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Boost Electrical Engineering 3 phase converter, 1993

Converting single phase to 3 phase to run a lathe from domestic supply. Hopefully just replacing the 415V 20A contact ratings 4 pole relay but I'd like to know a bit about how it works , in general terms, as both coil and power useage contacts are u/s.

2 pairs of contacts paralleled to bring up to 40 amps rating. But I assume over time with bias to one set closing before the other one pair failed and then the second pair failed soon after but why the o/c coil , would there be a thermal fuse buried in the housing somewhere, lots of heat was developed from the bad contacts

I assume the converter is peincipally an autotransformer to create the other phase in conjunction with some capacitance. There is a boost function that is manual biased switch at start of motor or automatic if the lathe cuts through a hard spot, this brings in more capacitance via the relay it seems. There is also a reed relay with a few turns of the power amperage passing around it , presumably the auto function ,but the mystery is a small TO3 size bridge rectifier and electrolytic for a 100V or so DC supply for an offset or something

Reply to
N_Cook
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this textually sounds the sort of thing

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including

"FIG. 1 is a 3-winding induction motor supplied from a single-phase power supply with a phase control consisting of a capacitor connected to a tap on an autotransformer."

and

"The current in line L2 goes through a coil around a reed-relay so that the reed-relay contacts close when the current exceeds several times full load current, and the contacts open when the current is less than twice full load current. The coil is selected so that the contacts open when the motor shaft speed is greater than 80% of rated speed. The reed-relay contacts control a solid-state-switch which inserts the starting capacitor CS between terminals TC and T4. "

not Solid State Seitch in this one

Reply to
N_Cook

Sort of working order but will not drop out of boost mode. The voltage over the relay drops but not enough , it would seem , to make this replacement relay and so different coil demand, drop out. Will have to do some on site fudge adjustment to the original 6K8 dropper for this relay and check that strange bridge rectifier and offset DC function as no ac or dc without a load motor

Reply to
N_Cook

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