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Old 27th Feb 2023, 6:09 pm   #1
Michael Maurice
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Default Adding a motor control potentiometer to a heater.

I've had a very strange request, and that is to put a control to slow the motor down on a fan heater.

I have a Belling Tango fan heater that is working but I need it modified. I need an adjustable resistor fitted to slow the fan, increasing the convection heat. Thank you,

Ref our conversation please be advised; The fan heater is all metal.(Belling Tango 2)
It would not be unattended, use would be no more than 10 seconds.
I would not expect any guarantee.
If you undertake the work then this e-mail expressly confirms that work has been carried out at my risk, in other words this e-mail expressly absolves you of any liability.
Michael, if you feel unable to do this I will of course have 100% respect you position on this.


Personally I'm not happy about doing this, even if the customer does absolve me from liability.

I'd be interested to see what others think.
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Old 27th Feb 2023, 6:29 pm   #2
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Default Re: Adding a motor control potentiometer to a heater.

Firstly the techical side : If it's anything like the fan heaters I know, it'll be a shaded pole induction motor so putting a resistor in series (or a triac-based controller or) won't be that useful, And if you want to decrease airflow and increase tempeature, you _might_ get away with suitable baffles on the air inlet.

But I wouldn't touch such a job with a bargepole. Too much could go very wrong...
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Old 27th Feb 2023, 6:33 pm   #3
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Default Re: Adding a motor control potentiometer to a heater.

I certainly would run screaming away from this, scattering handfuls of garlic and salt behind me as I fled!
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Old 27th Feb 2023, 7:12 pm   #4
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Default Re: Adding a motor control potentiometer to a heater.

This is potentially dangerous. Fan heaters generally rely on the fan to keep the heating elements at the right temperature. Tell the customer to just buy a convector heater - it probably won't cost any more than paying you to make dubious modifications.
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Old 27th Feb 2023, 7:30 pm   #5
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Default Re: Adding a motor control potentiometer to a heater.

I'd be very curious why they wanted it done, but certainly wouldn't do it.

Edit: Perhaps they want a cheap hot air gun!
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Old 27th Feb 2023, 8:03 pm   #6
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Default Re: Adding a motor control potentiometer to a heater.

The Belling Tango 2 is described on its box as 'all metal' but I suspect that this is 1970's-speak for 'more metal than you might expect for the price'. There will certainly be insulators in there somewhere and you'd need to inspect them very carefully to check that they'll withstand any increased temperature. That might even go for the wood-effect coating on the cabinet.

Furthermore the box says Switches off automatically if outlet is obstructed. I don't know how any obstruction is detected, but it might be by sensing the airflow or the air temperature. I wouldn't be at all surprised if this safety mechanism frustrated your customer's aim. You'd have to be a lot braver than me to disable a safety mech.

You might point out to your customer that if this were to go badly wrong then it would be his relatives or Trading Standards who would be pursuing you in the courts. Neither of these would set much store by a message from him absolving you of responsibility.

Cheers,

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Old 27th Feb 2023, 8:19 pm   #7
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Default Re: Adding a motor control potentiometer to a heater.

Most fan heaters have two forms of overheat protection. Firstly a thermostat in the hot air path, if this is tripped then it resets automatically when the appliance cools.

As a "second line of defence" there is often a thermal fuse in addition, if this is tripped then the appliance should be replaced. The thermal fuse is not reset-able, and is not intended to be replaced.

Any deliberate reduction in the air flow is liable to operate either or both of these safety devices. As well as being arguably foolhardy. An alternative heating appliance should be considered, such as a convector heater, an electric hot air gun, a cooking ring, or a gas burner.
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Old 27th Feb 2023, 8:31 pm   #8
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Default Re: Adding a motor control potentiometer to a heater.

In UK law you cannot sign-away your rights. His email is worthless if anything was to go south!
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Old 27th Feb 2023, 11:00 pm   #9
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Default Re: Adding a motor control potentiometer to a heater.

Putting on my Safety Test Cap, I've tested fan heaters in the past and one particular test listed in the Standard (IEC 60335-1) is for testing the heater's cut-out functionality if the motor was to slow down for any reason. The heater has to be modified so that the element receives full mains but the motor is fed with reduced mains. Our usual method is to disconnect the motor feed and supply it through a variac. That way the element receives full mains but the motor is fed with reduced mains via the variac. We then adjust the motor down until the cut-out trips which it has to do before anything starts to burn.....! Some fan heaters use a low voltage motor with the element as a ballast.

Run from this Michael!
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Old 27th Feb 2023, 11:21 pm   #10
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Default Re: Adding a motor control potentiometer to a heater.

Now, well: I've had this unintentionally. Somehow the fan's bearings sucked some amount of horse or cat fur hair, don't know who of them was at guilt...
Anyway, the fan got slowed down more and more, and finally I noticed a strange smell and saw glowing heater elements, like in a big EIMAC transmitter valve.
Not good, I thought, and threw the master cutout switch of my shed! All of the electric heater found its way to the skip at once. After cooling down, of course.

Joe
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Old 27th Feb 2023, 11:57 pm   #11
Michael Maurice
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Default Re: Adding a motor control potentiometer to a heater.

I told the customer in my original email that I wouldn't do it, he then phoned me then sent me a second email.

I am not going to do it FULL STOP!
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Old 27th Feb 2023, 11:58 pm   #12
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Default Re: Adding a motor control potentiometer to a heater.

A very wise decision Michael
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Old 28th Feb 2023, 11:15 am   #13
broadgage
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Default Re: Adding a motor control potentiometer to a heater.

Quote:
Originally Posted by paulsherwin View Post
A very wise decision Michael
I agree.
It might however be interesting to know for what purpose it was proposed to reduce the fan speed. We could perhaps then make informed suggestions as to a more suitable means of achieving whatever the desired result is.
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Old 28th Feb 2023, 11:48 am   #14
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Default Re: Adding a motor control potentiometer to a heater.

In the original message, he said he wanted it to be slowed down in order to increase the heat. So he wants it to be run hotter than Belling intended....

And only for 10 seconds, and not left unattended? Sounds like a job for one of those DIY retail shed paint stripper guns. It's be cheaper, too.

David
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Old 28th Feb 2023, 12:40 pm   #15
turretslug
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Default Re: Adding a motor control potentiometer to a heater.

Heat-shrinking?

No, walk away. They're evidently aware that it's a dubious thing to do, hence all the caginess. Just don't!
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Old 28th Feb 2023, 2:44 pm   #16
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Default Re: Adding a motor control potentiometer to a heater.

Hi i had an orange color one years ago it has a thermal cut out in the heater assy. even obscuring the intake with a small object would cause it to cut out with a bright flash from the bimetal thermal switch do NOT get involved Mick
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Old 28th Feb 2023, 5:15 pm   #17
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Default Re: Adding a motor control potentiometer to a heater.

I'm pleased Michael's risk assessment says 'no.' In our industry where the show must go on, we cheat at a lot of things and customise and hack solutions with varying degrees of engineering rigour or lack of it. But customising a fanheater to overheat would not be acceptable unless it was part of a deliberate carefully supervised stunt with fire crew in attendance etc. Not knowing the application, it's hard to guess what a properly engineered solution would entail.

I think the Tango might be old enough that it doesn't contain a non-resettable thermal fuse, only a self-resetting bimetal stat. I don't know how the temperature at which it trips would compare with that of a modern heater. There was a 3kW version of the Tango. If the fans are the same and deliver the same airflow, then it would follow that the temperature rise through the unit would be 50% higher on the 3kW than the 2kW.
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Old 28th Feb 2023, 5:44 pm   #18
Michael Maurice
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Default Re: Adding a motor control potentiometer to a heater.

I thought about this and equated it with another scenario:

What if someone asked a mechanic to modify the braking system of a car to make it much less effective stating it would be used only on private land and they'd sign a disclaimer, but somehow the vehicle got driven on the road and there was an accident. Would the mechanic not be responsible?

As far as I'm concerned its not worth the hassle. Its bad enough that we have to somehow modify equipment (in a safe way) to get them to work again.

I've done that with a Beocentre 2002 but it worked and was perfectly safe.
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Old 2nd Mar 2023, 11:37 pm   #19
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Default Re: Adding a motor control potentiometer to a heater.

The only way to safely get away with slowing down the motor is by also reducing the voltage on the elements, a 110V transformer might work for the elements but the motor is likely to protest.
In English, it should be left alone.
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Old 3rd Mar 2023, 1:47 am   #20
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Default Re: Adding a motor control potentiometer to a heater.

Is there any chance of finding out what the purpose was to be ?
I'm sure we'd like to know just to put this to bed as it were.

Reminds me of an old mate of mine who would come up with crazy ideas that you knew wouldn't work but he would say " could we try it ? "

David.
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