Power Supply and Timer

What is your "unit"?

Pool timers should work.

Not much to go on.

Amazon.com: Pool Timers: Patio, Lawn & Garden

Its a water heater or steamer

I have such a timer on my water heater.

They work very well.

You could reduce the temperature at which your heater maintains the water.

Do you know any cheap ones like China made !!!

This type device would normally be controlled with a thermostat, not varying the voltage...

What does the 'power supply' part of the post's title refer to? Are the mains the 'power supply' to which you refer?

Is this a residential water heater? An industrial water heater? One to warm your tea? A boiler to make your steam? I'm not sure what you mean by 'steamer.'

Throw us a bone, mate. What exactly are you wanting to control?

You are right!!

I am talking of controlling the mains voltage going to my device.

Its a study project, they want something to keep water warm at constant temp and also produce steam at constant temp.

How much water? At what temperature? How much steam? Temperature? Pressure? Flow rate? Are these two separate devices? I'm asking because merely 'warm' water does not produce steam. Vapour yes, but not steam like for a steam turbine or something. How much power are you looking to control? Watts? Kilowatts? Megawatts?

1.21 gigawatts!?!

I really apologize for not providing all the information. But, I really dont have it.

All I can say that they want to combine a water heater and steamer that will give controlled output i.e. not too hot!! so hot water like for tea and hot steam like for facial spa.

Water reservoir may not exceed 1 lire capacity and heating coil is not yet selected. They are just looking for alternatives.

To make steam you've got to boil the water. How can boiling water be made 'not too hot'? Sounds to me like you need two heaters - one to maintain water temperature in one reservoir and one to boil water separately to make steam.

But if I can control power input I can provide just as much power to heat water or to produce steam.

So, it will be a container with a single heating coil which will be used to heat water from just a warm temperature to boiling hot and again maintain that temperature constant

I was actually thinking about some electrical device connected between the mains and the heater. This electrical device will have two knobs. One knob will act as a timer to keep the device on as dictated by the timer scale. Second knob will control the mains power that is supplied to the heater, in other words the heat produced by the heating coil. This way I can produce hot water, just warm enough to drink or make the water boil enough to produce facial spa that wont burn my skin.

Again, for the second knob, instead of controlling the mains power, I was thinking of switching the supply on and off at regular interval to control the heating of coil. What do you suggest is the better option?

Keeping aside the power requirement and all, I am just looking for some cheap or home made electrical devices that can do the job.

"in both cases the output of the thermostatic controller can be wired to the heater in parallel with the timer"

As you rightly suggested, are there any available devices you know of or can I make it at home? Do you have any expert opinion on this matter.

?

The temperature is limited by the boiling temperature of the contents at the ambient pressure. At sea level it is around 100degC for water, and a set of steam tables will show the temperature at different atmospheric pressures.

Sorry, but I think this design is unsafe in principle. Consider user 1, setting it for use as a steam spa. Shortly afterwards along comes user 2, only to spill boiling water on his hands when he is expecting only warm water. How are you going to prevent this happening?

If the "warm" water temperature setting is for e.g. making tea (see #16), I don't think peeps will be expecting to be able to wash their hands with it!

I didn't say wash hands, I said spill, as in accidentally. Tea-making water is not going to be as hot as on-going steam generation.

How much power your warm-water reservoir shouldn't be much. If the reservoir is well-insulated, maintaining it at temperature won't take much. Is the water consumed? Say, to make tea or something? Then it's a matter of how fast it's replenished and how fast you need to heat the incoming water. If the reservoir is open you'll need more power to keep it at temp. But a litre of water isn't much. I don't know about the steam requirements for facial units. Go to a shop that sells them and see what their power requirements are.

Is this what they/you are making? Some sort of steam-facial/hot water thingo?

If you make steam for a facial spa, I suppose you don't want to "superheat" that steam, otherwise it will be more than a facial "peel". People generally do not like when their face falls off the bone. Is this thing about the size of a vaporizer?

This is the new type of question.

A. Vague.

B. Mystery.

C. Guessing.

D. Your suggestion.

"How can I reduce or vary electrical power supplied to my unit?"

1. I'm guessing from your post's title that you mean 'power-supply unit'? It all depends on what the supply is expecting for input. Unless the power supply is designed to take a variable input voltage, typically it's expecting mains voltage within a certain tolerance and frequency. 105-130 VAC, 50-60 Hz for example.

2. Something like this, an interval timer?

Yes there are plenty of these devices....AC or DC? What is the voltage and amperage range? What sort of device? What would be the time on and off frequency and duration?

http://www.bkprecision.com/support/downloads/power-supply-guide.html

Its AC supply. 50 Hz frequency and 220 V.

Device is water heater or steamer.

On time may be 1 to 5 sec

Off time may be 1 to 5 sec

I may also need a device to switch off the heater after specific period, say 10min or 30 min. I guess there are some mechanical timers to do this job. But, then I also heard that its better to use some SCR to switch off the supply at some phase start or something

Switching that much amperage on and off so quickly would cook the contacts....contactors are usually rated by on and off cycles design life....you would blow through those life cycles in no time...What exactly are you trying to do?

It won't do the heaters any favors either.

Then what about controlling the mains power through some device as I mentioned earlier.

They must be doing that in commercial facial spa products

How much current are we switching? Use an interval timer to control a solid-state relay rated for the load and you're home free.

https://m.alibaba.com/guide/shop/conair-mdf2r-facial-sauna-system-with-timer_10241473.html

https://www.aliexpress.com/store/product/Modern-Electric-Teapot-Warmer/1459120_32291984949.html?aff_platform=link-c-tool&sk=UbMBqZZBm%3A&cpt=1482125599528&dp=55f7df79-92df-c42f-f14f-01591591e29c&af=132029&afref=&pid=132029&aff_trace_key=059becf2025f416e8ac1f4423c11ed82-1482125599528-02548-UbMBqZZBm

Go buy a facial spa, take it apart, and see what they are using. It might be a bi-metal contact strip, so that when it gets to temperature, it goes open circuit, although that does not seem particularly safe to be putting one's face near.

Heaters aren't typically reactive loads and solid-state relays sidestep the contacts problem anyway.

A trip to the local home improvements store is overdue; call it a fact-finding mission. Many of these stores stock all manner of home automation devices such as

• light sensors that switch stuff on and off dependent on daylight
• temperature sensors that switch stuff on and off dependent on ambient temperature and individual process temperatures
• timers that switch stuff on and off dependent on time
• presence detectors that switch stuff on and off dependent on room or building occupancy
• remote-actuation devices that switch stuff on and off dependent on commands sent from a phartsmone over the internet

Some of this stuff plugs into a wall socket and the appliance plugs into the device.

Other stuff is suitable for fixed installation; if in doubt consult a qualified Electrician.

These stores have so many of these things that they sell them just to get rid of them, so building them is superfluous.

As others have said, at normal atmospheric temperature the water won't get any hotter than boiling point (about 100ºC) - just right for tea.

I don't understand why you need both a power control and a timer.

I suggest you look at temperature controllers (e.g.) or maybe a simmerstat. If you search around you should find one which will hold the water just simmering (rather than boiling violently).

You can almost certainly get away with "bang-bang" (on-off) control, and with a resistive load (the heating coil), mechanical relay type output will be OK.

You might also like to search for "dimmer controllers" or similar. While I'm not suggesting a light cotroller (Power rating probably too low) they do work a little like you describe, but by only passing a (variable) proportion of each source wave through to the load.

That device with a bypass switch for "full steam" seems something like you describe.

Now!! Can you please also understand that where I come from ANY device connected to mains MUST be

• An approved device. (Not some home built prototype.)
• Installed by a licenced elecrician. (Do you have such qualifications?)

Caution also:- most crude dimmer circuits do not pass recent regulations for electrical interference.

My real suggestion is that if you are a Mech Eng, then find an Elect Eng and respect their training. Just as I might develop a mechanical concept, but would then have the detail done and confirmed by a Mech Eng.

You are absolutely right!

I was going to do that anyway

But, I always believed that some homework wont harm you. And getting some expert advice will help me to put my case in better way.

There is no better place than CR4.

Thanks a lot for all the suggestions and ideas. Now, I know what to do and what to look for.

Call an EE.

Without additional information about the type of voltage supply, it is really hard to answer your query.

If DC, you could perhaps look into "H" drives to achieve variable current supply that you control.

If DC, you will experience issues if you attempt to use a solid state relay, as it will fail to switch off once activated, typically. Use a physical solenoid relay (as is the relay on a car starter motor).

If AC, then various options are available including SCR, solid state chopper relay, physical relay, etc. On/off switch... depends on what you need it to do.

You/they should really consider a small electric batch heater for the hot water source then focus your attention on the steam source.

Good answer, as usual! Go mode, and blow mode.

Most kind of you, thanks!

Whether I should go for a dimmer or a SSR?

I searched on internet and they both seem to serve the purpose

What should be my criteria, if I want to choose between them?

such as cost, size, ease of control, accuracy, etc.

Cost and ease of incorporating into your device(s) should be two of the major concerns. The major concern is always electrical safety.

Careful! An SSR is just a Solid State Relay - all it can do is switch a supply on or off; it's the control circuit that matters (which could be identical to a dimmer control circuit).

And SSr's do not switch off DC power very well at all, it needs that zero crossing to reset.

The OP did say the 'power supply' is the mains.

OK, my bad, I too am using a relay (solid-state) that is driven by a relay board, driven by an Arduino, to turn on/off a 12 VDC supply at an outlet (on my experiment, not on the wall) that is 120 VAC, thus I am also switching the "mains".

That part I totally get.

DC switching SSRs are becoming more and more readily available these days (seems they usually have MOSFET outputs). Used to be hard to source and expensive - now well worth considering for switching tens of amps at tens of volts, which is tricky with electromech. relays (but SSRs are obvs. not suitable for safety applications!).

Nope, never want to use a SSR in safety applications.

Years ago I worked on the driverless rapid transit system used at Duke University, North Carolina, between their North and South hospitals. Parts of the switching was done by special, fail-safe electromechanical relays of the kind used by the railroads. Connected to the relay armature was a big metal weight designed to pull it into a known state in case of power failure. Outrageously expensive but so are train crashes.

John: do you happen to have some examples of the newer SSR's that might be of interest in pulsed DC applications I am interested in. For example, it is will known (found in the writings of Bokris of TAMU) that pulsed DC electrolysis of water is more efficient with higher gas production than constant current DC.

Crydom make a range. The RS Components website is currently off-line, but there are more examples there.

I went to the RS Component International web and it was up, but for North America, the only SSRs I found there were Crydom. Good links, thank you much.