SSR or Mechanical Relay, Contactor

[clintoffutt]

Is there a preference to run the compressor of a fermentation freezer? I have a BCS-462. I would also like to use the unit to power some heating lamps/pads for dual temperature control and would like to use the same electrical device to handle the switching.

[JonW]

If you are only doing on/off control (no PWM), then it really doesn't matter which you use. My preference is the SSR's because I like mounting them to the panel and they have easy to use terminals on them.

[thebigrip]

I have a question about the SSR or Contactor as well, but for heating elements. I have looked at older posts as well but had these specific questions.

We are getting together a panel for (6) 5500 watt elements running 240v. It looks like getting (6) 40amp 120volt coil, 2 pole contacts to control each element separately would be the best way to go cost wise ($13 bucks each) however I wanted to make sure this concept would work without SSR's (it seems most blueprints employ both SSR and contactors for safety) and I wanted to find out about longevity and noice. Many people say the only disadvantage to a contactor is the noise but I don't know how loud this actually is? Also, that SSR's generate a lot of heat and 12 of them certainly would.

Any thoughts or people that want to weigh in would be appreciated.

[clintoffutt]

So is hysteresis mode considered PWM?

I figured hysteresis mode would be the best way to run heat/cool dual controlled fermentation freezers, correct?

[JonW]

There are a few differences to consider when choosing SSR relays or mechanical relays (contactors).

Switching current - how much current does the relay require to switch the load? SSR's generally are very few milli-amps and can usually be driven directly from the BCS. If using relays or contactors, you need to make sure that they include a darlington transistor for switching the coil and they will also require a separate power supply for powering the relays.

Switching frequency - How often will the device switch on and off? Relays are not designed for being turned on and off frequently, but SSR's are. If you are going to use the relay somewhere where it will cycle a lot, I would use an SSR. For refrigeration or fermentation, relays would be just fine. For (most) heating elements on a brew rig, I'd use SSR's so you could also use PWM.

Load current - The amps you draw from your device (pump, element, etc.) also affects your choice of relay. Standard 10-20 amp SSR's will switch anything brew system related with the exception of heating elements. For most elements, you should be using the much higher rated 40-50 amp SSR's and heat sinks. This is the area where SSR's start to get more expensive. A contactor can easily handle the current of the elements and be less expensive, but you couldn't do rapid switching with it (PWM). If you do hysteresis with the elements, you could use just a contactor though.

So, there is no easy answer to which is best as there are several things you need to consider.

[clearwaterbrewer]

I would use the powertail... it is a relay (contactor), but it is self contained, so you just run a cat5 cable to it (one wire for signal ground, one for temp, and one for control..) and use power local to the freezer...

http://www.powerswitchtail.com/Pages/default.aspx

[Rick]

I'm using the powertail idea for some of my fermentation control. With cheap SSRs you can build a single one for ~$12. For heating/cooling I put 2 SSRs in a double sized metal outlet box (heat sink) and have a standard split duplex outlet for heating and cooling with neon indicators. Now I'm putting a central box together to clean up the wire mess around the BCS. Keystone Cat5 connectors work well for SSR and probe connections, as has been previously mentioned.