Simultaneously charge and discharge Li-ion 18650 - Page 1
Forum section: electronics / beginners

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 07:47:35 am
content: Hi all,I have a digital radio, that (while it officially requires 4x1.5v cells) will operate from the 5v supply of a USB charger or a USB power bank. What I am aiming to do is to throw an 18650 or two into the space where the 4 ‘C’ cells are supposed to go, along with a charge controller of some sort (this is the crux of my question, but read on). However, I am really wanting to have the radio continuously plugged into a USB power source, which operates the radio AND keeps the battery topped up (or that the radio is constantly powered from the battery, and the external supply is just to charge the battery). In the event of the power supply failing due to external power supply issues, I want the 18650 to take over kind of seamlessly, so I don’t lose all my settings on the radio.I have previously toyed with the TP4056 charge controller, but I don’t think that is suitable in this application (or is it?)Can anyone suggest the appropriate module for both charge control AND USB 5v output at the same time - if such a thing exists?TIA Graham

author: iMo
author_rank: Super Contributor
timestamp: June 22, 2023, 08:03:54 am
content: 5V off the USB charger is not enough voltage to charge 2x 18650 in series (2x 4.2V = 8.4V topped).The option would be to use 1x 18650, charged via the 4056, and use a low EMI step-up converter to create those 6V for the radio..

author: radiolistener
author_rank: Super Contributor
timestamp: June 22, 2023, 08:04:37 am
content: Quote from: smithg27 on June 22, 2023, 07:47:35 amNote that if your charger has PWM it will produce a lot of RFI and yoir radio sensitivity will be dramatically affected.The same with charger cable, to USB. Since it will be connected to USB charger it has SMPS which produce a lot of RFI. The same if you're planning to charge it from PC or power bank they all produce a lot of RFI, which prevents your receiver to receive weak singals...For example, when I connect my phone to a power bank (ANKER) it produce a lot of RFI which prevents to listen FM radio (weak stations) even if I put the charger in another room 10-20 meters away...Regarding to the charge and use at the same time, you're needs to implement a switch between battery and charger for your device. This switch should trigger when there is voltage on device power connector, so it will disconnect your device from battery and connect it directly to the power supply and at the same time it will connect charger to the power supply.But this is very bad idea to use it for radio receiver due to RFI produced by SMPS/PWM at USB power supply and PWM in charger circuit...

author: tunk
author_rank: Super Contributor
timestamp: June 22, 2023, 09:54:53 am
content: You could try a web search with these keywords: ups module 5v

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 09:57:48 am
content: Thanks for the response, iMo, but perhaps I didn’t make myself clear enough… the radio can operate perfectly at just 5v, so can be adapted to be powered by an external USB power supply and/or power-bank, etc. THAT is what I’m trying to achieve… a means of powering the radio from an external USB power source, and adding a built in power-bank as a backup to the external USB power, but I want that power-bank to always be topped off to 100% as long as the external USB power is connected.No need for the step up to 6v, just basic 5v USB supply is sufficient.When I mentioned TWO 18650s, I meant in parallel - the TP4056 is capable of charging two cells in parallel (assuming certain pre-requisite conditions like the cells being balanced), though it will obviously take longer to get to 100%.

author: tunk
author_rank: Super Contributor
timestamp: June 22, 2023, 10:03:23 am
content: Also seem to remember that Andreas Spiess made a video,possibly this:https://youtu.be/-SJbdPvgQnE

author: iMo
author_rank: Super Contributor
timestamp: June 22, 2023, 10:08:15 am
content: Quote from: smithg27 on June 22, 2023, 09:57:48 amThen use the USB voltage wired to the radio's power, charge the battery pack via the 4056 from the same USB, and do wire the output of the 18650 battery pack via a schottky diode to the radio's power.

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 10:09:39 am
content: Thanks radiolistener. All this talk of interference is a bit of a concern, though, I didn’t experience any when I connected the radio to a USB supply to test the principle. Is the interference only on weak channels? If that’s so, then it’s not a major concern to me

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 10:14:17 am
content: Thanks tunk I’ll check that out.

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 10:20:01 am
content: Cheers iMo. I’ll have to look up how Schottky diodes workbut yes, I’m beginning to think that simply wiring the load and the TP4056 in parallel (with some sort of diode back feed protection, I guess), could be the answer…

author: Infraviolet
author_rank: Super Contributor
timestamp: June 22, 2023, 11:35:43 am
content: This sort of thing might be your answer:https://www.adafruit.com/product/1944or look at the schematics and design a modified version for tighter spaces and or multi-cell voltages or something like that.

author: smithg27
author_rank: Newbie
timestamp: June 22, 2023, 12:14:01 pm
content: Cheers Infraviolet - I’ll look that up too.

author: Peabody
author_rank: Super Contributor
timestamp: June 22, 2023, 01:37:24 pm
content: For 18650s in parallel, you can use a TP4056 charger module. It's a linear charger, so won't make much noise. But then you would need a boost converter to produce the 5V supply to the radio, and that might be noisy. Anyway, below is a circuit for that. The 5V input independently powers both the battery charging and the output, but if it disappears, the battery automatically takes over. It's called "load sharing" or "power path".

author: smithg27
author_rank: Newbie
timestamp: June 24, 2023, 10:39:24 pm
content: Thanks Peabody - this appears to capture the essence of what I am trying to achieve perfectly.

author: Peabody
author_rank: Super Contributor
timestamp: June 24, 2023, 10:51:13 pm
content: I'm not sure about this, but if you use two batteries in parallel, I think you would want to use the TP4056 which also includes the DW01 battery protection module, and then use unprotected batteries. You want both batteries to always have the same voltage.