Question regarding minimum power required?

[MrAdamH]

Hi there. I'm not sure if this is the right section of the forum to ask, but I'll try my luck

I'm working on a DIY project for measuring power consumption from my electricity meter using a serial connection interface on the meter.
I'd really like to power a Raspberry Pi Zero W or similar directly from the meter, so I don't have to pull wires from somewhere else.

There is a power output (VCC-pin) inside the electricity meter, but it is below the usual 5V required by a Raspberry Pi, and I am wondering whether the voltage and amp is enough to be converted to something a Raspberry Pi W Zero could run off of?



Hope you can help a beginner out.

Thanks

[davidcoton]

No, that will not power a Pi0. The voltage may be ok if you are not using USB or HDMI, but the current capacity is inadequate.

[MrAdamH]

No, that will not power a Pi0. The voltage may be ok if you are not using USB or HDMI, but the current capacity is inadequate.

That's too bad - but thank you for the honest answer!

[boyoh]

Leave the meter connection alone, That is for
Power board use, Use a non intrusive connection
A C/T current transformer clamp on the meter
Cable to a converter transmitter is what you
Want Search the web for one.
Leave mains power alone, Unless you know
What you are doing.
Regards Boyoh
Retired Electrical / Electronics Technician

[MrAdamH]

Leave the meter connection alone, That is for
Power board use, Use a non intrusive connection
A C/T current transformer clamp on the meter
Cable to a converter transmitter is what you
Want Search the web for one.
Leave mains power alone, Unless you know
What you are doing.
Regards Boyoh
Retired Electrical / Electronics Technician

It is pretty non-intrusive, as you can buy commercial power meter modules (they are very expensive though) that use the same connection.
As you can see in the image below, it's a power/data port used specifically for external access.

[davidcoton]

I will add that Boyoh is right. If it is the supplier's meter, you should not make any connection to it (unless you get written permission)
Also, you need to be familiar with the relevant regulations (In the UK, BS7671 IET Wiring Regulations, 18th Edition) for the quality of your wiring, even if you are not directly connecting to the mains. You can measure consumption with a clip-on current transformer and an A2D add-on for the Pi, just assume the nominal voltage to avoid mains connections.

[MrAdamH]

I will add that Boyoh is right. If it is the supplier's meter, you should not make any connection to it (unless you get written permission)
Also, you need to be familiar with the relevant regulations (In the UK, BS7671 IET Wiring Regulations, 18th Edition) for the quality of your wiring, even if you are not directly connecting to the mains. You can measure consumption with a clip-on current transformer and an A2D add-on for the Pi, just assume the nominal voltage to avoid mains connections.

I've been in contact with my supply company, who has been giving me updates on DLMS/COSEM support for measuring electricity usage.
They sent me and other interested people all this documentation, so they are well aware that people try to communicate with the meter themself.

Right now I have a Raspberry Pi mounted above, but it requires external power which doesn't really have much wife approval factor.



I don't see the problem in using an official external interface to power a small board?
You can already buy something like this that uses the interface:
https://www.elmodul.dk/smart-me-kamstrup-modul

[davidcoton]

Regs and accepted practice vary from place to place. UK rules are quite restrictive. Sounds like your supplier is more enlightened or less risk-averse.

[MrAdamH]

Regs and accepted practice vary from place to place. UK rules are quite restrictive. Sounds like your supplier is more enlightened or less risk-averse.

Must be.

I may be looking at something like a Wemos D1 Mini and see whether it can run off of the small amount of amps coming from the meter.

[boyoh]

Can i recommend a course in basic electronics?
And understanding Ohms Law, Then you will
Understand circuit current requirements
The RaspberryPi is not plug & Play.

Regards BoyOh

[neilgl]

My D1 mini reading temperatures and sending to pi via mqtt seems to be running at 40mA (5V USB PSU)

[MrAdamH]

Can i recommend a course in basic electronics?
And understanding Ohms Law, Then you will
Understand circuit current requirements
The RaspberryPi is not plug & Play.

Regards BoyOh

I did have electronics in high school, so I know the basics, but it's been a while (some of it has disappeared from memory).
As far as I remember from high school, it is possible to convert between voltages/amps, but with gains/losses in one or the other.

[B.Goode]

As far as I remember from high school, it is possible to convert between voltages/amps, but with gains/losses in one or the other.

I think you are mis-remembering...

Volts (potential difference) and amps (current) are different attributes of the behaviour of an electrical circuit. You can't meaningfully convert between them.

[MrAdamH]

As far as I remember from high school, it is possible to convert between voltages/amps, but with gains/losses in one or the other.

I think you are mis-remembering...

Volts (potential difference) and amps (current) are different attributes of the behaviour of an electrical circuit. You can't meaningfully convert between them.

I didn't mean convert between them, but convert a source with A volt / B amp, to another voltage, which would then affect the amps of course.

[davidcoton]

... convert a source with A volt / B amp, to another voltage, which would then affect the amps of course.

Yes the current (amps) through a wire multiplied by its potential relative to a common ground (volts) gives the power (watts), which is a constant (allowing for losses as heat, etc). So if you convert a 5V supply to 3V3, and draw 1A6 from the lower voltage, that is 5W28, so the current from the 5V supply will be a little over 1A (in practice, more, because of losses in conversion).

[MrAdamH]

... convert a source with A volt / B amp, to another voltage, which would then affect the amps of course.

Yes the current (amps) through a wire multiplied by its potential relative to a common ground (volts) gives the power (watts), which is a constant (allowing for losses as heat, etc). So if you convert a 5V supply to 3V3, and draw 1A6 from the lower voltage, that is 5W28, so the current from the 5V supply will be a little over 1A (in practice, more, because of losses in conversion).

Thanks for the explanation, I think I know where my mind had the wrong idea now

[boyoh]

Point to remember is

The strength of a current (amps) is directly proportional to a pressure ( volts) between two points.

But is inversely proportional to its Resistance (ohms )

Regards BoyOh