Charging battery with a wide voltage range using multiplus 2 and Victron mppt vs non Victron mppt

[Nswoffgridinstaller]

Hi

I would like a multiplus 2 with ac coupled solar to charge a battery bank with 65v absorb, 54v float and discharge down to 38 volts.

I would also like a Victron mppt to be dc coupled to do the same charging profile. However the datasheet says that the Victron mppt has a max battery charge voltage range only up to 60v (62 for equalisation at a tiny current).

The easysolar datasheet does reference a 38 to 66v range, does anyone know if the mppt can charge at this rate within the easysolar unit?

Can I get a Victron mppt to charge at absorb 65v? Which model could do this if any?

If I can’t get a Victron mppt has anyone successfully integrated a multiplus 2 with a non-Victron mppt (ie Morningstar genstar with a 72v max and with an optional shunt that I imagine might be able to tell the Victron Cerbo the sum total current being charged from both sources and thus potentially allow the multiplus 2 to manage the multiplus 2 current output to the battery? Will this work?

Sorry for the wordy explanation.

[tstiller]

Hi @Nswoffgridinstaller, welcome to our forum

Which model are you referring to? The “small” SmartSolar chargers can easily be set up past 60V. I personally have a system that charges in Bulk up to 61.5 V. The entire RS line will definitely be limited to 60 V on the DC side, just like the new Multi models 4.5k, 6.5k, and 20k.

[Dominik]

Hello. RS models are limited to 60V as tstiller sayed.

Older 250V variants can charge much higher.

Also i guess when you want to run 18S LifePo4 pack then old Multi is the best choice + SmartSolar 250/100 VE.Can or similar.

But if you need higher voltage on PV string then you may need to consider either AC coupling (Prefered), or you can use smart shunt to measure DC production , Or if you are comfortable with bit of programming you can integrate also some third party MPPTs. I have tried that wit Studer and it worked nicely. But it was just because i upgraded friends PV from Studer to Victron. And MPPTs were already on the wall and connected. In any other way i would recommend to go AC Couple.

[Dominik]

Beauty of Victron is that is is highly customisable and they dont losk it down. They even encourage it. That is why i started working with them and they became my favourite brand quite quickly.

[Nswoffgridinstaller]

Thanks for the welcome @tstiller , I’m super impressed with the swift feedback on the forum! Thanks for the advice

In terms of ideal system components, I’d be aiming for :

Grid: Australian ongrid Single phase 230v 50hz

Inverter: Multiplus 2 15kva 48/15000/200/100 230v

Pv Inverter: Ac coupled solar 8 to 12kw ( Question: do Victron have coms managed control with any third party Pv inverters (ie as selectronic do with fronius and firmer) or do they just use frequency shift? )

Mppt: ideally a solution which allows for 15kw of panels and charges at 65v. I only mentioned the easysolar units because I noticed the listed battery voltage range on the datasheet. I couldn’t see the same 38 to 66v range on the other 250/100 etc mppt datasheets. But scrolling through the net I did see a reference to 69.54v (but can’t find this figure on a Victron datasheet or manual etc). If the 250/100 GX can do 65v then I’d be happy with it. Can you confirm this?

So would two of the MPPT 250/100 GX (are these the same as the ve can options? They do have the ve can port) be the best Victron option that can charge at 65v? I could get 7350w (3 strings of 5 x 490w panels) on each one unit.

I know there are restrictions on the ac coupled frequency controlled Pv inverter size ie 1:1 with the multiplus 2. Are there restrictions on the dc coupled mppt size as well? I’d like to restrict the sum charge of ac coupled and dc coupled pv to 0.25C which would be approx 12kw. I know the potential pv sum total could be much higher then this, but I’m presuming and hoping that the Cerbo will be able to regulate the ac coupled pv current coming from the multiplus 2 into the battery? Would the Cerbo also be able to regulate the current coming into the battery via the 250/100 mppt or would it only be able to control voltage and monitoring?

Thanks @Dominik , I can definitely see the value in using a Studer/ Morningstar/midnite mppt as it would be much easier to run I /2 string/s vs 3/6. But would the Cerbo be able to regulate the Studer Mppt current and voltage or just monitor it? I know I could set up the same absorb, float charging voltage parameters on the Studer and understand that I could use the Victron smart shunt.

Yes the AC coupled pv only will definitely be able to regulate the current to the batteries in a simpler way. I do prefer system design which have both ac and dc coupled pv. I’m not a massive fan of frequency shift. But in this system the benefits of having some ac coupled out way the fallbacks given that the site has some high daytime loads which can be supported in part by the ac coupled PV and I unfortunately cant use the smartsolar 450/200 because the battery charge voltage range doesn’t appear to extend to 65v.

I’m interested in learning some programming for third party MPPTs could you send me a link on how you would recommend doing this? Would programming allow the Cerbo to regulate the studer/morningstar mppt output current and voltage? Is the Cerbo able to regulate the Victron mppt 250/100 output current and voltage?

The last part of the puzzle is the state of charge approximation. The voltage curve on the batteries is very flat and I’d like a maximum 25% DOD and for this to be calibrated by the net discharge amount of kWh rather then voltage. Ie when there is a 15kwh net discharge (35kwh of remaining capacity), calculated by the total capacity eg 50kwh plus the sum charge of all ac and dc coupled pv kwh less the total discharge kWh and less losses) that the generator would start.

There would also be a benefit to stopping the charging slightly earlier based on net charged kwh rather than peak 65v voltage. But I’m not too fused about this.

I appreciate your generous advice. I do like what I’m learning about Victron and am leaning towards using it for other jobs.

[Dominik]

I have one istalation with 250/85 MPPT and highest voltage i can set is 65V. Also checked 250/100 and its the same. So i am affraid that is max. Also be careful with DC MPPTs from Victron if you have geid feed - in enabled. Then it will not throttle charge current and just go full power until absorbtion voltage no mater what BMS or DVCC says. Thats why im most instalations i do i use AC Coupled. That can throttle down the charging but downside is limited chrge current of the Multis (Charger has less power than inverter). I will share some gjthub repos to start with but your mai friends will be keywords Victron, Dbus, MQTT and NodeRed. We have 2AM here right now so i will reach back

in the morning .

[Nswoffgridinstaller]

Thanks @Dominik. Have a good sleep mate!

65v is great! I only need 64v ish so with some voltage drop, a 65v maximum should work well.

Interesting to hear about how the Victron system behaves when the Victron mppts have grid feed-in activated.

The batteries for this particular job can tolerate high absorb currents, but that’s great to know for many other battery systems that require reduced current for different stages of their charge capacity - thanks.

Just to clarify my understanding on your comments for the Victron mppt, If I put:

1 x 250/100 mppt (instead of 2) with a potential charge rate of 6500w (65 x 100) but perhaps I reduce the Pv size from 3 strings of 5 x 490w panels down to 3 strings of 4 panels and a maximum potential of 90a and 5880w.

Plus

1 x 12kw single phase Pv ac coupled inverter with 16kws of panels.

Are you saying that:

A) just the 12kw Pv inverter will be de throttled and that the other Victron mppt will just pass all of its potential power through to inverter/battery terminals. So in the example above I would potentially get an uncontrolled 5.8kw (which in the current system design represents approx 0.1C).

Or

B) neither the 12kw pv inverter or 250/100 mppt would dethrottle because the added dc coupling to the system would also affected the ac coupled inverter regulation as well.

Also, just wanted to ask: Do any third party mppts work to dethrottle the current output when the grid feedin is activated? Ie Morningstar or Studer etc

I did notice the charge rate of 200a max on the 15kva inverter which would charge at a max of close to 13kw - I assume the 1:1 ratio would be based on the maximum charge rate vs the discharge of 15kw, right?

Also, I’m very interested in any feedback from anyone on how to program generator activation based on net kWh discharged versus activation off traditional voltage sensing. Is there anyone that can help me on this? (See my previous post)

[Dominik]

Cerbo will not control any other brand mppts (For obvious reason). But you can program your way around it depends only on your skill and amount of time (or someone elses) you are willing to invest. But i think if you dont have grid feed in enabled then victron mppts are the best choice.

For sizing the MPPT i recommend using victrons MPPT Calculator. Works nicely and i am using it too.

Now to throttling behaviour:

Victron has ability to control AC Coupled solar via SunSpec protocol. (I have tested only SolarEdge).

But regarding to battery when DC grid feed in is enabled: DC MPPT will run full power up to full battery and then start exporting.

AC Coupled solar will throttle only if power going out to grid exceeds max export power.

On AC Coupled it is nice that inverter will regulate the power going from AC to DC side obeying DVCC Limits. No matter if feed in is enabled/disabled.

1:1 Rule applies to VA rating of the inverter ( 15kVA means you can connect up to 15kW ) I have on one instalation 66kW inverter and 60kVa of multis but you need to limit in the settings of the inverter max power to 60kW. So if you get better deal for higher power inverter no problem just need to make sure that you dont exceed 1:1 either via settings or installing less panels . Also rule applies only if connected to AC Out. If you use energy meter and connect to AC In you can use as powerful AC Coupled as you want.

To programming generator : It should be fairly straight forward. You can set it up either to Voltage or SOC. So if you have SmartShunt (Very precise) it will calculate SOC based on energy charged/discharged. So once you SOC is accurate then generator starting will be too. VE Bus SOC can synchronise with Shunt via Cerbo.

Also as i promised useful links :

https://github.com/victronenergy/venus/wiki/dbus#settings

GitHub - mr-manuel/venus-os_dbus-mqtt-solar-charger: This Venus OS driver gets the data from MQTT and...

[Nswoffgridinstaller]

Yes I agree. On pure off grid jobs a Victron mppt is definitely the go.

This particular site has intermittent grid blackouts.

Yes I’ve used frequency shift control on other inverters to enable ac pv coupled dethrottling. (I was told Solaredge dethrottles and then shuts down at 51hz. Is that right?)

Ok understood, the Victron mppt, when on grid, will operate with no dethrottle all the way till the battery is full and then the power export via the multi.

Yes I agree, the ac coupled management of current and voltage to the battery is ideal for ongrid.

Ok got it re 15kva multiplus being able to accept 15kw of ac coupled solar from any inverter size 15kw and over as long as pv inverter power rating is restricted to 15kw or panels are equal or less then 15kw.

Thank you! This is great news re generator start based on soc: “So if you have SmartShunt (Very precise) it will calculate SOC based on energy charged/discharged.”

Thanks for the useful links I had a bit of a browse through. I’ll need to find and learn a structured approach that provides a process of what to do. Do you know if there is a beginners guide as to how to use the link information?

Also, just interested in your opinion on ac vs dc coupling..

I’ve found that on off grid sites where there are large load shifts over the day and if the site’s batteries are near full and there are also random isolated clouds moving around the sky on a sunny day, that the Pv ac coupled power doesn’t get curtailed fast enough via frequency shift for some lithium bms’s liking and that some bms’s will shut down to protect the batteries from over charge due to the excess power from a sudden load drop and or a cloud adding quickly that causes a power generation surge.

Whereas hybrid inverters with dc coupled solar will always dethrottle their power faster. That’s why I was hoping that victron’s mppts would work.

Do the smartsolar 450/200 work with the Cerbo to provide commands (which are followed) to dethrottle the current going into the battery? (I realise that this mppt won’t work for the job I have been describing in this post, but I’d like to know for other jobs that use different batteries ie Pylontech and where I would like to use an on grid setting with the smartsolar 450/200 mppt).

Thanks for the massive help so far mate! You have certainly helped me a great deal and I am now looking forward to giving the system a go with:

1 x 15kw multiplus 2

1 x 15kw pv rated inverter

1 x Cerbo GX

1 x GX touch 50

1 x smartshunt

1 x mppt 250/100 GX and 5880w panels (because the battery is fine with the maximum potential amount of 5880w)

Is there anything else that I’m missing?

[Dominik]

DC Coupled will regulate fastest in theese scenarious because it is regulated based on battery voltage. Problem with AC coupled is that frquency shift can take little time and in that case energy need to go somewhere. And because DC and AC are coupled via Transformer in Multi it is proportional. So if you dont want the AC voltage to raise too much you need to feed the energy to DC. On pylontech it is managed by not charging the battery to full voltage. Also lot of BMSes offer settings to set up requested charge voltage. What i do i usually charge lifepo4 to 3.45V/cell. That will still ensure balancing can happen and also that it will charge fully. And leaves some headroom for AC Coupled solar to throttle.

But i tend to use Pylontech or build my own batteries. (Charging i mentioned above is relevan to my batteries . For pylontech i use settings from manual)

New RS series are awesome from hardware standpoint. But you are limited to 15 or 16s packs and also software leaves something to be desired. It is quite new product and it is not as well understood and known as old ve bus products.

Ofc keep in mind you need substantial DC circuit for 15KVA. Add some fuses and also some means of disconnecting DC.

I also tend to add one lightbulb or resistor to precharge DC circuit because especially with larger systems inrush DC to inverters/chargers/mppts is quite big and makes starting up the system from dark quite dificult or in case of pylontech even impossible.

If you will make it happen please share some pictures i would be happy to see it .

Also if you need help with programming tag me in a post i will try to help .

Also keep in mind that transformer-based inverters require much thicker cabling than high frequency ones of same power.

[Nswoffgridinstaller]

Thanks @Dominik,

I was just looking over my previous post to you and the parts list… just to clarify, would I still use the smartshunt to calibrate net discharge soc (of sum ac and dc coupled solar) for generator activation? Or would the VE Can connection to the Cerbo on the mppt 250/100 provide the mppt current nbers for Cerbo processing?

Also, I’ve install many selectronic systems with a pre charge circuit. That I run from the selectronic sp pro inverter precharge terminal to small 10a inline fuses and a small dc breaker through then to the dc battery bus (or battery bank terminals depending on system size). When you say: “ I also tend to add one lightbulb or resistor to precharge DC circuit because especially with larger systems inrush DC to inverters/ chargers/ mppts is quite big and makes starting up the system from dark quite dificult or in case of pylontech even impossible.” Do you run this precharge circuit from the inverter battery dc terminals? Or is there a specific precharge terminal on the inverter that allows this? And would it be possible to draw the circuit for me which shows the resistor/ light bulb please?

I’ll definitely send you a message with pictures on the final system installed.

Based on my understanding of the conversation so far, am I correct in saying that I’d only need special coding if I sought to integrate a non Victron mppt into the system? My understanding so far is that the key points of complexity are the soc calibration to kWh discharged from battery and allocating an accurate full charge number into the existing fields of the standard Victron settings and the integration of a smart shunt to the Victron 250/100 mppt to allow the Cerbo to collect total sum charge current and that this is also available for me to program on the standard Victron settings..? Are these statements correct? Or does the smartshunt integration require special coding?

Thanks Again

[Dominik]

Depends what you mean by special coding. If you use victron component setup is pretty nice and straight forward via UI. For Multiplus you will need MK3 and victron connect/ ve bus configurator. But that is only for first setup to put it into split-phase. Then you can do setup even remotely via vrm .

Also how do you plan to connect generator ?

Multiplus has only one AC-In so it is either on grid or on generator. Not both as it woul always need reconfiguring. (There was something with using two multis in and usimg one AC in as grid and other as generator but i never tested that.

And smart shunt is very useful to determine accirate SOC. Yes multi and also mppt has its own battery monitor but it is pretty inacurate (DC current on multi is calculated value from AC current). Even the BMS is pretty inaccurate. So if you want your SOC to be precise for more than two days then you need shunt.

Here is difference between JK-BMS and shunt. BMS drifted 25% in 10 days .

This is data that shunt shows. It basically counts Ah . What is most interesting to you is percentage anyway. You do first charge /discharge of the battery to find out real capacity and then you know total energy of the pack. Then you set it as a battery capacity and you have accurate SOC.

And my precharge it is nothing fancy. It is literally just light bulb parallel to the DC disconnect. It saved my butt few times (not victron) when dc side of inverter blew dead short. If i just flip the switch it will make nice fireworks and almost soiled my pants and made backflip. With simple bulb across the main dc switch you forst turn on the bulb and it goes bright for about a second then dims down to nothing . That is good time to turn main DC on. If it stays bright however well i dont want to tell you what to do but you may not want to flip that switch

[Nswoffgridinstaller]

Hahaha! Yes the moment of truth when you turn on a system for the first time usually gets the heart rate up a bit. I’ve experienced the inrush current load noises as well! I’ll definitely start putting a light bulb in parallel. Good suggestion!

Btw in Australia we use single 230v 50hz or three phase 400v, not split phase as in the US.

The new UI looks pretty impressive with its extra detail.

Yes, good pickup. I think I will probably put a transfer switch on the grid input and allow the customer to switch connection to a generator when he is ready to go completely off line, if that’s what he wants to do. Obviously a generator can’t receive Pv export so maybe I’ll need a relay driven changeover switch that’s operated from the Victron touch screen - would that be how you would do it?

You mentioned: “using two multis in and usimg one AC in as grid and other as generator” this sounds interesting I’ll look into this!

Do you have any resistance to using eg two smaller multis verses one larger one? (Other than higher component costs, added wiring and more setup time) I mean are there increasing points of possible failure with integration issues with multiple smaller multis or is there better redundancy in the event that a component needs replacing..? What’s your perspective on this?

Just to clarify is that picture of a smart shunt Victron history record page displaying data of a smart shunt positioned only between the battery and a Victron mppt? Or is it between the battery and the multiplus? If I wanted to get a combined “accurate reading” are you suggesting getting two shunts? Will the shunts be plugged into the Cerbo? And is there a limit to the number of shunts I can connect?

Also is the listed history on your screen shot of reported

“Discharged energy 3069.0kWh” recorded from the sole multiplus?

while is the

“Charged energy 3156.2kWh” is the recorded sum total of the mppt and the multiplus? Right? Or just the multiplus or just the mppt?

[Dominik]

1. Good ! 3-Phases for the win ! We in Slovakia(Central Europe) are also 3-Phase.
2. Settings for generator and grid are different. And require loading new parameters to multi. Not as straight forward. If it is one time change no problem. But if he wants to switch between them some time… You may want to look into quattro. They have 2 AC Ins and are built exactly for this application. But they are quite bit more expensive. On AC In 1 you hook up grid and AC In 2 you connect generator. And if grid is down for too long then it will start up a generator and charge batteries from it.
3. I always suggest to use one big inverter instead of two smaller. Redundancy is not also as beneficial .. Let me explain : You build 3-phase system with 2 units in parallel (6 inverters total). If one of them fails entire system turns off (VE Bus error) same as if one overloads or you turn it off via switch .
4. I use smart shunt only to measure the total going in or out of the battery so it goes Battery > Shunt > DC Bus with multi and MPPTs, Cerbo and everything else. This way you know how much energy is left in battery. Both multi and MPPT have internal counter which is enough i think for informational purposes (VRM or UI). But not precise enough to base energy left in the battery. If you would do a full cycle every day or two it would be fine. If not then it will start to drift pretty fast.
5. Values in screenshot from Shunt are total to and from battery. I have Just Multi and AC Coupled Solar. So all my charge goes thru Multi . When you look into the visualisations in VRM it will make more sense .

Or with DC Mppt + AC Coupled

[Nswoffgridinstaller]

1. I was in Romania last year for a bit. I’d definitely like to spend time in Slovakia one day! Half my family are German. 85% of homes, small businesses and small farms are single phase 230v in Australia.

2. Mmmmm, In Australia the multiplus 2 has 4777.2:2020 Amd 2:2024 cert and cec approval but the Quattro doesn’t. Otherwise yes it would definitely be the go as you explained. But I could potentially put a grid protection relay between the grid and the Quattro grid input and that would, I think, comply. I also saw in a blog that stated two exactly the same model Multiplus 2 with same power ratings and firmware, maybe able to have one connect to the grid and the other connect to a generator and for the cerbo to switch between them.

3. Mmm why do you suggest to use one big inverter instead of two equal size smaller ones that add up to the same total power..?

4. Yes well designed with the battery to smartshunt and then dc bus and then mppt and multi. With this setup are there any reasons why you would still favour ac coupled pv to dc coupled mppt pv? Given the ac coupled frequency shift surge potential.

5. Understood thanks @Dominik

[Dominik]

1. Sure let me know we can grab some coffee I also dream about visiting australia but it is literally oposite side of the world so need to save up for that. And it was actually in my bucket list to be called “Mate” by australian Didnt expect it on solar forum but thanks mate !
2. Okay did not know that. We also use U/F Guards in case inverter is not compliant. But you need to add a contactor to input which counds redundant to me.
3. Because with two smaller ones complexity goes up. You need to make same length runs and hide cables somewhere. Also idle consumption is higher i think. And i struggle to find a benefit. Ofc for bigger instalations it is necessary. U until recently it was not possible to paralell bigger units than 5kVA so i have instalation with 12 units in 3 Phase/Paralell. And it looks pretty neat have to say but it takes lots of space and that is not always possible.
4. I always prefer AC coupled over DC when i am designing an instalation. First reason is not being able to reduce current with DVCC when feed in is enabled, and second is that i increase available AC power (Which is the most important one on most installations i think). Because at my house i have 5kVA multi + 4kW ac soupled Solaredge. And in summer when there is nice day i can easily pull 6-7kW even in offgrid. I have my custom load shedding programmed in Node Red and HomeAssistant so even when shade comes it will throttle or turn off unnecesary appliances like EV charger or water heater and so on. And when sun comes back up everything starts again. Victrons inverters can handle quite a lot of abuse and they hold for long enough time for some kind of regulation come in.

[Nswoffgridinstaller]

1. Sounds good I will if I venture that way Thanks mate. I’ve been to Chek republic and had a past girlfriend that was Slovakian. Haha

2. Yes same in Australia, I would have to use the Quattro (if I wanted a generator backup, the customer is concerned of bush fires so wants this as backup when the grid fails) with the grid relay and contactor.

3. Yes good points. If I needed more then 15kva. I’d still lean towards having two units with the same power and models and firmware. I’d probably over spec it to 2 x 15kva instead of 2x10kva based on your comments.

4. Yes Victron have been around a long time and their price point is competitive with most Chinese brands and have tremendous flexibility.

I like your “load shedding programmed in Node Red and HomeAssistant so even when shade comes it will throttle or turn off unnecesary appliances like EV charger or water heater and so on” I’ll have to look into this! Could you recommend any how i could do this as well?

[Dominik]

Somehow did not get the notification that you replied

But to the point.

This is how i control the EV charger in one of my instalations. Here i focused mainly on Time of use and current limiting due to weak grid . When i pulled too much current one of the phases dropped down too much and EV thought it is a fault and disconnected. So i regulate it in a way that i try to keep all phases over 220V.

You can see the charger riding that voltage - Basically i scale it 220-225V to 8-16A.

And this is how i manage the EV charging on the other instalation. There is different goal - To be as much offgrid as possible (old Multi ESS is kinda slow so it takes a while to balance loads so some overflows to the grid always happen). So i have programmed basically 3 modes - All modes have load shedding so no matter what i set up in manual (you can see 16A in the screen) It will allow to charge only with current available from multis. I have setting of maximum current from Multi (18A works well for my application) and it basically tries to control it to not go over. If available current is under 6A (min setting on wallbox) then it stops charging. And resumes after there is power available and timeout has passed. I am kind of proud of it as i have few other instalations with original victron EVSE and they work not as good i would say.

I have made 3 modes (more like hijacked victrons modes)

Auto - Use full power of inverters + AC Coupled solar and also stop charging under certain SOC

Manual - You can limit current manually but still protects inverters from overload. (It can lower current but your set current is a higher limit)

Schedule - I made this as Solar Only mode - So charge with all available solar power AC+DC. If not enough solar then stop charging.

Also made an dashboard to monitor the inverters and calculate some parameters - for example min/max values for current day or to count overloads to be able to tune parameters of control loop.

(Dont mind minimum battery voltage i was loading assistants today and had to restart it so it showed 1V for a moment) But you can see that even 5kVA inverters can hold much more for significant amount of time. This is basically nothing for them already.