- Joined
- Dec 25, 2011
- Messages
- 10,552
Kernbigo,
The fan performance decreases as the motor RPM decreases To a first approximation, the motor RPM is directly proportional to the applied voltage. The current draw, however, does not fall off proportional to the voltage or RPM. So at low RPM, the fan may not adequately cool the motor. You partially offset this problem by using a motor 33% larger than the maximum recommended HP. But even so, if you had ever run it very slowly with a significant load, it would undoubtedly have overheated.
Wes,
If the motor that you are going to use is 3250 RPM max and is rated to run at that RPM continuously, then you should calculate the motor and countershaft pulley diameters required to get 2072 (or thereabouts) spindle RPM with the motor running at 3250 and using the same motor belt (so that the belt tensioner will still work to tighten both belts at the same time.. The required diameters will be somewhere between the existing two diameters of the two standard 2-step pulleys. For comparison, If you were to use the existing low speed steps, the maximum spindle RPM would be approximately 1290 RPM at 3250 motor RPM. On the high speed steps it would be 3904 RPM. And probably quite dangerous. But in any case, you don't want to use anything on the motor that is smaller than the small step as it is near the minimum recommended for a B-section belt.
The fan performance decreases as the motor RPM decreases To a first approximation, the motor RPM is directly proportional to the applied voltage. The current draw, however, does not fall off proportional to the voltage or RPM. So at low RPM, the fan may not adequately cool the motor. You partially offset this problem by using a motor 33% larger than the maximum recommended HP. But even so, if you had ever run it very slowly with a significant load, it would undoubtedly have overheated.
Wes,
If the motor that you are going to use is 3250 RPM max and is rated to run at that RPM continuously, then you should calculate the motor and countershaft pulley diameters required to get 2072 (or thereabouts) spindle RPM with the motor running at 3250 and using the same motor belt (so that the belt tensioner will still work to tighten both belts at the same time.. The required diameters will be somewhere between the existing two diameters of the two standard 2-step pulleys. For comparison, If you were to use the existing low speed steps, the maximum spindle RPM would be approximately 1290 RPM at 3250 motor RPM. On the high speed steps it would be 3904 RPM. And probably quite dangerous. But in any case, you don't want to use anything on the motor that is smaller than the small step as it is near the minimum recommended for a B-section belt.
