Newbie needs help with Bachmann Tram DCC conversion

[Jack1]

Hi All

 

I write software for industrial machines, so getting phase 1 of my project up and running, a OO guage DCC layout complete with track position sensing, automatic points and engine start/stop sequences was a run of the mill task for me.  My track layout is loosley based on the Crich tram museum, (without the interlaced section underneath the bridge).

 

The next phase is to convert a Bachmann Branchline tram to DCC.  If successful I want to have at least 4 of these trams running under automatic control.  I have read all the arguments, for and against,  regarding coreless motors and DCC and all the advice about the quality of decoders.  The results seems to be a mixed bag of success and failure, but I have decided it is worth trying at least once.

 

My question is, I am unsure of the value of the volt drop resistor to put in series with the motor.  I have seen it written that it is a 47ohm but this seems rather low.  As the coreless motors are typically 100mA at 4.5volt on a normal 12volt DC track then ohms law gives you around 8Kohms for the resistor.  But how do you calculate it for DCC?   I would rather not burn the motor out before I have had a chance to actually get it turning.  

 

Any help would be greatfully received.

[Andy Reichert]

I'm not sure why you would want to put any resistance in series with the motor?

 

Andy

[Porcy Mane]

The Bachmann trams:

http://www.ehattons.com/50341/Bachmann_Branchline_CE00608_Tram_car_in_red/StockDetail.aspx

I have seen (and are in the process of modifying) have the standard Bachmann inductor and capacitor set up. The motors would appear to be 12 volt and I have run them successfully on a 12 volt dc controller without the inductors and capacitors. They run superbly in both instances at all speeds but only have one axle drive

So as Andy asks, why do you want to fit a resistor?

 

Porcy

[Jack1]

It is my understanding the coreless motors are only 4.5 volts but I accept this may be wrong information as I have read a lot of contradicting arguments.  The one fact I am sure about is that the brusless armatures of these motors are made with permanent magenets.  The chopped DC (PWM) supply will cause eddy currents in the magnet cores and any coreless motor will overheat to some degree wether the motor and supply voltages match or not.

 

The inductors and capacitors you mention Porcy, I assume is the filter network (shouldn't that be resistor and capacitor?)  Any motor will run without them, although some motors benefit from them at slow speed.

 

So I don't know if I need a resistor.  Has anyone actually got one of the OO guage Branchline or Hong Kong trams running on DCC?

[Andy Reichert]

If the motor concerned is in a RTR model rated for 12v DC operation, then you don't need a resistor to run it from a DCC chip. It is always a good idea to buy DCC chips that are more compatible with more delicate motors such as coreless instrument motor types. Although those motors are generally too expensive to be fitted in RTR models as standard.

 

The marketing names for later decoders that support coreless motors vary, but they all involve sending a higher pulse frequency to the motor than the earlier design basic decoders used.

 

Andy  (electrical engineer)

[Porcy Mane]

It is my understanding the coreless motors are only 4.5 volts but I accept this may be wrong information as I have read a lot of contradicting arguments.  

You may well be right. Do you have a source for that information?

I'm assuming the motor to be 12 volt after a few running tests (Not very scientific at that)

 

What I did was; running the motor bogie on its own (with the circuit board and led circuits disconnected) with 12.35  volts applied it ran at the same speed as the whole tram ran "out of the box". At 12.35 volts current consumption was 20 mA. With a thermocouple applied the metal housing of the motor body the temperature rise was only 2 ºC over 10 minutes.

Out of the box at 12.35 volts the current consumption was 30 mA.

I used 4 different voltage sources. An old AGW controller, an even older Codar controller,  and a Morley Vector Controller (non having  feedback) and finally a Maplins bench supply.

The motor bogie on its own ran identically on all runs.

 

The inductors and capacitors you mention Porcy, I assume is the filter network (shouldn't that be resistor and capacitor?)  Any motor will run without them, although some motors benefit from them at slow speed

 

  

They look like Axial lead inductors to me. 7.4µh. Bachmann (or their subcontractors) kindly silk screen a "L" onto the PCB where the inductors are located. I suppose they could be giving us a bum steer.

 

 

So I don't know if I need a resistor.  Has anyone actually got one of the OO guage Branchline or Hong Kong trams running on DCC?

 

I haven't but it doesn't look like a hard job. Go with a good quality chip that's OK for coreless motors. Something like a Zimo. If it turns out that it is a 4.5 v motor you can always crank back V high using the CV's.

P

[Alan J Kirkman]

Are we talking about the Bachmann US etc Brill and PCC cars with definitely 12v can motors or the Hong Kong cars or the Birkenhead versions with certainly resistors in the circuit as it comes and what we all suspect is a low voltage motor. I don't use DCC but in converting HK cars to live overhead I've been very careful to include the existing circuitry.

[Jack1]

I have purchaced a Birkenhead version this week and have decided to install the decoder with the motor resistors in circuit and will see what happens.  If all goes well I will get a decoder tomorrow and install it on Sunday.  

[Andy Reichert]

Are we talking about the Bachmann US etc Brill and PCC cars with definitely 12v can motors or the Hong Kong cars or the Birkenhead versions with certainly resistors in the circuit as it comes and what we all suspect is a low voltage motor. I don't use DCC but in converting HK cars to live overhead I've been very careful to include the existing circuitry.

 

Just guessing is going to lead to a whole bunch more of internet misinformation.

 

You may well be right. Do you have a source for that information?

I'm assuming the motor to be 12 volt after a few running tests (Not very scientific at that)

 

What I did was; running the motor bogie on its own (with the circuit board and led circuits disconnected) with 12.35  volts applied it ran at the same speed as the whole tram ran "out of the box". At 12.35 volts current consumption was 20 mA. With a thermocouple applied the metal housing of the motor body the temperature rise was only 2 ºC over 10 minutes.

Out of the box at 12.35 volts the current consumption was 30 mA.

I used 4 different voltage sources. An old AGW controller, an even older Codar controller,  and a Morley Vector Controller (non having  feedback) and finally a Maplins bench supply.

The motor bogie on its own ran identically on all runs.

 

  

They look like Axial lead inductors to me. 7.4µh. Bachmann (or their subcontractors) kindly silk screen a "L" onto the PCB where the inductors are located. I suppose they could be giving us a bum steer.

 

 

I haven't but it doesn't look like a hard job. Go with a good quality chip that's OK for coreless motors. Something like a Zimo. If it turns out that it is a 4.5 v motor you can always crank back V high using the CV's.

P

 

Unless I'm missing something, this seems to be a well conducted test showing that these are 12 v motors. Anti-interference inductors that look like resistors are quite likely to be there. Resistors to drop the motor voltage down to 6 v or 3 v are not at all likely, as the wide variation of speed with load performance they would cause would be awful.

 

Andy

[melmerby]

It is my understanding the coreless motors are only 4.5 volts but I accept this may be wrong information as I have read a lot of contradicting arguments.  The one fact I am sure about is that the brusless armatures of these motors are made with permanent magenets.  The chopped DC (PWM) supply will cause eddy currents in the magnet cores and any coreless motor will overheat to some degree wether the motor and supply voltages match or not.

 

The inductors and capacitors you mention Porcy, I assume is the filter network (shouldn't that be resistor and capacitor?)  Any motor will run without them, although some motors benefit from them at slow speed.

 

So I don't know if I need a resistor.  Has anyone actually got one of the OO guage Branchline or Hong Kong trams running on DCC?

Standard coreless motors aren't necessarily brush less

Those for modelling application usually aren't. A brusheless motor needs a driver board to provide the cogging normally provided by the commutator segments.

They have the normal external permanent magnets but do not have an iron core for the windings.

This means the inductance is much lower than normal.

They have the advantage of low inertia and hence rapid acceleration compared to an iron core.

 

They should not be connected across a DCC supply without an appropriate decoder and definitely not used on the pulse stretching address 0, which will likely destroy them.

 

AFAIK there is no reason to use resistors in models intended for 12v use as 12v motors are so plentiful, using a lower voltage would be insane!

 

Keith

 

EDIT I used to service equipment with coreless brushed 12v DC motors in, made by Japanese companies such as Canon etc.

They were typically 12-18mm in diameter and from 25-40mm long with a concentric gearbox on the end.

More's the pity I didn't realise at the time their possible use in modelling!

[Porcy Mane]

Are we talking about the Bachmann US etc Brill and PCC cars with definitely 12v can motors or the Hong Kong cars or the Birkenhead versions with certainly resistors in the circuit as it comes and what we all suspect is a low voltage motor. I don't use DCC but in converting HK cars to live overhead I've been very careful to include the existing circuitry.

 

Alan,

having just read-read  your post #7; You say, "resistor" but I say, "inductor". Sounds like that could be a good song title.

You may interested in the following as you seem so adamant that the Bachmann Hong Kong/Birkenhead tram is fitted with resistors. Perhaps you would like to comment on the following.

 

Time for some very simple objectivity.

1)

 According to their colour coding, yellow, violet, gold and silver, if they are resistors their value would be 4.7 ohm  with a 10% tolerance. A rare beast indeed. If wired in series before and after the motor (Why?) as they are, their theoretical value could lie anywhere between 8.46 ohm  and 10.34 ohm.

That's a very small resistance with a very wide tolerance if trying to get a 4.5 volt motor (4.5v the value mentioned in a previous post) to run reasonably well and without overheating under 12 volts. I'll keep things simple and ignore the power rating of resistors.

By design the colour coding of a 4.7 µH inductor is the same as above.

As a real world example, Nigel Lawton provides a 100 ohm resistor (1% tolerance) for use with his 6 volt motor when it is to be used on 12v systems and a 150 ohm  resistor to use it on Marklin systems.

Here are a couple of pics of the B'mann circuit board.

Tram PCB Upper face showing suppression Components.

Tram PCB lower face. Note no components. Just tracks.

 

2)

 Although visually similar to resistors they look like axial lead inductors to my eyes. There are subtle differences. Take a look here:

http://www.ebay.com/itm/100-PCS-4-7uH-1-4W-0307-Color-Ring-Inductor-Axial-Color-Wheel-inductance-4-7-UH-/121363662008?pt=LH_DefaultDomain_0&hash=item1c41d684b8

 

3) For electrical suppression, Bachmann have been fitting inductors (and capacitors) to their loco circuit boards for an age. They have followed the SI system and electrical convention by silk screen printing an L (Usually L1 & L2) to show position of the inductors. Their HK/B-head trams are no different.

For the uninitiated L = inductance, R = Resistance.

But enough of what some would call subjective observations...

Tram PCB with inductor removed to show L2 printed on surface.

 

4)

 Time to try a simple and objective test. Lets measure the resistance of the resistance. We would expect a reading somewhere between 4.23 Ω & 5.17 Ω. That's 4.7ohm +/- 10% according to the resistance band code. Just to be certain the component  is removed from the circuit board so that we pick up no spurious resistance from anywhere else in the circuit.

What's this??? See picture. A reading of nominal resistance.  0.29 ohm

Just about what I'd expect to see from an inductor.

Measuring resistance of component.

 

So there we have it. You say, "resistor", I say, "inductor". There are a couple of surface mount resistors in the tram but they are there purely for reducing the voltage to the LED and as such, are on the separate LED circuit boards

 

Finally take a look at the photograph of the motor. You will see there are no resistors fitted between motor and circuit board. A fact borne out by the Bachmann official exploded diagram Theoretically the motor may be fitted with a resistance inside its small casing but apart from its normal internal resistance  I think that highly unlikely.

Bachmann Tram Motor bogie in component form.

 

Can you provide any basis for your certainty that the Bachmann Hong Kong/Birkenhead tram is fitted with resistors please? I'm perfectly happy to be told that the tram is fitted with resistors (and a low voltage motor) but will need to see some evidence.

I look forward to your reply.

Happy modelling,

 

Porcy  (Trying to dispel some myths)

 

Edited as the forum editor keeps changing the ohm symbol for a question mark.

[Huw Griffiths]

I'd definitely agree with the "inductors" suggestion - partly because of what's been said in the previous post - partly because I've also seen them used in a number of other Bachmann products.

 

Changing the subject slightly, the motor - and double worm / pinion reduction drive - look rather interesting.

 

 

Huw.

[glennofootscray]

Looks easy enough to fit a decoder to, just a case of separating the motor wires from the chassis, solder the red and black decoder wires to the chassis pin and the grey and orange wires to the motor lead, insulate the motor leads with heat shrink, plonk the assembly on the programing track, give it a number and then tweak the CVs to your liking.

 

When that is all done, then phaff about with the lights.

 

I would more than likely have this model, but I don't think it would fit under the railway bridge of Victoria Street.

 

Regards Glenn

[Alan J Kirkman]

All I know is that there is something there which i didn't want to cut out of the circuit in case it was a resitanceor and a low voltage motor, and all I said was be careful as I didn't want to lull anyone into false sense of security!  When we asked Bachmann service people at Warley what the new harness was on the Brills and PCCS they had no idea!!!  I then merely asked for confirmation as you just posted an ambiguous statement. Frankly unless you are modelling Birkenhead today ( and they're not really right for that wrong body style 1986 not 1849/50 or Hong Kong I see no need to ever find out as the mechanism while interesting is too awkward to source and financially uncompetitive to usuing a 4w drive Halling  KSW which isn't much higher. Frankly I find the attitude on here to be very different from the normal cameraderie of the ranks of Tramway Modellers. Perhaps it is too much hiding behind webnames. We have a happy and helpful hobby generally.   

[Jack1]

I am sorry this post has caused animosity amongst you.  Thank you for the valuable comment in the earlier posts.  Meanwhile I have bought and converted a Birkenhead tram using a Hornby decoder.  It is running over all speeds much better than I was expecting, so much so i have just ordered another one.  Hopefully getting another two in a few weeks.  

 

My own findings when I was able to take the tram apart is that the motor is twelve volts.  The two resistor/capacitor networks shown in Porcy's picture (post #13) are used for the front/tail lights.

 

May I suggest Porcy and Alan do a virtual handshake and let the matter drop.

[Alan J Kirkman]

Frankly I'm glad to hear it is 12v. Shocking that Bachmann couldn't tell us! Sadly one or two exhibitors have had these mechanisms fail on them  which is most unfortunate as the Only available spare is another tram. If this mechanism was available and gets a good reputation it should be a way forward fro many kits with full interiors etc but as things stand with some poor reports and no separate availability and the possible power and adhesion problems of only one axle driven it is a blind alley. A Halling KSW does a better job nearly as low and cheaper. I therefore have no real interest in it and only sought to understand and clarification in the interests of my members. Mark Casson (Red Devil on here) and I ahve been working on something much more interesting as we've been reporting on the Tramway Modelling group on Facebook.

. 

[Andy Reichert]

Frankly I'm glad to hear it is 12v. Shocking that Bachmann couldn't tell us! Sadly one or two exhibitors have had these mechanisms fail on them  which is most unfortunate as the Only available spare is another tram. If this mechanism was available and gets a good reputation it should be a way forward fro many kits with full interiors etc but as things stand with some poor reports and no separate availability and the possible power and adhesion problems of only one axle driven it is a blind alley. A Halling KSW does a better job nearly as low and cheaper. I therefore have no real interest in it and only sought to understand and clarification in the interests of my members. Mark Casson (Red Devil on here) and I ahve been working on something much more interesting as we've been reporting on the Tramway Modelling group on Facebook.

. 

 

One axle driven is the way something like 95% of the way of the worlds buses, cars and lorries have worked successfully for going on 100 years. And still do as the best solution. It's not a problem of itself. Just a matter of designing something properly to work well that way. 

 

I thought the double worm drive is a rather ingenious mechanism. I can see many other possible uses.

 

Andy

[RobClogs]

... as we've been reporting on the Tramway Modelling group on Facebook.

. 

A link to that group might have been helpful here, Alan. I suppose you don't mean this one: https://www.facebook.com/ModelTrams , which seems to be dead in the water. I can't see any recent postings there.

 

Similarly moribund, it seems, is the Yahoo Model-Trams group, which used to be a good forum until Y! implemented what the Germans call a Worsebettering. Have all the tram modellers flocked to Facebook? I'm afraid you've lost me then; I've got no Facebook account, nor am I going to open one. I don't trust Facebook which thinks it's beneficial to manipulate the selection of messages you get to see, and I much prefer forums like RMweb and NGRM-online.

[Red Devil]

A link to that group might have been helpful here, Alan. I suppose you don't mean this one: https://www.facebook.com/ModelTrams , which seems to be dead in the water. I can't see any recent postings there.

 

Similarly moribund, it seems, is the Yahoo Model-Trams group, which used to be a good forum until Y! implemented what the Germans call a Worsebettering. Have all the tram modellers flocked to Facebook? I'm afraid you've lost me then; I've got no Facebook account, nor am I going to open one. I don't trust Facebook which thinks it's beneficial to manipulate the selection of messages you get to see, and I much prefer forums like RMweb and NGRM-online.

Nope it's not that one.... it's this for those who want to use it https://www.facebook.com/groups/modeltrams/ .

 

I think there are other reasons as to the Yahoo groups Model Trams page decline as well as the newer Facebook page.......

[Red Devil]

One axle driven is the way something like 95% of the way of the worlds buses, cars and lorries have worked successfully for going on 100 years. And still do as the best solution. It's not a problem of itself. Just a matter of designing something properly to work well that way. 

 

I thought the double worm drive is a rather ingenious mechanism. I can see many other possible uses.

 

Andy

That may be true, but having tried the Bachmann HK tram chassis on my own layout I know that it doesn't do quite what I want it to and the single axle drive doesn't perform as well as double axle drives on my fierce curves, so given the option I'd prefer a double axle drive, it's pretty academic really as the chassis isn't available as a pare part and I'll be honest I'm not going to pay 20 plus quid more for a full tram that doesn't perform as well as as a chassis option.

 

Nothing against the HK, just doesn't work well for me......and one burnt out one after trying it left me even less inclined to persevere with experiments, I may have just been unlucky but it hardly bodes well for me, again no other experience other than my own findings and I'd bet that for most it would be ok. 

[Alan J Kirkman]

One of the down sides of one axle drive in 4w trams is the laws of physics. Particularly the laws of motions and its application to the spring force of the trolley pole on the wire. If your powered axle is  trailing then the pole pressure adds to the adhesion, but reverse at the terminus and the pole force transfers to the unpowered axle and indeed unloads the driven one somewhat, Exactly the same Phenomenon that makes a 4-6-0 like a King slightly more surefooted on starting than a Pacific like a Duchess the pull though the drawbar adds to the loading on the rear axle. 4 wheel drive avoids this and is correct for trams. I didn't want to post any link to another page until I'd spoken to Paul Derick at Heaton Park on Sunday, as a courtesy, but now Mark has so be it.

[Andy Reichert]

One of the down sides of one axle drive in 4w trams is the laws of physics. Particularly the laws of motions and its application to the spring force of the trolley pole on the wire. If your powered axle is  trailing then the pole pressure adds to the adhesion, but reverse at the terminus and the pole force transfers to the unpowered axle and indeed unloads the driven one somewhat, Exactly the same Phenomenon that makes a 4-6-0 like a King slightly more surefooted on starting than a Pacific like a Duchess the pull though the drawbar adds to the loading on the rear axle. 4 wheel drive avoids this and is correct for trams. I didn't want to post any link to another page until I'd spoken to Paul Derick at Heaton Park on Sunday, as a courtesy, but now Mark has so be it.

 

The effects of the Laws of Physics vary with the numbers involved. A relatively light model 4 wheeler, with a relatively high pressure trolley pole should behave as you say. OTOH, a relatively heavy model  4 wheeler, with a relatively low pressure trolley pole, might see little or no perceptible difference.  What matters to us if course, is that the finished model drives reliably and satisfactorily,  as per it's control setting, in both directions. And that's something that requires taking multiple design factors into consideration to achieve.

 

I'm not sure whether your thoughts on the steam locos refer to prototypes or their models. I'll defer to the experts in the case of the prototypes' behaviours. Full size steam locos are well outside of my field of experience.

 

Andy

 

PS. I'm sorry to hear that there were actually recorded motor failures experienced on the Bachmann HK chassis. That's something that shouldn't happen in a well designed model.

[Alan J Kirkman]

Andy I only refer to the laws of Physics that  explain the problems that we experienced over the years! Single axle drive trams run better when the driven axle is under the pole. There's more that enough written up about real steam. Bachmann HK trams have failed on 3 exhibitors to my knowledge in that I was there also exhibiting when they happened or I was told of a failed experiment by Mark. At the recent Totally Transport exhibition I was asked by another exhibitor to look at his that had also stopped, to my surprise when I tried to clip the test leads to the undriven wheels and apply power while nothing at first happened I tried turning the powered axle with my fingers on the wheels and it seemed to start to turn. A few more rubs and it was rotating but wouldn't restart if turned off.  A few more goes and it would restart and even reverse. Slackening the two screws under the base seemed to restore performance and testing the cart without the body on Doug's two rail layout was satisfactory so we put the body back on and it behaved all day. I was surprised to be able to force some rotation by hand against the Worm gears. I have no real idea what the mech was or wasn't doing and we all await further news from Doug as to what the future holds for this mechanism. It seems these mechanism is a mixed blessing. 

[Red Devil]

As said before the Bachmann HK is a nice model, its mechanism is probably ok for the majority, however as a drive unit for other trams it is in my opinion the wrong place to start from, why buy a ready to run item that is dearer than pretty much anything else to hack about an invalidate any warranty when there are several bespoke chassis that can purchased as such that offer as good performance for less outlay? Halling, Black Beetle etc etc.

 

If it was available as a spare item then yes use it by all means, if you're going to run it as a HK car then yep, no problem but as a power source for other trams, again in my opinion only, I'd be thinking along the lines of' yes you'll get there but you wouldn't want to start from here' to paraphrase an old cliche.

 

Not trying to put the OP off in anyway but that's what I've found.  

[Swifty11]

Although not completely relevant, could I ask those who have the Bachmann trams, do they fit around first radius curves? 

 

thanks, Tom