Ski Builders Forum

You're right montucky that as the wire diameter increases the resistance lowers.

lower resistance will get you more power, so you either have to choose a different wire or use shorter wires or combine these two.

Seems like the thicker the less resistance as it carries the current more efficiently?

very right
resistance should be inverse proportional to surface area of the cross section (inverse proportional to r^2) and proportional to wire's length.
consider multiple wires (with same length & dia) connected in parallel, as one resistance that has a cross section surface area the addition of the all individual wires c-section areas.
the total resistance in this case, is the resistance that one wire has divided by the number of the wires (1 wire gives 10ohms, 2 wires -double area- will give 5)
power P=I*V
voltage is equal in all wires as they are parallel connected
current I=V/R as higher resistance allows less current to go through the wire
to increase I, you d probably have to reduce R -in other words to increase the wire's diameter

i don't want to misguide you, but from small trials i run i came with quite a less watts/m2 than crismp (no pid, just dimmer). but again bare in mind that my wires were running free without conducting heat to anything but the air. (things might change alot if an alu sheet starts sucking up that heat). btw the one part silicon is a pain but it might work at the end

Current scares the shit out of me, i don even think to go 230V...

edit: oops sory, i would'n reply if i had seen the 2 above posts on that page

damn I have no idea what I am doing can't wait to get shocked and burn the house down.

So at 22 awg and your dims and wire config and a 110V I get over 2520 watts?

Howe many amps will that draw? 22amps? that won't work.


At 26 ga @ 7.5 ohms/meter and 110 and your setup I get 1008 watts and 9 amps.


To much or not enough?

my brain hurts.

maybe 10 wires at your length at a 22 ga and 1.025 ohms and get 19661 watts and 17 amps? Will I die?

volts, smolts, amps will kill people.

you're going to be fine with just about 1000w i guess. We never really use more than that for both blankets we already have and we get to 90°C really quick.

230V are scary! thats why we never touch our cassettes when the heat is on...we just don't trust our insulation that much. same will go for the new blankets.

Plywood has posted this in an earlier thread:

plywood wrote:[...] then you have to set a area-heat-output. (flächenheizleistung for the germans) this area-heat-output is measured in Watt per squaremeter. so, by setting the wanted heat-output you determine the temperature you want to reach with your heating. i found somewhere a table with some heat-outputs and temperatures referred to it...so i used this table and appreciated the needed heat output:

area-heat-output (W/m2) temperature (°C)
224 -------------------------------- 38
449 -------------------------------- 55
673 -------------------------------- 70
898 -------------------------------- 83
1122 ------------------------------- 95
1347 ------------------------------ 104

well, as i said, i found this table somewhere. i think it was in an article about tempering from a professional manufacturer - that`s why there are such precise datas of heat-output and temperature. [...]

... compared to this ...

chrismp wrote:you're going to be fine with just about 1000w i guess. We never really use more than that for both blankets we already have and we get to 90°C really quick.

I think that makes sense.

Cheers, Christoph

MontuckyMadman wrote: volts, smolts, amps will kill people.

volts will kill people, amps will burn down houses
I remember when my sisters husband shows up all shaking & trembling, asks for a beer, empty it, and then tells me how he got an electric shock in his shower. It was the scariest and most bizarre experience he ever lived (& mind you, he has been a very naughty young man), said his brain went off resonating @ 50Hz
finally he was knocked down to the bathroom floor and survived it to come and empty all my bottles that night
his arms hairs were still raised from fear when he left

about plywood's board:
i think for a given watt/m2 blanket the final temperature will vary depending on the rate that the heat is flowing to the "environment" (laminate, air, press etc)

Hi guys, I'm from an elecrtical background so can offer some advise here. First of all your blankets and controller should have some form of electrical protection. In NZ we use earthing to provide a fault path for current to blow a circuit breaker, so in the event of a burn out heater touching your metal it should immediately kill the circuit mains input. Better still is a residual current device or RCD which compares phase and neutral for any small current imbalance due to earth leakage and if there is a difference even small like a few milliamps it opens the circuit and isolates the mains supply. Consult an electrician (a good one) if you're in doubt, a lot safer and piece of mind, especially if you have family/friends/employess around!

cheers
Rich

Jibber wrote:Plywood has posted this in an earlier thread:

plywood wrote:[...] then you have to set a area-heat-output. (flächenheizleistung for the germans) this area-heat-output is measured in Watt per squaremeter. so, by setting the wanted heat-output you determine the temperature you want to reach with your heating. i found somewhere a table with some heat-outputs and temperatures referred to it...so i used this table and appreciated the needed heat output:

area-heat-output (W/m2) temperature (°C)
224 -------------------------------- 38
449 -------------------------------- 55
673 -------------------------------- 70
898 -------------------------------- 83
1122 ------------------------------- 95
1347 ------------------------------ 104

well, as i said, i found this table somewhere. i think it was in an article about tempering from a professional manufacturer - that`s why there are such precise datas of heat-output and temperature. [...]

... compared to this ...

chrismp wrote:you're going to be fine with just about 1000w i guess. We never really use more than that for both blankets we already have and we get to 90°C really quick.

I think that makes sense.

Cheers, Christoph

OK so If I recall the blanket I have at 13cm wide and 170 long is 1500 watts and ripped to temp insanely quick. 82C


So essentially 1000 watts over a 1 square meter per blanket will work just fine.

Chris any way you can post some pics of your finished blanket for us?

MontuckyMadman wrote:Chris any way you can post some pics of your finished blanket for us?

not before the weekend, sry. i don't have the key to our shop atm :P

how are the results with the blanket? holding up well to pressings and pressures and heat?

This link has good design details.
http://www.tslaerospace.com/product/hea ... ket1_9.pdf

couldn't take any pictures this weekend...it was snowing so much, i just had to get out and ride

but i got on the phone with my friend who has it lying at home at the moment. he claims that we have a problem with too much heat being generated where the resistance wires are connected to the lead wire causing the silicone to smoke off.
we'll have to figure out something to get better insulation in this part...maybe some teflon insulated wire will do.
the blanket hasn't seen any high pressure yet.
other than that it appears to be working well

did you use a bus terminal thing like made of AL or something that all the parallel connections go into before connecting to the lead?

like here

nope, prolly should have done that...we just used a single connector for each lead wire and put all the resistance wires in there.
i think we'll try to pry the connection area open again and redo the connections.

Please Please let us now when you cook something under pressure with this setup. I am mm's away from buying all the crap to try this but I want you to guinea pig before I blow $60
PLEASE??