EricSan
Active Member
- Joined
- Dec 28, 2023
- Messages
- 199
- Reaction score
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- Location
- Central PA
- Country
- United States
- Dash Cam
- Viofo 139A Pro 2-ch w/ DIY 276Wh LTO parking battery
Interesting thermal behavior, thanks for sharing your data! Cooler temps are always nicer when dealing with current handling! There seems to be a sweet spot in there in the context of current vs thermal rise (thermal efficiency vs your reported electrical efficiency). Dividing thermal rise by current flow, we get some interesting ratios from your test data (smaller numbers represent greater efficiency):
8A = 5.25 c/A
10A = 4.80 c/A
12A = 4.42 c/A
16A = 4.31 c/A
20A = 4.50 c/A
So, it looks like there is a sweet spot in terms of thermal rise/current somewhere between 12A and 18A. Using thermal paste to couple the back of the charger to the inside chassis wall will likely result in lower temps for the charger board as the heat is spread over a larger surface area. Thermal behavior at 8A to 10A (typical car charging rate?) seems like a nice improvement over the original, smaller charger board. Not really a surprise given the more robust construction of the newer charger, though.
In the context of my own LTO battery box, I was not a very good scientist: I made three different changes all at once, so I'm not sure which one of these changes is responsible for my lack of current backflow. Ooops....
Here are the changes I made:
1) Switched from utility outlet charging to direct from battery charging
2) Added a time delay relay so the LTO doesn't draw power until about 8s after starting the car
3) Added an anti-backflow diode between the charger board and the battery pack
With these three changes in place, I'm not seeing any current backflow, even with a fully charged parking battery at 16.0v. Since my anti-backflow diode was exhibiting extremely high temperatures (over 100c) while charging from my SMPS power supply, I tried an experiment: When I bypassed the diode with a wire jumper, there was still no current backflow. Looking at the BMS log file, the time-based "current limiter" did not activatie, either.
From the perspective that fewer parts is likely to result in better reliability over time, I'm thinking I'll just remove the anti-backflow diode and leave the rest alone. The disappointing part is that I'm not sure which change led to the elimination of the current backflow. It was one of the following: a) switching from the utility outlet to direct to battery charging, b) adding the time delay relay, or c) the combination of both.
Regardless, I now have two different cars where a 16v LTO parking battery is wired directly to the car battery through a time delay relay. Neither parking battery backflows current anymore.
8A = 5.25 c/A
10A = 4.80 c/A
12A = 4.42 c/A
16A = 4.31 c/A
20A = 4.50 c/A
So, it looks like there is a sweet spot in terms of thermal rise/current somewhere between 12A and 18A. Using thermal paste to couple the back of the charger to the inside chassis wall will likely result in lower temps for the charger board as the heat is spread over a larger surface area. Thermal behavior at 8A to 10A (typical car charging rate?) seems like a nice improvement over the original, smaller charger board. Not really a surprise given the more robust construction of the newer charger, though.
In the context of my own LTO battery box, I was not a very good scientist: I made three different changes all at once, so I'm not sure which one of these changes is responsible for my lack of current backflow. Ooops....
Here are the changes I made:
1) Switched from utility outlet charging to direct from battery charging
2) Added a time delay relay so the LTO doesn't draw power until about 8s after starting the car
3) Added an anti-backflow diode between the charger board and the battery pack
With these three changes in place, I'm not seeing any current backflow, even with a fully charged parking battery at 16.0v. Since my anti-backflow diode was exhibiting extremely high temperatures (over 100c) while charging from my SMPS power supply, I tried an experiment: When I bypassed the diode with a wire jumper, there was still no current backflow. Looking at the BMS log file, the time-based "current limiter" did not activatie, either.
From the perspective that fewer parts is likely to result in better reliability over time, I'm thinking I'll just remove the anti-backflow diode and leave the rest alone. The disappointing part is that I'm not sure which change led to the elimination of the current backflow. It was one of the following: a) switching from the utility outlet to direct to battery charging, b) adding the time delay relay, or c) the combination of both.
Regardless, I now have two different cars where a 16v LTO parking battery is wired directly to the car battery through a time delay relay. Neither parking battery backflows current anymore.
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