switching between 2 sockets on a timer

[califauna]

Hi everyone,

I'm trying to get a couple of appliaces going on a generator but they take too much current when they're both on at the same time.

I'd like to know the best way to switch between 2 plugs on a timer, so one is on for a minute or 2, then it switches to the other plug for 1 minute or two, and repeats like that.

There is this which Ive found, the boyu intermittent timer, but it only supports 3 Amps max:

http://www.ebay.co.uk/itm/BOYU-Intermittent-Timer-Switch-all-aquarium-tank-/160336636193

I dont mind buying something prebuilt, or wiring into a box or something, whatever can work and preferably will be fairly inexpensive.

Thanks for any help.

 

[Mursal]

A basic timer with a low current output (0.5A) controlling a contactor (mains relay) with contacts having a current rating well above your maximum load current.

Tie one load to the normally closed contacts (NC) and the other load to the normally open contacts (NO). With the timer output "off", the NC contacts will be closed and that load will power up. With the timer output "on" the NO contacts will be closed and that load will power up.
The timer will toggle between the two loads, but only one will be on at any time.

What do you think?

Trying to find one with everything built in, for you
http://www.ebay.co.uk/sch/i.html?_sacat=0&_nkw=mains+timer&_pgn=3&_skc=100&rt=nc

Just find one with NO and NC outputs (with minute increments) and you're sorted

 

[califauna]

THanks Mursal. I guess I would need a transformer as well, or something with a transformer inside , as the relays Im seeing are 12v.

 

[Mursal]

Something like this will run on high voltage control timer circuit.
Save using a transformer

Just an example
http://www.ebay.co.uk/itm/MAIN-POWE...t=LH_DefaultDomain_3&var=&hash=item1c2a8577eb

But hold tight, some of the other lads will point you to a fully enclosed timer with NO, NC outputs. Save you all the hassle of design/wiring etc.
Unless, you like that sort of thing?

The output from the generator has RCD protection for the user? If not put an RCD plug/socket on.

 

[bernardgreen]

Using two relays is better than using one change over relay. The timer switches one or the other relay.

It avoids any risk of an arc over as the contacts switch the supply from one load to the other

Using plug in relays adds a bit to the cost but simplifies assembly and later replacement of a relay.

From RS Components

Relay 350 664 and relay base 253 4044 should do what you want. The relay base can be DIN rail mounted or fixed to a panel with M3 bolts.

http://uk.rs-online.com/web/p/non-latching-relays/0350664A/

http://uk.rs-online.com/web/p/relay-sockets/2534044/

Other makes and other suppliers are available

 

[Lectrician]

A din rail mount 'recycle' timer (or multifunction timer), the output switching a changeover relay and the changeover relay switching two contactors. If the timer has changeover contacts, omit the changeover relay.



Third one down: http://www.edcscotland.co.uk/acatalog/EDC_Products_Electronic_Timers_214.html

 

[califauna]

Thanks for all those ideas and links. Looks like this is going to be more comlicated than I thought! I was hoping to buy something like a plug outlet strip with timer built in, but I see from the posts there are the problems of the high current draw and arcing etc so I guess it needs the specialised equipment.

The current drawn at any one time is up to 11 or 12 amps. Some of these links are for products rated at 10 amps, but with for example, a maximum switching current of 20 A. Does this mean that a continuous current of 12 Amps could be supported without damaging the product (if its 'rated' at 10 amps)?

 

[big-all]

perhaps telling us the actual items concerned there rating there likely use
the capacity off the generator [max and continuous] may help other ideas or suggestion

 

[califauna]

the items are kettle 2800 Watts, and food heater 1500 Watts. The gernerator is 2800 Max, 2600 sustained.

FOund louds of power strips with timers but they cant control the outlets according to intervals. They can only be programmed to come on or off at programmed times of the day, with a limit (eg 16 times per day)

 

[califauna]

Actually its a water urn (like a big upright kettle), not a kettle exacly , so it higher wattage.

Is it possible to exchange or Magyver the existing element in a water urn so that it is a lower wattage? not important that it heats the water ultra quick, just that is consumes less power.

Its a Swan 00534 (obsolete)

 

[big-all]

ok another question what is you anticipated volume per hour off boiling water

we need to work out if the load is great than the power available

another idea is 2 elements in the urn [1k+1.5k]with a change over switch
so something like urn 1kw and food 1500w or change the switch to give 1k plus 1500w to the urn

 

[Mursal]

If you are switching 12A I would use contacts rated at least 20A continuous.

And if your on and off times are short, you may have to fit snubbers to reduce the arcing on the contacts. But don't run the contacts at or near their maximum continuous current rating, as they will only give you trouble.
It doesn't half get complicated

Edit 1
I see one load will load the genny to the max? Not the best approach for reliability. Consider trading up to a 5KW and your sorted.

 

[califauna]

the items are kettle 2800 Watts, and food heater 1500 Watts. The gernerator is 2800 Max, 2600 sustained, so it can run one or the other but not both at the same time.

I am looking for alternative solutions to going up in size of generator as I assume the fuel expenses increase, (as well as outlay for generator of course).

 

[Mursal]

......

 

[big-all]

would it not be possible to change to gas for all or some off the load
much cheaper to run and much quieter