Ramtuff, thanks for the followup thread. I understand the heater element setup and the plumbing. Pretty ingenious, BTW!Ramtuff said:This is the control panel for the system.
Thanks!blue85prspctr said:Ramtuff, thanks for the followup thread. I understand the heater element setup and the plumbing. Pretty ingenious, BTW!
I'll have to ask my Dad about that, because he set that up and I never bothered to ask.blue85prspctr said:Is the flowmeter output analog or PPS(M)? May I assume DC output?
The PLC, relays, flow meter, pressure relief vavle and a few other odds and ends were bought of of E-bay for dirt cheap. other things like the electrical enclosure, and most of the pipe and fittings we aquired at places like garage sales for real cheap.blue85prspctr said:Your original post on this subject stated a cost of $200 for the whole project. Where did you get a PLC and some means to program it for under $200?
The PLC you see attached to the backpanel actually operates the system, and the other one you see sitting at the bottom of the enclosure is just sitting there. He was going to use it, but liked the other one better.blue85prspctr said:I see two module type things in the enclosure. I'm guessing one is the PLC. What's the other?
The other relays control various other functions of our water system...secondary pump, a few electrical valves, and other various sensors...all not related to the insta-hot. There's only four relays actually used for the four heating elements.blue85prspctr said:I count four heater elements and eleven relays to drive them. Are the relays special types or standard? Connected in parallel?
Each element is 4500 watts for a combined total of 18000 watts. This can be controlled by the PLC though. Lets say you're in the shower, and all four elements are on, and the water temp is 140 degrees. Obviously way to hot. You can then tweak the PLC program and turn down it's ouput to let's say 90 percent and then the water temp will be 115 degrees.blue85prspctr said:What's the heater wattage?
I'm fairly certain that it would. Even though it's homebuilt, the unit does have a cover on it, and all the electrical components are in a Nema 12 electrical enclosure.blue85prspctr said:Would this gizmo pass an electrical inspection?
It was determined experimentally. We actually had to put the unit online before it was finished (needed some minor programming changes and the relief valve wasn't installed yet), because our hot water tank went on us around 10 or 11 one night, so we weren't really at the point to figure out the kick-in points mathematically. We did some quick plumbing to hook it into the existing system, turned the breaker on, the played with it for a little bit.blue85prspctr said:Were the kick-in points for the additional heaters:
a. determined experimentally
b. gotten from some set of plans
c. derived from calculations
I would think the temp sensor would have to be after the first element and the flow meter. Otherwise It would be sensing cold water all the time or maybe I'm just mis-understanding you.blue85prspctr said:Just something that occurred to me - Since there's a PLC running this, by adding a temperature sensor on the inlet side, the kick in points for heaters 2-4 could be automatically adjusted.
What I meant was, if the incoming water temperature is, say 60 deg. then setpoints A, B, and C are used. If the incoming temperature is down to 50 deg. then use setpoints E, F, G. If it's 40 deg. (brrr!!) use setpoints I, J, K, and so on. Or, with some programming, the PLC could apply an algorithm to adjust the setpoints. Something like A, B, C, all multiplied by some factor based on the inlet water temperature. Just a thought.Ramtuff said:I would think the temp sensor would have to be after the first element and the flow meter. Otherwise It would be sensing cold water all the time or maybe I'm just mis-understanding you.