I have an old Hobart welder (TR-300-HF) which frequently drops to its
lowest current setting at any given range (e.g. 50A at 50-250A). It
welds fine in this state, but having only 3 current levels is annoying.
No amount of foot pedaling or turning the current knob seems to fix
this problem when it happens. Assuming the potentiometers in the
current knob and foot pedal are OK, what is the most likely cause?
What should I check first?
Sounds like you blew your main reactaince coil.
Sometimes they can be repaired, but more often they have to be replaced.
I had an old P&H 300 TIG that died that way.
The Hobart should be repairable.
Thermal arc supports those old large Hobarts for parts.
Get it to a repair shop if possible.
If you were in Seattle I could give you to excellent repair shops to
take it to.
Those old machines do have a limited lifespan mainly from the insulation
on the transformers finally drying out so much it just fails.
The old grey Lincoln Idealarcs have the same problem.
Luckily those old machines are so simple that they are pretty easy to
Welding Instructor - South Seattle Comm. Coll.
- Divers Institute of Technology
Check your foot cable...
Maybe you have a broken wire in it - and it reverts to low. Maybe a short does
Up near the machine interface - where it might kink and yank a wire out or on
end - or in the middle - look for a pinched/broken area.
I don't doubt Ernie on anything - just some trouble shooting concepts.
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member
I wonder if, on these older machines, that one could simply pour some
"Formvar" into the transformer, as best they can, and let is sit near a
heater or heated with a heat gun, in order to 'renew' the varnish on the
wire BEFORE the old varnish dries to the point of cracking and therefore
I know that it is common to take large electric motors in and have the stator
(the fixed outer part) re-varnished and baked. If you have one you're worried
about, why not call a motor shop and ask if their process might work on your
Both are large magnetic arrangments of conductors ..
Of course, it might be hard to get varnish in between the transformer
If you were to submerge the transformer in epoxy and pull a vacuum on
the thing, you might be able to reinsulate the windings.
Anyhow, After looking at my welder, I don't think its the transformer.
There are actually 3 separate transformers (corresponding to the 3
current ranges), with the coils made out of rectangular copper bar.
The epoxy looks to be in good shape, and each turn is spaced by
insulating slats about 3/32" thick so air can pass between each loop.
It looks like the whole assembly was then dipped in more epoxy. It all
seems to be in good shape, and Its unlikely that all 3 transformers
would fail at the exact same time and manner, but I get the same
symptoms on each current setting.
I know now that its a saturatable reactor system, so the current output
is controlled by a DC electromagnet wound into each transformer. I
think these are OK too, because its only supposed to be ~24V DC
(according to Dennis at Arcowelder, who was very helpful), and a short
would cause my welder's output to go up. Full power to the DC coil
should bring the welder to its lowest current, which is exactly what is
happening. I'll check the output on the PC board next. This is all
pretty new to me, so I could be wrong.
Grant Erwin wrote:
I think that you are doing the right thing, which is talking to
knowledgeable people and poking around with a multimeter.
Did you check what the potentiometers are telling the control board?
When you turn the potentiometer knobs, do these inputs change _right
at where they enter the board_?
I am not having a problem, at least not yet.
However, I am pretty sure that one could simply pour and brush on Formvar so
as to permeate the interstices in the windings. Naturally, it wouldn't be
like re-wound and baked but my guess is that it would do well.
I don't think it would hurt anything.
On Tue, 27 Jun 2006 00:46:01 GMT, Ernie Leimkuhler
I think he has one in the bone yard
Ask for Dennis
"If thy pride is sorely vexed when others disparage your offering, be
as lamb's wool is to cold rain and the Gore-tex of Odin's raiment
is to gullshit in the gale, for thy angst shall vex them not at
all. Yea, they shall scorn thee all the more. Rejoice in
sharing what you have to share without expectation of adoration,
knowing that sharing your treasure does not diminish your treasure
but enriches it."
- Onni 1:33
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