Just a quick skull-wrenched module-based pack of extra juice and converters
for recycling old notebook LiPo cells, mainly 18650s, I've bought some of those BYOB (bring your own batteries) banks from eBay. I also tried to research how one gets to know the internal resistance of a battery.
So If I understood correctly I'll get the internal resistance by measuring the battery voltage with and without a known load and use the following formula:
The batteries I'm using are sanyo ur18650F, typical Capacity is 2600mAh and charging current is 1.75A per cell. That's way more the powerbank is able to deliver, as it seems. Input is rated 1A. So what happens if it can't deliver more?
I was using some 1A charger boards and 500mA USB boost modules before, but with my buddies power bank I ran in some problems. First of all he has an iPhone. He plugged his brand new power bank in and nothing happened. So a bit of googling confirmed our suspicion that apple does something "weird" (meh, who would have known) or at least something of they're own when it comes to charging. Best place to start was this: https://learn.adafruit.com/minty-boost/icharging
So in addition to an LED mod I'll have to work out the resistor stuff. The power bank of my boss had a button that turned on the function for charging an iPhone. Maybe it is enough to shortly put 2V and 2.8V on the D+ and D- rails.
New charger board 0.49 EUR
TP4056 board with DW01 protection for LiPo cell (over and undercharge)
eBay search: (pcm, protection) (lipo, liion, li-ion, lithium) charger
New boost board 1.69 EUR
eBay search: 2A 5V USB boost
I'm currently building a second version for a friend with his old battery cells from another macbook. The cells are Sony Fukushima US604496 that are selling for 60USD on a site I found them (10 on ebay though). Holy Moly. 2500mAh per cell, and these are 2 of them joined together.
I also found 4 Coslight CA603696 LiPos with 2150mAh in an old Laptop battery pack.
Something to consider, especially for friends of apple stuff.
I've played around with the idea to create a little board with two cell chargers and two step down (3.3V and 5V) and a step up 12V circuits. For practice I've created this little LiPo charger board, that allows to be chained.
INFO: s stands for serial and p stands for parallel, might be obvious / might spare googling
I'm trying to find out what would make more sense. I have 4 cells of 2750mAh and I want to use a second cell to upgrade this device. So I have to decide - do I want more voltage or more capacity. I have this 2-6.8V input to 5V-20V output converter which is fixed to 12V (note to myself: I should check that) and could get some step-down regulators for 5V and 3.3V when I use the 2s1p configuration. OTOH, when I use the 1s2p configuration, I probably still can use the 12V booster, get more power and could use a buck booster for 5V. Not sure about the 3.3V vs. drop-out voltage of a 1117 though. I could add a direct out of the lipos, but it sounds a bit dangerous having them out in the open.
In case of charging: I'd use a lipo usb 1A charger per cell and a switch capable of switching the cells into charging mode vs. use mode. I might even switch between 1s2p and 2s1p, if it is plausible.https://learn.adafruit.com/multi-cell-lipo-charging/fast-multi-cell-charger
I designed an additional case for the banana plug connectors and chemically welded it with an acetone/abs solution to the case. When the 12V converter arrives, I will connect those plugs the following way: GREEN - LiPo Out, RED is 5V and yellow is 12V.
I may add a second cell to get even more power but want to safely load the cells so I want to have two LiPo chargers.
Thinking of adding 3.3V, 5V, 9V and 12V converters with lab bench ports. Would be cool.