10000W 220v Voltage control

Using Arduino Project Guidance
1

Hi guys, first post here :smiley:

I'm from Brazil, so sorry in advance about my English.

I'm new in this arduino world. I'm C# full time programmer, so code will not be a problem, but I'm really new to electronics, and that will be a challenge I'm willing to get used to :slight_smile:

I'm very aware that i need to start from the basics, but for my goal project, I at least need to know if it is feasible before I start learning and buying kits.

So, here's the goal project I need you guys to take a look:

Here in Brazil we are not used to use external water heaters, so regular resistive 220v 7500W showers are quite common here.

Most of the problem we have here is that most basic showers don't have a dimmer to control the temperature, only like 2 or 3 switches like hot, warm, not much hot and off.

Well, some showers have a dimmer, but even so, there's differences between the input water temperature (hot or cold days), that will, in the end, make you aways need to ajuste the temperature.

My Ideia is:

A control panel wired to the shower where you set the temperature you want for the water, the desired flux, and a start/stop button.

The start button will send a command to one serve valve inside the shower, that will open the water according to the flux desired, that will be monitored by a flux sensor. the shower will start to heat until the desired temperature is reached, and then starts to dimming the Voltage to keep that temperature. If the temperature is not reachable, due to the high flux choosed or because it's a cold day, then the flux is reduced automatically to match the temperature choosed. The stop button closes the servo valve and that's it.

Well, the question is, is it feasible?

Thanks in advance!

2

A control panel wired to the shower

I'm really new to electronics

Stop right there. There are too many things that can go wrong, and a lethal outcome is the result of too many of those.

3

aarg:
Stop right there. There are too many things that can go wrong, and a lethal outcome is the result of too many of those.

:smiley: Okie, let's make it hypothetical then

Do a highly skilled electronic engineer, Harvard's one, with MIT PhD be able to do it using arduino?

4

Electricity and water do not mix and you're ignoring the fact that the problem was solved many, many years ago with thermostatic mixing valves which are 100% mechanical devices.

5

xralfx:
:smiley: Okie, let's make it hypothetical then

Do a highly skilled electronic engineer, Harvard's one, with MIT PhD be able to do it using arduino?

Because you could doesn't imply you should and being educated means nothing in the context of the discussion.

Edit: of course the the EE could do it and would know not to, it's a really dumb idea. The phD would apply for a research grant and after a years work, realize it had no viability since prior art has existed for fifty plus years.

6

Guys, Okie, I guess I started in the wrong foot here...

Once again, here, 98% of the population uses electric showers. They are common and we don't have mixing valves simply because we have only one cold water pipe entering in the shower, and the shower do the rest heating the water. There is already an electric/water situation right above my head. They work by heating the income water by a 7500W 220v resistance, that keep in full contact with the water.

Putting a temperature sensor at the end of the shower is not a big deal. Making a servo valve to open/close the single cold water pipe is not a big deal either, although a little bit tricky. Monitor the water flux to talk to the servo valve isn't that hard, so, the only thing that is really bothering me, is if is possible to control the voltage. Be able to electronically adjust de Voltage is the main goal.

Once again, sorry about my English

7

Btw, I really don't think it's a bad idea.

Think with me. You go to the shower, press the temperature you want, the flux you want, and then start... All you have to do is wait a few seconds to the system adjust your settings and then you are ready to go.

8

"Well, the question is, is it feasible?"

Of course it is feasible but you will need many safeguards. For example, you will need to make sure that the water is flowing at the desired rate BEFORE any heat is applied or you risk scolding the user.

9

stowite:
"Well, the question is, is it feasible?"

Of course it is feasible but you will need many safeguards. For example, you will need to make sure that the water is flowing at the desired rate BEFORE any heat is applied or you risk scolding the user.

Sure! the process will start first by adjusting the flow, then the electronic dimmer will start acting, increasing the current until the temperature is reached, or, at 100% 220v, inform the servo valve to decrease flow

Edit: btw, the resistance is activated mechanically, that means only if a minimum amount of water is capable of mechanically elevate the main contact, the resistance is activated

10

You can't instantly heat water and you don't "dim" a heater... You cycle it on & off. I'm sure you've noticed that your furnace (if you need on in Brazil :wink: ) cycles on & off. Refrigerators & air conditioners do the same thing.

So, you can set the temperature of the water heater by cycling it and you can do that with an Arduino. All you need is a heat sensor and a relay. You can get a [u]Solid State Relay[/u] that can be directly controlled by the Arduino, and the industrial type with screw terminals are super-easy to wire-up. (A regular electro-mechanical relay will need a driver circuit for the coil.)

11

DVDdoug:
You can't instantly heat water and you don't "dim" a heater...

Not true. They do exist.

We have such an instant on heater (it takes up to 28 kW or so - 380V three phase with 32A main fuses). We have the cheaper version - just two settings, high and low, other models have three settings - but there also exist electronically regulated ones, where you indeed can set the output temperature of the water and it will adjust the power to get to the desired temperature.

That said, I wouldn't try to DIY one. The power draw is pretty big, at the ground floor there are some impressive cables coming out of the ground, each floor has 64A, 3 phase available, mostly of course wired as 220V single phase supply.

12

SCR or Triac clipping dimmers exist but using some DIY ebay nonsense for this is irresponsible.
Luckily it would likely be exclusively expensive to make this properly.
It's time certain countries begin regulating towards responsible solutions that already exist.

Do you have 16mm2 cables for your showers?
I live in the arctic and we don't even have that big main inlet circuit breakers.

13

540×540 45.2 KB

Here's a image of an ordinary 220v shower in Brazil

Cold water enters, hot water goes down.

The little stick over there? A dimmer that reduces the voltage to the resistance, making it more or less effective, thus heating more or less the water.

Edit. Cables are 6mm and 40amp circuit breaker, nothing else

14

I know you guys are jealous about our ultra high shower technology, I know, take your time to understand this complex system, I will not leave, I promise :smiley:

Here, a external water heater, or furnace system, although it's a lot better solution, can cost us like 5.000usd. this shower can live like 10 years and cost like 30usd

15

Cold water enters, hot water goes down.

I haven't seen that before but it's similar to a "tankless water heater". The normal hot/warm switch probably uses 2 heating elements, similar to a 3-way light bulb.

Yes, it is possible to "dim" the heat but it's rare... You can use a solid state relay if you find one that's "non-zero crossing" or approved for "phase control". Many (most?) high-power solid state relays switch-on at the zero crossing because it's better with inductive loads and it's less likely to make a glitch/noise on the power line. But with phase-controlled dimming that won't work because you need to power-on in the middle of a cycle. (Most of solid state relays are made with TRIACs, and a TRIAC will ONLY turn-off at the zero crossing, and that's OK... That's what you want with a phase-controlled dimmer.)

It's possible to build your own solid state relay with a TRIAC and a special optical-isolator (and a couple of other components). But, with this high-power stuff you are likely to fry some components during development/testing/troubleshooting and of course it can be dangerous! With a solid-state relay you only have to make a couple of high voltage connections, and as long as they are insulated and/or you don't touch when powered-up, it's safe... If you build it yourself, you'll probably be probing-around dangerous voltages... Also since it's for a shower, it's probably best if the high-voltage stuff is made by professionals.

[u]How Dimmers Work[/u].

There is also something called "cycle control" where the power is switched off for a number of full-cycles and then off for a number of full-cycles. (A "zero-crossing" relay is OK for this.)

In either case you need to monitor the phase to find the AC zero-crossings, and for that you'll need optical or transformer isolation (so the Arduino is not directly connected to the power line). The relay provides isolation on the output side.

You should be able to find some dimmer examples. You'll just have to scale-up the power handling (easy if you can find an appropriate solid-state relay) and add temperature measurement/feedback. (I've made a microcontroller dimmer, but it was a long time ago and I didn't use an Arduino.)

I'd suggest you start with low power (maybe dim a light bulb) and you might want to start with low voltage... The first time I built something like this I tested it at 12VAC (using a transformer I already had on-hand) and a 12V light bulb. (But some solid state relays won't work at low voltages.)

16

DVDdoug:
Many (most?) high-power solid state relays switch-on at the zero crossing because it's better with inductive loads and it's less likely to make a glitch/noise on the power line.

Better check those statements.
Leo..

17

Some thoughts...

  • Be aware that the casing and wiring will take some effort. The SSRs will need heatsinks. So this part of your system will need to be installed in a dry and ventilated place.
  • The temperature control will be inside the shower. So this part will need to be waterprof. The easiest is probably a simple potentiometer or 2 up/down switches or an incremental switcher.
  • You will need to rewire the original heating switches. This part is safety-critical, because it is in wet environment.*
  • The water temperature sensor needs to be as close as possible behind the heaters for good regulation.
  • For the actual regulation, a P-I loop is probably the easiest.
  • For a slow reaction system like water heating, zero crossing is plenty fast enough. No need for phase angle switching.
  • Do the worst case math for the size of the heatsinks, or else your SSRs will not survive very long.
  • or you insert the SSRs in the mains distribution box, after the MCBs for the shower.

Considering all that, this is probably the reason why there is no commercial solution. A few switches are much easier and cheaper :slight_smile:
On the other hand, a well designed system which is easy to install, might have commercial potential...

18

There is a basic observation / assumption that the water heater is a standalone unit - approved to electrocute and/or cleanse people in the country of sale.

So - then the question becomes much simpler...
Can I achieve duty-cycle control of the heating element to follow a preset value, and a thermo sensor in the water path?

Yes, with the provisions that you work alongside a skilled & licensed sparkie to ensure that mains, people, water and control circuits never come together.
Worth adding some protection (secondary over-temp etc) to avoid burnout and electronics failure.

Its been done (literally) a million times before - closed-loop, temperature control system.

19

lastchancename:
Yes, with the provisions that you work alongside a skilled & licensed sparkie to ensure that mains, people, water and control circuits never come together.

I like that :slight_smile:
To specify more precisely:

  • People and water should come together, that's the whole point :slight_smile:
  • Mains is the bad guy, should not come together with either people, water or control circuit. I.e. the temperature sensor mounting should not leak.
  • People and control circuit need some interaction, that's the user interface.
  • Mains and control circuit are linked via the SSR. It has an optocoupler inside, to ensure electrical separation.

If I had an electrical shower, I would do the project. With timer for the wife :slight_smile: Alas, we have a hot water storage tank which is heated by wood fire. Saves money on the electricity bill...

20

Had you made it? I'm trying something very similar, I just want to set the temperature, I'm not worried about start/stop valve nor if cannot reach the temperature reduce the flow.
But note that I want to control the outgoing water temperature and the quantity of the electricity I will need send to the resistance will depend of the incoming water. Try to think as the following: you start your shower and the water incoming is 20C and you want 37C so you need a quantity of power to heat the water, After 1 minute or 2 after the incoming temperature goes to 37C (i can explain how but is not the case here), so now to get 37C outgoing I don't need send any power to the resistance.
Another important think that seems that was not noticed here about tankless water heater is that usually the are located before the shower handle what means that they have always water pressure on it, but the shower head with resistance only have water (and pressure) on it after you open the shower handle.