# Clarification of MiniBMS



## Moltenmetal (Mar 20, 2014)

_Firstly, do 'MiniBMS Cell Module' have fuses on the PCB? if yes are they replaceable?
_
Not that I'm aware of.

_Secondly, Is the one wire interfacing opto isolated from the batteries?
_
The alarm loop consists of a bunch of normally closed relays- one on each celltop board- which are wired in series. Any cell being in HVC or LVC opens its cell board's relay. The state of those relays is sensed by a header board powered off the 12VDC auxiliary battery. Isolation between the HV batteries and the 12V auxiliary battery is therefore nearly perfect, limited by the isolation rating of the relays used.

_Thirdly, does the 'MiniBMS Head End Board' check for LV and HV at all times (when powered)?_

Yes, but which one it assumes is happening depends on the state of the key switch input. HVCs are going to occur only when the key switch is off, and LVCs will occur only when the key switch is on.

_Forthly, can 'MiniBMS Head End Board' be powered by a separate power source (ie no common ground between low voltage system and high volatge system), would this interfere with the cell loop communication/monitoring?_ 

This is exactly how my car is wired- there is no connection between the HV B- and the 12V aux B- (in my car, that is chassis ground). No connection via the BMS or any other part.


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## lalith (Nov 18, 2015)

thank you for the clarification

since our car is a series hybrid, onboard recharging of batteries can be done
hence the necessity to simultaneously monitor HV and LV of accumulators

from what I understand from the manual and your reply
the alarms for hv and lv are based on the ignition pin (on the BMS headboard)

would it be possible to toggle ignition pin on & off to thus monitoring both??


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## Moltenmetal (Mar 20, 2014)

It's simpler than you think!

The celltop boards will open their relay whenever the cell they're monitoring goes into EITHER HVC or LVC. In either case, they sound an alarm (there's an output on the header board which drives an external buzzer that you supply). You simply use that alarm buzzer output to actuate whatever devices you want.

Be aware though that when all cells in the loop go back to a "good" state, i.e. rise above or fall below the HVC/LVC point, the buzzer turns back off again.

Originally my charger control interlock was operated off this buzzer output. That meant that the charger would bounce on and off again, never really shutting off the charger until the charger itself reached the high voltage cutoff.

There are individual outputs on the header board to drive relays for HV and LV alarm trips, and these outputs LATCH. Which one of these is active depends on the state of the keyswitch input, and they latch until the keyswitch is cycled.


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