Why isn't there many soldering station that uses a switch-mode converter? - Page 1
Forum section: electronics / projects

author: technix
author_rank: Super Contributor
timestamp: December 18, 2018, 05:44:22 am
content: Dave already have one of those soldering iron power supplies blowing up on him. That got me thinking: why isn't many soldering stations use switch-mode converters, which can be easily made to work with a wide input voltage and is irrelevant of the input frequency.One design idea for a switch-mode soldering station is use a laptop power brick as the universal input converter that emits 19.5V 3A. Then use an adjustable buck converter to implement the feedback-controlled heater driver.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 18, 2018, 06:01:13 am
content: Quote from: technix on December 18, 2018, 05:44:22 amThat's what the TS100 did.

author: ataradov
author_rank: Super Contributor
timestamp: December 18, 2018, 06:05:17 am
content: From "reputable" vendors - laziness and legacy. PACE still designs new products with some hardcore obsolete 8051 MCUs in them in PLCC package.I think there is a reasonably good switcher soldering stations sold on AliExpress. I'll try to find the link.Ok, it was banggood. Here it ishttps://www.banggood.com/Mini-V3_0-T12-Digital-Temperature-Controller-Soldering-Station-Soldering-Iron-Tips-T12-K-p-1338117.htmlI've seen some good reviews of that station.And for completeness here are the tipshttps://www.banggood.com/10pcs-T12-Soldering-Iron-Tips-Set-for-HAKKO-FX951-FX952-p-1191594.html

author: Nusa
author_rank: Super Contributor
timestamp: December 18, 2018, 06:29:05 am
content: Dave is something of a special case. Most of us don't have to worry much about having ~120V hardware lying around to accidentally plug into ~240V power. Especially those of us that live in ~120V areas, as the reverse case isn't very dramatic.Soldering irons are just an ideal scenario for transformers. Once you've got low voltage AC, all you have to do is connect it to the heater, add triac control and a control system and you're done. The tip heater doesn't care if it gets AC or DC, nor does it require any power conditioning. Plus you get isolation for free with a transformer.Yes, modern irons will need some DC for the fancy displays and control systems, but a few diodes and caps will give you enough for that purpose. No need to switch to a full-fledged switching supply just for that.

author: ataradov
author_rank: Super Contributor
timestamp: December 18, 2018, 06:33:16 am
content: Quote from: Nusa on December 18, 2018, 06:29:05 amSize and cost are also factors here. Big transformers are expensive. Actually, if I knew about that $50 Chinese station, I would not have bought Pace ADS-200.Also, not having that marketing dude write "we are sorry" email may be nice.

author: Berni
author_rank: Super Contributor
timestamp: December 18, 2018, 06:39:37 am
content: I only see it as a good thing. Its always nice to see a big reliable chunk of iron in there. No heavily stressed caps to dry out, no switching noise and when is the last time you had lightning blow up something running from a transformer?I have seen universal input 110/220V transformer power supplies tho. Some of the old Keithley bench DMMs use it. It actually starts up in 110V mode but has a softstart resistor that limits the current in case it is plugged into 220V. This makes the transformer give a bit of a angry buzz as it saturates, but the current in the primary is limited by the softstart resistor so nothing bad happens to it. A second or so later a circuit realizes its running on 220V and clicks a relay that switches the transformer taps into 220V mode, the angry buzz stops and it continues running in 220V mode. If you plug it into 110V then it just turns on without any buzz or relay click.

author: 001
author_rank: Super Contributor
timestamp: December 18, 2018, 07:34:29 am
content: SMPS also have a problem with grounding and leakageIt is not good do get about 80V at iron tipIt can kill components

author: Shock
author_rank: Super Contributor
timestamp: December 18, 2018, 08:45:08 am
content: I'll take an iron transformer any day. The downside is extra cost for decent transformers, everything else is a benefit - weight, esd/operator safety, reliability, longevity.

author: technix
author_rank: Super Contributor
timestamp: December 18, 2018, 10:42:57 am
content: Quote from: 001 on December 18, 2018, 07:34:29 amThere are SMPS power bricks that uses three-prong mains connector that has an resistively earthed negative terminal. And that type of power bricks with a rated output of 12V/5A and 20V/3A are pretty much standard products now costing less than a big hunk of iron as used in transformers of that type.12V/5A ones usually use the standard center-positive barrel jack too for further standardization. 20V/3A ones also mostly uses a common laptop power connector.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 10:48:05 am
content: You could make the circuit intelligent and get a transformer and use the same power system. Like a voltage detect that prevents energy from being used if its not used with the right taps, or even automatic switching. It should have power good and earth ground detect as a lab iron IMO those would be nice features.I don't want that tip making noise that can harm something like a spectrum analyzer if you have it soldered into the circuit when you are prototyping something like a RF filter and you forget to disconnect the SA and touch it with the iron or something. It needs to be safe for the best microwave equipment and other sensitive devices (assuming you don't have ridiculous earth grounds in your lab).

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 10:54:34 am
content: Quote from: Nusa on December 18, 2018, 06:29:05 amyou want to use a quality circuit because its used inside a electronics lab not an out door light dimmer. Don't take shortcuts just because the process control step time constant is long you need to care about your operating environment. Those irons are running very often and if there is a few people in the same room and you shove some kinda bootleg ass power system into it you will have problems or ruined experiments. Some evil charge pump to save a 50 cent LDO or whatever can cost a good product. And you want it to be reliable and repeatable without weird failure modes because of cheap power systems.Save that kind of stuff for something like a wood engraver in a wood shop. Or a hot knife tool for plastics work or whatever.

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2018, 11:01:00 am
content: Quote from: technix on December 18, 2018, 10:42:57 amAnother solution is to connect the output to earth, via a Y capacitor, which is very common in switched mode power supplies with a non-earthed output.In my experience most soldering irons have an earthed tip, so it's a non-issue.I don't know why switched mode power supplies in soldering irons, aren't as common as they are in other pieces of equipment, such as oscilloscopes.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 11:02:10 am
content: yea but if the earth pin gets loose or something its probably going to much worse then a conventional supply because of the high frequencies being usedi kinda want filtered DC there I don't give a shit about the costmagnetic field

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 18, 2018, 11:02:22 am
content: There was a Youtube comment that suggested that AC is preferable for high temp heating as migration within the element was an issue.I have no idea how plausible that is at soldering temperatures - any metallurgists here ?

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 11:04:28 am
content: Well I read literature for kilns and they have migration problems at high currents with DC because the fields cause the wires to bendI actually wonder if it would be annoying and pick up parts. Maybe its a bad idea. The plating is iron.

author: technix
author_rank: Super Contributor
timestamp: December 18, 2018, 01:10:39 pm
content: Quote from: mikeselectricstuff on December 18, 2018, 11:02:22 amQuote from: coppercone2 on December 18, 2018, 11:04:28 amSwitch-mode converters can implement H-bridge output, hence still outputting AC power.Quote from: Shock on December 18, 2018, 08:45:08 amIron transformer and a quality SMPS costs about the same here in China.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 01:12:20 pm
content: thats nasty HF emi from the square waves at significant power levels near components coupled by iron.

author: Benta
author_rank: Super Contributor
timestamp: December 18, 2018, 01:20:54 pm
content: It's simply nice to have a heavy base that doesn't skitter all over your workbench. That's reason enough for me to prefer an old fashioned transformer.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 01:29:22 pm
content: you can add a steel plate to it to weigh it down, or you use a nice steel chassis.

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2018, 01:44:48 pm
content: Quote from: coppercone2 on December 18, 2018, 11:02:10 amI would have thought that a soldering iron with an SMPS would also be DC, but it could be HF AC if they cheaped out and used a halogen lamp style transformer based supply.There are greater risks associated with a poor earth connection, especially if the PSU chassis is metal. EMC would be the least of my worries.

author: perieanuo
author_rank: Frequent Contributor
timestamp: December 18, 2018, 02:25:24 pm
content: Quote from: mikeselectricstuff on December 18, 2018, 11:02:22 amIn fine, first comment that point why AC is preferred, tip has longer life.Envoyé de mon iPad en utilisant Tapatalk

author: Benta
author_rank: Super Contributor
timestamp: December 18, 2018, 03:33:09 pm
content: Quote from: coppercone2 on December 18, 2018, 01:29:22 pmOf course you can. But as a transformer is so cheap anyway, why bother? It's just more complication.,

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 03:36:20 pm
content: well with a transformer it would be nice to have a steel chassis anyway since its low frequency and in a electronics lab next to circuits being prototyped.

author: wraper
author_rank: Unknown
timestamp: December 18, 2018, 03:38:40 pm
content: Quote from: 001 on December 18, 2018, 07:34:29 amDoes not matter. All ESD safe stations have grounded tip.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2018, 03:41:35 pm
content: do you consider that joint between the soldering iron tip and the handle to be good as its frequently thermally cycled and hot oxidizing etc?I would err on caution with it. There is alot of demand placed on that joint.

author: technix
author_rank: Super Contributor
timestamp: December 18, 2018, 04:29:06 pm
content: Quote from: Benta on December 18, 2018, 03:33:09 pmOnce again, standard external SMPS bricks costs about as much as transformers here in China, and I do need some kind of heat sinking for the power MOSFETs so a metal chassis is actually preferred.

author: David Hess
author_rank: Super Contributor
timestamp: December 18, 2018, 07:24:45 pm
content: Quote from: ataradov on December 18, 2018, 06:33:16 amSize and weight are actually an advantage for something sitting on a desk which you do not want to knock around and a transformer is more reliable than a switching regulator except when it is operated at twice its rated voltage which is hardly a common problem.Number of switching regulators I have had fail: countless, I could fill a trash can with them. Number of transformers I have had fail: one doorbell transformer 20 years ago.If you are buying custom transformers in the quantify Weller does, then the cost is much lower.

author: LapTop006
author_rank: Unknown
timestamp: December 19, 2018, 12:25:18 pm
content: Quote from: Nusa on December 18, 2018, 06:29:05 amIt's more common than you might think, I work with a bunch of deployment engineers who are always travelling to various datacenters, even in 110v parts of the world it's not uncommon to only have >200v power easily available (sometimes 208, but usually 220-250v).

author: coppercone2
author_rank: Super Contributor
timestamp: December 19, 2018, 01:41:21 pm
content: I am pretty sure the art of electronics or some other book had a nice circuit for protecting transformers from this.

author: Nusa
author_rank: Super Contributor
timestamp: December 19, 2018, 02:05:04 pm
content: Quote from: LapTop006 on December 19, 2018, 12:25:18 pmWell, speaking as one of those in the 120V world, I've got 240V available. But I don't have a single US 240V plug to C13 connector cord. Not a single one. One underlying problem is that the C13/C14 connector standard is used for multiple voltages internationally. If the unit had had a hard-wired cord (which, ironically, would make it cheaper to manufacture), this accident never would have happened.

author: Nusa
author_rank: Super Contributor
timestamp: December 19, 2018, 02:46:10 pm
content: Quote from: coppercone2 on December 19, 2018, 01:41:21 pmFirst have a fuse on the AC line. Pick a fuse value that will never blow in normal operation, but not needlessly large. This is just basic safety, even if there's a loophole in regulations.For over-voltage protection: add an appropriate varistor between line and neutral, after the fuse. The varistor will conduct when its voltage spec is exceeded causing the fuse to pop very quickly. Transformer survives.

author: technix
author_rank: Super Contributor
timestamp: December 19, 2018, 05:58:58 pm
content: Quote from: LapTop006 on December 19, 2018, 12:25:18 pmLet’s not mention Japan... They have both 120V and 240V systems within the same country. From Nagoya to Fukushima the mains suddenly runs on a different voltage.

author: LapTop006
author_rank: Unknown
timestamp: December 20, 2018, 02:53:52 am
content: Quote from: blueskull on December 19, 2018, 06:51:33 pmFunny you should mention that.Japan was one of the places where we had a DC that couldn't do standard voltage.This got extra funny when a telco didn't have any demarc boxes that would work off 208.Even sillier, that telco was the owner of the DC...

author: Berni
author_rank: Super Contributor
timestamp: December 20, 2018, 10:32:00 am
content: Quote from: blueskull on December 19, 2018, 06:51:33 pmJapan has both 50 Hz and 60 Hz ? Why in the world would they do that.

author: diyaudio
author_rank: Frequent Contributor
timestamp: December 20, 2018, 10:41:25 am
content: Interestingly the advantage of a EI core vs a switch mode power supply.Bad.- A decent SMPS is expensive.- The base of the station will be to flimsy on the desk. The EI core acts as a damper weight.- Take into account this thing will be used on expensive circuitsA transformer is just cheaper overall, for the function and purpose.I think better innovation needs to be applied to solder-station cord quality, ergonomics of the head and iron tip aesthetically and functionally.

author: BrianHG
author_rank: Super Contributor
timestamp: December 20, 2018, 11:00:49 am
content: Quote from: wraper on December 18, 2018, 03:38:40 pmAt times, I want my floating tip, isolated from the mains via a split-bobbin transformer.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2018, 03:38:34 pm
content: Quote from: BrianHG on December 20, 2018, 11:00:49 amI have an extra completely isolated output on my isolation transformer for this with a high voltage high value resistor to drain charge to ground.

author: wraper
author_rank: Unknown
timestamp: December 20, 2018, 05:08:01 pm
content: Quote from: BrianHG on December 20, 2018, 11:00:49 amThat means you want tool inherently not safe for static sensitive parts.EDIT: and it also means you are not going to use any good soldering station.

author: wraper
author_rank: Unknown
timestamp: December 20, 2018, 05:10:17 pm
content: Quote from: David Hess on December 20, 2018, 03:38:34 pmWith bleeding resistor, even SMPS output won't be floating high. Although you should not go too high in resistor value if there is Y capacitor between primary/secondary.

author: mariush
author_rank: Super Contributor
timestamp: December 20, 2018, 07:34:18 pm
content: Going a bit sideways ... I wonder if some engineer at a soldering station manufacturer ever had the idea " hey, since we have a 24v AC transformer inside, let's add a one channel adjustable linear power supply, 0..18v 1-2A , at the bottom of the station ..."Wouldn't add too much to the BOM...

author: wraper
author_rank: Unknown
timestamp: December 20, 2018, 07:35:59 pm
content: Quote from: mariush on December 20, 2018, 07:34:18 pmAnd that would be pretty stupid Idea. You can buy crap stations with PSU, though.