I have constructed my first pack, 4S8Pwith a basic 4S BMS,the $5 type from eBay - Model:HX-4S-F30A(couldn't post a link). The batteries are Li-Ion18650s. All the voltages are proper. ~16.4V on B+/B- as well as P+/P-. B1,B2 and B3 are ~4.17V.
I built the pack to replace a 12V SLA battery used in a golf trolley. In hindsight, I should have used Li-Fe 3.2V cells.
Accepting that my pack is out of spec with the intended load, I performed some tests with two different 12V loads. The first was with the golf trolley which has a 200W motor, an LCD display, a switch and a speed control. The cart worked "on the bench" just fine during a short few minute test. As you might expect, the motor spins faster if I turn up the potentiometer. As for the LCD and electronics (the cart has a USB port on it to charge a GPS), there must be a voltage regulator that drops the voltage to 5V. My research says such regulators are designed to accept input voltages well over 14V, so the output of my pack at ~16V doesn't pose a problem.
The second load I tested is where I encountered something that I need help with. I connected a 12V 400W DC to AC inverter and plugged a 75W light into the AC side of the inverter. My pack powered the inverter briefly for about 15 seconds then shut down. What I can't figure out is whether it was the inverter shutting down because of overvoltage or the BMS of the pack. After the shutdown, the voltage on P+/P- was <1V. Even after disconnecting the leads to the load the P+/P- voltage remained <1V. The only way I could reset the BMS was to connect it to the charger. Adding to the confusion, I just completed the same test again but the shutdown didn't happen. It's been running for over 5 minutes. The voltage on P+/P- while running declined from ~16V at start to ~15.5V around the 3 minute mark. If it was the inverter that shut down on overvoltage, how is it that the BMS is triggered into a state that partially shuts down the voltage to P+/P-?
Appreciate any guidance or insight.
I built the pack to replace a 12V SLA battery used in a golf trolley. In hindsight, I should have used Li-Fe 3.2V cells.
Accepting that my pack is out of spec with the intended load, I performed some tests with two different 12V loads. The first was with the golf trolley which has a 200W motor, an LCD display, a switch and a speed control. The cart worked "on the bench" just fine during a short few minute test. As you might expect, the motor spins faster if I turn up the potentiometer. As for the LCD and electronics (the cart has a USB port on it to charge a GPS), there must be a voltage regulator that drops the voltage to 5V. My research says such regulators are designed to accept input voltages well over 14V, so the output of my pack at ~16V doesn't pose a problem.
The second load I tested is where I encountered something that I need help with. I connected a 12V 400W DC to AC inverter and plugged a 75W light into the AC side of the inverter. My pack powered the inverter briefly for about 15 seconds then shut down. What I can't figure out is whether it was the inverter shutting down because of overvoltage or the BMS of the pack. After the shutdown, the voltage on P+/P- was <1V. Even after disconnecting the leads to the load the P+/P- voltage remained <1V. The only way I could reset the BMS was to connect it to the charger. Adding to the confusion, I just completed the same test again but the shutdown didn't happen. It's been running for over 5 minutes. The voltage on P+/P- while running declined from ~16V at start to ~15.5V around the 3 minute mark. If it was the inverter that shut down on overvoltage, how is it that the BMS is triggered into a state that partially shuts down the voltage to P+/P-?
Appreciate any guidance or insight.