Cheap Relays

[RukyCon]

Hello, i want to know your opinion on relays you can get from sites like ebay, banggood, etc. The reason i want to know is because i've been hearing some people calling them good or decent or something like that.
Now i know they won't be as good as the name brand manufacturers but that does not mean they can't be used at all, right?
Thanks.
^{Note: I don't buy all of my electronic components from ebay or banggood, i do sometimes buy electronic components from mouser or digikey.}

[georges80]

Your location flag shows US. I can't imagine why you wouldn't just order from a US distributor (mouser/digikey etc as you state you already use). You will get a 'real' part with complete datasheet/specs etc.

I understand folk in other countries ordering from various grey markets, but within the US we have decent prices for small volume components and not need to deal with suspect components/performance issues (let alone suspect sourcing and handling of those parts in the grey market source/delivery chain).

cheers,
george.

[Yansi]

From my experience I would strongly recommend against using cheap OneHungLow contact switching devices. Doesn't matter if small PCB relays or DIN mounted contactors.

Those brand name ones aren't expensive at all, if you choose from a standard series. Takamisawa, Omron, Finder, Schrack, TE,... are the ones to go.

[RukyCon]

The two most common brands you can find are Hui Ke and Songle.
I looked up both brands and i could not find much info about Hui Ke (i did find a email address) but Songle has a website with datasheets of most of their relays. (The datasheets also have UL numbers in them)
But of course as most of us know that does not always mean the Songle relays on ebay are real.

[Yansi]

I do not think there is a need to buy cheap relays, unless producing large volumes of stuff where price is the significant design considerations.

For example: Omron G5LE can be bough for $1, readily available at multiple distributors. Why bothering with the Songle Chinese equivalent even though the Songle costs half that? I think $1 is a fair price for a reliable relay of that size.

I would never trust a Chinese relay. I have seen so much melted or blown to shits relays over time,... just no. We've had problems even with cheap small brand relays made in the EU*. Can't imagine what those Chinese would do.

*Relpol to be exact. Avoid it!

[RukyCon]

For example: Omron G5LE can be bough for $1, readily available at multiple distributors. Why bothering with the Songle Chinese equivalent even though the Songle costs half that? I think $1 is a fair price for a reliable relay of that size.

The Omron ones may be cheap but that low price is usually outweighed by the shipping cost...

I would never trust a Chinese relay. I have seen so much melted or blown to shits relays over time,... just no. We've had problems even with cheap small brand relays made in the EU*. Can't imagine what those Chinese would do.

Now what if i used the cheap ones at less than half their rated current.

BTW when i do need a relay for a high current application i do end up using a name brand one. Here i'm just talking about relays for medium to low current applications.

[NiHaoMike]

For low voltage DC, use automotive relays which are specifically designed for that.

[ez24]

You may have better luck if you use 10% of what they say.  ie don't use more than 1a for a 10a relay. Seems to work for me.  Blueskill what do you think, should it be 1%?

In the 80's and I went into a factory in Taiwan and asked what was the power rating for an amp - they said whatever I wanted could be printed on it.  So a real 1w amp could easily be a 1000w amp!  Magic 

[RukyCon]

I cracked open one of the cheap relays i have (Songle SRD) and it looks decent.

[Simon]

Things like relays appear simple and hard to get wrong until you realise that actually to last for the amount of cycles real good design is required. Of course if you don't need the relay to last long then it probably does not matter.

[RukyCon]

I cracked open one of the cheap relays i have (Songle SRD) and it looks decent.

The money shot is under the metal cover, the contacts. There are 2 discs (for type A/B, 3 for type C) welded on opposite contacts of the cantilever, that's what determines the lifetime.
Good relays have platinum, palladium or rhodium plated contacts, cheap relays have nickel plated contacts. Gold plated contacts are rubbish for power relays, don't fall into the trap.
Gold is too soft to resist the arc. But the non oxidizable property means gold relays have very low minimum contact voltage (no oxide to breakdown), so gold contacts are commonly used in low voltage signal relays.

It's hard to tell what they are but here is a close-up of the contacts.

[John Heath]

Mass produced at high volume is one rule of thumb. If they make 100 of thousands then any bugs in it production and design have already been worked out. Cheap does not necessarily mean bad. 

[rrinker]

 I was planning to use Songle SRD series in my project, but then I am only switching about 15V square wave AC at usually no current flow, worst case less than 1 amp. The contacts will have to carry less than 1 amp max, at that voltage, but when switching there ideally should be no load. I suspect these will be just fine.

[John Heath]

I was planning to use Songle SRD series in my project, but then I am only switching about 15V square wave AC at usually no current flow, worst case less than 1 amp. The contacts will have to carry less than 1 amp max, at that voltage, but when switching there ideally should be no load. I suspect these will be just fine.

A no load relay is a whole different story. Watch out for the wetting current spec. Relays depend on wetting current , spar on contact for self cleaning. The spar will resurface the contacts to keep them clean. If no current then they can be hit and miss after a while.

[Refrigerator]

[Simon]

High power contactors do not cost lots of money for no reason. If you are greatly underrating the relay you may be ok.

[Leo Bodnar]

We use these reassuringly expensive Tyco Electronics relays bought from DigiKey or Farnell because we want quality and peace of mind when it comes to safety.  We have only used a thousand or so.

One day freshly installed relay does not want to relay and be ready to save someone's day. 
Broken straight out of the tube. 
So we open it up and find an alpha particle (or somebody's lunch) in there.

Leo

[ez24]

While on relay stories - once I had to replace a refrigerator relay.  I opened the old one and found a dead ant between the contacts.  I was pissed that I did not check the contacts first.  I could have just blown it out.