Steve McMullen / batteries, electrical inspector, on-road inspector

If you organize a 1-on-1 with this person, then fill in the timeslot and your name in the table below.

Question 1: What are your thoughts on E-Fuses (e.g. BTS7080-1EPA or TPS1H160-Q1) vs traditional fuses for circuit protection on the LV side?

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• low voltage systems - they are great because they can be cheaper

• efuses right for the mains because they are high speed

• efuses are more predictable in general

• zonka/other relays similar → most durable high voltage relays

• Relay contacts fuse

Question 2: What are features that you would like to see in future BPS/BMS implementations?

• Battery should have no sources or sinks
  Power BPS from the Auxiliary

• should always be able to tell when the BPS has tripped remotely

• prefer that even AFEs and LTC6812 are not powered by main

  • if its powered off of main and is in UV → then it will continue to drain and cause a latent failure

• Plan remote charge of the

• Under voltage increase probability of latent failure

Under voltage cells

• precipitate out lithium for the anode and serves as a pathway for dendrites to form

• really bad under voltage will make this worse

• Latent failures will happen

• Consider changing LV voltage cutoff and HV cutoff for the

  • Impedance on the

• Impedance measured for the cells follows discharge/charge curve critical slope (the difference in impedance of each cell affects this significantly)

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Question 3: What are some ways that you have seem to decrease electrical system cost while maintain easy repairs (e.g. not just putting everything on one PCB)?

Question 4: Safe ways to store batteries - discord post follow-up

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• if no losses on the pack, then there should be no failures during storage

• bad cells will degrade the pack

• other usual measures for storing batteries

Question 5: What backup planning strategies (as it refers to components and alternates) have you seen most successful when going to comp?

• Testing and backup assemblies

• Common unit - change on the fly

• Lots of backups

• maybe sponsor reflow ovens → lots of reflow ovens being recycled

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Question 6: What tool investments for manufacturing are worthwhile to have at a higher (and inevitably more expensive) quality? Ex. We have realized investing into brand-name crimping tools has significantly increased our quality of crimp and uph.

• adequate resolution is needed

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Question 7: Do you have any strategies/suggestions for PCB manufacturing without access to a work bay?

• Just outsource it, see if companies will sponsor - part-assembling at JLCPCB

Other:

• theoretically 16% outliers on either side of the normal distribution for cells for testing (normal distribution characteristics)

• have to check the cells within 6 months to make sure none of the outliers are deficient

• put the outliers in a separate isolated container

• Some people will just get rid of reflow ovens - keep track of industry

• Dan was a battery guy at Missouri

  • Won with lead acid batteries in the age of NiMH and NiCd

• Push for 1000 miles of testing!!!

• GM EV1

  • Steve designed the motor and gear train and battery

  • All cars were destroyed - protect liability

• Michigan has both Ford and GM as sponsorships

  • Sponsor with the engineers

• ‘Tesla can’t get along without active balancing or sorting'

• Getting air through the cells

  • Airstream such that the cross secitonal area grows as it travels along

  • Distributed airflow via perfboard (distribution method)

  • Maintain flow in the battery pack

  • You know the heat in the cells - that will dictate the amount of air through the cells.

  • How much heat can you get into the air?

• Conical washers - make sure to use them

  • Not enough length of bolt to cause stretch in the bolt

  • Busbar heats up and cools down - relaxes the pressure over time

• Post-assembly thermal test on the connection methods

  • IR camera, etc.

  • Steve is a bit worried about the stainless for the material flow

• Need to have SoC (voltage) for each of the supplemental

• can have self powered sensor if it is not driving the car in any way

  • Don’t want 40 sensors and no supplemental

  • WSC does not allow any supplementals

• Teams that have tried to modify Tritiums have caused Tritium problems…

  • Western Michigan has used Tritiums for quite some time

• Lengths can be pretty estimated for wiring diagram because small changes can happen on the fly

  • maybe have an extra foot of wire

  • label wire on either ends of the interconnects

• Abrasion failures - suspension-caused

  • motor sense leads

  • Power leads

  • Pigtails and such to the array - pulling contact sense off the arrays

  • ALWAYS RESTRAIN WIRES - EVERY PIECE

    • Holds up in weather and heat

    • addition to wiring diagram

Feb 25

Question 1: What are the areas of innovation in battery technology?

• Energy capacity is going up

• Anyone that does balancing is wasting energy …?

  • Weaker cell limits the pack

Question 2: How do people enter this field

• industry is going leaps and bounds

• ???

Question 3: What kind of skills needed to be better with battery technology?

• Have to understand characterization of batteries

  • So a bunch of chemical knowledge of cells and their energy capacity and how that affects electricity

• BatteryUniversity - website for learning stuff about batteries

  • compendium for battery knowledge

Question 4: In your experience doing inspections, common problems seen with solar cars?

• Checks regulations to use

• Teams usually forget:

  • Power labels on switch and driver compartment

  • Labels on emergency switch

• More extreme problems:

  • Teams don’t have an isolated car

  • Dynamic braking