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AndrewP

12v DC supply

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I have a standard Hornby R695 controllor but have just been given a motorised turntable that seems to need a DC output but the controllor only has 16vAC output. Just wondering if anyone can advise how to wire up the turntable?

 

thanks

Andy

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2nd cheap controller seems the obvious. 

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Thanks John, do you mean buy a cheap controller with a 12v ac output just to be used for the turntable? sorry if i'm being a bit thick but i'm new to this an djust trying to get things going for my son. Andy

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How much power does the turntable need? It should be in the documentation somewhere as x milliamps or y watts (if y watts divide y by 12 to get Amps). 

 

once you know what current it needs then buy a 12v wall wart that is large enough for not a lot of money and just use it on the turntable. something like this will probbaly work 

 

https://www.amazon.co.uk/JnDeeTM-Supply-ADAPTER-Transformer-TRANSFORMER/dp/B00CXYNV48?ref_=fsclp_pl_dp_2

 

 

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40 minutes ago, AndrewP said:

Thanks John, do you mean buy a cheap controller with a 12v ac output just to be used for the turntable? sorry if i'm being a bit thick but i'm new to this an djust trying to get things going for my son. Andy

 

Yes, that was my thinking.

 

WiMorrison’s suggestion also good.  I’ve done something similar in last day or so for the fan in my power-box, as that is a one-speed, always on when the power is connected, application. My suggestion of a controller is that you can possibly/probably control the turntable’s speed.

 

Edited by john new

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Feed the turntable through a bridge rectifier, they usually cost about £1 from a decent electrical supply shop, or make one from 4  X  1N400 diodes, look bridge rectifier up on line for instructions.   Diode drop, the voltage drop across a diode, drops 16V AC to around 12V DC.

 

If you get a wall wart make sure it is DC, a 12 volt AC one will be no better than your existing 16volt AC supply

 

 

Screenshot (51).png

Edited by DavidCBroad
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It isn’t diode drop that makes 16v ac into 12v dc, it is the inversion of the inversion of the negative (or positive) half of the ac. The resultant wave form is seen as ‘dc’ with root mean square value of approx 12v (16 * 1.414).

 

To make the output real dc the rectified waveform still needs smoothing.

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9 hours ago, AndrewP said:

Thanks John, do you mean buy a cheap controller with a 12v ac output just to be used for the turntable? sorry if i'm being a bit thick but i'm new to this an djust trying to get things going for my son. Andy

 

I’ve just spotted you have said DC first time around and 12V AC subsequently (typo?). My earlier answers assumed DC was what you meant.

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2 hours ago, WIMorrison said:

It isn’t diode drop that makes 16v ac into 12v dc, it is the inversion of the inversion of the negative (or positive) half of the ac. The resultant wave form is seen as ‘dc’ with root mean square value of approx 12v (16 * 1.414).

 

To make the output real dc the rectified waveform still needs smoothing.

 

You do realise the 16V of the 16V ac is already an RMS value? What you are saying is only true if the 16v ac was 16v peak rather than RMS, which it isn't. It is therefore the resistance of the diodes which brings it down to 12V dc rms.

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9 hours ago, DavidCBroad said:

Feed the turntable through a bridge rectifier, they usually cost about £1 from a decent electrical supply shop, or make one from 4  X  1N400 diodes, look bridge rectifier up on line for instructions.   Diode drop, the voltage drop across a diode, drops 16V AC to around 12V DC

 

3 hours ago, WIMorrison said:

It isn’t diode drop that makes 16v ac into 12v dc, it is the inversion of the inversion of the negative (or positive) half of the ac. The resultant wave form is seen as ‘dc’ with root mean square value of approx 12v (16 * 1.414).

 

To make the output real dc the rectified waveform still needs smoothing.

 

Er, no. The 16V AC is RMS. When rectified and smoothed it will be over 20V DC. DO NOT try this on your 12V turmtable.

 

Just buy a 12V "wallwart" plug in power supply.

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8 minutes ago, Titan said:

 

You do realise the 16V of the 16V ac is already an RMS value? What you are saying is only true if the 16v ac was 16v peak rather than RMS, which it isn't. It is therefore the resistance of the diodes which brings it down to 12V dc rms.

 

Still wrong!

 

If the AC were 16V peak then the rectified and smoothed DC would be 16V, not 12V.

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And Titan's reference to 'the resistance of the diodes' is misleading. Diodes do not have resistance in the normal sense. They have a threshold voltage, 0.7 volts for silicon and 0.3 for germanium, but once past this their resistance is very small.

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20 minutes ago, Titan said:

 

You do realise the 16V of the 16V ac is already an RMS value? What you are saying is only true if the 16v ac was 16v peak rather than RMS, which it isn't. It is therefore the resistance of the diodes which brings it down to 12V dc rms.

 

Are you sure it is already RMS?

 

I understood that the quoted measurements were as stated and interpreted them as peak to peak and not measured, hence my statements. I understood that 16v ac became the norm on model railways because 16v peak to peak provides ~12v RMS which when rectified and smoothed provided the nominal 12v voltage that people always quote.

 

I wont comment on the diodes as other have already explained that this is wrong.

 

But I am sure that someone will correct me if I am wrong ;)

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This is a good discussion but I'm not sure it's helping the OP who may not have knowledge at the level of detail being debated.

 

I'm assuming the turntable needs 12v DC so he is right that using the 16v AC won't work. The turntable will not work with AC current, it will need a low voltage DC supply, if he is not confident and doesn't want to meake the necessary alterations to convert the 16vAC to 12v DC then the second cheap controller or even something like the old Scalextric transformer rectifier seems like an easy solution. An old Hornby R911, R912 or similar can be found for under a fiver and with the control knob set to full will work the mechanism simply by connecting the two output wires to the terminals for the turntable. 

Edited by andyman7
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One needs to be careful bandying about terms here 

 

The ( Average )  DC voltage output of full bridge rectifier with capacitor smoothing is a value determined by the nature and type of load current , and both the peak Vac and hence peak Vdc is a meaningless figure unless accompanied by the known load.  People are mixing up DC peak values, VacPeak and Vac RMS here 

Edited by Junctionmad

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100% of the "12 volt DC"  controllers with  "16 volt AC" uncontrolled  outputs I have ever seen, Hornby Dublo, Triang, Hammant and Morgan, OnTrack etc have the "16 volt"  AC uncontrolled output rectified via a bridge rectifier to provide the "12 volt DC"   That "12 volts" is often 21 or 24 volts off load.  Don't confuse this model railway "12 volts"  with Computer 12 volts which generally is 12 volts or automotive 12 volts which is typically 13.8 to 14.2 volts 

 

The OP has no mention of 12 volts so If the turntable is for a model railway it should be designed for what could easily be up to 20 volts

 

A "12 volt DC" wall wart designed for model railway use may be fine,   I wouldn't use a scalextric power unit, 

 

If cost is an issue you could try a single diode in the feed and run it at half wave, it might turn at a slower, more realistic, speed.

I await a learned dissertation on this suggestion which will surely follow,

14 hours ago, AndrewP said:

Thanks John, do you mean buy a cheap controller with a 12v ac output just to be used for the turntable? sorry if i'm being a bit thick but i'm new to this an djust trying to get things going for my son. Andy

 

Absolutely NOT. You need a DC output.    Don't use a 12 volt AC wall wart, it simply won't work.  

 

1 hour ago, Crosland said:

 

Just buy a 12V "wallwart" plug in power supply.

 

I think he means  "Just buy a 12V DC wallwart" plug in power supply." 

 

 

Screenshot (51).png

Screenshot (51)a.png

Edited by DavidCBroad

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33 minutes ago, andyman7 said:

This is a good discussion but I'm not sure it's helping the OP who may not have knowledge at the level of detail being debated.

 

I'm assuming the turntable needs 12v DC so he is right that using the 16v AC won't work. The turntable will not work with AC current, it will need a low voltage DC supply, if he is not confident and doesn't want to meake the necessary alterations to convert the 16vAC to 12v DC then the second cheap controller or even something like the old Scalextric transformer rectifier seems like an easy solution. An old Hornby R911, R912 or similar can be found for under a fiver and with the control knob set to full will work the mechanism simply by connecting the two output wires to the terminals for the turntable. 

Fact is, no one has actually asked what model of turntable it is!

 

Many turntables will run too fast on 12 Volts and so might make it difficult to spot it correctly at an exit/entrance road.

 

Perhaps a switched 12 volt REGULATED DC supply might be better, then a speed that works well can be selected.

 

This one is from Australia, but the type is what is needed.

 

https://www.jaycar.com.au/12w-3-12vdc-switchmode-plugpack-with-usb-outlet/p/MP3312

 

 

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Just a simple question to the op. 

 

Do you need the turntable to rotate at the same time that you are running  trains on the track? 

 

If not then a switch on the track output of the controller to choose whether it feeds the track or the TT would work nicely. 

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3 hours ago, DavidCBroad said:

100% of the "12 volt DC"  controllers with  "16 volt AC" uncontrolled  outputs I have ever seen, Hornby Dublo, Triang, Hammant and Morgan, OnTrack etc have the "16 volt"  AC uncontrolled output rectified via a bridge rectifier to provide the "12 volt DC"   That "12 volts" is often 21 or 24 volts off load.  Don't confuse this model railway "12 volts"  with Computer 12 volts which generally is 12 volts or automotive 12 volts which is typically 13.8 to 14.2 volts 

 

Don't be silly.

 

12V is 12V is..., regardless of where it comes from. If it's 21 or 24V then it is not 12V. If the OP says 12V then we have to credit them with a certain amount of intelligence. By all means question them to get more information but do nit second guess what is being asked or stated.

 

Only the real railway might claim to have the "wrong sort of volts". Maybe that's what all those new Siemens trains were unable to restart when power came back on after the recent blackout. Perhaps ther were expecting German volts instead of English volts.

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I can't help thinking you are both correct.  I have an assortment of wall warts and when I attach my multimeter none of them actually deliver (unloaded) the voltage indicated by the information printed on them.  The worse case is one claiming to be 12v DC showing 19v DC.  I had an idea to re-use them for a dedicated point motor circuit but in the end decided to purchase a couple of inexpensive regulated supplies which appear to deliver exactly what they should.

 

BTW  Volts are Italian.  :jester:

 

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Forget about other power supplies, wire it as the standard Hornby turntable, as follows:

 

Hope this helps

Rick

 

07565d3d6222e5b9de8fb8b7ac7977eb (1).jpg

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2 hours ago, teaky said:

I can't help thinking you are both correct.  I have an assortment of wall warts and when I attach my multimeter none of them actually deliver (unloaded) the voltage indicated by the information printed on them.  The worse case is one claiming to be 12v DC showing 19v DC.  I had an idea to re-use them for a dedicated point motor circuit but in the end decided to purchase a couple of inexpensive regulated supplies which appear to deliver exactly what they should.

 

BTW  Volts are Italian.  https://www.rmweb.co.uk/community/uploads/emoticons/default_jester.gif

 

 

You must buy rubbish PSUs :(

Many modern wall supplies are switched mode and are much better regulated. I've just tried some lying around.

A 12v 1.25A one was 12.14v, a 12v 2A one was 12.3v and a 5.1V 3A one was 5.28v all off load.

(In fact they not very modern, all are 10+ years old!)

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10 hours ago, Dave John said:

Just a simple question to the op. 

 

Do you need the turntable to rotate at the same time that you are running  trains on the track? 

 

If not then a switch on the track output of the controller to choose whether it feeds the track or the TT would work nicely. 

This does seem like an easier solution. The loco on the turntable will certainly not want to be moving.

Depending on what turntable you have, you may need better control than 12v on/off anyway.

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9 hours ago, teaky said:

I can't help thinking you are both correct.  I have an assortment of wall warts and when I attach my multimeter none of them actually deliver (unloaded) the voltage indicated by the information printed on them.  The worse case is one claiming to be 12v DC showing 19v DC.  I had an idea to re-use them for a dedicated point motor circuit but in the end decided to purchase a couple of inexpensive regulated supplies which appear to deliver exactly what they should.

 

BTW  Volts are Italian.  https://www.rmweb.co.uk/community/uploads/emoticons/default_jester.gif

 

Most "12 Volt" power supplies supplied with equipment are not regulated, but when connected to the specified load, give roughly the correct voltage. Any unregulated power supply will invariably be high on no load.

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