Hakko clone (Yihua 936) thermal conductivity

[Crumble]

Hi all,

I might be starting something here that has already been told a thousand times, but I couldn't find it. It's about the Yihua 936 clone and its thermal performance. I used a cheap HQ brand soldering station (must have been €50-100) for years, but after seeing a video of bigclivedotcom (below) I decided to buy a cheap chinese soldering station as a spare and to test how it worked. I had few  little issues with the HQ brand one, but nothing major. One of them was a wire had come loose and heated the grip quite considerably. I was able to fix that before major problems occurred. Secondly, the tip had corroded solidly onto the element, so I knew that if it failed I would have to find a replacement iron too, but had no confirmed source of them because searching for HQ on internet turns up al LOT of products (eventually I found one on a Dutch website).

After a while the soldering station did break down (element went open circuit) and I started using the Yihua one. I had actually "calibrated" the soldering iron with the Hakko clone soldering iron thermometer bigclive had mentioned (at ~12:55 in the below video). It took quite some adjustments, it was initially 100°C high, and my HQ one even more.

It did solder quite a lot less satisfatory, especially on big joints, so I decided to investigate and experiment with it, I had little to lose. Given the fact the temperature it got up to the same value and was reasonably stable it seemed to quite inresponsive. Even when cooling the tip down with some water the duty cycle of the heating element did not obviously increase, implying the thermal coupling was not optimal. This was not surprising because the tip had quite some play in it. Clive seemed to have little issue with it and just used a big bit which could store more heat, I was less tolerant and found some connections to be hard to make, especially when using my (smaller) tip on it.

To remedy it I tried to add a layer of thin 0,1mm copper foil between element and tip. I added a small amount of ceramic grease (with a 1500°C rating) to increase coupling even further (and aid the rather tight assembly). This however had little noticable effect, so I returned to just soldering more patiently and preparing for just buying a new element for my previous soldering iron, assuming the tip was just not made of a thermally conductive material. I had no thermal camera, because I was actually quite curious about the temperature distribution in the tip. I did order a new soldering iron (w/o station though) to be able to use different tips. The tip was quite stuck to the element so I could not remove it anymore and thus required a new soldering iron.

Afterwards I wanted to try the copper foil method again with the other element too. It turned out it was different, the element is ceramic externally instead of metal and it shattered when I was forcing a sleeve over it. It turns out the resistive wire is around a central rod, but there was no fill of ceramic cement at all in this one, so it does not actually physically touch the outer shell:



Does anyone have any experience with improving thermal conductivity between element and tip? Is it possible to obtain the ceramic cement that is being used to fill the element here in the EU? I'll probably switch back to the other soldering iron once I get the spares, but I like experimenting to check if a reasonable solution is possible. Right now I can't solder on large pads without bumping the temp up quite considerably (I went up to 450°C at times). There may have been topics about this before, I just could not find them.

[DBecker]

That's an old heater element design, using nichrome wire wound over a pre-fired ceramic rod and sleeve.

Modern designs use a zig-zag foil embedded close to the surface of the ceramic rod, which is then fired to seal it.  This has better thermal coupling, and the sealed foil can be an alloy that changes resistance less with temperature. There is also much less inductance and a minimal magnetic field since it's essentially one or even 'zero' turns.  (Squint at the old design and try to distinguish it from a 'ceramic core inductor' or 'electromagnet'.)

Cheap heating elements are notorious for being under-sized, and cheap tips for being oversized.  It doesn't seem to cost more to buy better heating elements and tips with inner sleeves, but you'll need to get lucky with where you buy.

[Crumble]

That's interesting to know, is there a way of telling from the outside? Probably not... Personally I'm not that worried about inductance with 50Hz, you'll need a hell of a lot of inductance to make a difference (or a large diameter to create any decent fields). Thermal coupling seems to be the downfall with this soldering iron, which I think is a pity (but hey, the iron was $3,15 ).

Further teardown photos: the element seems to be different from the one Clive took to bits. It lacks the thermal cement, but the resistance wire seems to be spot welded rather than just twisted together, which seems more reliable. It lacks the metal outside of the other element, but this should be inconsequential. It does seem not all 936 clones are the same.

Fully exposed element w/o twisted together part



Spot weld in sleeve

[DBecker]

You can sometimes see the foil pattern on the heating element surface, especially after installing tips highlights the surface texture.

[xavier60]

The 936a clones that are advertised to use the Japanese heater have much better performance. Like this one, http://www.ebay.com.au/itm/60W-SOLDERING-IRON-STATION-Japanese-Heating-Element-Digital-ESD-Safe-YH936A-/261507553932?epid=720876893&hash=item3ce3109a8c:g:qAkAAOSwd4tT0ytH
A common problem is that the nut that attaches the tip holder to the handle is weak. I reinforce it with polyester thread and epoxy.

[Crumble]

Ow, thats interesting... I did not know that. I am struggling to find a seller for the tip alone though (and one that ships to NL). While searching for "Japanese 936" I did find an interesting comment on one of the reviews for the "generic" one:

Excellent soldering iron for its price

Pro:

- Very fast heating, comfortable.
- Outperforms my much more expensive Solomon SL-NI iron (with Solomon SL-20 station).
- That 936 iron is compatible with my Solomon SL-20 station, although internal trimming of the station was required to give accurate temperature control and reading (without trimming the station, the temperature value was off by about 100*C).


Contra (all of them are admissible for the price, and can be fixed):

- Need to buy a new tip, because the accessory tip is made of steel (not steel coated copper, which is normal; this one is steel in the whole cross section, with missing copper tube insert in the hole).
- Cable is not heat resistant, have to be careful not to melt it (my Solomon SL-NI iron's cable also not heat resistant for 3 times this price, so not a problem)
- heating element (or its wires) is shorter by about 4mm than needed: the point of the heating element (which contains the heat sensor) doesn't reach the bottom of the hole in the tip (at least with the accessory tip, I haven't received the desired copper-cored replacement yet), so doesn't measure the tip temperature accurately, it measures the heating element's temperature instead. More accurate temperature control can be achieved by letting the end of the heating element touch the bottom of the tip's hole. I've managed to achieve this by filing off 4mm from the adapter's plastic nut, letting it screwed 4mm further into the handle. Now it works significantly better.

A new one is on its way, hopefully it will be better. I might be able to experiment with that one (hopefully not breaking it like this one).

[4CX35000]

Does anyone have any experience with improving thermal conductivity between element and tip? Is it possible to obtain the ceramic cement that is being used to fill the element here in the EU? I'll probably switch back to the other soldering iron once I get the spares, but I like experimenting to check if a reasonable solution is possible. Right now I can't solder on large pads without bumping the temp up quite considerably (I went up to 450°C at times). There may have been topics about this before, I just could not find them.

I have a Katsu 936D for everyday usage which is the digital version of your solder station. I tend to leave it running for most of the day and do all sorts of soldering so the iron tends to live a varied life. Knowing how I work, I decided to buy several cheap irons and bits from eBay (HK and China) with the attitude that if they get damaged then they are easy and cheap to replace. The downside is the thermal conductivity can vary and the iron lead is a little short, but it is good enough for the majority of work I do which is a mix of R&D Prototyping.

I have the temperature set to 350C which works fine for my speed of soldering and for the majority of soldering it is acceptable, but it does perform poorly when soldering something large such as chassis connector or transformer tapping and this down to the poor thermal conductivity as the controller is not being pushed hard to produce more heat, this can be easily seen on the digital version.

I did think of using a small pen type metal spring and shortening it to be long enough to make contact between the ceramic rod and the tip itself. If time allows over the weekend I will see if I can find some pens and see if it will work.

For more professional work I have a high quality Weller which has excellent performance, but the bits can be expensive and I wouldn't want to use that for everyday use. For the larger connections and thick wire I have a very powerful Antex 100 watt iron.

So my attitude is to use the cheap Katsu everyday and save the Weller for high quality work.

[Crumble]

I must admit I'm being a little bit cheap here. I know soldering irons like this have disadvantages, I'm just trying to get the most out of it. Unfortunately I have no alternative soldering iron right now, but I might just invest in better gear. I am having issues I find myself heating up joints to far or too hot, especially when using braid (which sucks away heat quite dramatically) on prototyping boards. In such cases you need something with large thermal mass or quick response times. I heard very good stories about JBC soldering stations, but these can easily cost €400, which is quite steep for hobbying. Unfortunately the irons from China seem to differ in quality so you'll never know what you'll get (which is quite often the issue with cheap stuff).

[DBecker]

The low-end "936" types are amazing for the price.  For only a few dollars you can get close to the performance of a top-level iron from two technology generations ago.  Replacement parts are very inexpensive.  It costs only a few dollars to get a set of tips to find out which you prefer for different use cases.  But there are multiple combinations thermal sensor types and heater voltages, and plenty of poor quality parts advertised exactly the same as good parts.

The next step up is the 'T12' type.  This design is only one generation old, with much better thermal coupling between the sensor, heater and tip. That results in better temperature control, even with a simple thermostatic controller.  Parts costs more than the '936' types, especially if you want a complete selection of tips, but they are still quite reasonable.  A big plus is that there are far fewer bad quality clones and a single thermal sensor type -- this alone is worth the extra cost.

[daybyter]

[xavier60]

I have been stuffing alfoil up inside the tip to fill in the space at the end of the sensor. It doesn't seem to make much difference.

[Crumble]

@DBecker: Certainly interesting, I may do the pencil/copper paste trick.

I am seeing two issues though:

• Tips are sometimes made of steel as in the comment I quoted. I tested the one I received with one of the irons and it seems to have been made of some kind of (slightly soft) steel all the way through, while another one I tested that came in a set of 5 had a rather thick layer (>0,5mm) of steel around a copper coloured base.
• At least one type of element seems to be hollow, obstructing heat flow.

It looks like it's un unknown if either issue exists. I'll just order another one and will let you guys know if it is any better. Might be a while though. ;-)

[DBecker]

With cheap tips I check that they are somewhat attracted a magnet to verify that they are iron plated, then cut a notch to verify that they are copper cored.  Almost all have been copper with a substantial iron plating. 

A 936 type iron has the heating conductors near the surface of the ceramic element.  The tips conduct heat from the sides, and needs a snug fit or an intermediate sleeve.  Other irons have a heat-conducting metal core with externally wrapped with exposed nichrome wire.  That end of that core need good contact with the tip, sometimes achieved with a spring-loaded sleeve or heating element..

[Crumble]

Yeah, just the one that came with the iron was not. I filed through it for quite a bit, and no copper appeared.

I understand what you are saying, but clive's had the element wire poured in with ceramic cement and therefore was mechanically connected with the element. I had already added a rather tight sleeve made of 0,1mm copper foil between the element and the tip and performance was still poor. When I took the newer iron apart I found that its element was just inside a cavity without any fill of cement, creating a barrier. So the iron I photographed here is different from either of the options you mentioned.

I would not have known this without destroying it and I have no idea if the other iron is the same (it just has poor performance. IMO this cavity will be the one single greatest barrier of heat flow in the unit, and I am looking for a way of finding how the iron is constructed without destroying it. Right now I'm just going to order a new one and see if it performs any better. When using the sponge to cool the tip the duty cycle should change noticably, but right now it just doesn't.

[Crumble]

Ok, next chapter in the Yihua soldering iron saga: I got the new one. This one had a ceramic element and an iron tip. I found the element tip to be about 0,5cm shorter than the cavity in the tip, so thermal contact was bound to be quite poor. Additionally, it has the "traditional" ~0,1mm play around the element, reducing hopes it will make decent thermal contact with the element. While playing with it, I found the ceramic sleeve over the resistance wire to be removed quite easily, revealing the resistor wire. It turns out the tip is not filled with ceramic cement after all, it is just the tip that seems top be closed off with it (this might also have been the case with the previous iron, but I broke it before I "experimented it off"). Hardly any cement seems to have gone into the element, it just seems to have closed of the tip and fixed the thermocouple.



Inside of the ceramic tube there were some remains of the cement, but very little. The wire does not seem to have been covered in it at all and a little seems to have been present at the bottom.



I am starting to give up any hope of finding a well-made unit I can reasonably alter to give greater thermal performance. Eventually, I'll probably buy a decent soldering station, this stuff seems to be quite poorly and inconsistently made. It's a shame, because the thermal performance would have been greatly increased if a) the tips supplied were actually made of copper and b) some effort was put into making the thermal contact better. The former can easily be arranged, seperate tips are often copper, but the latter is difficult to remedy, especially when it is essentially glued shut. The basis is there, but it seems to have been made in a hurry and at least two thermal barriers are left, causing poor performance.