On 1 Jan 2006 13:06:45 -0800, "mj" wrote:

I tried posting this earlier, but I got an error message when I went to
post it. So, I am not sure the first message went anywhere. If this is
a double post, I apologize.

I am attempting to build a resistance soldering unit from a small car
battery charger. I am following these directions:

http://www.trainweb.org/girr/tips/tips1/solderer.pdf

I am using a 12v 6a charger that, I think, is too small. I can just get
two pieces of .005 brass sheet soldered together before the charger
circuit breaker shuts off the charger. The charger will run for about
6-7 seconds. This should heat it up within 3 seconds. I would like to
solder up to around .025 brass sheets together too. I found a 12/30/75
amp charger at Menards that is probably my next step. But I would like
to be able to vary the current coming out. Do I need a variac for this?
Does this go on the input (110v) or the output (12v) side of the
charger? What specs (volts/amps/watts) should I look for on this? I
also know that I could use a filament transformer of around 6.3v 6-20
amps on the secondary in place of the battery charger. Any suggestions
on which is better? I KNOW that using a light dimmer switch for the
adjustment setting is a bad idea.

I already know that American Beauty and PBL sells these. But for around
$500 for a 250 watt model, I think I will screw around with this some
more. I am bidding on a 300 watt model on ebay right now.

I also searched around the Internet for more instructions. But
everything I found was pretty vague. I am electronics illiterate, but I
can usually figure stuff out with some clear directions.

ANY help on this would be greatly appreciated.

THANKS!

You're not getting nearly enough current from a small battery charger.
One 500-watt resistance soldering box (Wassco Glo-Melt model 105-B2)
has voltage taps from 1.0 to 5.8 volts -- which, at 500 watts would be
500 to 86 amps.

You might try a soldering gun --without the tip. My (old) Weller
D-550 delivers 240 or 325 watts at 1.5 volts. That's 160 and 216 amps
-- if the load resistance is low enough to accept it. There's one
;ike it on EBay right now:

http://cgi.ebay.com/ws/eBayISAPI.dll...y=46 413&rd=1

Looks like current production D550's are rated at 260/200 watts.
The D650 is rated at 300/200 watts. You might also try a 150 from
HF( item 42685) for $9.99. You could use two or more in series or
parallel to get more heat.

The tubes on the Weller are threaded 7/16-14 so you could connect to
it with a couple of bolts. Use very heavy wire like #4 welding
cable, automotive ground braid or copper strip for (short)
connections from soldering gun to work and stinger. The issue isn't
overheating the wire, but minimizing voltage drop everywhere but in
the load itself.

Yes, a variac would be the best control. With a variac, I'd tape the
trigger down on the gun and use the variac to control it. A foot
switch might be handy too.