The data sheet (and model name) is pretty clear – maximum battery charging current is 70A at “up to 25C ambient” (footnote) – at Vbatt=53V this is 3.7kW.
The derating table shown above is rather better hidden, this suggests the following derating for charging:
25C : 3.7kW (100%)
30C : 3.5kW (95%)
35C : 3.3kW (88%)
40C : 3.0kW (80%)
50C : 2.3kW (62%)
I would assume that this is the ambient air temperature at the cooling fan input, since this is the only thing the user can see or have any control of – internal temperatures are not visible.
However I actually have a RuuviTag temperature sensor placed right there, and I see considerably worse derating than this with my Quattro…
I also note the new 6k5 model is much better when hot, only derates to 95% at 40C… (100A to 95A)
If you’re correct I would call that sneaky at best, and just plain deception at worst…
What is a number like that supposed to mean other than continuous, if it doesn’t specify any time limit? You’re not going to just charge a battery for a few minutes, are you?
The AC numbers for output are continuous, why should the battery charging current be anything else?
I’m annoyed about this, because when the system was being specified a big enough generator (9kVA) was deliberately chosen to be able to keep up with Quattro 48/10000/140 battery charging at 140A (35kWh LFP battery bank). and together with a system power audit this gave a prediction for generator running time required.
But it turns out that generator hours are more than 40% longer than expected – actually, I’ve seen charging current drop below 100A after several hours, so closer to +50%…
And that’s having added external fans triggered by the fan monitor to blow cool air into the Quattro and suck hot air out.
Funny, it just looks to me like the data sheet is being “economical with the truth”…
How else are users supposed to know what performance to expect, other than by reading the data sheet?
(yes I read it carefully including all the application notes, so I was expecting a small drop-off in charging current – but nothing like as big as I found)
Also note that one of the quoted advantages of the 6k5 is “better high-temperature performance”, and as well as the AC output (which is considerably better) they quote derating for the charging current for the first time – and it’s only 100A to 95A at 40C (5% drop), compared to 20% in the table given above.
That says to me that Victron are perfectly aware of this weakness in the older models, because the newer ones are much better and they make a point of this – without actually saying out loud “the old ones are bad for this, tough luck if you bought one”, the implication is pretty clear…
(not to mention the fact that the real-world derating seems to be considerably worse than even the table quoted above)
I have worked in the electronics industry for more than 40 years, and this is not what I would expect from a reputable supplier like Victron.
As does mine, even for inverting.
But, since I don’t believe anyone should size a system to operate at 100% for anything other than short periods, I had designed my setups to be with 70% of the max ratings.
As a warm weather region where ambient is regularly above 30C and at 5000ft (ISA plus 25C), that is prudent and my systems have not let me down.
I wouldn’t plan to run an audio amplifier at 100%, it would be nasty, power electronics aren’t much different.
At sea-level, in Norway, I might do it differently
New end-users and self installers could also ask themself if they know what they are doing and/or ask people with a lot more experience for advice. It’s free and prevents people from running into issues like this.
That being said. Perhaps it is time to sell the Multiplus II and get a new 6K5 Or keep the Multiplus you have now and get a second one. Or just accept the limitations and install additional fans at the bottom. Whatever you do keep it blue
Sorry Nick, but I think you’re making excuses for Victron here. If the data sheet says “continuous output power at xx deg C = yyyy W” then the unit should damn well be able to produce that, no ifs or buts, and sustain this for at least for several hours.
I agree that it would be unwise to design a system do sustain this 24/7/365 for lifetime/reliability reasons but that’s not what we’re talking about here – generating full power for several hours continuous running (but not every day all year) is perfectly normal operation for a generator or a charger/inverter.
If it was aimed at me – thanks for the condescending advice…
(experience still doesn’t make up for the fact that the units don’t do what their data sheets say though, does it?)
This wasn’t a self-install system, it was done by a boatbuilder with experience of these systems – and he did warn me that the Quattro was unlikely to maintain the specified power for long periods, because they don’t even do that on the bench. However the sheer size of the current drop-off – even with the added fans – was still a nasty surprise…
There isn’t enough space to replace the Quattro 48/10000/140 with two of the newer units, and they’re too tall anyway – otherwise I would…
No. It wasn’t. Note that I mentioned replacing his Multiplus II or adding one. It certainly also nothing personal, but it is good advice in general. Isn’t it?
Now. To me personally this is like installing a MCB, RCD or RCBO. I need to install one with at least 20% headroom. Sometimes even more, due to higher temperatures. And lord do I know high temperatures in shipping. Which is where my interest in Victron started at the age of 15. I was that kid who installed batteries in cramped places during my summer holidays Anyway. Cooling might be another option. That’s also what happens on ships…and at my place at home. My AC does what it needs to do, but I get it. That is perhaps too much on a smaller boat. In that case it’s ventilation what you need. Like you don’t already know
@akc Below is a snapshot of a 6 year old Multiplus-II showing prolonged charging at close to 7OA and that being off-grid from a generator. The customer has always pushed the system to its limits. Fair to say you may have an internal temp sensor issue which should be investigated. Once resolved, search for the diy fans which I personally were astonished to see the huge difference it can make. Also worth opening it up and doing a visual inspection for possible obstructions.
I’m not disagreeing that for long-term usage it’s not wise to run things like generators or charger/inverters all the time at their continuous rating, this is good practice and well understood – something like 80% is the usual recommendation for high-duty-cycle use.
However running for a few hours per day (and not 365 days a year) is a very different case, and ought to be supported by anything which has a continuous rating in its data sheet – like the Quattro or Multiplus. If I want to charge my 700Ah battery bank up from 20% to 100% (maybe every few days?) this should take 4hrs at 140A, this is not an abnormal or unusual requirement for running a generator or charging a battery.
I have measured the temperature at the Quattro 48/10000/140 fan air inlet – which surely by definition is the “temperature” referred to in the data sheet, what else could it mean? – and it doesn’t get much above 30C, which according to the Victron derating table should drop the charging current by around 10% – but actually it drops by about 30%. That’s with external cooling fans pushing cool air into the electrics cabinet from outside the boat and pulling hot air out from the top of the cabinet where the Quattro hot air exits, so it’s difficult to see how this could be improved.
That looks to me as if it’s not meeting specification — and talking to my boatbuilder this behaviour is not unusual, “they all do it”.
So being blunt, I fail to see why it seems I’m being blamed for designing the system wrongly when this use case is perfectly normal, and Victron are not even though it seems clear that the Quattro is not doing what the data sheet and Victron supplemental information says it should be doing – and that this isn’t a one-off faulty unit, it’s “normal” behaviour…
P.S. I’m a big fan of both Victron and the kit they build which is generally excellent, as is the support – but in this case I think they have fallen below their usual high standards.
First and foremost. Nobody could possibly blame you for anything. That’s not how this community normally operates. With some exceptions perhaps, but yeah. What else is new, right. Ok. I checked with a couple of boating folks and asked them what to they see. Huge difference between summer and winter time, duh. Who would have guessed.
What I can tell. From my own personal experience, is that the efficiency drops with high(er) loads. To me nothing new, and that is why I keep it running cool and don’t usually go overboard with my loads. Don’t own/have a chiller running myself, but professionally, that is the first thing that we install.
I know that efficiency falls off with higher loads, both from my own measurements and the Victron data. That’s expected, it happens with most power circuits, including generators (peak efficiency is usually at around 75%-80% load). But we’re talking about efficiency drops of maybe 5% or so – and anyway for a charger that should mean the input power goes up and it gets hotter, but the rated output current doesn’t – or at least, it should only fall off by the specified amount, which should be about 10% here according to Victron’s “charger current derating” table.
The problem is that it doesn’t, it drops by typically 30% or so in summer (30C-35C air inlet temperature) not 10% (actually the lowest figure I saw was only about 90A after a few hours running which was a 35% drop). I measured it again in October (air inlet temperature 20-25C) and it still dropped back to around 100A (30% drop) – so yes, a small difference between winter and summer, the current derating went from pretty bad to even badder…
(and incidentally, even when turned on from cold I’ve never once seen 140A into the batteries, it’s rare to see more than just over 130A – boatbuilder’s commenst was “yeah, that’s normal – you probably won’t get much more than 100A after a couple of hours”…)
P.S. Before anyone suggests it might be the BMS or cells – this uses REC-BMS (no MOSFETs) and 700Ah Winston cells, and is perfectly happy putting out 400A with the motor (series hybrid) and cooker both running flat out…
P.P.S. Same for generator, that will happily put out the full 9kW specified (e.g. with loads above), and I’ve never seen it close to this when charging – 130A is about 6.9kW into the batteries or 7.7kW from the generator. And yes, those charging losses (I measure about 11%) are also bigger than the specification…
@ejrossouw Thanks for this screen, it made me realized that there were older graphs on the VRM and that the current behaviour (at least at charging) is somewhat recent
Once support finishes with diagnostics regarding hightemp alerts during discharge will go back and recheck/redo all configs/wirings. Derating started roughly when I added a second battery to the stack by the look of it, so will need to check if its a hardware/software issue.
We have a small MP 2000 that runs about 6 hours per day at max capacity. At 1300m elevation and 30 degrees outside air temperature, I do expect some derating. I Just looked at the numbers and its 80-85% derated from its max continues capacity of 1600W. The MP II gets to 49 degrees C at the top of the unit on a 30 degree C day. It’s been doing this for about 11 months now. Have not seen any deterioration.
I would expect a MPII 5000 to do something similar. It should maintain between 3.2 and 3.4 kW output power continuously. At least for 6 hours.
Could it be the BMS and the comms between your 2 batteries somehow decide to limit the input current?
Doesn’t look like it. I have reverted now to the previous situation (completely removed wiring linking second battery, removed aggregate battery and using only dbus-serial-battery), so basically back to how it was when I was getting 4kw stable, and it still drops the connection down after 3-4 min or so. Will see what happens tonight when the battery discharges a bit, but I am not holding my breath too much.
Confirmed by editing the driver (setting logging debug points on every instruction which variates CCL) that it is not changing it. Looks more and more likely that Multiplus decides by itself to do so due to some internal (hidden) calculations.
Given that not all of people are seeing such a massive drop (of approx 30%) I am inclined to believe that there might be a common issue with either a therm sensor or maybe a heatsink detaching slightly.
Hopefully my warranty case will proceed smoothly, maybe it will help others.
@akc One of the first question in fault fing should be “what has changed” Hope it puts you on the right track for an easy solutions like possibly a wrong battery profile.
Anyway. Cooling might be another option. That’s also what happens on ships…and at my place at home. My AC does what it needs to do, but I get it. That is perhaps too much on a smaller boat. In that case it’s ventilation what you need. Like you don’t already know 
