PRS iCharger Monstrosity
we're working on making this thing prettier and safer for 2019. stay tuned.
at Blue's suggestion, we picked up two 12V 100A server rack power supplies, to make a hacked 24V 100A power supply, because the icharger needs ~4.5~30 V input, and is more efficient the closer you get the input voltage to the nominal voltage of the pack you're charging. Since we're charging a 12s3p Chevy Volt battery, and the iCharger does not offer 12S charging, we charged the pack in two halves, (6s3p) so aimed for a nominal charge voltage of 24V.
To hack the power supplies together, special care was taken to ensure the grounds and DC bus voltage "0V" rails were managed successfully. since the supplies' outputs are connected in series, ideally none of: the DC bus 0V, earth ground, or the 120VAC neutral wire will be connected to the chassis of the power supply to ensure the 12V "center tap" of the charger is entirely isolated. unfortunately for this build, the particular server-rack power supplies we got had the chassis of both supplies tied each to the earth ground and to the 0V bus. upon inspection, disconnecting the earth ground from the chassis was accessible (a single ground lug tied the cable to the chassis where the 120 entered the supply.) but disconnecting the 0vdc rail proved to be more difficult. in the end, we left the 0vdc bus connected to the chassis, which means one of the supplies has 12vdc, 100A potential tied to the chassis. this was scary. so care was taken to prevent anyone from touching the chassis of either supply, by putting them in a plastic box, and mounting them to a wooden sub-panel with physical isolation from each other. 10AWG wire was run between them, and to banana plugs for the icharger.
We noticed sparking in the xt60 when connecting the battery to the charger, and some research yielded that the 0vdc of the battery should be connected second, after the vcc on the battery is connected to the charger, so we implemented a switch (the same regulation PRS key that is in the kart.) on the 0vdc line in between the xt60 that goes to the battery and the charger, to leave the 0vdc line open when plugging in the battery, then closing the 0vdc line last inside the key contacts.