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cold heat soldering iron.

C

Clive Mitchell

Jan 1, 1970
0
I just got one of those cold heat soldering irons today. It's a battery
operated soldering iron that has the unusual characteristic of only
generating heat on the solder joint. I bought it out of interest to see
what the technology was like, and whether it was going to be as ground
breakingly wonderful as their marketing department would have us
believe.

I tried it out and was rather surprised to find that it instantly cooked
a small pad before I could get the solder near it, and lifted the pad
clean off the circuit board. After a bit of practice I was able to do
modestly successful solder joints on average sized pads, but even with
some practice it wasn't performing anywhere near as usefully as a
conventional iron.

The unit operates by passing current through the object to be heated.
The tip is a conductive ceramic that is split like a quill with an
insulator in between the two halves. When you turn the unit on a white
LED illuminates the area of work while a red LED indicates when a
connection has been made and heat is being generated. When you make the
connection there is often a spark from the pad being heated, and the
ceramic heats in the vicinity of the tip where it's tapered in.

I originally thought that maybe the design was as simple as the power
from the four AA alkaline cells being passed directly through the tip,
but found some info that suggested there was a PCB inside to generate a
lower voltage at higher current. There's not. The battery pack IS
connected directly to the tips via a suspiciously small slide switch.
There is a circuit board inside, but it holds the resistor for the white
LED and a mystery surface mount chip that has had it's number scrubbed
off. It's obviously a comparator or op-amp, since it's function is
purely to light the red LED when the unit is making contact with the
workpiece. It detects this scenario by simply measuring the battery
pack voltage which is dragged down significantly by the near short
circuit at the tip! A zener is used as a crude voltage reference to
detect the dip.

They don't recommend rechargeable batteries, presumable because the
lower internal resistance may cause excessive current to flow. It may
also be because the dip in the alkaline cells when loaded is about the
same as a rechargeable pack could sustain, so the led circuit might not
work.

You don't actually need the red LED to know contact has been made. The
white LED dips significantly when contact is made.

I did find one use for the iron. It seems OK for reflowing solder
joints, so might be quite handy from a service aspect. Quite frankly
though, I'd suggest that a small gas powered iron is not only cheaper,
but has much greater functionality in a lighting technicians toolbox.

Other slight niggles. If you're used to applying a brief burst of extra
pressure to a soldering iron when using it to melt a troublesome joint,
then you may break the ceramic tip. I guess from the repeated warnings
that this has been happening a lot. The tip also tends to get a slight
layer of flux on it which insulates it preventing the device making a
proper connection.

In short, it's a novelty. Don't waste your money.
 
T

TKM

Jan 1, 1970
0
I did find one use for the iron. It seems OK for reflowing solder joints,
so might be quite handy from a service aspect. Quite frankly though, I'd
suggest that a small gas powered iron is not only cheaper, but has much
greater functionality in a lighting technicians toolbox.

Other slight niggles. If you're used to applying a brief burst of extra
pressure to a soldering iron when using it to melt a troublesome joint,
then you may break the ceramic tip. I guess from the repeated warnings
that this has been happening a lot. The tip also tends to get a slight
layer of flux on it which insulates it preventing the device making a
proper connection.

In short, it's a novelty. Don't waste your money.

Any worries aboout the voltage getting into the wrong place and frying
semiconductors?

Terry McGowan
 
C

Clive Mitchell

Jan 1, 1970
0
In message said:
Any worries aboout the voltage getting into the wrong place and frying
semiconductors?

Absolutely. This thing will happily blow the crap out of anything in
the same way that you could by simply connecting a 6V battery pack
across something like an LED.

It wouldn't be hard to complete a circuit through something that was
already soldered in at one end and it's other lead and the adjacent pad.

It's an interesting device, but ill conceived for electronic work. I'm
sure it'll be ideal for some specialist application though.
 

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