0
\$\begingroup\$

I'm trying to understand the power consumption of an esp32 with BLE enabled and transmitting. Its datasheet provides the following table:

enter image description here

As you can see, it provides the power consumtions in mA. I don't understand this, shouldn't it be mAh?

EDIT

The new version of the datasheet (see https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf) uses dB instead, so the question is no longer valid.

\$\endgroup\$
9
  • 6
    \$\begingroup\$ Why do you think it should be mAh? \$\endgroup\$
    – Hearth
    Commented Sep 23, 2023 at 12:22
  • \$\begingroup\$ I have edited the post to ask for watts instead, as I believe mAh doesn't make sense either, as you say. \$\endgroup\$
    – user222967
    Commented Sep 23, 2023 at 12:30
  • 1
    \$\begingroup\$ Dan - Hi, Please note the site rule which requires that when a post includes content (e.g. text, image, photo etc.) copied or adapted from elsewhere, that content must be correctly referenced. As a minimum, for online material, the source webpage or PDF etc. should be linked (see that rule regarding references for books / articles etc.). Therefore please can you edit your question to include the original source PDF link for that image (and please include references in future). Thanks. \$\endgroup\$
    – SamGibson ♦
    Commented Sep 23, 2023 at 12:30
  • \$\begingroup\$ I have rolled back your edit. On this site, after an answer has been posted, you should not change a question in a way that undermines the answer given. \$\endgroup\$
    – Math Keeps Me Busy
    Commented Sep 23, 2023 at 12:33
  • 1
    \$\begingroup\$ @Dan - Hi, Thanks for adding the required link. However I don't understand what you mean when you say the new datasheet version "now expresses power consumptions for BLE in dB, so this post is no longer valid". Table 4-4 on page 47 of the current version looks to be exactly the same as the table 17 which you copied into the question (from an older datasheet version, I guess?). So the question seems to be just as valid now as before - it could just mention that the table in the question is (currently) now labeled 4-4 rather than 17. Yes? \$\endgroup\$
    – SamGibson ♦
    Commented Sep 23, 2023 at 12:45

1 Answer 1

Reset to default
4
\$\begingroup\$

mAh is not a unit of power, it is a unit of charge. It is an abbreviation for milli-amp-hours.

mA is also not a unit of power, but of current. It is an abbreviation for milli-amps.

mW is a unit of power, i.e. milliwatts.

If you have a device supplied by a fixed voltage, and know the current drawn by the device, you can calculate the power drawn by a device, using this formula

$$P = VI$$

where \$P\$ is the power, \$I\$ is the current, and \$V\$ is the voltage applied to the device.

That is the case for your ESP32 and the table in question. The table is based on the assumption that the ESP32 is powered by a 3.3V supply.

If you have a load with a fixed. a fixed resistance, then one can find the power (i.e. mW) from the current using the formula

$$P=I^2 R$$

This is not the case for your ESP32, but this formula is useful in many other cases.

\$\endgroup\$
3
  • \$\begingroup\$ But the table states "Power consumption specifications". Given that mA is not a unit of power, what does it mean in this table? \$\endgroup\$
    – user222967
    Commented Sep 23, 2023 at 12:26
  • \$\begingroup\$ A more useful formula to show in this specific question would be P=U*I since U is fixed and specified to 3.3V. \$\endgroup\$
    – Klas-Kenny
    Commented Sep 23, 2023 at 12:28
  • \$\begingroup\$ I have just seen the table states that such measurements were taken at 3.3V, so that would allow to calculate the watts. \$\endgroup\$
    – user222967
    Commented Sep 23, 2023 at 12:30