JohnJayMack
New Member
- Joined
- Dec 22, 2020
- Messages
- 25
My next post goes into the final building phase. During my testing, I was able to get a pretty steady 111 amps for about 1 hour. The limit on the current draw was due to my inverter and load and not the battery. During the test, I was looking for any signs of conductor/connection heating.
High current is one component of I^2 * R heating. Any loose connection, high resistance pathway, or other construction issue will show up as a hot spot. Inside the battery, I found no hot spots. The only elevated temperature that I found was in the 8 awg wires. I used 3 wires in both positive and negative circuits. The wires felt barely warmer than ambient. I could not find any warm spot in the interior cell connections. Outside of the battery, I used 8 awg wires for my connections not because they were correctly sized, but because that is what I had. All of those wires got very hot to the touch.
The limiting device in my test appears to be the inverter. Initially, the heater that I had plugged into the inverter started on HIGH. The current draw went to somewhere around 160 amps. Both the inverter and the BMS safety circuits were in overload conditions. I was trying to get the load down before the protection circuits operated and I did not spend time documenting the high current excursion.
As I think about the test, I think that the inverter began to complain due to lower input voltage. I think that the voltage at the inverter was well below the output voltage at the battery due to voltage drops in my undersized connection wires. When I do my next test, I will measure voltages at several points.
Each cell is rated for both a 1C and a 3C continuous discharge rate. The 1C rate is 6 amps. Since the continuous draw during my test was approximately 88% of 1C, each cell would have been contributing approximately 5.28 amps. I believe that all cells in each section were contributing because the cell imbalance readings stayed very small. If a cell were not working, the other cells could easily makeup the current but the fewer cells working would cause a greater imbalance in the inter-section voltages.
Hope this helps. I will cover again when I post my next couple of sections.
Jay
High current is one component of I^2 * R heating. Any loose connection, high resistance pathway, or other construction issue will show up as a hot spot. Inside the battery, I found no hot spots. The only elevated temperature that I found was in the 8 awg wires. I used 3 wires in both positive and negative circuits. The wires felt barely warmer than ambient. I could not find any warm spot in the interior cell connections. Outside of the battery, I used 8 awg wires for my connections not because they were correctly sized, but because that is what I had. All of those wires got very hot to the touch.
The limiting device in my test appears to be the inverter. Initially, the heater that I had plugged into the inverter started on HIGH. The current draw went to somewhere around 160 amps. Both the inverter and the BMS safety circuits were in overload conditions. I was trying to get the load down before the protection circuits operated and I did not spend time documenting the high current excursion.
As I think about the test, I think that the inverter began to complain due to lower input voltage. I think that the voltage at the inverter was well below the output voltage at the battery due to voltage drops in my undersized connection wires. When I do my next test, I will measure voltages at several points.
Each cell is rated for both a 1C and a 3C continuous discharge rate. The 1C rate is 6 amps. Since the continuous draw during my test was approximately 88% of 1C, each cell would have been contributing approximately 5.28 amps. I believe that all cells in each section were contributing because the cell imbalance readings stayed very small. If a cell were not working, the other cells could easily makeup the current but the fewer cells working would cause a greater imbalance in the inter-section voltages.
Hope this helps. I will cover again when I post my next couple of sections.
Jay