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Hi Folks,  Got a problem with my point motors that I'm puzzling over. My DC layout has approx 22 point motors (though never more than 2 used together) with a mix of Peco & Seep motors and 2 * PPI4 from Block signalling.  Up until recently, all has worked fine using a Gaugemaster CDU.  I noticed that after first switching on the power, it was taking longer for the points to be usable and eventually those furthest from the CDU didn't switch at all.  Assuming a duff CDU, I bought a replacement single capacitor one from Block signalling. On the bench, it worked fine switching one motor running off the 15v AC from a very old Hornby controller. Connecting it to the layout using 16v AC from my  Gaugemaster dual controller, nothing worked. Swapped the old Hornby controller in, and CDU got hot and began smoking.  I have tested every switch on my control panel and the wiring if working as it should.  Strangely, removing the CDU and connecting to the 12v DC on the Hornby and cerefully trying each point, they all work perfectly (naturally those in pairs took two flicks of the switch to move both motors). Now wondering if the old CDU was OK and it's the 16v AC output on the controller at fault.  Bit if a loss to know where to look next to resolve the problem. If anyone has an idea, it would be welcomed.  I don't have a multimeter.

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Which CDU started to smoke? I would suspect this one has now failed.

I have never used a Block Signalling one, but the Gaugemaster is quite well built.

It would be useful to know what caused it to smoke. My first reaction would be to measure the output of whatever supply you were using with a multimeter...but you don't have one.

Since you made a point of mentioning this, you know it would be useful in this instance & would take a lot of the guesswork away. Cheaper ones cost less than a CDU. They are less accurate than something more expensive but good enough for basic faultfinding.

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Many people find the idea of using a multimeter quite daunting. But it shouldn't be really. Using it for the basics of DC voltage and Ohms should be very simple, and you can find out about other ranges as you grow in confidence. Plenty of people on here will help.

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CDU getting hot and smoking is a new one on me.  Mine just go Bang or Pop and spray liquid over the immediate area when the Capacitor is over charged.    Suggest you return the unit to the manufacturer.  I can't see the input causing an issue as long as it  is designed for AC input, if its for DC input then yes smoking is not unexpected.  I find different super cheapo  multimeters give different readings of AC voltage and "!6" volt AC outputs are often more like 21 volts on the meter off load. When you get he meter check for continuity on the output leads from the CDU, there really shouldn't be any continuity until you throw a switch, if there is track it down before installing a new CDU.   A £1 LED torch from P****Land and a couple of leads makes a half decent continuity tester.

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3 hours ago, DavidCBroad said:

  I can't see the input causing an issue as long as it  is designed for AC input, if its for DC input then yes smoking is not unexpected. 

Why would a CDU smoke if you fed it DC rather than AC? Surely the VALUE of the voltage that might cause the smoke, if it is too high?

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26 minutes ago, kevinlms said:

Why would a CDU smoke if you fed it DC rather than AC? Surely the VALUE of the voltage that might cause the smoke, if it is too high?

 

I suppose it depends on the design but I'd guess they typically have a bridge-rectifier at the power input in which case it should not make a lot of difference whether it's fed from AC or DC as long as the bridge-rectifier can handle the charging current on DC.

 

Excessive input voltage is a likely reason for a catastrophic failure. As David says an output nominally rated at 15 volts RMS AC under full load could easily output 21 volts RMS on no load, or even more depending on the quality of the transformer. But it's worse than that. At 21 volts RMS the peak voltage is almost 30 volts and unless the CDU has some circuitry to limit the voltage that's the voltage the capacitor(s) will charge to.

 

That's OK if they are 50 volt capacitors but it's definitely not OK if they are 25 volt capacitors.

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5 hours ago, kevinlms said:

Why would a CDU smoke if you fed it DC rather than AC? Surely the VALUE of the voltage that might cause the smoke, if it is too high?

 

My father remarked that his CDU was getting hot. That is a Gaugemaster CDU which I think he is feeding from the 16v AC output from a Gaugemaster controller, so it should not be overloaded.

Unfortunately his layout is in the loft & I had a broken leg last time I was there, so I was unable to troubleshoot it.

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I wrote  " I can't see the input causing an issue as long as it  is designed for AC input, if its for DC input then yes smoking is not unexpected. "

If its DC and fed ACit may not like it, like DC motors, Feed them 12 volts 1 amp AC and they smoke, I know, Been there done that.

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13 minutes ago, DavidCBroad said:

I wrote  " I can't see the input causing an issue as long as it  is designed for AC input, if its for DC input then yes smoking is not unexpected. "

If its DC and fed ACit may not like it, like DC motors, Feed them 12 volts 1 amp AC and they smoke, I know, Been there done that.

Never heard of a CDU intended to be fed from DC for throwing solenoid point motors.

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9 minutes ago, kevinlms said:

Never heard of a CDU intended to be fed from DC for throwing solenoid point motors.

Nor have I, not off the shelf ones, but there is no reason to use AC, the CDU has to rectify AC to DC to charge the capacitor so a DC one would have less components.   My own Capacitor assisted  solenoid systems are fed with DC.

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11 hours ago, DavidCBroad said:

so a DC one would have less components.

 

Not so many if it was designed to prevent buyers destroying it. A single diode could do that but a bridge would make it much more robust.

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On 16/10/2020 at 03:21, DavidCBroad said:

Nor have I, not off the shelf ones, but there is no reason to use AC, the CDU has to rectify AC to DC to charge the capacitor so a DC one would have less components.   My own Capacitor assisted  solenoid systems are fed with DC.

Should have guessed - one would have less components To save the cost of one of the cheapest electronic components around - a diode or bridge rectifier.

Still if you don't believe in resistors for LED's, I guess it figures.

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2 hours ago, kevinlms said:

Should have guessed - one would have less components To save the cost of one of the cheapest electronic components around - a diode or bridge rectifier.

Still if you don't believe in resistors for LED's, I guess it figures.

It's also about making things reliable and if it ain't fitted it can't fail.   The trouble is making the small CDUs reliable means most struggle to move 3 or more points at a time.  I need to shift 6 at once in the hidden sidings so I went with a big 24 volt (may be 28, I haven't seen it for years)  capacitor,  diode matrix and electric pencil and after we sorted out load balancing it just works, its well over 30 years old, same capacitor, same points, same diodes and almost all the same motors, none of which failed electrically, Its used twice weekly, not laid up for months.      Real 1970s technology  Like the Austin Allagro.

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2 hours ago, DavidCBroad said:

  Real 1970s technology  Like the Austin Allagro.

 

Ah, the car that the wheels used to fall off!!!

 

I learned to drive in my father's  Allegro :) It was the version with the normal, round, steering wheel.

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4 hours ago, DavidCBroad said:

It's also about making things reliable and if it ain't fitted it can't fail.   The trouble is making the small CDUs reliable means most struggle to move 3 or more points at a time.  I need to shift 6 at once in the hidden sidings so I went with a big 24 volt (may be 28, I haven't seen it for years)  capacitor,  diode matrix and electric pencil and after we sorted out load balancing it just works, its well over 30 years old, same capacitor, same points, same diodes and almost all the same motors, none of which failed electrically, Its used twice weekly, not laid up for months.      Real 1970s technology  Like the Austin Allagro.

You have to work at it to blow a diode on the input of a CDU.

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2 hours ago, kevinlms said:

You have to work at it to blow a diode on the input of a CDU.

 

Indeed, and you can expect a diode to work for 350 million hours before it conks-out.

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17 hours ago, AndyID said:

 

Indeed, and you can expect a diode to work for 350 million hours before it conks-out.

I guess I'll never know!

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5 hours ago, kevinlms said:

I guess I'll never know!

 

Of course you could have one go pop next week but it is fairly unlikely :)

 

(Not like a computer I had to maintain. Germanium transistors - every time it was switched on there was a very good chance it would blow another one.)

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  • 4 weeks later...

OK, think the new CDU may be faulty or simply not up to the job. Got a multimeter and checked everything and all seems OK. Replaced with a new Gaugemaster unit and all seems well. Having lots of fun now testing & sorting my pile of resistors!

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2 hours ago, Paul4256 said:

OK, think the new CDU may be faulty or simply not up to the job. Got a multimeter and checked everything and all seems OK. Replaced with a new Gaugemaster unit and all seems well. Having lots of fun now testing & sorting my pile of resistors!

 

I knew a guy who tested a bunch of fuses until they managed to stop him. :)

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