backchannel: automating disconnect of a DC-DC charger
first thoughts
from a post on reddit
i went to a 20amp which was fine when the van was idling, but blew as soon as I started driving
Spitballing here, but this might suggest the alternator is unable to spare the 20A+ while idling. The reasoning:
- battery is still in Bulk and wants full 20A charging
- vehicle idling - alternator is unable to comfortably meet demand from the DC-DC, fuse is not in danger (althought the alt may be)
- vehicle driving - alternator RPM increases so it can meet high current demand
- fuse pops
I would consider adding in a disabling/derating switch for times you get caught idling (like long red lights or a traffic jam).
second thoughts - automating the above
After ensuring wiring & fusing are correct per the manual I would use a multimeter to measure voltage at the DC-DC charger’s input terminals:
- while idling and charger disabled
- while idling and charger enabled <- if lower, the alt is overloaded
- with engine revved to ~2000rpm and charger running - if stable with charger on/off, the alt can handle the load while driving.
With this information we could use a low voltage disconnect to control either the D+ or Low Current terminals of this particular DC-DC (Renogy 20A). The cutoff would happen when voltage drops below the first measurement above.