Temperature controlled iron with a variable wattage station?

[FenderBender]

Hello,

I have a Weller WLC100 variable wattage soldering station. I took it apart. It's essentially just a light dimmer. Woohoo...

WLC100- http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=037103059963

It came with a non-temperature controlled iron- http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=037103191151


Well the iron seems to be loosing it's ability to heat up quickly, so I thought instead of replacing it with the standard iron, would it be of any benefit to replace it with a temperature controlled iron like this- http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=037103593610


The station varies wattage by varying voltage. Current is constant I believe??


Any opinions? The question I have is: What exactly does temperature controlled mean? If it's supposed to keep the tip at 850degrees F, and it's only getting a set voltage, will it subsequently draw more current to make up for it? I guess I'm just confused as to what the definition of temperature controlled is, for an iron, not a station.

Thanks.

[cybergibbons]

Variable wattage is a bit of a compromise. As it says, it varies the power to the heater. For small tasks, you generally need less power than large ones. But the tip will heat up when not used and then cool down as soon as you use it i.e. it doesn't respond to the power required to maintain a given temperature.

The Weller WP35 is a fixed temperature iron i.e. it uses some form of feedback to maintain a fixed non-adjustable temperature. This is 450degC i.e. way too hot for most electronic work. It is meant for stained glass and the like.

I'd either just replace the heater (which may be failing), or get a decent temperature controlled iron (Hakko FX-888 seems to be popular), or better still, go with Metcal and stop caring about temperature.

[FenderBender]

I understand what you are saying, but if I had it attached to my variable wattage station, would the WP35 not be adjustable accordingly?

Or does temperature controlled mean at a fixed temperature, not just temperature stabilization?

Thanks.

[IanB]

What exactly does temperature controlled mean?

Usually it works together with the base. There is some kind of temperature sensor at the tip that connects to a feedback control circuit in the base station. When the tip cools down more power is supplied and when the tip heats up less power is supplied. Ideally the tip would remain at a constant temperature all the time, but in practical irons there is some variation. More expensive irons are able to control the tip temperature more precisely and minimize temperature variations.

However, for the home user you don't need such precision. I have an FX-888 and it is more than adequate for any typical soldering task.

[FenderBender]

What exactly does temperature controlled mean?

Usually it works together with the base. There is some kind of temperature sensor at the tip that connects to a feedback control circuit in the base station. When the tip cools down more power is supplied and when the tip heats up less power is supplied. Ideally the tip would remain at a constant temperature all the time, but in practical irons there is some variation. More expensive irons are able to control the tip temperature more precisely and minimize temperature variations.

However, for the home user you don't need such precision. I have an FX-888 and it is more than adequate for any typical soldering task.

Yeah usually I would think temperature controlled would mean it communicates with the station to monitor tip temperature and supply power accordingly.

However- the WP35 is a 120V unit with a standard 3-prong plug, nothing fancy like you see on the Hakkos or others. So the feedback is sort of internal to the iron...So if I feed a variable voltage into the WP35 temperature controlled iron...what happens? Does it stabilize tip temperature, but not at one particular temperature? Is that possible? I presume they use some sort of PTC/NTC?

[IanB]

However- the WP35 is a 120V unit with a standard 3-prong plug, nothing fancy like you see on the Hakkos or others. So the feedback is sort of internal to the iron...So if I feed a variable voltage into the WP35 temperature controlled iron...what happens? Does it stabilize tip temperature, but not at one particular temperature? Is that possible? I presume they use some sort of PTC/NTC?

It's not likely to work. A typical control loop acts as a buffer, separating the thing to be controlled from external influences. So for example a temperature control loop will try to maintain a constant temperature of say 450°C in spite of variations in supply voltage. That's its job: "keep the temperature at 450°C no matter what". So if you reduce the supply voltage, or feed it with a dimmer circuit, it will simply think the world is conspiring against it and it will try to compensate by drawing more current to make up for the lower voltage. If it does everything it can and it still can't make 450°C it will drop out of control and let the temperature fall. Now you will have an unregulated system and the temperature could vary all over the place.

What you need to do in control theory to get different temperatures is have access to the temperature control set point. This is what the control dial does on the base station of a temperature controlled iron. If the iron has a fixed temperature and no control dial, then it can only operate at the temperature it was preset at by the factory.

[FenderBender]

However- the WP35 is a 120V unit with a standard 3-prong plug, nothing fancy like you see on the Hakkos or others. So the feedback is sort of internal to the iron...So if I feed a variable voltage into the WP35 temperature controlled iron...what happens? Does it stabilize tip temperature, but not at one particular temperature? Is that possible? I presume they use some sort of PTC/NTC?

It's not likely to work. A typical control loop acts as a buffer, separating the thing to be controlled from external influences. So for example a temperature control loop will try to maintain a constant temperature of say 450°C in spite of variations in supply voltage. That's its job: "keep the temperature at 450°C no matter what". So if you reduce the supply voltage, or feed it with a dimmer circuit, it will simply think the world is conspiring against it and it will try to compensate by drawing more current to make up for the lower voltage. If it does everything it can and it still can't make 450°C it will drop out of control and let the temperature fall. Now you will have an unregulated system and the temperature could vary all over the place.

What you need to do in control theory to get different temperatures is have access to the temperature control set point. This is what the control dial does on the base station of a temperature controlled iron. If the iron has a fixed temperature and no control dial, then it can only operate at the temperature it was preset at by the factory.

Thanks. Yeah I mentioned before, I thought that it might just start drawing a crapton of current to compensate.

I wasn't sure if the temperature control on these irons was set or not. I guess it is. Might have to go with one of those Attens or rip off Hakkos...Or I could just get a new heater....hmmmmm

[saturation]

This type of iron maybe of an old style technology for fixed temp irons using a metal strip thermocouple in the handle, preadjusted for the iron's tip, ~ 700F.   Its simply a temperature sensitive on/off switch directly attached to line voltage and a resistive heating element almost like you'd find in clothes dryers of old.

Theoretically, if you attach it to a low cost station with a rheostat or triac as a variable output voltage source or adjustable duty cycle, it should reduce the temp output accordingly, but at an unknown temperature, you'll have to wing it.  At low settings, the iron will be underpowered, so the thermocouple is always closed, in a futile attempt to heat up the iron.  Also, there is no feedback from this too, so if the tip is cool or too hot from various heat loads, the station output will not compensate, you'd have to do that by hand. 

Without the station, there is feedback, as the tip cools from soldering the thermocouple will close to allow the tip to heat up, and it opens to limit the maximum tip temp.

The difference between this old style temp control and the soldering stations is the speed of the response to temperature changes, the tightness of the feedback loop, and lower operating voltage; the plug in wall irons run at line voltage.

Low cost as it is, its very likely using a resistive heating element, in which case the output power is reduced with reduced volts or duty cycle.

[FenderBender]

Thank you.

Well I bought this when I was naive...well more naive.

Even Sparkfun has a 936 knock off...

http://www.sparkfun.com/products/10707

Might look into that one since they actually give you an internal shot. How nice of them.

Brass sponge. Nice. Build would have to conform to US regulations I think? Local shipping.

I don't know. Looks like a win win, unless you don't live in the US. Then China all the way baby.

[saturation]

You're welcome.  I see the Weller WP35 is ~ $35-50!  You're better off with a Hakko clone like Sparkfuns, or any others.  It may perform <= Hakko but the whole station cost as much as a the WP35, and likely will be better than the WP35.  Buy a Chinese brand from a vendor or brand name with some reputation so there's a better bet its reliable and won't break in a few months.

Thank you.

Well I bought this when I was naive...well more naive.

Even Sparkfun has a 936 knock off...

http://www.sparkfun.com/products/10707

Might look into that one since they actually give you an internal shot. How nice of them.

Brass sponge. Nice. Build would have to conform to US regulations I think? Local shipping.

I don't know. Looks like a win win, unless you don't live in the US. Then China all the way baby.

[cybergibbons]

Why do you care what heating profile a soldering iron has to get up to temperature? You care about how it behaves once at temperature.

I've been using Metcal station for a good few years now, and really have never felt the need to alter temperature. A lot of people who spend their working day doing rework also prefer them.