Converting a R317-070 (HST) motor to DCC

[Johnbw]

I am struggling to do this correctly, having completed one model with no success.   I have read many posts and also articles by Brian Lambert and others but cannot find a solution  that works.

When tested with a multimeter, the brush arms are isolated , so ok, but when I connect either right rear wheels to the motor case, I get a reading, and (according to one article I read) this is BAD news!  I do not see how I can isolate the wheels or why I need to isolate them from the motor!

I would appreciate any help!

[Chrissaf]

....or why I need to isolate them from the motor!

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Because if you don't you will have an electrical path between the DCC input to the decoder and the decoder output to the motor. This will damage the decoder. The decoder has to sit electrically in the electrical path between the wheels and motor, thus the motor has to be totally isolated from the wheels first.

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I do not see how I can isolate the wheels

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I am assuming this loco has a 'Ringfield' motor. Ringfield conversions are covered on this page. I suspect from your issue description you need to follow the 'Method 2' conversion.

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https://www.brian-lambert.co.uk/DCC_Page_1.html#Bookmark12

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TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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[ColinB]

Have another look at the motor it is probably one of two things. It is either the screws that hold the brush holder on, on a lot of motors one of the screws screws into the plastic and then the metal of the motor, or if you look under the brush holder spade connections, under one of them there is sometimes a lug that the brush holder rests against. Hornby try and catch you out by including a wire to chassis from the brush holder, you remove it and think that is it. I converted mine to DCC and I don't think it was that difficult. The most difficult bit was replacing the lights with leds, I wanted white and red ones. If you have the motor where the brush holder screws into the body, I usually tap both holes out and replace with m3 or m2.5 nylon screws. Do both so that next time you take it apart you don't mix them up. It is cheaper than a new decoder.

[96RAF]

You say you have isolated the motor brushes from the wheels. That is exactly what you are trying to do. The motor housing stays live and the left hand brush is isolated either by use of a nylon screw or reworking the peg on the housing that bears on the left hand brush retainer. The right hand brush is usually already isolated.

 

Once both are definitely isolated you can connect your decoder wires directly to the brush retainers.

 

Colin - I use common anode 3-legged bicolour red/white leds for certain locos, especially in those older Hornby models that used a single filament lamp and a plastic prism to emulate separate light units. This immediately gives me white forward and red rearward lights.  I just noticed in one of my articles that I call them positive anode red/white leds. I meant common anode of course.

[ColinB]

Thanks for the info RAF96, I think was trying to make it more realistic by having separate leds. I think for the HST I used tower leds stacked next to each other on each side, I think the pain was linking them together, to reduce the number of wires. 

[96RAF]

Colin

My standard install these days is to use a central resistor board using 1K SMD resistors. This makes installing multiple leds at each end of the loco a little easier.

 

This is the circuit and an installed board. You can just about see the SMD resistors bridging the vero tracks in the picture.

/media/tinymce_upload/3eeb2333397cda7a516d54ea8fff4350.JPG

 

/media/tinymce_upload/d00023eaac86dbc2f39067fb37a2a7e8.jpg

[Flashbang]

Hi

JohnBW contacted me directly for advice/help with the conversion.  Unfortunately this Ringfield motor is probably the hardest to convert but it can be done with care.  So I though for completeness I would post an edit of my reply to John for anyone else wishing to undertake this conversion.

 

Your Ringfield motor has two flat Phosphor Bronze brush strips.  The left hand strip is held to the Ringfield motors metal casing, which is behind the front plastic face, by the screw.  The left hand strip and its screw are the problem one. The right hand one is threaded into the plastic cover only.  On this motor it is quite a hard conversion process!   It is absolutely essential that the connection to the metal chassis and then onto the wheels is removed by insulating the left hand screw and its brush strip. Failure to ensure the strip is insulated will result in immediate decoder failure on applying DCC power!

 

How to do this…. As the front cover is plastic it’s the left hand screw being threaded into the rear metal chassis that causing the problem.    Replacing it with a nylon screw is the simplest.  The alternative is to use a plastic top hat bush as used by electronic circuit builders to insulated transistors from their metal heat sinks. However, finding one that is of the correct size may be an issue! The Top Hat stops the screw from making contact to the left hand strip. (I’ve attached a typical example image of a Transistor Top Hat)    The third method is to make your own insulated bush and insulated flat washer and this could involve opening up the hole in the left hand brush strip and making a new short insulated sleeve and insulated washer for the front. The screw then sits inside the short sleeve and the flat insulated washer stops the screw head from touching the brush strip.    The final method would be to make the brush strips fixing exactly the same as the right-hand strips fixing.  Here you would need to drill out the threaded section in the right hand sides metal chassis and open it up even more to a larger size and similar size to the right hand side,  but it can be a large round hole. This will involve a lot of drilling.  If you do any drilling etc don’t forget the motor has a large magnet and the very last thing you need is for metal swarf to get onto the magnet or the motors armature etc.  Once its opened up a slightly larger screw can be used to grip into the plastic cover so its similar to and as per the right hand strip.

 

This YouTube video shows the strip down procedure and at around 8.40 minutes in it shows clearly the problem you have with the screw connecting the right hand brush strip to the metal chassis.

Below is a typical Transistor Top Hat nylon or plastic bush...

 /media/tinymce_upload/9a5b84668afe56f1c046c4061625b33e.JPG

REMEMBER:  Always test the left hand strip has no connection to the wheels or any metal chassis BEFORE connecting the decoder wires.  An expensive lesson will be learnt in the cost of a new decoder if there is a connection!

[ColinB]

Two things, what I did with that type of motor is to tap the hole out with M3 or M2.5 dependent on the existing hole size, then use nylon screws with the same thread, it is a much better solution than trying to put a parallel thread nylon washer into a self tapped hole. On some of them the plastic is thick enough to tap, and use short laptop screws to hold them on. In answer to RAF96, I either use "commoned" single in line resistor packs or a pcb I get from LaisDCC with smd ristors on it. SIL resistor packs are better as you can choose different values. I just found it difficult because I was trying to be too clever/lazy and basically bend the LED leads on one side together to form a common anode.

[Flashbang]

I wasn't sure whether to reply or not? But I have to ask... What is....  "trying to put a parallel thread nylon washer into a self tapped hole." ??   Never heard of this!   Can you enlighten please? 

[ColinB]

Sorry, should have read parallel thread nylon screw into a self tapped hole. I actually did one this afternoon, if the brush holder is thick enough, by tapping the plastic you can use 4 mm long normal M3 screws, you have to slightly enlarge the  cut outs in the brush retainers. As the plastic is about 5 mm  thick, it works. Nylon screws are not the toughest of things so forcing then into a self tapped hole is asking for trouble. I did try M2.5 but the original hole is slightly too big.