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Neo
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Joined: 25 Mar 2006
Posts: 6
Location: UK
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 Posted: Mon Mar 27, 2006 10:48 am Post subject: UK Ovens? |
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I've searched the forums but can't find anything relating to this so I thought I'd ask here. I apologise if this has been bought up before and I've missed it. 
I've been reading through your tutorial Jim, and I think much of it seems based on the US 110v? Although I am quite handy around the workshop I'll admit I'm pretty stupid when it comes to working out amps and currents etc so this might just come across as a stupid question.
I've managed to get hold of the nichrome wire and standoffs that Jim suggests but if I follow the tutorial to the letter will I be able to connect this up safely to a 240 mains supply? |
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jegner
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Joined: 30 May 2003
Posts: 2144
Location: Texas, USA
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| Posted: Mon Mar 27, 2006 11:16 am Post subject: |
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Thats come up before, and I'll let one of the UK members here attempt to address this. I know the US uses 110V and much of the UK and other places use 220V for house current.
There would be a difference, but I don't know enough about electricy to tell you what would need to be changed in order to make this work.
Blaxmyth might have this answer? |
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ANH trooper
Master
Joined: 20 Oct 2005
Posts: 305
Location: UK
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| Posted: Mon Mar 27, 2006 5:42 pm Post subject: |
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| I'm interested to know too as I wouldn't mind an electric oven.I do know that we use a transformer at work for our 110v power tools so maybe this is all you need? |
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Neo
Newbie
Joined: 25 Mar 2006
Posts: 6
Location: UK
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| Posted: Tue Mar 28, 2006 3:18 am Post subject: |
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| ANH trooper wrote: | | I do know that we use a transformer at work for our 110v power tools so maybe this is all you need? |
I've thought about doing that but I'm not sure if the oven would 'trip' the transformer with it having to draw 30 amps?
I knew I should have become an electrician  |
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thebluecanary
Expert
Joined: 02 Feb 2006
Posts: 123
Location: St. Louis, MO
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jegner
Site Admin
Joined: 30 May 2003
Posts: 2144
Location: Texas, USA
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| Posted: Tue Mar 28, 2006 8:59 am Post subject: |
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I forgot about that great thread! Yes, there are some math formulas that will help those folks that want to adapt the 110V design to be used on a 220V supply.
Great info on that thread!
Jim |
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ANH trooper
Master
Joined: 20 Oct 2005
Posts: 305
Location: UK
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| Posted: Sun Apr 16, 2006 8:07 am Post subject: |
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Any news on your oven yet Neo?
Can you tell me where you got the wire and stand offs please?
I am going to have a go at making an electric oven and need supplies.I got all the info I need on here except for UK suppliers.I'm sure I'll have a few questions along the way but I need to get started on this ASAP!
I have already made new metal holding frames for my new flip-top former,and I'm using my exsisting oven but with electric heating rather than my gas burners.I really need the even heat that the wire coils will provide.
-Paul. |
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crashmann
Guru
Joined: 27 Sep 2005
Posts: 501
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| Posted: Sun Apr 16, 2006 9:58 am Post subject: |
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Hey Neo and Paul,
I've seen this question come up in the past (I think there's someone in Australia that needed help with the calculations too). I enjoy a good challenge, especially a math problem, but there's one detail I've always wondered about the 240 volt countries. What rating are your circuit breakers?
In the US with our 110 / 120 volt circuits, the normal breakers are 15 amps, and heavier duty are 20 amps.
Please let me know.
In the meantime, I'll break out the calculator and work up some numbers based on the output wattage of my oven.
Charlie |
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ANH trooper
Master
Joined: 20 Oct 2005
Posts: 305
Location: UK
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| Posted: Sun Apr 16, 2006 11:20 am Post subject: |
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Well there is a sticker on one of the boxes and it reads-
110V-45A
240V-45A
415V-30A
I don't know if that has anything to do with the individual breakers or not but I will be able to find out during the week.
-Paul. |
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crashmann
Guru
Joined: 27 Sep 2005
Posts: 501
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| Posted: Sun Apr 16, 2006 11:25 pm Post subject: |
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Ok, I was expecting the amp ratings on the breakers to be half of the 120 volt circuits (since 240 is double the voltage) Anyway...
It looks like Peter has already done the math for us in a previous post:
| peterb wrote: |
......
Ok, to calculate the length needed to output 2300 wats at 230 volts, it would be
<pre>2300 / 230 = 10 amps
Rt = 230 / 10 = 23 ohms
4 * (1/R) = 1/Rt = 0.0434
R = 92 ohms
Re = 92 * 4 = 368 ohms
CoiledLength = 368 / 3 = 122.66 coiled inches = 10.22 coiled feet
</pre>
So for people in 230 volt countries, you'll need 4 times the length of wire, but you can run it off half the amps.
For metric people, a direct conversion from www.infraredheaters.com works out to a wire of 6.35 mm diameter with a resistance of 3.2 ohms per meter.
However, the closest wire I can find is 6mm diameter, with a resistance of 3.8 ohms per meter, which means that I would need 96.84 straight meters to get 368 ohms
Please note that these calculations are in an "ideal" world
If there are any errors, please notify me, and I'll make changes |
However, I think the nichrome coil calculation went a little too long. I'll show you my math:
My oven runs on 120 VAC at 20.5 amps
Multiply those two numbers to calculate power 120VAC * 20.5A = 2460 watts
This is the goal we are shooting for, but with 240 VAC for the souce
2460 watts / 240VAC = 10.25 amps (flowing through the entire circuit)
Now we need to calculate the total resistance for the circuit
R = V / A
R = 240VAC / 10.25 amps = 23.41 ohms for the entire circuit
However (assuming we are building an oven with 4 segments just like Jim's) we need to multiply the total resistance by 4 to calculate the resistance for each segment
23.41 ohms x 4 segments = 93.64 ohms for each segment of the oven
The nichrome wire has approximately 3 ohms of resistance per inch of tightly coiled wire. So to calculate the length of wire we need for each segment:
93.64 ohms / 3 ohms per inch = 31 1/4" of tightly coiled nichrome wire for each segment
To calculate the total length of nichrome wire for the entire oven, multiply the segment length by 4 segments:
31.25" * 4 segments = 125" of tightly coiled nichrome wire for the entire oven
Considering Infra-red heaters sells their wire in 10' pieces, you will need slightly more than one coil of wire to setup your oven.
As you work on the wiring, be sure to use your ohmmeter to measure resistance for each segment (should be 93.64 ohms) before connecting it to the terminals on the oven base.
Then measure resistance from terminal A to terminal E (should be 23.41 ohms)
Of course, these numbers are based on ideal conditions, and you may find it necessary to "tweak" and "tune" your oven to acheive peak output before tripping your electrical breaker.
=== Legal Disclaimer ===
Again, these numbers are based on calculations from my Introduction to Electronics class from over 6 years ago, and my practical experience with my current working oven. Please, if you have any question about the calculations above then post them here, or even better, ask a REAL electrician
A friend of mine warned me that 120 volts will throw you, but 240 volts will hold you!
Good luck!
Charlie
TI-386 |
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ANH trooper
Master
Joined: 20 Oct 2005
Posts: 305
Location: UK
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Neo
Newbie
Joined: 25 Mar 2006
Posts: 6
Location: UK
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| Posted: Mon Apr 17, 2006 3:45 am Post subject: |
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| ANH trooper wrote: | Any news on your oven yet Neo?
Can you tell me where you got the wire and stand offs please?
I am going to have a go at making an electric oven and need supplies.I got all the info I need on here except for UK suppliers.I'm sure I'll have a few questions along the way but I need to get started on this ASAP!
I have already made new metal holding frames for my new flip-top former,and I'm using my exsisting oven but with electric heating rather than my gas burners.I really need the even heat that the wire coils will provide.
-Paul. |
Hi Paul,
I have a friend in the U.S who bought the nichrome wire and standoffs Jim recommended and posted them to me, you just can't get hold of them in the UK for safety reasons (apparently). The shipping was a lot cheaper than shipping it direct from Infrared heaters. I can ask him to ship me another lot if you can cover the price?
It was strongly suggested not to wind my own wire - I was told to buy pre-coiled so I don't know if you want to try buying that wire and winding it yourself?
I spoke to an electrician and oven engineer about the oven for the UK and Charlie is spot on with the calculations.
On precoiled wire, if you measure the resistance across the entire oven circuit it should read 23R and across each parallel circuit it needs to measure 94R. I'm not an electrician or oven engineer by any stretch of the imagination and feel lost with all these calculations so I had to ask for a step by step guide
This is what the oven engineer told me to do:
1. Use Supalux for the oven base and walls (this is a cheap calcium silicate board)
2. Place all the cermaic standoffs in the oven.
3. Stretch the nichrome wire across all the standoffs on the first parallel circuit and keep measuring the resistance until I hit 94R. You can change the resistance by stretching the wire. Once I have approx 94R on the first parallel circuit, fit it properly, then repeat for the other 3 parallel circuits in the oven.
4. Once all 4 parallel circuits are attached, measure the resistance across the entire oven and it should read around 23R. Then switch it on with a big wooden stick - the longer the better 
I only had ten feet of nichrome wire, so had to manage with that, so my resistance was a little off and some circuits glowed a little more than others but the oven ran fine and my vacformer was up and running. It uses just under 11A, so I put an 15A breaker fuse into my distribution box and run the oven direct from that. The rest power my plug sockets. The oven never tripped my breaker.
However, I then spoke to a vacuform engineer and he said that while the oven will work, it would be a better idea to use infared heating strips, because it'll save on electric, warm up faster and produce more convection heat which is more important for a vacformer. After looking at the price of an infared heater, I decided against it so he suggested using the home heaters.
I went out to the local pound shop and bought 6 of those infared/halgoen heaters. I'll post a pic up if you don't know what I'm on about - they were £12 each. I stripped them down and just took the infared elements out with the mounting posts, dropped them in another supalux oven, wired them up and WOW!!!. It gets the plastic to forming temperature in half the time and really gets the edges warm too. I have to secure the elements to the oven a little better and sort out my messy wiring but they certainly do the job! |
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jegner
Site Admin
Joined: 30 May 2003
Posts: 2144
Location: Texas, USA
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| Posted: Mon Apr 17, 2006 7:40 am Post subject: |
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Some great info!
Thanks for sharing. Wiring your own oven, even with a detailed guide can be a challenge. I tried to find an 'off the shelf' alternative for the heater, but even the cheap ceramic heaters did not heat evenly, and the Thurston James design, for the home vacuum former wanting to make trooper armor etc. work great.
I rebuilt my oven after a disasterous plastic overheat melted onto the coils. I was amazed, how quickly I could repair and rebuidl the oven, and I think that now, I get as good if not better heating. |
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ANH trooper
Master
Joined: 20 Oct 2005
Posts: 305
Location: UK
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| Posted: Mon Apr 17, 2006 12:13 pm Post subject: |
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Oh that's great news Neo!
I would much rather use the infrared heaters.Electricity really scares but it sounds pretty easy to make the oven in your desription.I say easy,but I am not really that confident.I like the big wooden stick tip...LOL 
So I am well looking forward to your oven now mate.If I can get it all done for under a tonne I'll be laughing
-Paul. |
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crashmann
Guru
Joined: 27 Sep 2005
Posts: 501
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| Posted: Mon Apr 17, 2006 1:01 pm Post subject: |
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Hi Paul,
That looks like the right kind of wiring. I looked up a conversion chart to go from square mm to AWG, and .640mm is equivalent to 22 AWG:
http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html
Then I checked the length, and 30m of straight wire works out to be 98 feet. PeterB calculated how many inches of straight wire goes into a 1 inch length coiled wire:
| Quote: | | 1 coiled inch = 40 * 0.903 = 36.128 straight inches |
So, if you need 125" of coiled wire, and you were to buy the equivalent in straight wire to "roll your own" you would need:
125" coiled wire x 40 coils per inch x 0.903" (length of one coil) = 4515" of straight wire = 114.7 meters of straight wire.
You would need almost 4 spools of what the auction is listing, and the description says the wire does not come on a bobbin!?! 
(Is it a tangled mess in a box?!?)
Plus, that's going to be a lot of wire to coil up! It would be much easier to get it pre-coiled then stretch from there. Although the Infra-red heaters nichrome is 5" too short, it may still work for you (depending on whether you have a 11 amp breaker, or higher capacity) Let me know if you need me to act as a relay for the wire
Neo's infrared / halogen heaters intrigue me. I'd love to see a picture of what you're talking about to see if I could find the equivalent here in the States.
Thanks!
Charlie
TI-386 |
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