Lad Limiting/Switchng 230v

[hotponyshoes]

So, I do a bit of mobil catering, we are fairly well sorted with a power distribution system to break down out from anything upto a 63a outlet on a big site genny.
Most of the equipment we plug into the distro is normal 13a plugs although it's all pretty much 3000w bits of kit so pulling the full 13a.

An example of the problem,
Yesterday, we are running off of a generator with a single 32a outlet.
Kit connected:
Food warmer, 1500w, pid controlled.
Griddle, 3000w, mechanical thermost.
Induction hob, 500-3000w adjustable
Hand wash, 3000w, instant heating - you press a button on this and it pumps out hot water for 30secs. No tank, just an instant heater element inside.
So, 45a Total max load.

When setting up I can just turn on one at a time, let each warm up before turning on the next.
The warmer and griddle are then just turning themselves on/off to maintain temp and I can run the induction at a lower power if the other 2 are both heating.

However, 3 times yesterday the outlet breaker on the generator tripped when someone pressed the button for the hot hand-wash.

Mainly annoying because to save the noise I normally position the generator as far away as possible.

I'd like a lightweight, compact solution if anyone knows of anything?

I'm thinking of a box with one plug, 2 sockets. Plug the hand-wash into 'outlet 1' and griddle into 'outlet 2'. This would have a switching/change-over contactor inside.
When it detects a load on outlet 1 it disconnects outlet 2 until outlet 1 has finished.

However, there must be some sort of control circuit inside the hand-wash so I'd need outlet 1 to be live all the time to power that.
So, something like 'if more than 1a load on outlet one disconnect outlet 2'.

Something din-rail mounting that could replace a normal breaker would be ideal!!

 

[Robotstar5]

Use 'AC current sensing relay" as a search term gets quite a few hits.

I can recommend products from Dold Industries and Broyce Control

 

[daleyd]

A small programmable relay like a Siemens logo (or similar) and a control box with some push buttons and/or selector switches? You could easily put some logic in to control that set up.

You could probably do it with hardwiring, and a few relays/contactors (a selector switch would allow only one of the 2 outlets on) - however the beauty with programmable stuff is it’s easy to change the logic, add timers if you wanted in the future.

 

[Erie Fred]

.....unplug the hot hand wash.....

 

[minimutly]

A simple changeover switch - from handwash to " other" load would be nice and simple?

 

[daleyd]

Sorry just re read your description, yes a current sensing relay as @Robotstar5 said might be simplest option.

 

[hotponyshoes]

Use 'AC current sensing relay" as a search term gets quite a few hits.

I can recommend products from Dold Industries and Broyce Control

Ah ha!
That sounds exactly like what I am after..
Quick search finds this

LMCCR-2A | Broyce Control, UK

The product is designed to monitor current in a feed to a load. An auxiliary supply (required to power the unit) must be present for the product to function. Two monitoring modes available: Under current: In normal operation, the relay is in the energised state (monitored current above the set...

broycecontrol.com

Wiring diagram


This one is rated at 8a but if I can find a 13a version I could..
Connect A2 & A2 to the bus bar,
Connect B1 & B2 to the sink socket
Take a live from the bus bar to 15,
Connect 16 to socket 2 (for the griddle)

Set the monitor to anything above whatever the sink control electronics use (gues 1a)

So a box with 2 outlets, both would be live. No.2 would be automatically turned off when No.1 pulled more than 1a but No.1 would still have the full 13a available.
Once the sink stops pumping hot water the griddle will turn back on.

That's if I'm understanding the diagram/function correctly?
Also, the relay requires auxiliary power for it to function which I guess are the unmarked connections but I could just feed these from the bus bars as well?

 

[sparkysy]

Can you not just use a mini contactor to control this, I would use the NC contacts to power the griddle and the NO contacts to power the hand wash. Use the push switch & timer for the water heater to power the coil in the contactor.
In standard operation the grill has power, if the button is pressed the grill is taken off power until the heater times out.
This is assuming that the control circuit for the water heater can take the extra current from the contactor coil.

 

[hotponyshoes]

Can you not just use a mini contactor to control this, I would use the NC contacts to power the griddle and the NO contacts to power the hand wash. Use the push switch & timer for the water heater to power the coil in the contactor.
In standard operation the grill has power, if the button is pressed the grill is taken off power until the heater times out.
This is assuming that the control circuit for the water heater can take the extra current from the contactor coil.

I might have to use a contactor in conjunction with the load sensing relay unless I can find a relay rated to 13a

I could use the water heater as the controller but that would mean running cables out of it somehow and would have to plug it in etc.

We also use different bits of kit depending on the event and sometimes I'm not the one setting it up & using it.

I'd like a solution where I could just lable the sockets so you just plug things in and it all takes care of itself

Edit, I suppose I could fit the contactor inside the water heater and fit a socket into the heater casing and plug the griddle into that...

 

[hotponyshoes]

Just to clarify from someone who's used these relays before...

If I set the relay to 2a
The supply/monitored current to/from the relay is not interrupted or limited in any way once the 2a is exceeded?
And that part of the relay is capable of carrying 13a?

All that happens when more than 2a is drawn is that the relay is triggered?

 

[hotponyshoes]

Still messing with this, I sourced a Broyce M3MCR current sensing relay.

Didn't read the data sheet first.
It's only rated at 8a on the primary side.
Output side is not a problem as I cam use a contactor but is there any way I can use a contactor or something for the load monitoring side so I can pull 13a?

Obvious solution would be a sensing relay rated to 13a. I can find 16a rated ones but they are chinese looking cheap things and I think I'd trust the Broyce one more than those..

 

[hotponyshoes]

Maybe I can answer my last question myself.
Or confuse things further!..

Basically, I want to run 2x 13a sockets from a single 13a Plug.
So automatically switch one socket on/off

Could I wire up a change-over contactor.
Control the contactor from the sense relay.

So, both sockets are live. I am only drawing 13a from socket B.
When socket A detects a draw above 1a the contactor engages and disconnects B.
At the same time it connects to A.

That would mean A has a parrallel connection via both the sense relay and the contactor. That should (might!) stop me melting the 8a rated sense relay.
Although, the data sheet mentions a 10a overload condition but I'm not sure what that means?

 

[voipio]

A manual changeover to switch between the water heater and griddle sockets, with the switch located next to the water heater, or a 30 or 45 second timer that performs the changeover, would do the trick. The total load without the water heater is 34A, so you're already running beyond the limit, even without the water heater.

A potential problem with current sensing relays is that there will be a momentary overload condition, before the changeover occurs, that could trip the generator overload protection device.

 

[hotponyshoes]

A manual changeover to switch between the water heater and griddle sockets, with the switch located next to the water heater, or a 30 or 45 second timer that performs the changeover, would do the trick. The total load without the water heater is 34A, so you're already running beyond the limit, even without the water heater.

A potential problem with current sensing relays is that there will be a momentary overload condition, before the changeover occurs, that could trip the generator overload protection device.

I'm running over the limit but diversity allows it all to work (mostly)
It's all fitted with protection so noting bad should happen...

The issue with a manual switch is mainly you have to operate it manually which is just one more thing to do. If we were going to do it manually we could just turn off something else first.
Also, the button for the sink is knee operated. That's a food hygiene thing so if you touch raw meat you can wash your hands without touching anything else (like a manual switch)

I might just look at fitting an inlet/outlet to the sink. Plug the sink in, plug the griddle into the sink. Firing up the sink cuts off the outlet socket.

But, that needs ip connections plus I'll still need to overcome the 8a limit on the relay somehow..

 

[Misterg]

is there any way I can use a contactor or something for the load monitoring side so I can pull 13a?

Datasheet says to use a "suitable" current transformer to monitor higher currents.

https://www.farnell.com/datasheets/16705.pdf

Has got a sensing range of either 20-500mA or 0.2 to 5A so something like a 20:5 CT should bring your load currents into the switching range (on the higher setting).

Maybe something like this?

https://uk.farnell.com/hobut/ct160-5-h7/transformer-current-20-5-ratio/dp/1758725

All I know about CTs though, is NEVER to operate them without a load. One of our resident electrical gurus might be able to recommend something suitable.

 

[awemawson]

Battery being charged by the genny and feeding an inverter rated a bit more than your load.