Kadee uncouplers and 3amp power supply?

[Highlandman]

I am going to be using Kadee electromagnetic uncouplers on my Salcombe Harbour layout, Kadee state that a suitable power source should be 16-18v DC 3amp. Now here's the problem. I can find plenty of 16-18v AC power supplies and I know I can use a bridge rectifier to convert the current to DC, but what about the ampage. Most plug in units are a lot less than 3 amps and some I have seen are 4 amps or more.

 

How will this effect me? I presume I should not go for less than 2-3 amps as the power the uncouplers draw might damage the power supply or the uncouplers might not work correctly. But can i use say a 4amp unit so there is some energy in reserve or will this damage the uncouplers.

 

If anyone can help by throwing some light onto this for me i would be most greatfull. A custom built 16v DC power supply will cost me about £50. If i can by a simple plug in unit for £20 - £30 it would be a lot easier.

 

All the best

 

Andy

[Brian]

Hi

How about a Laptop PSU? 18.5 volts dc at 3.5 Amps or more depending on type. The extra 0.5volts wont do any harm plus these are normally fully regulated PSUs so you get the voltage on the label, extremely little over or under volts regardless of load!

Often new on ebay for around £6.50 up. Note, some need the mains lead too!

ebay 18.5 volt PSUs

 

Extra current available is not a problem, the uncoupler (Or whatever is connected to the PSU) will only draw its required/rated current, so any spare within the PSU remains there unused. B)

[jamie92208]

You can always get a transformer like Gaugemaster sell and put that through a bridge rectifier they can kick out up to 3 amps at what is nominally 12vDC but is normally 16-17v. I think they call their the T9 but any transformer from soemwhere like Maplins or RS that has 16V AC 3A output will do together with a rectifier of at least 50VA capacity. As mentioned above use a higher rated item suc h as a 100VA rectifier if you can.

 

Jamie

[Glorious NSE]

Just reading the instructions on my one and it says 16v DC or 18v AC if that helps?

[Gordon H]

I presume I should not go for less than 2-3 amps as the power the uncouplers draw might damage the power supply or the uncouplers might not work correctly.

Correct. The power supply won't like it, and the uncoupler performance is likely to be diminished.

 

But can i use say a 4amp unit so there is some energy in reserve or will this damage the uncouplers.

Consider it this way... Every day you use '13A' rated mains sockets, but rarely does the thing you plug in actally draw this much current. In other words, having the capacity to provide a particular current doesn't automatically mean it will always be doing so.

Your uncoupler magnet will only draw as much current as its internal resistance will allow for the applied voltage.

I would suggest using a supply unit capable of providing about twice the expected current, so that it is only being stressed to half capacity or so. In this case a 5A supply would be appropriate, not quite twice the rating, but more than sufficient - and readily available as standard off-the-shelf units.

[Pete the Elaner]

Consider it this way... Every day you use '13A' rated mains sockets, but rarely does the thing you plug in actally draw this much current. In other words, having the capacity to provide a particular current doesn't

 

Good example. Illustrates the principle perfectly.

[Highlandman]

Thanks everyone for the input, it was all very informative. I have come to the conclusion that I can use a DCC 5amp power supply but will have to use a bridge rectifier to convert the output to DC.

 

One further question, every pack of uncouplers comes with a bridge rectifier included but am I right in thinking I only need to put one rectifier in the circuit after the power supply to operate all the uncouplers with a DC current?

[Gordon H]

One further question, every pack of uncouplers comes with a bridge rectifier included but am I right in thinking I only need to put one rectifier in the circuit after the power supply to operate all the uncouplers with a DC current?

So long as you only operate one of them at a time, yes.

[CUTLER2579]

Gordon H, on 07 September 2010 - 23:50 , said:

 

Consider it this way... Every day you use '13A' rated mains sockets, but rarely does the thing you plug in actally draw this much current. In other words, having the capacity to provide a particular current doesn't

 

Good example. Illustrates the principle perfectly.

 

That was exactly my thoughts when I read it,then thought about this reply only to then read yours. Brilliant example for a Non Technical person to understand.

Regards.