Here’s a first setup and test on the bench. The 24v power supply is connected up using some (Fake) Wago connectors to the power plug which is fused at 3A for safety. The plug is powered from my “Smoke Stop” device which will protect from overloads. It’s not fool-proof but, even if the power supply was a hard short LIVE to EARTH or NEUTRAL the worse that should happen is two 40w lamps light up. The power would be limited to a maximum of 20-30W and any delicate electronics should “survive” for another fight.
Thankfully when this was connected up all I saw was a brief flash of the bulbs when the capacitors inside the power supply charged up. They dimmed down and all was well. The supply was set to deliver 24v exactly.
Connecting the bed.
I powered off and attached the bed. I’d previously measured it as a DC resistance of 6.2 Ohm. Once connected to the 24V I’d expect around 3.87A to flow giving a total bed power of around 92W.
Initial tests show a DC current of 4A and a voltage of 23.9v at the bed connections,giving a measured wattage of 95.6W.
AC current at when delivering this 95.6W to the bed was 0.757A giving an input power of 185W so not very efficient!
I left this connected for around 2 minutes and monitored the temperature of the bed, power supply and cables to ensure all was well.
The bed got warm as expected but I didn’t measure it. The power supply was cool to touch but had warmed a little. All of the cables were fine. The test cables were 6A rated to perfectly fine for the use but maybe a bit lower than I would put into production. The voltage dropped over them was under 0.1V so the heat loss was under 0.5W over the 80cm combined length.
Everything so far went well as there was no smoke or bang!
But that’s easy to say as it’s just a power supply and bed.
The power supply has an annoying whine when on or off load so I need to check that. If it’s switching coil whine I’ll drop some nail varnish into it. If it doesn’t settle down it will need replaced. Further investigation required.
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