tpwchr avatar image
tpwchr asked

Multiplus I or II for an off-grid instalattion?

I am configuring a new system for an off-grid installation and I am not sure which device is more suitable for my case. I see that Multiplus I is 70-100A but Multiplus II is 70-50A.

I want to connect it to a solar panel array of 4800W and 4xPylontech 2,4kW batteries, plus the Victron MPPT 250V100A and the Victron Color Control GX at 48V + the additional genset in case batteries drop below certain level. Any suggestions? Thanks

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3 Answers
rrroonn avatar image
rrroonn answered ·

Hi @tpwchr,

some thoughts

Given that you have a 70 amp charger in both, I am not sure that it matters. Max charge current from 250V genset will be 1/5th of this ... 14 amps, so having a 50 amp transfer switch is never going to be an issue if you are off-grid (unless you have big additional loads that you will only run when the genset is running).

I would make sure that the genset is 'compatible' with the inverter. Check out before you buy.

Consider if you will manually or automatically start the genset and confirm the stop/start interface compatibility.

MMPT 250V100A - 250V will mean 4 parallel strings of 6 panels (assuming 24x200W panels)? Peak current could be close to 40amps Keep an eye on cable sizing, particularly if the panels are a significant distance from batteries. Keep any potential shading to a single string if possible to maximize power.

If you need to power large inductive loads such as bore/well pumps, be really careful to ensure that the inverter can handle their startup current requirements which could be 4-6 times their running requirements.

hope this helps,


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tpwchr avatar image tpwchr commented ·

Hi @rrroonn, thanks for answering. So why would it only charge at 1/5th of it? I would have thought that it would charge at 50A*48V=2400Wh. The generator is activated automatically when the battery drops to an specified level through the inverter.

Regarding the solar panels, I thought of 16x400Wp in 4 parallels of 4 series (199,2V41,44A).

Fortunately I dont have any of those special loads, just a normal house. Thanks!

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rrroonn avatar image rrroonn tpwchr commented ·

The current from the genset through the ATS (50A or 100A) would be 1/5th because the voltage is 5 times higher.

Also, FYI, 48V is a 'nominal voltage' and the batteries will spend much of their time around 50-52V. I use 50 for calculations because it is easier.

Be careful with the panels - you need to make sure you don't exceed voltage limits. Not sure on your panels, but some 400W panels have a Voc of around 75V. Four of these in series would exceed the MPPT charger rating. You would have to drop back to strings of three panels. The MPPT charger will not start if the panel voltage is above 245V.

You need to review the specs of the panels you intend to use to ensure that series Voc is less than MPPT charger voltage rating and that Isc summed from all parallel strings is less than charger current rating.

I assume that you will have 2 x "MPPT 250V100A " to handle the power? The "MPPT 250V100A" is only rated to 5800W and you intend to install 6400W of panels. Having said that, I think that, provided the voltage and current ratings are not exceeded, then it is ok to have extra wattage, but the MPPT will only output its max power rating.

BTW, my system is on-grid but I designed the system to function equally well without the grid. In my case, I would have chosen the Quattro as it has two AC inputs - however it was not approved in AU for on-grid use, so I went with MP2. If you think you might at some stage go down the route of attaching to the grid, then consider the Quattro if it is approved in your country. It means that you can have grid going into one AC input and Genset into the other and prioritise AC-inputs. Much nicer than MP2 which is messy at best. I use a manual start and manual transfer switch for the genset - which, as I am on-grid, is rarely needed.



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tpwchr avatar image tpwchr rrroonn commented ·

Hi @rrrooonn, the Voc of these solar panels is 49.8V, so I expect to get a final setting of 199,2V 41,44A approx. So regarding limits, I think it's fine. Regarding the MPPT, it says max 5800W, but my panels would be 6400Wp. Do you think this is a problem? I have read many times that you can install more (10-20%) because almost never will reach that limit and its safe to do so as long as current and voltage are within limits. This is important because otherwise i will need to reduce the solar panels.

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tpwchr avatar image tpwchr rrroonn commented ·

And my installation is 100% off-grid because it doesnt have access to a powerline unfortunately!

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Paul B avatar image Paul B tpwchr commented ·

as long as you dont go over 250 volts you could put panels there that in theory put ot 10,000 watts the max the 250/100 will allow is a out put of 100 amps x battery voltage so at 58 volts thats 5800 watts the rest is just clipped off and not used at all, and as you say this happens at peak sun only.

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ejrossouw avatar image
ejrossouw answered ·

Hi @tpwchr For me the key consideration would be the slightly lower power consumption of the newer MPII model especially if you are 100% off-grid, it is also much lighter and just be mindful that the first generation MPIIs had m6 battery connectors vs M8 on the latest. Otherwise a no brainer given the processor and some upgrades to the boards, connectors etc. My MPII first gen has now been running almost two years completely unattended 6000miles away serving my holiday home I have been unable to visit ;)

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tpwchr avatar image tpwchr commented ·

Thanks for your reply @ejrossouw I made the choice and its going to be the MPII even though it would charge the batteries 50% slower than the MPI because of the 50A instead of 100A. Hopefully wont need the Genset too often. What do you think of the rest of my solar config?

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klim8skeptic avatar image klim8skeptic ♦ tpwchr commented ·

All 48-5000-xxxx inverter chargers seem to charge at 48v-70amp.



Multiplus II,

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ejrossouw avatar image ejrossouw tpwchr commented ·

The chargers are 70A DC on both versions and that is DC, so the 100A AC transfer switch is irrelevant. It will max out at about 15A on AC.

I cannot comment much without knowing more about the loads, peaks etc., but at a very high level under ideal circumstances, if there are no loads the batteries can easily be charged in about 2-3 hrs from 80% DOD. Just make sure the generator is powerful enough to handle the charging loads when it is required.

Another of my installations charges a 189Ah LG Chem RESU10 at 35A in under three hrs from 74% DOD to 95% (no solar though, but your MMPT should be even better being DC to DC) Of course it will depend on solar yield at the time as well as the loads which will be served first and then the battery will be charged.

Hope this helps.

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tpwchr avatar image tpwchr ejrossouw commented ·

Now I see that there is MPII and MPII GX. Is there any convienience of using MPII GX in my case?

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Paul B avatar image
Paul B answered ·

To be CLEAR The difference between the two models is the AC transfer current is 100amps on the multiplus or 50amps on the multiplus II so if the output from your generator is NEVER going to exceed 50 amps I would go for the MP II as its the lattest tech and as others say has lower no load standby power.

In reatlity you may never get that low in loads so pick the one that you may grow into . I suspect you will never get near the 50amp maximum so the MP II would be my choice

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