Does JK BMS have a 12V output?

[braincore]

You'd think I'd be able to easily answer this question from their manual, but they basically only enumerate the balancing wires and mains without any pinouts for their other ports (GPS, LCD, ...).

1. Is the JK BMS always on if the battery has sufficient power?
2. Is there a 12V or 5V output for running a microcontroller? I would assume so given the LCD attachments I've seen. Which pin is it and does anyone know how much power it provides?

It's in the mail currently, and I'm wondering if I need to buy a 72V-5V step down.

 

[amberwolf]

I don't know the specific BMS (no model provided so just generically), I haven't seen any of these that have a power supply to run anything else with. The displays I've seen for BMS usually require a separate power supply for them, which could be anything but 24v has been required for some of them (which is not a voltage normally found on any vehicle / etc these BMS would be used on, so it's a strange decision to use that voltage). (some may have a wide-range voltage input, and so work directly off the pack voltage)

My best guess is you'll need a separate DC-DC for any voltages other than full battery voltage, and if it's something that will need to communicate with the BMS or read any of it's signals, etc., then unless that's done over an opto-isolated bus, the DC-DC will need to have common ground with the BMS; if the stuff run by the DC-DC needs to work with the BMS regardless of pack I/O state, that ground has to go to the B-, not C- or P-.

That means the BMS can't turn that load off, regardless of what problem with the pack it detects that it's shutting off charge or discharge for. (because virtually all the BMS used in stuff we see here can only control the pack negative, not the positive, with the exception of the very few contactor-based types, which leave it up to the user to decide what connection(s) to break).

Most BMS will remain on as long as there is sufficient voltage from whatever portion of the pack powers it. (many do not run off the entire pack voltage, but only off one or more of the most-negative groups). Some have a power switch that turns off most of the BMS to conserve power (this also disconnects the rest of the system from the BMS input and output).