FETS 101
Part 1
**Fet- Field effect transistor
**MOSFET- upgraded fet, less internal resistance/ more amp capacity to be drawn
Questions and Answers:
--How high should I stack my fets?--
*** Depends on: motor, batteries, chassis, and how smooth of a car you want. You can do a silly 2x10 mosfet stack, and have it be very unsmooth, more fets lead to very unsmooth, driving cars and truck. Using the minimum amount of fets for a motor allows (most of the time) smoother power delivery, but higher chances of frying fets and stacks. An advantage to higher stacks is that they allow the motor to go to its full potential, total spin up, so it can achieve what is claimed. Smaller/ minimum stacks do not allow this, but key to racing circuit is about usable power. *** So, in a short summary:
**Go high for dyno queens, show cars, and speed runners
**Low for usable power, track racing
--Should I get a Woah Nelly, Spider or AM v2.2/v2.1:--
***I have heard mixed opinions about the v2.2, nelly, and spider. Nelly is no longer in production, with that aside, AM vs. Spider.
The AM v2 regulated board has it’s pros and cons, I myself have not tried one, but from research, opinions of skilled modders, they seem to dislike this board, from fets lifting off pads to inefficiency, and room.
I myself have had two spider v3.0s, and loved both. Work great, have fair amount of internal resistance (a LOT less than the v2.2, key is smaller fets for usable power, v2.2 is for dyno queens only). Only downside is removing stock fets, but that is not hard for a modder with a bit of knowledge, or skill. ***
Tips on removing stock fets:
--Ph2t’s method (I use it, and only will); basically cutting the fet legs with a hobby knife, instead of having any heat involved. This is a tad dangerous, as if the knife slips… (happened a few times, and made a mess)
--Regular method; Use desolder braid to remove the solder pre-applied, to the fets legs can be moved to lift off. I do not follow this method in any way, as ripping pads off is very easy while doing this (when solder turns solid, and a strand of braid is connected, when lifted, it can life a pad).
--Fixing lifted pads:
Basically, to fix lifted fet pads, you need some sort of jumper wire (stock potentiometer/servo motor wires would be best), and solder. You must locate board traces from the pin(s) of the pads that had been ripped/lifted, and locate their trace(s). You then tin the jumper wire, solder it to the corresponding fet legs, and solder it to the trace. This is not the easiest method, but after being soldered, I would do a test, and if it works, put some sort of glue over the solder point on the trace (dot of crazy glue, hot glue, etc..) so it doesn’t rip off.
Part 2
--Mosfets compatible with gen1 xmod: Vishay 4562, 8962, 8858, IRF7317, IRF7314, FDS8858CZ, and sp8m4 (8858cz is cheapest, and is almost equivalent to sp8m4 due to rds values on N channel, a tad more than sp8m4, but P channel cannot carry as many amps)
--Mosfets for Micro-t: Most of the above listed should work
--Mini-z: Same as above.
**Disclaimer: Some fets may not work, but based upon research input/output pins seem to be the same ***
*Typical data sheet for a mosfet (link is for 8858cz by Fairchild Semi)
http://www.fairchildsemi.com/ds/FD/FDS8858CZ.pdf
Internal resistance:
When you upgrade fets, your car/truck’s performance gains (most of the time), increase. The increasing gains can surpass others from many aspects, such as solder work, and internal resistance of the mosfets themselves. Internal resistance plays a MAJOR role in a smooth, linear, power-delivering vehicle. Some actually prefer fets with lots of internal resistance, and use higher stacks, as they like the “feel” of them better than others when driving.
Power hungry car and trucks will clearly require more fets upon chassis upgrades, motor and battery install. The more resistance, the more prone your boards are to frying the fets. With generation1, I would recommend the 8858cz by Fairchild Semi, or the SP8M4, as they have the least internal resistance, and when compared, are equal. (In the sense of amp draw/internal resistance)