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Blue Max

Manufacturers of Resistance Soldering Irons

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Don't use crocodile clips as the sharp points will get hot and make a mess of brass.

 

 

I disagree.  I use a croc all the time with no trouble though it can get warm if I am soldering thicker brass.  I filed the teeth off the clip and have had no problems.  I either clip the croc on to a convenient bit of the kit or just apply it like a second handpiece.

 

However, much depends on what you are using the unit for.  Thicker brass and larger joints require a bit more 'oomph' which, if you leave your foot on the switch for any length of time, does make the croc clip hot.  The voltage also makes a difference.  With the clip, I invariably have my LRM unit on 2 volts, 2.5 volts for a bigger job, 1.5 volts for more delicate soldering like half-etched leg supports on platform trolleys.  If one is using a metal plate, because the plate acts as a heat sink, higher voltages may be needed.

 

I suggest the bottom line is the need to try things out, to test and experiment on scrap brass before attacking your kit.  Keep the voltage as low as is necessary, your foot on the switch for no more than 1 or 2 seconds and, if soldering overlays where there are repeated 'zaps', leave a gap at least as long as the time you keep your foot down.  This should avoid the handpiece (and clip) getting hot.  Warm is normal; hot is not, so if it does get hot, you are either doing something not right, applying the current for too long or applying it too frequently.  I also see tips of probes glowing red hot.  For a 4mm model, this should be a rare occurrence and only with heftier soldering jobs.

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I built one using a redundant 300w ATX PSU from a PC. If you wire together all of the outputs for each voltage you can get 25-32A out of most PSU at a few volts (if you use the 3v and 5v outputs, you get 2v potential difference), plus the PSU has a thermal cutout and overload protection. You will likely need to short the power switch connector to ground to get the PSU to fire. Silicone insulated stranded wire rated at 40-50A is very flexible and you can get automotive connectors rated for 40-50A. I used a £2 foot switch from China and a 40A solid state relay to switch it on/off, an old soldering iron and big brass screw terminal connector works for the probe, and I use electrodes from spent batteries (open up a dead battery to find a nicely sized carbon rod) as I couldn't find welding rods the right diameter. A bit of mild steel plate and some magnets to hold stuff to it and it works well.

 

I'm not claiming it to be the equal of a professionally built £150 machine, but for an outlay of about £10-15 it's rather good.

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I disagree.  I use a croc all the time with no trouble though it can get warm if I am soldering thicker brass.  I filed the teeth off the clip and have had no problems.  I either clip the croc on to a convenient bit of the kit or just apply it like a second handpiece.

 

However, much depends on what you are using the unit for.  Thicker brass and larger joints require a bit more 'oomph' which, if you leave your foot on the switch for any length of time, does make the croc clip hot.  The voltage also makes a difference.  With the clip, I invariably have my LRM unit on 2 volts, 2.5 volts for a bigger job, 1.5 volts for more delicate soldering like half-etched leg supports on platform trolleys.  If one is using a metal plate, because the plate acts as a heat sink, higher voltages may be needed.

 

I suggest the bottom line is the need to try things out, to test and experiment on scrap brass before attacking your kit.  Keep the voltage as low as is necessary, your foot on the switch for no more than 1 or 2 seconds and, if soldering overlays where there are repeated 'zaps', leave a gap at least as long as the time you keep your foot down.  This should avoid the handpiece (and clip) getting hot.  Warm is normal; hot is not, so if it does get hot, you are either doing something not right, applying the current for too long or applying it too frequently.  I also see tips of probes glowing red hot.  For a 4mm model, this should be a rare occurrence and only with heftier soldering jobs.

Agree with all you have said.  I too have a croc clip filed (and filled with graphite).  The filing/filling is obviously meant to spread the point of contact.  Lets just say that if you don't file it down and go it a bit then you have a risk of damage.  As you say there are pro's and cons to metal plates and a useful attachment is a lead connected to a tag that can be bolted to a chassis once it reaches that point.

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Another vote for the LRM unit. Really great service and a nice unit.

 

Forget finding a chunk of metal for a base. Bryn put me onto kitchen foil wrapped round a balsa block - it doesn't heatsink and it's easy to pin stuff down

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