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Charger PCB for 18650 Batts

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daveyk:
Here is PCB that will charge one or two 18650 Batts in parallel:
https://www.amazon.com/gp/product/B07PKND8KG/ref=ppx_yo_dt_b_asin_title_o07_s01?ie=UTF8&psc=1

I can't find one that will charge two in series.

Between 3D printing the box and experimenting, I've attached a picture.

I may be okay as I have found boost boards that can take between 2-24volts in and put between 5-28volt out:  https://www.amazon.com/gp/product/B089Y7NDCR/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

My idea is a some some project boxes with their own regulator PCB (such as the one above), and then use this as power.   This solution is not ideal.  I was hoping for the ~8volts of two 18650 in series to then be regulated down or boosted up.  I just couldn't find a USB chargeable PCB to charge two of them in series.

Thoughts....

First project box is the PCB that draws the Tek Logo on a scope screen.  I bought that board off of EBAY from the Tek Museum.  With the 3D printer, I can print silly little weekend project boxes for such things.  Maybe I can make a larger project box that can hold the project and the batteries and be charged with USB.  This is just a start.

Phil_G:
Hi Dave, just be aware that 18650 only defines the cell dimensions, not chemistry and therefore doesnt define the charging voltage.
LiFePo4 cells are available in 18650 format (A123 etc) and these are 3.6v charge, Lithium Ion are also available in 18650 size and are 4.2v charge.  Some are 4.1v and less common HV's are 4.35v.   If you want to avoid fires you do need to check. The term "18650 charger" only makes sense if the chemistry is stated, or if the voltage is switchable or its auto detect.  I suspect these cheap boards are neither and the only chemistry I can see in the ad is 'lithium' which doesnt help!   Further, if charging in series its much preferred (and much safer) to balance charge so you will need an intermediate tap between the cells and the charger should support balance charging,  ie individual cell voltage sensing and appropriate current dumping.
Cheers   :)
Phil

ledtester:
Using isolated DC-DC converters you can charge up each cell with separate 1-cell charger boards (like the TP4056) as demonstrated here:

More Details on the Balanced 3S Lithium Cell Charger using the TP4056
https://youtu.be/cBM0aUGW87Q

But consider that the B0505 converters are limited to 1W (maybe 2W) so that will impact charge time.

I think I'd adopt the strategy found in power banks... put the cells in parallel and boost the voltage to level you need to run your application.

Edit: mention that the Dc-DC converters need to be isolated

daveyk:
That is my current idea, but finding a boost board that works with 3.6-4.1 volt input is difficult.  I have found these: https://www.amazon.com/gp/product/B089Y7NDCR/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I guess I will find out how well those work when I get them.

The design I am using now (two batteries in parallel) came from thingiverse.

daveyk:
I agree that lithium Ion batteries are scary.  I never leave ANY lithium batteries charge when I am not in my shop.   

I was doing test software development on an instrument I worked on for the company I used to work at.  I had been at it about 6 hours when it shut down.  I realized I had been running on batteries (a 12v (13.6v) pack made up of a whole bunch of 18650 Lithium Ion batteries with a controller PCB heat shrunk on the bottom of the pack).  Anyway, I plugged the charger in and continued working on my code.  Some time later, I smelled smoke.  The battery pack was on-fire.  I pulled the pack off the back pf the instrument and ran outside with it and slung it on my driveway and left it burn.  Without being sealed to the instrument, only the PCB heat shrunk to the battery pack burned.  We had customers with this same instrument and pack that had left them charging over night that did catch the batts on fire and the melted remains of the instrument were on the floor below the bench as it burned through the bench top to the floor (or that is how I heard it).  This and my fire led to a complete redesign of the battery charger.  If I wasn't there working on my program at the time, I could have lost my house.

Since then, I have never left ANY battery charge without me around other than the lead acid battery in my cars, which are not parked near the house.

Look at those battery powered scooters/hover boards that were burning houses down all over the country a few years back.  Lithium Ion is scary.

Hell, I don't even leave a coffee pot or toaster plugged in when not using them.  A brand new house, not far from here when down to the foundation from a BUNN coffee pot that somehow failed.   I saw Elon Musk in an interview a few weeks ago say that more house fires are caused my dryers and toasters than battery fire.  I do NOT believe that.

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