Homebuilt ht oven ramp up times.

Tod Lowe

Tod Lowe

Well-Known Member
Hey guys.
I have my heat treat oven ramping up!
What kind of times are you seeing getting to certain temps?
After an hour I'm at 730 degrees. My elements don't seem to be glowing like in the pics I have seen.
Thanks.
 
the other day it took my evenheat 18.5" nearly 2 hours to get to 1950F in my 60 degree garage.
 
That sounds slow, my Evenheat heats to 1500 in less than an hour at full ramp speed.
If you are using a digital controller, you may be able to set the ramp speed at different rates, eg 750 degrees per hr. that is the way an Evenheat is. At full the elements should glow for sure. Hope this helps.
Dale
 
I thought my sugar was slow.
24" sugar creek will get to 1930 in 1hr:50min
BUT, it will very about 50-60 degrees for 45 min
Think I will stop gripping about it and find something else to bit@# about. [at my age, thats what I do best]
Jerry
 
I let mine run for two hours and only got to 900 degrees. I was losing some heat out the sides but didnt think it was be enough to hold it
back from getting hotter.
I did look inside at 900 and the entire elements were glowing at this temp.
The elements instructions say they need to be stretched out to a min of 60 inches. Im prolly around 64 inches . Would that affect them heating up?

Im running one relay where I see some guys running two. What difference would that make and also my relay got really hot....Is this Normal?

We were going to wire it up at 240 but my brother in law checked resistance on the element at 18 i think. He mumbled something about ohms law and said we could use a 110 outlet so we did.

Im going to insulate it some more and try it again and chart the times.
 
Shankmaker said:
The elements instructions say they need to be stretched out to a min of 60 inches. I'm prolly around 64 inches . Would that affect them heating up?

I'm running one relay where I see some guys running two. What difference would that make and also my relay got really hot....Is this Normal?

We were going to wire it up at 240 but my brother in law checked resistance on the element at 18 i think. He mumbled something about ohms law and said we could use a 110 outlet so we did
Click to expand...

First question - 60 inch minimum stretch, 64 inches shouldn't be a problem.

Second question - No this is not normal. How big is the heat sink you mounted the solid state relay too? You did mount the relay to a heat sink with heat transfer paste, right? You can google your relay manufacturer and usually find a heat sink that is rated for 120 or 240 volt wiring available.

Last statement - Using Ohm's law, an 18 Ohm load at 120 volts draws 800 watts and gives about 2,730 BTU's of heating power. That same resistive load at 240 volts will draw 3,200 watts and gives about 10,930 BTU's of heating power. Is the wire rated for 240 volt usage? If so my advise, FWIW, would be to get another relay and run the oven on 240 volts. Your oven will gain a huge BTU output, nearly four times more, by rewiring it for 240 volt input. This should help it reach higher temperatures in less time.

You want the second relay to insure that both powered legs are being cycled by the controller. This way when you shut it off the coil has no voltage going to it from either leg of the circuit. Rewiring it this way will keep you from doing the smack your hand and break something dance. Especially if you reach into the oven to grab a blade with a metal handled tool and accidentally touch the coil :eek::D:eek:

I am no longer a licensed electrician and am not offering professional advise. If you are unsure of what you are doing please seek help from a qualified controls electrician.
 
My understanding is that those elements are designed for 240V operation (if they're the same ones I have). One relay should be just fine, depending on how you wired it up. I just throw the master power switch to ensure no juice through the coils when I reach in.

My homebuilt will get to 1500F on the TC in about 10 minutes. Of course, the oven needs to soak to get an accurate internal temperature before heat treating, so I leave it on for an hour at that temp before heat treating anyway.

You'd be surprised at how much heat loss can slow you down. The heat needs to be concentrated, and a well sealed oven will get you there and hold temps more accurately than a drafty oven.

--nathan
 
Thanks mike!
I'm definately not an electrician. My brother in law is doing the wiring for me.
I will pass this info on to him and we will go from there. This was the maiden run to find problems and we did. The easiest wAy was the 110 route but I see 240 is the best way
to go. Thanks again man.
 
I believe that the relays are typically rated for 110 or 240V and a specific amperage as well, so make sure you have the proper relay.

--nathan
 
silver_pilate said:
I believe that the relays are typically rated for 110 or 240V and a specific amperage as well, so make sure you have the proper relay.

--nathan
Click to expand...

Thanks Nathan.
Yours ramps up fast.:cool:
After reading what others have said about the sides of the box not really getting hot I dont understand why mine did.
Im going to wrap the sides in kawool and button it back up. The top and bottom already have a blanket of kawool over the brick.
 
silver_pilate said:
I believe that the relays are typically rated for 110 or 240V and a specific amperage as well, so make sure you have the proper relay.

--nathan
Click to expand...

Nathan you're right, they are rated for both load voltage and amperage as well as control coil voltage.

I may as well go on record as being a safety nut, so please bear with me. ;) The other relay rating critical to personal safety is the type of relay, single pole single throw (SPST) or double pole single throw (DPST). The SPST is safest for 120V circuits (one hot lead), whereas the DPST is safest for 240V circuits (two hot leads). Most controllers will be able to operate one DPST or two SPST relays as they draw minimal milli-amps on their control input coil.

All commercially made heat treat ovens I have seen that are operated on 240V use a DPST relay. There may be heat treat ovens made somewhere for 240V that don't use a DPST relay, but I'd have to believe they couldn't pass UL testing and approval to be sold in the U.S.A. If it's a good enough method for UL approval, it's good enough for me :D

Mike
 
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