Going to replace the stepdown transformers in the IBM 1130 being restored

INADEQUATE TRANSFORMER CAPACITY RAISES SAFETY ISSUES

Portions of the IBM 1130 system require 115V supply thus when a machine is configured to attach to 208V or 230V mains, stepdown transformers were used in the machine to deliver the lower voltage. Specifically, two transformers T2 and T3 are configured in machines that attach to higher voltages.

Transformer T3 is used solely to power some convenience outlets, the normal US household duplex outlets, which are inside the covers of the IBM 1130 processor and inside the 1442 Card Reader/Punch. These are generally used to power oscilloscopes and other test gear, but have been used for vacuum cleaners and floor washing machinery in data centers. 

The transformer has its primary inputs protected by fuses F3 and F4, thus limiting the current that can be drawn through all the attached convenience outlets to a maximum of 6.5A at 115V. The transformers that are installed in the machine right now are rated at 300VA, thus they cannot support the roughly 750VA that the outlets could pull. The result in that situation is that the transformer overheats, perhaps is damaged but in the worst case could burn. 

Temporarily, I am protecting against that risk by lowering the fuse sizes in F3 and F4 to keep the load within T3's 300VA capability. Longer term, I will purchase a new stepdown transformer good for at least 750VA and place that in the 1130 along with the original fuse sizes. 

Transformer T2 is used to provide 115V to a number of destinations in the machine, per the design, plus one additional load that is unique to this machine. As designed by IBM, this transformer provides 115VAC for the cooling fans in the machine. It also provides 115VAC for peripherals such as the internal disk drive, the console printer and in other system devices such as paper tape peripherals or plotter. 

Since our machine has had most of its cooling fans in the 1130 replaced with 230V motors, they no longer are attached to T2. On the other hand, the lighting power supply that is used by all the incandescent bulbs behind the main display panel is a part that comes in two types. One type is 115VAC only, the other type is only 208 or 230V. Since this machine was originally configured for 115VAC, I had to provide the power to this supply from T2.

The primaries for T2 are not protected by fuses. Instead there are fuses to limit some but not all of the draw on it. Fuse F7 limits the 115V load for the incandescent light power supply to 1A. Fuse F6 limits the load for the console printer motor, disk drive motor, and disk drive cooling fan to 3.25A. These sum to almost 500VA which exceeds the capability of T2 even without it driving the seven cooling fans in the processor box. Without blowing fuses this could produce overheating and perhaps burning of transformer T2.

I will replace this transformer with one having sufficient capacity to power all the gear and the original 115V cooling fans, even though I won't convert back to those fans at this time.