View Full Version : MR-03 Sports Blowing Fets

2016.06.09, 11:08 AM
OK, so here is another question with regards to the sports chassis. There are about 10 new guys that picked up MR-03 Sports cars at the track that is racing mini-z. Of the 10+ guys running them at least 5 have blown fets on them when they put in the 70T motors.

I know that they weren't geared high as they were running only 6 or 7 tooth pinions with the stock diff or Kyosho ball diff.

Anyone else have issues running the 70T in the sports chassis? I know we had several people run them with no issues so I'm not sure what is going on over there at the track.

Maybe they aren't being careful when screwing in the motor terminals and that's the problem. Just looking for some info. :confused:

I'm keeping busy changing fet here lately, I haven't been this busy with fets since the AM cars were being run. :eek:

2016.06.09, 11:20 AM
i can';t recall fets being an issue with the sports series at our track. it's mostly range or intermittent shut off. good thing fet replacement is cheap.

2016.06.09, 01:16 PM
With any of the PN 70T motors you have to be very careful that the motor wire "eyelets" don't come in contact with the little tiny gizmo hidden under the center tab of the top cover where the motor wires connect. Don't know what that thing is or does but it is not happy having a too close proximity with the negative wire. Be sure to trim the eyelets down to a smaller diameter or cut them off and solder the stock connectors onto the motor wires. Since that particular motor doesn't seem to be very happy with regular doses of "com" drops make sure the motor stays cleaned out and the throttle isn't held "on" while the car is nosed into a solid object. I have seen this issue even with an 80T motor.

2016.06.09, 02:29 PM
thanks Mike, Several of them are coming to race tonight and I'll discuss this with them. Hopefully we can cut down on their misfortune with blowing the boards.

2016.06.10, 07:25 AM
Keeping the throttle with stuck wheels may burn the fets. If they are experts on Mini-z, would not be an issue, but new guys don't know that the fet current goes very high when you keep the throttle trigger pushed after a crash and the car doesn't move.

No problems on our track too, but some drivers in Brazil had already burned some fets on the same way.

2016.06.10, 07:43 AM
Most of these guys are 10th scale off road racers, so you'd expect they would know with the throttle. It seemed most had the issues with their cars after changing motors or adding aftermarket parts so I tend to think that they were getting the battery terminals in contact with the little thing between the terminal mounts.

2016.06.10, 08:11 AM
If any driver comes from a background of racing where reverse isn't allowed then the first thing that comes to mind is to blip the throttle a couple of times to induce bounce back so they can drive off without being marshaled.

I do suspect though that the main issue is the motor wires coming in contact with something unfriendly.