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110v/220v Oven calculator
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Joined: 04 Sep 2006
Posts: 705
Location: Austin, Texas

PostPosted: Thu Dec 28, 2006 9:48 am    Post subject: Reply with quote

OK, thanks.

I don't think I want to depend on the peculiarities of where I'm currently living, so I'm redoing the design a bit.

(One reason I want cheap variable zoned power is to compensate for local conditions as well as for different plastics.)

Instead of three outer loops, I just have two now, so I can have two fixed and two variable-power segments. That gives me more flexibility---I can put two on one 15-amp circuit and two on another, or three on one 20-amp circuit and one on another (leaving room for a vacuum cleaner without turning the oven off), etc. I guess I can wire it for 220 without changing the coils, too, just by connecting pairs of segments together in series. (Assuming I have ample-amperage infinite switches or something.)

In the new 4-segment layout, the shortest segment is 84 inches (the smaller outer loop) and the longest is 144 (the longer inner spiral). The longest one also needs the least wire, to generate teh right watts/inch, so it'll be stretched even further... I'm wondering if I can stretch the nichrome coil that far without it doing something strange.

I guess that will be stretching it about 60 percent further than for a standard TJ oven... any idea if that's likely to be a problem? (If so I can stretch it somewhat less, and have it be less powerful, and turn the other spiral up more to compensate, up to a point.)

Hmmm... maybe I should try stretching that segment before I drill any holes.
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com
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Joined: 04 Jul 2007
Posts: 34
Location: Aurora Colorado

PostPosted: Thu Jul 05, 2007 3:39 pm    Post subject: Reply with quote

A while back drcrash added this to this topic “Is there headroom hidden in a 20-amp circuit, such that it can generally handle 21 (or 22 or 23) amps without complaint?”

I would have thought he had an answer by now, but here is the over kill.
1) Most circuit breakers do not trip because of extra current, but extra heat. The current flows through a bimetallic strip which, when it becomes overheated from excessive current, bends away from a latch and trips (opens) current path. The current in question is of course what is flowing through the oven, but it is also limited by the size of wire in the building, connection resistance, etc.

2) Circuit breakers are used to protect the building wiring from the excessive heat. They are NOT there to protect what is plugged in.

3) A book based on the National electrical code I have states “A circuit breaker has a definite time delay. It will carry 80 percent of its rated load indefinitely, a small overload for a considerable time, and will trip quickly on a large overload.”

I have seen circuit breakers “wear out” in aircraft. They are not designed like a switch (for the most part anyhow) to where they will trip without any overload.

Hope this helps…
Never force anything, always get the bigger hammer.
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Joined: 27 Sep 2005
Posts: 497

PostPosted: Sun Jul 08, 2007 9:26 pm    Post subject: Reply with quote

Wow, I don't know how I missed these postings, but I was able to borrow an ammeter from a friend and found my oven was running around 21 amps on a 20 amp breaker. I have run it continuously for 8 hours at a time without tripping the breaker. But if you plug anything else into that circuit, boink!

I'm sure there is some wiggle room on the breakers.

For the rest of the questions... Umm, too many words. I'll have to think about them, unless you've already built the oven. In that case, post your findings Smile

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Joined: 16 Jul 2011
Posts: 1
Location: florida

PostPosted: Sat Jul 16, 2011 7:40 pm    Post subject: Reply with quote

I'm trying to build a 5-segment oven, and I want to fit three fixed-wattage segments on one 15-amp circuit and two variable-wattage segments on another. That means my three fixed-wattage segments can only average 5 amps each. Laughing Laughing
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