Hello Gentleman (and ladies?),
My company manufactures an automotive assembly that uses a small 24VDC motor to pump fluid. We recently went through a round of EMC testing under SAE J1113-41 guidelines.
To make a long story short our product behaves very well until the motor turns on. At this point emissions go through the roof. The product is well above an acceptable limit.
A little background. The PCB and pump motor are housed in a custom molded plastic enclosure. It is not possible to change the housing at this time in case you were going to recommend metal. The motor sits on top of the PCB and is housed in its own plastic pump sub-assembly (again, cannot change). The circuit board is a 4 layer board with dedicated power and ground planes. The pump is switched on and off with a N-channel MOSFET low side drive transistor. Two wires (approximately 30mm each) go from the circuit board to the pump. I have
1000pf capacitors placed on the PCB from the point of entry of each wire to the PCB and ground (common mode filters I believe). I also have a 100nF SMD capacitor placed between the pump motor wire leads at the point where the wires leave the board. The PCB seems to be immune to the high levels of RE. We have had no problems even considering the fact that this noisy pump sits right on top of the PCB. My big concern is what this motor might do to other electronics. We would like to meet SAE J-1113 guidelines for at least a region IV device, preferably region III or higher.I tried to attenuate RE by connecting the motors metal body to the ground plane of my PCB. It did not seem to help much.
Do you have any suggestions? Is there something I can do to my assembly to quiet down RE ( like metalized paint on interior of housing)? Is there something that can be changed with the pump design to reduce RE?
Looking for any hints you have to offer.
Thank you,
George