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semiraue avatar image
semiraue asked

Sizing charge controller and panels for new battery pack


Hi All,

I have below off-grid setup at the moment for power most of my DC devices (lights,router,nas,nvr,etc..) on my remote house.

  • 2x JAM solar 460W panels in parallel this
  • victron smart solar mppt 100 1 20 charge controller (12/24/48v)
  • 12v 100AH deep cycle Sealed lead acid battery

I'm not sure these panels are too much for the controller. and most of the time I can only see max 291w of P Max(photo_2022-03-19_18-47-39.jpg). does this means controller reach it's maximum capacity?

I'm planning to upgrade my setup to more powerful AC off-grid system to power my entire house. also to run smaller server rack.

I'm planning to buy below new items

  • 4x sok 206Ah lifepo4 batteries
  • or 1x jakiper 48v 100ah rack mount lifepo4 battery
  • Meanwell TS-3000 inverter this

If I purchase these new equipment, can I use them with my existing PV array and charge controller ? or do I need to add more panels or change my charge controller ?

if can use, do I need to connect panels in series ? since each panel Voc is only 50.01V?

I was planning to buy 12v inverter with 1x 12v LFP battery. but on many sites I saw that if making off-grid setup more than 3000W better go with 48v system. invert from 48v->230v is better than 12v->230v as many sites suggested. Is this true ? my usage is not more than 2000w. but for future improvement I would like to have 3000w inverter.

battery chargingchargerSolar Panel
photo-2022-03-19-18-47-39.jpg (69.4 KiB)
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nickdb avatar image nickdb ♦♦ commented ·
You have chosen a non-victron ecosystem, apart from the mppt. You really should be asking the suppliers of your equipment if they will support your choices.

A 20A mppt can produce a maximum of 240W at 12V, 480W@24V and 960W@48V.

At 12V your mppt is the limiting factor for your panels.

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wkirby answered ·

Change to 48V at your earliest convenience.
Your cabling can be smaller size for the same power. Your charge controller will output four times the power on a 48V system than a 12V system, like nickdb described earlier.
There are a much wider choice of 48V lithium batteries available.

Series connection of your panels would be necessary for a 48V system, because 50V PV Voltage will be too low. However with series connection your PV Voltage will be too high for a 100/20 charge controller and it will likely be damaged by excessive PV Voltage, the limit is 100V.

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semiraue avatar image semiraue commented ·

Thanks for this. I will go for the 48v system then. either with four 12v batteries or one 48v server rack battery. but as you said if I connect panels in series do I need to buy a larger controller ? when I check the datasheet it says


1a) If more PV power is connected, the controller will limit input power.
1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V
2) A PV array with a higher short circuit current may damage the controller.

Does this mean if I input more than 100V PV volts the controller will limit the input power and if I input more than 20A from PV it may damage the controller ?


Also my MAX PV Voltage never go beyond 46V so far.


Basically more Volts are ok but more Amps will damage it?

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kevgermany avatar image kevgermany ♦♦ semiraue commented ·
Much worse. If you exceed PV voltage it will destroy the controller. And be aware that PV voltage increases as temperature decreases, so coldest winter temperatures need to be accounted for.

What is safe, but not in excess, is more power.

There's a calculator on the vuctron energy site which will match controllers to your panels.


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semiraue avatar image semiraue kevgermany ♦♦ commented ·

Thanks. Panel Voc is 50.1 which in series100.2. I saw in some posts that slight over voltage is not an issue for these controllers (correct me if I’m wrong). I tested Victron calculator and it wont suggest anything below 135 I think due to Voc.

When I use this site to calculate, it shows Solar Panel Array Max Voltage will be 116.40V if temperature drops to estimated low temperature. With my current parallel config, panels only output max 46V according to data from the charge controller. So can I safely assume the panels won't output more than 50.1V and use the existing controller I have ?

There is no winter. setup based in Sri Lanka. and the temperature stays quite same throughout the year

If I really cannot use this controller, what is the best way to keep it and improve my setup to hold more power?

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semiraue avatar image semiraue semiraue commented ·

I tested the calculation again with correct temperature data. The location's minimum temperature never went below 23 Celsius (68 Fahrenheit) for the past three years. When I add the Estimated Low Temperature value to 60Fahrenheit (8 lower than lowest in the location) it gives me Solar Panel Array Max Voltage as 102V. In this case, is it okay to use the 100 1 20 controller ?

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semiraue avatar image semiraue semiraue commented ·

I would really appreciate it if you could input some thoughts to the calculation I did.

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kevgermany avatar image kevgermany ♦♦ semiraue commented ·
Check for your panels but VOC is usually quoted at 25C. Dropping to 23C has negligible effect.

You are on the limit for this controller with series panels.

What is the temperature compensation for the panels? Your voltage increase seems too high. Temp compensation is usually given in millivolts/C.

As you have the panels and controller, it would be safest to go with a 24V system and put the panels in parallel.


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