New LiFePo4 Install

[Dockhead]

System overview:


8x 300 a/h 3.2v cells in 1P8S configuration charged from 100amp * 24v alternator and 24/5000/120 Victron Multiplus. Technical loads (inverter, windlass, thruster, winches) connected to lithium bank.


220 amp/hours * 24v lead-acid secondary bank charged from LiFePo4 bank via Sterling 35A B2B charger. House loads (excluding inverter, windlass, thruster, winches) connected to lead bank.


Alternator isolated from lithium bank with Latching Relay 1 (100+ amps) connected to LVC terminal of BMS, and protected from open circuit condition with Sterling Alternator Protector.


Inverter/charger isolated from lithium bank with Latching Relay 2 (500+ amps) connected to both LVC and HVC terminals of BMS.


Lithium bank load bus isolated from lithium bank with Latching Relay 3 (500+ amps) connected to LVC terminals of BMS.




Controls:



1. Automatic shut down of charging from Multiplus and alternator upon reaching target SOC (via BMS? Or battery monitor?).


2. Automatic shut down of charging from Multiplus and alternator upon (a) exceeding voltage limit; or (b) exceeding battery temperature limit.


3. Automatic shut down of inverter upon falling below low voltage limit.
Automatic shut down of B2B charger upon falling below low voltage limit.


4. Automatically open Latching Relay 1 and 2 upon exceeding high voltage limit with delay.


5. Automatically open Latching Relays 2 and 3 upon falling below low voltage limit with delay, with manual override.


6. Alternator control (external panel mount control for Sterling or Balmar regulator)


7. Inverter/charger control (Venus or Color Control GX?)




Alarms:


1. High or low voltage


2. High or low SOC.


3. High or low battery temperature.


Monitors:


1. Lithium bank SOC, cumulative amp hours in/out, voltage (Color Control for all?).


2. Lead bank SOC (SmartGauge), cumulative amp hours in/out (Victron), voltage.





Parts list:


1. 8x Winston prismatic cells.


2. BMS (which one?)


3. 2x 500 amp latching relays; 1x 100 amp latching relay


4. Sterling alternator protector


5. Sterling or Balmar alternator regulator.


6. Sterling 35a B2B charger.


7. Upgraded Multiplus (5000/24/120)


8. Color Control GX (or Venus?)


9. Temperature probe and display (or can be done on Color Control GX?)




What do you guys think?

[Dockhead]

One note to this: Somewhat unusual system architecture results from configuration of my boat's electrical system. My boat was built with two lead-acid banks, one supplying house loads, the other technical loads. It makes sense to leave the house bank in place, and this will add about 120 amp hours of usable power and back up the lithium system, both of which are somewhat useful and worthwhile considering it's free. I would not do it this way if I were building from scratch. Downside of this is the power consumption of the B2B charger.



So the lithium goes in place of the battery box for the original technical loads bank.

[mbartosch]

Sounds vaguely similar to the setup on our Entropy.
You might gain some ideas for your design from our system description: https://www.entropypool.de/2015/05/1...system-design/

Some comments:
alternator should go to HVC, not LVC (if properly protected against voltage spikes, I prefer direct connection to main contactor and cutting field via shutting off the external regulator)
Inverter/charger combined is difficult. I chose attaching it to the charge bus and separately cutting 230 V shore supply by NC HVC relay
- automatic shutdown via SoC is possible by simulation of HVC event e. g. via the programmable relay in a BMV 700 or a Victron CGX
- don’t bother with temperature sensors.

Really, have a look at our blog post...

[tanglewood]

My gut reaction is that it’s overly complicated.

Set charge sources to stay below damage levels. Set inverter to disconnect before damaging low voltage. Set alarms on approach to damaging voltages, both high and low. Last resort disconnect if damaging voltages reached.

If the chargers are set up correctly, the BMSS should never need to do anything. It’s just there in case things go wrong. I have never felt charge and discharge busses are needed, and they aren’t even possible with an inverter charger which is most boats. In a year, by BMS has done exactly nothing, as it should.

[Dockhead]

Originally Posted by tanglewood

My gut reaction is that it’s overly complicated.

Set charge sources to stay below damage levels. Set inverter to disconnect before damaging low voltage. Set alarms on approach to damaging voltages, both high and low. Last resort disconnect if damaging voltages reached.

If the chargers are set up correctly, the BMSS should never need to do anything. It’s just there in case things go wrong. I have never felt charge and discharge busses are needed, and they aren’t even possible with an inverter charger which is most boats. In a year, by BMS has done exactly nothing, as it should.

I don't think that contradicts anything I posted. Of course, the LVC and HVC are emergency measures which should never come into play. The charging sources are programmable and these programs should be the primary control of charging. The BMS is just a safety device.


Inverter/charger can be disconnected in the event of a high voltage event by cutting the AC power (as Mbartosch helpfully pointed out). So in that case the latching relay between I/C and lithium bank can be actuated solely by a low voltage event.

[mikedefieslife]

The Inverter doesn't need a LVD. It can be set to disconnect at 12.8v so even in the most extreme case of 3 cells being fully charged and one at closer to empty, you'd never get a cell below 2.55v

[Dockhead]

Originally Posted by mikedefieslife

The Inverter doesn't need a LVD. It can be set to disconnect at 12.8v so even in the most extreme case of 3 cells being fully charged and one at closer to empty, you'd never get a cell below 2.55v

Yes, but what if it malfunctions? The LVC and HVC are last-ditch lines of defense to protect the cells in case the gear malfunctions. Victron stuff does malfunction once in a while.


I like the idea of someone else above to put the LVC in the AC power supply line. 1/10 of the amperage and less of a faff.