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aeroelasticmz
2006.03.14, 08:14 AM
Hi ppl,

Got some questions about motor here, thanks in advances:

When the FET burnt, its due to the motor drawing more current than the FET can take, if this is correct, what is the deciding factor on how many current is drawn on a motor.

is it the turns of the coil, or the strength of the magnet?

the higher the rpm, the higher the current drawn, is this correct?

what about the turns of coils compared to rpm, directly proportional or inversely?

I am not sure if this is what actually happened, if someone could explain more about it, its highly appreciated. Thanks.

byebye
2006.03.14, 01:39 PM
Well I'm shooting from the hip here. Less turns requires more amps and stronger magnets to turn the armature. So with higher gearing(lessturns per rotation) it takes more power(amps) to turn the motor. With a FET upgrade there is less resistance which allows you to put more amps through to the motor.

-Byebye

imxlr8ed
2006.03.14, 02:09 PM
Pretty decent write-up here... might help.

http://www.the-rc-zone.com/articles/understandingmotors.php

aeroelasticmz
2006.03.14, 03:21 PM
Thanks a lot for the information guys, will try and read article first.. cheers

imxlr8ed
2006.03.14, 04:06 PM
Actually, the article just kinda gets you started... as far as fets go, I can only explain in layman's terms.

If you picture the electrons flowing to the motor through the fets, through the wires, from the batteries, picture the fets as a weak valve so to speak. Now, provide resistance to the motor, be it direct resistance to the motor itself, or it's own internal "resistance" (the amperage required to push the next armature through the magnetic field, determined by the amount of turns) and the whole connection becomes say, pressurized with water (electrons). Eventually enough "pressure" builds up in the fet, it just springs a leak (toasted). When you run a turbo fet, the internal resistance is less, meaning, it can take a lot more pressure before it pops, it moves the "water" through faster !

I hope I'm making some kind of sense here. :o
Stock fets can fry for a number of reasons... in all my time with these cars, majority of the time it seems to be some kind of direct drivetrain resistance or accidental wire crossing that fries them.

Good luck !

Draconious
2006.03.14, 04:22 PM
the fets burn when they overheat...
hotter motors, pull more amps thus heating the speed control way faster... in some cases instantly...
even a stock motor can blow the fets, if you overload the motor.. say full throttle for a few minutes while holding the tires from moving... kinda like you trying to push a building... your gona get tired fast, but not go no were. lol.

imxlr8ed
2006.03.14, 05:12 PM
[QUOTE=Draconious]the fets burn when they overheat... QUOTE]

Right !
That heat is caused by all those electrons trying to get somewhere real fast, but they can't... so they just build up and "sit" in the fet, at the exchange point and get excited until they burn the transistor gate.

aeroelasticmz
2006.03.15, 01:59 AM
[QUOTE=Draconious]the fets burn when they overheat... QUOTE]

Right !
That heat is caused by all those electrons trying to get somewhere real fast, but they can't... so they just build up and "sit" in the fet, at the exchange point and get excited until they burn the transistor gate.

Thanks again ppl for all the explanation.

if the amount of turns is less in the motor, is it more powerful? or the other way round?
appreciated.

kittysniper101
2006.03.15, 04:31 PM
Thanks again ppl for all the explanation.

if the amount of turns is less in the motor, is it more powerful? or the other way round?
appreciated.
if you use less turns you typically use thicker wire and that will suck up more current quicker. this type of wind will be more powerfull (torque wise and speed wise) that an armature with more winds of thinner wire, it will also kill fets faster and easier. another thing that determines the properties of the motor is the armature and commutator. a "fat" type of com allows for better current flow and better heat resistance so that it will not explode. The type of armature you want is a long solid type armature, this will increase the tourque per wind. hopefully that covered some good basics ;)

aeroelasticmz
2006.03.15, 07:01 PM
if you use less turns you typically use thicker wire and that will suck up more current quicker. this type of wind will be more powerfull (torque wise and speed wise) that an armature with more winds of thinner wire, it will also kill fets faster and easier. another thing that determines the properties of the motor is the armature and commutator. a "fat" type of com allows for better current flow and better heat resistance so that it will not explode. The type of armature you want is a long solid type armature, this will increase the tourque per wind. hopefully that covered some good basics ;)

Thanks for the reply, ya it gives a lot better idea. welcome to the forum..