Charging and playing TPA3110 at the same time ?

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Hi oxl,

Just a brief comment ... Li-ion batteries in my experience do need balancing when connected in series. They may start out almost having the same voltage across the cells but over time the voltages drift and some of them may go into the high voltage region where the cells are worn faster than the other cells. This will diminish life span and likely increase internal resistances.

Also, if you want to float charge them (constant voltage always on) another DIYA member some time ago suggested using 4.05 VDC per cell ... However, I recently read somewhere (probably batteryuniversity.com) that quality Li-ion cells are less prone to over-voltage damage than lower quality cells. I personally would guess that Panasonic, Sanyo, Samsung, Sony and the likes would be quality cells. I personally float charge my cells at 4.08 volts but very precisely keep them at this voltage using a TL431 circuitry placed across each cell. A TL431 datasheet may show a suitable circuitry - otherwise be welcome to send me a PM.

If the current draw on the cells generally is not that high they will not get more than just luke warm when charging. If you try to download a datasheet for one of the cells you consider using you will see that the inner resistance of the cell typically is somewhere between 10 mohms and ~100 mohms. You can calculate the power dissipation into the batteries from P=R*I squared - where I is the average current you use to charge the battery. Considering that you will use a 2*15w amplifier I reckon it would be fine to just use regular heat shrink tube.

As I float charge my batteries (charger always on) I don't yet use a low battery voltage monitor circuit.

I personally solder the cells together using just a short piece of solid copper wire (e.g. 1mm) between the poles. I set my soldering iron to 450 degr. C and do the soldering as fast as possible which in most cases means less than 5 - 7 seconds heating. Before soldering I gently abrade the surfaces to be soldered with a fine grain sandpaper. Otherwise the solder may not adhere well on the pole surfaces of the battery.

Hope this may help.

Good luck with your endeavor :)

Jesper
 
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A P.S.: If the amplifier you are considering using can operate at 13.3 - 13.8 VDC I personally would use a sealed lead acid battery instead. Much simpler to make the charger (LM317T with current limiting & sufficient heatsinking - see datasheet) and these batteries are also quite rugged. Something like this:

https://www.dba.dk/robotplaeneklipper-cadero/id-1040056281/

with the LM317T set to 13.6 VDC and e.g. 1A current limiting.

Cheers,

Jesper
 
for automatic switching you need load sharing as per prev post of links i did. other wise your charging while using batt, not ideal. or you manual switch or you use a barrel plug socket with a built in switch so when power for charger is connected it disconnects batt from amp and powers amp from external power supply, that you just plugged in. i guess you should expect a pop during plug in or something using that solution.

or use sure/wondom ready made board (see prev links). however there seams to be no boost converter so sures ready made batt + amp combination can’t do full power of amp IC/chip. but the batt + bms + charger unit i linked to looks like it would do what you want? you can charge/power it using a solar panel as it has a built in mttp charger, so just directly connect "12v" (18v) solar panel.
 
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The protection boards do not implement the proper charging profile for lithium batteries; their purpose is to protect from over-charging, over-discharging, and keep the cells balanced. There's a vast choice of cheap things for charging 1S lithium batteries, but all I've found for 3S are a couple of modules based on SY6912 or MAX745 chips.
I got one of those SY6912 charger boards, and jumpered it to charge a 3S4P 18650 pack; it did get painfully hot (using a 15V input), so I removed two of the R050 SMD shunt resistors. And then one day I plugged it into the pack and smoke came out of the SY6912 chip. So, although standby/parasitic current drain from the pack is very low, maybe it would be better to connect to the battery through a rectifier (ideal or Schottky); that would mean the battery wouldn't get charged to 100%, but could extend battery life.
I'd already ordered a second board (before the first burnt); the new one has two R025 shunt resistors (original board had four R050 resistors), and a "3R3" inductor instead of 4.7 uH.
The only other board I've found for 3S packs uses a MAX745 (can do 1 to 4S), but costs about $10 US each; I'll order one, hoping it's more robust than the SY6912.
 
In the past I salvaged some Li-Ion-18650-cells from notebook packs that did not charge anymore. There I found some cells measuring 3.3V, others with 2.9V. Obviously undervoltage protection had disconnected the cells from their terminals. So I charged all cells in a 4-slot charger with 4 separate charging channels - and guess what? The capacity of all cells was still in the ballpark of 2000mAh. And btw, these packs contained charge balancing circuitry. So my best bet is: Forget about charge-balancing but use single cell charging to get the most ouf of your batteries.
 
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