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48v Panels to 12v batteries

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Blair Mullen

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I have 48v solar panels and my batteries in my motorhome are 12v. I have a 3000w inverter already installed, and I have chosen the 400w panels because of their physical dimensions and where I can fit them on my roof. So I would like to know and understand what the best way is to connect the panels to my 12v system. I have room for 5 400w panels and I plan on installing another 5 using a retracting system on the roof so there would be 10 in total when finished. Do i need to go to a 48v battery bank first, then to my 12v or can I go from 48v solar controller to a 48v to 12v converter to my battery?

Thanks for your help and advice
Blair
 
Ooohhh... can of worms here. Is your 3kw inverter 48v or 12v? If it's 12v you're going to need multiple SCC's to utilize 4000 watts of panels! For a 12v system you're looking at 400a of MPPT charge controller. If you were using heavy AC loads like mini-splits, electric hot plates, MargaritaMaster-9000's, etc then a 48v system would make sense. 3kw is still pretty top end of what 12v systems can do.

So, your options would be either a 48v battery bank so you can use 1 or 2 SCC's and then a BIG step-down transformer for the 12v loads ( not that you'll ever find one capable of feeding a 3kw inverter) OR go to a 48v system and new inverter and only step down for the lighter weight 12v loads, OR go with 400a worth of SCC's and keep everything natively 12v.

With 4kw of panels, you could have 15kw plus of battery capacity which is like 3 of the rack mount batteries. That's a standard house size array.
 
I learned the panel voltage is pretty much irrelevant to the system voltage.

The solar charge controller converts panel voltage to match your battery voltage.

Whatever voltage you inverter requires is what voltage you battery needs to be.

I was looking at 12v to start with. While they make 12v 3000w inverters they will require a huge amperage to operate. That means lots of heat.

For 3000w I’m planning a 24v setup which puts the amperage at about 125A at max draw. Volts * Amps = Watts

Amperage determines things like fuses and wire sizes.


As for panel voltage. As long as your voltage is higher than the battery voltage the SCC should be able to convert it and charge the battery.

When choosing the SCC it needs to handle both the voltage and amperage coming in from the panels.

You change panel input amps & voltages by hooking them in parallel or series connections.

Series multiplies volts.
Parallel multiplies amps.
 
Rednecktek said:
Ooohhh... can of worms here. Is your 3kw inverter 48v or 12v? If it's 12v you're going to need multiple SCC's to utilize 4000 watts of panels! For a 12v system you're looking at 400a of MPPT charge controller. If you were using heavy AC loads like mini-splits, electric hot plates, MargaritaMaster-9000's, etc then a 48v system would make sense. 3kw is still pretty top end of what 12v systems can do.

So, your options would be either a 48v battery bank so you can use 1 or 2 SCC's and then a BIG step-down transformer for the 12v loads ( not that you'll ever find one capable of feeding a 3kw inverter) OR go to a 48v system and new inverter and only step down for the lighter weight 12v loads, OR go with 400a worth of SCC's and keep everything natively 12v.

With 4kw of panels, you could have 15kw plus of battery capacity which is like 3 of the rack mount batteries. That's a standard house size
Click to expand...
I like your Handle, some around my neck of the woods would call me a Red Neck lol. I should have explained better, my inverter is 12v, bought a GoPower transfer switch, after seeing what was inside and the xtra room i ordered a second relay put it in the box and then was able to wire it so shore power flows straight through, generator can start after 30 sec it will kick in, if i want inverter, the second relay will energize and cut off everything else and i got 3000 watts of battery at 115vac
I think I can fit 5 of the 400w 48voc 9.57sc amps panels on my roof, and plan to install so i can extend 5 more out when boondocking. Here's my thinking, they are flat mounted so I'm not going to get full wattage and most of the time its partly cloudy so I'm thinking on a fully overcast day I should be able to get at least 10%, 400w to charge my batteries, I do want to use the AC which is just under 1500w, but we can shut it off to use mic or coffee pot fridge is propane & 115v, so I only need enough battery and what i can fit in the limited space i got cause she won't let me use her space.
 
AmpD said:
I learned the panel voltage is pretty much irrelevant to the system voltage.

The solar charge controller converts panel voltage to match your battery voltage.

Whatever voltage you inverter requires is what voltage you battery needs to be.

I was looking at 12v to start with. While they make 12v 3000w inverters they will require a huge amperage to operate. That means lots of heat.

For 3000w I’m planning a 24v setup which puts the amperage at about 125A at max draw. Volts * Amps = Watts

Amperage determines things like fuses and wire sizes.


As for panel voltage. As long as your voltage is higher than the battery voltage the SCC should be able to convert it and charge the battery.

When choosing the SCC it needs to handle both the voltage and amperage coming in from the panels.

You change panel input amps & voltages by hooking them in parallel or series connections.

Series multiplies volts.
Parallel multiplies amps.
Click to expand...
I was thinking the same thing but wasn't sure if that's how it worked, so here is what I'm planning on doing but not sure if I'm correct

I should have explained better, my inverter is 12v, bought a GoPower transfer switch, after seeing what was inside and the xtra room i ordered a second relay put it in the box and then was able to wire it so shore power flows straight through, generator can start after 30 sec it will kick in, if i want inverter, the second relay will energize and cut off everything else and i got 3000 watts of battery at 115vac
I think I can fit 5 of the 400w 48voc 9.57sc amps panels on my roof, and plan to install so i can extend 5 more out when boondocking. Here's my thinking, they are flat mounted so I'm not going to get full wattage and most of the time its partly cloudy so I'm thinking on a fully overcast day I should be able to get at least 10%, 400w to charge my batteries, I do want to use the AC which is just under 1500w, but we can shut it off to use mic or coffee pot fridge is propane & 115v, so I only need enough battery and what i can fit in the limited space i got cause she won't let me use her space to last 2-3 days and if it is over cast i probably won't need the AC
Thanks for the advice and thoughts
Blair
 
Im new to this stuff, So can i get away with just using a 48v scc to charge my 12v battery bank?
thanks
Blair
 
Review the charge controller specifications. It all depends on the model you purchase as to what voltage it is capable of. You can also use more than one in a system.

You want it to be able handle the maximum volts and amps coming from the panels as well as output enough amps at the battery voltage to make use of your panels output.

For example a victron 150/45 will accept 150v max input, 50a input, and output the following:

650w@12v
1300w@24v
1950@36v
2600@48v

It is supposed to automatically detect battery voltage aside from a 36v configuration.

Im not pushing brands here just giving an example. There are plenty of scc’s out there.

I’m also new and have yet to even own a system. Just sharing the info I’ve picked up hoping to help. Thank you @pollenface for clarifying the heat/amps thing. I wasn’t trying to confuse anyone for sure.
 
Last edited:
With 4000w of panels you'll want a 48v battery system and 2 mppts, one for the retractable and other for the main. 48v means the mppts are 1/4 of the price and well worth a 48 to 12v converter. Swap the inverter out for a 48v as well.
 
AmpD said:
Review the charge controller specifications. It all depends on the model you purchase as to what voltage it is capable of. You can also use more than one in a system.

You want it to be able handle the maximum volts and amps coming from the panels as well as output enough amps at the battery voltage to make use of your panels output.

For example a victron 150/45 will accept 150v max input, 50a input, and output the following:

650w@12v
1300w@24v
1950@36v
2600@48v

It is supposed to automatically detect battery voltage aside from a 36v configuration.

Im not pushing brands here just giving an example. There are plenty of scc’s out there.

I’m also new and have yet to even own a system. Just sharing the info I’ve picked up hoping to help. Thank you @pollenface for clarifying the heat/amps thing. I wasn’t trying to confuse anyone for sure.
Click to expand...
thanks
 
justinm001 said:
With 4000w of panels you'll want a 48v battery system and 2 mppts, one for the retractable and other for the main. 48v means the mppts are 1/4 of the price and well worth a 48 to 12v converter. Swap the inverter out for a 48v as well.
Click to expand...
thanks all things i have to digest
 
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