Mains input current waveform into fan heater?

[ocset]

Hello,

Is the mains input current into this fan heater (or any similar one) when on 2kW likely to be a sine wave?
Presumably the current sine wave will be in phase with the mains voltage?

Also, when on "cold blower", i presume the waveform is just sine but with lower amplitude.

https://www.trotec24.co.uk/machines/heating/fan-heaters/tfh-20-e-fan-heater.html?rc=5b89253657&rc=5b89253657&gclid=EAIaIQobChMIof-u14_72AIV7rvtCh3zIQ59EAQYASABEgJP2fD_BwE

[SeanB]

Will be mostly resistive at 2kW, with a slight inductive component from the fan induction motor. On cold it will be a 300VA load or so as the fan motor will be the only thing drawing current, and will have a lagging power factor of around 0.6 to 0.8, depending on how efficient the motor is.

[ocset]

Thanks,
Do you know what devices in the fan that they use to prevent overvoltages to the fan when the mains plug switch is turned off near to when the inductive current is at its peak?     

I presume its something like two series'd ,  bidirectional 250V TVS's across live/Neutral?
 

[floobydust]

A fan motor/switch doesn't care about transients, there is no TVS or MOV in this kind of product.

[dmills]

Why would you bother with MOVs in a heater of all things?

Also from experience using those things as dummy loads (Ours are the white ones, but I think the product is probably the same), in fan only mode they kick like a bitch when you open the circuit, that motor has magnetising inductance that is not at all subtle (The heater thermostat also arcs in a very visible way not good for the contacts, or my HF radio, but CHEAP!).

Do not expect such a motor to be particularly sinusoidal in current either (even if the mains voltage is), they run by design rather too close to saturation in the magnetics just for cost minimisation. 

Regards, Dan.

[ocset]

in fan only mode they kick like a bitch when you open the circuit, that motor has magnetising inductance that is not at all subtle

Thanks, this is why we were thinking of adding a 500V bidirectional TVS in  ...across live/neutral of the mains input to the fan heater.....since it will at least stop the switch contacts getting arc damage when the mains switch to the  fan is suddenly opened?

...specially since we may actually be switching the mains off with a back-to-back dual IGBT AC switch in the live line, and we dont want our IGBTs getting overvoltaged when they suddenly switch off the mains to this fan heater...So a bidirectional TVS in the AC input, downstream of the semiconductor on/off switch would be a good idea?

[dmills]

Just WHY are you modifying cheap ass shit like these heaters?

I mean sure they actually make quite nice moderately nasty loads (surprisingly usefully nasty actually), and for a cheap sling em in the bottom of a soak rack and use them to load things up they are a reasonable thing (And cheap to replace when not if they break), but I see little value in modifying junk when there are far more reasonable options out there. 

The metal cased convection version make nicer loads, being basically resistive all the time, and an oil filled radiator has the virtue of not tending to set things on fire....

Now as it happens, I like junky loads that put out nasty RF from arcing contacts and honking great spikes when you open the contactor, for testing control gear these are far more valuable then some nice non inductive resistor, but why would you clean the load up?
Far better to design the control gear to survive the worst the POS can throw at it (I also have a universal motor driven angle grinder with the suppression cap removed (Great stress relief when combined with some scrap car parts) and a modest stick welder as test loads for when I have some power product I want to verify).

[ocset]

Just WHY are you modifying cheap ass shit like these heaters?

Thanks, in our office, 1kw is often too hot, but we can't set it to say 300w, so we wish to duty cycle the fan (eg 10 seconds on, 20 seconds off, repeating) so that it gives , on average, 300w
 

[IanB]

Thanks, in our office, 1kw is often too hot, but we can't set it to say 300w, so we wish to duty cycle the fan (eg 10 seconds on, 20 seconds off, repeating) so that it gives , on average, 300w
 

Why don't you just buy a slightly more expensive heater that has thermostatic control?

I'm sure you don't mean that you will duty cycle the fan as that would be daft, you probably mean to duty cycle the unit as a whole (at least I hope that's what you mean). But it would be much more sensible to leave the fan running and just break into the heater circuit. You could put a simple phase angle dimmer control on the heater, or better yet a zero crossing whole cycle load controller.

[picandmix]

Thanks, in our office, 1kw is often too hot,
 

Really ? ?   

What about the heaters internal thermostat, is that not working ?

Switching a load like that every few seconds is just asking for problems, much more useful to add a remote electronic temp sensor and a simple 25A SSR,  what I have used for years.

The thing you are really thinking about is PID, though you really need to separate the fan from the heating element so it runs at full all the time to keep the air circulating in the room.
https://playground.arduino.cc/Code/PIDLibrary

[picandmix]

If you really are talking about  making home brew modifications to an electrical device used in an office environment are you aware of the rules regarding such things ?

All electrical devices used in public  need strict design safety approval etc etc which yours will not have.

Anyone injured or property damaged, eg by electrical fire,  means you will be personally liable and likely to receive heavy fines and / or imprisonment.

Do what you like to yourself, but involving other people is a different matter.

[dmills]

There are requirements if you bring a product to market, but I think there is nothing for a product your company merely uses internally, apart from the usual electricity at work, factories act, and desirability of complying with best practise.

Now I would not be bothering to butcher a cheap heater, anyones time is worth more then that, but if you think about it there are many, many little weird one off bits of mains powered kit in most workshops, none of which are certified as such.

I am all in favour of safety and complying with the rules (at least when you can, selectively ignore them when you must!), but lets not pretend more rules exist then actually do.

Regards, Dan.

[capt bullshot]

Just WHY are you modifying cheap ass shit like these heaters?

Thanks, in our office, 1kw is often too hot, but we can't set it to say 300w, so we wish to duty cycle the fan (eg 10 seconds on, 20 seconds off, repeating) so that it gives , on average, 300w
 

Anyway, the way to go would be to duty cycle the heater, not the fan. If you turn off the fan while the heater element is still on, it'll either burn or some kind of overtemperature protection (maybe irreversible) kicks in. Usually one uses a triac or a SSR for that purpose.

For the electronics nerd's way, I'd recommend you to get a 1kW power supply and a 1kW electronic load. Then you'd just connect the load to the supply to have a quite idiot proof and fine grained adjustable source of heat ... Been there, done that long time ago, when boss forgot to order fuel oil for the central heating system in winter 

[ocset]

Switching a load like that every few seconds is just asking for problems,

Thanks, we could do it say 1 minute ON, 2 minutes OFF.

Also, i appreciate it would be better to take the fan to bits and duty cycle just the heating element....but we wish to have a kind of quick fix, and may make many, so we dont want to be lumbered with taking apart lots of fans.

All electrical devices used in public  need strict design safety approval etc etc which yours will not have.

Thanks, but thankfully after Brexit we can do what we like in our own country, as long as its safe.
I dont see how a simple switch switching a heater fan on and off (i min on, 2 mins off)  is going to do any harm?, we will have a fuse in the unit, and make it in a fire-proof plastic box, there will be no  vent-holes into which childs fingers can be poked.

[Monkeh]

Switching a load like that every few seconds is just asking for problems,

Thanks, we could do it say 1 minute ON, 2 minutes OFF.

Also, i appreciate it would be better to take the fan to bits and duty cycle just the heating element....but we wish to have a kind of quick fix, and may make many, so we dont want to be lumbered with taking apart lots of fans.

Make many? For what?

Just go buy a different heater and stop being daft.

[ocset]

Just go buy a different heater and stop being daft.

Thanks, as you know, many people cannot afford a better heater.
But a little box of tricks like i describe can help them get through the winter without having to make too many visits to the food banks.

[Monkeh]

Just go buy a different heater and stop being daft.

Thanks, as you know, many people cannot afford a better heater.
But a little box of tricks like i describe can help them get through the winter without having to make too many visits to the food banks.

You.. want to manufacture and sell a dodgy, probably unsafe addon to a fan heater for people who can't afford a fan heater?

thankfully after Brexit we can do what we like in our own country, as long as its safe.

No, it doesn't work that way. Leaving the EU will not suddenly mean you can do whatever you like as long as you think it's okay.

[Gyro]

Both of Argos's cheapest fan heaters (essentials range at <£20) have adjustable thermostats - so do all the more expensive ones, of course. The cheapie one I bought years ago for thawing out the car has one too.

http://www.argos.co.uk/search/fan-heater/

You would be far better concentrating on the appalling development process of your lighting products, rather than pratting about with something that is totally redundant and for which you have done zero market research. 


P.S. Tesco's cheapest heater (Daewoo) at £11.99 also has a thermostat!
P.P.S. Yay, Amazon £10.34, CPC £8.34, ebay wins at £4.00, all with thermostats!

[ocset]

Thanks, My cheapo also has a thermostat, but it turns itself off and stays off far too long. I think this is the usual case.

[Ian.M]

Its the usual case because the thermostat cuts off the fan motor as well as the heating element.  Mod it so the fan power is tapped from before the thermostat, so the fan runs all the time unless the control switch is at 0, leaving the heating element under the control of the thermostat, and it will continue to circulate the air in the room and respond far quicker maintaining a much more even temperature.  However you need to avoid pointing it directly at anyone as it will cyclically blow hot and cold which is very distracting.

[Zero999]

How about getting an external plug-in thermostat?
https://www.maplin.co.uk/p/timeguard-plug-in-thermostat-with-24-hour-time-control-a04ta

[floobydust]

my hunch is this experiment is for testing AC generators... Why else use IGBT's to switch power to a heater 

[ocset]

Thanks, the Fan Heater switcher is as attached. 
I think this could sell well.   
(deliberate mistake is the IGBT drive volts are too low, and needs remedy)

[dmills]

No fuse, no interference suppression, and the fan motor will get real upset about the waveform and may overheat even without the heater being on:palm:...

Also, £2.24 for the transformer, a couple of quid for the rest, say maybe £7 for the PCA, plus case and such, say £10 BOM, means £25 factory gate absolute minimum, meh, cheaper to use a light dimmer and about as effective, they are made in huge numbers so they get proper economies of scale.

Then we come to getting it CE and such certified so your insurance carrier will play ball, and it will be legal to sell.....

Nope, and you really need to stop playing in the bottomfeeder market there is money to be made down there but it requires massive vertical integration which you do not have.

Regards, Dan.

[drussell]

I'm starting to think that treez is just trolling... 

[ocset]

motor will get real upset about the waveform

Thanks, it will be 1 minute ON, 2 minutes OFF...repeated...

[Gyro]

I'm starting to think that treez is just trolling... 

I don't know about trolling, but his habit of drip feeding information (and intentions) after a reasonably simple looking OP certainly makes it difficult to 'see the wood for the treez'. 

[T3sl4co1l]

Just WHY are you modifying cheap ass shit like these heaters?

Thanks, in our office, 1kw is often too hot, but we can't set it to say 300w, so we wish to duty cycle the fan (eg 10 seconds on, 20 seconds off, repeating) so that it gives , on average, 300w
 

Just go buy a different heater and stop being daft.

Thanks, as you know, many people cannot afford a better heater.
But a little box of tricks like i describe can help them get through the winter without having to make too many visits to the food banks.

For all those of you following these threads -- keep these above quotes in mind.

Presumably, the OP has found himself in a tight situation.  Whether through poor finances or what -- who knows -- he has only managed to find a job, so similarly fraught, that they can hardly afford to give him minimum wage (that is, in pocket -- less taxes, interest, rent and what have you).  Perhaps worse than that, as he is unable to afford a mere heater.

As for those situations, whether his behavior can be changed, or not, who knows; but we should at least keep in mind generosity, for those less fortunate than we are.

Tim

[Delta]

So you are planning to market a £25+ add-on product to people who can't afford half that price for a heater with a thermostat?

Superb.

[floobydust]

I question the narrative - is this a product development post, or a poor man's solution soliciting help with our pity?

OP has firmware to write, a HV enclosure, heatsinks, parts costs, regulatory risk... and that's false economy.
A proportional PID controller is $10, 4kW triac phase-controller $2, on eBay or Ali.
Compare to $1,000+ in engineering design work... when a high/low heater is all that is needed.

It feels like manipulating the community to get design help on something, related to mains transients on LED lighting....

[Gregg]

Just WHY are you modifying cheap ass shit like these heaters?

Thanks, in our office, 1kw is often too hot, but we can't set it to say 300w, so we wish to duty cycle the fan (eg 10 seconds on, 20 seconds off, repeating) so that it gives , on average, 300w
 

Just go buy a different heater and stop being daft.

Thanks, as you know, many people cannot afford a better heater.
But a little box of tricks like i describe can help them get through the winter without having to make too many visits to the food banks.

For all those of you following these threads -- keep these above quotes in mind.

Presumably, the OP has found himself in a tight situation.  Whether through poor finances or what -- who knows -- he has only managed to find a job, so similarly fraught, that they can hardly afford to give him minimum wage (that is, in pocket -- less taxes, interest, rent and what have you).  Perhaps worse than that, as he is unable to afford a mere heater.

As for those situations, whether his behavior can be changed, or not, who knows; but we should at least keep in mind generosity, for those less fortunate than we are.

Tim

Not to judge or diagnose the OP, but I have witnessed this type of behavior in coworkers at least 5 times in the past.
It starts out rather innocently with the person seemingly acting in a devoted or obsessive compulsive manner.  The objects of interest are of vary narrow scope and the person affected refuses advice that is contrary to what they envision.  They often skip from one subject of manically devoted concentration to another.  As time goes on, they get worse and worse, until they can hardly function or communicate with others.  They get paranoid that nobody sees things the way they do.
In the people I have known exhibiting these symptoms, the cause has been methamphetamines.  It is really too bad that some intelligent people get caught up in this trap.