I would chime in with everybody suggesting that the fan failed (due to mechanical stress, maybe).
Last year I started tracing a similar 858D rework station (without the soldering iron part). In my station (which looks very similar) the transformer creates 10V and 30V (both AC). The 30V are then used to power the fan. In the end I measured about 28V at the terminal for the fan that is rated for 24V. I guess constant overloading will take its toll.
If you are interested have a look at the pictures from my teardown and my reverse engineered schematics:
https://blog.enbewe.de/tags/858d/
What caused David2's Yihau/WEP 898D+ SMD rework station to literally melt down?
Autopsy time.
Dave please stay away from crappy soldering stations or your building insurance will cancel your contract.
No Wellers and other crap anymore. Play safe !
My theory:
If air isn't flowing then the sensor can't measure the temperature of the heating element correctly - it's a couple of centimeters away from it.
That was my first thought as well. Wondering what temperature it's able to measure when the fan is off compared to when it's on, would be interesting. Surely even if air was not flowing, the air temperature around the sensor must have gotten pretty high...
It's a very lousy design anyway. Doesn't seem to have been tested if the fan fails. No detection of fan failure. No additional protection from overheating.
I happen to have an Atten 858D+, don't know if it's any better. It looks very similar. I'll be cautious when using it now.
My Youyue 858D+ can dish out up to 33V to the 24V fan... don't use it at full speed!
They're just hair dryer heating elements. I measure:
120V 6.1A 19.8 ohms; 727W.
240V 3.4A 71.6 ohms, 805W.
That generic heatsink I've measured 32°C/W and the usual rule of thumb for TRIAC/SSR dissipation is 1W per amp.
40% heater duty cycle gives over 100°C so I could see a heat issue for 120V systems where the TRIAC runs hotter.
I've added a GFI powerbar to my workbench, I wonder if Dave has one.
This is a repost of my schematic for the Youyue 858D+, including the wrong switched neutral, which was fixed.
Why not try to power the fan, to see if it works correctly?
It's 'Yihua', not 'Yihau'. many people likely won't see this video when searching before buying this station.
These kind of system should check the current to the fan. If excessive current or no current is detected : shut down the heater.
That way if the fan fails short or open, the heater will shut down. all that is required is a small resistor and a sense amp. the micro can do the rest.
I am wondering why people still use triac's for this kind of stuff these days ... stick a mosfet in a bridge rectifier and you have much better control.
- you can switch on much closer to at zero cross.
- you can turn off at any point in time.
- you create less electrical noise due to phase chopping
- your load does not get hammered with 'hard' voltage spikes every time , it gets a nice clean ramp-up
Here are some fan current waveforms. Easy to pick off with a data slicer and very expensive LM358
Another EEVblog member instead made an analog voltage for RPM. Typically 200-600Hz. There is a 1/f relationship to RPM and I think it's a 4-pole motor.
But one problem I found adding a digital tach to the fan circuit, is the MCU needs another timer/counter to measure RPM. Arduino ATMega328P is already busy doing LED mux and PID so it would be a bit of work.
Easier to go bluepill or ATMega328PB, then you want a better display, and it never ends...
These kind of system should check the current to the fan. If excessive current or no current is detected : shut down the heater.
That way if the fan fails short or open, the heater will shut down. all that is required is a small resistor and a sense amp. the micro can do the rest.
Easier, cheaper, and ultimately more reliable would be a simple thermal cutout mechanically bonded to the metal tube part of the handle.
Then if the tube gets hot enough to melt the plastic handle, for any reason, the device would positively shut down.
These kind of system should check the current to the fan. If excessive current or no current is detected : shut down the heater.
That way if the fan fails short or open, the heater will shut down. all that is required is a small resistor and a sense amp. the micro can do the rest.
Easier, cheaper, and ultimately more reliable would be a simple thermal cutout mechanically bonded to the metal tube part of the handle.
Then if the tube gets hot enough to melt the plastic handle, for any reason, the device would positively shut down.
That's how decent stations are made. They have thermal fuse just before the heater. If heater is powered without airflow, it will be simply disconnected.
I am wondering why people still use triac's for this kind of stuff these days ... stick a mosfet in a bridge rectifier and you have much better control.
- you can switch on much closer to at zero cross.
- you can turn off at any point in time.
- you create less electrical noise due to phase chopping
- your load does not get hammered with 'hard' voltage spikes every time , it gets a nice clean ramp-up
One word: cost. It's switching a resistance heater in this application, no need for extra complexity... and if the MOSFET shorts out, you have the same problem.
Not just soldering irons. Fans fail, sensors go bad, circuits short out and chips fail. Redundant safety devices are necessary!
I have seen fans fail to blow but still happily draw reasonable current. With a blocked inlet or stuck rotor, the fan will still draw power. Once found a cheap fan where the fan blades had become disconnected from the motor. A friction fit had failed.
The heater current drops during operation. Initial resistance of a cold heater will be highest, and the fuse will be sized accordingly to limit nuisance failures. The heater would not overload the fuse unless the ceramic support failed allowing the heater element to short.
To prevent a fire, a thermal fuse would be added in circuit with the heater. Best location would be in the power lead that goes through the center of the ceramic to the far end of the element. Value would be much higher than normal operating temperatures, but well below meltdown. Without this I doubt the device is actually CE rated.
Dave, please check: is there is a thermal fuse? It may have been ignored as it doesn't affect normal operation.
I was browsing Yihua's website for a bit after watching this video. It seems they were already aware of this failure mode (fan dead, hot air fries itself). Contrary to the older models, some (not all) of the more recent models actually have the following listed as a feature:
Protection function for air gun fan malfunction: at the process of using the air gun, the air gun features shutoff protection functionality that automatically turns off the heating element when the fan is stopped to protect handle and ensure safe operation.
Good to know they already figured out this was a potential issue and "fixed" it. YIIHUAAA!! (Sorry, couldn't resist.) Not so good is that this probably means quite a few people almost burned down the house.
Example:
http://yihua-gz.com/Products_detail.asp?id=811