Looking for Relays

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  #1  
Old 12-27-12, 09:49 AM
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Looking for Relays

Just doing some research for possible electric homebrewing...When I see PID Controllers running anywhere from $1400-2700, I start thinking of ways I could make one for much cheaper.

I also can't decide between mechanical relays and solid state relays. I've read that SSRs tend to fail closed while mechanical tend to fail open, but I've also heard that mechanical ones can be prone to welding the contacts in the on-position when arcing to close the circult, so they may be just as prone to failing closed. (Side note 1: Will quick arcing trip an AFCI, such as arching when flipping a switch on or maybe a relay closing? Side note 2: Is there such a thing as a breaker that includes both Arc Fault and Ground fault interrupters?)

Anyway. Trying to find relays that will be able to safely switch a load of 23 Amps at 240V AC. Either I"m looking in the wrong places, or they're just hard to find.

Thanks!

Nic
 
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Old 12-27-12, 10:12 AM
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Have you checked ebay? Lots of Chinese sellers of PID controllers along with both solid state and mechanical relays.
 
  #3  
Old 12-27-12, 10:32 AM
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Yes I saw some SSRs on Ebay, I think every single one I looked at was either from Hong Kong or China, wasn't really sure what the quality was like. I'll have to search for some PID controllers, though.

I thought about doing a PIC controller and writing a simple application. Might not technically be Proportional Integral Derivative but might be close enough. I guess it depends on how much it would cost. I'll have to find some good thermocouple probes as well.

I was just a bit wary of buying stuff from the other side of the planet in case one fails a year or two down the road and then I'm stuck trying to find another one of the same spec. I could always buy 2 or 3 times as many as I need and use sockets to make for quick replacement.
 
  #4  
Old 12-27-12, 11:24 AM
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SSRs are pretty much universal in their mounting and terminal designations. If one failed you could always go for an American manufacturer which probably has their products made in Asia or Mexico. Mechanical relays are much more varied in their mounting and terminal arrangement.

Whichever type of relay you choose remember to size it generously in regard to voltage and amperage. If your load is 23 amperes don't use a 25 ampere relay but instead upsize to at least 30 amperes and 40 amperes isn't overkill. Use relays with a higher voltage rating as well. If you use SS relays don't forget the heat sink and maybe even forced cooling.

I've purchased several SS relays from China without having a problem with their use. I don't know about longevity or using them at close to their ratings though. And while I have yet to purchase any of the low-cost ($20-$50) PID controllers (no real need) I suspect they are no worse than the $100-$200 controllers available from American companies, most of which are made in Asia.

If you want to do comparison shopping with a well-known American distributor check out Allied Electronics. Getting their catalog will keep you busy for hours.

Allied Electronics

Allied has no minimum to order and they sell to anyone. I have been a satisfied customer for decades.
 
  #5  
Old 12-27-12, 01:08 PM
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You should do some reading in the automated brewing section of Home Brew Talk. Questions like yours come up regularly and almost every method of controlling a brew sculpture has been covered in pretty good depth from high end PC controlled systems to low cost ghetto rigs.
 
  #6  
Old 12-28-12, 08:33 AM
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Look at the Watlow controllers. They are made in the USA(at least the one's I have are) and can be repaired if they malfunction. I've been using the Watlows and Fotek ssr's on my powdercoat ovens for years without a single failure.
 
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Old 12-29-12, 03:10 AM
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Mouser Electronics also sells almost everything under the sun. Single lots too.
Link to their online SSR search engine.


Solid State Relays | Mouser
 
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