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### The energy consumed by a raspberry card

Posted: **Fri Feb 14, 2020 7:55 pm**

by **Ghada HJ**

Hello,

I am doing an end-of-study internship and I have a question on how to know the energy consumed by a raspberry card or other cards and the sensors that go with it?

Thank you in advance for your feedback.

### Re: The energy consumed by a raspberry card

Posted: **Fri Feb 14, 2020 11:47 pm**

by **drgeoff**

Ghada HJ wrote: ↑Fri Feb 14, 2020 7:55 pm

Hello,

I am doing an end-of-study internship and I have a question on how to know the energy consumed by a raspberry card or other cards and the sensors that go with it?

Thank you in advance for your feedback.

You can know the energy consumed by a RPi by at least two methods:

1. Measure it.

2. Use a search engine to find the page at raspberrypi.org which lists that information for various RPi models.

### Re: The energy consumed by a raspberry card

Posted: **Sat Feb 15, 2020 12:04 am**

by **LTolledo**

drgeoff wrote:1. Measure it.

+1

its better to get it on your own

what ever results you get you cannot dispute. (unless you want to argue with yourself

)

### Re: The energy consumed by a raspberry card

Posted: **Sat Feb 15, 2020 11:37 pm**

by **boyoh**

First is to check the voltage and the current , then using Ohms Law to give you the Wattage.

You do the tests on / load and off/ load . For testing on load use a high wattage high specs

resistor . Make Shure the resistor you use will not take the current beyond the Pi full load

Then the rest is up to you. Use a good quality Meter

If you ever do tests using two identical PIs do not expect identical readings

this could be due to component tolerance.

Regards BoyOh

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 9:29 am**

by **drgeoff**

boyoh wrote: ↑Sat Feb 15, 2020 11:37 pm

First is to check the voltage and the current , then using Ohms Law to give you the Wattage.

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 11:13 am**

by **boyoh**

drgeoff wrote: ↑Sun Feb 16, 2020 9:29 am

boyoh wrote: ↑Sat Feb 15, 2020 11:37 pm

First is to check the voltage and the current , then using Ohms Law to give you the Wattage.

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 11:19 am**

by **GlowInTheDark**

Of course, without further clarification, we have no idea what OP is actually interested in.

My general first take on this is that we're talking about cost. I.e., how much does it cost me to run a Pi, say, 24/7 for a year. Obviously, this boils down to figuring out Kwh, then multiplying that by your local cost per Kwh.

Alternatively, they may be going at this from a global warming perspective: How much sea level rise am I causing by running a Pi, say, 24/7 for a year?

Other perspectives are, of course, also possible.

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 3:04 pm**

by **Heater**

I don't see any ambiguity in: "how to know the energy consumed by a raspberry card or other cards and the sensors that go with it?"

Except it would be better to ask about power (Watts) rather than energy (Joules) but never mind.

That brings us to measuring voltage and current, current sense resistors and Ohms Law!

I reckon I could get an accurate enough estimate of Pi power consumption with my 5 dollar multi-meter in five minutes.

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 3:10 pm**

by **Paeryn**

boyoh wrote: ↑Sun Feb 16, 2020 11:13 am

drgeoff wrote: ↑Sun Feb 16, 2020 9:29 am

boyoh wrote: ↑Sat Feb 15, 2020 11:37 pm

First is to check the voltage and the current , then using Ohms Law to give you the Wattage.

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

But as drgeoff said, Ohm's law has nothing to do with power. You said "first check the voltage and current,

**then** using Ohm's law to give wattage." If you know the voltage and the current then the power is simply

**P = VI**, you cannot apply Ohm's law to calculate power from voltage and current, all Ohm's law will tell you is the resistance. From the rest of your post it looks like you were suggesting using resistance and voltage to calcule current (where Ohm's law is relevant) but that isn't what you said at the start where you stated that you use Ohm's law to calculate power once you know voltage and current.

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 5:12 pm**

by **boyoh**

Paeryn wrote: ↑Sun Feb 16, 2020 3:10 pm

boyoh wrote: ↑Sun Feb 16, 2020 11:13 am

drgeoff wrote: ↑Sun Feb 16, 2020 9:29 am

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

But as drgeoff said, Ohm's law has nothing to do with power. You said "first check the voltage and current,

**then** using Ohm's law to give wattage." If you know the voltage and the current then the power is simply

**P = VI**, you cannot apply Ohm's law to calculate power from voltage and current, all Ohm's law will tell you is the resistance. From the rest of your post it looks like you were suggesting using resistance and voltage to calcule current (where Ohm's law is relevant) but that isn't what you said at the start where you stated that you use Ohm's law to calculate power once you know voltage and current.

From BoyOh

Then by using Ohm’s law and substituting for the values of V, I and R the formula for electrical power can be found as:

To find the Power (P)

[ P = V x I ] P (watts) = V (volts) x I (amps)

Also:

[ P = V2 ÷ R ] P (watts) = V2 (volts) ÷ R (Ω)

Also:

[ P = I2 x R ] P (watts) = I2 (amps) x R (Ω)

Again, the three quantities have been superimposed into a triangle this time called a Power Triangle with power at the top and current and voltage at the bottom. Again, this arrangement represents the actual position of each quantity within the Ohms law power formulas

### Re: The energy consumed by a raspberry card

Posted: **Sun Feb 16, 2020 5:37 pm**

by **davidcoton**

Sorry, Boyoh, but you are misremembering what is Ohm's Law and what is Watt's Law.

**Ohm's Law** concerns the relationship of voltage (V, in Volts), current (I, in Amps) and Resistance (R, in Ohms).

**V=IR**

**Watt's Law** concerns the relationship of power (P, in Watts), voltage (V, in Volts) and current (I, in Amps).

**P=VI**

You are right that we can derive secondary formulae to determine any one quantity from any other two. The written form you give is misleading because the "2" representing the square operator doesn't show as a superior (raised) character. They should look like this:

**P=V²/R**

P=I²R

Other notations are available, such as "*" for multiply and the one you used divide (I can find it in Unicode but not make it work here).

### Re: The energy consumed by a raspberry card

Posted: **Mon Feb 17, 2020 5:34 pm**

by **boyoh**

davidcoton wrote: ↑Sun Feb 16, 2020 5:37 pm

Sorry, Boyoh, but you are misremembering what is Ohm's Law and what is Watt's Law.

**Ohm's Law** concerns the relationship of voltage (V, in Volts), current (I, in Amps) and Resistance (R, in Ohms).

**V=IR**
**Watt's Law** concerns the relationship of power (P, in Watts), voltage (V, in Volts) and current (I, in Amps).

**P=VI**
You are right that we can derive secondary formulae to determine any one quantity from any other two. The written form you give is misleading because the "2" representing the square operator doesn't show as a superior (raised) character. They should look like this:

**P=V²/R**

P=I²R
Other notations are available, such as "*" for multiply and the one you used divide (I can find it in Unicode but not make it work here).

From BoyOh

Well you've all been giving me a battering, So I will I throw the towel in , So I will aft to watch my Ps & Qs sorry I mean

MY OHMS & Watts Regards BoyOh

### Re: The energy consumed by a raspberry card

Posted: **Mon Feb 17, 2020 8:40 pm**

by **boyoh**

Paeryn wrote: ↑Sun Feb 16, 2020 3:10 pm

boyoh wrote: ↑Sun Feb 16, 2020 11:13 am

drgeoff wrote: ↑Sun Feb 16, 2020 9:29 am

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

But as drgeoff said, Ohm's law has nothing to do with power. You said "first check the voltage and current,

**then** using Ohm's law to give wattage." If you know the voltage and the current then the power is simply

**P = VI**, you cannot apply Ohm's law to calculate power from voltage and current, all Ohm's law will tell you is the resistance. From the rest of your post it looks like you were suggesting using resistance and voltage to calcule current (where Ohm's law is relevant) but that isn't what you said at the start where you stated that you use Ohm's law to calculate power once you know voltage and current.

BoyOh

- THE-PIE-CHART-FOR-OHM’S-LAW[1].png (95.86 KiB) Viewed 426 times

### Re: The energy consumed by a raspberry card

Posted: **Mon Feb 17, 2020 11:00 pm**

by **boyoh**

boyoh wrote: ↑Mon Feb 17, 2020 8:40 pm

Paeryn wrote: ↑Sun Feb 16, 2020 3:10 pm

boyoh wrote: ↑Sun Feb 16, 2020 11:13 am

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

But as drgeoff said, Ohm's law has nothing to do with power. You said "first check the voltage and current,

**then** using Ohm's law to give wattage." If you know the voltage and the current then the power is simply

**P = VI**, you cannot apply Ohm's law to calculate power from voltage and current, all Ohm's law will tell you is the resistance. From the rest of your post it looks like you were suggesting using resistance and voltage to calcule current (where Ohm's law is relevant) but that isn't what you said at the start where you stated that you use Ohm's law to calculate power once you know voltage and current.

BoyOhTHE-PIE-CHART-FOR-OHM’S-LAW[1].png

Ohm’s law can be used to find volts, watts, amps, or ohms if any two values are known. This can be done using the Ohm’s law and power formulas above. The Ohm’s law wheel shows all of the formulas that can be used to find volts, watts, amps, or ohms.

### Re: The energy consumed by a raspberry card

Posted: **Mon Feb 17, 2020 11:29 pm**

by **Paeryn**

That's a combination of Ohm's law and Watt's law.

Ohm's law is specifically *the relationship between voltage, current and resistance*,

V = I × R

Watt's law is specifically *the relationship between power, current and voltage*,

P = I × V

Watt's law is actually a combination of Joule's law and Ohm's law (Watt was into steam not electricity, they just named it after him).

Joule's law is specifically *the relationship between power, current and resistance*, (it's actually "power of heat generated is proportional to the resistance times current squared" but the units are conveniently defined)

P = I² × R

So to say that Ohm's law can tell you power is technically incorrect, you need Watt's law to do that. These are (together with Kirchhoff's two laws) the four basic fundamentals. Just because Watt had nothing to do with his law doesn't mean that it should be attributed to Ohm.

### Re: The energy consumed by a raspberry card

Posted: **Mon Feb 17, 2020 11:46 pm**

by **davidcoton**

boyoh wrote: ↑Mon Feb 17, 2020 8:40 pm

BoyOhTHE-PIE-CHART-FOR-OHM’S-LAW[1].png

What Paeryn said.

Plus, that graphic appears to have two incorrect formulae -- the ones involving square roots.

Should be:

**P=√(PR)**

I=√(P/R)
At least I think so. It's late

### Re: The energy consumed by a raspberry card

Posted: **Tue Feb 18, 2020 12:28 pm**

by **boyoh**

Paeryn wrote: ↑Sun Feb 16, 2020 3:10 pm

boyoh wrote: ↑Sun Feb 16, 2020 11:13 am

drgeoff wrote: ↑Sun Feb 16, 2020 9:29 am

Ohm's Law concerns voltage, current and resistance. It is irrelevant if one has values for voltage and current and wishes to calculate power ("wattage").

from BoyOh

The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer

If you read the posters question you will see the Word ENERGY

Regards BoyOh

But as drgeoff said, Ohm's law has nothing to do with power. You said "first check the voltage and current,

**then** using Ohm's law to give wattage." If you know the voltage and the current then the power is simply

**P = VI**, you cannot apply Ohm's law to calculate power from voltage and current, all Ohm's law will tell you is the resistance. From the rest of your post it looks like you were suggesting using resistance and voltage to calcule current (where Ohm's law is relevant) but that isn't what you said at the start where you stated that you use Ohm's law to calculate power once you know voltage and current.

BoyOh

Ohm’s Law Pie Chart is a great tool to make quick electric calculations (see a picture). It includes twelve patterns which address any mode of famous electric law. Instead of searching for reference to one of these particular formulas somewhere else, here you cover all the calculation approaches to Ohm’s principal at this single easy-to-use chart. The chart is seeable and understandable. It is fun to use even for kids, and it’s tasty – remember, it’s a “pie”! ( OHM'S PRINCIPAL's )

### Re: The energy consumed by a raspberry card

Posted: **Tue Feb 18, 2020 12:37 pm**

by **drgeoff**

@Boyoh

When in a hole, stop digging.

Now you've shown that you don't know the difference between "principle" and "principal"

### Re: The energy consumed by a raspberry card

Posted: **Tue Feb 18, 2020 3:23 pm**

by **boyoh**

- ohms-law.gif (8.08 KiB) Viewed 306 times

davidcoton wrote: ↑Mon Feb 17, 2020 11:46 pm

boyoh wrote: ↑Mon Feb 17, 2020 8:40 pm

BoyOhTHE-PIE-CHART-FOR-OHM’S-LAW[1].png

What Paeryn said.

Plus, that graphic appears to have two incorrect formulae -- the ones involving square roots.

Should be:

**P=√(PR)**

I=√(P/R)
At least I think so. It's late

BoyOh You said the last chart was wrong, I hope this one is correct ,and as no Printers Error