# Precharge Circuit with Dual BMS/Dual charger



## TooQik (May 4, 2013)

Hi,

I'm trying to pick a BMS system for my build and am working through design considerations before making a purchase.

I'm planning on using two Brusa NLG513 chargers to charge a 650 VDC nom battery pack. I've been reading through the Elithion website and have put together the following circuit diagram for the proposed precharge circuit to precharge both Brusa chargers as well as any load:



Does anyone know whether the second Elithion BMS (labelled Elithion BMS - 2) will function as desired with the K3 negative contactor control disconnected? Or can/should this be wired in parallel with the K3 negative contactor control of the first Elithion BMS?

Any other comments and suggestions are more than welcome.

Thanks in advance.
Chris.


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## Elithion (Oct 6, 2009)

Hello Chris,

You have chosen the only BMS out there that can do what you need, with only 1 BMS master. 
A single Elithion Pro BMS can manage a split battery with two chargers in series, and a single load.
It can even let you use a single charger to charge both halves of the battery pack. That saves you a charger, but charges more slowly.









I see that you placed the chargers on the wrong side of the contactors, though: the chargers go on the battery side of the contactors, not on the load side.


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## major (Apr 4, 2008)

There has been a recent release of an application note claiming the necessity of precharging these Brusa chargers. See: http://www.metricmind.com/data/mmc_006.pdf I too think the chargers should be permanently connected to the batteries and not disconnected via the contactor(s). When hard wiring the battery-charger circuit, precharge the charger manually with a resistor as the last battery connection is made. Repeat that precharge whenever the battery is disconnected for service. You can turn off the chargers on the AC side or by the signal wire into the multipin plug.


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## TooQik (May 4, 2013)

Thanks Davide and major.

As major pointed out, I was trying to design the circuit in order to precharge both Brusa chargers as well as the load. My aim was to try and use as few contactors as possible and only have DC voltage at the chargers/load when the vehicle was being charged or driven. Other than the advantage of requiring less components for the build, are there any other pros/cons to not having a permanent precharge circuit for the chargers?

What I haven't indicated in my circuit diagram is that the battery pack will not be split into equal parts ie. part pack voltage seen by each charger/BMS will not be the same. From my reading on your website Davide, this dictates that I require two BMS masters, especially given that I'd like to use the CAN bus to control the chargers.

While a single BMS master would be great, I don't believe it could control two chargers via the CAN bus without changes to its software, nor could it control separate precharge of each charger without both hardware and software changes. Please correct me if I'm wrong, as I'd really like to be wrong with this comment.


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