Suppressor thingy wiring on motors

[n9]

I mean the capacitor/inductor combo wired to motors for interference suppression. (Is there a proper name for this?)

 

Pretty sure these things often just get removed for locos on DCC if/when it interferes with performance, but I'm curious as to the wiring. This is from a Dapol loco:

 

 

The pic isn't the greatest (sorry), but the black (-) wire from the motor ends up connected to the orange (+) wire leading to the positive terminal on the board, and the red (+) wire from the motor ends up connected to the grey (-) wire leading to the negative terminal on the board. (In the pic, the red motor wire runs to the farthest capacitor pin but it's concealed behind the black motor wire running to the nearest capacitor pin.)

 

 

I'm curious why the polarity gets switched over. Is it because the polarity doesn't matter? Or is it because it has to be switched over for the capacitor/inductors to do their thing?

 

Thanks!

[smokebox]

Generally the capacitor is wired in parallel with the motor and the inductors are in series with the motor feeds.  There may also be ferrite beads threaded on to the motor feed wires.  Bachmann locos often have 3 capacitors, 1 across the motor terminals and the other 2 connected from the motor terminals to the motor case.

[34theletterbetweenB&D]

1 hour ago, n9 said:

I mean the capacitor/inductor combo wired to motors for interference suppression. (Is there a proper name for this?)

Common term is a Radio Frequency Interference  (RFI) suppression circuit.

 

The polarities you are reading are irrelevant to the RFI suppression. And frankly you don't want to read too much into these descriptions on model PCB's in my experience; so long as the assembly operation performing the  wiring gets the correct rail polarities to the motor terminals so that a DC loco goes in the expected  direction, that's job done. 

[peterm1]

If you want the cap's out, simply cut them off. If you want the inductors out, you have to replace them with wire.

[n9]

Thanks for the replies! Maybe I need another coffee, but I'm not too clear that they answered my question. So I'll try to rephrase:

 

In my example above, why did Dapol take the black negative wire from the motor and solder it through the suppression circuit to the positive terminal on the board, and take the red positive wire from the motor and solder it through the suppression circuit to the negative terminal on the board?

 

I ask because I would have expected the opposite: the black motor wire to go through the suppression circuit and end up at the negative terminal on the board, and the red motor wire to go through the suppression circuit and end up at the positive terminal on the board.

 

I'm just dead curious why it got wired that way. Thanks!

[Nigelcliffe]

34 minutes ago, n9 said:

Thanks for the replies! Maybe I need another coffee, but I'm not too clear that they answered my question. So I'll try to rephrase:

 

In my example above, why did Dapol take the black negative wire from the motor and solder it through the suppression circuit to the positive terminal on the board, and take the red positive wire from the motor and solder it through the suppression circuit to the negative terminal on the board?

 

I ask because I would have expected the opposite: the black motor wire to go through the suppression circuit and end up at the negative terminal on the board, and the red motor wire to go through the suppression circuit and end up at the positive terminal on the board.

 

I'm just dead curious why it got wired that way. Thanks!

 

Manufacturers are under no obligation to stick to wiring colour conventions.    So, if red is connected to negative, that doesn't matter to them. 

 

 

 

[34theletterbetweenB&D]

44 minutes ago, n9 said:

I'm just dead curious why it got wired that way.

Assuming that the model you illustrate is in original ex-factory condition, there will have been a Bill of Materials and  Assembly Instruction (or equivalent term) for whoever got that task in China. If you are that curious, ask Dapol if they can supply it.

[n9]

Alright, so let's see if I've understood. Assuming DC operation:

 

1. The suppressor circuit, which in this case is a capacitor with an inductor soldered to each of its legs, doesn't care about polarity; if you supply it with positive to either leg with negative to the other, it will do its suppressing thing.

2. A positive and negative motor feed ending up respectively at the corresponding positive and negative terminals on the board, just means the forward direction of the locomotive will be, say A. But if those feeds are switched over (as in this case) it just means the forward direction of the locomotive will be B instead of A.

 

Maybe I should have posted this in the non-DCC electronics section, but is this correct?

 

Thanks

[34theletterbetweenB&D]

1. Yes.

2. Yes. (Hopefully the model has overall been wired to conform to the DC convention of right rail positive, it moves forward. This is with respect to a 'driver sitting in a cab', easy enough for steam locos with a single cab and the forward direction clearly defined by the boiler ahead of the cab. With twin cabbed D&E the same should apply to whichever cab is the no.1 end in UK railway terms.)

[peterm1]

I have Hornby loco's where the wires are all black and others where the red is connected to the left wheels instead of the right. So it seems like Raffertys rules for wiring. Having said that, I've corrected the wiring in most of the loco's that have been wrong, just for my own satisfaction. But which is the A or B end of my Bachmann DP2???

[34theletterbetweenB&D]

On 20/02/2024 at 23:40, peterm1 said:

I have Hornby loco's where the wires are all black and others where the red is connected to the left wheels instead of the right. So it seems like Raffertys rules for wiring...

You and me both on rewiring, I like to be able to see at a glance what's what. That's why I prefer hardwiring decoders, red wire to the right side pick up strip , black to the left side, orange and grey to the motor terminals, snip, ship, snip the other five wires. So reliable. (I haven't heard mention of Rafferty in years, that brought a smile.)

 

On 20/02/2024 at 23:40, peterm1 said:

But which is the A or B end of my Bachmann DP2???

If Bachmann offered a DP2 it would be the radiator fan end.

Let's assume it's a Bachmann DP1, in which case I believe the A end is where the steam heat boiler water supply intake was located. May be some more information on this site:

http://www.napier-chronicles.co.uk/

[DCB]

Am I right in assuming the supression issue went away with the change to Digital TV?   I remember our Bachmann B1 interfered with the bloke over the road's TV.nothing else did,  and my Hornby Dublo which absolutely blotted out my parents 405 lines black and white TV 60 years ago no longer raises a flicker on our Digital TV.
The B1 gained some ceramic capacitors but I think we just parked it in the end.
 

[Crosland]

The requirement for suppression is a basic requirement, not related to TV and, in any case, terrestrial digital TV still uses the same frequencies as analogue.

 

Most interference caused to TVs, at least in more recent times  is due to poor aerial installation and wiring.

[peterm1]

You're right. It's a DP1. Raffertys rules usually prevail when I'm working on the layout. :-)

 

[34theletterbetweenB&D]

10 hours ago, DCB said:

Am I right in assuming the suppression issue went away with the change to Digital TV?...

No because there are still folks using analogue radio among other things. But in 'everyday practical terms', digital broadcasting has so much signal redundancy and error correction that 'the old problem' has gone away.

10 hours ago, DCB said:

I remember our Bachmann B1 interfered with the bloke over the road's TV.

That would be a split chassis specimen? The motor in the larger split chassis mechanisms, Mabuchi FK130, was a very variable device in this respect, although robust and reliable to the extent that I have never yet had one fail to look inside.

BUT,,

and it's a big but as you can see! , three of those I have threw off spikes in the 100V range when running on DC, first discovered when I put my hand down on wet rail outdoors as an A4 mechanism approached and gave me a 'warning'. Took it to one of the folks in a conformance testing lab of my then employer, and he laughed his head off at its 'fruity' performance. When I took up DCC I tried a decoder on the 'proven criminal', and it didn't put out anything measureable; and it has done the decoder no harm twenty years on, last of my Bachmann split chassis still running (in the A3 body I had fitted it inside). Ah, the lengths one had to go to for proper loco drive models, back in the day...

[NIK]

Hi,

 

Some DC motors sold to fit in model loco kits etc have varistors fitted internally which may limit voltage spikes.

 

Whether they help with EMC I don't know as the varistors could be there to protect the commutator.

 

Regards

 

Nik

 

 

[mezzoman253]

21 hours ago, DCB said:

Am I right in assuming the supression issue went away with the change to Digital TV?   I remember our Bachmann B1 interfered with the bloke over the road's TV.nothing else did,  and my Hornby Dublo which absolutely blotted out my parents 405 lines black and white TV 60 years ago no longer raises a flicker on our Digital TV.
The B1 gained some ceramic capacitors but I think we just parked it in the end.
 

60 years ago there was no legal requirement for equipment to have suppression, although the effects were known, and, to a greater extent, equipment did have it fitted. 20 or so years ago the Legal requirement to have it fitted was introduced. Hence all the gubbins round the motor.

 

Also electronic equipment it better protected from interference now. It has to legally conform to standards that allow it to work under certain levels interference AND not produce interference above certain levels. Unfortunately many imported products do not conform to these standards. Mainly cheap knock offs and Far Eastern imports.

 

The main issue, in the modelling world, lies with DC or DCC ready loco's, they need suppression components. If DCC fitted or retro fitted, the decoder takes care of that (onboard components).