Using 4 250w panels to charge 48v 100ah

[777man]

I have 4 12v 100ah lifepo4 batteries and 4 250w solar panels. Im trying to determine what charger/inverter i need to do 48v.

if the panels have an open current voltage of 37.6, in series would this give me 150v?
So i would need a controlled that handles over 150v and my 8amps is negligible.

Or would it be better to series- parallel the panels and get 75.2v and roughly 16amps.

Looks like the charge controller usually go by amps 20,30,50 etc. if my panels were in series I would only have 8amps so what size controller do I need?

 

[Goboatingnow]

For safety’s sake the solar controller should be speced at Vopencircuit

 

[BentleyJ]

Couple of clarifications.
1) Voc means Voltage Open Circuit (nothing attached or no current flow)
2) Amperage ratings on Solar Charge Controllers are generally based on the Output current to the battery not the input from the panels. The 8.27A Pmax of your panels is not negligible, its a specification that is used to determine how many watts are going in which then can be used to determine the output amps at the charging voltage of that particular battery.

For simplicity, I would recommend looking for a charge controller that is rated at 250V so you can connect all 4 panels in series then there are only 2 wires. Probably going to cost a little more though.

 

[777man]

Couple of clarifications.
1) Voc means Voltage Open Circuit (nothing attached or no current flow)
2) Amperage ratings on Solar Charge Controllers are generally based on the Output current to the battery not the input from the panels. The 8.27A Pmax of your panels is not negligible, its a specification that is used to determine how many watts are going in which then can be used to determine the output amps at the charging voltage of that particular battery.

For simplicity, I would recommend looking for a charge controller that is rated at 250V so you can connect all 4 panels in series then there are only 2 wires. Probably going to cost a little more though.

Thanks. Im finding that generally the mppt controllers are 150v in an affordable range. It would be cheaper to buy a little more wire and do a series parallel if that would work.

 

[BentleyJ]

Thanks. Im finding that generally the mppt controllers are 150v in an affordable range. It would be cheaper to buy a little more wire and do a series parallel if that would work.

Ya, the Victron 250V SCC is $600 to $700.
Series Parallel will work using simple MC4 "Y" connectors. You don't need a combiner box or anything else.

 

[Daddy Tanuki]

The real question is if your batteries will play nice when wired in parallel for 48 volts…

 

[Northernchateau]

Let me ask, what are you plans with this solar set-up?
The more infomation you share the better members can help guide you in the right direction and help you avoid spenind money on things that won't work.

 

[777man]

Let me ask, what are you plans with this solar set-up?
The more infomation you share the better members can help guide you in the right direction and help you avoid spenind money on things that won't work.

Sometimes the power goes out for a day or two during bad weather when limbs fall on lines. I have a deep freezer and fridge with a lot a pricy meat. I just want a small solar backup just floating incase i need to use it. Since I already have 4 250w panels and 4 12v 100ah lifepo4 batteries with 100a bms on each, I would like to buy a charger and inverter or combo on the cheap that can do the trick. Im guessing ill buy 2awg wire and connect the batteries to 48v as they can go up to 4s. Im thinking a 3 or 5 kw inverter would be fine. Freezers are on and off through the day.

 

[Daddy Tanuki]

Sometimes the power goes out for a day or two during bad weather when limbs fall on lines. I have a deep freezer and fridge with a lot a pricy meat. I just want a small solar backup just floating incase i need to use it. Since I already have 4 250w panels and 4 12v 100ah lifepo4 batteries with 100a bms on each, I would like to buy a charger and inverter or combo on the cheap that can do the trick. Im guessing ill buy 2awg wire and connect the batteries to 48v as they can go up to 4s. Im thinking a 3 or 5 kw inverter would be fine. Freezers are on and off through the day.

Can your proposed batteries play together in a series setup? Many of them cannot and they will quickly go out of balance with each other.

 

[MichaelK]

Since I already have 4 250w panels and 4 12v 100ah lifepo4 batteries with 100a bms on each, I would like to buy a charger and inverter or combo on the cheap that can do the trick. Im guessing ill buy 2awg wire and connect the batteries to 48v as they can go up to 4s. Im thinking a 3 or 5 kw inverter would be fine. Freezers are on and off through the day.

Configuration depends on the electronics. With a 48V battery bank, you want >72V for proper MPPT function, and some AiO units have a minimum voltage requirement of 80V. So, 2S2P doesn't look like the best combination. What you can do is wire them in series for 150V and couple them to a 200V controller, like the Epever 5420AN. I have Midnight200 controllers, and I've operated my arrays as 4S for years now.

A better option I think would be to get two additional 250W panels and wire them 3S2P. That way you'll get the voltage above the 72V lower limit, but never exceed the 150V limit.

BTW, I think 2gauge is too light for the battery to inverter connections. I use 3/0 for my 24V system, and 4/0 for my 48V system.

 

[Daddy Tanuki]

Can your proposed batteries play together in a series setup? Many of them cannot and they will quickly go out of balance with each other.

If the BMS of each battery is not communicating with each other then one can shut down early As it’s fully charged and your other three batteries will not get fully charged.

 

[777man]

Configuration depends on the electronics. With a 48V battery bank, you want >72V for proper MPPT function, and some AiO units have a minimum voltage requirement of 80V. So, 2S2P doesn't look like the best combination. What you can do is wire them in series for 150V and couple them to a 200V controller, like the Epever 5420AN. I have Midnight200 controllers, and I've operated my arrays as 4S for years now.

A better option I think would be to get two additional 250W panels and wire them 3S2P. That way you'll get the voltage above the 72V lower limit, but never exceed the 150V limit.

BTW, I think 2gauge is too light for the battery to inverter connections. I use 3/0 for my 24V system, and 4/0 for my 48V system.

How about I do a 24v battery set up and and do 2s2p on the panels and therefore I can buy cheaper charge controller since the volt requirement is less. My panels max volts are around 37 so id be at 74v which should be plenty for 24v correct?

 

[MichaelK]

How about I do a 24v battery set up and and do 2s2p on the panels and therefore I can buy cheaper charge controller since the volt requirement is less. My panels max volts are around 37 so id be at 74v which should be plenty for 24v correct?

2S2P will put your solar input at 16A at ~60V, so that's perfect for a 24V system. At freezing, your panels are likely to be putting out 80Voc, and even at -40F, only 94Voc, so you are good to go with 24V.

With two 24V battery strings, that's 200Ah at 24V, so your array is likely to give you (1000W/25Vcharging) X 85% = 34A in the real-world, so a less expensive controller, like Epever's 4210AN will work. Keep in mind though that it won't allow much future expansion. It might be a wiser choice to spend a bit more up front, and get the 5420AN or 6420AN to facilitate future panel upgrades. I myself quickly upgraded my 24V system to 2000W of panels (4S2P).

BTW, which battery will you be using. Can you provide a link? You have not yet answered the question as to whether or not this battery's BMS handles serial connections?

 

[Quattrohead]

A unit like this one will do everything you want today and allow for expansion in the future.
SPF 3000 TL

 

[BlueMarblePA]

A unit like this one will do everything you want today and allow for expansion in the future.
SPF 3000 TL

Wow. I am setting up a very similar system. 4 panels 38.8 VOC each and 8.78 Amps each. Am wondering if the MPP LP6548 would be appropriate for similar set up. https://www.mppsolar.com/v3/splitphase-lv6548/