I have a 40W soldering iron; I need to solder a small transistor in a PCB. I guessing 40 watts is too much heat for that task, so could I add a incandescent bulb in series with the iron to reduce the heat? If so; what watt lamp? (40, 60, ect) Thanks
You need to give the make and model of your soldering iron in order to give a definitive answer.
If your soldering iron heater element is powered from a step-down transformer you can use the old technique of inserting a power diode in series with the heater element so that the element receives only half wave pulses of current. You can arrange for the diode to be switched in or out of circuit as required.
As long as the soldering iron is directly hooked up to the AC power and not step-down transformer powered or not DC powered there are two easy ways of reducing the soldering iron temp:
electricitym . . .
The diode trick seems to work better than the light bulb series idea I had before. It is just a standard cheap iron that plugs directly into AC. Thanks for the help!
The light dimmer approach has been featured in ARRL Handbook since 1970s, when the dimmers first came on the consumer market. BTW, did you know that the Weller WLC100 solder station is just a 40 watt stick iron with such an OEM light dimmer? The Weller WPC300 is the controller without the iron.
Read all about it
No, 40 watts is fine. The trick is to not keep the iron on the joint too long, and with a high powered iron it isn't necessary to do so- the joint can be soldered in a second or two. Transistors are a lot more robust than many people think- I don't recall ever destroying one by soldering iron heat, and that includes SMDs. If it's not a surface mount device, you could always clip something to the legs to act as a heat shunt if the heat worries you.
It is a common misconception that a low powered iron is required for circuit work- it isn't. In fact, low powered irons can sometimes do more damage than high powered irons in some cases, for example if the iron is underpowered the user may keep it on the joint for too long and the sustained heat can cause component damage and lifted PCB pads.
I have had to use all sorts of irons in emergency situations, from 12 watt to 100 watt, and prefer a hot iron over a cooler one every time.
Dave
"Dave D" hath wroth:
The son of a friend did a senior project in college modelling and testing such a heat sink. His theory was that if you removed heat from the joint by attaching a thermal radiator such as a "protection" clip, the total amount of heat (BTU's) required to solder the connection would increase sufficiently to burn the circuit board. I believe he proved his point, but I didn't read the report. I can see his point. In the bad old daze of long xsistor leads, a clip placed near the component would not remove that much heat. However, the same clip adjacent to the joint would radiate quite a bit of heat away from the joint requiring that the soldering iron remain on the joint longer. However, at this point, the discussion is academic as I rarely see anything resembling an accessible and exposed xsistor lead long enough to attach a clip.
Agreed. I use a temp controlled 700F soldering iron with a rather large tip. I work as fast as possible. Tinning the joint with some fresh solder is often a big help. If you use a low temperature iron or a very fine tip, the heat affected zone on the board is much larger than if you use hot iron and big tip.
Agreed. However, it's not really the wattage of the iron that's important. Wattage ratings set the upper temperature limit of the iron if it's not temperature controlled. The size of the tip is very important. If you use a very fine precision pointed tip, the amount of heat that can be transfered is very small. There just isn't enough surface area to do a proper job. Fine tips are required for SMT components, where a larger tip would hit adjacent parts or pins, but for where there's room, a big tip works better.
I guess I should mumble something about what I consider a suitable tip. Forget about the ones that come to a sharp point. A Weller PTA7 with a 0.062 screwdriver tip is good for most everything I do. I have a collection of other sizes specialized soldering, but the generic PTA7 works for everything except the really big jobs (solder lugs) and the really fine work (SMT).
If you're in the market for a soldering station, I suggest one of the various Weller products that has some form of tip temperature control. One of these:
-- Jeff Liebermann jeffl@comix.santa-cruz.ca.us 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Another trick is to use a transformer with secondary taps at various % of the mains in and wire the secondary antiphase in series with the element to subtract voltage from the mains, even easier is an old type transformer with several taps for various mains voltages - then its possible to just use the primary as an autotransformer.
Another trick is to use a transformer with secondary taps at various % of the mains in and wire the secondary antiphase in series with the element to subtract voltage from the mains, even easier is an old type transformer with several taps for various mains voltages - then its possible to just use the primary as an autotransformer.
Another trick is to use a transformer with secondary taps at various % of the mains in and wire the secondary antiphase in series with the element to subtract voltage from the mains, even easier is an old type transformer with several taps for various mains voltages - then its possible to just use the primary as an autotransformer.
.... that is 3 tricks if I am counting correctly.
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The server's been playing silly buggers all evening, it keeps telling me "server could not be found" then sends the post 3x all with identical time stamp!
"ian field" wrote in news:oeqcg.19613$ snipped-for-privacy@newsfe3-gui.ntli.net:
Use an ordinary lamp dimmer;they will handle 100W lamps.
-- Jim Yanik jyanik at kua.net
I've tried em all, including unplugging the iron before it gets too hot!
I bought a cjeap Radio Shack iron for trips, has diode switch right in the handle for two settings.
greg
Jim Yanik wrote in news:Xns97CC7F11182AEjyanikkuanet@129.250.170.83:
FYI,I mounted a triac-lamp dimmer in a plastic double outlet box,and mounted a dual outlet in the 2nd space,and use it primarily as a speed control for my old model 270 Dremel hand grinder. But I can use it for anything that plugs into a standard 120 VAC outlet.
-- Jim Yanik jyanik at kua.net
It's all in how you use it, I've used a 40W iron (and a few times a 140W gun) to solder delicate components, and in fact I find it's less likely to damage things using an overpowered iron where you have the heat on for only a moment than an underpowered iron where you have to keep it on the part heat soaking everything.
A light dimmer or diode in series will reduce the temperature of the iron, but if it were me, I'd use it as-is and try to keep the iron on the joint for only as long as necessary.
I would agree with your comments.
In the 60's - 70's when we had our soldering irons on the go 24/7 we would use the diode switch simply to reduce the temperature during the periods when the iron wasn't actually soldering anything. It was simply used as a "standby" position so that it would heat up to maximum very quickly when the diode was switched out and soldering re-commenced. When a non temperature controlled iron is left on permanently without being used it tends to overheat the element and the tip because no heat is ever being drawn from it as it would during soldering. Many irons developed black scaling which causes metal to flake off the tip and the heater element thus resulting in rapid oxidation and demise of the iron.
As a result, diode switching to standby assisted in prolonging the life of the heater element and the iron itself.
There may be concerns about switching spikes damaging the element - but much depends on the design of the iron.
The iron I use is an Antex X-25 which has a slender rod element which pushes into a hollow bit, so I imagine the resistance wire in the element is thin and very compact wound. Despite not using any form of dimming the irons were only lasting a few weeks (continuous all day use) As my PC often crashed and there were bursts of crackles on the radio, I guessed that the problem was caused by line transients. A plugtop transient absorber fitted to the iron's lead cured the reliability problem - the irons now last over a year. The moral of the story being - some irons can be damaged by noisy mains!
"ian field" wrote in news:b%_cg.8268$ snipped-for-privacy@newsfe1-gui.ntli.net:
I have a couple of Antex 15 W irons. I love them! I used them at Tektronix for 20 years with no problems like that,too. You must have some BAD power mains. Perhaps the "transients" are far too high.Your power company should be notified,have them put a monitor on your line and fix the problem.
-- Jim Yanik jyanik at kua.net
That is the trick that Heath kit used with the old 6 volt GE soldering irons. Transformer had 4, 5 and 6 volt taps - used with rotary switch on front for Low, Medium and High
gb
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