Following this up, I've been doing some investigations with my Electron to see what the current drawn is with various expansions connected (and not connected) and two different external PSUs.
First is with the Acorn PSU @ 21.3VAC:
Next I tried a laptop PSU @ 19.3VDC from RetroClinic:
The Plus 1 is a RetroHardware one and has an ABR and ElkSD Plus 1 connected. The Plus 2 is also a RetroHardware remake and has an ElkEconet (without a cable connected) and a JustRAM cartridge; I've also added and removed a Pi Zero 2W + Plus 2 adapter.
The power on the +5V connection to the motherboard I'm measuring with a multimeter. The wall power I'm using one of those plug-in home power monitors on the mains socket: I don't know how accurate it is (at least, it only goes to one decimal place, but it does read consistently) and it's obviously measuring the power supplied to the external PSU, rather than the power coming out of it and going into the Electron, so the efficiency of the external PSU, as well as the internal one, will be included in the total efficiency.
This is mostly consistent with your figures but doesn't give the sharp drop off in efficiency, when going over 1.5A on the +5V line. Is this just variation in the internal PSU, or am I measuring something wrongly?
As an aside no current appears to be flowing through the -5V line into the Electron motherboard (although it is measuring -5V) - scanning the circuit diagram, I can only see this fed to the cassette circuit, so is that going to be quiet, unless the cassette interface is used?
First is with the Acorn PSU @ 21.3VAC:
Code:
Config A @ +5V W @ +5W W @ wall Efficiency--------------------- ------- ------- -------- ----------Electron 0.665 3.325 6.4 52.0%Plus 1 0.910 4.550 8.4 54.2%Plus 2 1.274 6.370 11.9 53.5%Plus 2 w/ Pi 1.391 6.955 13.1 53.1%Plus 2 w/ Pi + Plus 1 1.614 8.070 15.7 51.4%Code:
Config A @ +5V W @ +5W W @ wall Efficiency--------------------- ------- ------- -------- ----------Electron 0.665 3.325 6.4 52.0%Plus 1 0.911 4.555 8.5 53.6%Plus 2 1.272 6.360 11.7 54.4%Plus 2 w/ Pi 1.386 6.930 12.7 54.6%Plus 2 w/ Pi + Plus 1 1.621 8.105 15.0 54.0%The power on the +5V connection to the motherboard I'm measuring with a multimeter. The wall power I'm using one of those plug-in home power monitors on the mains socket: I don't know how accurate it is (at least, it only goes to one decimal place, but it does read consistently) and it's obviously measuring the power supplied to the external PSU, rather than the power coming out of it and going into the Electron, so the efficiency of the external PSU, as well as the internal one, will be included in the total efficiency.
This is mostly consistent with your figures but doesn't give the sharp drop off in efficiency, when going over 1.5A on the +5V line. Is this just variation in the internal PSU, or am I measuring something wrongly?
As an aside no current appears to be flowing through the -5V line into the Electron motherboard (although it is measuring -5V) - scanning the circuit diagram, I can only see this fed to the cassette circuit, so is that going to be quiet, unless the cassette interface is used?
Statistics: Posted by Mince — Thu Jul 24, 2025 9:36 am