A friend of mine here on Whidbey Island has a welding business. It's
pretty new, only a few years now. Anyway, he called me yesterday with
an electrical problem. Puget Sound Energy (PSE) has had complaints
from neighbors about voltage spikes or drops, my friend wasn't clear
on this, but they showed him a graph which I have yet to see. The
solution PSE is proposing is a new xmfr at the pole. PSE told my
friend the problem is because of the hard starting welder. The welder
is an older xmfr type machine with lots of copper. At full load it is
rated at 11 kw, which is about 46 amps. But I don't know what the
current spkies to when he first steps on the pedal. The machine is now
wired for single phase but can be wired for three phase. What he wants
to know is if he ran the welder from a Rotary Phase Converter would
the current spikes and voltage drops be less. I don't know. I also
don't know if there is a way besides my friend paying thousands for
PSE to install a new xmfr on the pole for this situation to be
ameliorated. He can't afford at this time for a new welder with a
softer start setting. Besides, the hard fast start means his employee
can make more welds. Any help would be greatly appreciated.
You could look into turning it on with a Zero Crossing Relay.
Can you check the voltage, current and power fector with a scope?
On Thursday, October 30, 2014 1:36:31 PM UTC-4, Jim Wilkins wrote:
. What he
Not a good idea. This is from Wiki.
When a transformer is first energized, a transient current up to 10 to 15 t
imes larger than the rated transformer current can flow for several cycles.
Toroidal transformers, using less copper for the same power handling, can
have up to 60 times inrush to running current. Worst case inrush happens wh
en the primary winding is connected at an instant around the zero-crossing
of the primary voltage, (which for a pure inductance would be the current m
aximum in the AC cycle) and if the polarity of the voltage half cycle has t
he same polarity as the remnance in the iron core has. (The magnetic remane
nce was left high from a preceding half cycle). Unless the windings and cor
e are sized to normally never exceed 50% of saturation, (and in an efficien
t transformer they never are, such a construction would be overly heavy and
inefficient) then during such a start up the core will be saturated. This
can also be expressed as the remnant magnetism in normal operation is nearl
y as high as the saturation magnetism at the "knee" of the hysteresis loop.
Once the core saturates however, the winding inductance appears greatly re
duced, and only the resistance of the primary side windings and the impedan
ce of the power line are limiting the current. As saturation occurs for par
t half cycles only, harmonic rich waveforms can be generated, and can cause
problems to other equipment.
For large transformers with low winding resistance and high inductance, the
se inrush currents can last for several seconds until the transient has die
d away (decay time proportional to ~XL/R)and the regular AC equilibrium is
established. To avoid magnetic inrush, only for transformers with an air ga
p in the core, the inductive load needs to be synchronously connected near
a supply voltage peak, in contrast with the zero voltage switching which is
desirable to minimize sharp edged current transients with resistive loads
such as high power heaters. But for toroidal transformers only a premagneti
sing procedure before switching on allows to start those transformers witho
ut any inrush current peak.
I would contact the welder manufacturer and ask them if they know of any go
od solutions. And maybe contact the power company and ask them the same qu
He can't be the only one with that problem.
It depends on the contract that he signed for power, or the regulations
in your state.
There's a good chance that anyone using power beyond normal residential
use is expected to pay for any necessary upgrades -- it varies by state,
and I wouldn't even have a clue as to what the rules are in Oregon.
For that matter, in most places if you want power run to your house
you've got to pay for it, by the foot.
On Thu, 30 Oct 2014 12:17:56 -0700, firstname.lastname@example.org wrote:
You might look into power factor correction caps for the welder.
There's plenty of misinformation about this online without my adding
to it, but my understanding is that a welder with PF correction will
draw more current at idle, but less under load. Not sure what it'll
do, if anything, about surges.
Re who's responsible, in my area there are certain single phase loads
that the power company can force you to remove if they cause problems.
Single phase motors larger than 5HP, for example.
On Thursday, October 30, 2014 3:47:56 PM UTC-4, Ned Simmons wrote:
I think your understanding is wrong. With power factor correction the current at idle will be less. Under load it will also be less, but the difference may be almost unmeasureable.
But you are right. Correcting the power factor may make things enough better that he will not have to do anything else.
On Thursday, October 30, 2014 7:58:06 PM UTC-4, Ned Simmons wrote:
urrent at idle will be less. Under load it will also be less, but the diff
erence may be almost unmeasureable.
I do not understand the Miller chart. On my own welder , I added PFC capac
itors which reduced the idle current. Did not measure the current while w
elding, but my understanding of transformers makes me think that while weld
ing the imaginary current would stay the same , but the real current would
be much bigger. So the effect of power factor correction would be negligib
le while welding.
I looked for information on other welders but did not find any.
A rotary phase converter may help, but I wouldn't expect it to cut the
problem by more than a factor of 2/3, and very possibly not even that.
I'm just guessing, though.
There may be soft-start add-on kits out there that will be cheaper than
either a transformer or a new welder.
If he's got an established business he may be able to get a business
loan. He'd have to be willing to get into debt, and have enough proof of
income to swing it, though.
Eric - a "soft start" on/off switch might be a possible cure. In concept
it turns on the current when the cycle is nearly over and then turns of as
the current passes zero. On the next cycle the current is turned a little
earlier. After ?? cycles full power is turned on for all cycles.
Mouser Electronics shows a 40 amp triac, which is the "switch" in a
soft start device, for roughly $2. Probably need a micro controller to
control the triac - $.50, along with a pc board & some caps & a transistor
or 2. Then a "heat sink" and, probably, a healthy fan.
All told, the cost isn't much so someone has probably built such a
gadget for sale as an "add on". If you can't find one, look for someone to
build it and offer to do some testing for him.
Sounds like a phase angle controller powering a transformer which while
it works, I've done it on a Xformer for a TIG supply to ramp up/down the
current, is electrically very noisy as you end up potentially putting
maximum AC voltage into the transformer suddenly rather than the normal
build up from zero so high transient currents. I didn't see the effect
on the flourescent lights as I was welding but when it was pointed out
to me and I had a look they did significantly flicker during the
transition phase from 0 to full on power. No neighbours complained and I
checked with one about HF interference with their TV and no problems.
Subsequently I have gone to an inverter TIG and at higher currents
upsets the ADSL modem in the house but I don't know of anyone else
having any issues. Likely I should fit a suitable filter at the welder
supply but I'm the only one with the issue with losing ADSL connection
when welding at higher currents. I think a soft start might work in a
more friendly manner.
Soft start may not be the ideal. When welding, if a soft start is
used, it takes longer to do the weld. This not only translates to
lower throughput it also frustrates the worker who wants to get as
many parts out the door as possible. I know that for me, as a
machinist, even when I worked for someone else, I hated stuff that
slowed me down. At the end of the day my pay would be the same but I,
like most folks, jest wanna git the job done. Thanks for your
suggestion though, it may be that even though not ideal in all
situations it will be the best solution. I will consider this when I
try to help my friend out. I had to use soft start on one of my CNC
machines in the past when the power available was just a little too
low. Fortunately for me I was able to adjust the spindle drive for a
Eric - I'm guessing you're associating "soft start" with motors and the
long times inherent with heavy weight & limited horse power. I
checked the inductance of a 10 amp 120 volt transformer & it showed .5
henry. The time for 240 volts & 46 amps comes to .095 seconds. (t inductance * current / voltage).
Keep in mind that I am guessing on this, but if you can find an addon
"soft start" device with adjustable timing, it might be effective.
I'd like to hear the result, too.
Soft start on a welder takes longer than for a motor. This is an
adjustment on the welder itself. And even though it is pretty fast it
is not ideal. Especially when welding aluminum because you want the
metal to get hot as fast as possible. So the technique is to stomp on
the pedal all the way to get the maximum current. Then as soon as a
puddle starts to form the current is decreased. If the aluminum is
heated slowly too much if the heat spreads into the surrounding metal.
After several inches of welding in a localized area the work gets
really hot until it is too hot to handle. Heating the metal fast,
applying the filler fast, and getting off of the pedal makes for
higher throughput. Today my friend is emailing me the graph from the
power company so I will learn more and will post results here. I will
also post the results of the final fix, whatever it is.
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