Hi guys!
I am currently working in a project where by we want to replace a battery charging and gauging system with either the BQ27421 or the BQ27621. Later on we ordered the evaluation boards for both (BQ27621-G1 and BQ27421-G1A) including the EV2400. Also ordered a charger which is the BQ2432-EVM.
I have also installed BQStudios and it successfully detects the 621 default settings.
My setup is fairly simple. I have a battery that's rated at 3.7V 165mAh with a max discharge current of 155mA. My load is a 30ohm power resistor which in this case is connected to the output of the 2432EVM board. I have a ammeter connected from the battery to the charger just to measure the "current" in and out the battery and use that to compare with that shown on BQstudio.
Following the instructions on the "user's guide" here: SLUUAM6B. I have wired everything as shown on page 9. So my procedure is as follows so far:
- Connect the battery (about 70% is it's charge say approximately) to the EVM which in parallel is connected to the 2432 charger (which remains off for now) and then connect it to the 621's B+/- and thermistor at Bin. Then I connect that to EV2400 through the I2C port and run up BQstudio which automatically detects everything but the registers are preset. So I change some parameters on the Q&A tab on BQ Studio with the following:
Design Voltage = 3700mV
Nominal Capacity = 165mAh
Nominal Energy = 5700mWh
Taper Current = 150 0.1Hr Rate
Empty Voltage = 3200mV
Apologies for making this too lengthy so I'll go straight to the questions.
As I set the above (briefly letting the Data memory be read then going back to Q&A parameter and saving the above) it takes about a minute or so to see the change occur on the registers. This is when I power on the charger and notice an excessive current on the "Effective Current" which gradually but inaccurately decreases. After letting the charger run for about 15mins, I disconnect it and connect the load. This does the same thing and the current seems inaccurate comparing it to that being read from the ammeter.
This makes me question the state of charge parameter too as the effective power reading is off the charts too. Comparing this to 421 which I believe has a sense resistor thus giving a proper close to accurate current reading, it seems something isn't right.
Is there something I am doing wrong? I have tried manually writing the i2c commands given on the quickstarters guide but I'm not really sure if I have been doing it correctly (been sending the commands through Control() parameter on the register)
Apologies again for making this a lengthy post, I wanted you to know all the variables so as to diagnose the problem quicker.
Cheers