MULTIPLUS II Charging Limitation

Q&A and troubleshooting
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1

Well First Day :slight_smile: with my now working system and lots more issues and questions

I have got the Octopus GO tariff 5 hours of cheap energy 8.5p per kWh

I have four US 5000 batteries {probably going to add a fifth one soon}

BUT my Multiplus II

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can only charge my batteries at a maximum rate of 70A

SO looking for the cheapest {and most sensible way} of upping this to fully charge my batteries if they are heavily discharged say down at 20%

One option is to put in a EV Smart Charger then I can change my tariff to Octopus Intelligent GO
That does two/three things

  1. I get SIX hours of cheap energy. one more than the FIVE the GO tariff and it starts an hour earlier
  2. It is 1.5p per kWh cheaper
  3. I can get cheap (during the day) energy to charge my car {I am told on a YTV that people have been gaming the OIG tariff and NOW octopus are limiting charging your car to a maximum of Six hours
  4. YTV’s https://www.youtube.com/watch?v=TSoBVFDR1mA https://www.youtube.com/watch?v=8ye7-HYe2OA

So what are the other VE options ??? Change my Multiplus II to a version that has greater charging capacity? Add another 48/5000/70 inverter? OR WHAT???

2

Four US5000 batteries (4.8kWh each) need 15.4kWh to get them from 20% SoC to 15% SoC, at 70A (3.4kW) that would take about 4.5 hours, which is less than your 5/6 hours on the cheap tariff – so what’s the reason for faster charging?

(but note that the MP II won’t necessarily sustain 70A for long periods of time, current is likely to drop off as it heats up – my Quattro 48/10000 is rated at 140A but it never manages that, and drops to 100A or even lower after several hours)

Your cheapest option would be to add another identical MP II 48/5000/70. Or you could sell that and replace it with something bigger/newer, depending on how much current you want – the new MP II 48/6k5 is rated at 100A and drops off less when hot, and can be paralleled up if you want even more current. The 48/10000 is rated at 140A (same as two 48/5000). Or there’s now a brand new huge one (Multiplus-CL 48/20000) with 250A charging current… :wink:

3

This is ONLY DAY ONE of this BSS

I did not understand the figures in your reply :frowning:

Also I need a fifth US5000 to handle my house loads even a sixth one would give me some headroom

Tonight I expect my batteries to be at 20% SOC before 00:30 when the charging starts, so tomorrow after 5 hours charging without my EV being charged I will know what the situation is at 05:30 {guess I have an early start} I may wake up at 03:00 to check charging rates ETC

Having found some issues with the figures that VRM reports I will just look at the remote console

4

I guess that a simple battery charger would be much cheaper. You can find a 48V/20A LFP charger for less than 150 €.

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5

BUT how do I set up a charge timer can the Multiplus II and the CERBO GX control these?

Just a thought, I think the CERBO GX can time MPPT SOLAR CONTROLLERS so maybe I can have two solar controllers {OR Wire the chargers in series with one MPPT Solar Controller} taking the energy from two of these 48V chargers and charging the batteries when Octopus is doing its Octopus Go cheap rate electricity

I have enough space for another MP2 48 5000 70 and as i have two Lynx Distributors it would be easy to slip in another 200A fuse in one of the slots. The A/C side will need another isolator {I do have a spare one) and of course I need my electrician to do the A/C wiring. Finding a nice cheap MP2 inverter close by or with someone who want to ship it to me might be a problem.

SO MAYBE the sensible answer is to put in a Smart EV charger and then change my tariff to Octopus Intelligent GO as this will do three things start charging the batteries an hour earlier and charge them for an extra hour six hours instead of five and charge them much faster than the granny charger can. This is probably the sensible long term solution as I have a 40kWh battery to put in the Leaf {once the weather improves and my vehicle engineer is available}so the Leaf will be getting used a lot more as the range will be both sensible and useful.

I think the batteries are going to be at 20% SOC well before midnight :roll_eyes:

Tomorrow I will have more info regarding the overnight charging :wink:

WATCH THIS SPACE

6

Indeed, but 20A doesn’t add much to 70A – and how do you control it automatically together with the MP II so they go on/off together?

7

So why don’t you buy 5 of them?

The MP2 can control a relay that can turn the chargers on and off. With a Victron SmartShunt you can get info of the charge amps into VenusOS.

8

i use a Huawei R4950G2 to support my MP” while charging

You will find many projects on this together with venus

Control could be done by some Node Red scripts

Be aware - these cheap chargers as you showed - 48V is not enough for LiFEPo4 - something like 55V are needed

9

“48V” does not tell the real voltage but the “voltage class” of the battery. The MPII even has the “48V” in it’s name, and of course it can work with a 16s LFP battery which has a nominal voltage of 51.2V and a maximum of 58.4V.

10

Hi Tom, the OP has Pylontech batteries which are 15s. What external charger output voltages will work with them?

When using additional external chargers alongside the MP2 charger, is it necessary to match the DC voltages from the various sources, or do they all just equalise naturally by themselves?

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11

Hi David. I have more-or-less the same setup. I have the 48/5000/70 MP2 and 7 off US3000 pylons (these are the heaviest I can lift :slight_smile: On Octopus Go I can get about 65% SoC increase in the 5 off-peak hours. This is just about enough for me and I’m researching ways to increase the charge speed to support larger battery banks like ours in Winter when daytime PV recharging is so limited.
One option is the 48/10000/140 but my DNO is hesitant about authorising that. But those plug-in 2kW DC rectifiers are not notifiable and can be run in conjunction with the “Peak Shaving” settings in your GX device to prevent stressing your main grid fuse. What value is your main fuse?
But as I asked above, I haven’t learned what rules apply for setting the DC voltages of external chargers.

12

I would have to google for these just as you.

They can’t equalize by themselves, unless their charging voltage limits can be set by the user. When you have a source which delivers a fixed voltage of 54V then this can’t adjust itself to 55.2V (which I have set as the limit for my 16s battery). And when the charger has a unchangeable max charge voltage of 58.4V then it will continue charging when all other sources with i.e. 55.2V since long have stopped charging.

13

Thanks Tom,

I understand all of that, but it’s not quite where I’m stuck. The scenario is MP2 and an external charger both charging simultaneously.
When the battery is at a low SoC (say 20% for example) Then VRM will report its voltage as, say 49 volts.
At that instant, is it OK for your external charger source to be fixed at say 53V when the MP2 charger may be at some different output voltage (perhaps lower than the external charger by a couple of volts)
Correspondingly, if the external charger is set to, say, 53V what will happen ? I can imagine that at low SoC the external charger delivers its full output but then as the battery SoC rises to the point where battery voltage equals 53V, the external charger stops contributing charge and the MP2 charger continues and completes the charge unaided.
Is this what happens? (Or, unless I switch it off does current flow into the external charger in some way and cause a nuisance).
Thanks for your help!

14

When both can adjust their charging voltage according to the needs of your battery then there is no problem with having them both parallel on your battery, as long as all chargers together don’t exceed the maximal charging current (for LFP batteries mostly 0.5C).

The chargers usually are not connected to the BMS and therefore they don’t know anything about the SOC (which anyhow mostly is wrong). They know the voltage, and they dont need to know more.

Have you ever charged the lead battery in your car with a external charging device? There is absolutely no problem to have 2 or 3 chargers parallel on the battery, as long as the maximal charging current is not exceeded.

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15

Do yourself a favour, sell the 5kVA and replace it with a 10kVA.
You will be able to run more in your property as well, derating will be less of an issue.
Adding more stuff and complexity that does not natively integrate into the ecosystem, as a beginner, is a great way to end up with problems.

Just keep it simple (and supported).

16

My understanding is Victron will at some point release a 48V standalone charger (ip43?). That will presumably communicate via ve.direct with a cerbo or venus os.

Other option is a rectifier, something like an ecoworthy 60A, or eg4 chargeverter (100A), or you can brew up your own with some telecom rectifier units. Anything with a rectifier tends to be annoyingly loud however due to the small fast spinning fans.

My dream charger is one or more mean well HEP 2300W power supplies. Completely passively cooled operation and silent, but you pay for that. Also takes a good bit of wall space.

17

I can see the advantages of that solution and I have an application in with my DNO to do that. However…

What I’m picking up from some of the advice here and in other threads is

  1. Multiple fixed voltage DC sources can be connected and don’t have to be exactly the same voltage as each other, just be lower than the max charge voltage of the battery.
  2. Keep the available charge power to the battery below 0.5C

But I may be misinterpreting this sentence…

@TomBerger Do you mean that the external chargers need to be capable of varying their output voltage as the charge progresses? ie. they need to be battery chargers rather than fixed voltage rectifiers? Or perhaps you mean that a fixed voltage source just has to be set up to be appropriate for the max voltage of the battery.

Thanks for giving detail on this :slight_smile:

18

As stated " There is absolutely no problem to have 2 or 3 chargers parallel on the battery, as long as the maximal charging current is not exceeded."

All chargers connected in parallel will simply charge to there set voltages , irrelevant if they are different or the same.
Only communication between them will change this.

19

Increasing cooling may decrease charging derating, potentially increasing continued high charging current.
But as others have said, get bigger suitable sized equipment.

20

WOW thanks for all that input

VERY SADLY no one addressed my using MPPT controllers and faking solar energy with these 48V 35A chargers

SO some hard data. My daily house use in somewhere between 22kWh and 25kWh and I knew this first go at a BSS was going to be undersized so none of this is a surprise really. Some things are a BIG SURPRISE the VRM display data not correlating to the Console data. THAT I find somewhat annoying and confusing.

BUT ONWARD

System Update
Everything seems to be working well but with a few issues
Two bits of Victron software for system monitoring management and maintenance are not in agreement. Displaying the data on the console that is attached to the system with an HDMI cable seems to be telling the truth. However using the online VRM tool I get totally different information and data
I can use the VRM and look at a remote console and again the remote console seems accurate but when I flip back to the basic configuration page, the data is not identical or correct and the little blue trains that indicate current flow on the VRM display there are NONE on the PV Inverter YET show on the console display see videos below and there you can also see the mismatch of the Grid energy (Even though there is NOTHING going to the Grid)

Then I knew that the batteries were undersized for my house loads (typically 22/25kWh per day) I have nominally 20kWh but with a discharge to 20% only 16kWh even if I discharge to 10% 18kWh even at the Pylonyech allowed 95% discharge rate I have only 19.2 kWh of battery capacity.

Today I changed the 20% to 10% and we will see what happens tonight

Yesterday my batteries hit the 20% mark at 22:00 (10PM)

And this morning at 05:30 (5;30AM) when my cheap energy ends and the MP2 charging schedule also ends the batteries were at 99% SOC

THEN the multiplus II model I have has a 70A charger output (nominally) but won’t maintain 70A for long certainly not five or six hours (I am told) (I am not going to get up at 03:00 halfway through my 5 hour charging period to see what the charge rate the MP2 is outputting)

So what I have is a nice system that is actually too small to handle my house loads (needs more batteries) and an inverter charger that cannot fully charge my batteries in the cheap energy five hour time limit and when I increase my battery capacity that problem is going to be worse.

One fix is change the inverter for a more powerful version OR double up inverters and run them in parallel with one master and the other a slave OR find another way of charging my batteries during the cheap energy times PLUS of course adding at least one US5000 battery or maybe even two more PHEW

But adding a smart EV car charger will give me cheaper energy 1.5 p cheaper, during the low cost time AND give me six hours instead of five to charge the batteries BUT only when I change tariffs to the intelligent GO tariff which does require a smart EV car charger.

SO I think this is the first upgrade to the BSS (give it SIX hours of cheap electricity) and then see how much energy my inverter charger can return to the batteries plus (maybe) add one more US 5000 battery, there is just’ room in that cabinet for one more US5000 battery.

Also with dynamic ESS I think when Octopus do cheap energy rates during the day the MP2 will {somehow} know that and will start to charge my batteries