Solar battery and V2L

[Tig170]

How so?

Apologies - went off thread (with my quattro II - (dual AC input)) but anyone could use some of these newly released: Victron Orion -Tr 12/48V-8A (380W) Isolated DC-DC Converter(s) to trickle charge their 48v system via V2L in winter?

 

[torfinn]

Apologies - went off thread (with my quattro II - (dual AC input)) but anyone could use some of these newly released: Victron Orion -Tr 12/48V-8A (380W) Isolated DC-DC Converter(s) to trickle charge their 48v system via V2L in winter?

Well no, unfortunately you cannot use DC-DC as V2L outputs AC.... . You can of course use a 48V charger from Victron which also has CAN connectivity so it's absolutely possible to link it to a multiplus II via CERBO.

 

[Coulomb]

As both @wattmatters and I have repeated, forced disconnection of charge or discharge current via the MOSFET's is a final safety device that, in normal operation, should never happen. Think of that action as being like a safety belt or airbag in car. Yes, it will do its job and protect your LiFePO4's, but the situation that it triggers should ideally never happen.

I used to believe that too. But now I'm not so sure.
I came across this post explaining how the pair of MOSFET banks works:

BMS MOSFETs Explained

I'm writing this post since it seems there is a lot of confusion (especially in the comment section of a certain youtuber in Australia) on why both MOSFETs in a typical single port BMS are controlled individually and why/how this works when they're in the same series circuit. It will hopefully...

diysolarforum.com

It seems that it's possible to disable charging and discharging pretty much independently, and with relatively low loss. I'm not sure how inexpensive inverters with poor control loops will react to a BMS stopping charging; I guess it looks to the inverter that the internal resistance has suddenly risen dramatically battery terminal voltage rises suddenly), so the inverter should get the hint to stop charging. Even if the control system has significant overshoot (mine certainly do), the battery electrolytics can handle a bit of over-voltage for a few tens of seconds, and if there is a sudden load, the battery voltage should suddenly go down and the battery can quickly respond to the load.

How well this works in practice remains to be seen, though @johnb80 finds it works smoothly with his Victron system. I expect the Victron inverters to have excellent control systems though, unlike the less expensive inverters.

Comments welcome.

 

[johnb80]

I used to believe that too. But now I'm not so sure.
I came across this post explaining how the pair of MOSFET banks works:

BMS MOSFETs Explained

I'm writing this post since it seems there is a lot of confusion (especially in the comment section of a certain youtuber in Australia) on why both MOSFETs in a typical single port BMS are controlled individually and why/how this works when they're in the same series circuit. It will hopefully...

diysolarforum.com

Nice write up, good explanation. Once we have several devices in parallel the current ratings of the system go up dramatically and power dissipation goes down.

It seems that it's possible to disable charging and discharging pretty much independently, and with relatively low loss. I'm not sure how inexpensive inverters with poor control loops will react to a BMS stopping charging;

The battery load / supply is relatively benign, no nasty inductive kicks etc. The inverters tend to use SWMPSU controller chips controlling charging current and these switch at a relatively high frequency. Due to the frequency they can respond rapidly to changing load, I doubt there will be any nasty spikes on the DC bus at either side of the switching device.

I guess it looks to the inverter that the internal resistance has suddenly risen dramatically battery terminal voltage rises suddenly), so the inverter should get the hint to stop charging. Even if the control system has significant overshoot (mine certainly do), the battery electrolytics can handle a bit of over-voltage for a few tens of seconds, and if there is a sudden load, the battery voltage should suddenly go down and the battery can quickly respond to the load.

It will be milliseconds as opposed to seconds.

How well this works in practice remains to be seen, though @johnb80 finds it works smoothly with his Victron system. I expect the Victron inverters to have excellent control systems though, unlike the less expensive inverters.

Comments welcome.

I drive system into the limits once per week to cause BMS calibration routine to run. Normal operation the batteries run 10 - 90% so the BMS doesn't always cause the processes to stop. When operating from the independent battery charger I aim for a terminal voltage circa 80% so again the BMS doesn't stop the process. I have run it to the extremes at the very start of my system for several days whilst getting the systems to run properly and not once did it give any cause for concern in temperature / voltage spikes etc.

 

[Coulomb]

The inverters tend to use SWMPSU controller chips controlling charging current and these switch at a relatively high frequency. Due to the frequency they can respond rapidly to changing load, I doubt there will be any nasty spikes on the DC bus at either side of the switching device.

They certainly can respond quickly, if the firmware is properly written. Alas, at the bottom end of the market, which is all that was affordable when I bought mine (late 2016), the PI (Proportional Integral) control loops don't account for integral wind-up, so the overshoots sometimes are in the order of 20 seconds. It's really frustrating to watch.

Alas, it hasn't bothered me enough to find and patch the firmware. I've had a few half hearted goes at finding the main ones, but 8-bit assembly language with many pushes, pops, and stack accesses make it very hard to follow. Fortunately, this 8-bit code is only the PV code in my case, but that seems to be where the worst overshoots occur.

 

[johnb80]

They certainly can respond quickly, if the firmware is properly written. Alas, at the bottom end of the market, which is all that was affordable when I bought mine (late 2016), the PI (Proportional Integral) control loops don't account for integral wind-up, so the overshoots sometimes are in the order of 20 seconds. It's really frustrating to watch.

I was thinking more in terms of the MOSFETS, no nastys would come back to damage them.
The PI on your inverters sounds awful, poorly implemented and tuned. I spent a little time contracting to an Instrumentation and tuning company, they used a specialist piece of equipment (protuner) that monitored a process. You did a step change to the process in manual, it recorded what happened and then calculated the PID values to input to the control system. Running the protuner on a cracker in an oil refinery it gave the PID values and a well experienced old school controls engineer flatly refused to put the values into the system. After a a very heated debate he was overruled by management and the result was a very stable process with three time the throughput LOL. It was amazing just how many poorly tuned systems were out there in industry wasting loads of time and energy etc.

Alas, it hasn't bothered me enough to find and patch the firmware. I've had a few half hearted goes at finding the main ones, but 8-bit assembly language with many pushes, pops, and stack accesses make it very hard to follow. Fortunately, this 8-bit code is only the PV code in my case, but that seems to be where the worst overshoots occur.

What processor? I spent a good few years writing z80 based real time machine control programs and I'm sure somewhere I have a REVAS for z80 if it would help.

 

[Coulomb]

What processor?

It's an NXP MC9S08AC48, apparently part of the HCS08 family. Not one of the 30 or so assembly languages that I've used before, so I had to learn it from scratch. It had irritating features, like the TSX (Transfer Stack to indeX register) instruction would take one off the value, so what was at say offset 6 from the stack (referenced as 6,sp), is now at 7,x! Also, x sometimes represents a 16 bit register (really h concatenated with x) and sometimes an 8 bit register (the low half of hx).

Z80 was one of my early processors, and I disassembled many Z80 programs. Ida Pro, my disassembler of choice, has a Z80 front end, though by the time I started using Ida (Pro or not), I'd stopped analysing Z80 programs.

Edit: Apologies for the thread drift. We older posters have a tendency towards nostalgia.

 

[johnb80]

It's an NXP MC9S08AC48, apparently part of the HCS08 family. Not one of the 30 or so assembly languages that I've used before, so I had to learn it from scratch. It had irritating features, like the TSX (Transfer Stack to indeX register) instruction would take one off the value, so what was at say offset 6 from the stack (referenced as 6,sp), is now at 7,x! Also, x sometimes represents a 16 bit register (really h concatenated with x) and sometimes an 8 bit register (the low half of hx).

There are some weird instruction sets in different devices, I found it difficult to change between hardware. I did quite a bit with PIC chips the speed absolutely threw me, I struggled at the start.

Z80 was one of my early processors, and I disassembled many Z80 programs. Ida Pro, my disassembler of choice, has a Z80 front end, though by the time I started using Ida (Pro or not), I'd stopped analysing Z80 programs.

I used the hitachi 64180 Z80 based processer but with built in i/o, serial, CTC etc.

Edit: Apologies for the thread drift. We older posters have a tendency towards nostalgia.

Aye, Nostalgia is not what it used to be

 

[AmperaE]

That is what I intend to do too. Inspired by others on here that have done the same (@Bricktop X PWR and @wattmatters, IIRC).

Something like a Chargeverter or similar would work well, though probably an overkill with the MG4's limited V2L output of 2.2kW. There are some DIY options too.

Edited to add.... unless your inverter has an additional 'generator' input, in which case you can connect directly to the inverter from the V2L output and avoid the cost/complexity of an additional battery charger.

I do have a Solax X1-Hyb-6.0-LV-EU inverter with a GEN AC input port and a 2x 5.3kWh Solax T-BAT-SYS-LV-D53 battterypack. I was under the assumption that it would work out of the box (save some configuration) for my MG4. But unfortunately it does not work and Solax UK has confirmed that V2L is a completely different concept than a diesel generator and it is never going to work. They have something called 'SolaX PV-Genset solution' but it seems to work for diesel generators only (with ATS or Dry contact communication). Anyone any ideas or got it working ?

 

[hojnikb]

I do have a Solax X1-Hyb-6.0-LV-EU inverter with a GEN AC input port and a 2x 5.3kW Solax T-BAT-SYS-LV-D53 battterypack. I was under the assumption that it would work out of the box (save some configuration) for my MG4. But unfortunately it does not work and Solax UK has confirmed that V2L is a completely different concept than a diesel generator and it is never going to work. They have something called 'SolaX PV-Genset solution' but it seems to work for diesel generators only (with ATS or Dry contact communication). Anyone any ideas or got it working ?

Why wouldnt it work? A V2L output from MG4 is no different than output from a interver style generator. Both will generate pure sinewave AC with little distortion.

 

[siteguru]

Earthing?

 

[Tig170]

Earthing?

Most UK systems are combined with the neutral, nevertheless its a good point.

 

[Everest]

Will mull this over, but wondering if the Solax can only utilise its AC GEN input when the grid is down?

 

[siteguru]

Most UK systems are combined with the neutral, nevertheless its a good point.

Maybe so ... but the "earth" on the MG4 is floating and so is likely to trip out - either by the MG4 itself or via the generator unit.

 

[wattmatters]

They have something called 'SolaX PV-Genset solution' but it seems to work for diesel generators only (with ATS or Dry contact communication). Anyone any ideas or got it working ?

In general (but noting every individual case is specific), the MG4 is not suitable for direct connection to a home's wiring system with a standard earth-neutral link.

It will detect a fault and shut down the discharge session. V2L is expecting an isolated load (e.g. a plug in appliance).

The easiest way to make it work is to use the V2L to power a separate and isolated battery charger, and for the home to be powered by its own inverter drawing from the batteries.

There are other work arounds I'm sure, but best left to qualified electricians and engineers.

 

[AmperaE]

Why wouldnt it work? A V2L output from MG4 is no different than output from a interver style generator. Both will generate pure sinewave AC with little distortion.

My thought indeed, why wouldn't it work. In my manual Solax defines a Smart Load concept for the GEN port:
The generator port has three options:
• None: No device is connected to the generator port;
• Load: The generator port is connected to a load;
There are two types of Battery: Lead acid (Voltage type) and Lithium (SOC type).
» Smart Load Battery Off Voltage/SOC: When the voltage/SOC is lower than
the set value, the battery will no longer supply power to the smart load;
» Smart Load Battery On Voltage/SOC: When the voltage/SOC is higher than
the set value, the battery will supply power to the smart load again.
Smart Load Battery Off Voltage: Default:48V, range:40-52V
Smart Load Battery On Voltage: Default:52V, range:41-53V
Smart Load Battery Off SOC: Default:30%, range:15-80%
Smart Load Battery On SOC: Default:50%, range:30-85%
• Generator: The generator port is connected to the generator.

So the gen port seems bi-directional. And Solax support tells me that a generator will only work if it has either an ATS (automatic transfer switch) or a separate communication cable (dry-contact). So I'm kind of lost...

Do you know anyone who got this working ?

 

[AmperaE]

Will mull this over, but wondering if the Solax can only utilise its AC GEN input when the grid is down?

Not sure. tested both situations. In on-grid mode nothing to be seen on the inverter and the MG4 keeps discharging. In off-grid mode the inverter detects something but switches off the EPS (essential power supply) to the house and gets stuck in a checking status. Also in this case I see no values from the V2L in the inverter display. We ran a cable from the gen port to an outside box and fitted a plug on that end. That's plugged in to the V2L socket.

 

[T1 Terry]

The Victron Multiplus and Quattro inverter range have a sensing circuit to determine if the supply has an earth/neutral link, if it doesn't, it can turn a relay on to create the link between earth and neutral. The other choice is to use a RVD (Residual Voltage Device) in place of the standard RCD ( Residual Current Device). These do the job of an RCD as well as a reverse polarity connection safety switch.

Inverters and generators are floating earth devices, so there is a line 1 and line 2, not active and neutral

T1 Terry

 

[Everest]

Not sure. tested both situations. In on-grid mode nothing to be seen on the inverter and the MG4 keeps discharging. In off-grid mode the inverter detects something but switches off the EPS (essential power supply) to the house and gets stuck in a checking status.

I did some searching and found the below on Solax's support site, albeit 6 months out-of-date...

Regarding mode "mode c", it would appear that Solax have not yet got the generator software working (if I'm reading their Chinglish corectly). That might explain why you saw the inverter got stuck in a "checking state". Suggest you contact Solax again to see if there are any firmware dates available or scheduled.

Having said that, my concern is with mode "b", load mode; as you say, the gen port can be bi-directional. I would be very wary of connecting your V2L output to a port that could supply grid power - the voltages and AC synchronisation would not match and would likely result in destroying your V2L inverter in the MG.

Safer, as myself and @wattmatters suggested in this thread, is to use an isolated charger directly to the batteries. That will also bypass any earthing requirements, which would, in turn, depend on your specific property's earthing arrangement and need for a sparky.

What is the function of "smart load" in my X1-Hybrid-LV setttings?​

Peter
6 months ago Updated

It is related to the function of generator port on the inverter, the generator port has three options:
a. None: No device is connected to the generator port;
b. Load: The generator port is connected to a load; Under this situation, this port actions as eps port as well. And the normal EPS port load power plus this port load power should be less than the max EPS port output power.
Settings options:
a1: Smart Load Battery Off Voltage: When the voltage is below the minimum value, the battery will no longer supply power to the smart load;
a2: Smart Load Battery On Voltage: When the voltage returns to normal, the battery will supply power to the smart load again.
c. Generator: The generator port is connected to the generator; Currently this function is in developing.

 

[AmperaE]

I did some searching and found the below on Solax's support site, albeit 6 months out-of-date...

Regarding mode "mode c", it would appear that Solax have not yet got the generator software working (if I'm reading their Chinglish corectly). That might explain why you saw the inverter got stuck in a "checking state". Suggest you contact Solax again to see if there are any firmware dates available or scheduled.

Having said that, my concern is with mode "b", load mode; as you say, the gen port can be bi-directional. I would be very wary of connecting your V2L output to a port that could supply grid power - the voltages and AC synchronisation would not match and would likely result in destroying your V2L inverter in the MG.

Safer, as myself and @wattmatters suggested in this thread, is to use an isolated charger directly to the batteries. That will also bypass any earthing requirements, which would, in turn, depend on your specific property's earthing arrangement and need for a sparky.

What is the function of "smart load" in my X1-Hybrid-LV setttings?​

Peter
6 months ago Updated

It is related to the function of generator port on the inverter, the generator port has three options:
a. None: No device is connected to the generator port;
b. Load: The generator port is connected to a load; Under this situation, this port actions as eps port as well. And the normal EPS port load power plus this port load power should be less than the max EPS port output power.
Settings options:
a1: Smart Load Battery Off Voltage: When the voltage is below the minimum value, the battery will no longer supply power to the smart load;
a2: Smart Load Battery On Voltage: When the voltage returns to normal, the battery will supply power to the smart load again.
c. Generator: The generator port is connected to the generator; Currently this function is in developing.

They seem to be further now, but I'm going to check this with Solax and my mcs installer anyway. I'm pretty sure I've received two inverter firmware updates lately. Solax pushed the last one on the 23th. They claim that the gen port input is designed for diesel generators with ATS or dry-contact communication only. And looking at the config settings in my inverter it's all designed to let the inverter be in the lead of starting and stopping the generator.
I agree on the bi-directional part. Although it's configurable, a mistake is easily made. Also dangerous because we currently have a naked standard uk plug in the outside wall box.
Thanks very much for your help. Much appreciated