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

Darkwood · Aug 10, 2012

My last note would be to avoid confusion and uncertanty you should fit a row of indicator lamps to signal what is on, anyone walking up to the panel wont be any wiser as to the operational state its in, using a N/O contact (aux if necessary) wire a control on lamp, heater 1, heater 2 and pump lamps as well as a initial power lamp....... i think you'll start to appreciate how a good background is needed before designing and building a panel on your own.
Personally i would have fitted a plc programmed it up lost a few relays added a flow sensor and temp read-out as well as a overtemp sensor all controlling the system in case of problems.... yes a little more advanced but giving it the PRO - touch.
Your system is functional but as it stands it is functionally confusing as to what it on and off at any given time and at a minimum id implicate indication lamps.

spark 68 · Aug 10, 2012

Another thing I would look at, is providing indicator status lamps for the various items, when you get it working.
You could use the spare contacts on the stop/start contactors (terminals 5&6 on Richards drawing).

As DW said it is debateable whether you actually need an E-Stop or more correctly EPO (Emergency Power Off).

Cross posted with DW above lol

jparker86 · Aug 10, 2012

darkwood said:
My last note would be to avoid confusion and uncertanty you should fit a row of indicator lamps to signal what is on, anyone walking up to the panel wont be any wiser as to the operational state its in, using a N/O contact (aux if necessary) wire a control on lamp, heater 1, heater 2 and pump lamps as well as a initial power lamp....... i think you'll start to appreciate how a good background is needed before designing and building a panel on your own.
Personally i would have fitted a plc programmed it up lost a few relays added a flow sensor and temp read-out as well as a overtemp sensor all controlling the system in case of problems.... yes a little more advanced but giving it the PRO - touch.
Your system is functional but as it stands it is functionally confusing as to what it on and off at any given time and at a minimum id implicate indication lamps.

Hello Darkwood,
Yep I already have the wheels in motion for this- it would have two indicator lamps. One to show the heater is active and another to show it is drawing heat.
Im just thinking on the drawing that has been done, can I use a 2 pole instead of the three shown?

Darkwood · Aug 10, 2012

If a third pole isn't required then you can fit the 2pole i think you shown earlier, the calling heat lamp can just be connected to the stat sw wire as the same with any other lamp just double up in the circuit where it requires a signal, although when you advance you will design the lamp indication etc through there own aux contacts but no harm in doubling up on your learning curve. Also for future ref.... control voltages are usually reduced to both heighten safety and allow to export control circuits and sensing outside the panel itself in a safe manor...24v dc is common but can vary in the industry.... last note would be to run slotted trunking to neaten your control system it may mean a larger box but looks more pro'.

Knobhead · Aug 10, 2012

darkwood said:
you could ask tony as he dont do alot all day :lol:

Cheeky sod!

JP a latching stop P/B does not meet the requirements of an emergency stop.

Darkwood · Aug 10, 2012

Heres a recent one i did just to express the slotted trunking suggestion and how neat a simple cheap addition actually looks.

jparker86 · Aug 10, 2012

darkwood said:
View attachment 14003 Heres a recent one i did just to express the slotted trunking suggestion and how neat a simple cheap addition actually looks.

Can you enlarge it?

Darkwood · Aug 10, 2012

jparker86 said:
Can you enlarge it?

im trying bare with me

jparker86 · Aug 10, 2012

darkwood said:
im trying bare with me

Darkwood thanks for bearing with me.
As I said I only need two poles so you think that contactor I posted earlier with 1,2,3,4 + A1 + A2 will be ok? It doesn't have any NO contacts though. But looking at this drawing it doesnt matter? Correct?

Darkwood · Aug 10, 2012

Trying to see if can get it larger.

Contactors are generally N/O ..this is the de-energised state the one you have i assume has 2 N/O poles that close when coil is energised, re' this pick it would normally not be as tight and compact but has some space restrictions as it was a sample and will have all its internals removed and fitted into a main cab of a larger control system, also due to this just been a temp' set up ive left out a cooling fan and filter just in case any keen eyes try pulling me on it.

jparker86 · Aug 10, 2012

Wow that looks ace Darkwood. This is what I will hopefully one day achieve lol.
So what I will do now is go home and try and figure out what you guys have done and report this evening with another drawing.

Darkwood · Aug 10, 2012

:blush5:...... believe it or not this is a simpler set up than yours, dont get overwelmed by the drives but it was rushed and i was restricted with spec's on the cab' size so got a little more crowded than i like, only difference here to yours is the trunking and the numbering of all cables but you can see what a £10 worth of extra gear can achieve.

jparker86 · Aug 10, 2012

darkwood said:
:blush5:...... believe it or not this is a simpler set up than yours, dont get overwelmed by the drives but it was rushed and i was restricted with spec's on the cab' size so got a little more crowded than i like, only difference here to yours is the trunking and the numbering of all cables but you can see what a £10 worth of extra gear can achieve.

You see as much as I would love to pay someone to do the job first time around, I love to know how things work.
When I sell a pce of equipment I love to know how each and everything works. Before I come on this forum I wasn't that clued up on how a contactor worked, etc... and to be honest I am probably still a bit lost but at least now if anything goes wrong or the customer asks me a question I can give him an answer based on my experiences and that in my business is priceless. I hate nothing more than speaking with someone about something and he says "Ill have to ask my boss...".
I have drew the control circuit out on paper and see what you think. Please let me know if I have got all the wires going to the correct place. (please ignore the writing diagram which doesnt have anything going to A1!)

Darkwood · Aug 10, 2012

it would function but it is poor design, consider a latching stop button or holding stop in, at the same time push start this will pull the contactor in, your stop button should be before the start in series and take your latching relay source from the outgoing off the stop button, this way it breaks both power to the start button and power to the latch loop.
Put your stop before your start in series then take your supply to terminal marked 2 from the out going of the stop or input of the start (same thing)

If you follow that ....now if you hold stop in and press start it wont pull the contactor in.

Knobhead · Aug 10, 2012

jparker86 said:
When I sell a pce of equipment I love to know how each and everything works.

Out of curiosity what do you normally sell?

jparker86 · Aug 10, 2012

Tony said:
Out of curiosity what do you normally sell?

I sell industrial equipment that filtrates liquid into a 5 micron level ensuring particle free liquids. Mainly aimed at oil people who buy and or collect used vegetable oil and want it filtering down to remove solids.

spark 68 · Aug 10, 2012

Hi JP,

Try this

jparker86 · Aug 10, 2012

spark 68 said:
Hi JP,

Try this

Thanks Spark, I was following the drawing cause it says on the drawing to have the stop button interrupt the live into l1? Is this not correct?

spark 68 · Aug 10, 2012

jparker86 said:
Thanks Spark, I was following the drawing cause it says on the drawing to have the stop button interrupt the live into l1? Is this not correct?

On the drawing I did, the stop is above the start button, it is just conventionally done this way, as it interrupts both the coil and the contact.

In fact the drawing I gave you is more like this:

Edit: Drawing corrected after Richard pointed out my mistake

jparker86 · Aug 10, 2012

I think part of my trouble was understanding how the start button stays closed when it's normally open. Am I correct in saying that the moment the start button is pressed it is feeding in a loop and as a result stays retained

spark 68 · Aug 10, 2012

jparker86 said:
I think part of my trouble was understanding how the start button stays closed when it's normally open. Am I correct in saying that the moment the start button is pressed it is feeding in a loop and as a result stays retained

Your start button is N/O , it closes temporarily (when you press it), this energises the coil pulling in the contacts, one of the contacts then keeps the coil energised even after the start button has opened again (finger off), ie. it is self sustaining, until you break the circuit again with the stop button.

Richard Burns · Aug 10, 2012

The "switch" 1-2 is supplying the coil in parallel with the start supply. Once the contactor is energised using the start button it closes 1-2 which then supplies the coil and so keeps the contactor actuated.

To stop the contactor you need to interrupt the supply going to 2 to deactivate the contactor, the two mods above would leave the contactor actuated, as they are disconnecting the start button supply to A1, perhaps try this.
Edit talking rubbish here, this would not work, you could never start!

Edit2 the stop button is NC so it would work, what an idiot, think before posting!!!

spark 68 · Aug 10, 2012

You are of course 100% correct Richard, my mistake LOL, Iam in the middle of filling in an EIC and not paying attention.

I will edit the above drawings.

Edit: I did make a mistake on my drawing too though Richard, it's that time of night on a Friday lol.

jparker86 · Aug 10, 2012

Ok so the above drawing would work?

Richard Burns · Aug 10, 2012

Sorry Jp all gets a bit vague at this point.

My drawing in post 97 would work and would disconnect the contactor when you press the stop button, however this would not disconnect the supply to terminal 3 in the drawing (although the contactor being off would stop the supply to the stat). Spark68 has edited his picture in post 94 so that all the supplies to all the terminals in the contactor (bar the neutral) will be disconnected by the stop button and will also work and be more secure (in case of the contactor welding closed, etc.)

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