XPost: sci.physics, alt.solar.thermal   
   From: amdx@knology.net   
      
   On 11/1/2011 10:17 AM, Morris Dovey wrote:   
   > On 10/31/11 1:55 AM, Morris Dovey wrote:   
   >   
   >> Now can we please go back and figure out the heater itself so there's   
   >> something to measure?   
   >   
   > Following up - I just ordered a 100' spool of NiCr wire on eBay and   
   > picked up a piece of 3/8"OD (1/4"ID) copper tubing and piece of   
   > HardyBoard (work surface for brazing this stuff together) from Home Depot.   
   >   
   > According to my calculations, a 12" length of #40 NiCr wire should   
   > provide about 250W of heating and draw about 2A at 115VAC.   
   >   
   > I'm going build /two/ heaters so I can try both the DPDT relay with an   
   > op-amp circuit and the SSR/thermocouple/TC amp approaches. I'm   
   > interested in learning how many cycles a relay can switch 2A before it   
   > welds the contacts together; and I'm interested to see how much   
   > crosstalk there will be between 115VAC and 5VDC pairs inside a 1/4" cavity.   
   >   
   > When the wire arrives I'll connect a 12" length to the mains and see how   
   > it behaves.   
   >   
   > Thanks to all for sharing ideas and suggestions!   
   >   
      Sorry, I need to ask, Will the NiCr handle 250 watts per 12".   
   Just thinking about my toaster and I know the NiCr is longer than   
   12". I know it is different wire, but still want to ask.   
                          Thanks, Mikek   
      
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