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Heavy Soldering With Hot Air

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MrAl

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Hi,

Note this query is about soldering a *large* connection with a hot air rework station, not about soldering tiny surface mount parts. I'm talking 8 or 6 gauge wire onto say lug terminals, or even soldering two 6 gauge wires together end to end maybe with a hook formed in each end.

Normally the bigger the bulk metal of the connection is the bigger the soldering iron required. For small 22 gauge wires a 30 watt iron would do nicely, but for much larger wires and large lugs we might have to go up to say 300 watts. That would be a big iron.

Well many hot air rework stations come with 500+ watt hot air stations. I have to wonder if we could solder a large connection with this kind of tool, like say two 6 gauge wires.

Anybody ever try this ? I couldnt find much about it on the web as everything is geared toward SMD work with the hot air soldering tools.
 
You probably will be able to, the drawbacks will be it'll take ages to get the connections hot enough, which also means that you'll probably also do quite a bit of heat damage to the cable insulation or other components nearby.
 
Hi,

Yes thanks that's something else to think about.

But say we dont care about the insulation, that maybe there even is no insulation.

Then what the question boils down to is this:

If we compare a 500 watt soldering iron (large of course) to a 500 watt hot air rework station tool, will we get the same heat from the hot air tool as with the soldering iron?

And even more to the point:
If we can 'just' solder one 6 gauge wire to a big lug with a 500 watt real iron, can we 'just' solder the same thing with a hot air rework tool? By 'just' solder i mean it might take a minute to heat up the joint, and it would solder this 6 gauge wire to the lug but it would not be able to solder a 4 gauge wire. So the question is, if the real iron can solder a given large joint where it is near the point where it cant go any bigger, can the equally rated hot air tool do the same thing?
 
I searched for using hot-air for such things as plumbing and armature repair. I dislike You Tube, but here is one claim that it works:
. The gun used may need a different nozzle than is used in a standard rework station. On the same search page were several blog entries asking a similar question with responses saying it didn't work.

However, if you consider plumbing and other examples of torch soldering, how is a torch different from a hot air station (aside from the obvious chemical differences in a flame)? My guess is that hot air will work by itself for what you describe, but you may need to turn the temp up quite far to compensate for the greater heat dissipation and/or be prepared for heating a large section. At some point, the section will dissipate >500W or so and you will never get up to temperature. I think soldering something much larger, say copper gutters and downspouts or large copper pipe, would be a real problem.

John
 
Hi John,

Very interesting as you bring up a good point that brings one aspect of this question to light that i hadnt thought about yet, and that is temperature, especially that of the heat source.

The simplified electrical equivalent of a heat source and sink could be a voltage source and resistor and capacitor in series. Of course the total resistance and capacitance would be distributed along the spacial dimension say 'x', so it would be similar to a transmission line, but we can still look at it as a more simple circuit of just the voltage source, two resistors, and two capacitors (forming a low pass circuit) and with one more load resistor at the output. The joint we want to heat is the node of the first cap, and the node of the second cap is a unwanted sink we are stuck with because of the physical structure.

In the case of the small wires, we have a heat source and a certain thermal resistance and heat capacity, and the small wires conduct little and the total heat capacity is relatively small, so even a lowish temperature could raise the joint to the temperature required to melt solder.
But with larger wires if we increase the total power but done increase the temperature, by the time the conduction takes place to where we need it to be the temperature might be too low to melt solder.
In your example we have a large copper structure and we apply heat. If we have 100 watts of heat at a lower temperature it may never heat the joint enough because the conduction rate is too fast. If we increase the temperature and keep the wattage the same, we may actually get enough heat to the joint, because the transfer of heat is also dependent on time.
With a torch we have a very high temperature to work with and that creates mildly hot localized temperature rise. With the same power but lower temperature the material may conduct away too much heat before the joint gets to heat up enough.

In the electrical circuit, it would look like (say) a 100v source and (say) two 100 ohm resistors and (say) two 10000uf caps. We have a 100 watts, but it's going to take time to raise the voltage at the first node due to the 100v source. If we increase the source to 200v we can get the node to change faster <rough analogy>.

So what this means is that i also have to consider the temperature of the source as well as the total power the source can deliver. If the solder gun gets up to 600 degrees C then the hot air itself must reach 600 degrees otherwise they are not equivalent. So now the question is just how hot do the hot air soldering tools air get:?

I'll search around a little and see what i can find out, but if anyone has any more info that would be nice too.
 
Hi,

Note this query is about soldering a *large* connection with a hot air rework station, not about soldering tiny surface mount parts. I'm talking 8 or 6 gauge wire onto say lug terminals, or even soldering two 6 gauge wires together end to end maybe with a hook formed in each end.

Normally the bigger the bulk metal of the connection is the bigger the soldering iron required. For small 22 gauge wires a 30 watt iron would do nicely, but for much larger wires and large lugs we might have to go up to say 300 watts. That would be a big iron.

Well many hot air rework stations come with 500+ watt hot air stations. I have to wonder if we could solder a large connection with this kind of tool, like say two 6 gauge wires.

Anybody ever try this ? I couldnt find much about it on the web as everything is geared toward SMD work with the hot air soldering tools.
Hi Mr Al,
I have used my hot air gun to solder wires to large aligator clips, the ones that normally clip to a car battery. The hot air gun is what I normally use on shrink tubing.
 
Hi,

Is that a hot air gun or a hot air rework station hot air tool?
Hot air guns are typically 1000 watt or better. I thought about that too but never got around to trying it. If that works then that would be great too. I guess i'll just have to try it. I already have a hot air gun so i dont have to buy anything else.

I was recently thinking about the hot air tool so i could do small parts, but i really need to solder big stuff more. I have a SMD LED i need to solder too, but that can wait i guess.
 
Hi,

Is that a hot air gun or a hot air rework station hot air tool?
Hot air guns are typically 1000 watt or better. I thought about that too but never got around to trying it. If that works then that would be great too. I guess i'll just have to try it. I already have a hot air gun so i dont have to buy anything else.

I was recently thinking about the hot air tool so i could do small parts, but i really need to solder big stuff more. I have a SMD LED i need to solder too, but that can wait i guess.
Mr Al,
I use a hot air gun, the kind you can hold in your hand. I typically use larger diameter solder and hold a piece at the solder point with one hand and the hot air gun with the other hand.
 
Hi,

Thanks, this sounds like something i am just going to have to try i guess.

Side story, i bought a big soldering iron from Harbor Freight and the tip melted after only two or three uses :)
Most of the stuff i got from them works more or less ok, so this was a surprise.
 
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