Electron Ultra Power Supply
I am re-visiting the new Power Supply Unit as the supply I built for the latest Ultra gets extremely hot. My first thought was that by adding the second processor to the main PCB it has tipped the DC/DC converter over the edge of its power dissipation limit without an additional heatsink. I engineered a large piece of aluminium to act as a heatsink and that seems to regulate the heat very well.
I looked at the specification of the DC/DC converter and it claims the converter is capable of running without a heatsink up to 35W. I measured the power consumption of the PCB at 5V. It draws 1.8A which works out about 9 Watts, well within the dissipation specification.
Measuring the power through the DC/DC converter and it works out to 14W. This seems quite inefficient for this converter.
Before I build another unit I thought I'd update the PSU PCB to include smoothing capacitors on the out of both the plus & minus five volts and to include mounting holes for a heatsink. I want to make the heatsink a lot smaller to keep it within the footprint of the PSU circuit board.
Something else I'm experimenting with is just using a 5V 3A plug top power supply through the same PSU PCB.
With this setup there is a small amount of interference on the mode 0 & 3 screens so this idea is now abandoned.
With the new PSU PCB assembled I tried it out first without heatsink then if I need to I'll add a heatsink. I set it up on the bench and fitted it with a load to draw 2.4A (a good bit over the 1.8A that is required), it got hot.. so I fitted a smaller heatsink than before and that seems to regulate the heat dissipation.
This DC/DC converter has good voltage regulation with only a 30mV drop from no load to 2.4A load but it is quite inefficient with a lot of heat dissipation.
With that in mind I thought I'd try another DC/DC converter.
I set this one up as before with a load of 2.4A at 5V and the heat generated is about 30% less but the voltage regulation is worse at 100mV drop between no and 2.4A load. I fitted a small heatsink and ajusted the off load output voltage to 5.05V so under load it would settle at 4.95V.
Trying both PSU's in the Electron the original (blue) DC/DC converter heats up the top of the case, not too hot but noticably. The other DC/DC converter (red) runs much cooler and has little effect on heating the case so I'll elect to use this one in future.
The Electron Ultra is getting close to the original power block capacity (19VAC 14W) so I looked out an old Maplin Transformer 12VAC 3A (36VA) to use and to give me some comfort when using addition cartridges such a the Slogger Pegasus 400 with a Gotek drive or the sound card - both these can add 100-200mA load.
I was at an ABUG scotland meeting recently where I took two Electron Ultra's, one had the red DC/DC converter powered from the original power block and the other had the blue DC/DC converter powered from the Maplin block and both performed well having been switched on for over seven hours.
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