I'm using XY-SWJA buck-boost converter with modifiable constant current. Can't find a datasheet for that one, so I'm just posting a link to a store offer - LINK
I've set it to charge at 5.2v with 450mA, however all it manages to charge at is ~200mA.
Even if I increase the charge voltage to 6.5v, the current stays the same... The TP4056 is set by factory default to charge with 1A max current, so it shouldn't be an issue.
Can be the case... The offers for all LiPos on the store where I buy them say all can be charged with 0.5c. But the specs for all those aftermarket batteries are questionable at best, and outright lies at worst. I would have to test those batteries for actual capacity. I wouldn't be surprised if it turned out the battery has 400-500 mAh instead of 1Ah.
Will do that later and post results. In the meantime, I managed to find and plug in a 2250 mAh 18650 LiIon. It charged at 400 mA but no more than that, and that one is suppose to charge at 1c. Same problem - barely half of the declared charging current.
I think I see the DMM inline with the battery negative wire.
If so, then the shunt resistance and lead resistance of the DMM could be your problem.
The battery should be connected directly to the charging board. Avoiding thin wires and bad connections. Charging current should be measured on the supply/input side of the charging board.
The TP4056 is a linear charger, so input current should be the same as battery current.
It's not a problem to measure voltage at the battery terminals.
Leo..
What is the battery voltage at that current.
What is the current SOC (state of charge) of the battery.
An almost charged battery will slowly taper off to a trickle charge, before stopping at 4.2volt.
You can find the charging graph in the datasheet you posted.
Note that there might be only a relative short time that the battery can actually take 1Amp.
Leo..
The battery is almost 4.15v when connected to charging station, 3.65v when in open circuit.
I connected a 2250mAh LiIon battery and a measuring setup with according to your guidence, and now the current is basically whatever I set it. Can be way more than 1A, but TP can't handle more.
Your battery is marked 52 34 50 - but from screen measurement (using breadboard for scale), its dimensions look somewhat smaller than 52x34, are they correct? Also, is it 5.0 mm thick?
Those are 2 different LiPos. The one in the first pic is 1000mAh, the one with breadboards is 3500mAh. Both LiPos don't want to charge correctly and have a large voltage drop when disconnected from charging. I assume they have a huge resistance and are simply used up, since the LiIon seems to work just fine.
We are missing a critically important bit of information.
What provides the power TO that board? Its the bit you omit from your pictures far right here
I didn't run a particular test to check the power supply, but as written earlier, I was able to charge the green LiIon with 7V*900mA (including buck converter's efficiency). I believe it should be more than able to supply the same to a 3500mAh LiPo. Am I wrong?
Did you do that outside, with safety glasses on.
Over-voltage fast charging is sort-off ok for a flooded cell lead acid car battery, but I could be explosive for a LiPo. The whole idea of using a LiPo charger is to never expose the LiPo to >4.2volt.
I wouldn't trust that battery in my house anymore.
Leo..
