Self-sufficient system on the boat

DIY
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1

Hello, I would like to run 4 × 12 V 640 Ah LiFePO4 batteries on my boat in series at 48 V / 51.2 V. The manufacturer/seller is Humsienk. There are 6 solar panels installed, with a total output of approx. 3,000 W. 1× MPPT 150/60, 2× MPPT 150/85, Cerbo GX, BMV 712. At the moment, I am using 4 × 12 V 290 Ah C100 lead-acid batteries as a 12 V system with a 3,000 W inverter supplying 230 V. This is to be replaced by a MultiPlus-II 4k5 230 V. Can this work as described, and what additional equipment, such as a balancer, will be required?

Kind regards,
Thomas

2

What is the wattage here 3000 is total?

Why do you need so many mppts and such large ones for the 6 panels?

3kW at 48v is only 62.5amps

You definitely need the balancers and a nice bus bar

3

I did write that I’m currently working with a 12 V system, where 3000 W / 14.8 V = 202.7 A. I want to switch to 48 V.

4

@Tommy10365

LFP batteries need to be balanced, which is the job of a BMS.
I am not aware of any “normal” batteries with a BMS that works across multiple batteries, i.e. one that can balance cells between batteries connected in series.
While three batteries are not yet fully charged, one may already reach its limit and shut down to protect the battery from failure or fire.

Please check whether the BMSs of the batteries can balance cells across the batteries when connected in series.

Please also check whether the battery’s BMS is compatible with Victron. The BMS information is used for control. If it is not compatible, you should provide for a SmartShunt.

It may be that the Victron Smart LFP batteries with Lynx Smart NG BMS can balance across multiple batteries. I am not familiar with them.

In general, I would recommend a managed battery with the appropriate voltage. There are many 52 V (16s) batteries with 5 kWh (100 Ah) or 16 kWh (314 Ah). These can be connected in parallel and thus distributed close to one another around the boat. The most common form factor is 19" rack-mount. There are also special Victron-compatible, waterproof batteries for the marine sector with the relevant certification, but they are considerably more expensive.

If, in addition to shore power, you also have an AC generator, such as a Fischer Panda, you will need a Quattro instead of an MP2.

Please bear in mind that the MP2’s VA ratings are specified at 25°C.
Allow for approximately 80% VA → W, so 3000 VA → 2400 W at 25°C. If it is warmer on the boat, derate the power accordingly.
The MP2 units hum and must be mounted with decoupling to dampen structure-borne noise.
The high-frequency Multi RS inverters do not hum, but they are more expensive.

On the boat, please provide galvanic isolation for shore power, for example using Victron’s isolation transformers. These are also available for 120/240 volts if you are heading across the Atlantic. The isolation transformers have a few extra turns on the “boat side” to compensate for the voltage drop in the generally poor shore-power cables.

If the voltage is even worse, you could also charge the DC bus directly using a TelKo PSU. The onboard AC network would then be independent of the shore-power voltage, and you would not need a Quattro with a simultaneous AC generator either.
A single-phase AC generator can also be connected via a TelKo PSU.

On a boat, the PV panels are usually oriented differently and partially shaded.
Because of the shading, it is best to use strings that are as short as possible.
You need 5 V more PV input voltage than the battery voltage. So you need around 60 V+ PV voltage. This is usually achieved with two panels in series.
An MPPT 150/45 in a 2s2p configuration is then probably the most economical option.

You can also combine it with microinverters. These usually have one MPPT per panel. The MP2 would charge the excess power from the microinverters into the battery. I did this at my house because of heavy shading.

For the DC bus, I recommend a Lynx Distributor. There is free software for it that allows you to monitor the fuses and receive a corresponding alarm in Venus OS.

I hope these suggestions help you

5

Ok. I guess i was too simple in the opening of the discussion.
Let me be more explicit in the question then.

Do you need/want them for self sufficient reasons in this next system?
Will you need extra kilowatts of power now and can you add more panels on your boat or it this all the space you have?
Are they all on different facing directions so will need different tracking?

This and many other good points above for building a 48v bank.(including being sure the manufacturer support series connect)

If shape of space is a consideration?
If it is not it is actually way safer and better (for space and other reasons) to use a 48v battery bank.

6

Yes, it’s about being self-sufficient. In spring, summer and autumn, my current setup is no problem. But in winter, when the heating is running, it becomes difficult to manage 14 days without access to mains power. All the solar panels are installed horizontally, but they can be tilted to around 50° if needed. One set of two panels with the 60 A MPPT connected in series, plus two sets of two 585 W panels, each with an 85 A MPPT, connected in series. This also provides the necessary voltage.

7

Additional solar panels are planned for both port and starboard, mounted vertically. Approximately 4 × 200 W. However, these should only cover the winter months and then be removed again. A specific orientation of the panels is rarely possible, as we are predominantly at anchor and our position is constantly changing due to wind and currents.

8

As other recommended, save the hassle and get a 48v battery directly.

9

The Victron Lithium NG batteries are available in 48V/100Ah.