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OK I admit it I bought a train set for the young un @ Christmas and now I am Fixated


Seriously tho, I bought one of the Hornby new surface mounted point motors with the idea in mind that as they are a new possibly improved product, they may not draw as much current as the older versions of points motors.

I have been googling like mad but I can't find that figure, and it definately isnt on the packet or in the instructions


My thinking is that if I connect two motors into one of the four available connections on the Hornby Points Decoder
R8247 to operate a cross over pair of points I can operate maybe 5 or 6 sets of points from one Points Decoder.

I have added a picture of the points motor if it helps

picture of points motor

If I am wrong in this line of thought please let me know ?
 

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*** To know the current draw all you need do is measure the impedance of one coil and then apply Ohms Law, which is for calculating issues relating to ohms, volts, amps, watts etc...

to measure:
* set any multimeter to ohms (Ohms = Omega symbol = horse shoe shaped symbol) , make sure the probes are also in the right socket.
* if you have a choice selects a low value scale (say 0~1,000 ohms)
*place one probe on the common terminal/wire of the point motor, the other probe on either left or right coil terminal/wire.

You now have the data you need.

In its simplest form as here, amps(I) = volts(E) divided by resistance® , or I=E/R and watts (VA) = volts multiplied by resistance

for example, a Peco point motor is generally 4 ohms +/1 a wee bit.

If the voltage of your transformer is 16 volts, then divide 16 x 4 and you have the momentary current draw which is 4 amps.

Its good to ask this question and know the answer... Almost certainly though, you will have problems driving more than one point motor from an acessory decoder, and despite hornbys recommendations it is not a good idea to try and power accessory decoders from the DCC track or DCC control unit. You will find that it will momentarily shut down the whole system when you change points as there is not enough power to do both!

Richard
 

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Discussion Starter · #3 ·
OK Richard, Thanks for that information


I've got you on the measurement for amps, I just need to borrow a multi meter, which I will do at the weekend.

I planned to power the points decoder using the 16V output from a DC controller but now I see that the aux output is AC, the point motor is rated 12V - 17V = = = 15V~ I'm not sure about the points decoder Voltage yet as the DCC Controller aux output is 15V DC

Now I am really confused is ~ AC and === DC can I use that DC Aux as a power supply for the points decoder or am I best to wire it all through switches?

What is the best power supply to use for points motors ?

I could use a set up of 4 Pass Contact Switches but the cost of 4 of them is almost as much as the points decoder and they wont look as nice
any different options please let me know ?

Sorry to be a pain but could you explain in laymans terms why there would be a problem running two points motors from one output from the points decoder, is it likely to blow the decoder unit if I try it ?

Many Thanks in anticipation
 

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*** For switches, use standard normally off pushbuttons ex maplin - they will be cheap.

You can use DC or AC. The peco/hornby coil is actually wound as a DC coil but either works fine.

The problem with trying to throw two is the power it consumes - if its the same transformer thats feeding the layout, the points will ned all its power for a moment.

I haven't specifically measured a Hornby coil but suspect it'll be a low impedance like Peco - in which case that means a momentary 8 amps for two.... thats huge power need all at one time.

I like uisng an old laptop computer power supply - several amps at 18 volts DC and often free as they always still work when the laptop they came with has died!

Richard
 

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These points motors have a resistance of 3.4 - 3.8 ohm and therefore draw a LOT of current and are best used with a CDU (capacitor discharge unit). I am using them with a Lenz LS150 accessory decoder and found that providing anything but the maximum 45VA on the AC input causes the decoder to trip on some of the point motors when activated. The LS150 does not have CDU, so the current is drawn directly from the transformer. In the case of the LS150 you must be careful not to exceed the 45VA on the AC input, as it will cause the short circuit protection to fail - you can avoid this by putting a 10ohm resistor in line with the transformer, that has a rating higher than 45VA, to limit the current.

Note. On several other forums it has been noted that using these point motors with a Hornby Select controller and a Hornby accessory decoder, causes the Select controller to reset, because it is starved of power while the points activate. The Select ships with a 1 amp transformer.

These points motors have a very small hole to connect to the points bar and, unless you modify them, does not work with Peco points. The pin on the Peco points is quite thick and will have to be trimmed down. The points motor does not have enough material to enlarge the hole.

You must also be careful not to pulse the points motor too long as it will fry. Typically it only needs power for 10ms or so, so be careful when selecting a switch that it does not make a permanent connection. Once again this can be avoided by using a CDU as it will only provide power while the capacitor discharges. Several very simple circuits are around on the internet to build your own CDU.
 
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