Model Railway Forum

Hello All,

Is there a certain capacity for CDU's. Going on various sites there are numerous sizes but nothing in recommendations. I have a computer power unit rated up to 24v DC and 5amp. Using Dcc's AE point motors. I can't see me needing to switch any more than 3 points at a time probably just two as a rule.

Thanks in advance here.

Dirk

Hi,

CDUs are used only with Solenoid point motors, as their stored energy is released in one short but powerful pulse. This pulse is sufficient to operate several solinoids all at once and the more microfarad capacitance used the stronger the pulse becomes. So a CDU with say 2200uF could operate approx two solinoids easily and may operate three if the wiring is of sufficent size and the wire run is fairly short between CDU/Switch/Motor. Upgrade to 4700uF and you will store more energy and be able to operate more solinoids all at once and so on with incresing amounts of microfarads.
Its second enhancemet is that once its been discharged into solinoid coil(s) it cannot recharge if any operating switch is left in the On position. This also prevents coil burn out as only a very low current is allowed to flow via the discharged CDU typically just a few milliamps.

Without a CDU the above are no longer available and using a direct power supply will of course work, but it can cause coil burn out should any switch remain On for too long.

So you take the chance if using the power supply stated, which will work ok.

Punch output from a CDU is a factor of applied voltage squared, so the more voltage you have (within CDU spec) the better.

Thank you for the reply. The AE solenoids are coil type and recommended operating voltage
24-15v.

Dirk