Relay Design and Wiring

[paulgill28]

I am trying to understand how a relay system works and have designed a circuit and a ladder diagram all as attached for an 8 PIN relay, a current sensor and a delay off timer relay. It is the sort of thing one might use with work shop power tools for automatic switch on and delayed off for a chip extractor with a manual override to run the extractor independently of the power tools operation.

In essence the chip extractor will run when a power tool is switched on, The dust extractor will run until the power tool is switch off but with say a 10 second delay (dust extractor runs on for 10 seconds after power tool switched off). There should be an override button to allow the chip extractor to be run independently of the power tools together with an off button to stop the override. Indicator lights to show whether the system is in Auto (delayed Time off mode) - Blue light, Override Mode - Green light or Off Mode - Red Light.

The normal state of the system should be off and showing a steady red light. When a power tool is being used the system should show a Blue light (Auto mode) whilst the delayed stop timer relay is activated and a Green light when the system is operating in override mode.

The components are:

• a Green Brook PRR208 -230 VAC DPDT (changeover) 8 pin 10 amp relay with 2 NO and 2 NC switch terminals and base,
• a delay off adjustable timer relay 250 VAC 16amp 50/60 Hz and,
• a self powered current sensor switch adjustable 0.3 ~ 30 amps normally open
• a momentary RED push button switch with both N/O and N/C contact terminal choice
• a momentary GREEN push button switch with both N/O and N/C contact terminal choice
• LED indicator lamps 230-380V 20mA in Red, Blue and GREEN
• 1 x Single gang 13A power socket outlet wired to the main relay - for dust extractor power
• 3 x double gang 13A power socket outlets wired in parallel - for power tool power
• Power source - single phase 240VAC on a 32A rated breaker
• Dust extractor - 1,200 W 230V - max current draw 5.22A

The dust extractor is powered from a single 13 amp socket outlet running through the change over relay rated at 10amps. The power tools are powered from 3 x 2 gang 13amp socket outlets.

I think my logic of how the circuitry works is generally correct, however the one problem I am having is to understand how I can wire the system so that the override light is off when socket outlet no. 4 is being powered when the timer relay has been triggered and is controlling the power to the socket outlet. Perhaps I need an 11 PIN relay. I tried designing it with a DPST NO relay but this didn't give me the flexibility I needed.

The light indicator logic should be:

• Auto mode - power tool use (current flow) determines power to dust extractor - Blue light on, RED light off, green light off
• Override mode - Green push button operation latches CR1 relay coil - GREEN light on, Red light off, blue light off
• Stop mode - Red push button cuts power to override circuit putting CR1 relay back to unenergized state - STOP light on, Blue light off, Green light off

If anyone is able to help with the logic and to solve my indicator light issue I would much appreciate the help and any suggestions/comments as to how to resolve the issue.

I would also appreciate to know if my ladder diagram wire numbering is correct. I am not sure I fully understand how wire numbering is applied.

 

[James]

6ED1057-3BA03-0AA8 | Siemens LOGO! Series PLC CPU Starter Kit for Use with LOGO! V8.3, 115 V ac/dc, 230 V ac/dc Supply, Relay Output, | RS

uk.rs-online.com

By the time you have wired and re wired the relays to suit your needs, you would find you are better off with something like this.

Dead easy to program, drag and drop ladder logic.
Probably not much more than your relays.
You will still need your current sensor though.

 

[paulgill28]

6ED1057-3BA03-0AA8 | Siemens LOGO! Series PLC CPU Starter Kit for Use with LOGO! V8.3, 115 V ac/dc, 230 V ac/dc Supply, Relay Output, | RS

uk.rs-online.com

By the time you have wired and re wired the relays to suit your needs, you would find you are better off with something like this.

Dead easy to program, drag and drop ladder logic.
Probably not much more than your relays.
You will still need your current sensor though.

Thanks James but seems like a much more expensive solution to me. This for me is more about learning how to wire relays from scratch and the logic.

 

[davesparks]

You can get rid of most of the complication with a simple 3 position switch for Auto-Off-Manual.

Your ladder diagram doesn't work, I think the biggest issue is that you are trying to represent physical relays and wiring on a ladder diagram when it is a programming language which provides the instructions to a PLC or programmable relay.

If you want to play around with ladder logic you can download the trial version of the Siemens logo software which allows you to draw ladder diagrams and simulate them, you just can't download a program to a logo from the trial version.

 

[paulgill28]

You can get rid of most of the complication with a simple 3 position switch for Auto-Off-Manual.

Your ladder diagram doesn't work, I think the biggest issue is that you are trying to represent physical relays and wiring on a ladder diagram when it is a programming language which provides the instructions to a PLC or programmable relay.

If you want to play around with ladder logic you can download the trial version of the Siemens logo software which allows you to draw ladder diagrams and simulate them, you just can't download a program to a logo from the trial version.

Dave thanks for this. I appreciate what you are saying regards the 3 way switch and already considered this but I wanted to try and work it out using lights, push buttons and relays more as as an intellectual exercise and for learning purposes.

As for the ladder diagram I was following this guy amongst others on:

So I suppose there are more than one way of doing ladder diagrams and what they are used for. They are also used for air conditioning systems I understand.

Thanks anyway for your time.

 

[Spoon]

So I suppose there are more than one way of doing ladder diagrams and what they are used for. They are also used for air conditioning systems I understand.

I watch a YouTube channel that repairs pinball machines and the old pinball machines use ladder diagrams for the relay logic.

 

[paulgill28]

I watch a YouTube channel that repairs pinball machines and the old pinball machines use ladder diagrams for the relay logic.

Thanks I'll take a look and see if I can find it.

 

[ElectroChem]

Thanks I'll take a look and see if I can find it.

Maybe not the channel Spoon was thinking of but one called Technology Connections has done some features on old pinball machines.

Ladder logic can absolutely represent physical relays, that's where it started. In regards to your system, I wouldn't switch the extractor through the 8-pin relay, their contacts are not up to the job despite saying 10 Amp. Rather I would use the relay to switch a stronger contactor that powers the extractor.

Keep working on your diagram, as Dave said there are some issues that will stop it working as you intend so come up with a V2 and we'll take another look.

 

[Spoon]

The guys who I watch every now and then are these

 

[paulgill28]

The guys who I watch every now and then are these

Thanks

 

[paulgill28]

Maybe not the channel Spoon was thinking of but one called Technology Connections has done some features on old pinball machines.

Ladder logic can absolutely represent physical relays, that's where it started. In regards to your system, I wouldn't switch the extractor through the 8-pin relay, their contacts are not up to the job despite saying 10 Amp. Rather I would use the relay to switch a stronger contactor that powers the extractor.

Keep working on your diagram, as Dave said there are some issues that will stop it working as you intend so come up with a V2 and we'll take another look.

I have updated the circuit diagram (see Rev.1 attached) having introduced another 8 pin relay and another momentary push button switch to overcome my lamp illumination problem from previously. I think the logic of the circuit now works.

I hear what you say about contactors which is what I originally looked at but concluded as the max current draw of the extractor is only just over 5 amps I could use relays, especially as I can get a good deal on them. Contactors are much more expensive so opted for the relays. Given that the system will only get occasional use and extraction will never be for more than a minute or two each time I figured relays would be cheaper overall even if one fails and I have to replace it. However now that the return current for socket outlets 1, 2 & 3 have to go through relay CR3 I might be inclined to see if I can find a contactor with one NO and one NC switch as the current draw for the power tools could be as high as 10.5 Amps for my router table. Only one power tool will ever be in operation at once. Haven't so far found a suitable contactor at reasonable cost that can be DIN rail mounted.

I've also attached operating instructions for the circuit with all the switch states for each button operation. Still working on a revised ladder diagram for these circuit revisions.

Any comments would be gratefully appreciated.

 

[James]

LC1D09P7 | Schneider Electric TeSys D LC1D Contactor, 230 V ac Coil, 3-Pole, 9 A, 4 kW, 3NO, 690 V ac | RS

uk.rs-online.com

 

[paulgill28]

LC1D09P7 | Schneider Electric TeSys D LC1D Contactor, 230 V ac Coil, 3-Pole, 9 A, 4 kW, 3NO, 690 V ac | RS

uk.rs-online.com

Thanks. Already come across this one, but at £50 seems expensive for what I need.

 

[ElectroChem]

Thanks. Already come across this one, but at £50 seems expensive for what I need.

FuseBox INC202 Contactor DP 20A 230V N/O 2 Pole Heating Lighting Din Rail Mount

FuseBox INC202 Contactor DP 20A 230V N/O 2 Pole Heating Lighting Din Rail Mount- £6.59

lamplec.co.uk

 

[paulgill28]

FuseBox INC202 Contactor DP 20A 230V N/O 2 Pole Heating Lighting Din Rail Mount

FuseBox INC202 Contactor DP 20A 230V N/O 2 Pole Heating Lighting Din Rail Mount- £6.59

lamplec.co.uk

This contactor you suggested unfortunately only has two NO switches rather than 1 NC and 1 NO required for the CR3 current sensing bypass relay/contactor, but I have now found an inexpensive one which has 1 NC and 1 NO and is rated to 25 amps:

Heschen Household AC Contactor, HS1-25, 2 Pole 1NO 1NC, AC 220V/230V Coil Voltage 25 Amp, 35 mm DIN Rail Mount which is rated as Ui~ 500V, Ue~ 250V, Ie (AC-7a) 25A and Ie (AC - 7b) 9A.​

Do you know whether this would be OK for a 2,400W 230VAC Router motor which I presume can have a max load of 2400/230=10.43 Amps? Ie (AC - 7b) for this contactor above seems to be stated as 9 amps.

I understand Utilization category AC-7b under the IEC/EN 61095 standard describes conditions for controlling domestic motor loads, including those with high starting currents, like washing machines, dishwashers, and other household appliances with motors.

While the specific maximum load under AC-7b can vary depending on the manufacturer, design, and specific application, this category generally accounts for significant inductive loads, with higher inrush or starting currents. The key focus in AC-7b is the ability to withstand these high starting currents and control high-power motors without damage or failure.

That said, there isn't a universally specified maximum load in terms of wattage or amperage. Instead, the limits are defined by specific products that comply with this category. Factors that determine a device's suitability for AC-7b include:

• Motor power: How much power the controlled motors draw during normal operation.
• Starting current: The initial surge of current when the motor starts. This can be several times higher than the running current.
• Switching frequency: The expected frequency of turning the motor on and off.

Unfortunately I don't have the specification load profile for the router motor other than its Voltage and Power rating, 10,000 - 22,000 RPM, relevant standards EN 60034-1:2010 and the Low Voltage Directive 2006/95/EC and it has a soft start feature which I presume avoids higher start up loads.