Extra Low Voltage devices

Transparent · 2022-06-12T17:07:00Z

Extra Low Voltage (ELV) refers to electricity supplies of 50v and below. These are usually DC, but need not be so. Why Extra Low Voltage?... because the regional electricity Distribution Network Operators already use the term Low Voltage to refer to 240v (single-phase) and 440v (3-phase) which feeds our homes. Over on the topic Anyone want to share costs on batteries, we've been discussing the merits of those batteries being grid-tied or off-grid. In the course of those discussions I have dropped in a number of diagrams similar to this: In this topic we are concerning ourselves with the bottom-right of that graphic. These are devices in the home which can be run directly from the battery rather than via the 240v AC output of the off-grid inverter. Why should we want to do that? A householder is permitted to run their own cables and sockets for ELV. Employing a qualified electrician is not mandatory. Devices powered directly from the battery will remain live in the event of a power-cut It is more efficient to connect devices this way Each time we pass the stored electricity through a conversion unit to change its voltage/frequency, we lose some of the energy in the process. It makes little sense to take the 48v DC from a Storage Battery, pass it through the Inverter to create 240v AC, and then use a 'transformer plug' to connect a landline phone at 12v DC.

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Topic starter 19/06/2022 6:20 pm

Posted by: @derek-m

Having looked at the specification for several DC to DC Converters, they would appear to have efficiencies within the 80% to 90% range

Well the ones I have here are certainly more efficient than that!

The monitor in front of me is running on 19v which has been supplied from a DC-DC Converter with 54v input.

If it were only 80% efficient then it would be emitting 11.4w as heat. But there isn't enough temperature rise on the aluminium case for me to measure it as being any different from ambient.

I'd need to insert an ammeter into the circuit to get an actual figure. But everything is hard-wired, so that'll have to wait for another day.

Perhaps the 80-90% figure you're reading is when the DC-DC Converter is being used at its full current rating. It's rare that I'd run a Converter above 80% of the specified max current.

Save energy... recycle electrons!

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