What’s the Latest Wisdom on removal of TV Suppressor/Capacitors?

[Pendragon Sailing]

Not being an electronic whizz myself, what’s the latest wisdom from those in the know around the removal (or not) of the little orange suppressors/capacitors we see inside our locos. I’m aware that manufacturers have to fit them because of “Regulations”, but as users of (HM)DCC, are they considered better out than in?

What say the experts out there?

[Fishmanoz]

Latest advice? Nothing has changed in over 10 years since well-designed DCC decoders have been available.

They are redundant and a potential source of a failed component (previously reported on the forums) so remove them.

Same goes for any suppression inductors included, not often found these days.

[SteveM6]

Only ever taken out one from over 120 DCC locos. The remaining 119 run absolutely fine.

[Fishmanoz]

Steve, note redundant not terminal, and component failure having caused a short across the decoder motor drive. ColinB if my memory serves.

And note these suppressors are across the motor drive of each loco, not across the track like the capacitors in analog power tracks which must be removed.

And there have been forum reports of problems solved with removal although, as with Steve’s experience, not always the case.

But, they can do no good leaving them there and may cause harm. Remove.

[ColinB]

Yes I did report it on a class 66 if I remember rightly, it shorted out and took the decoder with it. I think on most of the newer models the circuitry is on the DC header. If I am converting an old model to DCC, I remove them but if the loco is brand new I don't touch them. I think on that class 66, Hornby were using a cheap load of capacitors, there were a lot that failed at the time.

[Thomas-349483]

I would rather take them out, I'd hope hm7k has decent protection, but any component Bridgeing the motor contacts can't be good for it. Of the 4 locos without sockets I've added dcc to, 3 worked fine without capacitors, and the one with a cap made a mess of a decoder, whether there's a correlation or I'm bad with soldering i don't know, but that's my experience

[96RAF]

Hornby 'advice' is that those components exist in DC mode to suppress RFI due to inductive loads in the motor, intermittent contact between track and wheels, bad pick-ups, etc.

With a decoder connected in circuit none of the above apply so they can safely be removed.

The simple logical solution would be to have any components required to suppress RFI in DC mode attached to the blanking plate, then when that was removed the suppression would be removed with it.

[sir john]

Couldn't agree more raf recently I had cause to dismantle a bachmann deltic as the pickup wire on a bogie had come adrift what was hidden under the motor? two suppressors which I duly removed but would never have known they were there without dismantling the whole loco.

[ntpntpntp]

The suppression caps across the motor can affect back-EMF sensing which is one reason why it's often recommended to remove them when fitting a DCC decoder.

I've seen poorly specified caps on cheap G scale locos blown by DCC.

I agree with @96RAF in that the suppression components really should be built into the DC blanking plate nowadays. I've come across a few instances where that's been the case but it's by no means universally done.

[96RAF]

It has been confirmed that whilst on-motor suppression is not required under DCC fit, it could be advisable to have these components across the rail pickups within the loco when in DC running mode. Logic would say mount these on the blanking plate.