Q
Qwerty
Out of interest was this a solution from the electricians forum?
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J
john56897452
No......I clicked from your answer re lowering the wattage. Many thanks for that.
Might help other people with the quartz tile UHF confliction. Dimmers for 700w plus are available.
Might help other people with the quartz tile UHF confliction. Dimmers for 700w plus are available.
A dimmer switch wouldn't be suitable for use with UFH.
A dimmer takes away voltage therefore dropping the voltage of the heating cable below 230v will not give any power to the cable thus not heating the element at all and most likey buring the dimmer out.
J
john56897452
Surely dropping the voltage drops the current available drawn by the heating cable hence controlling the heat (current drawn = heat, the max at 240v would be 300w). How can say a 700w rated dimmer be burnt out by a 300w max load? The cable is rated for 240v not dependent on 240v. Applying voltage via a variac would produce the same results.
Using ohms law 240v at 300w would draw 1.25a. The current would not change by varying the voltage but the wattage would. If the voltage dropped to 120v the wattage rated by the heater wires would be 150w. Conversely to drop the wattage to a low 100w would require a voltage reduction to 80v. I think.
Using ohms law 240v at 300w would draw 1.25a. The current would not change by varying the voltage but the wattage would. If the voltage dropped to 120v the wattage rated by the heater wires would be 150w. Conversely to drop the wattage to a low 100w would require a voltage reduction to 80v. I think.
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F
Flintstone
I don't beleive there is a 300w kit available.
On the subject of spacing, the warm up dcm pro, which is probably the same cable, have a strange recommendation, can anyone enlighten me on how you run that at 190w per m? Do you alternate the spacing ?
On the subject of spacing, the warm up dcm pro, which is probably the same cable, have a strange recommendation, can anyone enlighten me on how you run that at 190w per m? Do you alternate the spacing ?
It's down to the spacings of the cables, if you want 200w/m2 for a heating cable you'd do the following,
5 x 200 = 1000w so you need 1000w cable to heat that area at 200w/m2, you then find a cable around that wattage, so ours would be an Elektra 980w 98m Cable.
You then have to work the spacings out by doing the area divided by the length of the cable. 5 / 98 = 0.051. You then have your cable spacings of 51mm.
If you'd want 160w/m2 or 100w/m2 then you'd just change the equation around to suit them wattages and find a cable to suit.
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David Rogers
TF
John,
Ohms Law is that V=iR where V = voltage, i = current and R = resistance (all applied to DC, but works for many sorts of AC too). The resistance of your UFH cable doesn't change with voltage, but is ultimately responsible for the heat output (watts) defined as i.V. If the cable is rated at 300W with a 240V supply (1.25 amps), then the resistance is 192 ohms (R = V/i = 240/1.25).
If you reduce your voltage to 120V, Ohm's calculation suggests that your new current through that same resistance will be 0.625 amps (i = V/R = 120/192), generating a total heating wattage of only 75W (watts = Vi = 120*0.625) - very much less than you imagine.
I agree with the comment about how modern dimmers on AC supplies actually work (they might either 'chop off' the peak voltage or else 'chop off' the time for which the full voltage is applied). They do not work in the same way as the good old (wire-wound) variable resistances of yesteryear. Whilst I doubt you will fry the dimmer (whatever they're doing, their output will be limited by the 192 ohm resistance of the UFH cable), you should maybe seek advice from the dimmer manufacturer/UFH cable supplier. Good Luck!
J
john56897452
Thanks David,
So the maths were about in the right area. Found a 10amp 1000w rated dimmer switch that should be more than up to the job. The theory stands though by reducing the voltage to say even 120v only 75w will be achieved by the heating wire. Still controlled by the floor sensor even if it takes all day to reach 20 c. This has got to be kind to the tiles and more than meets the tile manufacturers recommended 150w spec.
So the maths were about in the right area. Found a 10amp 1000w rated dimmer switch that should be more than up to the job. The theory stands though by reducing the voltage to say even 120v only 75w will be achieved by the heating wire. Still controlled by the floor sensor even if it takes all day to reach 20 c. This has got to be kind to the tiles and more than meets the tile manufacturers recommended 150w spec.
Q
Qwerty
Do keep us updated with how you get on with this. Do you have a infra red thermometer to read the surface temperature?
J
john56897452
Yes I do have a hand held infrared thermometer. Just waiting for the dimmer to arrive before wiring everything up. Floor been laid about three weeks now so should be ready.
There are similar tiling threads here
