Hi
I've read around a lot but get confused by differing answers and general ignorance on my part... I just want to guestimate how many A's I can mod my tiny 6 Fet or a 9 fet controller shunt to before blowing a fet - as it can be an expensive experment - so looking for very rough 'rule of thumb' kind of answers rather than deep understanding. (Unlikely ever...)
Ok so it's 'phase current' I should worry about which may be, say, 3X battery (shunt) current.
6 fets, so 2 per phase, but each one of the pair takes the full phase current - right? So is the phase current each pair sees the whole current (approx 3X shunt say, modded to 25A =75A) in the motor or only 1/3 of that i.e. 25A?
Fets are STP75NF75 (see attached) rated 80A max with 11mOhms R at 40A. I worked out 46mOhms at 80A at 175C as dissipates 300W max in a perfect cooling environment. Rtheta(ja) is 62.5C/W. 2 thermal constants=about 1C/W. Plus anything else?
Any rules of thumb re heat dissipation away from fets with average alu block in the average Chinese mass-produced controller??
So can those fets likely take the 25A OK or is it just wild guesswork?
I have a mid-drive Tonaro so presumably the fact I can up rpm by changing down gears will help stop torque, and thus current, shooting up as motor Power=torque*rpm (I saw somewhere)? But how much of a protection is that grinding up hills slowly on full throttle?
Thanks
I've read around a lot but get confused by differing answers and general ignorance on my part... I just want to guestimate how many A's I can mod my tiny 6 Fet or a 9 fet controller shunt to before blowing a fet - as it can be an expensive experment - so looking for very rough 'rule of thumb' kind of answers rather than deep understanding. (Unlikely ever...)
Ok so it's 'phase current' I should worry about which may be, say, 3X battery (shunt) current.
6 fets, so 2 per phase, but each one of the pair takes the full phase current - right? So is the phase current each pair sees the whole current (approx 3X shunt say, modded to 25A =75A) in the motor or only 1/3 of that i.e. 25A?
Fets are STP75NF75 (see attached) rated 80A max with 11mOhms R at 40A. I worked out 46mOhms at 80A at 175C as dissipates 300W max in a perfect cooling environment. Rtheta(ja) is 62.5C/W. 2 thermal constants=about 1C/W. Plus anything else?
Any rules of thumb re heat dissipation away from fets with average alu block in the average Chinese mass-produced controller??
So can those fets likely take the 25A OK or is it just wild guesswork?
I have a mid-drive Tonaro so presumably the fact I can up rpm by changing down gears will help stop torque, and thus current, shooting up as motor Power=torque*rpm (I saw somewhere)? But how much of a protection is that grinding up hills slowly on full throttle?
Thanks