[Stevie]

Honestly, I was nervous at first. Mark's help has been immensely valuable. I am also taking individual sections from Kal's build and simplifying where I can (illuminated switches).

I do wish I could go smaller on the enclosure, but auber sells one with the two PID holes factory cut for $82.50 with a heat sink. I think the extra size and cost is worth not needing to cut those two holes. I'm planning on keeping everything else round where I can.

[Stevie]

I cleaned up the wiring by making the sheet size 8.5x14 and landscape. Much easier to read and all of the traces are tidier.

Mark, everything look ok to you but for the possible issue with the neutral control leads? I will most likely order an extra pair of blocks and use them if I have the space. I think I will be ok if I arrange the relays lower in the enclosure behind the power and pump switches. That would leave the center wide open. I could also just switch the power to the controllers, but I like the idea of having them powered.

[Stevie]

Mark, I think I came up with a solution to opening the control leads with the three position controller selector. I imagine the control signal is sent out over the positive and received by the negative. If I open the negative with the three position switch, the inactive controller can send all the signals it wants over the positive with no ill effects.

Am I right or am I crazy?

EDIT - I think I figured it out myself. If the positive leads are bridged and controller A is sending a signal, controller B might get confused. I guess the only way is to use three block pairs. 1 for the positive control, one for the negative control, and one for the 120v coil. I should have enough room to accommodate the depth.

I made some small revisions as well. I took your advise regarding splitting the 120v items across the two legs. I am wiring one pump to one leg and the hot bus with the other pump to the other leg.

Thanks again for the assistance.

[AmandaK]

Can I ask you two a newbie question?

What is the main advantage of the DPDT relay? I've been talking about this project with our lead electrical engineer here at work and he seems to think that having a breaker(s) is the simpler way to go.

[mabrungard]

I just use 2 regular SSRs to control both legs of my 240v heating circuits. The control wiring is just piggybacked  to both SSRs for control. Using a breaker is too manual for me.

By the way, I use the big 30a and 50a dryer plugs and receptacles on each of my heating circuits and on the connection between the spa panel and the brewery control panel so that I can always have a true disconnection to meet my lock-out, tag-out mentality. I find there is no need for the more expensive twist-lock plugs and receptacles since the dryer plugs are pretty hard to separate as they are. If you can easily pull one of those plugs out, you are more of a man than I am.

[Stevie]

Good call to have a few bucks Martin.

The first really controls power to the whole box. The second relay controls power to the element and the ssr control how much power that is (or how often power is on.

Some of my brew buddies are recommending adding additional breakers in the control panel. Won't the 30A breaker in the electric panel coupled with the gfci in the spa panel be sufficient? I have fuses wired to protect the 120 items.

[S. cerevisiae]

Can I ask you two a newbie question?

What is the main advantage of the DPDT relay? I've been talking about this project with our lead electrical engineer here at work and he seems to think that having a breaker(s) is the simpler way to go.

The first DPDT relay allows the brewer to control 240VAC up to the relay current rating on a multi-element unit using a 120VAC 10A switch.  It's effectively a relay-based 240VAC power switch for the unit.   The element DPDT relays are a safeguard against dry firing and shorted SSRs.  Neither are necessary on a single element 120VAC controller as long as the power switch is capable of carrying 20A, and one is careful to not energize the unit before filling the heated vessel above the height of the element.  While the DPDT 240VAC power relay may appear to be superfluous component on a multi-element 240VAC controller, it allows one to use a master magnetic kill switch as an operator safety device.
 
With that said, a lot of Kal's design is based on the premise that the unit needs that be "washdown" safe.  If one looks at Kal's brewery, it designed so that he can hose the place down.  Most home brewers do not need this level of industrialization because their home breweries are a secondary use of a space within their homes.

[S. cerevisiae]

For those who may be looking for a high-quality 240VAC SSR for a reasonable price, the eBay seller linked below is selling new Crydom 240VAC 75A SSRs with a control input voltage of 3-32VDC for $14.99 + shipping. 


http://www.ebay.com/itm/CRYDOM-SOLID-STATE-RELAY-D2475-240-VAC-75A-NEW-/131597913845?hash=item1ea3d8cef5


A Crydom SSR is a huge step up in quality from a Chinese SSR.  Mouser sells this SSR for $77.38.

www.mouser.com/ProductDetail/Crydom/D2475/?qs=sGAEpiMZZMtq49AUx5G3778uEJUSSwFqGIGUKB5xmyo%3d

[Stevie]

I've been looking for Crydom based on your recommendation and saw his listing. Too bad he doesn't have the 40A model for a few bucks less.

What is the main benefit? Longer life/reliability?

[S. cerevisiae]

I've been looking for Crydom based on your recommendation and saw his listing. Too bad he doesn't have the 40A model for a few bucks less.

What is the main benefit? Longer life/reliability?

The main benefits are guaranteed performance at the specified ratings and higher reliability (a lot of Chinese SSRs that are rated for a 3-32 VDC control signal will not turn on at 3.3 volts, which makes driving them directly from a GPIO pin on a modern single board computer or microcontroller board impossible without a logic level converter).  A 75A SSR can be used in place of a 25A or 40A SSR.  The current rating is the maximum current that the SSR can handle, not the minimum current that it can handle.  The current rating of a semi-conductor is based on the amount of heat that it can dissipate.  An SSR is based on silicon-controlled rectifiers, which are a type of diode.    All diodes have what is known as a forward voltage drop (Vf).  The forward voltage drop multiplied by the current rating is the amount of heat in watts that an SSR can dissipate.

[Stevie]

I get that it would work, would just be nice to save a few bucks with a 30A. The PID leads seem to be 12v mostly, so I shouldn't need to worry about that, but buying a cheap ssr with a backup is basically the same price as the Crydom from that seller.

[S. cerevisiae]

I get that it would work, would just be nice to save a few bucks with a 30A. The PID leads seem to be 12v mostly, so I shouldn't need to worry about that, but buying a cheap ssr with a backup is basically the same price as the Crydom from that seller.

I was raised by a man who spent over forty years of his life repairing and calibrating electronic devices (I also spent the early part of my career in the MIL-SPEC world).  I learned a lot about real world versus textbook engineering from him.  One of the things that I learned was to buy the best quality components that I can afford at the best price at which they can be acquired.  The quality of Chinese components leaves a lot to be desired because quality control only happens if the company placing the order demands it.  The average Chinese-made SSR with a backup is still not as reliable as the average North American or Japanese-manufactured SSR, and we are dealing with a device that is carrying mains electricity.  The same thing can be said about electromechanical relays.


By the way, if I manage to complete the project that I am planning to work on in the winter, you are going to wish that you had purchased an SSR that was guaranteed to turn on at 3.3 VDC.

[Stevie]

I have a new idea regarding the controller switching. Hopefully I can explain it properly.

Two switches with 3 NO blocks and 1 NC block each. The NO blocks will provide the power to the coil and switch both control leads while the NC block will be used to cut power to the ssr if both switches are in the on position. Essentially the left switch will only energize if the right switch is in the closed position and vice versa. This would add an additional switch, but eliminates two indicators if I use illuminated switches. So the net number of components on the panel goes down by own.

The idea is to avoid needing a switch with three block pairs which could cause issues if with clearance.