Selco Genesis 90, Repair Manual

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Instruments and conventions for performing diagnosis and repair 5
3) INSTRUMENTS AND CONVENTIONS FOR PERFOR-
MING DIAGNOSIS AND REPAIR
3.1) Instruments for basic diagnosis
The following are required:
- a multimeter w
ith the following scales:
Ohm: from 0 to a few Mohm
Diode testing
Direct voltage (Vdc): from mVdc to 700 Vdc
Alternating voltage (Vac): from 10 Vac to 500 Vac
NOTE: You are advised to use an instrument with
automatic scale since it is not theoretically possible to
predict the electrical quantity to be measured when
the machine has broken down.
- an DC ammeter clamp at least in class 2.5 with e.o.s. 100A pk
- alternatively to the ammeter clamp, a shunt can be used with
value 60 mV @ 100 A.
NOTES:
* remember that other types of shunts can also be used,
but accuracy is reduced with higher capacities, whe-
reas with lower capacities the measurement must be
taken quickly to avoid overheating of the shunt
* once fitted, the shunt can be at dangerous potentials!
* the ammeter clamp is preferable as it is more practical
3.2) Repair tools
- complete set of fork spanners
- complete set of pipe spanners for hexagonal nuts
- complete set of blade screwdrivers
- complete set of Phillips screwdrivers
- complete set of Allen keys
- Phillips torque screwdriver for M3 screws with tigh-
tening torque adjustable range from 1 to 3 Nxm,
accuracy 0.1 Nxm
- crimper for insulated wire terminals (blue, red and
yellow)
- pliers for AMP contacts
- tweezers and cutting nippers - type commonly used
for electronic components
- tongs (dimensions suitable for closing gas pipe
clamps)
- welder for electronic components, minimum power
50 W
- portable electric drill
3.3) Grid load
Use of grid load can speed up fault tracing and machine testing.
Just remember that a fixed power resistor applied to machine's
output is somewhat equivalent to a welding arc, but only inside
of a narrow output voltage range, whose center value can be
determined by the formula:
PLASMA CUTTING:
V
OUT
80 + 0.4 x I
OUT
Es.: 100Vdc @ 50A
116Vdc @ 90A
etc.
If output voltage goes too much above or below the rated value,
the generator could either saturate and in both cases real out-
put current could be much different from expected value.
Grid load resistor's rated power is also important, 'cos a 116Vdc
@ 90A grid load produces 10kW to be dissipated by air cooling.
So, when using grid load, pay attention to both out-
put current & output voltage and use correct resi-
stance value & power!