LiFePo4 High Level Schematic

[Steve_C]

I am in the process of trying to finalize my overall Schematic for my Electrical system. I have created a high level flow of the system to make sure I am on the right track before creating a much more detailed schematic.

Its a lot easier to get the high level right before I go to too much trouble. I also think its easier to get meaningful input and help if I keep it clear and simple to start with.

Some things are not going to change. This will be a 24 Volt system, with a 800 AH capacity. I already have the Blue Sea ML-RBS solenoids. I currently plan to use a REC BMS. ALL of the fuse sizes listed are just place holders and will be refined as I do my system loading. I will use a Victron Quatro as I want to be able to have more than 1 AC source. The actual inverter size will likely evolve. I am planning to have a large number of 24 direct loads and avoid going thru the inverter if reasonably possible.

At this point I am mainly concerned with the placement of Fuses and breakers. having a Inverter/Charger than can have current flow in both directions is something that I want to be very careful with.

Also the REC - Relay Module will very likely be replaced by a home built Relay/Interface such as the one CatNewBee used in his design. I am experimenting with it now. Either way the sole purpose is to convert a continuous output signal to a momentary signal for use by the ML-RBS

I will not initially tie the stock alternators to this system, and plan to add a High Output Alternator to the system at some point in the future. I can address that separately later.

I am hopeful that this will evolve into something clear and simple enough to be useful to others as well as myself.

Thanks for any constructive input!

[Steve_C]

I also attached as a jpeg in case because the PDF requires download.

[smac999]

Inverter chargers are tricky because you want to stop both the charge and / or the load. You are only cutting off the load. A high voltage problem the the victron would cut off the wrong switch. A victron bms would control it via data cable. It may have an input terminal you can use to control it from a bms

The 500a fuse in the charge bus looks huge. And the 300 on the load looks small. That fuse should be bigger then the inverter fuse not the same size . You don’t want an inverter problem taking out the whole load bus.

[Steve_C]

Originally Posted by smac999

Inverter chargers are tricky because you want to stop both the charge and / or the load. You are only cutting off the load. A high voltage problem the the victron would cut off the wrong switch. A victron bms would control it via data cable. It may have an input terminal you can use to control it from a bms

The 500a fuse in the charge bus looks huge. And the 300 on the load looks small. That fuse should be bigger then the inverter fuse not the same size . You don’t want an inverter problem taking out the whole load bus.

Yeah, the fuse labels are just place holders for now. As I finalize the actual loads and inverter/charger sizes I will determine optimal sizes.

The REC BMS does have CAN support so it is my understanding that I can utilize that as well. I will also likely add a Victron BMV-712 Battery Monitor.

These are kind of details I need to flush out.

[mbartosch]

Originally Posted by smac999

Inverter chargers are tricky because you want to stop both the charge and / or the load. You are only cutting off the load. A high voltage problem the the victron would cut off the wrong switch. A victron bms would control it via data cable. It may have an input terminal you can use to control it from a bms

LiFePO4 system design pattern „BMS controlled Inverter/Charger“:
- connect DC side to BMS controlled load bus
- AC input to I/C via NC relay contact, relay triggered by BMS HVC

[YARGESOL]

REC BMS makes now "Victron compatible ABMS" . This will require GX device to be connected via CAN cable (as OP mentioned, he will go for this step). Then, ABMS will controll ALL VICTRON devices via CAN. Accroding to REC:"Victron CAN protocol is used to control all Victron devices via CAN bus and not by disabling them with power contactor. Power contactor is for extreme disconnection only.Only one contactor can control all victron devices..."
They provide a cirquite schema for connection - will try to load it here

[Steve_C]

Originally Posted by YARGESOL

REC BMS makes now "Victron compatible ABMS" . This will require GX device to be connected via CAN cable (as OP mentioned, he will go for this step). Then, ABMS will controll ALL VICTRON devices via CAN. Accroding to REC:"Victron CAN protocol is used to control all Victron devices via CAN bus and not by disabling them with power contactor. Power contactor is for extreme disconnection only.Only one contactor can control all victron devices..."
They provide a cirquite schema for connection - will try to load it here

That is what I am really planning for and trying to really clarify in my mind right now. The Blue Sea relays would only be there to provide disconnect if voltage exceeded normal parameters used by the CAN settings. I would probably set these up where I would manually engage (Close/enable) them and let the system open them.

At this point I am trying to make sure the flow of the system with relationship to fuses, switches and the charge and discharge buses are correct.

[nebster]

Now I see why you were worried about the bus bars' ampacity.

You should wire your pack differently: put multiple, single bars across those 8p blocks tapped at, say, cells 2+4+6+8 and then on the next one 1+3+5+7. For the tricky two at the bottom, use a few regular wires tapped off similarly, space permitting. (It doesn't matter if the resistance between block 4 and block 5 is different than the other inter-block resistances.)

This is how Frey builds up their big packs as well.

If you do it that way, you don't need to do any stacking of multiple bars to get ampacity. (Nor should you in the first place: you'll get slightly uneven wear across your 8p blocks if you wire it the way you have it drawn.)

[Steve_C]

I did finally find a source for custom bus bars that's really reasonable. For a single bar to reach all the way across 8 cells would only be about $15. That would be 6 mm (1/4 inch) thick x 30 mm (1 1/4") and tin plated. That would be rated at around 500 amps or more.

The connections between cells is easy to do as you suggest, and the only two points that are a problem are both at the one you mentioned at the back and the final take out points for Pos & Neg. I will likely do as you suggest with cable for the one in the back, that's not much of a stretch.

I also could layout the pack differently. I actually have about 6 variations of that drawn. Once I get ready to fit the pack into its final resting place I'll know whats best.

I have spent my entire adult life working on high voltage, high amperage equipment and have immense respect for keeping things well laid out and protected. I simply cannot rest until I have thought thru all of the possibilities and made sure I haven't overlooked anything.

[Steve_C]

Updated slightly, I didn't get many comments on the first version! It must be almost perfect

Or everyone is getting tired of reviewing these!

[nebster]

Yeah, if you can manage to put them all in a linear format like that, you'll have an exact copy of the way they build them up at the factory, and you can avoid having to debate with yourself whether to fuse those short jumper wires at the "bottom."

For the wires coming off, I used bluesea terminal fuses. (Do account for clearance if you go that route.)

[Steve_C]

Originally Posted by nebster

Yeah, if you can manage to put them all in a linear format like that, you'll have an exact copy of the way they build them up at the factory, and you can avoid having to debate with yourself whether to fuse those short jumper wires at the "bottom."

For the wires coming off, I used bluesea terminal fuses. (Do account for clearance if you go that route.)

I've been looking at those. I've never used them but what a great compact way to put a big fuse in. I really like Blue Sea equipment.

[nebster]

Originally Posted by Steve_C

I've been looking at those. I've never used them but what a great compact way to put a big fuse in. I really like Blue Sea equipment.

Indeed. Very compact, interrupt ratings comparable to class T, *and* maximum safety since there is no unprotected wire ahead of the fuse. It's rare to get a bunch of wins with almost no tradeoff, so, yay.

I use them at the*bus-up and distribution bars as well.

[Steve_C]

Updated again, I realized I didn't need two separate fuses between the Bank and the HVC and LVC contactors. Sometimes I need to create the visual and just look at for a while, and then slowly evolve it till I am comfortable with it.

I am now creating a much more detailed wiring layout just for the interface between the BMS and the HVC & LVC switches, along with the manual remote switches to override and monitor what the state of these are.

[ronstory]

I noticed you are setting up separate charge and discharge busses, but have an inverter/charger connected to the discharge bus. If you want to keep the charge and discharge busses, you will likely need a dedicated charger and separate inverter.

Or you can just combine charge / discharge sources/sinks but managing the HVC and LVC gets tricky. That said, you have canbus, so there may be some cool thresholds you can do with the I/C but make sure that critical DC items like bilge pump will still get power.

Will you have a backup battery?