4 MOT power supply
As a power supply for my 4"
TC and other high voltage experiments which require some power I've connected
four MOTs in series to get 8 kVAC RMS.
The MOTs on the lower side of the foto below are unmodified with their cores grounded.
The other two MOTs are immersed in paraffin oil. Here in Germany there are drain
pipe fittings with an inner diameter of about 120mm which are perfectly suited
for housings. The lids aren't glued to the fittings but are held in place by rubber
seals - which is as good as glueing, pulling out the lids out of the fittings
requires brute force. For electrical connection I've screwed blade terminals to
the lids, internally the screws are connected to the MOTs by wires with PVC hoses
shoved over them for additional insulation. After the power supply was finished
I've found out that the paraffin oil removes the softener from the PVC. Luckily
further experiments showed that the hoses don't get brittle but just become stiff
- doesn't seem to be a problem. The side of the high voltage winding which is
normally connected to the core has been disconnected from the same and isulated
from the core with epoxy resin.
Due to the small housings I've only needed about 3/4 liters of paraffin oil per
MOT. The valves were used to evacuate the housings to remove air bubbles trapped
in the transformers. Furthermore they prevent pressure buildup in case of an internal
arc-over.
Unfortunately the fotos I took during the construction were lost because of a
disk crash. Murphy in action - this would never have happened to photos I can
take again.
The four MOTs and the plywood board they're mounted on weight about 32 kg,
thus the sturdy steel handles.
Closeup of the MOT housing. The blade connectors on the backside are the 230V
inputs, the connector on the right front is the 2kV input and the connector
on the left front is the 4kV output.
The 4 MOT PSU is connected in series with a welding transformer with shorted
secondary. At the lowest current setting of the welding transformer the shortcut
circuit of the PSU is about 300mA (the MOTs' nominal rating). But I can crank
up the transformer to maximum current without the MOTs even getting warm.