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/
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: <Snip> -- "There is nothing new under the sun but there are lots of old things we don't know." -- Ambrose Bierce
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/<Snip>
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: <Snip>
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: <Snip> -- "There is nothing new under the sun but there are lots of old things we don't know." -- Ambrose Bierce
Many thanks folks. Good deal at 1/2 power, not 1/4 :-) At 19:34 7/25/2006, you wrote: <Snip> John Nanci AlChemist at large Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/
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.
On 7/26/06, David B. Westebbe wrote: <Snip> The heat output (wattage consumed) of the nichrome may only be minimally affected, but the surface temp of the nichrome element certainly is affected by the air flow. Carry it to the limit point - NO AIR FLOW - and the element overheats and burns out. Safe Journeys and Sweet Music Justin Marquez (Snyder, TX)
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: <Snip> -- "There is nothing new under the sun but there are lots of old things we don't know." -- Ambrose Bierce
<Snip> Good point. This makes my previous point, that one might be able to = easily calculate the heat output, but one would have a much harder time = calculating the temperature of the system.
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?
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
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
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: <Snip> -- Steven Hay hay.steve -AT- gmail.com Barry Paradox: Consider k to be the greatest element of the set of natural numbers whose description require maximum of 50 words: "(k+1) is a natural number which requires more than 50 words to describe it."
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: <Snip> -- "There is nothing new under the sun but there are lots of old things we don't know." -- Ambrose Bierce
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.