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Four-wire Noctua PC fans are used for battery cooling. Details of PWM and tachometer operation can be found in Noctua’s whitepaper Noctua_PWM_specifications_white_paper.pdf.
Change Log
Revision 2
High voltage interlock loop?
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Carrier should provide isolated power to the AFEs, ideally at a voltage already equal to one of the required rails to minimize external components. 5V is much easier to provide than 51V, and can be done with something like this J0505N-1WR3.
This is to satisfy regulations section 8.6.A.4 requiring that no loads be connected to the main pack before the primary fuse and relays. Currently the AFEs are being powered off the voltage taps from the main pack. While we have done this in the past and have not been called out for it, we wish to avoid complications at scrutineering.
Given that there are 4 outputs, we can probably get rid of the iso 3V3 regulator that is currently for the current sense interface too and drop down the 5 to 3v3 for that with an LDO or buck
Should add voltage monitoring for the aux battery
Passive protection for the aux battery is required to be in the battery enclosure as per regs section 8.4. This is a dumb rule but the fix is low effort so we will make the change.
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Replace inrush current limiting (ICL) circuit with the one on UV cutoff.
Simpler, cheaper
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Reduce number of fans?
Add pullup for MISO on LTC6820
Pin is open drain
Change 12V input fuse to same value as aux input
Fan startup current exceeds 1A, which blows the 0.5A fuse
Connect fan PWM to an FT pin
The PWM pin is pulled up to 5V by the fan, and non FT pins are only tolerant up to 4V. FT pins can be found in the pin definitions section of the datasheet, make sure it has a timer attached to it as well.