Microwave oven tranformers
Fuling,
If you can obtain the power tranmsformers from a pair of similar or identical scrapped domestic microwave ovens you may be able to use the two transformers to make your HV power supply. Here in North America old ovens show up at the curb for the trashman, or can sometimes be obtained from appliance service shops for free as scrap if you talk to the technician.
The typical oven transformer has a heavy 120 volt primary winding, a ~1900-2000 volt secondary good for several hundred mA with the innermost end of the winding connected to the iron core, and a few turns of HV insulated wire to produce ~3.15 volts at 20 amps or so for the magnetron filament.
If you wire the primaries of two identical transformers in series so that each will only get about 60 volts instead of 120 volts you can get 1000-0-1000 VAC at several hundred mA from the pair. You will need to hammer out the magnetic shunts and remove the filament windings to create core window space. To make the two transformers act as one they need a common magnetic circuit. To make this work get some enamel insulated wire, say #12 or #14 AWG and wind as many turns as you can in the available core window on each transformer. Make the coil on each transformer the same number of turns. If you can get 20-30 turns on each you should be OK. Hook these two windings together. The proper polarity will be when the primary current is minimum. Negligible current will be drawn from the mains in this configuration if the polarity of the extra windings are correct. If they are backwards the transformers will draw heavy current and look like a short to the mains. Placing a 120 volt household light bulb in series with the mains is a good way to test for minimum current without making fireworks.
Use a simple two diode full-wave rectifier which uses the grounded center tap of your two transformers connected to the chassis. With choke input filter you will get right around 1000 VDC, just right for an 813 project.
Please remember at all times that these voltages at the high current available are lethal and mistakes are not allowed.
Cheers,
Rob
Fuling,
If you can obtain the power tranmsformers from a pair of similar or identical scrapped domestic microwave ovens you may be able to use the two transformers to make your HV power supply. Here in North America old ovens show up at the curb for the trashman, or can sometimes be obtained from appliance service shops for free as scrap if you talk to the technician.
The typical oven transformer has a heavy 120 volt primary winding, a ~1900-2000 volt secondary good for several hundred mA with the innermost end of the winding connected to the iron core, and a few turns of HV insulated wire to produce ~3.15 volts at 20 amps or so for the magnetron filament.
If you wire the primaries of two identical transformers in series so that each will only get about 60 volts instead of 120 volts you can get 1000-0-1000 VAC at several hundred mA from the pair. You will need to hammer out the magnetic shunts and remove the filament windings to create core window space. To make the two transformers act as one they need a common magnetic circuit. To make this work get some enamel insulated wire, say #12 or #14 AWG and wind as many turns as you can in the available core window on each transformer. Make the coil on each transformer the same number of turns. If you can get 20-30 turns on each you should be OK. Hook these two windings together. The proper polarity will be when the primary current is minimum. Negligible current will be drawn from the mains in this configuration if the polarity of the extra windings are correct. If they are backwards the transformers will draw heavy current and look like a short to the mains. Placing a 120 volt household light bulb in series with the mains is a good way to test for minimum current without making fireworks.
Use a simple two diode full-wave rectifier which uses the grounded center tap of your two transformers connected to the chassis. With choke input filter you will get right around 1000 VDC, just right for an 813 project.
Please remember at all times that these voltages at the high current available are lethal and mistakes are not allowed.
Cheers,
Rob
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