question

Miner avatar image
Miner asked

Seperate multiplus for charging only or some other battery charger?

Possibly an odd scenario but please bear with me....


Multiplus 2 48/5000 charging ~20kw batteries (4xUS5000 pylontech batteries) during specific cheap rate times. Outside of that time, multiplus to use battery storage for whole house use and extra from grid when needed or when run out.

The above is fairly simple, there is also solar (MPPT) but no more than 2kw during summer so unlikely to top up batteries most of the year. There could be a limitation of the cheap tarrif time not being long enough to fully charge the batteries so I am wondering that if there was another multiplus (say 48/3000) or perhaps a battery charger / smart solar charger or something similar (with its own cheap tariff / rate or say a generator - max 10-16amps 230v) could this be added into the mix to charge either at the same time as the original multiplus or on its own schedule? This inverter/charger would be for battery charging only, not providing power for the house or anything else.

Thanks in advance for any recommendations.

Multiplus-II
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Michelle Konzack avatar image Michelle Konzack commented ·
If you configure the 48/3000 as "Charger Only" then there is no problem in the existing system.


You have to be only careful, if you switch the ACin From the Grid to Generator, because you will probably need to limit the ACin current, depending on the GenSet you use.


SInce you should not load a GenSet with more then 2/3 of the rated continious power, a GenSet with 3-4kW continius power would vbe perfect, because then you can use the same settings for the Grid and Generator, sice it will also draw not more energy from the Grid.


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Miner avatar image Miner Michelle Konzack commented ·
Thank you @Michelle Konzack would you recommend the 2nd charger be a multiplus 2 48/3000 over a different charger? e.g. the compact multiplus 48/1200/13 ? Or would the compact one not integrate nicely with the multiplus 2? There is a cerbo GX already available.
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snoobler avatar image snoobler Miner commented ·

You need to select it based on the anticipated needed current. The unit you reference only provides 13A of charging.


No meaningful integration with the Cerbo is permitted unless you run a second identical inverter in parallel.


The VE.Direct inverters can be connected to a Cerbo in addition to the VE.Bus inverter, but it is only visible in the Cerbo device list with limited control - pretty much just setting AC input current and switching the inverter to on/off/charger only mode.





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Miner avatar image Miner snoobler commented ·
Thanks @snoobler theres not a massive need for anything large for this supplimentary charger so I would expect up to 16a max could be available for this charger to take advantage of. This is purely to assist with topping up the batteries if the original multiplus could not do this during the cheap offpeak times and might only be once a week.


My only concern is the 2nd charger needs to be aware of the SOC of the batteries so that it does indeed stop charging if they are full and know if the other multiplus is also charging. This is where I am not sure if I can get away with a multi compact inverters or the multiplus 2 48/3000 or because I already have the 48/5000 then i need to get another of those? (again the 2nd inverter is purely for charging)


Thanks again.


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snoobler avatar image snoobler Miner commented ·

The unit you reference only allows a maximum of 13A. Make sure you don't confuse input amps with output amps. If you have 16A of SOURCE current available, that's 16*230V = 3680W. 3680W/48V = 77A of which the 48/1200 can only supply 13A. If you've already converted it to 16A of output, disregard.


The only two options that can be connected to your Cerbo are:


  1. A second MPII 48/5000 identical to the one you have configured in parallel on the VE.Bus.
  2. A VE.Direct inverter (very limited visibility and functionality only through Cerbo menus).


You can add any inverter/charger or even simply a charger of the desired voltage to the system.


The charger does not need to know SoC. It simply needs to be programmed for the correct absorption voltage.



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Miner avatar image Miner snoobler commented ·

Thanks @snoobler , 16a would be source current but I am not too fussed about the charging rate if im honest. This is more to just use up some available power and to satisfy a requirement to use this power occasionally (or lose the benefit) I could just put a phantom load on this feed or something wasteful but I wanted to try use it for topping up the batteries. This power is meant to be for an EV but thats not going to be available for at least 8 months or more hence me trying to use it.


Another 48/5000 inverter is currently out of my budget which is why i wanted a cheaper one like the 48/3000 or the compacts.

Looking at the VE.Direct inverters i can only see ones which look like they dont charge and are for pulling power from batteries / outputting AC unless I am looking at the wrong products?

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snoobler avatar image snoobler Miner commented ·
Your are correct. I thought some of the MP were VE.Direct capable, but that's only the Phoenix inverters, and they have no charger function, so that eliminates any connection to the Cerbo.


You would need to get a MP or a completely separate 48V charger and program them to the suitable absorption/float voltages.

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Miner avatar image Miner snoobler commented ·

Looks like all the MP are VE bus now. Could a multiplus operate independently without knowledge of the rest of the system as long as it knows the absorption/float voltages of the batteries? and then it can work along side the other inverter/charger?


If not then I'll need to do some more thinking about a possible way to do this.


Thanks for all your help here.

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4 Answers
snoobler avatar image
snoobler answered ·

These are prior answers to this question.

"The charger does not need to know SoC. It simply needs to be programmed for the correct absorption voltage."

"You would need to get a MP or a completely separate 48V charger and program them to the suitable absorption/float voltages."

There is no issue attaching a second MP of a different size with no connection to the Cerbo or the rest of the system (besides the battery) purely for the purposes of charging with AC.

The 48/1200-13 you reference could simply be attached to the battery and then powered via an AC source. Your connection to the battery must pass through any shunt you have installed.

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Miner avatar image Miner commented ·
@snoobler Perfect, that certainly helps with my initial thought process to supplement the charging. Very much appreciate all your time and guidance clarifying things for me.


I just need to decide which inverter charger will be best for efficiencies within my leftover budget.


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jameswest avatar image
jameswest answered ·

Once you've made a decision @Miner do let me know what you went with as I'm in a similar situation. Really don't want another MPII 5000 but need the extra charging using off-peak rates during the winter months.

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Miner avatar image Miner commented ·
Will do
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Michelle Konzack avatar image
Michelle Konzack answered ·

There is an advantage of a dedicated CHARGER vers a MultiPlus:


All Victron and LEAB charger I have ever used can cope with the last crap (Frequency shifting, bad sin wave, voltage fluctuations, ...) of GenSets, while the MultiPlus IS VERY PICKY.


I have a HPG BS3500 (2500W continious power) which does not work at all with ,y MultiPlus-II 24/5000. I use currently only one LEAB ABC2430 and one LEAB LPC2415 to run it smouthly. I can not even attach my second LEAB LPC2415 or even a Invacare 24/8 then the Generator stop working.


If you have not a big system, where you need something in the range of 6-10kW, then you have very bad luck with small cheap Generators

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Miner avatar image
Miner answered ·

Hi all, having thought about this a little more, I am not sure if a secondary charger/inverter directly on the DC side will work when isolated from the GX/bms controller. I think Pylontech require the in built BMS to dictate charging currents etc.. (via the comms to the gx device) so having an inverter not connected to this doing its own thing (even with the float/absorbtion set) wouldnt work, unless I am missunderstanding?


So now my new train of thought is an MPPT charge controller with a 'battery charger' as the pv input. The one im looking at is a variable current charger 5-25~ amp for 48v batteries (i think the charging voltage is 58.4v so should always be above the battery voltage)


Does this sound pheasable? doing this then meants the MPPT is connected to the comms and then can be controlled alltogether. The next consideration is to have a seperate MPPT like the SmartSolar 150/35 deidcated for this charger, or look to utilise the spare input on my 250/100 (as this will never be near max with my pv array). I'm thinking a dedicated one for what the cost is for the 150/35 and along with the cost of the charger all this will be significantly cheaper than any inverter/charger solution.


Thanks again for your thoughts and consideration on this topic.

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Alexandra avatar image Alexandra ♦ commented ·

Make sure the battery charger can handle it's output being shorted. The mppt will do that if it thinks there is a problem with the battery.

You could have one of the inverters in the system switch a really when the system is in bulk charge (that controls the switch state on the extra inverter off/charge). When the system leaves bulk it switches off the absorption can be taken care of by the main system.

Each inverter charges at 50A up to 70A if no derating. In theory the batteries can take 200A do the four together won't kill the batteries.

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Miner avatar image Miner Alexandra ♦ commented ·

Thanks, didnt realise it shorted in certain scenarios I just assumed it would open circuit. But yeah the charger does have Overheating protection. Overcurrent protection. Low voltage protection. Reverse connect protection. Short circuit protection. But perhaps I will test those protections if this is a viable solution.

Yeah your thought process on the relay was something I was considering also but your idea to stop after bulk does seem like a sensible option.

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snoobler avatar image snoobler commented ·

Pylontech doesn't "require" any of what you state. When interfaced with a GX device, it provides voltage and current control limits to the system; however, this is NOT required. The BMS can still engage protection.


ANY charger will work provided it's properly programmed for the battery absorption voltage.


There are literally many thousands of people charging LFP batteries without closed loop communications.


Using a battery charger as an MPPT input is not likely to work reliably. A battery charger expects to see battery voltage before it will operation in most cases. The MPPT does not provide a voltage at its PV inputs. An actual power supply will work.

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Miner avatar image Miner snoobler commented ·

Thanks @snoobler , I was just taking information in from other topics and from victrons own pylontech page (https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom) which seems to state that a GX is needed and to be connected for various reasons which was originally then my reason to look an going the MPPT route. But unless theres a reason not too the MPPT route sounds like a more cost effective route, especially if this allows to save funds for an identical MP for future parallel.

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Alexandra avatar image Alexandra ♦ Miner commented ·
All that is really required is not overamping in charge and definitely not overvoltage charging. But at 51v and 52v that is not possible.
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Miner avatar image Miner Alexandra ♦ commented ·

This is why I think its probably best to let victron and the pylontech BMS handle everything and charge through the MPPT.

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