Replace hoverboard MOSFET. Any?

[edugimeno]

Hi There.,
I have a hoverboard with a fried RU6888R mosfet
According to PDF, it is a N channel 68volt 88 Amp MOSFET, TO-220
Can I just use ANY MOSFET which is N channel, >=68volt, >88Amps, in TO220 format? Also same pin order "GDS"
I can't find any "official" replacement for this one I'm looking for

Thanks!

[stj]

Re: Replace hoverboard MOSFET. Any?

if you also watch the gate capacitance < relates to switching speed
and the Rds-ON / on resistance < must be equal or lower or it will generate more heat.

[edugimeno]

Re: Replace hoverboard MOSFET. Any?

Thanks STJ, will 6mOhm to 8mOhm be noticeable?
I found IRFB4410 to be a candidate but has these 2 extra mOhms...

Thanks

[stj]

Re: Replace hoverboard MOSFET. Any?

that should be fine.

[budm]

Re: Replace hoverboard MOSFET. Any?

RU6888R has input capacitance of 2900pF.
IRFB4410 is 5150pF.
It may not be turned ON/OFF fast enough, may be the circuit has dead time adjustment.
https://cdn.badcaps-static.com/pdfs/...19d1be1cc7.pdf
" Typical values of input (Ciss), output (Coss) and reverse transfer (Crss) capacitances given in the data
sheets are used by circuit designers as a starting point in determining circuit component values. The data
sheet capacitances are defined in terms of the equivalent circuit capacitances" Also read about Gate Charge.

[edugimeno]

Re: Replace hoverboard MOSFET. Any?

Ok, but in this case this is for a hoverboard controller board. This mosfet drives one of the 3 coils in a wheel. It will have a switching frequency of 3x Rev Per Second, so basically if the wheel is 5.5" diameter and the max speed is 15kph, max speed will be 10 rps at full speed, so it will probably switch (only af full speed) af 30 Hz. Maybe my maths are a little wrong and it has to switch 2 times for each turn which will give 60 Hz or maybe even double, but we're moving in this range.

Will this capacitance still be critical in this particular use?

Thanks!

RU6888R has input capacitance of 2900pF.
IRFB4410 is 5150pF.
It may not be turned ON/OFF fast enough, may be the circuit has dead time adjustment.
https://cdn.badcaps-static.com/pdfs/...19d1be1cc7.pdf
" Typical values of input (Ciss), output (Coss) and reverse transfer (Crss) capacitances given in the data
sheets are used by circuit designers as a starting point in determining circuit component values. The data
sheet capacitances are defined in terms of the equivalent circuit capacitances" Also read about Gate Charge.

[stj]

Re: Replace hoverboard MOSFET. Any?

no, the motor is not driven by one pulse per field for each revolution.

[budm]

Re: Replace hoverboard MOSFET. Any?

You need to trace the cicut from the Gate of the MOSFET's to the IC that drives those MOSFET' s, once you find the IC then look up the spec sheet and application notes/circuit then you can see how the Motor is driven.

[edugimeno]

Re: Replace hoverboard MOSFET. Any?

Someone reverse-engineered an schematic, link here
The oulse comes from a microcontroller, 3 transistors are in between the micro and the mosfet

[edugimeno]

Re: Replace hoverboard MOSFET. Any?

Actually the mosfet in this schematic I linked above, from another hoverboard (but they are all the same), uses an 110n8f6 mosfet with an input capacitance of 9000pF, so this leads me to think that 5000pF may still be good, am I right?

[budm]

Re: Replace hoverboard MOSFET. Any?

As you can see, it is 3-phase drive topology. You see how the MOSFET's are connected, if one is not completed OFF while another is on then you will have disaster, since it is MCU based, they can adjust dead times.
https://hackaday.io/project/3176-gat...time-insertion
http://www.modularcircuits.com/blog/...ridge-control/
http://www.ti.com/product/LM5106
You can try the substitute and find out.