Control Panel for 3ph Heaters

jparker86 · Aug 8, 2012

Hello,
I am new to the forum and would be most grateful if anyone here could help me with a project I am working on.

I have a control panel which I have made that controls 2 x heaters and 1 x pump.

Both heaters are 6kW (three phase) and the pump is single phase.

It all works, and I have on/off push buttons to operate the heaters and pump all run via the emergency stop button.

Where I am stuck is that my three phase heaters have a built in thermostat, which switches the contactor from on to off when the heat exceeds x degrees. My problem is that with my current design, unless someone presses the start button again it wont switch back on!

Under my current design, the thermostat isn't installed I left this until last (I underestimated how easy it would be).

Currently, all that happens is the device will turn on and off.

What I want is for the thermostat to cut in and cut off the power to the heater when temperature gets too high.

In my head I am thinking the best idea would be to have a contactor which is controlled via the on/off buttons, and that powers another contactor that is controlled by the thermostat?... or am I missing something that could help me?

I below attach the wiring diagram for both the heater in question and the control circuit diagram.

Any help would be gratefuly rec'd.

[ElectriciansForums.net] Control Panel for 3ph Heaters

jparker86 · Aug 9, 2012

Swicade said:
jparker 86....refer back to post #13 kindly donated by Tony as that is spot on. Only thing i'll add is afew more bits to the key offered:-

K1/1 = N/O contact on pump contactor (K1)
Sw1 = Rotary on/off switch for Heater bank 1 contactor (K2)
Sw2 = Rotary on/off switch for Heater bank 2 contactor (K3)
Th1 = Thermostat on Heater bank 1
Th2 = Thermostat on Heater bank 2

Definitely rotary switches on heater bank circuits instead of push buttons.

Hello,

I don't know why but the equipment that it is controlling specified the control panel must have a push button. No idea why! :-(

Swicade · Aug 9, 2012

What equipment is this panel supplying?

I can understand the pump requireing push button control put cant personaly see how push/button control would work the heater side due to the thermostats.

jparker86 · Aug 9, 2012

Swicade said:
What equipment is this panel supplying?

I can understand the pump requireing push button control put cant personaly see how push/button control would work the heater side due to the thermostats.

It's supplying heat and circulation to a massive water tank. The customer would usually have a 200L tank which would be worked via 1 or 2 single phase heaters. Due to the size of this tank I am having to put a much bigger load on the heaters, hence the 3ph.

One requirement is they are push buttons, I did question this and was told the other systems have push buttons so this must also! Maybe it has to do with their user manual or something, but I originally thought a selector switch would have been a much easier system.

Swicade · Aug 9, 2012

May be an idea to grab one of thier user manual's and go from there...really cant get my head around push buttons for heater controls with the thermostats in circuit.....got meself all confused now.

jparker86 · Aug 9, 2012

Swicade said:
May be an idea to grab one of thier user manual's and go from there...really cant get my head around push buttons for heater controls with the thermostats in circuit.....got meself all confused now.

I'll go back to customer and say that using push buttons is not possible! Just a shame becuase the panels are already done with buttons inside them. Hopfully ill be able to use the same holders.

spark 68 · Aug 9, 2012

Do you need seperate stop/start buttons for each heater ?, or just one stop start button for both heaters ?

Don't give up yet, you had the right idea in your first post, ie. use the stop/start (latching contactor) for the supply or control to the thermostatically controlled heater circuit.

I would use the latching contactor/relay contacts to control the coil for the thermostat part,ie in series with your thermostat to the second (and third) heater contactor.

jparker86 · Aug 9, 2012

spark 68 said:
Do you need seperate stop/start buttons for each heater ?, or just one stop start button for both heaters ?

Don't give up yet, you had the right idea in your first post, ie. use the stop/start (latching contactor) for the supply or control to the thermostatically controlled heater circuit.

I would use the latching contactor/relay contacts to control the coil for the thermostat part,ie in series with your thermostat to the second (and third) heater contactor.

This is what I want to do but getting unstuck here. It seems that no matter how I do it, once the thermostat kills my contactor, so does the stop circuit which in turn gives power to my a1 on the main contactor.

I want both heaters to work independently

spark 68 · Aug 9, 2012

jparker86 said:
This is what I want to do but getting unstuck here. It seems that no matter how I do it, once the thermostat kills my contactor, so does the stop circuit which in turn gives power to my a1 on the main contactor.

I want both heaters to work independently

Because you are mixing the thermostatic controlled part up with the latching part, try and seperate the controls.

So do you need two sets of stop/starts (4 Buttons) for the two heaters ?

jparker86 · Aug 9, 2012

spark 68 said:
Because you are mixing the thermostatic controlled part up with the latching part, try and seperate the controls.

So do you need two sets of stop/starts (4 Buttons) for the two heaters ?

Yeah I do. I got another contactor (shown in a previous post) and I took a live feed from main mcb supplying my control circuit going into 1 and from 2 it went to thermostat back from stat to a1 on my main four pole contactor. Existing cable going to a1 on main contactor I switched to a1 on the new contactor and this is fed from stop circuit. Worked when stat asked for heat but as soon as it removed power to main contactor the stop circuit didn't have any power to feed back to the new contactor, this is where I got stuck

spark 68 · Aug 9, 2012

OK,

You will need four contactors to do what you are trying to do (for the heater part alone).

You will need two self latching contactors (one for each heater), use one of the unused pair of contacts off of each of your start/stop contactors, ie. ones not used in the latch circuit, to feed a switched supply in series with the thermostatic controlled contactor (ie. in series with each thermostat and coil).

This way you can independantly control each heater, and each thermostat can control the second contactor independent from the latch (stop/start) contactor.

It is difficult to put into words, I may see if I can draw it for you.

jparker86 · Aug 9, 2012

spark 68 said:
OK,

You will need four contactors to do what you are trying to do (for the heater part alone).

You will need two self latching contactors (one for each heater), use one of the unused pair of contacts off of each of your start/stop contactors, ie. ones not used in the latch circuit, to feed a switched supply in series with the thermostatic controlled contactor (ie. in series with each thermostat and coil).

This way you can independantly control each heater, and each thermostat can control the second contactor independent from the latch (stop/start) contactor.

It is difficult to put into words, I may see if I can draw it for you.

That would be fantastic.

Darkwood · Aug 10, 2012

spark 68 said:
OK,

You will need four contactors to do what you are trying to do (for the heater part alone).

You will need two self latching contactors (one for each heater), use one of the unused pair of contacts off of each of your start/stop contactors, ie. ones not used in the latch circuit, to feed a switched supply in series with the thermostatic controlled contactor (ie. in series with each thermostat and coil).

This way you can independantly control each heater, and each thermostat can control the second contactor independent from the latch (stop/start) contactor.

It is difficult to put into words, I may see if I can draw it for you.

Your explanation for the heating side alone only needs 3 contactors, you say 4 but only explain 3
The heating contactors should not be latching as the need to drop out when stat opens, its the closed stat switch which holds the coil in.

On a tangent a risk assessment would probably negate the need for a E-Stop but would require more info, but your wiring plan shows it as a latching stop button and wont comply the way you have connected it as this would usually incorporate a safety relay, although it not a problem helping you JP i feel you are jumping in the deep end here before you can swim. there are so many other factors to be considered excluding the control system that come with experience and as im not their to see the install its hard to pre-empt you
If your fitting all this in an enclosure like a push button panel then theirs things like indicator lamps, door interlocks etc etc... to be considered as their are guidelines to follow which is clear you are unaware off.
As you dont seem to be any further ill draft you a simple form schematic but this is only on the info you have supplied so bare with me ive a busy few days ahead.

spark 68 · Aug 10, 2012

Hi DW,

No he needs 4 in total for the heating alone, He needs two latches (start/stop) independent from each other, and two stat controlled contactors, again independent from one another.

Have a look at this drawing, and see if i have made a mistake, I have drawn the controls for one heater, he would need to duplicate this apart from the E-Stop, which is common to the whole panel.

I have added the drawing in PDF as the image is too small to see

Darkwood · Aug 10, 2012

You have shown a diagram with 2 contactors on, K1 is you initial latching contactor (k1/1), k2 is your first heater control and using the common connection K1/2 to supply you 2nd heater would be fine, less expensive and leave more room as it removes the need for the extra contactor. (excluding E-stop and pump controls)

jparker86 · Aug 10, 2012

darkwood said:
You have shown a diagram with 2 contactors on, K1 is you initial latching contactor (k1/1), k2 is your first heater control and using the common connection K1/2 to supply you 2nd heater would be fine, less expensive and leave more room as it removes the need for the extra contactor. (excluding E-stop and pump controls)

I think I understand the drawing, and I think my problem in my current design is the stop button is after the start button!... Spark68 / Darkwood thanks very much for all your help and time. Really do appreciate it very much. Here is a picture of what I have at the moment.

Just going to sit and work out how I can redesign my current box to work like above.