Electric Bicycle Battery Charger RFI Modification 2013-07-14 OH7SV

Be aware of this power supply used in Chinese electric bicycle battery chargers. It was a very good "HF transmitter". The power supply was located 900 m from my QTH and the interference was S9+10dB at 80 meter band. There was a drifting interference at every 50kHz. I located the interference source location by using an active ferrite antenna and a battery powered JUMA RX1 receiver. It is a 24VDC lead acid battery charger, type is PAS36AA-W02401500. As you see in the picture the mains RF filter components were not installed.

I repaired the power supply by adding one current compensated common mode inductor and three capacitors according to the PCB markings. After the modification the interference disappeared totally. See the pictures and click them to enlarge.


This Chinese electric bicycle was sold by a Finnish distributor K-Citymarket Järvenpää branded "Matkaaja".

Added RFI filter schematics. Note! Use only approved X1/Y2 mains capacitors!

Home made current compensated common mode inductor. Toroidal core Amidon FT-50-77 2x15 turns wrap wire. Don't use enameled wire copper wire because the material 77 resistivity is very low (100 ohms/cm)

Inductor and three capacitors installed. On the left there are 2 x 10nF X1/Y2 and on the right 1 x 4n7nF X1/Y2 capacitor

On the bottom side the traces are cut for the common mode inductor. The core is fixed with two straps.