Building a DC Soldering Station. Project Desc/questions about trans temp/current - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 08, 2020, 02:11:40 am
content: Warning kind of a long post, actual questions are the last two paragraphs, the first part is just a description of the project and reasoning for my choices.Ok so along time ago I decided I wanted to build a soldering station instead of buying one, I picked out a case ordered it rounded up some parts and then put it all in a drawer while I moved on from one project to the next! 4 years down the line now and my POS sparkfun branded station (atten 936b) finally started carping out, well not so much the station just the heater, problem is I had ordered a bunch of genuine Hakko a1321 heaters along with my station parts years ago, when i went to use one the station wouldn't regulate the iron it just kept heating! I broke open that atten element and realized it had a K-thermocouple instead of a thermsistor and to boot it looks like the controller uses a diode for the thermocouples cold comp (this explains why the calibration always sucked), so I got my old weller/RatSchack 120v irons out and decided I would build my station because looking around for something in my price range the only acceptable stations were the pace ads200 and the 150w Ersa and cost more than the pace, neither of them were actually what I wanted although I could have settled on the pace ads200 if it had an encoder along with its up/down buttons... I don't understand why the fx888d is so popular with its awful up/down button interface.So here are my requirements1 At least 100W, obviously wattage is not everything but it does come in to play withheat up time, and at 100w continuous from a cold start i can melt lead free in 8seconds with a hakko a1321 heater!2 PID Control, no 0 cross bang bang control crap like most of the clones use... thismethod is for stoves not tools!3 Good UI, so far I plan to use a 2.4inch seed touch screen LCD with touch, A Vishayoptical rotary encoder knob and maybe some bigger buttons if I need them.4 DC heating control, now I know this is where im gonna get flack but I have threereasons for this #1 Higher frequency than 60Hz, so the heater output can be adujstedjust as fast as the ADC can read the sensor #2 Lately I have been doing a lot of workto my 96 4runner and plan on replacing the ECU with a homemade modified version ofSpeeduino ECU, working all those harnesses and adding a CAN bus will be much easierif I have a GOOD iron that I can easily run straight from the car without inverter! #3 Ijust understand a lot more about DC and digital control than I do when it comes tocontrolling triacs and and reading AC with a micro.5 I want to support multiple handles, and be able to stack enclosures on top that tap thestations power to control hot air, solder wire feed etc. For right now I want to buildhardware that will run either an a1321/a1322 (Hakko 937) based heater and alsosupports a1560 (Hakko FX888) along with T18 (Hakko 951) heater cartridges. So thatmeans I need to be able to read thermsistors along with thermocouples. I would alsolike to support induction based handles like the FX-100, but that is a future upgradethat requires research and what I am assuming is pretty decent money just for ahandle and tips (no clones out there if im correct). ATM im only using 936 basedhandles or a dummy load.6 Lastly and very importantly I want to build it to last a long ass time, using only parts Ihave on hand, except the handles of course and maybe a thermocouple controller chip.7 Oh its got to be IOT too, need to be able to switch it on from my phone at the grocerystore, and watch porn on the LCD, LOL jk jk jkSo lets get to the real questions already... Like I said I already have the enclosure (and smaller/bigger enclosure from the same Serpac line that will stack on it for extra modules) and am determined to make things fit, although it will be cramped. So far I have just built all the mains side stuff, rectifier, PI filter on the secondary and welded multiple HUGE (like from old sony AV receivers) heat sinks to gather and attached a few 20-100 watt power resistors on top so I can make a few different load sizes to test things, without having a hot iron rolling around or burning up a nice Hakko heater.For my transformers I am using two 24V 50VA E-cores in parallel, I know this inst the greatest way to do things BUT the actual 24V transformer I have that is rated for 4 amps takes up way to much of my enclosure and using two smaller 2 amp transformers allowed me to orientate things a little easier.So the issue im having at the moment is current draw and heat. An a1321 heater is only 3 to 3.5 ohms which will try and draw 8 amps if it can, So when I hook a heating element straight to the DC supply my transformers saturate, the element is able to draw 6 amps out of them and makes the voltage droop to 17v. I am wondering the best way to limit the current draw and I have three different ideas which I have parts on hand for.#1 My first idea is to use something like a 2n3055 and a sense resistor with some diodes,right after my PI filter that way the 2n3055 will turn on at 4amps and limit thecurrent. Problem is my enclosure is cramped and the rectifier runs warm alongwith the transformers already running hotter than id like (when I pull the full 100VA),im sure the transistor will just pump more heat requiring its own cooling.#2 Second idea is to use a non invasive style pulsed DC current sensor around the heaterwires and when it senses close to four amps I can start throttling the irons current byturning the PWM pin controlling the FET/Heater off and on, kind of like a nested PWMor a modulated pulse width modulation...#3 Lastly I could PWM the fet/iron while measuring the current to the heater observewhat duty cycle draws 4 amps and then scale the code to call that duty cycle 100%instead of using actual 100%. I am not sure this way is the safest way to make sure Inever saturate though... idkSecond problem I am having at the moment is the transformer heat, im not sure how hot a transformer can run though. When I push about 95watts through the dummy load and let it run the transformer laments top at 100C, like I said I'm not sure if that's too much, and obviously that will only happen at if a duty cycle allowing 4 amps is allowed to run for 5 minutes or so, but because of my enclosure my PI filter with my 4 huge 80C 6800uF 50V Elna caps are right next to the transformer and as I said above I want this station to last, Id love to never buy a new one and only upgrade this one for new handle tech. So my idea is if the transformer heat is not a big deal (its not under saturation as far as I can tell, at 100C it putting out 24V even and ~4 amps) maybe I can actually use insulation around the transformers and then separate them from the caps with an aluminum wall? If the transformer temps are too high I guess ill have to use some type of active cooling when loading them at 100%.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 08, 2020, 05:21:00 am
content: Why do you need to measure the current for PWM feedback control ? Should not the current be predictable by knowing the heater resistance, even the temperature is known so you can rely on resistance over temperature chart. Also the transformer if rated 100W combined (of pair of transformers) each should not try to deliver 100W in DC if you use large capacitors. With capacitors and bridges your max DC power available is 50-60W because each cycle the capacitors have ripple current spiking several times of average DC current.If all expected heaters can accept AC instead of DC, I'd use two separate circuits: AC with minimal parts, not caps, just opto solid state relay. And low power DC circuitry for controls, measurements.

author: viperidae
author_rank: Frequent Contributor
timestamp: January 08, 2020, 06:14:59 am
content: Is 60hz really too slow, considering the thermal mass?

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 08, 2020, 09:34:37 pm
content: Ok so here is the deal for anyone that didnt catch it, why I insist on DC4 DC heating control, now I know this is where im gonna get flack but I have threereasons for this #1 Higher frequency than 60Hz, so the heater output can be adujstedjust as fast as the ADC can read the sensor #2 Lately I have been doing a lot of workto my 96 4runner and plan on replacing the ECU with a homemade modified version ofSpeeduino ECU, working all those harnesses and adding a CAN bus will be much easierif I have a GOOD iron that I can easily run straight from the car battery without inverter! #3 Ijust understand a lot more about DC and digital control than I do when it comes tocontrolling triacs and and reading AC with a micro.And to add to that I have already wired and built the transformers as 1 along with soldering T and molex connectors on there in and out, so I can easily plug the station to a car battery, I also built a4 pole PI filter with 6800uf caps and homemade5mHinductor/chokes with hundreds of wraps around #26 iron cores in order to get the dc's peak to peak ripple down to less than 100mv at 24v with a 4amp pulsed draw. Im not willing to ditch the over engineering after all that time spent modeling filters, choosing/crimping connectors, and wrapping torroids. So figuring out how to get the heat down is really the only choice..As I said due to size/orientation in enclosure I stuck two 24V 50VA transformers in parallel instead of just using the 100VA I have on hand. I physically bonded them together by using JB Weld the left side of one transformers El core and sticking it to the right side of the other transformers El core. I did this not only because it made things easier to handle but because JB Weld is killer for heat transfer and I figured it would help too even the heat out between the two transformers when/if one is working harder than the other, I just pulled one of the transformers out of my Atten and the other out of a broke down Yihue someone gave me, they were both fused at two amps, they look identical (except the labels) and are the same physical size, but they do not have matching primary/secondary resistances. I cant find a data sheet ANYWHERE for either of them (big surprise) so I do not know there heat ratings. All I know is that when I hook up a 6ohm load and draw 4 amps, I get exactly 24 volts of rectified DC, using a scope to measure the secondary AC before rectifier shows no unexpected harmonics as it would if the transformers were saturated, lastly the transformers under full 4 amp load seem to top the cores temp at 100c which is 80c over ambient and im not sure if I should worry about that and if so what temperature should I be shooting for too make sure im not wearing them down early, or worse running them on the edge of melt down.@unitedatomsYou mentioned a resistance to temperature table for the thermsistor, I actually don't have one of those and figured that I would end up having to manually make one using a DMM to measure the PTC's resistance while using a thermo-couple to measure the heater temp. As far as I know a thermsistor be it PTC or NTC does not have a linear ohms to temp relationship that can be extrapolated unlike a thermocouple where the voltage increases linearly with temperature. This usually isn't a huge deal if you just order a PTC with a data sheet, but as far as I can tell hakko does not release the curve of PTC used in there heaters. I could and am hopefully wrong about this, as I haven't done much research beyond reading Hakko literature I can find which has gotten me nowhere. Im just not at the code point yet so it hasn't been a pressing issue, if you have any info on the thermsistors used in hakko a1321 and a1560 heaters, or know where I can find it, I would be grateful it will save a lot of time.concerning current draw, im not sure if you understand the problem correctly or if I dont understand your advice, Im not sure what you mean when you say I should just be able to use ohms law to figure it out.The problem is the transformers are rated at 24V 4A, when wired in parallel, if I connect a load under 6 ohms which will draw 4 amps, such as a 3 ohm Hakko Heater which can draw 8 amps according to ohms law, the transformers saturate and the DC voltage then droops down to about 17V, because the Hakko heater is drawing close to 8 amps the transformers where never intended to supply. As I said in my first post a Hakko a1321 heaters resistance is between 3 and 3.5 ohms and I want to support other restive heaters with various specs, so i never know the size of the loa d plugged in to the iron port could be 1ohm, could be 8ohms... I need a way to make sure that whatever the resistance of the heater is is never allowed to draw more than 4amps@24v.The only ideas I have is to use a 2n3055 and a current sense resistor with switching diodes right after the PI filter as a pass transistor. This seems like a simple bullet proof method to keep the transformers out of saturation. The issue is I would assume the 2n3055 will pump a lot of heat, futher adding to the issue of keeping the enclosure temps down.Secondly I could use a shunt resistor or a non contact pulsed dc current sensor to directly measure the current the pid loop is supplying to the heater and if it hits 4amps, use code to keep the pid in bounds. As with the solution above this is pretty close to bullet proof no matter what is shoved in to the stations iron connector.Lastly, and worst of all the ideas(in my opinion). I could just hook my DMM in 10A mode between the pwm/fet output and the heater, and step the duty cycle with the micro until i hit 4A on my DMM. So, say the heater draws 4amps when pwm'ed at a 70% duty cycle, I can now write a profile for that heater that never allows the duty cycle to be greater than 70%. This seems like a real PITA if I want to support multiple heater types though, even worse heaters of the same type are not the same resistance only with in there spec. Also seems like there potential for a bug in the code to screw everything up.Lastly using ohms law, I could measure the resistance of the attached heater and then adjust the voltage supplied to it to the appropriate level to make sure 100% duty cycle means 4 amps. This way sounds a bit overly complicated though. Im not really sure how I could dynamically raise and lower the voltage of the mosfets pwm output at 100 watts?I am open to any advice an ideas, they dont include driving the iron handles with mains AC. Im assuming to support an fx100 induction style handle (when i can pop $100 on one, plus tips), I will have to build an some type of high wattage 13.5mhz AC inverter to get good results, unless pulsed DC works fine, but I'm never that lucky!

author: David Hess
author_rank: Super Contributor
timestamp: January 09, 2020, 02:42:05 am
content: Quote from: viperidae on January 08, 2020, 06:14:59 amThe PID controlled soldering irons I am familiar with are even slower than that at perhaps 5 Hz. With the thermal mass of a typical soldering iron tip, there is no need to switch faster. Applying a whole number of AC line cycles with zero crossing switching is very viable.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 09, 2020, 03:42:37 pm
content: It's not just unnecessary to go faster due to thermal inertia, but also due to the fact you need to measure tip temperature! The temperature measurement itself can't be done very quick, and usually can't be done while the tip heater is ON with many tips that include the thermocouple... so that naturally limits frequency here as well.I have actually designed and built a soldering controller that uses JBC handles and tips (T210 and T245), in DC mode, and the PWM frequency I settled for was 100Hz. The 10ms period was basically split into a 2ms period for the temperature measurement, and 8ms (max) for heater control, which was naturally limiting power to 80% (a second hard current limit is implemented in the driver IC I used for this, basically a DC motor controller that has current limit and short-circuit detection, handy).So in any case, don't neglect the tip temp measurement part. It's not quite as easy nor can be done as fast as you may think.(Have postponed making a proper thread about it but I may do this when I get a chance...)

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 09, 2020, 07:00:14 pm
content: @Silconwizard, Thank you so much for the reply!! I didnt even think about just using one of the many motor driver with current limiting and overload protection. I have some around but im not sure if any are up to the power im running to the iron! Do you know which driver you used, when your iron is at the hard limit how hot does the driver get?I looked at the JBC T2xx handles or maybe they were the C Series handles, they were cartridge style handles like the FX951/T18 stuff but they were priced way higher than a genuine fx951 handle! I can even pick up a genuine Hakko induction handle for the FX100 for less than the JBC cartridge handles if I r ember right. Why did you choose JBC, is there actually $50-$70 of value in choosing JBC over Hakko? Like I said above I plan to use a 7 pin connector and support genuine 907/888/951 heaters/handles right off the bat, they are cheap abundant and even the clone stuff works reasonably well. The thing is I would like to support one really good handle also(which will be my main iron), be it an Ersa, a JBC, or a Hakko induction, I cant seem to find brand new pace handles without the station, and I have no desire for a metcal handle. So is JBC that much better than Hakko, and is 13mhz induction that much better than a top of the line cartridge handle like the 150W Ersa where the sensor is literally in the tip!As far as speed goes, im starting to wish I hadn't brought it up. Even if it is useless to pulse the iron any faster than 60Hz, it still does not negate all the other reasons I am using DC which are all more important than heating frequency, especially wanting to plug in directly to a car battery or pack of lith-ion's and still have a station at hand that can give me more options and power than say a TS-100 (I also don't trust these irons will have tips available for as long as a Hakko, so im not willing to invest in one). Im still building and testing the power supply and haven't even picked out what micro I am going to use yet, let alone gotten to experiment with the control loop. My idea was that a high frequency pid loop at least half the speed of the ADC was a good idea because even if there is thermal lags I can hopefully predict things like the iron touching a huge ground plane or to-220 much faster and have more time to predict the best path to reach temperature again without over or undershooting. I however did not take in to account the actual speed of a PTC or Thermocouple... So once I get to the code i will experiment and im sure everyone will have been right about the speed but it's definately not a reason to throw out all my work and replace it with a triac.

author: Shock
author_rank: Super Contributor
timestamp: January 09, 2020, 11:53:51 pm
content: The handpiece on the Pace ADS200, the TD200 is great. Aluminum and very cool and comfortable to work with. It has the same short tip working distance as Metcals. Hakko handpieces are an older design, plastic and not in the same league, besides that the Pace ADS200 is a 120W station and has the lowest cost of ownership.You might want to look at why you want a rotary encoder. If it's to adjust temperature, buttons work really well if done right and more reliable. When Pace brought out the ADS200 initially on the first production run temp adjustment was made in 5 degree increments but with their first firmware update they increased accuracy further and changed it to single digit control. It works really well now. Since the ADS200 is calibration free there is no need to go into menus or anything aside from using the temp up/down and preset button.But that said, Mbless on the forums here has already drawn out the entire Pace ADS200 schematic and built acustom controller and firmware for it. His doesn't have a rotary encoder either but you can add it of course.It crossed my mind early on it would be an ideal platform to mod. Mbless admits making a controller wasn't really necessary and I've come to the same conclusion after using it, nothing much to gain. For longevity the only custom part of the ADS200 is the firmware and you can get a replacement from Pace if required, otherwise it's a very simple circuit.My portable iron is a butane powered Dremel Versatip. It also comes with a knife, heat shrink and hot air attachment. In my tool bag I have a spare mains powered iron along with soldering supplies. It's better to have dedicated portable tools, I couldn't think of anything worse than packing up a soldering station and screwdrivers etc off my bench.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 10, 2020, 07:00:25 am
content: LMAO I have nooo plans to throw a station in my toolbag, I also have a portable bernzomatic heatgun/iron for that quick in the field with no power stuff. I plan to set the station on the dash of my truck while working where the glove box was, there is just no way in hell it would be convenient to use a butane rig for splicing the amount of wires involved with an ECU. As far as the encoder goes it will be used to scroll through some menu's for preset wattage limiting, pid graph, etc.. so not just changing the temperature. Like I said above the encoder is an optical vishay model someone gave me a long time ago so it should be pretty solid as far as not craping on me like a mechanical encoder.Thanks for the link to the pace schematic, I was reading the ads200 thread a few hours ago, but didnt get far enough to find the schematic etc, the thread has grown to like 40 pages now. Does anyone know exactly what type of thermocouple is in an ads200 handle, or why they used a 17bit adc? If I could get real solid specs on the temp sensor they use I may just call them and see if they will sell me a handle. I like that with a hakko I can spend 20/30 a tip for something that will last or 4 a tip and take a crap shoot, but in the end I would much rather just spend 10 a pop on 5 or so tips I know i most likely will never need to replace, and that is why I really like the pace handle!

author: Shock
author_rank: Super Contributor
timestamp: January 10, 2020, 08:48:11 am
content: Quote from: rwgast_lowlevellogicdesin on January 10, 2020, 07:00:25 amThe cartridges have a Type K thermocouple in series with the heater. The significant change on this model was that they combined two former models with standard and high mass tips into the one 120W station without requiring calibration between swapping geometries or series. I assume that aside from the accurate regulation the ADC is somehow involved in determining the tip inserted for any offset that may be required.Mbless mentions somewhere about the regulation accuracy of his controller being a little bit worse than Paces. There probably is a little secret sauce in the Pace station firmware but it won't stop you making a working controller.QuoteNo need to call them, they sell them on their online store for $95. They don't have particularly good freight rates as they tend to ship in bulk to distributors but see how you go.https://paceworldwide.com/td-200-soldering-iron

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 10, 2020, 09:52:34 pm
content: And you are positive the handle uses a K thermocouple? I only ask because looking online at the Hakko 951/t12 handles/carts it seems like most people say they use a K couple but there are oher who say they don't and have made some measurements that dont line up with a k at all, one instance of that claim with tests done can be found here,https://hackaday.io/project/94905-hakko-revenge/log/144548-hakko-t12-thermocouple-is-not-type-kT t12 handles are cheap enough and you can even get some nicer ones made of aluminum from china, but it bugs me there doesn't seem to be agreement on the actual sensor which makes a whole lot of unwanted work for me that im sure I already have to do for the 907/fx888 handles because I cant find a PTC curve for there sensors.$95 bucks is worth it for the handle if its the last one I ever need to buy, has good tips, and a truly known sensor! I would be in to a JBC handle but I dont think I can swallow the price of there tips!

author: Shock
author_rank: Super Contributor
timestamp: January 11, 2020, 12:37:21 am
content: Pace mentions it's Type K in the below video at 1:25. This is from a while back before the firmware enhancements and ESD testing.Don't automatically expect the T12 to be similar performance or Chinese handpieces to be the same quality or comfort. The Pace 1130 standard and 1131 ultra performance (high mass) series cartridges are 120W and are faster heating than the T12 which are standard sized and only 70W.