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Should I use AC or DC to power my CDU?

Although nowadays there are CDUs (Capacitor Discharge Units) designed for model railways that plug straight into the mains, it is still common practice for a lot of modellers to power them using the auxiliary ports on their controllers often leaving them with the dilemma of choosing between the DC and AC ports.
The instructions supplied with most CDUs are not shy in recommending that the devices should be used with an input from an AC auxiliary port and in some cases recommend a 24v input for best results, but the problem is that most of us have controllers with only 16v AC auxiliary ports and on some controllers only 12v DC, so are these controllers still adequate?
The job of a model railway specific CDU is to convert power received to DC and amplify it before storing it ready for use when required to operate point motors etc. From this perspective, there is a reasonable argument that more power is better because amplifying 24v is going to provide a lot more oomph than amplifying just 12, but at the end of the day how much power does a point motor actually need?

As it turns out (excuse the pun) not that much. Most CDUs will have an output of between 25v and 45v DC but will also proudly state that they can operate between three and six point-motors at the same time, and that's the important factor here. It's nice to have the power and ability to operate lots of points simultaneously, but, if you have no choice but to connect your CDU to a power supply of just 12v DC, then don't worry, you will just have to be mindful that multitasking may not be your CDUs forte but for switching turnouts one at a time, 12v through a CDU should be just fine.

Posted in: Power and control

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