Problem with points and small locos

[keithp1707821843]

Hello

In another post I asked about points and small locos. I have the Mitchel coal - 0-4-0 loco, anyhow it sometimes stops on the points. This I understand is due to a loss of power as it moves over the points, if it goes faster it is carried by momentum, but as the layout is a shunting yard, going faster does not always work. SO if I was to get a 0-6-0 loco would that resolve the issue? Anything bigger may not work, as it is a small shunting yard.

My other option is to use a loco at the front and one at the back, then if one loses power the other keeps going, but again a bit unrealistic.

Keith

[walkingthedog]

You could permanently attach a wagon with added pickups. Like this.

/media/tinymce_upload/37201aceec5687b063530e7eeec4d370.JPG

[EnGee]

Look up information on 'stay alive' circuits. There are quite a few postings on this subject. I have 2 small 0-6-0 shunters which were a pain but since fitting 'stay alive' they are perfect.

[LCDR]

The problem can be caused by the type of points you are using.

 

Hornby use a fairly long common crossing made of plastic which can result in a 'dead' spot which may cause short wheelbase  locomotives to lose the power. This can be agravated by a locomotive chassis on which the wheels are not perfectly level or by track work which is not perfectly flat and level, and also sometimes if the pick-up wipers are weak and not always in contact with the wheel rims. Other makes of points have the rails adjacent to the common crossing which are inset in the plastic moulding so go closer to the nose of the crossing. However even these still leave a gap and can be beset with issues.

 

The best answer is a 'live frog' arrangement whereby the common crossing (AKA Frog) is made of metal, and the polarity is swapped each time to point changes to avoid setting up a short circuit. Unfortunately train set points do not usually incorporate this feature.

[Buz]

Hi keihtp

0-4-0 locos are generaly problomatic on points as they have short wheel bases and can loose power on the plastic frogs.

0-6-0 locomotives are better having more pick wheels or wider spaced pick ups geting a good quality 0-6-0 should fix the problem.

As an alternative you can rig a brake van with pick ups and have that perminantly coupled to the 0-4-0 loco not ideal but it works.

regards John

[walkingthedog]

Stay alive assumes Keiths layout is DCC, which it may well be. 

[37lover]

WTD,

As I operate on DCC I haven't given much thought to stay alive on DC, not being an Electrics expert why can you not have stay alive on DC?

[LCDR]

The problem also affected the real railway, only in a slightly different way. Where track circuits were provided to operate signals and indicate to the signal man where a train was, the new short wheel base diesel shunters failed to operate the track circuits, and could, and did, vanish from the signalling diagram. To overcome this BR converted some flat wagons, usually container flats, to runner wagons often laying old rails on the deck to give them more weight, and coupled these to the loco to put more wheels in contact with the rails. 

 

The last I saw were the 03 class allocated to Gateshead which worked as station pilots at Newcastle Central.

[keithp1707821843]

Ok thanks. It is a normal DCC layout, DID look at stay live before, but not for me. 

How do you fix extra pickups then? In the first reply, I can't see how the wagon is attached apart from a normal coupling. If I could do that I think that would possibly work. Adding the extra loco also worked but it is a 1990's model and goes very quickly, so was almost too fast.

Keith

[LCDR]

You need a wagon with metal wheels and then use some nickel silver wire to make wipers that fit underneath rubbing to the back of the wheels. You could solder these to a piece of Paxolin circuit board screwed or glued under the wagon.  The two sides need to be electrically independent. You then need some fine insulated wire soldered to the loco pick ups, taken back to underneath the wagon and soldered to the circuit board. 

[walkingthedog]

WTD,

As I operate on DCC I haven't given much thought to stay alive on DC, not being an Electrics expert why can you not have stay alive on DC?

I looked it up and as far as I can see it would need a physically large capacitor that wouldn't fit in an OO loco. I might be wrong but that is how read it. I would imagine if it worked on DC it would  have been thought of years ago long before DCC. 

[Chrissaf]

.....not being an Electrics expert why can you not have stay alive on DC?

.

Because the DC voltage polarity on the rails reverses when you change direction and 'stay alives' are polarity sensitive and will swell up and explode if the voltage across them is reversed.

.

In DCC, the stay alive sits after the bridge rectifier and before the decoder, so the polarity across the 'stay alive' is alway constant and the right way round. It is the motor output of the decoder (after the 'stay alive') that reverses the DC polarity to the motor.

.

On DC, if you were to install a bridge rectifier to protect the 'stay alive' from being damaged, then the loco can then only go in the same direction regardless of whether the analogue controller is set for forward or reverse, because the bridge rectifier will always convert the changing rail polarity to the same voltage polarity applied to the motor.

.

Not only that, but in DC Analogue the track voltage is a variable and can be very low when the controller is set for minimal speed. On DCC, the track voltage is a constant after the bridge rectifier at about 14 - 15 volts DC. This higher voltage suits 'stay alive' operation better.

.

 

[walkingthedog]

Thanks Chris that makes sense. 

[Chrissaf]

Just to add.

.

If you fitted a decoder to a DC Analogue loco and ran it on the analogue layout using the decoder 'DC Operation' feature in CV29. Then you could still fit a 'stay alive' to it. This is where a large value 'stay alive' can be useful, because when the loco is going slowly and the DC track voltage is low. There needs to be more power storage capacity in the 'stay alive' to compensate.

.

How effective such a solution might be....I'm not sure, as it is not something I have experimented with. For example, if the loco has been travelling fast (high track voltage) and was then slowed down, would the higher residual voltage charge in the 'stay alive' keep the loco going at the previous high speed until it had discharged to the new lower level. In other words would there be a lot of delay in DC Analogue control......something I wouldn't like to say yay or nay to.

.

A 'stay alive' for direct use with DC Analogue would have to use a capacitor technology that is not sensitive to polarity. In fact, there are more capacitor types that are not sensitive to voltage polarity than those that are. The problem using such a capacitor for a 'stay alive' is the physical size. Capacitors that are not sensitive to voltage polarity have very small farad values. To create a 'stay alive' that has enough electrical power storage capacity to be useful using these non voltage sensitive capacitor types, would need a 'stay alive' the size of a household bar of soap. This is maybe where the reference to large physical size 'stay alive' capacitors came from in WTD's Google research.

.

[LCDR]

 

Extra pick-ups might be arranged 

/media/tinymce_upload/9685957b97a81624d032b0100e3ce856.jpg

 

Something like this?

[atom3624]

Thanks Chris from me.

 

I'd often wondered about a stay alive on DC myself.

 

Al.

[37lover]

And thanks from me also.

[keithp1707821843]

Ok thanks, I don't solder so perhaps the solution is a 0-6-0 loco or just keep the speed up. I did notice that when the loco had wagons attached, it did seem to get over the points, perhaps the current was getting through the wagons somehow? or just the extra weight pushed it over.

[walkingthedog]

An attached wagon makes absolutely no difference unless it supplies power to the loco via pickups and wire. 

 

Put a track pin as close to the centre of the points as possible. Having the points perfectly flat can make a difference. 

[96RAF]

Use these ESU items

/media/tinymce_upload/2b98f536411007f8ef273180729b4ef9.png

[ColinB]

I initially thought that there wouldn't be enough energy stored in the capacitor on the "stay alive" to drive the motor but I was wrong. I bought a DCC concepts decoder which came with one, so I used it and yes they definitely work. I even fitted them to some of my old Ringfied based locos, Lima and Hornby and they make a substantial difference, previously they stopped on pieces of dirty track but with the "stay alive" they didn't. YouChoos do a sophisticated board that if you use Chrissaf's data on connections, works well with Hornby TTS decoders. If you are using DCC it is an easier fix than adding extra pickups.