Replacing USB alimentation with batteries

Hi all,

As a homebrewer, I use some devices (iSpindel) to monitor fermentation parameters.
I also have small wifi relays, DIY made by someone else, which transmit measurements to my brewing software, and also display the latest ones.

These relays work very well but have a small drawback: they must be permanently supplied with 5V by a micro usb port.
They are devices that really consume very little and one solution is to use power banks to make them autonomous, however this is not very handy.

I would like to shunt the usb socket to insert two batteries (like 18650), the usb socket would then just be used to recharge them.
I'll also need a small switch to turn the device on/off.
Finally, a small charging indicator to know when the device needs to be recharged would be awesome.

Being very handy, the realization of this project does not scare me, including for the realization of the new boxes (there is not enough space in the current ones). However, I have very little knowledge of electronics, both in theory and hardware.

If some here could advise me on the components to buy and help me develop the assembly diagram I would be very grateful.
I post below various photos to illustrate my project. The red & black wire connects usb to the device.

Thanks in advance

Why not just buy a cheap 18650 UPS module, like this one:


Seems exactly what you're looking for.

Nigel Goodwin said:

Why not just buy a cheap 18650 UPS module, like this one:

5V 2*18650 Lithium Battery Charging UPS Uninterrupted Protection Integrated Board Boost Module With Battery Holder

Only US$4.99, buy best 5V 2*18650 Lithium Battery Charging UPS Uninterrupted Protection Integrated Board Boost Module With Battery Holder sale online store at wholesale price.

uk.banggood.com

Seems exactly what you're looking for.

Click to expand...

Wow, awesome.
Thanks so much, this seems indeed to be what I need.

So, if I understand well, this device includes a switch connector (7) and a charging indicator.
I'd also like to include a power indicator, do you think this one would work for me (the 2S version I guess) ?

bgaze said:

Wow, awesome.
Thanks so much, this seems indeed to be what I need.

Click to expand...

I bought three, for no particular reason

bgaze said:

So, if I understand well, this device includes a switch connector (7) and a charging indicator.
I'd also like to include a power indicator, do you think this one would work for me (the 2S version I guess) ?

Click to expand...

1S version, the batteries are simply in parallel - it should be fine.

I soldered a nice little slide switch across the switch connector - it has three connections, and lines up perfectly.

Awesome, thank you !

I was looking for a rocker switch but I didn't found a tiny one, so maybe I'll take this model :

bgaze said:

Awesome, thank you !

I was looking for a rocker switch but I didn't found a tiny one, so maybe I'll take this model :

Wendao DS-211 125V 2A 10mm Self Locking NO Switch Push Button Round 10pcs

Only US$8.99, buy best Wendao DS-211 125V 2A 10mm Self Locking NO Switch Push Button Round 10pcs. Used widely for circuits control in electromagnetic starter, contactor, and other electric circuits. sale online store at wholesale price.

uk.banggood.com

Click to expand...

They are nice switches, because they only require a round hole drilling I've got a number of those in stock.

I too spent a long time looking for small rocker switches, and ordered a load of the smallest I could find, but they weren't as small as I needed - annoyingly one of my Chinese component tester kits has a perfectly sized rocker switch, but I can't find them anywhere.

I found some on french amazon, 13x8 mm is small enoush for me

But you're right, just drilling a hole is cool

bgaze said:

I found some on french amazon, 13x8 mm is small enoush for me

https://www.amazon.fr/gp/product/B07DWBWS85/ref=ewc_pr_img_3?smid=A25GI8AK4G3KQ2&psc=1

But you're right, just drilling a hole is cool

Click to expand...

I'll have a look on Monday at work, see what size I've got - I suspect it's probably the same?.

Ok ;-)
I'm looking for batteries, do you think these will be ok with the charger ?

Look at laptop batteries from ebay, amazon, or some supplier that has some kind of warranty (so you know they won't knowingly sell bad stuff).

eg. You can get a battery that contains four or six decent quality cells for around £15 or less. They are generally easy to split open and the cells have link strips you can cut, or tags, making soldering easier and less likely to damage the cells.

eg.
Four 2.2AH cells for £13.99:

Six 2.2AH cells for £12.99 !

Also, most cheap cells claiming to be over 2.2AH have fake markings - I've never found one yet with genuine high capacity. Unless they are original Samsung etc., they are usually scams.

This is an example pack using cells from an old laptop battery; it's using series cells so has a battery monitoring and balance PCB attached.
You only need parallel so no balancing - but it should have some form of battery monitor / protection system to protect against over-charge or over-discharge, as that can be very bad - either burst or wrecked cells.

The original cell interconnecting strips are cut near the centre then the ends folded back to keep them inside the cell end area.

The grid clips for making up blocks of cells are available on ebay, such as these:

I use Samsung 2.6AH, but we order them from a specialist UK battery supplier in hundreds.

Generally, don't get too carried away believing specs, but as long as the price is low enough (and it works) then you're getting the correct spec battery for the price you pay, just not what it's labelled.

I did buy some higher rated 18650's from China, and they are slightly higher power - but they are also slightly larger physically, and won't fit in the space of a normal 18650

rjenkinsgb said:

You can get a battery that contains four or six decent quality cells for around £15 or less

Click to expand...

Awesome ! Thanks for the tips man