I recently had an issue with a drive that runs a 750w BLDC motor. The motor itself has no nameplate and the drive has no transformers, it is also fully potted so I can't really see what's going on. I'm going to assume that since the drive is small and mostly surface mount components other than 2 large capacitors that it is just rectifying 120v AC.
Since I'm not a fan of this drive for external control anyway I'm looking at replacing it with a new servo amp. Depending on what I choose the amp will either handle commutation (motor has hall sensors) or my controller can handle commutation. I'm not so much concerned about commutation right now, just the DC supply for the drive. I was going to build a DC unregulated power supply with a toroid transformer but the one I bought I realized will not supply enough current. With the 35+35 secondary toroid I was looking at ~100V DC after rectification but the transformer is only rated at 500va so as far as I can tell it's only going to supply <500w. These servo amps all use PWM for the motor power to control speed so the DC voltage isn't critical, it should be in the ballpark. For reference I spun this motor up to around 2500rpms and got 66V AC between phases. 2500rpms is the speed limit of the original drive.
Now I'm thinking I can just rectify 120v AC and skip the transformer. Isolation isn't critical since the rectified DC will be treated as the AC would. It's only for motor power and all of the low voltage controls are supplied by DC switching power supplies. The only thing I'm really concerned about is the voltage. I do not know exactly what this motors insulation can handle since there's no nameplate but I'm thinking ~120v is safe. I know that once rectified and filtered, the DC output voltage will be much higher. I'd like some help with capacitor values and a way to drop the output voltage back to around 100-120V on the output side without using a transformer. I have a 1000uf @ 250v capacitor I was going to use for the filter but I'm not sure if this is too large.
Since I'm not a fan of this drive for external control anyway I'm looking at replacing it with a new servo amp. Depending on what I choose the amp will either handle commutation (motor has hall sensors) or my controller can handle commutation. I'm not so much concerned about commutation right now, just the DC supply for the drive. I was going to build a DC unregulated power supply with a toroid transformer but the one I bought I realized will not supply enough current. With the 35+35 secondary toroid I was looking at ~100V DC after rectification but the transformer is only rated at 500va so as far as I can tell it's only going to supply <500w. These servo amps all use PWM for the motor power to control speed so the DC voltage isn't critical, it should be in the ballpark. For reference I spun this motor up to around 2500rpms and got 66V AC between phases. 2500rpms is the speed limit of the original drive.
Now I'm thinking I can just rectify 120v AC and skip the transformer. Isolation isn't critical since the rectified DC will be treated as the AC would. It's only for motor power and all of the low voltage controls are supplied by DC switching power supplies. The only thing I'm really concerned about is the voltage. I do not know exactly what this motors insulation can handle since there's no nameplate but I'm thinking ~120v is safe. I know that once rectified and filtered, the DC output voltage will be much higher. I'd like some help with capacitor values and a way to drop the output voltage back to around 100-120V on the output side without using a transformer. I have a 1000uf @ 250v capacitor I was going to use for the filter but I'm not sure if this is too large.
