Upgading the 4in1 to handle 3cells

[ghettorc]

I'm interested in modding my lama 4in1 to handle 3cells safely, I think replacing the mosfet with this one
http://www.newark.com/19K8391/semiconductors-discretes/product.us0?sku=international-rectifier-irlu7843pbf
should increase performance and make it safer with 3cells.
Will I still need to use a diode or will the mosfets internal one be enough?
Are there other components that will likely fail while using a 3 cell?
Stock mosfet is irf7413.
What guage wire should I use for wires going to the lama 180 motors?

[cstratton]

You'd have to make sure that the voltage regulation will be okay with that much input - which is one of those "probably, but might release the magic smoke" things unless you really understand the circuit.

On the MOSFET, one concern is that the measured .0033 ohm resistance is with 10v gate drive. You probably won't get that out of the 4-in-1, so the resistance will be higher (in effect, you won't be able to turn the MOSFET all the way on). Low on resistance, low gate drive voltage, high switching speed, and resistance to damage from voltage spikes are unfortunately parameters that sort of trade off with each other - can't get the best of all worlds.

Dug up the spec sheet - RDS on at VGS 4.5 isn't bad, and it should work even below that. If you try it, try it on 2 cells first so you are only dealing with one problem at a time.

[jeffs555]

The main problem with going from 2 cells to 3 will be the regulator, not the mosfet. Unless you are running wide open all the time, the average current through the mosfet won't increase that much. However, the power dissipation in the regulator will more than double. The power dissipated in the regulator is the battery voltage minus the output voltage(ie 5v) then multiplied by the servo current. For 2 cells this is 3v times the servo current. With 3 cells it will be 7v times the servo current. You will most likely have to add a heat sink, or go to a switching regulator.

[ghettorc]

Any idea which chip is the regulator for the lama v3s 4in1 so I can heat sink it? Can I wire the mosfet drain directly to the motors or will I need to put in a freewheeling diode and capacitor in parallel, like are on the board? Can you recommend a diode or capacitor if needed?
Thanks for all the help