I keep reading about controllers with 6 – 18 FETs; what is d advantage of more FETs? Quieter motor (less whine)? Other than that?
- Thread starter raedy07
- Start date
noise hasn't anything to do with fets, that's up to the motor physical design, motor speed, and control scheme.
more fets in the typical designs means more power, spreading the load between more individual cheap parts.
a good design with good parts (both of whcih cost more) and a good control scheme (software/firmware) with good tuning of controller-to-motor can get more power out of less parts.
with a typical bldc motor there's 3 phases so you will always have at least 6 parts, one for each side of each of three bridges, then mulitples up from there. 6, 12, 18, etc. sometimes you see 9, 15, etc because they'll skimp on one side of the bridge to get a little bit extra power but thats less useful.
don't pick your stuff based on numbers of parts, etc., pick it based on waht you need the system to do for you, under the specific conditions you need it to do it in, for the range/time you need it to do it for.
if you define the conditions, and your needs and how you want the system to behave, and how far you need to go, you can use those to figure out how much power it takes to do, what features it has to have to do what you want, and how big a controller, motor, and battery have to be to do that.
then you can find parts that do those thigns that fit in your budget, or find that the budget has to be increased to do whaty ou want or at least to do it reliably without risk of failure or fire, etc.
(moved these posts out of the diy newb faq since they dont' ahve anything to do with topic of creating the faq, are jsut another question to be answered )
more fets in the typical designs means more power, spreading the load between more individual cheap parts.
a good design with good parts (both of whcih cost more) and a good control scheme (software/firmware) with good tuning of controller-to-motor can get more power out of less parts.
with a typical bldc motor there's 3 phases so you will always have at least 6 parts, one for each side of each of three bridges, then mulitples up from there. 6, 12, 18, etc. sometimes you see 9, 15, etc because they'll skimp on one side of the bridge to get a little bit extra power but thats less useful.
don't pick your stuff based on numbers of parts, etc., pick it based on waht you need the system to do for you, under the specific conditions you need it to do it in, for the range/time you need it to do it for.
if you define the conditions, and your needs and how you want the system to behave, and how far you need to go, you can use those to figure out how much power it takes to do, what features it has to have to do what you want, and how big a controller, motor, and battery have to be to do that.
then you can find parts that do those thigns that fit in your budget, or find that the budget has to be increased to do whaty ou want or at least to do it reliably without risk of failure or fire, etc.
(moved these posts out of the diy newb faq since they dont' ahve anything to do with topic of creating the faq, are jsut another question to be answered
)
more FETs = more amp carrying capacity.
Controllers with particularly efficient FETs may have a reduced number versus say, a cheapo china brand.
Example:
China mystery FET 18FET controller = 40A battery limit
Infineon 18FET controller with 4110 FETs = 60A battery limit <-- because the FETs are much higher quality/efficiency and have lower resistance, thus can flow more power
Controllers with particularly efficient FETs may have a reduced number versus say, a cheapo china brand.
Example:
China mystery FET 18FET controller = 40A battery limit
Infineon 18FET controller with 4110 FETs = 60A battery limit <-- because the FETs are much higher quality/efficiency and have lower resistance, thus can flow more power
Last edited:
docw009
10 MW
It's like cylinders in a car engine,
not sure, but maybe you meant that the one with 4110 fets might be a higher current limit than the 40a since it's got better fets than the mystery fet unit?
to make it more confusing, 6fet units like the phaserunner can handle more not just because they have better fets but because the software controlling them is better so there's less risk of damaging them. for instance the prv6 has the same 40a battery current limit specified as the 18fet quoted above, and the pr might actually be able to do more than that if it's well-heatsinked.
also the pr has a better hardware design to get the heat out of them, since they';re bolted right to the externally-available heatsink of the pr instead of to a not-well-machined bar that's sorta kinda mounted to the case like either example in the quote above
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