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Can I wire two CDUs in parallel ?


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On 12/07/2021 at 13:04, Largechris said:

Thanks, tonight I’ve tested on my particular CDU and on 12V DC input I get 19.2V out, and on 16V AC input I get 21.0V out. 
 

 

 Actually there is nothing wrong with that. The CDU is capturing the peak voltage. The only difference between the two is that in the case of the H&M DC output there are two more diodes in the path which explains the slightly lower voltage when you use the DC output as opposed to the AC output.

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I use these relays

https://uk.rs-online.com/web/p/non-latching-relays/1762712/

 

Cheap and small but they come in a tube of 40. These seem to work fine with a 12 volt DC supply to the coil and the CDU power going through the switch part. I must confess I haven't given them a lot of use yet. 

 

I have been using these for over a year to change the polarity of my frogs and rails downstream of my unifrog points. https://uk.rs-online.com/web/p/latching-relays/1762920/  . SO far they have been perfect.

Edited by Chris M
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1 hour ago, Chris M said:

I use these relays

https://uk.rs-online.com/web/p/non-latching-relays/1762712/

 

Cheap and small but they come in a tube of 40. These seem to work fine with a 12 volt DC supply to the coil and the CDU power going through the switch part. I must confess I haven't given them a lot of use yet. 

 

I have been using these for over a year to change the polarity of my frogs and rails downstream of my unifrog points. https://uk.rs-online.com/web/p/latching-relays/1762920/  . SO far they have been perfect.

Perfect thanks

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8 hours ago, Largechris said:

Tried to get a measurement but don’t think my Voltmeter was really upto it if it’s that lumpy, was reading maybe 16V DC and 17.2V AC but would need an oscilloscope or something to prove some numbers.

I assume that you're joking about the oscilloscope!

 

A basic digital multimeter costing you a very modest sum, is more than adequate for measuring the input voltage to a CDU.

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3 minutes ago, kevinlms said:

I assume that you're joking about the oscilloscope!

 

A basic digital multimeter costing you a very modest sum, is more than adequate for measuring the input voltage to a CDU.

IIRC the '12V dc' output from a Duette is just full wave rectified ac so a cheap multimeter is unlikely to provide useful information beyond 'volts / no volts'. A cheap (as in 25 quid) oscilloscope will give a more meaningful display in terms of what voltage is actually being produced. 

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15 minutes ago, spamcan61 said:

IIRC the '12V dc' output from a Duette is just full wave rectified ac so a cheap multimeter is unlikely to provide useful information beyond 'volts / no volts'. A cheap (as in 25 quid) oscilloscope will give a more meaningful display in terms of what voltage is actually being produced. 

 

All meters whether cheap or expensive will measure the average DC voltage. The expensive ones might be a slightly more accurate than the cheap ones. The average voltage might indicate something like 12 volts when supplying power to a reasonable  load but the peak voltage will be much greater. The "off-load" voltage will be considerably higher too because transformers are not brilliant voltage regulators.

 

If a cheap meter says the average DC voltage is, say, 14 volts it probably is very close to 14 volts but the peak voltage will be much greater. IIRC about 1.4 times greater but don't quote me :)

 

CDUs charge the capacitors to the peak voltage (minus any voltage drops across any diodes in the path. We should not be in the slightest bit surprised that Chris is seeing the voltages he is seeing at his CDU.

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41 minutes ago, spamcan61 said:

IIRC the '12V dc' output from a Duette is just full wave rectified ac so a cheap multimeter is unlikely to provide useful information beyond 'volts / no volts'. A cheap (as in 25 quid) oscilloscope will give a more meaningful display in terms of what voltage is actually being produced. 

An oscilloscope is way over the top for this purpose. A much cheaper option would be to go out and buy a new plug pack of suitable ratings. Job done.

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1 hour ago, spamcan61 said:

IIRC the '12V dc' output from a Duette is just full wave rectified ac so a cheap multimeter is unlikely to provide useful information beyond 'volts / no volts'. A cheap (as in 25 quid) oscilloscope will give a more meaningful display in terms of what voltage is actually being produced. 

That was my guess from what I was reading on my cheapo meter... anyway easy way to resolve this -

 

Statistically 64% of forum members have a Duette to hand. I'm sure one or two have the requisite tech to get an accurate measurement. Just for interest.

Edited by Largechris
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4 hours ago, Largechris said:

That was my guess from what I was reading on my cheapo meter... anyway easy way to resolve this -

 

Statistically 64% of forum members have a Duette to hand. I'm sure one or two have the requisite tech to get an accurate measurement. Just for interest.

 

Mine is now used as a door stop........ Waits for the inevitable "I've had a Duette for 40 years and it still works like new"

Edited by newbryford
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19 hours ago, newbryford said:

 

So much for it saying 12vDC on the Duette!

 

At least one very well known supplier still calls stuff 12V that is far from it. Then wash their hands of the problem when a customer buys such stuff and uses it to destroy sensitive electronics.

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On 14/07/2021 at 11:52, Crosland said:

 

At least one very well known supplier still calls stuff 12V that is far from it. Then wash their hands of the problem when a customer buys such stuff and uses it to destroy sensitive electronics.

 

Is there a "Which" report or has it konked-out? (I've been away for some time.)

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My Duette showed 21 volts on my cheap multimeter on the "12 volt" output.   I am very good at blowing up capacitors, they go Bang and shoot out vile smelling yellow dye if connected in reverse or when they are Lucas 12 volt Motorcycle Capacitors they explode even when connected and used correctly.  I usually use 63volt Caps to give plenty of headroom (on both bikes and trains) but my diode matrix systems shift up to 6 H&M solenoids which are power hungry, approx twice as much as a Peco or Seep at a time.  Big Fat wires from car wiring looms rated for 5 amps continuously help but the number of points thrown at one time has to be limited to between four and six to avoid points being damaged.  Additional point motor solenoid coils are added via the matrix when only two points are thrown together (my down to up crossover)

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12 hours ago, DavidCBroad said:

My Duette showed 21 volts on my cheap multimeter on the "12 volt" output. 

But that is on no load. if you put a typical load of a loco of similar vintage, the voltage will drop below 21 volts.

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Just took a few measurements from my old Duette using a Triang Jinty as a load...

Accessory outputs - 

16v ac - 17.6v no load

12v dc - 14.3v no load, 13.4v under load - controller B resistance switch high.

^ ^ ^     - 16.43v no load, 14.4v under load - controller B resistance switch low.

 

Variable output full on -

High resistance 14.3v no load, 13.3v under load.

Low resistance 16.43v no load, 14.4v under load.

 

Edited to add that the 12v dc accessory output is affected by the resistance switch on controller B and gave the same readings as the controlled output full on.

 

 

 

Edited by Free At Last
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6 hours ago, Free At Last said:

Just took a few measurements from my old Duette using a Triang Jinty as a load...

Accessory outputs - 

16v ac - 17.6v no load

12v dc - 14.3v no load, 13.4v under load.

 

Variable output full on -

High resistance 14.3v no load, 13.3v under load.

Low resistance 16.43v no load, 14.4v under load.

 

 

 

 

Thanks for that. Were you using an analog or digital meter and may we know which make/model?

 

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22 hours ago, Free At Last said:

Just took a few measurements from my old Duette using a Triang Jinty as a load...

Accessory outputs - 

16v ac - 17.6v no load

12v dc - 14.3v no load, 13.4v under load.

 

Variable output full on -

High resistance 14.3v no load, 13.3v under load.

Low resistance 16.43v no load, 14.4v under load.

 

 

 

That's a big loss of volts from variable output to accessory output. As one variable output (on my 1970's Duette) is on the same overload cut out as the 12 volt DC accessory output and the other on the same one as the 16volt AC I would expect the 12volt accessory volts to be the same or slightly higher than the12 volt controlled low resistance.   

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4 hours ago, DavidCBroad said:

That's a big loss of volts from variable output to accessory output. As one variable output (on my 1970's Duette) is on the same overload cut out as the 12 volt DC accessory output and the other on the same one as the 16volt AC I would expect the 12volt accessory volts to be the same or slightly higher than the12 volt controlled low resistance.   

Just checked again and found the resistance switch on controller B affects the 12v DC accessory output and switching it gives the same readings as the controlled output. I didn't know that.

Edited by Free At Last
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