18650 Battery 5V Boost board. - Page 1
Forum section: electronics / beginners

author: ct1305
author_rank: Newbie
timestamp: August 21, 2022, 08:13:21 am
content: Hey guys,New to this forum along with electronics so go easy on me!I have purchased some 2 x 18650 5v battery boards to use in a small project, which has an average current draw around 50-75mA.The boards themselves state they have a minimum output 30mA current draw, and have two different modes via a slide switch.- Normal Mode: Auto sensing, anything below 30mA the board will switch off- Hold Mode: Board will stay on indefinitelyNow the issue begins with the board unable to stay on if it is switched to HOLD mode. I can see on the board this simply adds a 62ohm resistor to ground on the 5v output to stay above its required minimum output, but this does nothing. The board needs about 90-100mA to stay on. This obviously works with my project if I switch the resistor to ground and connect said project, however throwing away battery life seems silly. The manufacturer says the board is "faulty" however the other 3 boards also have the same issue.In the interest of learning more about electronics I would like to do some digging as to why, I have attached pictures of the 18650 board along with the PDF manual for the battery/output chip. Would anyone mind educating me on what part of the circuit is responsible for measuring the output current, and what defines the "minimum" output current required?Apologies if this is in the wrong area etc.ThanksChris

author: sleemanj
author_rank: Super Contributor
timestamp: August 21, 2022, 10:51:05 am
content: Measured internally to the IC, defined by the IC's characteristics, it is imprecise. Find a min load that works. I quick look at the datasheet I couldn't see another way to force it always on, but the translation isn't great, see the electronic ciggie example they provide that might be an on-while-pushed situation that might work.

author: ct1305
author_rank: Newbie
timestamp: August 21, 2022, 11:10:23 am
content: Thanks for the reply Sleemanj!Bugger, well if that's how it is then so be it, the example they give for "Key 2" boost button is just the momentary push button (on/off switch) that comes on the board. Push once to turn on, hold for 2.5 seconds to turn off. Interestingly if I keep pressing the switch over and over it will stay on, like I am resetting some timer. I will just tweak the "Hold Switch" resistor on the board to draw slightly less current to maximise the battery. Appreciate the help

author: Peabody
author_rank: Super Contributor
timestamp: August 21, 2022, 02:39:44 pm
content: This is typical behavior for a "powerbank" IC. Generally they are not appropriate for anything but charging batteries. In addition to low-current shutdown, they usually will not transition from external USB power to battery power without shutting down completely for a second or so, so they are not usable as a UPS. And most do not allow powering the project while charging the battery.However, the datasheet has two relevant values on page 7. One is the "Light load current shutdown threshold", which has min/typ/max values of 20/50/100 mA. The other is the "Light load detection period", which shows 5/10/20 seconds. So you do not have to sink excess current all the time. If you search for powerbank auto-off, you should find a variety of circuits that periodically sink extra current, but only for a few milliseconds. But if your project includes a microcontroller, you could just include code to do that, and add a transistor and resistor connected to a GPIO pin.The better solution for the future might be the single-cell version of this device - unless they've changed that circuit to auto-off too. It's called the "18650 battery shield V3". My copies have no auto-off, and will switch between USB and battery seamlessly. But they are a few years old. I'll attach pics of what they look like. Note however that they also make two-cell (V8) and four-cell (V9) versions which as far as I know are not ruined by auto-off, but they do not switch seamlessly. and I believe they also do not allow powering your project while charging, which the V3 will do.https://www.banggood.com/Geekcreit-ESP32-ESP32S-18650-Battery-Charge-Shield-V3-Micro-USB-Type-A-USB-0_5A-Test-Charging-Protection-Board-p-1265088.htmlThe V3 works well, but has some limitations you might need to deal with:

author: ct1305
author_rank: Newbie
timestamp: August 21, 2022, 11:10:30 pm
content: Great info Peabody! I will have a look at the single 18650 V3 boards in the future. However for the ones I have already have the use of the microcontroller pulsing an output to a transistor with a 100+mA load seems like a fantastic option, would there be any negatives to this? What sort of lifespan can be expected from the transistor switching constantly?ThanksChrisQuote from: Peabody on August 21, 2022, 02:39:44 pm

author: Peabody
author_rank: Super Contributor
timestamp: August 22, 2022, 04:10:16 am
content: The primary negative is that you still have to waste current, and battery life, just to keep the powerbank turned on. But the transistor won't be on all the time. It will only turn on every 20 seconds or so, and then only for a fraction of a second. So it probably won't even get warm. You'll have to experiment to determine the longest interval that still works, the minimum duration that works, and the minimum current that works.