Small mige overvoltage - looking to upgrade braking resistor mosfet


I’m trying to figure out what i can do about an overvoltage situation I keep hitting.

The motor is ST130-10010 Small MIGE, biss-c encoder. Simucube1, Ioni Pro HC drive. Max Current is maxed out at 25A (yes really)

I am using a 48V E-Bike battery to power this (yes really), granity/in-line voltmeter measures the voltage at 54.6V. This is a 20AH battery with typical discharge current of 30-40A, and peak of 60A, naturally, as it’s meant to go in a E-bike. It is great fun when it works right, and super quiet, best of all. no massive fans, and the charger sips power.

I’m playing rfactor2, pm-18 car. Issue i’m running into is when FFB is turned up to higher levels in game, certain kerbs, and at times crashes will result in an Over-voltage error 140404.

Granity FOV is maxed out at 58v
Overcurrent tolerance is Maximum
MCC = 25A
MMC = 25A
MR = 2.7
ML= 8.8

I’ve installed an external braking resistor - 100W 2.5 ohm, and that helped a bit, but I am still able to get it to error and go into overvoltage protection, i’ve doubled up these resistors as well for 1.25 ohm braking resistor, same deal.

I’ve tried reducing current to 60% - on the battery, and that still happens
I’ve tried using a proper 48V 30A switching power supply - still happens, even at 80%
I’ve tried reducing that switching power supply’s voltage to 43V - still happens - even at 80%
I’ve tried using a smaller E-bike battery with 36V rating, and it still happens

I’ve tried using a completely different (albeit same revision) simucube boards (I’ve got 4 of them), same results.
Months ago I tried the same thing with ST110-06030, with similar results

These errors happen during either sharp cornering when motor reverses torque direction and i’m still holding on, OR during high frequency torque reversal, kerbs, hitting other bits on the road.

It’s pretty clear that the braking resistor circuit can’t keep up with back EMF coming from the motor when it reverses

So my question is more for the granity electrical engineer folks:

  1. Anything obvious that can be done that I haven’t listed ?
  2. Q1 (SMD) + Q2 (TO-220 empty) spots on the SC1 board next to the stock braking resistors, are these the braking mosfets ? How is Q1 related to Q2 wiring wise? Q1 looks pretty small (couldn’t find the actual part, is that the component i’m maxing out ?
  3. If I wanted to replace the braking mosfet with something significantly bigger, anything to keep in mind as far as specs, pinout, ratings go ? Any traces I should be upgrading ?

My next step is to put in 2x 60V 50W zener diodes+resistors between HV and ground to try to limit HV spikes that way, but for some reason I don’t see that helping much.

I don’t care about warranty or burning up any of the components involved in this(mige, ioni pro hc, sc1 board) , as long as i can get it working eventually.

Halp !


First of all, reduce the MCC parameter to much lower, as in simucube application this doesn’t have to be at the high end of the range. Some 5A should be enough for this, as peaks will be driven with the MMC limit.

Also, having the FOV at maximum is not recommended as the IONI has hardware limit of 60V and it will issue the overvoltage fault if the resistor cannot dump the exess energy fast enough.

For 48V PSU the FOV setting is 49.5V. This doesn’t explain why you get this fault with 36V PSU though.

What is the IONI firmware version that you are using? From 1.7.0 the regeneration method was improved to reduce load to the resistor.

If possible, please measure the MOSFET for possible damages. Instructions for that are here:

Let me know what values you get.

Kind regards, Esa

From the software side, the behavior can very well be caused by you having the MCC and MMC parameters as the same values.

ioni firmware is 10718
sc firmware is 1.0.30

so latest on both.

i’ll try MCC at 20A and FOV @ 56.40, with supply at 54.8 VDC

Thank you.

looks like that fixed my overvoltage issue (MCC = 20A, FOV=56.4), thank you folks !

for the future, if i do end up grenading the mosfet from this kind of abuse, what can I replace it with (either q1 or q2)


Q1 and Q2 are in parallel to enable both through hole and surface mount MOSFET to be used.

With IONI FW 1.7.0 or higher, you don’t have to worry about the MOSFET :). Should it brake in any point, just let us know and we’ll check the currently available replacement part for it.

Kind regards, Esa