to do is to start with a relay that may be adequate AND derate it by the particular use. If also is important to have snubbers on the switching side of the relay to add useful life. Derating can easily be 40% reduction in current capacity. So a 5 amp relay in actual use may be used to only switch 3 amps.
  
  Here is a wikipedia entry on relays with discussion of derating --- http://en.wikipedia.org/wiki/Relay
  
  And here is a Pdf with more info on derating and extending useful life --- cp.literature.agilent.com/litweb/pdf/5988-6917EN.pdf
  
  You won't get much life out of a relay by going the opposite direction and attempting operation at the 'absolute max'. Those are intended to indicate safe limits for momentary abuses.