Hey guys, working on a revision to an old project. I amongst many have been using a Nexus 7 tablet as an in dash car PC. I was formerly powering it from a 5V DC USB port to the charging port of the tablet. Unfortunately whether from just chronic wear and tear or a poorly performing DC-DC regulator (CarNetix P2140) the battery is not able to sustain its charge via USB charging and the tablet won't boot without it. So long story short I want to emulate the tablet's native battery pictured below. This seems like a similar problem to what was described here: https://www.electronicspoint.com/samsung-galaxy-nexus-s-run-without-battery-t250655.html
The battery is rated at 3.7V, 4325mAh, 16Wh. Now based on my limited experience I figured I could buy a buck DC drop down regulator and supply the motherboard 3.7V directly in place of the battery. So I bought a dead battery and a buck regulator (LM2596). I tore the battery apart and found what appears to be a charging circuit along with a temperature probe. I soldered my buck regulor tuned to 3.7V to the terminals where the lithium-ion pack was previously connected. I figured it would be best to leave the rest of the board as is just in case there were any authenticity checks I wasn't aware of. You can see my current setup on my makeshift testing bench in the attached pictures.
I've tested the voltage on the tablet side and it reads ~3.90V, relative to the ~3.6-3.8V of the stock battery. The problem is, when I plug it in and power up the tablet the Google screen posts for half a second and then it shuts off. I've verified and a stock battery is still working so it's not the tablet itself.
I'm wondering if anybody has any suggestions to my approach? I've been thinking about cutting the charging board out of the circuit and just wiring the buck regulator to the motherboard but I want to be sure this is the right move before making changes to the factory wiring.
For reference my testing power supply is rated at 18.75V to 4.6A. (It's a knock off macbook charger from another project)
EDIT: I should state that I've tried and I've been unable to find any meaningful documentation on the charging board or the battery as a whole other then where to buy it as a replacement.
The battery is rated at 3.7V, 4325mAh, 16Wh. Now based on my limited experience I figured I could buy a buck DC drop down regulator and supply the motherboard 3.7V directly in place of the battery. So I bought a dead battery and a buck regulator (LM2596). I tore the battery apart and found what appears to be a charging circuit along with a temperature probe. I soldered my buck regulor tuned to 3.7V to the terminals where the lithium-ion pack was previously connected. I figured it would be best to leave the rest of the board as is just in case there were any authenticity checks I wasn't aware of. You can see my current setup on my makeshift testing bench in the attached pictures.
I've tested the voltage on the tablet side and it reads ~3.90V, relative to the ~3.6-3.8V of the stock battery. The problem is, when I plug it in and power up the tablet the Google screen posts for half a second and then it shuts off. I've verified and a stock battery is still working so it's not the tablet itself.
I'm wondering if anybody has any suggestions to my approach? I've been thinking about cutting the charging board out of the circuit and just wiring the buck regulator to the motherboard but I want to be sure this is the right move before making changes to the factory wiring.
For reference my testing power supply is rated at 18.75V to 4.6A. (It's a knock off macbook charger from another project)
EDIT: I should state that I've tried and I've been unable to find any meaningful documentation on the charging board or the battery as a whole other then where to buy it as a replacement.
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