Point motors and switches for a beginner

[BreatGritain]

Hello!

Please could I get your advice / input?

I've been trying to figure this out, but there's so much conflicting information on the internet it's starting to hurt.

I have two Hornby surface mounted point motors (well one now, blew one up playing...)

I tested one of the motors with a 12vdc PSU and a 2 gang light switch (one for trigger polarity, one for power) (I love playing with relays). It couldn't throw the points far enough. So I did more reading, removed the spring on the points, no good. More reading. Used a 19vdc 3.4aH PSU, it works perfectly! Then the motor blew up. I assume this is a fault in my dodgy light switch wiring, rather than using an unsuitable PSU. Although some clarity on the correct PSU to use would be great.

I have some hornby passing switches ordered, which will hopefully turn up soon. 

 

But now i've read that I should use a CDU. And the Hornby switches don't agree with these.

I just want a simple way to control two points, and any advice would be great.

 

Thank you!

Tom

[96RAF]

Solenoid point motors operate on a sudden pulse of current. If you apply a constant voltage for longer than around half a second you will burm out the motor coils - simple as that.

 

A CDU will help as it provides a burst of power when switched with a momentary (sprung to off) switch or passing contact switch. It then limits current flow as it recharges so protecting your solenoid motor if you inadverntantly keep the switch pressed or use the wrong type of switch.

 

As for not throwing the points far enough - that sounds like an alignment problem i.e. the motor is not mounted exactly central, hence one way it has spare movement and the other way it comes up short. Removing the points spring is not necessary and undesirable as it keeps the point blade thrown over after selection. You should refit it.

[BreatGritain]

Thank you for the reply RAF, very insightful.

What would you recommend as a solution?

Would you use the Hornby switches or a different type?

With or without CDU?

Which PSU? 12v 5ah, or 19v 3.4ah? Or another?

 

Thanks again.

 

Thanks again.

[96RAF]

I have my own system which works on analogue and DCC so would not be much use to you.

I use the 15vAC Aux output from a HM2000 anaolgue controller to power my GM CDU.

Manual switching is done by one of three 6-way rotary switches to select the point and a press to make switch for each route (straight or branch).

DCC operation is by way of relays.

 

You would be well advised to look at solenoid points operation on Brian Lambert’s web site where he explains why the Hornby switch is less than ideal for use with a CDU.

[Chrissaf]

Just to reiterate what RAF96 has advised (in his very first reply). You must use a switch that provides a momentary switching action. The DC coil resistance of a Solenoid motor is very low indeed. Typically 4 ohms (and no more than 12 ohms), this is virtually a 'short circuit'.

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• If you apply 12 volts across a 4 ohm load, your solenoid point motor will try to draw 3 amps.
• If you apply 19 volts across a 4 ohm load, your solenoid point motor will try to draw 4.75 amps.

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Currents at these levels will make a solenoid point motor initially smoke then quickly burn out. The voltage / current must only be applied for about 100 milliseconds (1/10th of a second). This is something that a CDU is designed to do. But even with a CDU in circuit, you MUST still use momentary action switches.

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If you have purchased Hornby R044 'Passing Contact' switches, these (as you have already said you understand) are not 100% compatible for use with a CDU. Personally, I would return these to where you bought them from and get a refund.

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If you want to use a lever type switch, then you can use switches from the PECO PL-26 range. The PL-26 switch is 100% compatible with a CDU. Your other alternative is to use a momentary action toggle switch. You have to be very careful to ensure the correct toggle switch type is purchased because they all look very similar in appearance.

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The correct type of switch has a central off position and the lever is sprung loaded to always return the switch to the centre off position when the lever is released.

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Normal electrical light switches are totally inappropriate for this type of application.

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You should also reinstate the spring in the point. Most Solenoid point motors do not lock over and need the point spring to maintain the point in its operated position. Only slow action 'stall motor' and 'servo' motor point operating motors should have the point spring optionally removed.

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Rather than reinvent the wheel....review my previous post linked below that describes in detail all the various switch types that can be used.

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https://www.hornby.com/uk-en/forum/points-25203/?p=1

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Note that the Toggle Switch link in the thread above is now 'out of date'. Here is a new working switch product link:

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In terms of power supply I would definitely use the 19 volt one instead of the 12 volt one and supplement that with the CDU using compatible momentary action switches.

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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]

I use centre off biased switches, you can get them off EBay, model railway suppliers or electronic component outlets. I have tried peco switches, but found they were not that brilliant and cost a lot more than normal switches.  I use a CDU, but at least with this set up the switch springs back so it is a lot more difficult to hold the current on the point motor two long if you do decide to not use a CDU. The only issue with CDU is if you use a large capacitor it takes a while for it to charge up again. If you want to use relays you need to find a way that they only connect for a certain time, by using a timer circuit.

[96RAF]

My relays are operated by firing the output from a DCC accessory decoder into the coil of the reLay. This pulse pulls in the relay long enough for the CDU to discharge through the relay main contacts, thus keeping the CDU and DCC totally isolated from each other, which is ESSENTIAL.

This setup is likely over complex for your present needs.

[Ard Lochan]

For a novice I would recommend these: Expo EZE-Wire Point Switch with Hornby Point Motor Harness 28071, They  are a doddle to use with a wirig diagram included, They also do a version for Peco points, If you shop around you can get them for 4 or 5 pounds.

[BreatGritain]

Thnk you all for the replies, apologies for not replying sooner but as a newbie I had hit my daily post limit.

I've bought some retracting on-off-on switches, a CDU and a replacement for the point motor that I destroyed. When it all turns up i'm fairly sure i've got it figured out now, thanks to your help.

I'll let you know how I get on,

Thanks again!

[ColinB]

I forgot to mention, there is someone on EBay that does educational aids for people learning electronics. They do a 5 or 8 way printed circuit board with biased switces and screw terminals especially for control of points, it is labelled as such. They are significantly cheaper than the other option offered. You can buy the board ready made or if you want it cheaper you can solder it yourself.