Leejosepho
DIY scratch-pad engineer
- Messages
- 2,483
- Reaction score
- 0
- Points
- 36
- Location
- 200 miles south of Little Rock
- Website
- www.nonameyet.org
You should be shooting for about 56 V ...
Since I know there are people who believe, for whatever reasons, you should not be helping me here – peace to all – maybe I should explain how I arrived at 70 volts for the piece of wire I have embedded in my bathroom floor. And of course, I will quickly reconsider my own computations if anyone can show me a better or more correct way to make some. In spite of how anybody else might ever approach telling somebody else how to heat or how not to heat any floor electrically, this is not an off-the-shelf situation and I must deal with the mechanical realities of whatever I actually have.
The mat I purchased was advertised as being 3’ X 20’, and it arrived in an EasyHeat box with this on the label:
SEC-8-20X36
15 Watts per SqFt
900 Watts Total – 208 Volts
However, I actually received a 3’ X 30’ mat with no label or specs of any kind, the seller did not have any further information available and EasyHeat did not respond to any of my several e-mails. So, I next began trying to learn whatever I needed to know so I would not end up burning down my house.
The mat I received covered 90 sq. ft., and that would amount to a total of 1350 watts *if* 15 watts per sq. ft. is correct for it. However, 50.1 ohms and 208 volts translate into a total of 864 watts rather than 1350 (90*15), and that low number would break down to a mere 9.6 watts per sq. ft. for a heating mat in a concrete floor ... and it has just now struck me that possibly that mat was intended for clearing a sidewalk rather than for heating a floor in a living space.
Question: Does anyone know what wattages are used for melting snow and ice on walkways and driveways or the like?
Knowing what it takes to get my floor above room temperature even when it is already relatively warm, I cannot imagine 9.6 watts melting ice from a frozen sidewalk in an ambient temperature well below freezing. But, maybe that assumption is wrong.
All considered, here are the computations I have used so far:
Original piece
3' x 30' mat = 90 sq ft
90*15=1350 watts total
50 ohms and 1350 watts coincide with 260 volts and 5.2 amps
Knowing 260 is a funny voltage, I next assumed the mat might be meant for 240 volts rather than 208, and with the wattage discrepancy amounting to some kind of safety factor related to its no-burn maximums. At that point, I began a great amount of careful and comprehensive testing before actually installing any wire anywhere, and I have since become convinced the following *maximums* are completely safe:
14-ohm cut piece installed in main-floor bath
14/50=.28 of original total
.28*1350=378 watts @ 72.75 volts @ 5.2 amps
24-ohm piece headed for one end of workshop
24/50=.48 of original total
.48*1350=648 watts @ 124.7 volts @ 5.2 amps
9-ohm piece headed for 2nd bath
9/50=.18 of original total
.18*1350=243 watts @ 46.77 volts @ 5.2 amps
Some of my recent posts show some different numbers where I had not first gone back and looked at my notes and such, but 70 is less that 72.75 and so on.
Thank you, Terry, for such a great place where I can continue to listen and learn while DIYing and still keeping my house in livable condition!
Last edited: