HOW TO CHECK YOUR SECONDARY CIRCUIT
BY THE VOLTAGE DROP METHOD
It is sometimes hard to tell which component of your spot welder has failed. We have put together this data sheet to assist you in trouble shooting your spot welder. USE THIS TEST ONLY AFTER THE SCR AND TRANSFORMER TEST AS SHOWN ON OUR C-21 / C-22 DATA SHEETS HAVE BEEN READ AND UNDERSTOOD.
This is for after testing your SCR & Transformer and weld control completely.
(Also check fuses
carefully for a voltage drop or replace before going further, many times
a fuse “cracks” or does not pass full current even though it reads full
voltage!)
After testing the primary circuit or changing the
transformer, weld control, circuit breaker etc, and weld current still does not
flow the problem is probably in the.”Secondary Circuit”.
This is the low voltage (2-16 Volt AC),
high current side of the weld transformer.
Testing of this circuit is not practical with a basic OHM
meter. Using the “voltage drop method”
with a VOM (analog) meter is usually the best method to find a problem.
Next: With a VOM
(analog meter) connect one lead at point “A” upper
tip, and other lead as far back on the upper arm, or to the face of
transformer. Operate welder and try to
weld.
There should be no voltage reading! If a voltage reading of 1 volt or more is
detected this shows a “voltage drop” and a bad dirty connection on the upper circuit. Move you voltage leads from the tip to the
holder and on across each joint to find the exact location of the voltage
drop. This should pin point a bad
connection.
In a like manor do the same thing on the “lower arm”. From Point “C” to Point “D”.
When welding a voltage of about
1.0 to 2.0 volts should appear across the weld tips, between points “A” to
“C”. Weld checkers and monitors will
help measure these secondary currents and voltages. Miyachi Model MM-326B and Dengensha WS-80 records these
values.
On cable type gun welders, ACJ or WCJ cables, these can be tested
with this “ voltage drop method ” to determine if they are going
bad. It is a good rule to measure these
when new and record the voltage drop as a reference later when testing for
problems or bad cables.
On foreign controls or machines with “Secondary Constant
Current” check the pick-up coil for continuity and proper operation or
exchange. This may be damaged.
Preventative Maintenance: Clean the weld tips or
electrodes. Check the complete secondary
loop connections for bad cables, shunts, connections, weld tip tapers and
holder to weld arm connections. These
should all be “clean and tight”. ( Clean all joints twice a year and use SS-30 Jet Lube)
Summary: Be Safe --
Safety is your responsibility.
Check Main Power Fuses & Connections to SCR & Welder.
Check SCR
& Weld Control
Clean Tips & Electrodes
Measure with a VOM (Analog) meter at key
points per above for trouble shooting.
Record weld voltages and current with a
weld checker
Document the machine for later trouble
shooting and testing to save down time.
Use the latest “micro-ohm” meters for
testing secondary resistance. (Yellow Box.)
Trouble shooting a spot welder is a step
by step process, do it carefully.
RWESCO can repair or replace any
SCR contactor or
Welding Transformer.
If you run into this problem please contact our office for further
assistance!
Welding
Equipment & Supply Co.
Phone: (317) 251-9406 Fax:
(317) 251-9407 C-23
HOW TO CHECK FOR A SHORTED SCR
It is sometimes hard to tell which
component of your spot welder has failed.
We have put together this data sheet to assist you in trouble shooting
your spot welders SCR and
Resistance Welder
Transformer.
SCR's will usually fail in the "ON" position. This means your transformer is providing
"FULL POWER" at "100%
HEAT" to your weld tips during the entire welding cycle, including squeeze
and hold. If you trip the foot switch
(or palm buttons) the tips will spark and expel metal immediately upon
contacting the work piece.
A quick check of this problem is to double the squeeze time
and reduce the percent heat and try again.
If you still have the same problem your SCR or the Welding Transformer may be the cause. The following is a simple way to isolate the
defective component:
A. With welder power on and without
operating foot switch, put a voltmeter
(set for
2-10 VAC) across the weld tips. (Secondary Side)
If you read
voltage within that range, your SCR or the WELDING TRANSFORMER is shorted.
B. Now open the
control cabinet and place a volt meter (Set for 220 or 440 volts AC depending on your plant voltage) across the (2) lugs
of your SCR contactor.
(Primary
Side)
If no voltage is detected, your SCR is shorted and should be returned
for repairs or replaced.
If you read your full line voltage (220 or 440),
your SCR is OK and the problem is the Welding Transformer.
RWESCO can repair or replace any
SCR contactor or
Welding Transformer.
If you run into this problem please contact our office for further
assistance!
Resistance
Welding Equipment & Supply Co.
Phone: (317) 251-9406 Fax:
(317) 251-9407 e-mail: rwesco@iquest.net
Visit us on the world wide web at: www.spotweldequip.com
C-21
QUICK TESTING WELD TRANSFORMERS
An Ohm meter test for a weld transformer
short to ground can be performed as follows.
1. Be sure to complete an SCR or Ignitron operation test to be
sure the contactor is not shorted.
Always check safety items first.
Then check SCR before starting.
2. Turn
off Power to the machine. Get a Ohm meter (analog) and another person to assist you. Place a wooden block between the tips to keep
them from touching.
Welder Firing Ignitrons:
3. Remove
the H1 Line from the “X” Bars.
Welder Firing SCR Contactor:
3. Remove
the H1 Line from one side of the SCR Contactor.
4. Using the Ohm Meter, hold one probe against the removed H1
Line. Make sure you are not touching any
portion of the control cabinet.
5. With
the other probe, touch the control cabinet, then the welders frame. Do this at all tap
locations.
6. If
you have continuity, the transformer is shorted to ground and must be sent to
the factory for evaluation and repair.
Contact our office for information and directions.
7. If
you do not have continuity, the transformer must be tested more
extensively. Continue with our test
sheet C-23, How to test weld transformers.
RWESCO can repair or replace any
SCR contactor or
Spot Welding Transformer.
If you run into this problem please contact our office for further
assistance!
Resistance Welding Equipment & Supply Co.
Phone: (317) 251-9406 Fax:
(317) 251-9407
e-mail:
rwesco@iquest.net Web Site:
www.spotweldequip.com C-22
HOW TO CHECK WELDER FOR TRANSFORMER TO GROUND
It is hard to tell which component of your spot welder has failed. We have put together this data sheet to assist you in trouble shooting your spot welders SCR and Welder Transformer.
If a welding transformer goes to
ground, you will read voltage at the weld tips.
If the tap setting is increaded the voltage
will increase. As the problem gets
worse, you will start blowing fuses. The
transformer must be rewound or a new unit installed.
A. With welder power on and without
operating foot switch, put a voltmeter
(set for
2-10 VAC) across the weld tips. (Secondary Side)
If you read
voltage within that range, your SCR or the WELDING
TRANSFORMER is shorted. If the voltage is higher then the secondary
name plate voltage on the machine,
the transformer should be suspected.
A High Pot or Meg Test should be performed on the
transformer to confirm that it is shorting to groung.
Welding transformers when shorted to
ground, and if the machine is not correctly connected to a solid earth ground,
can cause electrical shock. Grounding reactors are used to
prevent shock. The Grounding Reactor is
an additional winding connected across the L1 and L2 lugs for the transformer
and with a third line connected to ground.
If a voltage of around 24volts is sent across the connection, the
reactor will short to grond and trip the machines
circuit breaker.
One side of the secondary is normaly grounded. If
the Primary “A” shunts to ground, a path through the secondary is
established. A voltage across the tips
will be present.
RWESCO can repair or replace any
SCR contactor or
Welding Transformer.
If you run into this problem please contact our office for further
assistance!
Resistance
Welding Equipment & Supply Co.
Phone: (317) 251-9406 Fax:
(317) 251-9407 e-mail: rwesco@iquest.net
Visit us on the world wide web at: www.spotweldequip.com
C-23
TESTING WELD TRANSFORMERS
THIS IS THE LAST TEST TO TRY --
BE SAFE!
A voltage test for a weld
transformer can be performed as follows. Try this test after the tests from
sheet C120, C-121, C122, and C-123 have been completed.
1. Be sure to complete an SCR or Ignitron operation test to be
sure the contactor is not shorted.
2. Turn
off Power to the machine. Get a voltmeter
and another person to assist you. If possible feed in with
110 volts and the machine power off per below.
Welder Firing Ignitrons: Replace the entire
controller/timer!
Welder Firing SCR Contactor:
3. Jumper across the two main lugs of the SCR. Use a #4 or larger wire, approximately one foot long. Be sure the jumper does not touch anything else.
4. Have
your assistant turn on the Main Power.
5. Measure the
voltage across the upper and lower electrodes.
** Be sure the
tips are NOT touching! **
Use a wooden block to insulate between the weld tips!
6. Direct
your assistant to advance the tap switch on the
transformer through all settings.
(Unplugging the 110V or turning off the power to the
transformer each time!!)
7. If the voltage on the meter reads between 2 to 16 volts (or less with 110V) at each setting, and increases with each higher tap, the transformer is operating normally. If no voltage is measured at any setting, the transformer or it's wiring connections are faulty.
8. Turn
off the Power to the machine as soon as possible and remove 110V or the jumper.
9. Turn
the Power back on and recheck for voltage across the tips. If voltage is measured, the transformer is
probably shorted.
RWESCO can repair or replace any
SCR contactor or
Welding Transformer.
If you run into this problem please contact our office for further
assistance!
Resistance
Welding Equipment & Supply Co.
Phone: (317) 251-9406 Fax:
(317) 251-9407 e-mail: rwesco@iquest.net
Visit us on the world wide web at:
www.spotweldequip.com C-24