Trying to answer the few Qs above and then report on my crash-course on MOSFET-101:
Yes the Power (W) we address in this thread refers to the thermal power dissipated/generated inside a MOSFET as a result of driving a CIM motor. The absolute max power rating of these MOSFETs is much higher but that assumes ideal heat-sinks which we do not have in Jags nor Vics.
The most significant parameter we focussed on so far was the R DS(ON) resistance of a fully conducting MOSFET. Hence it is critical to now the Part Numer (PN) of the MOSFET in your speed controller. As usual, different generations (even batches) of Jags & Vics will have different PNs. One hopes the variations in the critical parameters will not be great - but life is not always such.
For the Jags we have discovered 4 PNs so far:
IRFB3206PBF 3mOhm
FDP038AN06A0 3.8mOhm
FDP050AN06A0 5mOhm
FDP8441 2.7mOhm
and for the Victors:
IRL3103 16mOhm
FDB6035AL 12.5mOhm
The R DS(ON) in mOhms is listed above as that is the critical parameter (so far). Since Power dissipation is P=I^2*R, one can see how important this number is.
As was pointed out, I may have mixed the use of RDS max and RDS typ, but as you will see shortly we have a bigger problem.
MOSFET-101:
A pretty good paper is "A Power MOSFET Tutorial":
http://www.microsemi.com/en/sites/de...es/APT0403.pdf
Using this and a few other (harder to read links below) papers on the web, I will summarise the pertinent points here:
http://www.eetimes.com/design/power-...tching-MOSFETs
http://www.btipnow.com/library/white...Parameters.pdf
Power losses (Pl) in any component operating in the switch-mode can be divided in three groups:
a) Conduction losses (Pc)
b) Switching losses (Psw)
c) Blocking (leakage) losses (Pb), normally being neglected as this is in the micro-Amp region.
a) Conduction Losses:
This is primarily our friend R DS(ON).
This value is highly affected by 2 other parameters:
(1) The Gate Voltage - the higher the gate the lower RDS. Luckily for us the Jag uses a MOSFET driver chip and one assumes drives it at near Battery voltage - I am guessing that the Victor has a similar driver. At 10V on the Gate we are down to the spec RDS.
(2) The temperature. The higher the junction empo the higher RDS. All MSOFET datasheets have that graph. The Y axis is typically a Normalized RDS, and X-axis T (C). One can see that from ambient 25C (spec RDS) to 150C RDS can almost double! So keep it cool
b) Switching Losses:
This is where it gets really messy...
There's 2 losses, Capacitance, and Crossover:
(b1) Capacitance loss:
This is due to charging and discharging the "capacitors" within a MOSFET. However with our 12V battery and 15KHz this is down to 1-2mW and also I think this energy is dissipated outside of the MOSFET so we can ignore it as far as heating goes.
(b2) Crossover loss:
This is more interesting. Essentially it is due to the "slow" swichover from full-ON to full-OFF and back. See Figures 14 and 15 in the first link above, and look at the bottom shaded "switching energy" graph. Now for some reason the MOSFETS we are using do not have a spec for this Eon, Eoff data. It is also apparent from the same graph that the Turn-On Rise Time, and Turn-Off Fall Time is not the time during which most of the energy is released! I find it hard to believe that the industry hasn't yet standardised on the representation of this parameter? We must have mentors that work at MOSFET manufacturing companies - how do we get to them?...
Anyhow, I did some back of the envelop and assuming similar energy curves as APT50M75B2LL for our Jags E switching is 0.5W. For the Vics that would be negligible due to the slower PWM cycle.
Therefore, if we use the following:
Jag MOSFET FDP8441
Vic MOSFET FDB6035AL
Motor Current 40A and 60A
Operating at red-hot 150 C junction T
PWM duty cycle 99%
we get the following power dissipation at the ON MOSFETs (40/60A):
Jag = 1.8/3.4W
Vic = 3.2/7.3W
And (no fan) T operating:
Jag = 137/238C
Vic = 227/479C
Jag wins hands down!
Something doesn't compute - as the Vics should all be burnt !
1. The fan probbaly has a very strong heat dissipation effect.
2. The Jags could be driven much harder than the Vics if only we dissabled the software cut-out mechanism
3. Lets open up a few Jags & Vics and confirm the PNs (maybe we can replace the PNs on the Vics with the better ones - they are only a couple of $ each -just kidding - its probably against the rules!
Here is the math for those who want to tinker:
P= I^2*R
R= RDStyp * the Temp factor
T=P*RJA+Tamb
Where:
I is the current in the ON MOSFET in Amps. Motor Current divided by 2 for Jag and by 3 for Victor.
R is from the MOSFET datasheet. Use RDS(ON) typical. Temp factor from the datasheet table.
Jag FDP8441 RDStyp=2.1mOhm, Temp factor (150C)=1.55
Vic FDB6035AL RDStyp=11mOhm, T factor (150C)=1.65
RJA is the Thermal Resistance Junction to Ambient from the datasheet:
Jag FDP8441 RJA=62C/W
Vic FDB6035AL RJA=62.5C/W
Tamb is 25C