fmueller87 avatar image
fmueller87 asked

Multiplus 48/1200/13 + BYD B-Box Pro 13.8

Dear community,

I wish to primarily charge the BYD 13.8 kWh (288 Ah) through 2 x MPPT solar chargers. The Multiplus 48/1200/13 is primarily used to power a constant (and max.) load of 700 Watts. It will be grid-connected and it is there to back up charge the BYD B-Box in case of bad weather days.

Question: is the 48/1200/13 with 13 Amp charging power sufficient for this purpose?

and: it has a transfer switch of 16 Amp, so for example, if the battery is empty, and the load is on at 700 watts (approx. 3 Amps at 230V), will the multiplus transfer the full load requirement and charge the battery at max capacity of 13 Amps simultaneously?

Or is it wise to go the Multiplus 48/3000/35?

Hope I was able to make myself clear!

Thanks very much!

Best regards,


BYD48v battery
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2 Answers
Anil Ghatikar avatar image
Anil Ghatikar answered ·

You have not indicated the MPPT charge controller/ PV capacity

1. Yes the 13 AMp charger is sufficient but when starting from LOW SOC you will wait a long time ( 13 amp for 288 Ah is almost 20 hours) But since BYD can be left at partial SOC it does not matter on short periods of a week when the sun is not enough

2. YES the multi will transfer the load to grid and also charge the battery at same the time ( so Input of multi will consume 700W load+ 650 watt- charging power+losses - around 1400 watt

3. If the PV is relatively large you can even implement IGNORE AC settings or ESS to maximize the use of solar which will use solar to feed load and charge battery at the same time even if grid is available

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fmueller87 avatar image fmueller87 commented ·

Thanks alot Anil for the detailed response.

1) This is wwhat i thought also (the BYD can be set for 10% SOC in off-grid situations), and yes that was my primary reasoning for this question, that the 13 amps will take a long time to charge it fully (as compared to a bigger Multiplus with say, 35 amp).

2) Perfect, excellent to know.

3) The PV will be 5,100 Watts, via 1 x MPPT 150/60 ( 3S x 3P - charging around 50 Amps max.) and 1 x MPPT 250/60 (4S - 2P charging around 50 Amperes max.).

The PV should be sufficient to run the load most of the day, and fully charge the battery for the night / a few hours of bad weather. The system will be located in Oman/Middle East, which has excellent sunlight year round and very few bad weather/overcast days.

For info/interest: 0.7 kW load for 24/7 operation = 16.8 kWh/day total consumption.

Thus, 13.8 kWh BYD battery (usable to 12.42 kWh) and 5.1 kWp solar running/charging the loads + battery should be sufficient for good redundancy in such a system. Then ESS settings will be used to maximize the solar use, with the grid only being used as a back-up option. This sounds feasible?

Thanks again, this community and the forum are great ressources!!

Best, Fabian

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JohnC avatar image JohnC ♦ fmueller87 commented ·

Hi Fabian. Reading mention of ESS suggests a Venus device too. By the time you add it all up, an Easysolar 3kVA should eat what you want to do. Prewired, nice'n'tidy, output breakers onboard. Plug'n'play. Compare the prices of the individual pieces you're looking at, and you may be surprised.

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fmueller87 avatar image fmueller87 JohnC ♦ commented ·

Hi John,

Yes you are correct, the EasySolar 3kVA is nice n tidy and price-wise should come to around the same with breakers and fuses n all, already included. However, the main reason I opted against it, was that it only accepts 4000 watts of solar power.

Writing this has brought me to an idea however, could I use the 4000 watts solar input of the Easy Solar and add an extra Smart MPPT charge controller for the remaining 1100 watts of solar?



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boekel avatar image boekel ♦ fmueller87 commented ·

you can add more MPPT's indeed.

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boekel avatar image
boekel answered ·

This should work, if the 700W load is not one with a heavy start-up peak.

What is the load? (if it's an air conditioner it will not work for example)

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fmueller87 avatar image fmueller87 commented ·

Thank you Boekel, the load is a computer with 700 W power supply, do not think it has a heavy start up current. The peak load (short duration) of the 48/1200/13 multiplus is indicated at 2400 Watts (i highly doubt that it will get anywhere near that).

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boekel avatar image boekel ♦ fmueller87 commented ·

That's no problem.

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