MIL-W-80040E
3.4.9 Ventilation system. Unless otherwise specified (see 6.2), a forced
air cooling system shall be provided. When furnished, forced air cooling
shall be provided by a single phase, totally enclosed, prelubricated, ball
bearing fan motor(s). The fan shall provide ventilation and cooling of all
component parts to meet the 100 percent duty cycle in 110°F ambient tempera-
ture. The fan assembly shall be mounted to withstand the vibration. Fan
blades shall be of material and design that will prevent fatigue failure under
conditions anticipated for these units.
3.4.9.1 Cooling fan control. When specified (see 6.2), the cooling fan
shall be provided with a control device to operate the fan only when the
transformer-rectifier system requires forced air cooling. Fan control may be
furnished when not specified, provided the control system is part of the manu-
facturer's standard design.
3.4.10 Insulation. Transformer insulation shall conform to NEMA EW 1. The
class of insulation system used shall permit continuous transformer operation
and performance.
3.4.11 Temperature rise. The maximum allowable temperature rise of the
various components of the power source shall conform to NEMA EW 1. Means
shall be provided to remove the main transformer from the "primary power line
before the temperature within the power source enclosure reaches a damaging
temperature.
3.4.12 Transformer. The transformer shall produce a continuous current
which, when rectified, shall have a direct current rating as specified in 1.2.
Transformer assemblies shall either be dipped and baked in class F or better
varnish and then mounted to the base also sealed with a material to withstand
extreme environmental conditions or all transformer and diode assemblies shall
be mounted to the base then dipped in air drying varnish and dried according
to the supplier's recommended drying practice.
3.4.13 Diodes. In combining diodes to obtain required output current, no
diode shall carry current in excess of its safe operating current under any
steady state or transient condition of welder operation. Paralleled diodes
shall share the current load (by using resistors, matched pairing, or other
means). Surge suppression protection shall be provided with capacity to reduce
any transient voltage peaks which would cause failure of the diodes from ei-
ther AC or DC reflected transients. The diode bank or stack shall be remov-
able as a unit to permit removal and replacement of individual diodes. The
diode stacks shall be installed to minimize the collection of foreign par-
ticles in and around the stacks. All heat sinks shall be coated with an anti-
corrosion material to withstand a salt water environment. All main power
diodes shall be protected from environmental damage by a material which com-
pletely seals the device.
3.4.14 Electrical requirements. The power source shall be wired to conform
to NFPA 70. Unless otherwise specified (see 6.2), the power source shall op-
erate on 3 phase, 60 Hertz (Hz) input power. The primary Input voltage on the
size 500 and 750 ampere power sources shall be either 230 volts or 460 volts,
as specified (see 6.2). The primary input voltage on the size 1000 and 1500
ampere power sources shall be 460 volts.
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