DIY 18650 soldering iron with regulated temperature control

Thread Starter

taith

Joined Apr 1, 2017
28
I'd like to make myself handy 18650 soldering iron, using K type thermocouple for regulated temperature control.
Planning to enclose 2 nichrome heaters and thermocouple within small metal head, filled with thermal cement/glue.
1 winding for constant preheat of the tip and second for temperature topping, controlled by said thermocouple regulated with potentiometer.
I'd like to include low voltage cutout for battery safety, and max current would be 5A as most 18650 batteries can handle this current no problem.

PS would it be possible to easily add multiple heaters controlled by said thermocouple, for example third heater for fast preheat, or extra power when temp drops too low (soldering bigger elements)
PPS I know making heating elements by myself will be lots of trial and error, I expect to fail spectacularly few times.
 

Alec_t

Joined Sep 17, 2013
14,313
I think having more than one heating element would add unnecessary complication, not least the problem of bulk and making satisfactory connections. The proper choice of single heating element and control circuit should be able to provide the wanted preheat and boost. A PWM method can provide a 0%-100% heat output.
 
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Thread Starter

taith

Joined Apr 1, 2017
28
I was thinking of something much simpler, K thermocouple amplifier steering low resistance MOSFET, not sure what elements to use for barebone circuit and if it would be source voltage sensitive.
Preheat part would be simply constantly on heater element, no steering (except power on switch)
 

smooth_jamie

Joined Jan 4, 2017
107
You can irons for $8.00 Why re-invent the wheel???
The $8 irons are a false economy. They won't last very long and they will be poor quality, you get what you pay for. It's also recommended that a temperature controlled iron is used rather than using a constant power type.

This sounds like an interesting project, I've not seen a battery powered iron before. I will be interested in how long it lasts on a full charge, power output etc.
 

Colin55

Joined Aug 27, 2015
519
I have a $12.00 240v Constant temp iron that has lasted many years and a station for $28.00 that has lasted 30 years. You are right. Alll my stuff is rubbish and wont last 12 months.
 

smooth_jamie

Joined Jan 4, 2017
107
I have a $12.00 240v Constant temp iron that has lasted many years and a station for $28.00 that has lasted 30 years. You are right. Alll my stuff is rubbish and wont last 12 months.
I'm sorry if I upset you Colin, I wasn't implying that your are a cheap-skate, I was just pointing out the obvious. Why do you think people spend more money on better quality tools? One reason is they last longer

I own a PC based oscilloscope that cost me $69 and it will probably last forever. That doesn't mean it does everything I need or that I don't need to upgrade to something more expensive later. It doesn't trigger very well, it (apparently) has a 20MHz bandwidth, the software is terrible and concequently it is only good for basic jobs. I've only had it a couple of years, so that's probably not going to last me much longer regardless of it's working state.

I also have a constant temp iron (I spent a bit more than $8) and I'm sure that will last years and years as well, not doubting you there. But if I spent $80 I would get an iron that would be better (don't you agree?). I think taith has a good project and he shoud be encouraged to pursue it, rather than setting for a very cheap soldering iron.
 

Colin55

Joined Aug 27, 2015
519
The cheap products are made out of the same materials as the expensive items.
This applies to almost everything: shoes, glasses, electronic components, and more. You can't talk about CRO's because you are not comparing apples with apples.
The tips on the cheap irons are just as good as the expensive irons and the poster is not going to produce a constant heat iron, if he lives to be 99.
 

smooth_jamie

Joined Jan 4, 2017
107
This applies to almost everything: shoes, glasses, electronic components, and more. You can't talk about CRO's because you are not comparing apples with apples.
How more hypocritical can you be in one sentence? I can't compare two differently prices scopes yet we can compare shoes and everything else? Also, my scope is digital, not cathode ray (big difference in price).

The cheap products are made out of the same materials as the expensive items.
Not true. Some claim to be identical (even look identical) but everything has to be made to a price point to make a profit. EDIT: I will admit there are exceptions though like Skoda and VW for example

For example take two multi-meters (say a Fluke and a cheap DMM like the ANENG 8009 which is currently quite popular). The ANENG is about $20 the Fluke is about $700. I have used both, and from my experience of using them both have a decent accuracy for what I want. However I know that if I use the ANENG for measuring mains voltages I take a danagerous risk because it is not tested and certified (while the Fluke has UL, CSA etc). That certification costs thousands and hence the cost price of the Fluke, but I know I will be safe because the level of money I paid for it reflects the work that has gone into making sure it's safe. This is the best example I can think of for buying better, more expensive tools.

Not convinced that paying more gives better quality? There are thousands of examples not related to engineering that I can think of where paying more.... gives me better

The tips on the cheap irons are just as good as the expensive irons and the poster is not going to produce a constant heat iron, if he lives to be 99.
Regardless of what tip you use, there is no question from many people that an adjustable temperature iron gives better results.
 
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Colin55

Joined Aug 27, 2015
519
Regardless of what tip you use, there is no question from many people that an adjustable temperature iron gives better results.


Of course it does but the tips 20 years ago got eaten out after a few months. Now the $12.00 irons last forever.
 

smooth_jamie

Joined Jan 4, 2017
107
"Regardless of what tip you use, there is no question from many people that an adjustable temperature iron gives better results."

Of course it does but the tips 20 years ago got eaten out after a few months. Now the $12.00 irons last forever.
So just to stubbornly make my point, back in post #4 you say "why re-invent the wheel" you've now answered your own question.
 

Thread Starter

taith

Joined Apr 1, 2017
28
Discussion over 8$ chinese knockoff is not the point, my goal is having handy mobile tool that I can use anywhere without electricity needed, all I'd need is charged 18650 from flashlight.
Considered making power bank one, but some might not provide enough power. (5W USB vs 20W 18650)
So yes, I could turn 8$ soldering station "mobile" with some tampering, but it would be use and not as practical.
PS I know there are propane soldering tools, not much temp regulation and risk of fire is real.
 
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