Soldering Iron: Cheap temperature control?

[Agent24]

Following on from my previous soldering iron thread, I decided 'what the heck' and bought myself a cheap 80 watt iron from my local hardware store.


Well, let me tell you this thing is powerful! I tested it out on an old board and couldn't find anything it wouldn't heat up. Capacitors came out much much easier, cleaning holes was a breeze, even those on power planes.

Of course, everything has it's downside, and being an unregulated iron it gets mighty hot. So hot in fact I was cleaning the tip more than I was soldering as it oxidizes FAST.

Can't measure the the temperature (there's something else I need) but I'm guessing it's 450°C+


So in hindsight maybe something a little less powerful would have been better but there's got to be a solution, right?

I started searching for mains-rated circuits that can control speeds\power etc and came up with a few things, found a few circuits for light dimmers.. then I figured, hey, why not just use an actual light dimmer - since I have the guts of one in my junk box anyway.

I recalled that last time I tried, it didn't work, but on inspection I found that one of the wires had a completely broken solder joint, so I reflowed that, tested with a lightbulb and away it went, perfectly!


Haven't tried it with the iron yet but I see no reason why it shouldn't work.

Calibration will be a problem, I guess I'll have to stick a label on by the knob and write some marks\notes after some experimentation.

Also there will be no feedback so no controllable recovery time but I'm hoping the large thermal mass will make up for that.

I'll probably add an LED as well which might show some kind of status as it will hopefully dim along with the iron.



Anyway, I should ask: Has anyone tried this idea before and if so, did it give good results?

[momaka]

Re: Soldering Iron: Cheap temperature control?

I haven't tried it, but it sounds good to me. 1 note, though - LED won't dim because it has a fairly constant voltage drop. You'll be better off with a small incandescent light bulb (that can take the voltage, of course).

The easiest voltage controller you can build is to add a single diode in series with the iron. This will cut the line voltage in half, so technically you will only get ~40W. And if you add a switch to bypass the diode, you can have 40W/80W operation by just changing the switch.

[PCBONEZ]

Re: Soldering Iron: Cheap temperature control?

Something like this may work.
http://www.harborfreight.com/router-...rol-43060.html

[Agent24]

Re: Soldering Iron: Cheap temperature control?

I haven't tried it, but it sounds good to me. 1 note, though - LED won't dim because it has a fairly constant voltage drop. You'll be better off with a small incandescent light bulb (that can take the voltage, of course).

The easiest voltage controller you can build is to add a single diode in series with the iron. This will cut the line voltage in half, so technically you will only get ~40W. And if you add a switch to bypass the diode, you can have 40W/80W operation by just changing the switch.

Ahh. I suppose one would have to make a more sophisticated device which actually measures the voltage etc and then drives an LED by PWM or something. Not something I would be able to figure out at this time, unfortunately.

Your idea of a small light bulb sounds OK but I don't want something blinding in my face... lowest I can think of is a 15 watt fridge light, that might be OK.

I might just implement the diode idea too though, maybe have a switch to change between variable, half power, and full power even.

Something like this may work.
http://www.harborfreight.com/router-...rol-43060.html

I suppose it would.. or would it? It's designed for a motor, and a soldering iron is just a plain resistive load as far as I know. Perhaps it wouldn't like it? (but I have no idea)

I don't think I'd need it though, the standard light dimmer should be able to do the job OK I expect.

[PCBONEZ]

Re: Soldering Iron: Cheap temperature control?

I suppose it would.. or would it? It's designed for a motor, and a soldering iron is just a plain resistive load as far as I know. Perhaps it wouldn't like it? (but I have no idea)

I don't think I'd need it though, the standard light dimmer should be able to do the job OK I expect.

Most of them work by switching a triac on-off so AC is applied only part of the time.
Sort of the AC equivalent to a PWM DC regulator.
Should work fine with a resistive load.

I'd be concerned a light dimmer would fry/melt.

Nah, I haven't actually tried either one either.. Just speculating.
.

[Toasty]

Re: Soldering Iron: Cheap temperature control?

Regular lamp dimmers have no problem with a resistive load. It's the inductive loads that kill them or the device. i.e.- using a CCFL is a no-no with 'standard' dimmers.

"Motor" controllers will handle a resistive load. They are designed for inductive, but will be fine with resistive.

Soldering irons that direct plug to outlet are resistive. Exception here would be the "guns" like a Weller that are a transformer in and of themselves. "Stations" on the other hand, are inductive as they use a transformer to drop the voltage to the iron.

.

[Agent24]

Re: Soldering Iron: Cheap temperature control?

I'd be concerned a light dimmer would fry/melt.

Well most dimmers seem designed for multiple bulbs in one room, and as far as I know handle around 400 watts for a basic one. The iron is only 80 watts so I think it can handle the load OK.

But in case, I just checked the dimmer - the TRIAC used is a Hutson 8T64A which claims it can handle up to 4 Amps. If my calculation is correct, the iron uses about 0.3 Amps, so it should be fine.


I've drawn up a diagram for a basic idea, I think it should be OK but just wondering about the Full\Variable switch. On full mode, the output of the dimmer will be connected to line voltage.

I don't think it will care but just want to make sure!

[momaka]

Re: Soldering Iron: Cheap temperature control?

I've drawn up a diagram for a basic idea, I think it should be OK but just wondering about the Full\Variable switch. On full mode, the output of the dimmer will be connected to line voltage.

I don't think it will care but just want to make sure!

Yes, the Full/Variable circuit should be fine. When set to Full power, the dimmer isn't connected to anything else on the input side, so the circuit for the light dimmer won't do anything.

[PCBONEZ]

Re: Soldering Iron: Cheap temperature control?

Looks like it will work.
Also looks like a router speed control. (-;
.

[Agent24]

Re: Soldering Iron: Cheap temperature control?

Looks like it will work.
Also looks like a router speed control. (-;
.

Yeah, but it will be made from almost all recycled parts so a lot cheaper

[inuyasha.rules]

Re: Soldering Iron: Cheap temperature control?

Yes it will work if your dimmer is grunts enough. I haven't done it myself but I have seen others that have. One guy used a made in china no name and it melted, but a good friend used I believe a GE or something brand and it works wonderfully. As stated above its basically a pwm circuit. Basically it varies when it turns power on furring the rise of the sinewave and conducts till it hits the zero crossing point. IIR the lowest most dimmers go is 50% duty cycle but due to low voltage at the end it will result in a bit more than 50% power drop. On a side note some dimmers have a small lamp or led bar to indicate power out. Finally for safety sake id suggest using a metal box that's grounded of course. It will help with heat dissipation as some dimmers run hot. Good luck

[delaware74b]

Re: Soldering Iron: Cheap temperature control?

Agent24 - Be aware some dimmers or motor speed controls (such as those sold at home improvement centers) have a minimum load in order to operate. Here in the US, the Lutron brand is one of the top sellers. Their digital control dimmers/speed controls require a minimum 40w load. With you being in NZ, I can't make a good recommendation for a dimmer.

[Agent24]

Re: Soldering Iron: Cheap temperature control?

It had no problem operating properly with a 60 watt lightbulb when I tested it, so I expect an 80 watt soldering iron would be much the same, wouldn't it?

[delaware74b]

Re: Soldering Iron: Cheap temperature control?

I don't think it'll be a problem. I know there are dimmers that won't operate properly without enough of a load on them.

[sam_sam_sam]

Re: Soldering Iron: Cheap temperature control?

I have soldering iron that a variable temp that look like light dimmer switch that had gone bad so I replaced with a very good dimmer switch and it work very good

So yes it will work

The only thing I had to remember is that with new dimmer switch the setting are different

I would look at the min load that you can use on it

[Agent24]

Re: Soldering Iron: Cheap temperature control?

Did you do anything in the way of calibration?

[sam_sam_sam]

Re: Soldering Iron: Cheap temperature control?

What I did was slowly move the knob from the lowest setting to the highest
until the solder melts wait about minute or two before moving the setting agian and then fine tune it after then put a mark on the case

[kaboom]

Re: Soldering Iron: Cheap temperature control?

Be aware some dimmers or motor speed controls (such as those sold at home improvement centers) have a minimum load in order to operate.

That's cause they cheat. First, they get the return for the gate drive ckt thru the load instead of a dedicated neutral (two wire dimmer). Second, the trigger ckt itself leaves something to be desired- hysteresis and dimming point (slightly) dependent on line voltage anyone?

I 'played' with a dimmer a while ago, needed a solid state relay but had only a dimmer. I added the neutral to an early 90's GE two-wire 600W dimmer and put a photocell across the dimmer's pot. An LED excited the cad cell. My control ckt switched/modulated the LED in the "optoisolator."

I remember it had excellent dimming range- as good as it was, but no hysteresis. Bring up the LED and the bulb would follow, drop the LED, so did the lamp. And when the lamp -just- went out, you could bring it back smoothly without advancing the control to get over a hysteresis point.

This all was for a little sound-to-light controller, but I ended up using a similar control ckt driving an IRF3205 and a low-voltage lamp instead. Less 'messy' and the smaller, higher intensity lamp was easier to focus. Plus, the original had 'too many violations'

[sam_sam_sam]

Re: Soldering Iron: Cheap temperature control?

kaboom

Do you have a circuit how you did this

I 'played' with a dimmer a while ago, needed a solid state relay but had only a dimmer. I added the neutral to an early 90's GE two-wire 600W dimmer and put a photocell across the dimmer's pot. An LED excited the cad cell. My control ckt switched/modulated the LED in the "optoisolator."

I remember it had excellent dimming range- as good as it was, but no hysteresis. Bring up the LED and the bulb would follow, drop the LED, so did the lamp. And when the lamp -just- went out, you could bring it back smoothly without advancing the control to get over a hysteresis point.

[kaboom]

Re: Soldering Iron: Cheap temperature control?

No.

I seem to remember that I also changed or added a resistor in series with the CdS cell.

This was about 8 years ago and was 'quick n dirty.' Another reason I abandoned it was this:

I wanted to control transformer primaries of things like pinspots in addition to plain lamps. To test this, I fed the (non dimmed) output of the triac into an unloaded linear power supply through an ammeter. I wanted to see what the no-load current was when powered by this thing vs the AC line. The meter indicated higher, and at the time I thought it was something like slight DC offset from asymmetrical triggering causing slight saturation. It's more likely that the meter wasn't reading accurately because of the sharp turn ons of the triac.

Either way, I abandoned it and have no diagrams. The STL that I built instead also doesn't exist anymore- yet another one with an IRFZ44 or 3205 replaced that one. And that one's in the junk box ATM.