# Hacking a soldering iron tip

#### camerart

Joined Feb 25, 2013
1,700
Hi,

A friend of mine has a soldering station similar to this:http://uk.farnell.com/weller/wr-3000m-uk-eu/desoldering-station-420w-230v/dp/1582381
I would like one but they are out of my league. I did buy a tip though to see if I could get it to work: http://uk.farnell.com/weller/rt2/tip-soldering-iron-needle-0-8mm/dp/8809879?CMP=i-bf9f-00001000

These are temperature controlled, so I assume there is a heating element and a sensor inside the tip. As you can see there are three points of connection. I checked the resistance at the jack plug: large contact GROUND to RING = 1.1 Ohm cold. GROUND to TIP = 1.9 Ohm cold. RING to TIP = 3.0 Ohm cold. GROUND to RING = 6.3 Ohm hot. GROUND to TIP = 0.0 Ohm hot. RING to TIP = 5.6 Ohm hot.

I need to know which is the heating element and which is the sensor. First I will try voltages 12 to 24 volts, then perhaps I will make a sensor controlled power supply.

Camerart.

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#### MrAl

Joined Jun 17, 2014
6,610
Hi,

If no one else has any direct info, you can ask your friend if you can make some measurements on his system. Make a connector adapter if needed for taking the measurements. You might be able to figure out what the element connections are that way, then after that the sensor connections. I would think they would both be common to ground, but i dont know anything about this particular iron handle.

They make solder stations a lot cheaper than that one, and they work quite well.

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
First off be advised that fully 60% of the price of production equipment is vested in the industrial/commercial service warranty -- IOW, as a private individual, you can very likely purchase the complete station new at Ca 50% 'list'
But to move on...

These are temperature controlled, so I assume there is a heating element and a sensor inside the tip.
Correct - Either thermistor or thermocouple -- A thermistor varies in resistance with temperature whereas a thermocouple 'translates' a temperature difference into an EMF.

I will assume 'cold' = room temperature?
What (approximate) temperature is 'hot'?
What are the inter-contact EMFs at each temperature?

Best regards
HP

#### camerart

Joined Feb 25, 2013
1,700
Hi,

If no one else has any direct info, you can ask your friend if you can make some measurements on his system. Make a connector adapter if needed for taking the measurements. You might be able to figure out what the element connections are that way, then after that the sensor connections. I would think they would both be common to ground, but i dont know anything about this particular iron handle.

They make solder stations a lot cheaper than that one, and they work quite well.
Just seen my spelling of Soldering

Hi Mr Al,

I'm reluctant to ask my friend, as he is professional, and if something I did affected his station, this would be a no no.

I'll see what suggestions come up, thanks.

C

#### camerart

Joined Feb 25, 2013
1,700
First off be advised that fully 60% of the price of production equipment is vested in the industrial/commercial service warranty -- IOW, as a private individual, you can very likely purchase the complete station new at Ca 50% 'list'
But to move on...

Correct - Either thermistor or thermocouple -- A thermistor varies in resistance with temperature whereas a thermocouple 'translates' a temperature difference into an EMF.

I will assume 'cold' = room temperature?
What (approximate) temperature is 'hot'?
What are the inter-contact EMFs at each temperature?

Best regards
HP
Hi HP,

Cold = room temp.
Hot = a second soldering iron touching the tip.

Can you explain 'contact EMFs' please?

C.

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
Hot = a second soldering iron touching the tip
Please attempt to heat the tip (as with a heat gun) to Ca. 350° C [~660° F]) --- If this is not an option, please allow plenty of time for the temp to stabilize prior to making measurements...

Can you explain 'contact EMFs' please?
By 'contacts' I refer to the 'points' from which you took the resistance measurements (i.e. Tip, Ring and Common)

EMF=Electromotive force (measured in Volts and denominations thereof) -- For these purposes please set your DMM for DC mV (Or, if using an auto-ranging instrument, simply DC Volts)

Best regards and good luck!
HP

#### camerart

Joined Feb 25, 2013
1,700
Please attempt to heat the tip (as with a heat gun) to Ca. 350° C [~660° F]) --- If this is not an option, please allow plenty of time for the temp to stabilize prior to making measurements...

By 'contacts' I refer to the 'points' from which you took the resistance measurements (i.e. Tip, Ring and Common)

EMF=Electromotive force (measured in Volts and denominations thereof) -- For these purposes please set your DMM for DC mV (Or, if using an auto-ranging instrument, simply DC Volts)

Best regards and good luck!
HP
HP,

There is no voltage on any of the 'jack plug' contacts, all voltage is at the 'jack socket' from the unit circuit.

C.

#### spinnaker

Joined Oct 29, 2009
7,837
Why not simply buy the tip for your iron and safe yourself a lot of grief?

#### dl324

Joined Mar 30, 2015
9,121
Why not simply buy the tip for your iron and safe yourself a lot of grief?
I was going to ask why the OP didn't just buy an affordable iron instead of trying to hack a tip from a high end unit. But I thought about it and restrained myself for a few hours.

#### Dodgydave

Joined Jun 22, 2012
8,469
Pins 1,2 are the heater, supply 24V to heat it up, check the pdf you uploaded, pins 3,4 sensor.

If you get it to heat up, you will need make a thermocouple amp and pwm controller to maintain the temperature.

#### MrAl

Joined Jun 17, 2014
6,610
Hi,

These iron tips are fast acting and high quality. I have a variety of irons, but none as fine and balanced as this one. I am soldering surface mount components, with very small pins and gaps.

C.
Hello again,

As HP was saying, and i had forgotten this myself with these irons, is that one type of heat sensor puts out an actual voltage (generates a voltage due to the thermal effect on the material) and the other does not put out a voltage but changes resistance. So the two main types of sensors are:
1. Puts out a voltage, although it is usually below 1v.
2. Changes resistance.

The one that puts out a voltage is called a themocouple. It puts out very low votlages like 10mv, 20mv, maybe up to 200mv or so but i'd have to look that up now. At 350 degrees C, it should go up to 200mv i think but you can look that up too for the type K or other thermocouple.
In any case, as the tip heats up you will see the voltage rise from near 0.000 to something like 10mv, then 20mv, then 100mv, etc. That will tell you it is a thermocouple.
On the other hand, if the voltage does not go up that high then it may be a thermistor type. The resistance of many irons is around 20 to 50 ohms or something like that, but this type will change resistance as the temperature goes up. You'll see it start at some resistance, then either go up or down depending on the type of thermistor.
Unfortunately there is a lot of room for variance here, because we dont know what kind of sensor they are using an there are a bunch of different kinds.
Some irons come apart so you can see the element inside. The sensor is usually built in but this one may be different.

It's hard to say what the element resistance will measure because it depends how they are driving it, and what the maximum power rating is for that element. They could be using AC too as many irons these days do. They control the temperature with a triac which turns the AC on and off. This one could use AC or DC, we dont know that either.

You might have to find some data on this. If not it may be hard to figure out unless you can make measurements with the iron in regular use. There are a lot of variables here.

1. Runs on AC or DC voltage, or both?
2. What level voltage?
3. What kind of sensor, resistive or thermocouple?
4. What max power level?
5. Max tip temperature?

#### camerart

Joined Feb 25, 2013
1,700
Respectfully, you're missing the point -- As I stated in post #3 -- a thermoelectric sensor (e.g. thermocouple) produces an EMF (non-linearly) proportional to a temperature difference (for these purposes think 'thermal battery') -- If the sensor is indeed producing EMF ('voltage', if you will) the resistance reading will be inaccurate - hence my suggestion...

Best regards
HP
HP,

Yes, I did miss your point. Zeros all round so not a thermocouple.

Thanks, C

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
Zeros all round so not a thermocouple.
Ok, then...

The 'cold' readings suggest that each 'device' (i.e. heater and sensor) are common to ground -- Hence R(tip to ring) = 1.9Ω+1.1Ω= However the 'Hot' readings are inconsistent with this in that we would expect a tip to ring resistance of 6.3Ω+0Ω=6.3Ω ≠5.6Ω) -- A discrepancy of 700mΩ (~11%) is not insignificant!

FWIW I suspect that the discrepancy owes to insufficient test temperature regulation - and (owing to the apparently negative temp coefficient) that the sensor is between tip and ground) -- that said - please don't act upon my latter 'hunch' at this time!

Please double check the 'hot' resistances. -- Additionally, please verify that the resistance readings are independent of polarity (i.e. test them 'each direction')

Best regards and please keep us posted
HP

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
@R!f@@ --- I apologize should I seem to have 'stepped' on your post --- I found it necessary to delete and resubmit my response owing to 'intractable' HTML errors

Contritely
HP

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#### R!f@@

Joined Apr 2, 2009
9,682
No worries HP.
Just thought it would throw some info to OP