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Q&A section for Micah
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Common pitfalls during scrutineering
Testability of the board
Read through the test procedure
Do a mock scrutineering test
test points, harness, etc.
Overcurrent test, etc. Know the direction
Go through temperature thermistors to a setpoint - check charge and discharge value
Behaves in the latching - must be able to see it
If you back down - cannot re-enable!
Latched until driver manually clears the fault
Top shell at testing station
Maybe just have a visual indicator that you can wire it
MOV battery packs
Make sure you can actually connect to them
Thermistor that you can actually connect
Long harnesses, etc.
PSU has alligator jumpers and banana lead.
Come with DOCUMENTATION filled out
check scrutineering sheet
Testing current sensing
Verifying gain of A/D
Connectorize it!
Monitoring while away from shop
Make sure that none are under 2.5V
Might have grown some dendrites
Question 2: Custom BPS vs off the shelf
Initially 75% used off the shelf BPS
Now, most teams do custom now
Question 3: Counting cells
Our modules are pretty compact
Loose cells
Modules and packing weight
Shouldn’t be an issue for us. Just bring an extra module
Question 4: Cooling
Battery pack cooling - airflow impacted by many things
Baffling and redirecting air to hot areas
Environmental heat differences with air travelling through the pack
Irradiance from the ground/array can induce heating into the pack
Insulate environment away from the pack
10 cells per thermistor is a good ratio
Most problems come from not having a balanced module
Question 4: Long leads?
Can cause issues with radio gear or main motor 3-phase wires
Might want to look into interference with radio gear
Shielded cables
Twist everything
cut down cross sectional area for radio noise
Lead length for passive/active balancing
Per-module sub boards to do the measurements and communicate it back to a control board
Would probably not recommend wireless for teams that are not an expert in it
Devices close together will introduce issues
Connectivity - don’t disconnect certain cells in the series stack
Just look at the way Tesla does it - not a bunch of extra monitoring
Flow temperature differences in cooling system
Remove as much complexity / remove room for external signals to enter the system
Minimize exposed wire coming off
Testability on boards can become a weakness
Question 4: Balancing?
Generally spend the effort on a well-made pack
Active balancing - activate with a plug-in system to use available power to rebalance things
But better for overall efficiency
Getting all states of charge - would have to monitor very carefully across all SoC
Assumption - teams have not put many cycles into the pack
Ripple through series stacks can cause isolation failures
Building their own DC-DC converters is hard to get right. If you’re doing it for all your modules
Loading or test equipment for simulations most teams do not have
Frequency response of the control loop - keying up radio next to it causes shorts
EMF and other noise sources to impact it
Gates - stray radio signals can turn them on
caps, zeners, proper driving circuitry short
Or make DC-DC modular enough to add on to sub-boards
Metal boxes would be good
Integration and getting the integration right - once that’s done you can worry about designing your own stuff.
Only a few teams have made power point trackers successfully.
Removable or settable fuses. At least have the built-in protection.
Start going back over designs and work on the ones that are beneficial to spend. A lot of it is just iteration.
“I think you guys have your stuff together”