Multi RS 48/6000/100 450/100 max array on a single mppt tracker

Inverters Victron
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Hi there ET forum people! :slight_smile:

The Victron Multi RS is new on the market so I’m not sure who out there has some hands on experience with it at this stage.

I read in the manual that it can handle 2x panel strings however each string should be limited to 3000W.

Maximum DC solar charging power - 6000 W total - 3000 W per tracker

I was hoping to run all my panels 8x CS545 on a single string, so as to be able to reuse my existing SPD, that would be 4360W ( 8x 545W) max, and I don’t have a problem with it clipping the power to 3000W, since beyond that, my battery capacity starts to be the limiting factor in the daily sun harvest.

  1. I would just like to know if that is a hard “inverter/mppt breaking” limit, or if it will just clip anything over 3000W?

  2. There is also the limitation of not exceeding 8x battery float voltage, so conservatively speaking on a 15 cell pack, that would be ~ 51.5V * 8 = 412V
    STC Voc per panel is 49.4V. so that would be (8x 49.4V) = 395.2V, which seems to me like it should be ok?

  3. Finally “The maximum operational input current for each tracker is 13 A.”
    With the CS545 at STC we have Imp 13.14 A and Isc 13.95 A (NMOT Imp is 10.52 A and Isc 11.25 A)

Personally on my existing setup, I have blown 30A fuses on my SPD on multiple occasions, running a 4s2p configuration, meaning at STC I’m supposed to have max 27.9A? (2x 13.95 A STC Isc?), yet somehow due to cloud bursts or who knows, I’m occasionally reaching 30A? (This is now, in summer conditions, in the WC)

Should this 13 A number, be a concern for me when considering this unit? or will the tracker limit the current to 13A to protect itself if required?
This is the "Maximum operational PV input current limit 13 A, as opposed to the “Max. PV short circuit current 16 A”

(I would like to be running a 8s1p configuration on a single tracker, ideally)

Thank you

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Extra information gathered in the meantime:

Multi RS 48/6000 tech specs

From the victron community post, it seems like having an oversized array on a single tracker might be ok, but one will at most be able to draw 3000W per tracker, is what I am deducing?
https://community.victronenergy.com/questions/167994/amount-of-solar-for-multi-rs-solar.html

Based on the victron mppt calculator though, it looks like my battery float voltage of ~51.5V might be the limiter in my case, so I may need to reduce a single string to 7s1p or 6s1p to stay under 8x51.5V limit under various temperature and weather conditions.

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The MPPT will limit the current (Amps) and you normally can oversize a bit on current. The extra will by clamped to the limit.
But you can never go over the voltage limit.

Power (Watts) are the voltage times the current (P = V x I).
The current limit of the MPPT is not on the PV side, but the battery side. So the battery voltage times the max current will give you your max power output. This also means that if your battey is empty (and have lower voltage) you will get a bit less power than when the battery is full (and the voltage is higher).

A 15 cell battery with 51.5V max voltage can go to about 42V when empty.

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Very interesting, thank you for the response!

I understand you can never go over the mppt input voltage limit. With regards to the current limit, I have never pushed my existing mppt (250/70) to its input current limit, so while I hear and read on forums that PV input current will be limited by the system/mppt in theory, I have not hands on tested it myself and I do then wonder why publish current limits in the first place on the input (PV side), if the mppt just clips/limits what it or the system cannot handle, then why have these limits, unless for completeness or perhaps there is another reason?

I have on my existing setup, experienced to what I suspect to be 15A currents from pv input on panels with STC spec that specifies 14A (or 13.95A). (I assume this from several 30A fuses blowing on a 2p4s setup usually during peak 12pm-2pm summer hours)

With regards to the the Multi RS if it states
Maximum operational PV input current limit 13 A
Max. PV short circuit current 16 A
With my panels pushing 15A operationally at times, I was just wondering if that should be a concern?

Could you hypothetically throw 30A-40A input PV current at such a system or more? I understand MC4 connectors have a limit of 30A, but if that limitation was not there would the Multi RS’s mppt just clip what it does not need/cannot handle/use? based on other conditions of the system, ie, battery level or its max transfer capacity or something else etc (I dont plan to do this, but I want to understand if its possible in theory)

So lets make this realistic, could you throw 28A PV input current at one of the Multi RS trackers and be ok, given that other aspects of the system could withstand it? ie. you kept input voltage under spec by 20% and not exceed your batt float V by 8x, your inverter/battery/cables/fuses can handle the charging current and everything else that goes with that.

My battery imposed limit should theoretically be 52.4V since it is a PACE based bms, and masquerading as Pylontech, and so Victron will hard limit it to 52.4V charging in software as part of what @plonkster mentioned somewhere in some thread. In the battery specs it states max 54V operating voltage range with a bms over-voltage cut off at 55V (and bulk charge voltage can be 54V) but with a Victron system I understand that condition will likely never be met ever. I limit the charge voltage on the DVCC at times to the 51.5V - 52.4V range for other reasons (experimenting with the high voltage alarms that I get from the PACE/pylontech bms while in balancing)

Power (Watts) are the voltage times the current (P = V x I).
The current limit of the MPPT is not on the PV side, but the battery side. So the battery voltage times the max current will give you your max power output. This also means that if your battey is empty (and have lower voltage) you will get a bit less power than when the battery is full (and the voltage is higher).
A 15 cell battery with 51.5V max voltage can go to about 42V when empty.

This is good info, thank you!

5

^ Victron MPPT calculator result seems to think I will be ok with a 7s1p config, with a 52.4 float voltage. A 8s1p would work if temperatures never dropped below 0 degrees celcius, but we know we should not tempt fate this way :smile:

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One thing I learned over the years from other clever people here, having run into that issue myself, is the lower the DC voltage of the system, like 15-cell versus 16-cell battery, small battery bank vs big one, the lower the production from the MPPT/panels, due to the lower voltages/amps one can use optimally.

One caters for that, no problem, so it is not an issue at all(!), just a titbit I thought to share.

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One thing I learned over the years from other clever people here, having run into that issue myself, is the lower the DC voltage of the system, like 15-cell versus 16-cell battery, small battery bank vs big one, the lower the production from the MPPT/panels, due to the lower voltages/amps one can use optimally.
One caters for that, no problem, so it is not an issue at all(!), just a titbit I thought to share.

Yeah, you can’t always fix your first child in post production, but you can maybe reuse some of the existing body parts for the next one! :laughing:

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@Louisvdw revisiting this point, and assuming for a moment that the battery charger is not the limiting factor here.

If there is a 3000w per tracker limit on the MultiRS can it be inferred that (if you keep below the max input voltage (450V) and under 8x your battery float voltage) and since minimum number of PV volts is 120V for startup, we have:

3000W/120V = 25A

Could one assume that if you had some super panel (or a similar power input source with these kind of characteristics) that gave you 120V and 25A input on the PV side that the multiRS tracker could handle that?

or 3000W/148.8V (that could be 3 of my CS545w panels VOC STC) = 20.2A input PV current

Then why even specify this in the manual?
Maximum operational PV input current limit 13 A
Max. PV short circuit current 16 A

3000W/48V = max battery charging current of 62.5A. That seems like a within sanity charging current for these kind of systems, so that seems like a reasonable scenario?

Thank you!

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@VicB7 it is always better to stick to the spesification limits that the device has. This keeps it within opperating limits so that the manufacturer is confident that their device can work and give you a decent lifetime.
If you go over outside these spesifications the device could still work but they will not have to hold the warrantee and your device might not have the same lifespan.

With that being said you can push some limits a bit. Voltage should always be within your limits. You can push the limits on the current a bit to give you a bit more power. The excess energy still need to go somewhere. To keep it simple lets just say that one of the ways to handle the extra energy is to get it converted to heat, and heated components are not the best for devices. The reason we add a bit PV power is to have more available for rainy days or in winter. The extra power will be clamped in summer when there is more sun.

To convert this to your RS question. It has 3000W available per tracker. It can handle max opperating current of 13A which it could get at 231V (3000W / 13A). Or if your PV string gives you 11A then it would reach 3000W at 272V.
These values it might only reach in full sun. Early in the morning as the sun rises your PV panels will not have enough energy yet and the panels will not give any output. As the sun rays angle and intensity improves your PV will start to produce.
The MPPT tracker needs at least 120V before it will activate and then the current would still not be much (lets assume 1A). So it will start producing 120W of power. The PV voltage actually moves to it’s operating votage quite fast in the mornings when it gets sun, but the current will move much slower up to when the sun is at around 90 degrees to your panels. In all of this the MPPT neetds to tray and reach the best energy draw from the panels to not let the votage drop. This is the optimum power point which is what the MPPT is looking for (Max Power Point Tracker).

So the 120V is not something you spec your system on. It is to indicate the bare minimum it will work on.

Up to now this is all on the PV side of things. But the PV needs to be converted to your 220V AC (for appliance usage) and also to your battery 48V DC (charging the battery). If your system produce 3000W from the PV and there is a 2000W AC appliance running then there is 1000W available to charge the battery. This will change as the PV change, the appliance usage change and the battery level change. You could also charge the battery from PV and from the utilities. That is the 100A charge limit you see.

1 Like
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Here is an example from my system (not a RS but the MPPT and strings work in the same way.
The first graph is the power ramp up this morning in watts (P), and the second graph is the voltage (V) and current (I). As P=V x I you can see the current slowly moving up as the sun gets better while the voltage is up to working levels quickly.

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@Louisvdw sincerely thank you very much for taking the time with your detailed response! :smiley:

Most of these concepts are familiar to me however you have no way of knowing what I know, and this kind of step by step write up can be very useful to anyone else reading, so thank you! :smiley:

If you go over outside these spesifications the device could still work but they will not have to hold the warrantee and your device might not have the same lifespan.

:+1:

You can push the limits on the current a bit to give you a bit more power. The excess energy still need to go somewhere. To keep it simple lets just say that one of the ways to handle the extra energy is to get it converted to heat, and heated components are not the best for devices.

This makes me think that the MultiRS tracker should then likely be ok with occasionally seeing 14A or 15A from my panels with a single series string setup.

The PV voltage actually moves to it’s operating votage quite fast in the mornings when it gets sun, but the current will move much slower up to when the sun is at around 90 degrees to your panels.

I wonder if I’ve seen these kind of current spikes to 15A occasionally (going over STC of 13.95A) since some of my panels are positioned flat at the moment so midday, summer stands to reason might be a situation where maximum current is generated.

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For completeness and context as to why I’m concerned with “operational” PV input currents of the ~15A range, this is the moment where my setup peaked to somewhere close to 30A and the SPD fuse blew, on a 4s2p setup about a week ago. I then realized in the afternoon, and replaced the fuse. On the VRM custom widget I tried to add the PV Current yet it does not show any data, that is why I’m using the PV power to calculate the current in the moment.