Timer switches and washing machines

[Keefiedee]

Can someone shed any light on this as it is puzzling me? Looking on eBay for "UK 3 Pin 24HR 24 Hour Timer Programmable Mains Wall Home Socket Plug-IN Switch", these are generally rated at 3200 or 3000 watts - yet they all look the same, and the one with the 3200 rating also includes a warning that it is not to be used for washing machines

- which is exactly what I do want it for. I haven't scrabbled round the back of my washing machine to see what wattage it is, but I can't see it being more than 3000 watts, so why should there be this warning?

Keith

[Roger Mills]

The important characteristic is how much current it can switch. 3200 watts is 13 amps - but some devices have much higher startup currents than this - which are not sustained for long enough to blow the fuse but which could nevertheless wreck the contacts in a time switch. Maybe washing machines come in the category?

[Jethro]

These timer switches tend to be just 2 pieces of contact that touch and release. Anything with a big motor in it will be an inductive load, which will cause arcing, and could fuse the contacts together. You'd need the timer switch to switch a contactor relay which you plug your washing machine into.

[Dave Liquorice]

I sort of thought that but all the washing machines I've ever encounterd don't start the motor the moment you switch 'em on or the heater come to that. They need to, at least partially, fill with water first... Thus the time switch won't be required to make/break a high load. Well not unless you are daft enough to set it such that it switches off before the cycle has finished...

[NT]

If that were the problem it wouldnt be washing machines they dont recommend, it would be appliances with high startup current.

And why would any timer manufacturer save 0.5p by shrinking the contacts to the point where they couldnt cope with any 13A load.

NT

[Brian Gaff]

Inductive loads?

Brian

[NT]

Washers are mainly resistive (element).

NT

[Owain]

Because when you make millions of something, all those 0.5ps add up.

Owain

[Jethro]

As others have posted, it's not usual for the machine to start with the motor on, so the load may not cause an arc ... I was just speculating why the OP was advised against using the timer for a washing machine.

So has mine, but I don't think we have ever used it.

[Peter Parry]

In case you inadvertently switch the machine off with the timer when it is operating at full load and speed. The contacts are not capable of handling the high back EMF and will often weld shut.

[Mike Clarke]

It could be the inability to handle the inductive load as some have said but another point to consider is that some washing machines with digital controls require you to press a "Start" button after selecting the programme. Pressing this button without the power being on will have no effect [1] so an external timer would not be appropriate. Perhaps they've had too many complaints from people who bought them and then found they were not suitable so decided to go for a dumb-ed down warning saying "not to be used for washing machines".

[1] yes you might be able to start the machine then turn off the power and set the timer to let the machine continue from where it left off. But it's a bit of a kludge.

[grimly4]

Similar on Grand Designs a couple of years back - holidaying couple's neighbour spotted a glow as the house went up at 2am; caused by a fridge/freezer in an attached outbuilding.

[NT]

Valid principle, but on a timer this is pretty well unheard of.

NT

[Adam Funk]

Good point. The timer I used to use for a washing machine was the kind with pins that you put in any holes in the on-ring and off-ring, along with a switch you could flip. I used to have only one pin in the timer to switch the machine on early in the morning, so the timer would never cut the machine off automatically. (I'd flip the switch to off immediately after setting the machine in the evening.)

[Adam Funk]

(See my other post just now: I used to set the timer to switch on automatically, but I switched it off myself.)

I'm an Economy 7 nerd.

[js.b1]

The cheap electromechanical timers can be quite poor quality, that includes ones from Asda Tesco etc.

They can stick on or more often off. More an issue with frost heating where walking in to 2oC floor temperature and vulnerable pipework.

Contacts are indeed small & flimsy. Bigger & far better quality contacts on a car window regulator switch for example.

They run warm on high loads. A 2kW load for 15mins generates quite noticeable heating. A washer is only going to run its 3kW heater for a very short time even on a 95oC wash though.

China generics supply a competent production sample and utter trash for production run. The money to be made is simply astronomically, but so is the money to be lost if you are not the cheapest and china is NOT a low cost area anymore compared to many other Asian makers.

So... how about an LCD timer, that avoids the crude mechanical contacts (=A32 plug-in timers are not Sangamo quality!) and might just get you a 16A rated relay. It will be rated less for inductive, but I think the only inductive load at startup is going to be the solenoid valves "juddering" if yours does that.

I would add, there are little flood alert alarms available for about =A34.99-9.99 - so you may want to add one of those... just in case.

Economy 7 does not save much on a wash unless 60-95oC, it is drying where it saves a fair chunk over a year.