Tuesday, 22 November 2016

6, 9 or 12 MOSFETs - Are more MOSFETs Better?

1 - Introduction


I am unsure what other applications MOSFETs could be used in other then EBike controllers, as that is as far as my limited knowledge of electronics extends, but I have pondered long and hard as to whether it is a worthwhile exercise upgrading my 6 MOSFET Controller, to a 9 MOSFET or 12 MOSFET controller.

Will there be any benefit?

2 - What is a MOSFET?


A MOSFET when used in an EBike controller works like a valve or gate that allows current to be drawn from the battery and used in the motor. The MOSFETs are there so as to switch off the current supplied from the battery when it reaches its minimum safe volatage.

The MOSFET is left "open" while the battery has charge left in it, but once a minimum voltage is reached the MOSFET is "closed" to prevent the battery becoming over discharged, which can damage the battery / cells.

3 - Are more MOSFETs Better?


A quick look for MOSFETs on google shopping will show you that they come in all sorts of sizes, in terms of their rated current. Some can handle 0.5A whilst others will handle 50A. So in order to say whether more MOSFETs are better, one would need to establish whether they were the same type of MOSFET, when comparing 2 controllers.


3 - 6, 9 or 12 MOSFETs


When looking at a controller from the same manufacturer say Crystalyte you can see that there controllers have more MOSFETs relative to the current they can handle. Their 15 Amp controller has 6 MOSFETs, whilsts their 25 Amp has 12 MOSFETs.

4 - Conclusions

If you are comparing EBike controllers from the same manufacturer then there is a chance that their 6 MOSFET controller will handle half the current of their 12 MOSFET controller. But this presumes the same MOSFETs are used in each.

So really the number of MOSFETs is not really important, concentrate instead on whether the controller receives good reviews, and pick the correct Amperage for you intended application.

For more advanced users some controllers can be programmed so say a 40A contoller with say 12 MOSFETs can be used to provide a maximum of 10A. This would possibly provide a benefit in terms reducing over heating, but using a high Amperage controller, when you do not need the amps, and have no means of controlling them may damage your motor.


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