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I would like to run 3 heaters (26 awg straight nichrome wire with slightly different lengths) in series to form one continuous heater with 3 different temperature zones.

All of the sections are connected using spot welds. I have tried connecting the sections with larger diameter 22awg nichrome and stainless steel wire, but the sections are not operating completely independently of one another. Of course, I could operate the 3 sections in parallel, but for my application it would be much better if the heater sections were run in series.

What could I use as a connection material between the sections so that each acts independently of the other 2 sections?

Dave Pierce
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    What do you mean by "independently"? If they are connected in series, the same current will flow through all of them. – Eugene Sh. Dec 11 '19 at 18:12
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    You can't get different temperature zones from either a series or parallel connection except by exploiting physical differences. – Chris Stratton Dec 11 '19 at 19:11
  • Length is a physical difference. – rdtsc Dec 11 '19 at 19:51
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    Agree with Eugene. The term "independently" can be construed in different meanings here. – SteveSh Dec 11 '19 at 20:20
  • Do you just want to use heavier wire to join together heating zones with non-heating regions in between? That could sort of work. Crimp connections are not uncommon. You probably want something heavier than 22 gauge for the interconnect though... – Chris Stratton Dec 11 '19 at 20:29
  • I am not sure what you mean by independent either. But you could connect the segments with heavy gauge copper wire or copper buss bar covered with thermal insulation to prevent the wire from transferring heat by direct conduction. – user57037 Dec 11 '19 at 20:33
  • "I would like to run 3 heaters...with 3 different temperature zones... I could operate the 3 sections in parallel, but for my application it would be much better if the heater sections were run in series." - and yet the opposite is happening. Why do you want to run them in series (where they are not independent) rather than in parallel (where they would be independent)? – Bruce Abbott Dec 12 '19 at 01:59
  • Thank you for your comments. Independent means that R1, R2, and R3 all run at different temperatures depending on the length of each resistance wire. I can calculate the wattage of each heater with voltage compensation for the differences in resistance. In my application it is better to NOT have additional wires for a parallel circuit going to the individual sections. What I need is some way to physically separate the heaters so that R1, R2, and R3 heat up to the theoretical calculated values. – Dave Pierce Dec 12 '19 at 09:10
  • Sounds like you need thermal isolation, or if thermal isolation cannot be achieved, then you need to account for it during the calculation stage. Use heavy gauge wire to join the heating elements. This will insure low self-heating of the wire. Insulate the wire thermally to insure that it does not become a source of thermal leakage between adjacent zones. – user57037 Dec 13 '19 at 20:58
  • Maybe you should just tune it by trial and error. If one section is too hot, use a shorter wire. If it is too cold, use a longer wire. Obviously, only one section can strictly be controlled by your control loop. Tune the others until they are good. – user57037 Dec 13 '19 at 21:02
  • You should be able to calculate the heat flow by conduction in the heater wire also. You may have to iterate a few times until your solution converges. – user57037 Dec 13 '19 at 21:13

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The sections will never operate independently of each other. If they are in series, then they all have the same amount of current running through them. If you change current to one, you are changing current to all of them.

I suppose you can have three temperature zones just by making each a different length of wire, but changing the lengths will have impact on the overall current, thus changing all the zones.

Scott Seidman
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  • I think the OP said that the three sections of nichrome were of slightly different lengths. That means that their resistances will be different, and so will there heat dissipations, even with the same current. – SteveSh Dec 11 '19 at 20:19
  • @SteveSh, yes, that's what the second paragraph means. This will provide different heat outputs in different regions, but not controllably --i.e., to a temperature set point. – Scott Seidman Dec 11 '19 at 20:26
  • The heat dissipations may be different, but the temperature might not. If the longer wire heats a proportionally larger area then length has no effect on temperature. – Bruce Abbott Dec 12 '19 at 02:07
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"What could I use as a connection material between the sections so that each acts independently of the other 2 sections?"

Not really an answer, but I don't know of such a material. If you wired the sections in parallel, you use something like a thermostat to control the individual sections. Or an electronics equivalent (temperature sensor, comparator, MOSFET).

With 3 sections in series, you are stuck with only being able to control the heat outputs of each section, not when they turn on.

SteveSh
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I don’t know if anyone answered your question but the answer is a ceramic (High temperature) terminal block. That’s what you were asking for, right?

Martin Leonard
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  • A big mass terminal block may solve the problem, but we are running the device to 500C and do not have room for a big block. This is also why we do not want a bunch of wires going to the device for parallel operation. We use high temperature wire for the 2 ends and that works. Adding 4 more wires would be a problem. The perfect solution would be a material or device that would separate the resistance sections so they operate as 3 independent sections. – Dave Pierce Dec 12 '19 at 15:08
  • We have temperature control circuit that adjusts the voltage to maintain the temperature. The control of this circuit is good to 0.1C. I know the voltage, I know the resistance, I know what the temperature should be, but I am not getting what I calculate, because the sections are not perfectly separated. – Dave Pierce Dec 12 '19 at 15:08
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Slide the 2 ends into a stainless steel ferrule, and crimp it. Bicycle shifter cables use these ferrules to finish the cut ends of the hard cable.

John Canon
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  • I tried using a heavy gauge stainless steel wire between the sections, but that was not enough. The voltage and current go through, but the resistance is not completely separated. – Dave Pierce Dec 12 '19 at 09:15