Do I need to reduce RF in Bachmann DCC install?

[gbcaboose]

I'm preparing to install a decoder in the tender of a Bachmann 4-8-2. I've heard and read that it's best to go ahead and remove the capacitors since they're there to reduce RF, and could possibly interfere with the decoder performance.

1.  Will it make a noticeable difference?
2.  Do I just remove them, or do I need to "jump" the connecting points.

I also read to remove the 'coil'. Not sure what/where that is.


Thanks, Mike


Thanks, Mike

[peteski]

What you read is true. You can freely remove those components. Coils (chokes) are cylindrical devices, usually black with fine wire wrapped around them.  I don't see any coils in your photo (they might be on the other side of that board or elsewhere).  They might have also been included on the original decoder for this loco (not on the circuit board shown in your photo).

[gbcaboose]

Here's a side view showing a rather large "coil" under the board. There's one on each side. These are much larger than I'm thinking they should be. Are these the one's to remove?

[peteski]

Here's a side view showing a rather large "coil" under the board. There's one on each side. These are much larger than I'm thinking they should be. Are these the one's to remove?

Yes, you can remove those and replace them with a piece of wire. Or just solder a piece of wire to the same terminals that each coil is soldered to (the wire will bypass them).  Either way the result is the same.  You should also remove the capacitors (the small beige components with silver ends without any markings on them).

[woodone]

Just remove the board and hard wire in the decoder. Don't forget you will need resistors for the Lights!
That will get rid of the caps and chokes in one clean soop!

[peteski]

Just remove the board and hard wire in the decoder. Don't forget you will need resistors for the Lights!
That will get rid of the caps and chokes in one clean soop!

Yes, if you are not using the original Bachmann wire harness that connects the loco with the tender (it uses the connector on the tender circuit board) then just removing the entire board makes sense.

[gbcaboose]

Thanks for the help. The plan is to use the original board and solder the decoder wires to to the labeled contacts (1-8) on the board. It appears to be pretty straight forward. The removal of the coils and capacitors is what I was unsure of. 

[Maletrain]

It seems that nobody answered one of your questions in the original post - whether or not you need to "jump the connecting points" after you remove the capacitors.

I am not sure I really know the answer to that.  I think you should not "jump" those opened connections, because on an RF filter, the capacitors usually bridge wires of opposite polarity, and "jumping" those wires creates a short.  But, in other circuits, capacitors are used in series with other components on the same wire, which would create an open circuit if the cap is removed without adding a bridge wire.  At least, an open circuit would be safer than a short, so at least first try it without jumping the capacitor gap, if nobody else posts a reliable answer, here. 

For the coils, which are in not bridging wires of opposite polarity, Peteski has already told you that you need to replace (or just bypass) those coils with a wire between their end points.

[C855B]

Remove the capacitors and do not bridge the empty pads. You will create shorts. In a DC circuit containing capacitors, the capacitors will be in parallel across the power leads. The chokes (coils) are in series in line with the power pass-through, and will need to be replaced with a jumper.

[gbcaboose]

Thanks for your help guys. I'm gonna work on this over Thanksgiving so if things go as planned I'll be able to give thanks that I still own an OPERATING 4-8-2. 

Mike

[Mike C]

My first sound install was a 2-10-2 . I just soldered the decoder to the marked places on the Bachmann board . Left the caps and chokes on , and it runs fine . But any other install I've done has been a conplete gut job , I hard wired the decoder straight to the wires from the loco . I cant tell the difference between performance of either method ....Mike

[peteski]

My first sound install was a 2-10-2 . I just soldered the decoder to the marked places on the Bachmann board . Left the caps and chokes on , and it runs fine . But any other install I've done has been a conplete gut job , I hard wired the decoder straight to the wires from the loco . I cant tell the difference between performance of either method ....Mike

There are so many different decoders and RFI suppression circuits out there that there is no hard rule that they are all not compatible.  After all, many models made in the recent years actually include the RFI suppression circuitry right on the factory-installed DCC decoder and they work fine.   But some decoders which use high frequency PWM pulses to  power the motor and BEMF for motor control act erratically when the RFI circuit is installed between the motor and the decoder. When installing a 3rd part decoder, it make sense to remove those components to be on the safe side.  My last bad experience with RFI circuitry was when I installed a Digitrax DZ125 decoder in the FVM 4-4-2 loco. It acted erratically until I bypassed the chokes and removed the caps.

I also just posted a new thread with more detailed info about this Bachmann tender and the circuit board.
https://www.therailwire.net/forum/index.php?topic=43310