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OK, you electrical types :-) I found an inexpensive heater coil (nichrome cast element) rated 220v, 1000 watts. If I use it for on 110 v, is that just simply 500 watts I get? John Nanci AlChemist at large Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/ |

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No, you'll get about 250 Watts. P = V * I = I^2 * R = V^2 / R Nichrome is non-linear, which is why I put the about in the first line. On 7/25/06, Alchemist John wrote: < |

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John - This site has a bunch of simple explanations and SAS-driven calculators for figuring out stuff having to do with Nichrome wire heaters:http://www.nicrome.com/< |

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Not likely. The heat to voltage ratio is non-linear. I've surfed the web for info, but it's a little scarce, at least for specific types of lamp. McSparky At 05:26 AM 7/25/2006 -0700, you wrote: < |

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Based on the RW80 heater alloy tables, resistance nonlinearity is 1:1.08over 20:1200 C range. Now, I don't know what temperatures the heating element will be at for either 220 V or 110 V applied, other than it is safe to say that it will be colder for the 110 V case. So let's just take the entire range to get an idea of the effect. Some back of the envelope scribbles indicate that a 1:1.08 resistance variation would translate into less than 20 Watts. So at 110 Volts applied you'd get more than the 250 Watts out but less than 270 Watts. On 7/25/06, David B. Westebbe wrote: < |

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Many thanks folks. Good deal at 1/2 power, not 1/4 :-) At 19:34 7/25/2006, you wrote: < |

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This is a multi-part message in MIME format. It is impossible to know the temperature, I think, because the volume = and mass which will be heated will have a direct impact on the temp. All = you can know, maybe, is the BTU output. As an example, I have a variable fan speed on my popper. The faster the fan, the lower the air temp But the temp of the nichrome is not = directly affected. |

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On 7/26/06, David B. Westebbe wrote: < |

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Not impossible, but not trivial. You end up with a thermodynamic model that's coupled with an electrical model. In days past you'd be solving simultaneous partial differential equations. Today you'd have modeling software iterating a solution on a computer. However, using the max temp range that the site provided data for, which I presume is the usable temperature range of the material, there's only 20 Watts of change. So using Ohm's law & assuming linear resistance is a good enough for most applications. On 7/26/06, David B. Westebbe wrote: < |

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This is a multi-part message in MIME format. However, using the max temp range that the site provided data for, which = I presume is the usable temperature range of the material, there's only 20 Watts of change. So using Ohm's law & assuming linear resistance is a = good enough for most applications. Can you expand on that? I'm thinking of swapping out the little = Nichrome wire in my 'Pumper for one that will produce more heat (in the stock = popper, there are 2 different nichrome coils - a big beefy one and a little = wimpy one). What I don't know is (a) will it make lots more heat if I use a different hunk of coiled Nichrome (resulting in a higher temp for any = given airflow) and (b), will I draw so much current that the circuit breaker = will trip? |

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This is a multi-part message in MIME format. MessageDavid, Don't do it. That little wimpy coil limits voltage to the fan which has = a low voltage motor. If you replace it with a heavier [thicker] gauge = the fan motor will be overpowered. If you want more heat, just shorten = the existing beefy one a bit. A 10% reduction in length will give you = roughly a 10% increase in power and will draw roughly 10% more amperage = which will still be within limits for even a 15A circuit. Most modern = households now have 20 amp breakers supplying wall outlets. Doug |

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I like your analysis, Michael. Is it so that "it will be colder for the 110 V case" ? No more so, I think, than you could say "A 480 volt motor is always higher powered than a 240 volt motor." OK, a 480 on 240 would be... If you are saying that a 220 volt (or higher) heater operating on the rated supply at a 100% duty cycle will be hotter than feeding it 110 volts, I certainly agree. 50% voltage will give 25% power in a resistive load- tungsten, nichrome or carbon. According to a Mozilla reference 1 kilowatt-hour (kWh) = 3413 British Thermal Units (Btu) So, 1 watt-hour = 3.413 BTU = 1kW for 3.6 seconds Lower power = Lower heat, But a particular heater may be designed for lower voltage and higher current for the same power, same heat capacity. Cheers -RayO, aka Opa! -- "When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty Wichita (ex- NYC Paramount) WurliTzer- 1976 |

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Its not all that bad, is it? As long as you have symmetry, it becomes a problem in 1-D and therefore an ODE. If I remember my thermo, you should be able to come to an estimation using some algebraic methods. Wish I remembered those equations. I'll blame a lack of TeX support in Google instead. Damn Google and their lack of TeX support. On 7/26/06, Michael Wascher wrote: < |

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As the temperature of the heater changes the resistance changes. That means the current changes (voltage is fixed in this case). Current change causes power dissipation to change. This causes a change in temperature. Back to the top. So you iterate as above, or you write the equations. Your electrical equations have resistance that is a function of temperature, and heat into the thermodynamic equations that are a function of electrical power, and everything is also a function of time. But, changes in the nichrome resistance are reallly quite small. Smaller than I had thought they were. So the quick calculations are close enough for most applications. On 7/26/06, Steve Hay wrote: < |

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This is a multi-part message in MIME format. Thanks for the advice, but I've got the motor covered already. I use a transformer fed by a triac to regulate motor speed. Currently, the two existing coils are in parallel. |