I'm charging my 3.7V 2750mAh Li-ion battery with a TP4056 charging module. It has 1 amps of max charging current but all I get is maximum 170mA. I tried decreasing the R3 resistance on the board, but that makes the current 15mA. Am I doing something wrong?

 

A circuit would help you and others help you resolve this issue, " I tried decreasing the R3 resistance on the board..." means nothing to anyone but you.
Have you looked at the datasheet and the PROG pin and its resistor?

 

A circuit would help you and others help you resolve this issue, " I tried decreasing the R3 resistance on the board..." means nothing to anyone but you.
Have you looked at the datasheet and the PROG pin and its resistor?

Sorry, I should have included it. I've attached the datasheet and a screenshot of the Rprog value table.

 

Well done! so where is R3?

 

Well done! so where is R3?

R3 is Rprog on the module PCB (sorry I forgot to mention that again)

 

OK, so according to the datasheet 1.2k should give you 1A charge current.
What was the original R3 value and what have you changed it to? I also presume the circuit/PCB is the same as the datasheet, or is it different?
Are you sure the battery is healthy and not charged? The datasheet also shows a 3-wire connection to the battery, have you just got a 2-wire connection? You could ground the TEMP pin to disable the temp sens as outlined in the datasheet however, I cannot advise you to do so if you are not familiar with chargers and the dangers of overcharging etc.

 

What's the state of the battery that you're attempting to charge? Is it totally dead / depleted (i.e., below 3V)?
Also, how long did you test the current while it was charging?

Note that the TP4056 has a "pre-charge" phase for batteries with voltages below 3V. During this phase, it charges between 100mA - 200mA for a while until the voltage rises to a higher value. Then it can safely charge at higher currents. Perhaps this is what you observed.