Charger in parallel with EasySolar

Q&A and troubleshooting
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1

I have an EasySolar-II 3000VA with a bank of 48v pylontech LiFePo4 batteries and a solar array connected to it.

I want to be able to charge the batteries in parallel with some sort of dumb 48v charger that runs from AC, the aim is not to have more total charging current available but rather that the additional charger would simply “support” the battery voltage (for example, holding the batteries at 70% for longer during discharge, so the inverter in the EasySolar would be supplying AC output while the secondary DC charger would be supplying that power on the DC side)

If it helps to clarify what I’m looking to do, the idea is that during the day the system is charging it’s own batteries and is also charging an EV. At night, the system starts discharging, it’s own batteries discharge a bit (let’s say to 70%) then the EV’s AC output (V2L) picks up the load via a DC charger connected to the EVs AC output and it holds the batteries at a voltage corresponding to 70% SOC while the EasySolar keeps inverting and supplying AC to the loads. At some point the EV hits its own lowest discharge target and cuts off the secondary charger, so now the pylontechs start discharging below 70% and keep supplying the AC loads until the minimum SOC is reached.

What’s the best way to do this? I don’t think victron sell a 48v AC charger, and putting a multiplus in seems both wasteful (I don’t need/want the inverter) and also potentially not the right thing to do as if you were paralleling them then the AC input source of both would need to be the same, whereas I specifically don’t want that: the AC input to the EasySolar is grid power, while the secondary charger should get it’s AC input from the EV.

Presumably I just want an AC to DC 48v charger, and can connect it to the DC side of the system without the EasySolar knowing it’s there or having any form of communication with it, and the EasySolar will simply see the batteries as holding up for longer because it doesn’t know the DC power is actually coming from another source than the batteries.

How does this work in terms of current and voltage also? Presumably it’s conceivable for both chargers to be charging the batteries simultaneously (although that’s not an intended mode of operation), so I need to make sure DC cables are sized appropriately for the maximum charge current of both chargers simultaneously. Are there any other safety considerations like that I might not have thought of?

If victron do make an AC to 48v charger suitable for this what model am I looking for and if they don’t what other options are well made and worth looking at?

2

The TG is the only 48v one i know. Its large though.
You have a 3kVa so it makes sense to just get another 2or 3kVa.

I usually use another inverter to charge the bank. I suppose you could set the charge amps at whatever it takes to offset the discharge to loads. My only concern is can the battery bank take the amps or have a way to safety cut it off if there is an unexpected event that messes with your idea working mode.

(and both chargers are set to exactly the same charge and float voltages a second charger is not a problem.)
Just remember the second one is not controlled by dvcc

The batteries ware reporting to the system. So there should not be an issue there.

Is there a reason why you aren’t just discharging the ev into the house circuit?

3

Thanks for the reply, I haven’t checked yet but my guess is even the full charge current of a pair of 3kva multis is safe with my batteries (4x pylontech US3000) as I recall the maximum charge current when I installed them being really large, much bigger than the EasySolar could ever supply.

That’s assuming they’re wanting full current though, but what I haven’t thought through carefully yet is when the BMS in the batteries starts requesting a lower current due to temperature, high state of charge or whatever else.

I guess if I bought a second multiplus to use it as a charger, it couldn’t be connected to the VE bus system (as then it would become a parallel system and want the same AC input source to both units) so I guess it would have no way to have communication with the batteries to limit it’s charge current.

It’s been a while since I set a system up, so I need to re-read the documentation, but I was thinking (and perhaps this is dumb) that the second charger should be configured differently to the one in the EasySolar - I was thinking the second one’s float voltage would be set lower than the main one, meaning the main charger in the EasySolar can charge the batteries all the way to full from the MPPT or AC in, whereas the second charger can’t charge them past a mid state of charge, so it just holds them up at a mid voltage once they get there. I’m not even sure if a completely dumb 48v DC power supply would be safe to use that way, with the output voltage set so that it can never charge the batteries above say 70%

When you say about discharging the EV directly into the AC system, I’m a bit concerned about doing that to be honest - would it not be the case in that scenario that if the house voltage got higher than the EV output that I’d be in danger of doing some sort of damage to the EV by having current flow back into it’s internal inverter (which I have no idea if it’s bidirectional and capable of doing that via the V2L adapter).

The added complication to connecting the car to the AC side is that the system is already slightly complex. The EasySolar I already mentioned is one of two, they’re not parallel - the ES3000 we’re discussing is located in an outbuilding, it takes it’s AC input from the AC output side of an ES5000 that is upstream of it in the house with it’s own separate bank of pylontechs and separate PV array.

The ES3000 in the outbuilding also feeds into the ES5000 in the house when the ES3000 has surplus power, seeing the AC in from the 5kva unit in the house as if it were a grid connection that it was feeding in to, and if the loads in the house are not consuming that fed in power that’s going to the AC output side of the ES5000 then it converts it to DC and charges it’s own batteries in the house using it.

As it is, this system works fine (I’m aware it’s not a recommended configuration, but I’ve had no problems with it and it’s been installed in this configuration for several years), but adding an additional third AC source to the bus where the AC in of the 3kva meets the AC out of the 5kva seems like it might not be a great idea.

The system I’ve described above is managed via an external control loop (Home Assistant using ModBus TCP to change the grid setpoint of the downstream ES3000 to feed more or less power into the house side depending on PV power and battery state of charge) so yeah there’s complexities and possible failure modes there that I think at the very least would need really careful thinking through, and more likely would be best to eliminate altogether by not adding any other source of power on the AC side.

The safer thing to do seemed to be to use the power to charge the batteries but with a low enough float voltage that there could never be a situation where the EV output ended up trying to overcharge the batteries. There’s also two sets of batteries to consider there as connecting the AC out of the EV directly to the system would result in that power being able to end up in the outbuilding batteries or the house batteries via the AC connection back to the house, and the EV would have no way to know the state of charge of either set of batteries to be able to cut out if they were undesirably full.

With the EVs AC output going into the AC side it seems there’s risks of unforeseen situations where there’s nowhere for the energy to go, while if that power is going to a charger that can only peak out at 52v (or whatever, pulling a number out of my head there) it seems very intrinsically safe with nothing much to fail.

4

This will happen naturally as with dvcc the pylons go much higher than the 52 and 51 set on the ve bus normally.

The method you are proposing with the separate charger is the least headache version of using V2L. I agree complex software control can cause unnecessary complexity. With HA I guess there can still be a it of control over the second in erter as well anyway for fine tuning

5

Ah that makes sense yeah I remember having read that page before, so I see that the default configuration suggested there would do something very similar to what I’m proposing.

Am I correct in saying you’re suggesting the second multiplus has no VE bus connection - it’s configured with the correct voltages as mentioned in that page, but because it has no communication with the batteries or the rest of the system it just operates as if it were in fallback mode using those configured values, hence never charging the batteries above 80% or so?

6

It won’t have a ve bus connection and be controlled as the main one is.

But you can add it for monitoring using the mk3 (and potentially some controls using node red - i haven’t tried HA this way.) to the GX
It will appear in the device list and you do have basic controls over it form there. Not it will not charge to full. Full and balanced is closer to 52.4v on pylons.

7

Ah yeah I get it, in fact although it would be more expensive initially I might consider using another identical EasySolar to do it then, as that way I can independently monitor and control it via ModBus TCP to it’s internal GX and it also gives the option of adding another PV array to that additional EasySolar later and using it in fallback/independent mode to assist charging until 80% during the day.

8

Also a good option.
I can only discuss possibility with you. How you spend your money is up to you.