Capacitor for motor RF suppression?

[Old Man Aaron]

I'm re-powering an Accucraft Baguley chassis using the battery pack and manual controls, leftover from my Essel Fowler rebuild.
Upon removing the original wiring from the Fowler, I noticed the ceramic capacitor soldered across the motor terminals, to suppress electrical noise from the motor. Figured "I probably should fit these to everything as a matter of course" - then promptly forgot about it.

This noise was quite evident when powering the un-suppressed Baguley's 12-24V motor:


I'm unsure of the value of cap I should be fitting to this and future battery locos.
Never took note of what was in the Fowler, and I'd rather not dismantle it to check, as reassembly would likely involve re-touching the paintwork.
What are you fellas using? Could I use the same caps for the little 3-6V machines? (HGLW, Sharples, etc)

Cheers,
Aaron

[GTB]

This noise was quite evident when powering the un-suppressed Baguley's 12-24V motor:

I'm unsure of the value of cap I should be fitting to this and future battery locos.

If what you are concerned about is the high pitched hum that can be heard in the video when the speed control is turned on, suppression caps won't fix that. The noise is a 'feature' of the speed control circuit design.

Small capacitors are used to suppress electrical 'noise', ie. voltage spikes from the commutator that can cause interference with the electronics in the speed control. It usually manifests as the esc randomly stopping, or resetting, or generally faffing about. It's more likely to happen with digital circuits such as an rc-esc, or a dcc decoder.

The usual noise suppression caps I've used are 0.1pF ceramic type. One across the brushes is the usual setup and sometimes if the motor is particularly noisy electrically, then two additional caps connecting each brush separately to the motor frame are added. If things get really bad, a ferrite core in the motor leads might also be necessary.

The audible hum you are hearing is probably due to the variable width pulses the speed control uses to control the motor. Most modern designs use a higher frequency that is inaudible to humans.

I use a simple analog dc speed control in my manual 6V battery powered railmotors, so there's no sound generated in the motor. I've never fitted suppressors to these, the speed controllers are more or less immune to electrical interference.

I've had issues with electrically noisy motors affecting the esc in an rc setup. In that case suppressors didn't work, the final fix was a replacement motor.

Regards,
Graeme

[GAP]

I'm re-powering an Accucraft Baguley chassis using the battery pack and manual controls, leftover from my Essel Fowler rebuild.
Upon removing the original wiring from the Fowler, I noticed the ceramic capacitor soldered across the motor terminals, to suppress electrical noise from the motor. Figured "I probably should fit these to everything as a matter of course" - then promptly forgot about it.

This noise was quite evident when powering the un-suppressed Baguley's 12-24V motor:


I'm unsure of the value of cap I should be fitting to this and future battery locos.
Never took note of what was in the Fowler, and I'd rather not dismantle it to check, as reassembly would likely involve re-touching the paintwork.
What are you fellas using? Could I use the same caps for the little 3-6V machines? (HGLW, Sharples, etc)

Cheers,
Aaron

I don't use anything I have an AM radio in my shed and it does not pick up any static.

[Phil.P]

Many of the cheap speed controllers use 2kHz,or less..
That is definitely the PWM frequency you can hear.

If you have plenty of room, you could fit a PWM to linear converter, which will kill the noise..
It won't help with the mechanical noise of the drive-train, though.

Phil.P

[Old Man Aaron]

Yes, the hum. I'm not surprised a simple capacitor won't cut it.

Small capacitors are used to suppress electrical 'noise', ie. voltage spikes from the commutator that can cause interference with the electronics in the speed control. It usually manifests as the esc randomly stopping, or resetting, or generally faffing about. It's more likely to happen with digital circuits such as an rc-esc, or a dcc decoder.

Well, that explains why my IP 3V-chassied Malcolm Moore gets erratic above half-throttle. A simple fix.

I'm not finding any 0.1pF capacitors that aren't surface-mount, let alone locally. Electronics aren't my forte - how absurd would it be to use a 1pf capacitor? They seem to be the lowest I can find locally.

I use a simple analog dc speed control in my manual 6V battery powered railmotors, so there's no sound generated in the motor. I've never fitted suppressors to these, the speed controllers are more or less immune to electrical interference.

I've had issues with electrically noisy motors affecting the esc in an rc setup. In that case suppressors didn't work, the final fix was a replacement motor.

A friend of mine also owns a Baguley - he's running RCS r/c, and if memory serves, it too makes this errant noise. And with the same voltage battery pack, it runs far more slowly than mine. I don't think his r/c is causing that. Call it confirmation bias, but I suspect these Baguleys are showing that famous Accucraft "quality" again.

The Essel Fowler's MFA gearmotor ran silently with the aforementioned manual controls..


I have another PWM unit, the Evilbay cheapy I used before switching to Deltang. 2 wires in, 2 wires out. It runs silently in anything I stick it in, so that'll do this loco. I'm selling it anyway.

Drive noise is amplified through the bench, nothing unusual for these Baguleys, they are reasonably quiet on the track.

[GTB]

That's what happens when you rely on a memory that's approaching it's use by date.......

I finally found the 'safe' place where I stashed the bag of suppression capacitors and they are 0.1uF ceramic. If you have got a decent Jaycar in town (not an agency) they should have them, as they are in the current catalog.


Accucraft seem to buy in Mabuchi electric motors. The one in the Walker railmotor that gave me so much strife was replaced with an equivalent MFA-Como motor and I've had no problems since, even though it has no suppression capacitors fitted.


OK I'll bite. What are you thinking of building that can be wrapped around a Roundhouse diesel mech?

Regards,
Graeme

[ge_rik]

I'm not finding any 0.1pF capacitors that aren't surface-mount, let alone locally. Electronics aren't my forte - how absurd would it be to use a 1pf capacitor? They seem to be the lowest I can find locally.

I think Graeme meant 0.1uF (= 100nF = 100000pF)

Rik

[drewzero1]

If it helps, I've noticed that my local electronics shop labels their uF as MF, since the u is really µ, short for 'micro'. Potato, potato.

[Old Man Aaron]

Aha! Thanks fellas. Just picked up two lifetimes' supply of caps for a tenner.

Forgot I even mentioned the RH chassis, had to look back through my own posts to find it.

The Baguley's fine as an "out of the box" cane loco - just paint it yellow. But as a prototype, it never really appealed to me.

The Clyde DHI-71 is more my thing, but I didn't have the confidence at the time to attempt building one - hence the Baguley.
I'm aware of the Tootle Engineering model, but those are so rare, I'm better off scratchbuilding. Same can be said for their Malcolm Moore.

Why not use the Baguley chassis? It's jackshaft is driven from the centre wheelset, while the Clyde/Roundhouse chassis uses the rear axle. RH frame is closer in size, too.

[GTB]

If it helps, I've noticed that my local electronics shop labels their uF as MF, since the u is really µ, short for 'micro'. Potato, potato.

I know the US has never come to grips with the metric system, but.......

A capital 'M' prefix on a metric unit such as a Farad signifies a million and the 'mu' symbol signifies a millionth, so he's only 12 orders of magnitude out.

Graeme

[GTB]

The Clyde DHI-71 is more my thing, but I didn't have the confidence at the time to attempt building one - hence the Baguley.

I had wondered if it might be a Clyde. I've only ever seen one of the Tootle Engineering models and that was years ago.

I occasionally have dark thoughts about building a Com-Eng, but try to avoid that particular black hole. There's already four steam loco projects on the bench in varying degrees of completion and I've no real need of another small diesel.

Regards,
Graeme

[drewzero1]

I know the US has never come to grips with the metric system, but.......

A capital 'M' prefix on a metric unit such as a Farad signifies a million and the 'mu' symbol signifies a millionth, so he's only 12 orders of magnitude out.

Graeme

You're absolutely right, and I have mentioned that to the guy at the shop, but his label maker only prints uppercase. I can only imagine how huge a megafarad capacitor would be!