Inductive spikes caused by compressor switching
Provided you have reasonable wiring design the likelihood is small. however, with poor components there is a strong likelihood of large spikes. The solution we recommend is the most robust design you can follow to protect the motor under most conditions.
The spikes that can result from switching off a compressor depend very much on the compressor in question, but as a guideline with a 230V compressor, then a 1000V spike is a reasonable approximation. That said, the spikes are very short, and what matters much more than the voltage is how much energy is in the spike - as it's this energy that has to be absorbed somewhere in the system.
Inside the motor, we have a component specifically to clamp these spikes, and for reference in the 230V motor it only begins to clamp at 510V. So below this level there is no issue at all. Above 510V, our clamping element will limit the voltage, and it does so by converting the energy in the spike into heat. If it's a low energy spike then there is no problem either, as this is what the clamp is designed to do. However if it's a moderately high energy spike then it can cause wear on the clamping element, and this can eventually cause premature motor failure.
This problem is not limited to the motor - as you say the same effect can cause a spark on the relay contacts (which can also cause the relay to wear out) and it can cause problems with solid state relays too, so the SSR designers also generally include a clamping element. So whether the overall system will have a problem is a hard thing to specify, as it depends on the spike energy (proportional to the size of the compressor) and also what other elements in the system are helping to dissipate this energy.
Solid state relays are better than electro-mechanical relays, as the spike from an inductive load can cause the relay to turn on by mistake, so they put big voltage snubbing circuits on their output side to prevent this from happening and this helps protect the bldc motor as well
So while its hard for us to make blind statements about any particular system:
- If you've already been using a BLDC motor in a specific system without problems, then if you switch to a Unada motor it will almost certainly be fine - all the BLDC motors have similar susceptibility to spikes and similar clamps on the inputs, so they all act about the same.
- If your system has a solid state relay in then its much less likely to have a problem than a traditional relay, so it will probably be ok as well.
- With an electro-mechanical relay there is more possibility of an issue, and particularly if you've seen a specific model that has problems due to spark damage to its relay contacts then it might be worthwhile taking some precautions if changing to a BLDC motor - Running the 3 wire way is one possibility, as is isolating the motor from the compressor with a secondary relay, or putting spike suppression components across the compressor.