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Why do speed controllers sometimes fail?

Why do speed controllers sometimes fail?

Here at 4QD we go to a lot of trouble to make sure our controllers are reliable. We make sure we have enough capacitance, we use the best mosfets we can find, we fit substantial heatsinks, we minimise the susceptibility to radiated and conducted noise, and we conduct extended life tests by running controllers on an automated test rig.

And yet very occasionally a customer will get a seemingly random failure. Actually there’s a clue in that sentence, in five years we’ve not had a single mosfet failure on our test rigs, the reason for that is that we take a lot of care with electrical noise suppression. Motors are electrically noisy things, just look at the back of an old electric drill to see the sparks. We’ve written a full article in our knowledgebase about motor noise and how to prevent it, it also describes other sources of noise, and some detail on mosfet failure modes. It’s well worth 10 minutes of your time reading this and taking the necessary steps to make sure that your controller doesn’t suffer an untimely end. If you just want the short “what do I need to do?” version have a look here.

We’re now shameless about plugging our suppression components. They don’t cost a lot but since we introduced them we have seen the field failure rate of our controllers drop significantly.

Categories: Miscellaneous

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