HT Oven Help

B

buckaroo

Well-Known Member
Having problems with my oven. I can hit 1000 in 30 to 40 minutes but it really slows down after that. It can take another hour or more to raise to 1850. Are the coils too small or could there be other problems. Can anyone on the forum help with coil size information.
 
I would expect a bit too little wattage in heating coils. Larger cubic volume requires more wattage. Take a look at the commercial ovens to see about what wattage they have per cubic foot of interior space and compare to what you have.

What is your cubic foot size? What is the wattage? Also, the type and amount of insulation will affect heating rate.

Ken H>
 
The coils are rated for 3120 watts. I am running 220 volts 20 amp. The coils are wired in series. Chamber size is 14 deep 4 high 5.5 wide. Using a PID with a 20 amp SSR. Built with k23 brick single layer with an additional 2 to 4 inches of vemiculite around all the sides.

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buckaroo said:
The coils are rated for 3120 watts. I am running 220 volts 20 amp. The coils are wired in series. Chamber size is 14 deep 4 high 5.5 wide. Using a PID with a 20 amp SSR. Built with k23 brick single layer with an additional 2 to 4 inches of vemiculite around all the sides.

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Click to expand...

I'm not sure I can offer any help with what is wrong - but by comparison, the EvenHeat KF18 has a much larger chamber, same rated wattage, will reach 1000F in 12-15 minutes, 1950F in under an hour. It has soft firebrick walls and a stainless sheet wrap around that.
 
Thanks. That is what is stumping me. This oven should be fast. I can't figure it out.

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You said the coils are wired in series? Are these 120vac coils? If they happen to be 220vac coils, then they should be paralleled, not series. What is the current draw?

By pass (jumper) your SSR completely so the coils are getting full power without control - that will give you an idea of how fast it will heat at max.

Ken H>
 
These are the specs for the coils from the manufacturer.
Specifications:

Material: Kanthal A1 Wire
Maximum Temperature: 2300°F
Power: 240 Vac, 13 Amps, 3120 Watts
Wire Size: .046", (17 AWG)
Unstretched Length: 41"
Minimum Operational (Stretched) Length: 60"
Maximum Stretched Length: 120"
Coil Outer Diameter: .280"
Pig Tail Length: 1-1/4"

If I wire parallel do I need to install a second ssr?
 
I know the very basics about electricity. I can wire light and switches. But this stuff is like a foreign language.

The specs above say 3120 watts but have I cut the watts down by wiring in series and not parallel?
 
Buck, "IF" each element is 240vac, and you have two of these elements? Then they MUCH be wired in parallel. It says you have a 4.5" pigtail on each end of each element? If so, then try wiring 240 across only one of the elements and see how it heats. I'm sure you know how to parallel, tie the pigtails together on each end, this would put the 240 circuit wire connecting to BOTH pigtails on the end. Yes, you're cutting your wattage in half (or less). Where the element requires 240 vac across the element, you're only getting 120 vac on each element with them in series.

Nope, you still will only need the two SSR you now have.... You do have a SSR in each leg of the 240 volts? Yes, it will work with only 1 SSR, but the "proper" way to to put a SSR in each leg - like putting a switch in a 240 circuit, 1 contact will stop the circuit, but there SHOULD be a contact to open in each leg of the 240.

If you wish to call and talk on phone, I can PM you my phone number, or you can PM me your phone number.

Good luck,
 
Thanks Ken. I built the oven off of the plans floating around the net. They call for 2 coils wired in series. What I found out today is it was supposed to be 120 volt coils. I opened it up today and removed the coils. Stretched one to the max of 120 inches and put it in. Fired it up and found my tcouple is bad. New one ordered so it will be a few days before I know if it is fixed.

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I'd not thought about the logistics of paralleling the coils in the oven. 120 vac so they could be series would be easier. Remember, with just one coil you've only got half the wattage of having both coils paralleled.

Good luck and let us know how it goes.
 
The Tcouple came in to day and I installed it and did a test run. The oven ran up to 1000 in 30 minutes and then ramped to 1500 in another 30 minutes. All I had time for today. Tomorrow I will run it up to the 1850 mark and see how it does.

Now here is my question. I was originally running 2 240 Vac, 13 Amps, 3120 Watts coils wired in series. I removed on and stretched the other to fit both sides of the oven. If I was to run 2 coils rated for 240 Vac, 13 Amps, 3120 Watts in parallel would this allow my oven to be even faster than what I have now or is it over kill.

I would like to thank all the dogs who helped me figure this out. Could not have done it with out you.
Dave
 
Let's see - you've got only one coil wired in place now? OK, if you stretched both coils and wired them in parallel, yes, you oven would heat faster. I don't "think" it would be overkill. The Evenheat 18" oven I've got will reach 1500F if well less than an hour. It takes just over an hour to reach 1900F. That last 400 to 500F is slower.

Do you have a way to check amp draw of your oven? Are you saying the specs on the coil is 240 vac, at 13 amps for 3120 watts for EACH coil? OR - was that spec for BOTH coils? If for both coils, then that's about what my Evenheat oven has.

Do you have a link to where you ordered the coils?

Ken H>
 
Got them from Budget Casting Supply http://www.budgetcastingsupply.com/Heating-Elements.php Item Number 7103. I used two of these originally. Now only one.

#7103 Specifications:

Material: Kanthal A1 Wire
Maximum Temperature: 2300°F
Power: 240 Vac, 13 Amps, 3120 Watts
Wire Size: .046", (17 AWG)
Unstretched Length: 41"
Minimum Operational (Stretched) Length: 60"
Maximum Stretched Length: 120"
Coil Outer Diameter: .280"
Pig Tail Length: 1-1/4"
 
OK, from my reading of specs, each element ais 3120 watts. If you wire both of them in the oven you will have 6140 watts at 26 amps. That twice what my even heat K18 oven has. That is a LOT of heat.

I can not see exactly you setup, so it's really hard( impossible) for me to say yea or nay on two elements. If your wiring is suitable for 26 amps, it "might" be ok to try it. It surely will heat faster, just keep an eye on the temperature rise..

Good luck!!!!!

Ken
 
I'd stick with the 3 kW myself. 6 kW would certainly be faster, but I think it would bring its own problems.

I'd be concerned about overheating the blade as a result of direct radiative heating. It is a known issue at tempering temperatures, but that sort of input might make it significant at Austenitizing temperatures too.

You are using pretty thin elements at 17 Ga. there have been a few element failures discussed on British Blades, one of them on an oven I built with 16 Ga coils. The failures were mostly (all?) when running at Stainless temperatures. I'd be wary of upping the heat input in case it makes the problem worse.

I have since changed to using 1.6mm dia. Kanthal A1 (about 14 Ga) for the elements in my ovens.

I have actually used 2 of the 16 Ga 3 kW elements in an oven, but it was a 42" sword oven built very much on the cheap and using cheap no-name IFBs which were much more dense than the JM23/K23 ones from Thermal Ceramics. The thermal mass was therefore much greater and the heat-up time was longer than on my 3 kW, 23" ovens built from the JM23s.

If I was in your position and really wanted to play about with it, rather than getting on and making knives, I'd wire things up to let me connect the elements in parallel for Austenitizing and in series for tempering. The reduced output for tempering would make it easier to get better control at the lower temperatures.
 
After the test run today I have decided to leave it as is. One coil. Ran it up to 1875 in good time so I'm happy. Again thank for all your input help and suggestions.

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Buckaroo, would you be so kind as to post your plans or the links you used?

I am starting the process to build my own oven as well and I am mystified by 240V electrics.

Specifically, I am looking for a parts list for electrics and a wiring diagram. Pics would be great too.

Thanks

Mike


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