Replace my cheap Chinese Off Grid inverter/charger

Q&A and troubleshooting
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1

Hi,

For years I have persisted with various Chinese inverter chargers for my mostly off grid solar system :grinning_face:

My existing system is a 7.5Kw solar array, consisting of two strings of 9 panels.

6 Pylontec US5000 batteries and an Axpert Max-E 11Kw charger/inverter.

I have a grid connection but do not feed into the grid.

I live on the island of Crete (35 degrees N Latitude)

I am looking to replace the Axpert with a Victron Charger/Inverter as I have finally given up on getting the Axpert tto communicate with the Pylontech batteries in any meaningful way. I have variations of this system for around 10 years now, although with none of the current components, the batteries are about 10 months old.

I am a refugee from the sailing community and have always thought of Victron as a rather over the top solution for a land based system, where the conditions are nowhere near as harsh as the marine environment.

The Victron Range is huge and I would like some recomendations as to which Victron Kit might work best for me?

Thank you to anyone who can offer advice,

Regards Peter

2

Hi Peter, the answer to your question naturally depends on your needs, and what is allowed in your region. Do you really need 11 kW of inverter power?

The most important questions are:

  • How much electricity do you consume per day, per year?
  • What is your base load?
  • What is your peak load, and how long does it last?
  • Can you easily distribute the peak loads?

Important: Iā€™m not familiar with the regulations for a grid-connected ESS in your region.

3

Do you want to keep it that way, or would you like to be able to feed back? No feeding back is relatively simple, feeding back would be an ESS config.

In any case, in order to get communications to work with the batteries you would need a GX device, can be a Cerbo, an integrated MP-GX or a selfmade RaspberryPI running the VenusOS.

4

Hi Tom

thanks for the input!

I use around 25Kwh per day. I mostly get by on the Pylontechs (around 29kwh) with solar as well

I have a spreadsheet showing consumption and generation, if itā€™s of interest? I have data going back several years, but only just on a year for the current setup.

The pricing for electricity here is very different from the UK, the first 300 units per month are the cheapest after that the cost rises dramatically. The local property tax is also related to your energy consumption and again that rises dramatically when you use more than 300 units a month, so there are major incentives to be as frugal as possible:-)

Peak loads are for cooking using an Induction hob, fan electric oven, in the summer thereā€™s some some 15Kw of airconditioning. Very occaisionally thereā€™s also a 4Kw immersion hetar, but 95% of the time thatā€™s taken care of by solar heating and in the winter thereā€™s an indirect coil attached to my pellet boiler, that adds to the base load in the winter, right now (17.45) the base load is around 435watts, made up of the pellet boiler, two freezers, a fridge, power for the internet via StarLink, some lights, all of which are LED.

Thereā€™s also a washing machine (1.2Kwh per load), dishwasher (0.8Kwh per load) and the usual collection of kitchen appliances, kettle, (3.0Kw) air fryer (1.4Kw) microwave (1.0Kw) being the other big consumers of units.

My current system is setup as follows:- Solar First with battery charging first priority, then battery and finally grid. From March until the beginning of October my grid consumption is minimal, it averages around 0.5 unit per day, November to the end of Feb it rises to around 5-10 units a day but is very weather dependent, We normally manage round a day and a half on battery/solar if the weather is cloudy. In the summer he batteries are normally fully charged by mid morning.

Distributing the peak loads is done as a matter of course, especially in the winter :slight_smile:

The peak load is probably from the hob at around 7.5Kw, but usually much less.

I started with a 5Kw solar inverter/charger, then went to two of them in parallel (both badge engineered Voltronics units) Coupled to 4 x 2.4KW Voltacon Solar llithium iron phosphate batteries.

Throughout there has always been problems with communications between the charger/inverters and the BMS in the batteries, along with endless firmware problems. On the failure of one of the 5Kw units last year I swapped to a Axpert 11Kw Max-E (also a Voltronics unit), running 18 panels in two strings of 9 panels, it was advertised as having a BMS with a setting for Pylontech Batteries, sadly that turned out to be only partially true.

No I donā€™t want to feed back into the grid.

I probably donā€™t need an 11Kw inverter (my grid connection only supplies 40A of single phase) 8Kw is probably enough. I know that matching the inverter size to the demand is important for efficiency, but as sometimes temperatures top 43degrees here I feel that having a large inverter running conservatively will be more reliable than one running at near maximum output?

5

With your daily consumption of 25 kWh, even an 8 kW inverter would only run in the low partial load range most of the time.

Is your house wiring single-phase? How is it connected to the power grid? What regulations apply in your region?

6

Hi @Luthier13

the Axpert 11Kw Max-E is an Hybrid PV Inverter / Battery Charger.

Only Hybrid
There is no direct equivalent at Victron. The Multi RS 6000 is the only hybrid from Victron can deliver 6000W, but cannot be paralleled.

Victron World
In the Victron world you usally connect everything via the 48V-DC-bus.

  • MultiPlus 2 (MP2) to generate AC and to charge battery from grid, generator or AC-PV
  • MPPT/RS to charge battery from PV

Additonal AC-PV-inverters can be connected. MP2 will charge the surplus AC-PV to the battery.

System Design
If you use energy while sun avialble, e.g. air condition, plan AC-PV for those loads. Victron works greate with Fornius AC-PV.
If you want to charge battery, use MPPT/RS for charing.
If you use energy from battery, use MP2.

Air Condition 15kW?!

Does you air condition really use 15kw power (not 15 kWh energy per day)?
If the air condition is not 15kW, but 15kW/day, than I would go with:

  • MP2 6k5 ā†’ 6,5kW at 25C from battery
  • Fronius Primo 4kW for direct usage, e.g. air condition + 500W
  • RS 450/100 5kW PV battery charger

ā†’ Cover the air condtion + 500W by AC-PV and use MPPT/RS for the rest of PV panels.

Victron Fronius
You can combine a Fronius Primo (singel phase) or Fronius Symo (three phase) with Victron MultiPlus 2.
If your want to use the full system offgrid or during grid failue, e.g. loading battery from AC-PV, the AC-PV must be smaller than rated capacity of MP2 (ā€œfactor 1:1 ruleā€)

Single Phase ~15kW

Fronius Primo 6kW + MP2 6k5 ā†’ combined 12,5 kW
Fronius Primo 8kW + MP2 8kVA ā†’ combined 14kW
Fronius Primo 8kW + MP 10k ā†’ combined 16kW

Three Pahse ~15kW
Three phase combinaton aroudn 15 kW max.
Fronius Symo 8kW + 3x MP2 5k ā†’ 18,5 kW

The MP2 5k and 6k5 are certified with their internal relays for most grids. The MP2 8k, 10k and 15k need external relays.

You can combine nearly every AC-PV wiht Victron MP2.

I would plan an air condtatio for the room wiht batteries, MP2 and Fronius.

Further readings:

7

I have a friend with an MPP Solar (similar) inverter and Iā€™ve noticed that if you let the inverter follow what Pylontech wants (CVL 53.2V), itā€™s too much for them and youā€™ll get a lot of high/over voltages and disconnects.
So itā€™s better to forget altogether the idea of communicating with BMS and just set the battery type to User (USE) and then the Bulk (CV) and Floating (FLV) voltages to the same 52.2V.
Donā€™t forget to adapt the Switch to Batt and Switch to Grid voltages accordingly, with the desired max current.
In other words the inverter will be like a ā€œdumbā€ CC/CV charger and the batteriesā€™ BMS will do the rest.
Works flawless for two years now.

8

Hi Tom,

Yes my house is single phase. My workshop was 3 phase, but as I sold all my 3 phase machinery before moving out here, that too is now single phase but is not part of the solar installation that Iā€™m talking about here.

Everything is connected to the grid via the charger/inverter, which is setup to not feed into the grid.

The regs here, until recently have been little more than a joke, a huge contrast to the UK, in the end as a registered electrician I was glad to retire.

Now they require permission to be grid tied although as is typical in Greece although you are not meant to feed back into the grid without permission, unless you have a modern digital smart meter they canā€™t tell :slight_smile: so donā€™t worry being the stance of installers here.

The grid tie deals here at the moment, and that changes almost on a monthly basis, are that you feed into the grid and they issue you with credits for any excess which you can use to ā€œclaimā€ back your electricity when your solar is insufficient, but those credits are only valid for 3 or 4 months, after that youā€™ve effectively donated your excess. There are various grants available and VAT exemption for solar products, depending on the money in the fund, but rather like the UK, the grants are only available if you use a registered installer, and their fees? You guessed it, materials cost plus 15%, the amount of the grant and VAT saved pus 20% to cover the installerā€™s income tax:-)))

When I bought this place I needed an electrical test certificate, a new rule here, this consisted of the local registered electrician turning up, me giving him a schematic wiring diagram of the system and him pressing the test button on the RCD a few times!.

Lights,sockets, A/C are connected to the same breaker, essentially one for each room and the wiring is all in 1.5sq mm!! How there was never a fire I have no idea.

The local transmission engineers are highly competent, but local domestic installers are not so good. Most ā€œprofessionalā€ installations Iā€™ve looked at would be condemned in the UK.

Many of my ex-pat friends have gone completely off grid to avoid any entanglements with the local network provider, which has the added advantage of them paying no local property taxes as all that information is derived from your electricity bill ā€¦

9

Thank you for the information, I wiill read the information in the links that you have provided.

Yes you are right the A/C uses around 15Kwh of electricity per day, on those days where itā€™s over 35Ā° C, the startup load approaches 8Kw, but as the A/C is all the modern inverter type that load soon drops off.

I have used the MPPT calculator which highlighted a problem for me:- 18 PV panels in two strings of 9 (each panel Voc 37.6 v, Impp 12.99A, Isc13.72A, Pmpp 410W) which is more than can be managed by a single MPPT controller, Iā€™ve not looked at somehow paralelling two controllers yet

10

Hi Alex,

Thanks for that, I was getting round to that way of thinking :smiling_face_with_sunglasses: thatā€™s more or less the way itā€™s configured at the moment as any setting other than USE gives a communication error code :grinning_face:.

Itā€™s way too easy to get dragged into thinking that the batteries must communicate with the BMS built into the batteries, whereas as you say better to treat the Inverter/charger as a dumb CC/CV charger than to try to get them to communicateā€¦ā€¦ Hopefully one day weā€™ll have some agreed standards for things like the communication cables, why canā€™t they set up the RJ45s to use a standard ethernet cable? I have a box full of ethernet cables with different wiring connections :grinning_face: as recommended by manufacturers, suppliers and various user groupsā€¦ā€¦..

11

Indeed, but in this case the core problem lies into the voltage supplied by the BMS, that CVL = 53.2V.
Even Victron is ignoring - in a way - what BMS is telling and sets the voltage much lower, to 52.4V.
Iā€™ve seen, through experimentation, that 52.2V is the lowest voltage for which the batteries still reach 100%.
As for the balance, donā€™t worry, it starts at 3.36V per cell - about 50.4V - so it will charge just fine.

Not advertise here against switching to Victron. Do it if you like tinkering and watching things. Iā€™ve done it. :slight_smile:
Just saying that you can also configure it and enjoy the ride with your equipment, which is a solid one (MPP Solar is OEM for Axpert) copied and cloned by a lot of companies (even Western)

12

Paralleling Victron MPPTs and RS is standard.
Easiest way is daisy chaining via CAN bus.
You can also parallel them via Ve.direct. The Cerbo GX (controller) supports 3 ports.

You can put up
To 9 panels per tracker on RS450. It will not saturated the single tracker output current of 80A, but the total of 100A if not east/west.

You can start with 5 panels per tracker on RS 450/100 und put 4 panels on a 4-1 micro grid inverter.

https://mppt.victronenergy.com/#7VZGxCoAwEEN_xaHTEaHXu1NKP8DBr5BS0MWh-P94dXNKpryEeE_2Xzgax2Iai1hIFvbengPT1q9Wz3aPhLJoAaecoQDLmgD1mPpNg3gzzGKQ1c1vL2ViGmRyMvEQegE

Or you go with MPPT 250 with up to 5 panels per string. Each string will provide around 45 A. E.g. with two string, use an MPPT 250/100. Or two strings each 4 panel on a MPPT 250/80.

https://mppt.victronenergy.com/#7VY8xDoAwDAO_wtApMhJJGqqqD2DgFaiqBAtDxf9FysZkT3e272QZfBEuFpeiFsTC3ttzYNr61erZ7kEoayxgyRkRYE0CRMfU7xrUl2FWgyYvv79kxDTM5GbiEfQC

Than add a Fronius Primo PV-Inverter for the other 8-10 panels.

The final design depends on the directions of your strings an shadows.

My Max string length is 2, why I use several 4in1 micro grid inverters in conjunction with my MP2s.