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  • Possible to make it a 110v?

    Well I plan on building a 9x7x6.5 oven but I was wondering if it would be possible to make it 110v? Also how many elements will I need? Anymore info about building something of this size that would be helpfull? I know, I have searched and things like that, mainly I'm just looking to see if something this size is able to be made with 110v power. I'm going to be using r-13 3.5 inch thick insulation. With a layer of 22g sheet metal covering that. Thanks!

  • #2
    Re: Possible to make it a 110v?

    Possible sure.

    The problem comes in how many amps can you supply via 110.

    Typically guys are using between 350-600ish watts per cu. ft.

    Your oven is 410 cu. ft. Using 350 watts per ft = 143,500 watts.

    Watts/volts = amps

    143,500/110 = 1,304 amps. Most house plugs are 20 amps so you only need 65 plugs, and about 10 neighbors to borrow outlets from.

    Even at 220 volts in the size your talking will be almost impossible. That big of an oven generally doesn't use electric anymore but gas/propane.

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    • #3
      Re: Possible to make it a 110v?

      Haha, well thanks for that info. What's the biggest you can go generally while still using 220v and not costing a fortune to run?

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      • #4
        Re: Possible to make it a 110v?

        Would it be possible to set up 8 3100w elements with like 2 household oven thermostats and contactors. I've searched a bit and this is what I come up with as far as people heating an oven this big. It'd be ran on 220v obviously.

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        • #5
          Re: Possible to make it a 110v?

          ty1295 is on the right track. If you halve the voltage you need to double the current to supply a given amount of power (which is measured in watts). A 220VAC oven that draws 50 amps would require 100 amps at 110VAC. Other down sides are that you will have higher waste power lost in your supply feed and you will have to use a significantly larger guage wire at the increased current level. This is why the voltage requiremens for industrial machinery generally starts at 220V, and 440V and 660V is not at all uncommon for high power equipment. Large industrial motors like to run off of three phase at 240V and above.

          I do question ty1295's estimate that you need 350W per cubic ft to heat your oven. This seems awful high. The example he cites is of a 410 cubic ft oven (9'x7'x6.5'). I have a really difficult time believing that you need 143.5 kW to heat an oven of that size. Just to give you a point of reference most moderate size homes are wired with a 200 amp service. At full load such a service could deliver 22 kW (in reality you would never come close to drawing that kind of load for any significant amount of time). The amount of power you need per cubic ft is a function of how good your insulation is and what kind of temperature ramp you want to support (i.e. how fast the temperature needs to rise in degrees/second). With good insulation and a reasonable ramp rate I would think you could cut that 350W/ft^3 from 1/2 to 1/5 that number.

          Lets say you have a commercial operation using ty's 143.5 kW oven. If we assume $0.09 per kilowatt - hour then it would cost $12.91 per hour to operate. Lets assume that the oven is in operation 20 hrs a week (i.e. 4 hrs per day). At that usage rate that oven is going to cost $1033 per month to run (or about $13,000 per year). You'd need to push a lot of product through that 9'x7'x6.5' oven just to pay the electric bill.

          In spite of the fact that I think his power number is too high, for an oven of the size you are talking about I think running it off of 110V is really unrealistic. The only way you might even come close to making it work is to have extremely effective insulation ($$$) and to be willing to tolerate a very slow ramp rate (i.e. warm up time to operating temp).

          I did look at the largest walk-in oven that Caswell sells. It is 190 cubic ft and requires 15 kW. That works out to about 79 W per cubic ft. I have no idea what the insulation factor is and the temp ramp rate it can achieve but considering that this oven is a little under half the volume you are considering and it runs off of 240V three phase tell me that 110V just ain't going to cut it.

          If I was a little more sober I could calculate the require power for a given oven volume, insulation factor and temperature ramp rate, but it is getting late and my math ability is fading fast.
          Last edited by engineerscott; 03-26-2006, 12:11 AM.

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          • #6
            Re: Possible to make it a 110v?

            Originally posted by engineerscott
            ty1295 is on the right track. If you halve the voltage you need to double the current to supply a given amount of power (which is measured in watts). A 220VAC oven that draws 50 amps would require 100 amps at 110VAC. Other down sides are that you will have higher waste power lost in your supply feed and you will have to use a significantly larger guage wire at the increased current level. This is why the voltage requiremens for industrial machinery generally starts at 220V, and 440V and 660V is not at all uncommon for high power equipment. Large industrial motors like to run off of three phase at 240V and above.

            I do question ty1295's estimate that you need 350W per cubic ft to heat your oven. This seems awful high. The example he cites is of a 410 cubic ft oven (9'x7'x6.5'). I have a really difficult time believing that you need 143.5 kW to heat an oven of that size. Just to give you a point of reference most moderate size homes are wired with a 200 amp service. At full load such a service could deliver 22 kW (in reality you would never come close to drawing that kind of load for any significant amount of time). The amount of power you need per cubic ft is a function of how good your insulation is and what kind of temperature ramp you want to support (i.e. how fast the temperature needs to rise in degrees/second). With good insulation and a reasonable ramp rate I would think you could cut that 350W/ft^3 from 1/2 to 1/5 that number.

            Lets say you have a commercial operation using ty's 143.5 kW oven. If we assume $0.09 per kilowatt - hour then it would cost $12.91 per hour to operate. Lets assume that the oven is in operation 20 hrs a week (i.e. 4 hrs per day). At that usage rate that oven is going to cost $1033 per month to run (or about $13,000 per year). You'd need to push a lot of product through that 9'x7'x6.5' oven just to pay the electric bill.

            In spite of the fact that I think his power number is too high, for an oven of the size you are talking about I think running it off of 110V is really unrealistic. The only way you might even come close to making it work is to have extremely effective insulation ($$$) and to be willing to tolerate a very slow ramp rate (i.e. warm up time to operating temp).

            I did look at the largest walk-in oven that Caswell sells. It is 190 cubic ft and requires 15 kW. That works out to about 79 W per cubic ft. I have no idea what the insulation factor is and the temp ramp rate it can achieve but considering that this oven is a little under half the volume you are considering and it runs off of 240V three phase tell me that 110V just ain't going to cut it.

            If I was a little more sober I could calculate the require power for a given oven volume, insulation factor and temperature ramp rate, but it is getting late and my math ability is fading fast.
            Wow thanks a lot for the information. Whenever you have time could you please calculate the reguired power I'll need and those other factors.

            Comment


            • #7
              Re: Possible to make it a 110v?

              Without doing any heavy duty calculations I would suggest that we have evidence that 80W/ft^3 is a reasonable number. If we plug that in we get 32.8 kW. At 220V this would require a 150 amp circuit (which would mean 300A at 110V). Where is this oven going to be used? If it is in a residential setting then it is almost certain that you do not have a sufficient electrical service to support that kind of current. If you are in a light industrial setting you probably either have or could get a service drop that big.

              Also, what are you going to use for heating elements? If you are going to use stove elements then lets assume that the element is 3 kW (a reasonable number for an average electric stove). You would need eleven 3 kW elements to get your 32.8 kW.

              I think at this point you need to step back and ask yourself if you really need an oven this large. If you really have to have a oven of the size you suggest then you either have to suck it up and sign up for a 150A 220V service or you could compromise on the W/ft^3 some. As you decrease the power per cubic feet at some point you are going to be unhappy with how long it takes to heat your oven or it gets so bad that it never gets up to your operating temperature.

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              • #8
                Re: Possible to make it a 110v?

                What about using 8 3100w elements under a 220v service with a 100 amp main breaker. Then I'd have two 50 amp breakers in the box that ran to two 50 amp contactors, then to the thermostats. Like [email protected] cape is doing, he says that his 8 3100w elements never even come close to 100 amp's even though the math says they would be over. I'd like to have a new 220v power source ran with a 125 amp main breaker, and have it soley dedicated to this oven.

                Does this sound reasonable?

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                • #9
                  Re: Possible to make it a 110v?

                  Looking back I think you are correct 350watts per cu ft is a bit high.

                  I think the rest of calculations are good, if you put in a more real watts/cu ft # though.

                  Comment


                  • #10
                    Re: Possible to make it a 110v?

                    A 220V 125A service would run your 8 x 3100W heater element array with a little overhead. This is the way I would go. Your total heating power would be 24.8 kW which would give you 60.5 W/ft^3. This is of course less than the 79 W/ft^3 that commercial oven that Caswell sells does, so you would expect it to heat up somewhat slower and it will not have as high of a max temperature unless you have better insulation (and since we don't know how well Caswell's oven is insulated we don't know how much better you'd have to be). That said, I suspect that this will be a workable oven for you.

                    Remember that if you run a oven heating element designed for 220V at 110V it will not pull the same power. At 220V a 3100W element draws about 14.1A. This equates to a resistance of about 15.6 ohm. If we assume that the resistance of this element is constant (which is actually incorrect since resistance is a function of temperature, although this assumption will do for our purposes) then at 110V this element will dissipate only 775 W. In truth since our assumption about the resistance is slightly wrong it will be a little higher, so lets be generous at call it 1000W. So, if you run your 8 elements at 110V you are only going to get at best 8 kW, which is only 19.5 W/ft^3. I doubt you are going to be happy with this amount of heat in your oven.

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                    • #11
                      Re: Possible to make it a 110v?

                      Dude I just built a 6x4x4 upright oven using 3 elements and tie it into a 100 amp 220 and it powers it up but it take some time to heat the hole thing about 45 minutes to 400 degrees and uses right at 60 amps. So I also new it would take some time to heat up this much area so i built a devider which is 4x4x2 to cut the time for smaller items such as wheels and intake that doesn't fit in my wall mounted oven.

                      Comment


                      • #12
                        Re: Possible to make it a 110v?

                        Originally posted by rjlandry
                        Dude I just built a 6x4x4 upright oven using 3 elements and tie it into a 100 amp 220 and it powers it up but it take some time to heat the hole thing about 45 minutes to 400 degrees and uses right at 60 amps. So I also new it would take some time to heat up this much area so i built a devider which is 4x4x2 to cut the time for smaller items such as wheels and intake that doesn't fit in my wall mounted oven.
                        Yea, that's a great idea....it's just 40 minutes is quite awhile to wait for the sucker to heat up. I'm looking to cut it down to 15-20.

                        Comment


                        • #13
                          Re: Possible to make it a 110v?

                          Originally posted by engineerscott
                          A 220V 125A service would run your 8 x 3100W heater element array with a little overhead. This is the way I would go. Your total heating power would be 24.8 kW which would give you 60.5 W/ft^3. This is of course less than the 79 W/ft^3 that commercial oven that Caswell sells does, so you would expect it to heat up somewhat slower and it will not have as high of a max temperature unless you have better insulation (and since we don't know how well Caswell's oven is insulated we don't know how much better you'd have to be). That said, I suspect that this will be a workable oven for you.

                          Remember that if you run a oven heating element designed for 220V at 110V it will not pull the same power. At 220V a 3100W element draws about 14.1A. This equates to a resistance of about 15.6 ohm. If we assume that the resistance of this element is constant (which is actually incorrect since resistance is a function of temperature, although this assumption will do for our purposes) then at 110V this element will dissipate only 775 W. In truth since our assumption about the resistance is slightly wrong it will be a little higher, so lets be generous at call it 1000W. So, if you run your 8 elements at 110V you are only going to get at best 8 kW, which is only 19.5 W/ft^3. I doubt you are going to be happy with this amount of heat in your oven.
                          Wow, thanks a lot, sounds like you know what your talking about. I'm going to be running two 50 amp breakers in a 100 amp main breaker box. Each 50 amp breaker will feed a contactor and then go to the thermostat and then it will feed 4 oven elements each. Think it will work out ok with 50 amps per 4 elements? I know math figures out for these 8 elements to draw over 100 amps, but in reality they don't draw that much, from what many have said.

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