Suppressor thingies

[Paul TParticipant @pault84577]

Can anyone tell me why there has to be so many electronic suppressor thingies fitted to motors?

Is there a valid reason for them or is it just to look clever.

Confused

[Paul TParticipant @pault84577]

[The Long BuildParticipant @thelongbuild]

I have never fitted them myself, but have a few models with them on and have wondered the very same thing as it seems to make no difference . But I'm sure there must be a valid reason

[Colin BishopModerator @colinbishop34627]

The older type of brushed motors could be electrically very 'dirty' with sparking from the commutators and this could affect the older types of RC gear using the 40mhz and 27mhz bands. The lastest 2.4 ghz sets are much less susceptible to interference and modern motors are 'cleaner'.

The purpose of supressors is to smooth out any arcing between the brushes and the commutator ring. These days they are probably not all that necessary but it does no harm to fit them as they cost pennies only. Sometimes you will find that motors come allready fitted with supressors.

Colin

[Dave MilbournParticipant @davemilbourn48782]

 

I'm always amazed at the reluctance of modellers to fit simple little capacitors to motors, especially if they've seen what can happen to a model on the water when one of the little blighters comes unsoldered. The model becomes uncontrollable. They cost only pennies and can be fitted in minutes.
As Colin says, 2.4GHz sets are not affected because no RF generated by a DC motor could ever venture into those microwave frequencies, but it's possible that your motors might be so "dirty" that the RFI they produce could affect others sailing on the pond. I suspect that the reluctance comes from the usual unreasoned dread of soldering, but I'm afraid that unless you learn how to do this (and it's not difficult0 then you may as well take up static modelling………….or knitting.
As for "looking clever", shame on you, Doc!

Dave M

Edited By Dave Milbourn on 26/09/2013 15:37:42

Edited By Dave Milbourn on 26/09/2013 15:38:00

Edited By Dave Milbourn on 26/09/2013 15:54:11

[Paul TParticipant @pault84577]

Dave

Its not a fear of soldering I have simply never understood the reason as I have never encountered a problem with 'un treated' motors, although it has to be said that I seldom sail in the company of others and so wouldn't know if my motors ever caused RF problems.

Paul

[Dave MilbournParticipant @davemilbourn48782]

Paul

Some motors – particularly smaller ones – are horribly electrically "noisy" and you can't use them with a radio without at least one suppressor. I would imagine that your kind of models would use larger motors with multiple poles and these produce far less RFI than the cheap Chinese Mabuchi and Johnson copies etc.
Ref soldering, you would be truly amazed at the lengths to which some folk will go to avoid soldering anything! You would probably not be surprised at the awful attempts at it which came across my bench during my tenure of ACTion. I could tell you a few tales, m'duck…………..

DM

Edited By Dave Milbourn on 26/09/2013 15:53:01

[Paul TParticipant @pault84577]

Dave

Its true that I do use larger multi pole motors in my models but I have used smaller motors in half scale prototypes and have never noticed a problem.

Is there any way that this RF noise can be measured and how do you work out what size or type of suppressor might be needed?

Paul

[Dave MilbournParticipant @davemilbourn48782]

There probably is a way of quantifying RFI but it would likely involve a lot of expensive test gear and would only prove that you either need a few cheap capacitors or you don't – as the case may be. If you can see sparks at the brushes then you really do need suppressors. For what they cost I'd say it's best to fit them anyway,
Type? Ceramic discs or blobs are fine. The big fat 250v ones pictured above (that's a 755 motor) are a quid a set from Component Shop; they also do a set of smaller ones for the same price. Avoid electrolytics at all costs – they go bang when fed with reverse voltage.
Value? 0.01-0.1uF for the ones between the terminals and the case; 0.1-0.47uF for the one across the terminals. It's not at all critical.
Job jobbed.
DM

Edited By Dave Milbourn on 26/09/2013 17:40:38

[Paul TParticipant @pault84577]

Value? 0.01-0.1uF for the ones between the terminals and the case; 0.1-0.47uF for the one across the terminals. It's not at all critical.

Dave

It might not be critical but its all double dutch to me…..what is uF and what are and why do electrolytics explode?

Job not jobbed just yet.

Paul

[Dave MilbournParticipant @davemilbourn48782]

Paul

uF is the short form of 'microfarad' (a unit of capacitance) while electrolytic capacitors are polarity-sensitive but ceramic capacitors are not. Details on Wikipedia if you're really curious – or insomniac.

All will be revealed in the MB Winter Special – well, all that you need to know,

DM

[Paul TParticipant @pault84577]

Dave

How did my question end up as an advert for your article in the Winter Special?

Paul

[Colin BishopModerator @colinbishop34627]

What! You haven't received the brown envelope yet Paul?

Colin

[Dave MilbournParticipant @davemilbourn48782]

Posted by Paul T on 26/09/2013 19:10:33:

Dave

How did my question end up as an advert for your article in the Winter Special?

Paul

I'm just lucky with my correspondence, I guess. Anyroad up, m'duck – it were written for thee and those like thee who think that anything which involves a battery and wires is a Black Art.
Clue: it's not.
DM

[Tony HadleyParticipant @tonyhadley]

What if a motor is suppressed to CE standard by the manufacturer, does this require additional capacitors to be fitted or should I await the item in the special?

Tony

Edited By Tony Hadley on 26/09/2013 20:25:23

[ashley needhamParticipant @ashleyneedham69188]

Chaps, chaps.. if toooo many questions are asked there will be NO article!!

Ashley

[Paul TParticipant @pault84577]

This subject has intrigued me and not just because I have inadvertently been promoting Daves article in the forthcoming winter special (thanks for the brown envelope Colin)

How far does this RF extend from a 'dirty' motor, is it localised to a few inches from the motor or does it cover the entire lake?

Whilst this RF problem wouldn't affect the modern microwave sets but what happens when incorrect wire sizes are used, we all know that the wires get hot but do they also radiate microwave interference?

Paul

[ashley needhamParticipant @ashleyneedham69188]

I have found that using incorrect wire sizes results in letting the SMOKE out, and as we all know, keeping the smoke in is what makes it all work.
Like paul, I have never had, or caused a problem to others with using unsupressed motors (on a couple of boats). HOWEVER usually I put one capacitor across the terminals. I think it may jsut depend on the build of your particular motor, I think that most Graupner motors have caps fitted internally judging by the extra wire on the main terminals. Ashley

[Dave MilbournParticipant @davemilbourn48782]

I've no plans to do any in-depth research into this – life's too short already. RFI is generated by the sparks created between the armature and the brushes, and some motors are much worse than others. I'm sure there are theorists and armchair physicists out there who would be only too happy to debate the matter ad infinitum but my position remains based on purely practical considerations.
Fitting suppressors is cheap and easy, so do it as a matter of course (especially if you're using a VHF radio e.g. 27 0r 40 MHz) and there's one potential problem nipped in the bud.
Beware of Graupner motors and assuming they all have internal suppressors. Not all Speed motors are already suppressed. Those which are will actually have a note to that effect in the small instruction sheet, and you will see very thin wires emerging from the plastic insulating bushes in the motor case alongside each of the brush terminals.
Tony – I have never seen a CE label and/or suppression certificate with any DC motor sold for model boats, and I would be wary of it if I had. Some Oriental manufacturers are very willing to print anything which is requested on a label (I have first-hand knowledge of this).
Paul – microwaves cook food; are used for cheap model radios (and practically every other "WiFi" application imaginable) and won't pass through water. Beyond that I'm as ignorant of them as the man on the Clapham omnibus. As I said, life's too short.

DM

[Colin BishopModerator @colinbishop34627]

Paul,

RF interference, as with other forms of electro-magnetic radiation, falls away quickly with distance so would be unlikely to cause a problem beyond the immediate surrounding of the offending boat depending on how 'dirty' the motor is. However, if the RX or its aerial are within a few inches of the source of interference when you are using the older type of RC gear then they can easily be affected with a common sympton being 'chattering' servos.

People restoring old boats fitted with the ancient Taycol type motors have found them very difficult to suppress indeed due to their crude construction.

You have to remember that the very earliest type of radio transmitters (not model ones) used a spark gap to generate the signal! RF signals from sparks can swamp all medium radio frequencies.

Colin

[Malcolm FraryParticipant @malcolmfrary95515]

Armchair theory. The energy that creates the interference starts in the motor. As it rotates, the coils are connected and disconnected from the power supply by the brushes and commutator. As everybody who has fiddled with pre-electronic car ignition systems will know, suddenly disconnecting a coil carrying current creates a big voltage and sparks. You get to see the sparks at the commutator when things get a bit worn, or there is some uneven-ness that the brush springs can't keep up with. The armature coil and surrounding bits form a resonant circuit. Since its largely accidental, it isn't finely tuned, but is up in the RF band. It has no effect until it gets out of the motor and finds some wire to act as an aerial. This is where supressors come in.

Capacitors provide a short circuit to RF but nothing else, so no RF energy escapes up the motor leads. Smaller values for higher frequencies, but interference happens on a broad spread anyway, so a wide range of values works equally well. Quite apart from their habit of exploding when reverse charged, the construction of electrolytics makes them unsuitable for suppression. Effectively, they are a coil, and are quite good at blocking higher frequencies.

Ferrite inductors like beads or those toroidal rings that you see occasionally allow low frequencies through (like PWM motor pulse) but block RF.

Twisting the motor leads (insulated, obviously) helps by providing a bit of capacitance and at the same time causing the fields generated by the interfering signal to cancel each other out.

While 2.4GHz is immune to RF interference generated by motors, if you generate enough, it can find its way into the power supply. While this is rare at the moment, it is just a matter of time before wire and semiconductor bourne interference becomes another black art topic due to basic good practice being ignored.

[Dave MilbournParticipant @davemilbourn48782]

"Good practice" were the two words I was groping for – many thanks, Malcolm.
There is a link to a very good article by David Harrison (of Model Sounds Inc, Canada) on the subject of RF interference and how to avoid/beat it; this link appears on another thread "Out with the old" by Paul Andrews. Like me, David H never uses a couple of words if he can get away with a couple of hundred, so the article is very comprehensive but not frighteningly technical.

Dave M

[Paul TParticipant @pault84577]

Good practise, Out with the Old, Tycol motors and Spark Transmitters are all comments that lead one to think that there was certainly a problem in the past with interference and that this problem was certainly due to limited technology.

But following this line of thought one is forced to ask the question of does this problem still exist or are we simply following 'good practise' without fully understanding why we are doing it.

Perhaps we are to set in our ways or simply unable to see beyond a perceived problem but it does beg the question that in the modern world do such sources of interference still exist.

Paul

[Dave MilbournParticipant @davemilbourn48782]

Tell you what, Doc. Connect up a brand-new Torpedo 500 to 12v, fire it up and watch the fireworks going on inside – then tell me RFI is a thing of the past. It's even more fun if you turn on an FM radio next to it.
From where I sit at least 50% of all problems with model boat electrics are down to failure to observe good practice. Examples are not fitting suppressors or fuses, poor quality wire, use of choc-block connectors, coiling long aerial wires up inside hulls, and switching on the receiver before the transmitter (and transmitter off before the receiver). O – I almost forgot the most common fault – not reading the instructions FIRST. If you get away with it then well done, you – but one day it will turn around and bite you. I have scars to prove it.

Dave M

[Paul TParticipant @pault84577]

Dave

Such a vehement response can only come from someone with hands on practical knowledge of the subject.

I bow to your superior knowledge and experience and from now on I will be fitting suppressors to my motors.

I presume that all of this subject will be covered in depth in your forthcoming article in the Winter Special. But one last question…..what is wrong with choc-block connectors?

Paul

Colin thats another brown envelope you owe me!

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