Mystery Box 2

[itsmoked]

This is the power circuit of 29kW on-demand water heater.

It is a single phase unit that has three of these identical circuits in it. I'm trying to ascertain if I can run it on three phases instead.

The top dotted box is the tank with the three elements in it.

Ok gents, what is happening inside the idiot mystery box?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Is the box physically connected to the vessel wall? Any other connections for a flow or pressure switch? My guess is that it provides switching when water is drawn from the heater. Any chance of a a photo?


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If we learn from our mistakes I'm getting a great education!

 

[burnt2x]

Might just give it a try, Keith:
Terminals 3,5, and 6 are connected to the return line. Terminals 1,2, and 4 energization is selectable at the "mystery box":
Heater 1 - terminals 1 and 3
Heater 2 - terminals 2 and 5
Heater 3 - terminals 4 and 6
A point unknown is why the return line (at terminal 3) has a wire brought to the mystery box! Or is this just a return line needed for indicators at the selector switch?

The best I can offer for the moment.

 

[itsmoked]

Your wish is my command...

This is a double unit. We have a triple unit. Each unit has three heating elements and is 9.6kW.

Note the black round thingyies. Those are the flow detectors.

The top of the tanks have something going on??? Is this a continuation of the dotted box maybe? Still what is the point?

The white clips on the outlet lines are the exit water temp sensors.


burnt2x; That Line[sub]leftside[/sub] brought down to the bottom box makes zero sense to me.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Does this have a pump motor ? (I don't see it in the photo). If yes, then motor is to be changed to 3 phase, no ?

Also, the neutral has to be brought out and grounded for safety.

 

[itsmoked]

Hi edison. No motor it's just plumbed into the hot water line.

No neutral that I see anywhere. Just those two Lines and the safety ground.

Oh and that V[sub]L-L[/sub] is 240VAC.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

I think the idjit box may have the neutral point since 1 2 & 4 (why not 1, 2 & 3 ? - shrug) should be joined to close the ckt. I would remove the tap between 3 & 5 and put the third phase on 3 and then ground the neutral (in the box)

The taps from 3 & 5 to the black box at the bottom should be for lamps, control contactor ?

Question on hydraulic ckt. Where is the center tap on the water inlet top going ?

What does the regulator marked 1 to 6 control ? Water flow ?

 

[ScottyUK]

Possibly a pressure sensor on the cylinder so that there is definite inlet pressure and definite flow before power is applied to the heaters?


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If we learn from our mistakes I'm getting a great education!

 

[roydm]

My guess is some sort of temperature control. You need something to compensate otherwise the temp would depend on flow rate.
Roy

 

[jghrist]

Looks to me like there are three thermostat (in the black box) controlled elements that heat the water faster depending on the water temperature.

I don't think you could easily connect three phases. Consider that you would have to connect them inside the black box and that you would need to connect the elements phase-to-phase not phase-to-neutral to get the proper voltage across the elements.

 

[ratz1]

Looks as a phase control unit (triac or antiparallel SCR's). All of the heaters are connected with one lead to the same phase terminal. Other lead of the heaters may be connected together inside the box and then to the phase control element. The wire connected to the phase lead may be needed for the SCR pulse synchronization.
Basicaly, chopping the line voltage the RMS power delivered to the resistances is continuously controlled.

 

[edison123]

I think ratz1 nailed it. It has to be some kinda wave chopping in the box to vary the current and the heat. If so, converting to 3 phase may not be possible.

 

[LionelHutz]

I'd agree with the others. There's likely a flow and inlet/outlet temperature sensors and the "box" is a PID based voltage controller that regulates the heater voltage and hence the power output to try to maintain the output water temperature.

If you have a triple unit you could likely put each "stage" across a different L-L on the 3-phase to get a somewhat balanced load but that'd be the best you could achieve.

 

[itsmoked]

Thanks all! These type heating elements burn out in an instant. Rather like a flash bulb filament, so I bet you're correct on them even monitoring the pressure.

I think ratz1 may indeed be on to something.
Each 'unit' seems to have a fairly large electronics control board which could explain/support some sort of PID scheme.
I'd just thought the contacts were opened and closed to do the control but that would be a lot of opening and closing of mechanical contacts.

edison123; That center tap on the inlet (I did a double take on it after you pointed it out), just loops over to join the manifold from the top.

I wonder if the switching elements are actually mechanically associated with the water tanks for cooling? That would make heatsink/efficiency sense. That would explain the dotted mystery box since the picture of the tank is inverted in the schematic.

LionelHutz; That was my thought as each module needs 240 and appears to be independent otherwise, except for a communications wire. We are attempting to get an answer from the maker about 3ph otherwise this whole thing will go off the rails because our 52kW generator will NOT appreciate a single phase load of 29kW...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[alehman]

Looks like the brains to me. These things usually have a mess of SCR's or similar devices to control the heating elements. The ones I've seen use the water tank as a heat sink for the SCR's. I'm guessing that's what's in mystery box. It's using the 240V from the switch and term 3 for its power supply and shunts the heater terminals 1, 2 and 4 back to the left Line terminal.

I'd bet the SCR's or whatever just turn each of the three heaters on or off as needed to supply water of the correct temp. I doubt there's anything as sophisticated as chopping going on. Besides that would create a really nasty waveform.

The 3-phase conversion would probably need a new mystery.

 

[ratz1]

Agree with alehaman. The pure phase control or chopping at 29kW/240V could produce very funny effects in all other consumers connected to the same supply branch.
Surely there shall be one or more ( 3?) triacs or SCR's , but the control strategy may be different.
If the heaters are rated ( 16 + 8 + 4 = 28 kW in total) you could achieve 7 different power levels. If the ON/OFF scheme is modulated with certain timing ( let say 200ms ON/ 200 ms OFF) the number of power power levels could be additionally increased, achieving practically continuous power control.

 

[itsmoked]

Yes sounds likely, especially with alehman's confirmation of my guess about water tank heatsinking.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith. If you connect the generator in delta or double delta, most 52 kW sets will happily supply 34 kW from one side of the delta. The current will be the same in all windings, but the angles between voltage and current will be off 120 degrees on two windings.
If you are stuck with wye, you can use a zig-zag connection (not to be confused with a zig-zag grounding connection) or a double delta connection to develop 240 volt single phase at 34 kW.
If you have a 10 lead generator we may have a problem but I think that we can solve it.
Your box may have a temperature limit and/or a pressure switch. It may be a simple contactor to close when pressure and temperature are within limits. The line from terminal 3 would be the return power for the contactor coil.
I have only seen (too many) the cheap "On-Demand" units where the temperature does vary with the flow.
I am sure that you have exhausted the web in search for answers.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

I would've never believed that Bill if you hadn't told me.

The generator is delta.

However what I haven't said is that the A/C load is 30kW and the oven is can hit 10kW and there are other typical loads.

We need to condition blocks of this water heater to be blocked out during, say, A/C operation.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Why did we start talking generators, do you have this away from the grid?
I must have missed that point.
Roy