Gav, It is still a little unknown what the current draw would be exactly at this stage because I would want to confirm my figuring with actual measurements once the displays were made.
However, Using the smaller blue 7 seg LEDs in my prototype a 'worst case' situation with all segments illuminated results in a current of just under 300ma from the 5V rail. It is not practical to use the 180V for supply as it is too high a voltage to deal with and has very low current availability. So with a full set of five display assemblys, and assuming 7 display types you are looking at about 1.5 Amps draw........
Worst case actually applies in this case as all segments on all displays are illuminated during display test. This is why I have commented that there is no way the original 5 volt power supply could be expected to provide an extra 1.5 amps - I believe it is stuggling as it stands....
The add-on 5 volt supply I have made is very, very simple and inexpensive and can provide 5 volts regulated at up to 3 amps so there is a 100% overhead. It is also very easy to wire in as it connects directly across the 12 volt AC terminals of the power transformer.
I am designing the display boards so that a standard 2.1mm DC connector (the round type found on almost all modern electronics) daisy chains the 5V to all boards. The display boards would have two of these connectors on them and I can get leads made with moulded 2.1mm plugs on each end VERY cheaply (actually I already have these made for a Melbourne customer as part of a project I build for them) and the PCB mounting sockets are also cheap. This would make wiring the extra 5 volts dead easy - just plug in the leads and tidy the wiring into the existing loom.
No strain on the already taxed 5 volt supply and plenty of current available to support the new displays. The aftermarket boards currently sold are very good but make no allowance for the 5 volt supply. This is a big mistake IMO.
