Hello! I’ve received my Batrium BMS a while ago (Core, 2x K9, Shunt, Expansion) and will start building my battery next week. I am unsure about some aspects of my planned design so hopefully someone can chime in.
Parts:
32x 280Ah LFP in series, two physical boxes
Batrium as above.
3.3kW TC / Elcon charger
Sevcon motor controllers, Victron GX.
three contactors, two of which are controlled by the Batrium. The other main by the Sevcon.
My questions:
the Batrium instructs the TC. There is a contactor connecting the TC & Battery B+. Will the closing of this contactor create a big inrush current in the TC’s output cap ? Can one add logic on having the TC precharge to the battery voltage before closing this contactor ? How is this accomplished?
can the Core also function as an AP? Or only work connected to an already present WiFi network? / can one connect Ethernet through a USB adapter?
will having the contactors in the same physical metal box with the K9 create too much electrical noise for it?
are flyback diodes / snubbers / precautions needed when using the Expansion’s relays to switch contactors (powered by the same 24v PSU). Any recommendations on these parts?
Thanks! I hope everything will physically fit. Using ‘standard’ Chinese home ESS boxes in the boat, with some extra high feet.
My understanding is that the TCs will not energise their output unless everything is OK (battery is connected, correct polarity etc). There is usually an output on the TC for a contactor that it will connect when it is ready, and has been allowed to charge over CAN by Batrium. Could you confirm whether this exists on your charger?
The Core will function as an AP if it is not configured to connect to an external AP, or if it can’t reach the one it is configured for.
We haven’t had any reports of contactors causing too much noise for our equipment.
Flyback diodes are a good idea. Some contactors have inbuilt electronics to handle the spikes and also reduce energy consumption while being held closed, so see if you can find out whether yours do. Just something with a big chunky package is best to absorb the energy. It also depends on how many times this will switch, relays can still work with inductive loads, it just shortens their life.
If you have trouble getting the boards into your enclosures, remember you can take the PCBs out of their green plastic, and shorten any cables you need to, just be very very careful with the pinout if you make your own cables. Also be careful that metal objects are not going to short out the pins on the back of the board if you take it out of the green plastic.
I’ve made some progress but this only comes with more questions!
I’ve contacted TC and they say there is a contactor and precharge circuit built into the TC 3.3kW charger. I would use a contactor inside the battery case anyway to not expose any live pins when the BMS shuts down. Is it possible to close this contactor when the charger is online on CAN?
I could use the 12v5a output of the charger to signal the BMS, but of course it would need more physical wiring.
I’ve been going a bit into the communications options over CAN; I would ideally have the following:
TC charger over CAN 250k
Victron comms over CAN 250k
Communicate with my Sevcon Gen4 motor controller over CAN 250k
Is it possible to combine CANbus protocols ? (So comm with both the TC and the Victron over the same CAN)
My Sevcon motor controller has flexible CAN messaging and I can set it up to receive various CAN messages - if the values correspond to whatever the motor controller expects:
(BDI = battery discharge indicator)
% BDI remaining charge Unsigned8 0 FFh 0 1% / bit
A Maximum battery discharge current Integer16 0 32767
A Maximum battery recharge current Integer16 -32768 0
If you would be keen to include a profile for the Sevcon motor controller (or the ability to combine protocols) I’d be a happy camper! If you would like to see more on how the sevcon organises flexible protocols let me know I can show you around a bit.
If you would like I can also fill in the custom protocol request
Or is there a way for me to write custom firmware for the BMS myself?
