Yes, one more issue with my heat treat oven

jtdesigns

jtdesigns

Joined
May 2, 2011
Messages
181
Now that I got the thermocouple reading correctly, I struggled a little to get to 1750 today as I was heat treating some A2. Finally realized that I ordered 2-240v elements which, according to Paul at Budget Castings, I am only getting half the power going to the elements because I have them wired in series. My question is this: can I safely run two leads from each SSR (one going to one element and the other going to other element...then repeating for other SSR if that makes any sense.) in parallel to get a tru 240v going to each element. My other option is to order 2--110v elements and wire them just like I have now (series).

Jeff
 
That would work, but it might be easier to just connect the coils directly in parallel.
If they are in series now, and there is a bolt at each end, and one tyeing them together in the middle, lets call those bolts A,B,and C.
Right now you have a wire from an SSR at A and C.
Move the C SSR lead to B.
Leave the other SSR lead at A.
Using a piece of 8-10 gauge wire, jumper A to C. Now it will run in parallel.
 
My only problem with your suggestion is that my "B" connector bolt is inside the heating chamber. I guess I could use another 4" stainless bolt and bring that connection outside but either way, I will have to get ahold of some more high temp wire to make the jumper connection.

Jeff
 
How much do you need? I have 100' of 14 gauge Kanthal A1. I don't want to part with much because Pelican wire no longer list 14 gauge and the prices have gone up. You can order a 50' bundle from these guys for just $15, but it might come as several pieces to make the 50'
 
Yes, That is how I would do it for "B". Run a longer bolt through the firebrick and make binding post "B" out of it.

The terminals for A to C are probably right next to each other, so you may not even need to use insulated wire. If within 3", just strip about 4-5" of the insulation on the power wire, wrap it once around A and tighten the nuts, then wrap it around C and tighten the nuts - Jumper is done. If they are far apart for some reason, use wire insulated with a covering suitable for hot environments.
 
My leads coming from the ssr are more than long enough so I will use a 5" piece off of one to make the jumper. Thanks guys!!
 
What is the output difference in series vs parallel ? The specs on the elements are "Power: 240 Vac, 13 Amps, 3120 Watts" Am I only getting 1560 watts if running in series ?
 
woohoo....running in parallel and she gets up to 950 in less than 5 minutes. Only went that high cause I didn't have anything to heat treat....need more steel:)..............thanks again for everyone's help.

Jeff
 
Spalted said:
What is the output difference in series vs parallel ? The specs on the elements are "Power: 240 Vac, 13 Amps, 3120 Watts" Am I only getting 1560 watts if running in series ?
Click to expand...

Alot....in series 120vac...in parallel 240vac. Basically you have the same situation as I did. I ordered 2 240v elements but was only running one lead from the ssr to the element with the elements connected in the middle which was running half power(series). I just reconnected so that I have one ssr lead going to one terminal end of the elements and the other ssr lead going to the middle connection with a jumper going from middle connection to remaining element's terminal end. Now I should be getting the full 3120 watts. I would have been fine in series if I had ordered 2 of the 120vac elements.
 
If you run the elements in series, instead of parallel, you don't get half the power, you get one quarter of the power.

Voltage = Current * Resistance.

The resistance of the coil is fixed (for all practical purposes)

Halving the Voltage will therefore also halve the current

Power = Current * Voltage

For half the current * half the Voltage, you'll get a quarter of the power.

Running the two elements in parallel should increase the power by a factor of 4.

From your description of the elements, it seems when you are running in parallel, you'll be drawing 26 Amps (each element drawing 13A at 240V) and producing 6240 Watts of heat. I don't know whether this may be an issue for your power supply (it normally would be over here in the UK).

If your supply will handle it, there's no real need to change the elements.

Accurate temperature control can be more difficult to achieve at low temperatures with big power inputs, and you've now got a big power input. I'd advise setting a slow ramp up to tempering temperature every time you temper, to minimize overshoot.

You may even find it's worth ramping to Austenitizing temperatures as well.
 
Well, as luck would have it...just as I was getting the performance I was expecting by changing over to parallel one of my elements burned in two inside the furnace. Looks like I get to re-order elements. Should I just go with 2- 110vac elements this time? Also is there a connection that is better than a split bolt connector (like some sort of high temp terminal ring, etc.)? I think the split bolt creates too much of a pinch point.

Jeff
 
Using approximate numbers:
Lets say the coils are 20 ohms each. Series makes the resistance double - 40 ohms. Parallel makes it half - 10 ohms.
Using Ohm's law - I=E/R - if the voltage is 220 VAC, with the coils in series at 40 ohms, the amperage is 5.5 amps , or about 1200 watts.
If the coils are in parallel at 10 ohms, the current is 22 amps , and the power is 4800 watts ...... four times the power.

You need to sit down and calculate the desired power output, and order a single element that draws that amount of power. If the desired length is 48", and the resistance is 10 ohms. order a coil with a resistance of .2 ohms per inch. The best way to get it right if this math isn't your long suit is to talk to the person at the supplier directly, and he/she should be able to sell you the proper coil. You need to know:
1) The length of the coil needed ( 48", 56", 72",?)
2) the wattage desired ( 3000, 3500, 4400, ?)
3) the voltage it will run on (220/230/240VAC - measure it with a meter, don't guess)
 
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So what would you do??? 2 elements at 240 or 2 elements at 120? I'm good for up to 15 amps each leg
 
One problem with the internet is I can't look at what you have and tell if it is what you said.

My guess is that the coils ordered were each the right resistance. When connected in parallel, they drew way too much current and burned up. What was the info on each coil?

If you order two, I would get the right size, and run it in series like you started. You need to calculate the total resistance, and order two that add up to that ohmage. So for 4800 watts, you would series wire two 5 ohm each coils ( 10 ohm total).

BTW, these numbers are just for example. I don't know your build and desired wattage.
 
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My build is 240vac w/ twin ssr. I originally ordered 2--240vac rated at 3100 watts from budget castings and had them wired in series. I then changed to parallel. I may have moved the elements enough to create a weak point. I probably should have ordered 2--120vac rated at 1500 watts each for a total of 3000 watts
 
I ordered two 240v elements also when i built mine. Figured out that I only needed one. So now I have an extra.

Not sure if you used the plans I found or not. But that's what confused me. Those plans where from overseas where thier system voltage is different.

You only need one 240v element.
 
jbblount said:
I ordered two 240v elements also when i built mine. Figured out that I only needed one. So now I have an extra.

Not sure if you used the plans I found or not. But that's what confused me. Those plans where from overseas where thier system voltage is different.

You only need one 240v element.
Click to expand...

Yep, thats pretty much what I did. Now, I think I will just order one 240v element even though my oven has slots cut in the brick for two elements.

Jeff
 
If you used Andy Gascoigne's plans, he built his in the UK, where the standard mains power outlet is rated 13A, 230 VAC. He bought his elements from BCS in the States, back when they were only listing the 110V elements. They have since started listing the 240V elements as well. I suspect this is where confusion has crept in, as I know of a couple of people that have done the same as you.

I use a pair of 110V, 13A elements, connected in series, rather than a single 240V element.

My reasoning is that only the straight "tails" run across the back of the oven, minimizing the heat input from that direction. If I used a 240V element, the coiled section would need to stretch across the back of the oven, providing more heat from that direction.

The door doesn't provide heating from the front, so it seems best to try to minimize heat from the back to maintain consistency throughout the oven.
 
I think that rating the elements by voltage is a poor idea. What the are is a length of wire that with so many ohms that will handle so many amps. Lets look at some things. First the heavier your wire the longer it will last, but the heavier the wire the less resistance it has. Now lets look at how many watts you want.
remember watts=voltsxamps, amps=volts divided by ohms. ohms divided by ohms per ft = length needed so these remain constant
220volts/20amps=11ohms, 220vX20a=4400watts 220v/15a=14.70hms, 220vX15a=3300watts
110volts/20amps=5.5ohms, 110vX20=2200watts 110v/15a=7.3ohms, 110vX15a=1650watts

Kanthal A1
50' of 14 gauge at .21 ohms per ft =10.5ohms 21 amps, 4629 watts at 220 It would be hard to find and use in longer length spools needed to add enough resistance to drop the amperage. The way it works is longer = more resistance meaning less amps and less watts.
Less is More!!

at 110v and 20 amps you need that 5.5 ohms so 3.3/.21(ohms per ft)=26.2ft and 110 at 15amps is 7.3/.21=34.8'

50' of 15 gauge at .27per ft =13.5 for 16.3 amps at 220v for 3586 watts with the whole 50'
220v at 20a needs 11 ohms so 11/.27=40.74ft 220v at 15a needs that 14.7ohms so 14.7/.27=54.4'
110v at 20a 5.5/.27 for 20.4' (20amps at 220v) 15 amps is 27.2ft
50' of 16 gauge at .34=17
50' of 17gauge at .43per ft=21.5
50 of 18 at .55per ftper ft=27.5
50 0f 19 at .63=31.5
I would never use 19 gauge elements sure I could
but its like this

if I wanted a 4400watt 220V oven using 20amps I would need that 11ohms of resistance 11ohms/.63ohms per ft=just 17 ft of 19 gauge wire. It would also burn out quick because 19 gauge won't handle 20 amps for crap. 15 at most for a while. I would use it at 13 amps.
timgunn's 13 amp 110 elements are probably 19gauge. 110v/13a=8.46ohms 8.46/.63per ft=13.43ft.
if they are better 18 gauge they would be 8.46ohms/.55=15.4ft
even better 17 gauge would be 19.7ft
16 gauge would be 24.9ft

See there you have 4 different 110V elements all rated at 13 amps and 1430 watts. I would always chose the heavier wire, the limit being how much coil can you get in your oven. The heavier wire means more length. This can be manipulated by the diameter of the element coils. The larger the diameter the less length the actual coil is.

I chose to use 14 gauge wire because I expect it to last way longer. I needed the whole 50 ft spool and Made my coils by turning the wire onto a piece of 1/2 all thread.

If I wanted a 15 amp 220 oven I would run 16 gauge wire and use 32.4 total length of wire.
you could call it a 220 element and get 3300watts or call it a 110 element and get 825 watts. If I got 2 110v 15 amp elements of 16 gauge they of course would each be 16.2 ft long before coiling.
 
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I have decided to make my own elements. Using your example, I keep getting a different number. What am I doing wrong.

Using: watts=volts x amps and amps=volts divided by ohms

3300=220x15

220volts divided by 15amps=14.663 ohms (amps=volts divided by ohms)

14.663 ohms divided by .3386 (ohms per foot 16 gauge Kanthal A-1)=43.30 feet of wire
 
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