Bridgeport Power power supply + power feed

[Robert Atkinson 2Participant @robertatkinson2]

That video has some over simplifications. You should not have to buy a VFD that has a higher power rating than the motor it drives. If you do and don’t turn the settings down thn you are putting the motor at risk of over loading.
Any suppler telling you to “go up a size” is likely selling lower quality drives. They are reducing their warranty risk and increasing their income at your expense.
There are two main issues wooth using older motors on VFDs, cooling and insulation breakdown. Cooling is only an issue on fan cooled motors when run at full torque (current) and reduced speed. Thiss is because the fan does not move as much air at lower speeds. It’s not so much of an issue for hobby use whare the duty cycle and loading are likely to be lower than full rating. If the motor does need full load at lower speed you can add a separate fixed speed cooling fan.
Insulation breakdown can be an issue due to the nature of the VFD output. The VFD output has fast voltage changes (PWM) that can result in voltage spikes across the motor windings. It’s difficult to quantify but keeping the cable between the VFD and motor short (few meteres rather than 10’s of meters) helps as does a good quality drive. For non-critical applications I would not worry about it. If it is a irreplacble motor you can fit a filter on the output of the VFD.

One thing people tend to forget is tha a VFD can increase the speed of a motor as well as decrease it. Even with a old motor those of us in 50Hz countries can increase the speed by 20% (max frequency 60Hz) as just about every motor is also rated for use at 60Hz. Even if you don’t need higher workin speed doing this with a change in pulley size allows lower  working speed without cooling issues due to reduced motor speed.

Robert.

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