I’m doing research for an EV conversion with a 45-50 kWh LFP battery. I want it run at 48V (or 54V really, as it will be a 2P18S battery with 400 Ah cells) for the following reasons:
Safety
Easier to get approved where I live
Option to use it as an additional battery (in other words, V2H), as the car will only be driven once a week
As I’m still in the research stage, I don’t have any hardware yet for either car or home. I’m planning to use a Cerbo+Touch in the car to display info from SmartShunt, BMS and controller. As far as I can foresee, there will be a simple 3 x Multiplus-setup in the home, probably with a stationary 25 kWh LFP battery and SmartSolar controllers for an 8-10 kWp solar array.
It probably isn’t as simple as I envision it, but the mobile battery would be connected via something like an Anderson plug and cable to the home system busbar, with a battery switch for safe (dis)connecting. Would it really be as simple as that? Or would it confuse the Multiplus if suddenly an 800 Ah battery is added to the system, and thus some form of communication or programming would be required? Maybe a separate charger would be needed to handle the mobile battery?
As a first step, I’m most interested to know what kind of connection is best to plug and unplug a mobile battery. Any tips or hands-on experience would be much appreciated.
Normally I would separate the two batteries and charge them both up to 100% SOC, disconnect and leave them for 30 mins to settle back, I would then connect them together, this should minimise any current flow between them. I would then leave them to settle.
But as you are connecting a home system to an EV there will be a imbalance between the home battery and the EV battery, so I would be very worried about a DC - DC connection between them. I would not connect different batteries together like this, even from the same manufacturer, if not bought together, can be an issue.
Personally I would keep the two separate, and connect the car at AC level if possible.
BTW, the only alternative I have found for the classic Anderson plug is this Powerpole PP120-180 (also from Anderson). It has to be something that fits 50-70 mm2 cables, but I don’t know what would be best with regards to connectivity and wear.
Can’t do AC, because that would defeat the purpose. Bidirectional charging at the AC level is much more difficult to achieve (for a layman such as me).
Again, I’m primarily interested in options to safely connect/disconnect a mobile battery from a Victrom home ESS, or whether it can be done at all. But of course, it would also be interesting to know how one could achieve a system with both a mobile battery and a stationary battery (and thus different SoC). At first, I thought each could be connect to a separate Multiplus, but I’ve learned that it doesn’t work that way.
PS needless to say, the car/mobile battery would park as close as possible to the home system, to keep cables as short as possible. Some kind of docking station would be funny, but I wouldn’t mind doing it manually.
The upper part would be used for AC charging (Type 2) via the on-board charger that converts to DC, but the lower part (the two big holes) would be ideal for two big fat cables that connect to the home ESS.
So, there’s an EV car with a 48V battery and a Multiplus in it. It arrives at a home with a simple three-phase Multiplus set-up (edit: grid-tied), including PV and a stationary battery. The car plugs in via cables to the DC bus of the home. What happens then? The Node-Red/MQTT stuff makes sure that the batteries do not balance (too quickly)? How does that work exactly?
Or does the car plug into AC (thanks to the on-board Multiplus)? But that’s not bidirectional, right?
I apologize for not being knowledgeable enough about Victron and these things in general. I have some experience with my home ESS (PV + Deye + LFP batteries, most of which I designed and installed myself), and now I want to design a good and (relatively) simple set-up for my next home that incorporates a converted car with a 48V battery, in other words a mobile battery on wheels that can plug into the system.
The options I see so far:
Somehow separate mobile and stationary battery on the DC side. I’ve looked at the Victron battery balancer, but that’s not a solution, I don’t think.
No stationary battery (or put a smal battery on the AC side for basic back-up, like Ecoflow or Bluetti)
Fred’s suggestion of putting a Multiplus in the car, if that works
I’ve thought about another way of separating mobile and stationary battery, namely by putting a three-way switch between them and the busbar, so that only one of two can be connected to the system at any time, never both.
Something like this switch that is used for marine purposes:
If the car were to be at home, I would let its battery be the bidirectional back-up battery for the home system. If it were to be full (because of sufficient PV power), I would then use the switch to switch to the stationary battery, so that surplus power can be stored there as well.
Likewise, if one battery was (almost) empty, I’d switch to the other.
The question is whether the system would tolerate this kind of switching. I also assume the batteries would need to have exactly the same amount of Ampère-hours?
