larry moe 'n curly wrote:
Michael A. Terrell wrote:
larry moe 'n curly wrote:
http://www.harborfreight.com/1500-watt-dual-temperature-heat-gun-572-1112-96289.html
$19.99 regular price. On sale for $9.99 at times.
I received their weekly e-mail right after I posted. It is on sale
for $7.99 with the coupon below:
http://www.harborfreightusa.com/html...7/images/2.jpg
Here is the user manual:
http://images.harborfreight.com/manu...6999/96289.pdf
The power switched popped out 3/16" when I pressed it (2 samples)
Then why did you buy one? Mine is fine, and I just picked one off
the shelf, yesterday. I already have an old B&D, and a five year old HF
heat gun. The case on the B&D melted when I had to preheat some 1.5"
copper pipe while assembling the cooling system on an old TTU-25B UHF TV
transmitter. I also needed an acetylene torch & a 175W Weller iron to
remove some damaged copper pipe from some custom 30 year old brass
fittings RCA used in that transmitter. The HF has been used to remove
floor tiles, on heat shrink, and to expand metal castings to remove
bearings.
The diode in series with the heating element is a 1N5408, rated
for 3 amps average. The heater draws 8A average on low.
So my question is, how long will this 3A diode last?
Where is the 1N5408 diode? It isn't listed in the parts list or
shown in the drawings:
http://images.harborfreight.com/manu...6999/96289.pdf
How long to you use a heat gun per application? Can you read a
datasheet, or only skim one? That 3 A rating is for continuous duty at
a high operating temperature, not intermittent. The peak current rating
is 200A. The case would likely melt before the diode would fail.
http://www.datasheetcatalog.org/datasheet/GeneralSemiconductor/mXyztrxt.pdf
I've seen four 1N4004 diodes in a bridge, in series with the heater in
a hair dryer to power the dc motor on the fan. Are you claiming that a
tool like that can only provide less than 120 watts of heat?
I bought the HF heat gun yesterday, and it has a manufacturing date of
Jan, 2010. Here's a photo of the inside, showing the 1N5408 diode
across the two poles of the switch:
http://farm4.static.flickr.com/3315/...3af89634_o.jpg
The switch popped out because the lower locking tab was squashed and
couldn't lock.
I've seen that in a lot of imported equipment, not just in tools.
I think there's a bridge of small diodes at the end of the fan motor.
There were none external to the motor in mine. Just two 1/8" fastons
that plugged onto the end of the motor.
Doesn't the continuous amp rating for a diode apply for any load
lasting more than something like one 60 Hz cycle (or half-cycle?). I
normally run a heat gun a lot longer than that, 
maybe up to 2
minutes at a time.
Have you used it for that two minutes? That should answer your
question, and show that it takes more than two minutes to damage it.
It takes time to heat the junction in the diode. The heat is
produced only when forward biased, and is from the forward voltage drop,
times the current flow. The higher the current, the faster it heats.
Since a heat gun usually gets very intermittent duty in low heat mode,
it works.
If it can handle a couple 200 amp half cycles while charging an
electrolytic in a piece of electronic equipment, it can handle the extra
current for the heating element even though it is above the 3A
continuous rating.
It looks like the motor is run from a tap on the heating element.
There is no schematic in the manual. I only saw the one diode, across
the switch in mine. Also, how often will you use one on low heat? I
rarely do, usually only when I accidentally hit the wrong end of the
rocker switch.
BTW, if that diode fails, all it will do is make it run at full heat
in either 'ON' position.
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.