Temperature controlled iron - no sensor

[Simon]

So I bought a Tenma temperature controlled soldering iron, took the iron apart, no sensor..... unless I'm missing something. so how is it regulating ? I put it in water and it ran full power, I tried to solder a large plane and it would not cope but it did not ramp the power up anyway like it did in water. So what is the crack, is this thing a fraud or not ?

[DL8RI]

If I had to guess, I'd say: 4-Wire-Measurement over the heater.
As I googled it has a 5-Pin-Connector, so one GND, two heating-power and two heating-sense.

Does it have two additional wires on the bottom-side?

[Simon]

only 3 wires come off the cable so unless the element resistance is temperature dependent. But that means that not only the tip must suffer a temperature loss but also the element, very poor.

[DL8RI]

very poor.

Well, that's to be expected. It's a very cheap station, so there have to be compromises.
In this price-region I'd rather stick to the mentioned Weller TCPs, regulated by the curie-temperature of the tip.

If it only has three wires, maybe they "pulse" it, like Dawgie suggested. You could look at it with a scope. On the other Hand it's not worth it.

[Simon]

Well they are probably current sensing the power to the tip, I'll investigate later

[NiHaoMike]

Tear down the control box.

[Zero999]

Tear down the control box.

Do this. I have a "temperature controlled" iron from Maplin and it's just a phase controlled lamp dimmer circuit with no feed back.

[Simon]

Yea I'm toying with the idea of ringing farnell up to tell them what a heap of shit they are selling and to take it back or to pull the thing apart on camera and expose it for the heap of shit it is so people are warned.

[Simon]

yea that is the one, sure it may have a pid system but it's taking an input from the wrong place, there are bad reviews of it elsewhere as well.

[Refrigerator]

3 wires you say? 
maybe it's like this:
1 = GND.
2 = power.
3 = sensor feedback.
They probably put a common GND between the sensor and the heating element. 

[Towger]

It could use something like a DS18B20. Can you see data coming backs from it?
There have been loads of these irons sold as faulty returns on eBay.

[pickle9000]

Schematic on the following thread (I think). Looks the same.

https://www.eevblog.com/forum/reviews/atten-938d-soldering-station/

[Simon]

yea that is the same model, just rebadged

[pickle9000]

So have you tried the iron out?

60 watts is up there so the warm up / recovery time should be pretty low. Replacement elements are cheap.

I have a couple Chinese stations (technically 3) here (Among things I took home when I retired). The biggest fault are the handle / cord assy and temp display accuracy. Cords are way to stiff and you really do need to open them up and make sure that they are soldered correctly. That said I haven't had any problems with any them. They where originally purchased through a Canadian seller so that may factor in. All over 3 years old and have a few hundred hours on each. The one branded Gordak looks pretty well built.

Anyway the good thing about Chinese stuff is that you can get parts, the bad part is that you may need them.   

[Simon]

yea, it won't react to a large ground plane, despite not being able to melt the solder the power graph does not go up much because the temp sensing is too far from the tip.

[Simon]

I checked the power unit, they have bridged the connectors so that what would be a sensing line is also the main power, probably so that they can use various irons

[nctnico]

yea, it won't react to a large ground plane, despite not being able to melt the solder the power graph does not go up much because the temp sensing is too far from the tip.

Your tip is probably way too small. If you want to solder to a ground plane you need a big tip like 4mm or 5mm wide and an 80W iron. My Ersa irons also use a 2 or 3 wire scheme to control the temperature.

[pickle9000]

One of the most under-appreciated bit's of soldering gear is a preheater. Even with a 30 watt iron you can get amazing things done. For proper rework it's pretty much a must.

The bigger the tip the better.

[sleemanj]

I think I saw some posts regarding a sensor-less element in the Dangerous Prototypes thread recently, wasn't paying much attention just happened to see them in the recent posts...
http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=2457&start=660#p56921

[neslekkim]

Build this project and put in that case, i think it's the same enclosure: http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=5264

[Zero999]

Interestingly that thread lists one of the Hakko models as having a sensor in series with the element.

This doesn't apply to the Hakko FX888D,m which has a separate sensor and in my experience melts solder well, even at low temperatures. I use leaded solder, have it set to 250^oC and it works perfectly.
http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Tools/fx888d.pdf

I'd recommend it, even though it's difficult/impossible to get hold of a 230V version so it needs to be run off a transformer in the UK, it's worth it.

[saturation]

My guess is this has a PTC ceramic heating element.  This is the kind used for hair dryers etc., and is self regulating.  Thus, what determines the heat output is proportionate to the power applied.  However, these elements are nonlinear and imprecise, e.g. not IPC level soldering iron quality.

http://www.sunlead.com.tw/p1.htm

[Simon]

Interestingly that thread lists one of the Hakko models as having a sensor in series with the element.

This doesn't apply to the Hakko FX888D,m which has a separate sensor and in my experience melts solder well, even at low temperatures. I use leaded solder, have it set to 250^oC and it works perfectly.
http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Tools/fx888d.pdf

I'd recommend it, even though it's difficult/impossible to get hold of a 230V version so it needs to be run off a transformer in the UK, it's worth it.

Well I'm looking to sort that one out, there is a UK distributor but they just have a basic html website and no way of buying online so I'm looking at bulk buying from them and redistributing, knock this tenma shit out of the water

[Zero999]

Well I'm looking to sort that one out, there is a UK distributor but they just have a basic html website and no way of buying online so I'm looking at bulk buying from them and redistributing, knock this tenma shit out of the water

Good luck with that. If all else fails how about ordering a large batch from the US and bundling them with transformer to sell to those in the UK?

[Simon]

Price has to work and most people making impulse buys will prefer no transformer