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Build: HLT Controller - STC-1000 with relay and float switch

Currently building a new controller for the HLT.  We wanted a circuit that monitors the temperature of the water in the HLT and fires up the element when required, also with the added protection of a float switch to protect the element before the water level drops below it.

Below is my initial wiring diagram.  I'm far from a professional when it comes to electronics, so any input would be appreciated.

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Check the stc specs and make sure it can switch DLC. Otherwise switch the 230v supply to the transformer

Hi Scott,  I've already built a quick prototype to check the wiring and it does switch DC, so I think I'm good on that front.  Just wanted to make sure I'm not missing anything else.  thanks for the response.

From what I have seen of photos of the STC1000 guts you should be good - looks like the relays are rated for 10A @ 277VAC / 28VDC http://www.hongfa.com/pro/HF3FF_en.html

What float switch are you using? And is all of this on a 15A plug/socket?

Thanks, yeah it looks like the DC side will be fine. I'm using this Float Switch. Running it from a 20A RCD socket.

DLC ment to be DC

Any reason you wouldn't use a cheap Sestos PID over the STC? 

More accurate control, just as cheap, no DC transformer required as they have 12VDC output specifically to power SSRs.

With the exchange rate what it is right now that thing would be about $NZ35 landed.

All very good points, and to be honest I had not really looked into a PID.  I already have most of the parts from other projects so I'm putting them to good use. Thanks for the heads up.

Have also seen people put a slow speed motor and stirrer into the HLT to make sure the temp is even.  I am going pid for HLT, I used my urn as an HLT the other day with no temp control other then me and a digital temp gauge,  it was so much better then heating water in kettles....

Project complete and all working well, albeit with the failings that were raised. The PID really is the way to go.  I get a 2-3deg overshoot after the element shuts off, the wiring is more complicated compared to the PID and I had to come up with a 24VDC supply.  Once Barry brought my attention to the PID's I decided not to spend anything on the project and made do with gear I had.  I ended up butchering two 12VDC power supplies and wired them in series to give me 24VDC.

All in all a fun project with a good learning curve and it gets me close to where I want to be for now, but I think I will be getting a PID sooner rather than later. 

Peter, I have read about people putting a stirrer in the HLT.  It makes sense as you often get a 1-2deg drop when you stir the pot.

Thanks for all the advice.

Nice work mate, sounds like a worthwhile part of the journey.

very much worth while.  got me head around quite a few things and now feel more confident to look into more comprehensive controllers.  let the fever begin! 


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