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LED for electric heater (UK)

R791945

Jun 19, 2015
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I have an oil filled electric heater. It has an on/ off led rocker switch and a separate thermostat adjuster knob. If I go out of the room when the thermostat has turned off the heat, the rocker switch is not lit up. It only lights when the heater is heating. I can therefore leave the heater on all night. I have been thinking how to avoid this:

I propose to install another led indicator that lights when the power is on, even when the rocker switch is not lit. I found a 230v, 22mm, panel indicator on CPC farnell that looks very suitable. I attach the spec sheet 2283118.pdf

I propose to wire the panel indicator in parallel into the rocker switch load side.

Can I assume this indicator works with 240v AC?
The heater is 1500w 240v. Will I need any resistors or other electronics between the power source and the lamp?
 

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kellys_eye

Jun 25, 2010
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Sounds like the switch is wired AFTER the thermostat to me - the switch being a simple neon-lit on/off rocker.

In which case what you plan won't work.
 

R791945

Jun 19, 2015
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The rocker switch turns off the power to the thermostat.
The thermostat switches the power to the heater and to the led in the rocker switch.
The rocker switch led comes on after the rocker switch is turned on and stays on until the temperature is reached when the led goes off, although the rocker switch is in the on position. If the rocker switch is turned off whilst the led light is on the power is cut to both the heater and the led.

This implies to me that the rocker switch is wired before the thermostat.
 

Bluejets

Oct 5, 2014
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Show us a schematic of how it is wired.
Your description of the setup does not match how you say it works.

Anyhow, just wire the new indicator across the main incoming lead.
Plugged in to the wall socket and turned on gives an indication from the new light.
Either that or plug it into a double adapter with a desk light maybe.

Specs don't say whether the LED is dc or ac.
 
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AnalogKid

Jun 10, 2015
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Big, beefy, and expensive, but it certainly will do the job.
 

kellys_eye

Jun 25, 2010
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I'd be interested to see the actual wiring in the OP's heater..... pics please!
 

twister

Feb 12, 2012
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A simple diode, a 6K resistor, and a led is all you need for 120 volts. 12K for 220V if my math is correct.
 

kellys_eye

Jun 25, 2010
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You also need a reverse-biasing diode wired across the LED.
 

AnalogKid

Jun 10, 2015
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Note - that "all you need" resistor is dissipating 2.4 W at 120, and 4.8 W at 240. For any reliability and safety you'd need a 10 W resistor rating. To meet safety agency rules you need two resistors in series and reinforced insulation around everything.

ak
 

twister

Feb 12, 2012
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Note - that "all you need" resistor is dissipating 2.4 W at 120, and 4.8 W at 240. For any reliability and safety you'd need a 10 W resistor rating. To meet safety agency rules you need two resistors in series and reinforced insulation around everything.

ak
Thanks anologkid. That is exactly right. I got to thinking about this simple circuit and decided to see if the diode was necessary. I used a 20K ohm resistor and a led. The led puts out plenty of lite. When I measured the voltages and current, it surprised me.
.. 0027A current and 55v across both the resistor and the led. The 1/8 watt resistor doesn't even hardly get warm. I thought that the voltage would almost all be across the resistor.
To the spell police. I spell some words like they sound, not like our crazy ancestors spelled them.
 

R791945

Jun 19, 2015
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So it seems that I can not just put the LED referred to in the first post across the incoming mains! I also need reverse-biasing diode, a simple diode, 12K for 220V 10 W resistor rating. two resistors in series and reinforced insulation as none of these extras are built into the housing of the led base. One of the comments indicated I could just put the led across the incoming mains, but that seems to have been over-ruled. I am a bit surprised at all the extras but feared they may be needed, hence the question. I have in the past opened up power switches with a led in the rocker only to see just the led going across the mains, with no sign of resistors, diodes and reverse-biasing diodes.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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I would get a neon indicator with the appropriate series resistor wired to come on when the power is turned on.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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I have in the past opened up power switches with a led in the rocker only to see just the led going across the mains, with no sign of resistors, diodes and reverse-biasing diodes.

I would be surprised as well.

My guess is that what you saw wasn't what you thought you saw.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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So it seems that I can not just put the LED referred to in the first post across the incoming mains! ...
Yes, you can. If you order it with a 230 V rating you can put it across the incoming 240 V mains. The description on the PDF page says "Multi-chip LED technology" whatever that means and the column with specifications says it draws 20 mA. Whatever other components are inside the lamp housing that allow it to function at 12 V, 24 V, 110 V or 230 V are not your concern. This blurb announcing the product claims it is NOT polarity sensitive and that it operates from 110 VAC and 230 VAC, which you specify when you order it. You should be okay wiring it directly across your mains, with or without a switch in series with this panel indicator. Note that this Chinese import also claims it operates from 12 V DC and 24 V DC, obviously addressing the automotive and marine market, but it probably means it operates from 12 V AC and 24 V AC.

In any event, all the comments about reverse-biasing diodes, simple diodes, and 20 watt rated series-connected 10 watt resistors with reinforced insulation are only valid if you want to construct a panel indicator from scratch using an LED of your selection. This commercial product, described in the PDF you linked, is all you need. Of course it IS Chinese engineering, so it may sooner or later go up in smoke through no fault of yours. OTOH, a neon-lamp built into a rocker switch requires only a very tiny 1/8 watt carbon-film resistor to light up visibly and this resistor is usually built-in as part of the switch.



... I have in the past opened up power switches with a led in the rocker only to see just the led going across the mains, with no sign of resistors, diodes and reverse-biasing diodes.
That statement means you didn't see what you thought you saw.

For proof, using proper personal protection equipment and a properly fused or circuit-breaker protected convenience outlet, try this experiment: Solder a common (cheap) red LED across the bare ends of, say, a 10-foot length of zip-cord with a convenience-outlet plug attached to the other end. Find a switched-off convenience outlet, plug the cord into it, stand back and flip the switch that turns the outlet on. You should be rewarded with a spectacular explosion of flame and hot plastic shrapnel, thus demonstrating to the skeptic (you) that it is NOT possible to connect an LED directly across the mains. Caveat: do not actually try this experiment at home. Permission to use a convenience outlet at your nearest fire department, with supervision, is suggested.
 

Bluejets

Oct 5, 2014
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One of the comments indicated I could just put the led across the incoming mains, but that seems to have been over-ruled.

No, I said "indicator" ....I assumed you would know enough not to put an LED across mains AC supply.

Still no layout drawing on the horizon?
 

twister

Feb 12, 2012
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So it seems that I can not just put the LED referred to in the first post across the incoming mains! I also need reverse-biasing diode, a simple diode, 12K for 220V 10 W resistor rating. two resistors in series and reinforced insulation as none of these extras are built into the housing of the led base. One of the comments indicated I could just put the led across the incoming mains, but that seems to have been over-ruled. I am a bit surprised at all the extras but feared they may be needed, hence the question. I have in the past opened up power switches with a led in the rocker only to see just the led going across the mains, with no sign of resistors, diodes and reverse-biasing diodes.
 

twister

Feb 12, 2012
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I just put a20k resistor and a led in an outlet to remind me to turn off my inverter. If I had 220v, a 40K should work. You do what you think best.
 

kellys_eye

Jun 25, 2010
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Back to the original post........

Is the heater on a standard flex and 13A plug? Is it 'portable' or fixed?

A fixed heater should be wired to a fused, switched connection, ostensibly one fitted with a neon power indicator anyway.

A portable heater will simply plug into any wall socket and this may be the issue, resolved with a neon (or similar) indicator across the mains input supply of the heater but it will NOT work connected across the heater power switch as this is, as already advised, on the switched side of the thermostat (which is normally wired in the neutral line - in all examples I've seen so far).

It's surprisingly difficult to establish a wiring diagram for the innards of this type of heater - there are many Youtube videos on their repair etc but very, very few actual schematics of the internal wiring - which is why the request to the OP to post the arrangement of the internal wiring....
 

BobK

Jan 5, 2010
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So it seems that I can not just put the LED referred to in the first post across the incoming mains!
You can, but it will not tell you whether the coffee maker is turned on or not. It will tell you whether you have mains power, though.

Bob
 
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