Arduino upgrade of a Weller VP800 desoldering station  - Page 1
Forum section: electronics / repair

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: January 16, 2017, 09:36:27 pm
content: Hi All,After spending a significant amount of time trying to fix the Weller VP800 desoldering station thata friend gave mehttps://www.eevblog.com/forum/repair/need-help-for-fixing-a-weller-vp800-desoldering-station/msg1086390/#msg1086390It was working, but not in a very satisfying manner. It was not heating fast enough, and the examination of the triacoutput with the scope did not gave very clean signal.Some other problem is that the triac driver, a SL443A, is no longer available, and the ones found on ebay arerefurbished and maybe not very reliable.So I decided to completely change the electronic part of the VP800.The new design comprises an arduino micro pro (so that it fits on the board),a zero crossing optocoupler (MOC3083), a triac (L4008L6, but it could be another one), and a few resistors.After looking for multiple designs, I end up with the most simple one.The actual temperature of the iron (T) is measured at an analog input of the arduinowith a voltage divisor with a 100 ohm resistor in series with the sensor of the heating element (resistor from 20 to 60 ohm).another analog input pin is used for the potentiometer of the Weller to set the wanted temperature (T0).The program on the arduino isif (T < T0 ) turn the triac ONelse turn the triac OFF.ON/OFF is forwarded to an output pin that is connected to the optocoupler.Thats all.All this could fit on a stripboard that can be put in place of the previous board.I just added an additional power supply to get DC 5 V from the AC 27 V provided by the transformer.As I had the arduino, I added a small oled display that I could fit in the Weller front panel to show the values of T and T0.The nice thing with MCU, is that you do not have to tune precisely everything.You make it.Then you evaluate the output, and then fit the parameters with least square to get the desired output scale.I could measure the temperature of the iron with a cheap clone of Hakko temperature tester.It took me a couple of hours and now everything is working, and the heating is much faster than before, so I am quitepleased by the result.The regulation of the temperature is perfect for my needs.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: January 19, 2017, 04:55:39 pm
content: This is the correspondence beetween the temperature requestedwith the original Weller pot knob and the T0 temperature displayed (Celsius)Pot T0400 400350 365300 295250 242200 181150 124100 7550 50Correspondence between the displayed actual temperature (T) and the measured temperature withthe clone of Hakko FG-100 (Tm), after verification of the behaviour of the measure with an other soldering iron (Celsius) .T Tm400 387350 361300 300250 265200 205150 150100 9050 47

author: Vtile
author_rank: Super Contributor
timestamp: January 19, 2017, 10:13:18 pm
content: So your control logic drives the Power/Triac to heater element when the sensor noticed that the tip of the iron is below set value. I don't see upper limit at all or any kind of heat control. Maybe I'm not just mis-understood the setup (I did not read the older thread, since I'm "closing the computer to get some sleep").If I'm understood your intentions correctly you do want to create bang-bang controller, you need to have also upper turn-off limit or ON have only certain time. Need some sleep now.PS.. I need that sleep... Arduino obviously do not have latched outputs.PPS. On the otherhand it now might be a nice 100k..500kHz oscillator depending the Arduino program sweep time and the lag which the mass of the heated system creates.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: January 19, 2017, 10:43:44 pm
content: This is the main part of the codeQuoteThere wont be any 100khz loop as the oled refresh is quite slow. So there is a natural delayin the loop.The mass of the desoldering iron tip provides also some inertia.It works well.I dont see any need for more complicated.

author: Vtile
author_rank: Super Contributor
timestamp: January 20, 2017, 01:12:29 pm
content: Oh, don't take me wrong I think this is cool repair/upgrade.Even better if it doesn't have problems and you were already aware of the possible shortcomings of the controller loop.

author: Kjelt
author_rank: Super Contributor
timestamp: January 20, 2017, 01:32:58 pm
content: Quote from: JacquesBBB on January 16, 2017, 09:36:27 pmAre you sure that is not inherent on the design. I have the old Weller desolder iron and it is sluggish/slow as hell compared to my new WX desoldering iron.Heating up to 350oC will take 2 to 3 minutes with the old design (50W and a lot of iron to heat) and 30 seconds with the new one (120W and lean design).

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: January 20, 2017, 02:48:34 pm
content: Quote from: Kjelt on January 20, 2017, 01:32:58 pmMaybe, but in my case it was much worse before the upgrade. I could never go to 300 C, and it was taking forever to reach usable temperature.Did not measure, but was more 20 mn than 2 mn.I will make the measure in the new setting.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: January 21, 2017, 01:15:39 pm
content: @Kjelt,This is what I find for the heating, starting with room temperatureTemp (C) time (mn:s)100 0:20150 0:36200 0:56250 1:23300 2:00350 3:00So quite in par with what you had, but much better than what I had before this repair,and very usable. Sure this does not change the max power of the iron, but this will be perfectfor me until the next upgrade.

author: Kjelt
author_rank: Super Contributor
timestamp: January 21, 2017, 06:45:47 pm
content: A job well done in repairing it

author: ctbully
author_rank: Newbie
timestamp: April 11, 2019, 10:53:12 pm
content: Hi, I am very interested in your design. I too got the VP801EC from a friend (without the desoldering gun) and I went ahead and ordered a Desoldering gun from a company in Poland (Still waiting for it to arrive). They were the cheapest. Today I opened up the station and lo and behold, the gun I ordered is 24V and the station provides 230V to the gun LOL. So I need to do exactly what you did except I need to provide an additional 24V 3A supply. There are two transformers inside mine and both output 25V so I might be in luck.Would you be so kind as to share your circuit design, please? I'm good with writing my own code but I battle a bit with the circuit design sometimes.ThanksJohn B.