Power ESP32 with batteries - Voltage Converter - Page 1
Forum section: electronics / projects

author: Nikos A.
author_rank: Regular Contributor
timestamp: October 21, 2019, 09:20:44 am
content: Hi everyone, I'm designing a project where I intend to power an ESP32 with 18650 batteries ( two batteries in parallel). This is the datasheethttps://cdn.shopify.com/s/files/1/0674/3651/files/lg-hg2-spec-sheet.pdfFrom the datasheet, I can see that the batterie if fully charged at 4.2V and the cut off voltage is 2.5V. I need 3.3V for the ESP32. Firstly, I was considering an LDO because of low quiescent current and dropout voltage. This looks fine to mehttps://eu.mouser.com/datasheet/2/268/MCP1700-Low-Quiescent-Current-LDO-20001826E-737536.pdfFor 3.3V out the input voltage according to the datasheet should be VIN >= (VOUT + 3.0%) + VDROPOUT which is around (3.3V +3%)+ 110mV = 3.5VThe 110mv dropout is at 150mA load (FIGURE 2-12 of the datasheet).My problem is 3.5V is quite high, and I would like to drain the battery at least 2.8 - 3V. But for such low voltage the output voltage of LDO is going to be under 3V and the ESP32 is going to malfunctionNext, I considered a buck/boost converter like this one below, but the quiescent current is much higher.https://www.pololu.com/product/2122/specsDo you have any suggestions?

author: Peabody
author_rank: Super Contributor
timestamp: October 21, 2019, 02:34:39 pm
content: Based on my memory of the discharge curve for an 18650, at 3.5V the battery is about 80% discharged, and voltage drops rapidly after that. It's possible the buck/boost converter would give you a shorter battery life than an LDO. I think that's particularly likely if your ESP32 spends any significant time sleeping (switching regulators are typically less efficient than LDOs at very low currents).But you may find that you need an LDO that will provide more current than the MCP1700. Nominally, 250ma should be plenty, but wifi devices can generate large current spikes when they transmit, and more headroom in the LDO helps deal with those. Also, there's a Youtube video by Andreas Spiess on powering the ESP8266, and he ends up recommending a large (1000µF) electrolytic cap on the 3.3V line to prevent voltage drops caused by the spikes.Hopefully those with lots of experience with the ESP32 can give you some good advice on this.

author: Kasper
author_rank: Frequent Contributor
timestamp: October 21, 2019, 04:07:27 pm
content: LDOs generally have lower quiescent current than switchers but you might find a buck that has better quiesc than the buck/boosts.If you can find a buck with low quiesc and low drop out then youre set. Else maybe a buck with low quiesc and put the batteries in series.Or have a button or other MCU switch power to the ESP and its regulator.

author: jbb
author_rank: Super Contributor
timestamp: October 21, 2019, 07:55:33 pm
content: As Peabody said, the LiIon will be mostly empty by the time you get below 3.5V. I wouldn't recommend drawing them down to 2.5V.I thoroughly recommend a buck converter with low quiescent current. You'll need to hunt through some data sheets. It's a common feature nowadays, but you have to be careful because many data sheets show off the quiescent currentwhen the buck is disabled.However,the cells have some resistance. If you apply heavy (Amps) current loads, the cell terminal voltages will dip. What other loads will you have on the battery?I looked at the ESP32 data sheet. It says the ESP32 works over a range of 2.3 - 3.6V (absolute maximum) and uses LDO regulators inside. If the other parts in your circuit allow, you could drive it with a 2.5V or 2.7V buck regulator and should get the same performance. This will save (3.3-2.7)/(3.3) = approx. 18% battery power (more or less, depends on buck regulator efficiency curves).

author: mariush
author_rank: Super Contributor
timestamp: October 21, 2019, 09:41:35 pm
content: Just use a switching regulator. For examplediodes-incorporated/AP65111https://www.digikey.com/product-detail/en/diodes-incorporated/AP65111AWU-7/AP65111AWU-7DICT-ND/7652826Datasheet:https://www.diodes.com/assets/Datasheets/AP65111A.pdfSee example circuit in datasheet, very easy to reproduce.diodes-incorporated/PAM2305https://www.digikey.com/product-detail/en/diodes-incorporated/PAM2305AABADJ/PAM2305AABADJDICT-ND/4505341datasheet:https://www.diodes.com/assets/Datasheets/PAM2305.pdfon-semiconductor/NCP1521https://www.digikey.com/product-detail/en/on-semiconductor/NCP1521BSNT1G/NCP1521BSNT1GOSCT-ND/1560581datasheet:https://www.onsemi.com/pub/Collateral/NCP1521B-D.PDFIf ESP32 works at 3.0v, I'd set the output voltage of the regulator to that... when the battery is at 3v, it's already pretty much depleted so it doesn't matter if input is too low.With LDO you'd waste a lot of energy, ex 3.6v in , 3.0v out ... ~83% ... the regulators above can be >95% efficient.

author: OwO
author_rank: Super Contributor
timestamp: October 22, 2019, 09:51:43 am
content: Use a buck converter if the esp32 will wake up more than 5 times per day, as that is when the active power draw averaged becomes comparable to the quiescent current of these SOT26 buck converters (assuming 5 seconds per wakeup and 300mA current draw). Also look carefully at the efficiency vs load current graphs in the datasheet. Choose something that has good efficiency at all points between 20mA and 500mA, as that's the region you will likely be operating in. I would probably use something like LC3406 or JW5211.

author: mikerj
author_rank: Super Contributor
timestamp: October 22, 2019, 10:20:42 am
content: Quote from: mariush on October 21, 2019, 09:41:35 pm4.5v minimum input voltage, doesn't seem to meet the OP's application.

author: mariush
author_rank: Super Contributor
timestamp: October 22, 2019, 11:21:50 am
content: Quote from: mikerj on October 22, 2019, 10:20:42 amOops ... missed that one.No matter, the other suggestions would work. PAM2305 works with 2.5v+, NCP1521 works with 2.7v+Good chips, easy to build a step-down converter with them

author: sorin
author_rank: Frequent Contributor
timestamp: October 22, 2019, 12:53:30 pm
content: 5 BUCK REGULATORS WITH LOW IQhttps://www.electronics-lab.com/5-buck-regulators-low-iq/

author: mariush
author_rank: Super Contributor
timestamp: October 22, 2019, 04:08:38 pm
content: Yeah, they have lower quiescent current but they're also 5-10x times more expensive in low volume and tougher to solder.exPAM2305 40uA , sot-23-5, $0.39 at 100BD70522GUL-E2 0.2-1uA , bga , $1.61 at 100You could get a higher capacity battery or just add a 3v coin cell and disable regulator when sleeping

author: Nikos A.
author_rank: Regular Contributor
timestamp: October 22, 2019, 08:25:47 pm
content: Thank you for your answers!!!First of all I have one question,Quote from: jbb on October 21, 2019, 07:55:33 pmAs Peabody mentioned and looking some datasheets I found the terms "active" and shutdown". What is the difference? Under what conditions the converter is getting shut down?I believe that I should proceed with a LDO. I measured the board with WiFi enabled and all the sensors connected and the max current consumption was 150mA. I will provide the necessary capacitance for the spikes that may occur during the WiFi connection. Furthermore, I will proceed with the Firebeetle board of DFrobot as I was able to measure 6uA under sleeping mode.https://wiki.dfrobot.com/FireBeetle_ESP32_IOT_Microcontroller(V3.0)__Supports_Wi-Fi_&_Bluetooth__SKU__DFR0478#target_2Moreover, you are right about the battery capacity at 3.5V. I will use 3100mAh 18650 battery and according to the website below most of them have been 80% discharged at 3.5V.https://lygte-info.dk/info/BatteryChargePercent%20UK.html

author: jbb
author_rank: Super Contributor
timestamp: October 22, 2019, 08:50:19 pm
content: If the regulator is for main power, it’s on all the time.Beware the marketers who try to sell based on the disabled quiescent current