Understanding Batteries and voltages

[John117]

Hi guys, I am planing on doing a solar project and saw a video saying that 48v batteries are the way to go nowadays. Because it is more efficient and cheap. I understand the efficient part, because you don't need thick cables, and that's the same reason it should be cheaper, right? (less copper)
Looking for batteries on Amazon I get these 2 as an example, obviously the 1k one is HUGE, and it should have more capacity but is it cheaper like watt-hour or something?

51.2V 100AH LiFePO4 Battery $1,099.99
12V 100Ah LiFePO4 Battery $170.99

I am guessing that W=Volts x Amps, right? Why not advertise the watts? And what if I have 4 solar panels that are 200w each but at 12v? Even if I connect them in series I can only get 48v, is that enough to charge the huge battery on this example? Do I have to always have a higher voltage than the battery in order to charge it right? So I probably have to add another panel in series to get 60v? I know panels are now coming in higher voltage also. But I just want to understand this.

**************************************************UPDATE ************************************

I just wanted to add my idea to see what you guys think



Thank you in advance!

 

[Nobodybusiness]

Hi guys, I am planing on doing a solar project and saw a video saying that 48v batteries are the way to go nowadays. Because it is more efficient and cheap. I understand the efficient part, because you don't need thick cables, and that's the same reason it should be cheaper, right? (less copper)
Looking for batteries on Amazon I get these 2 as an example, obviously the 1k one is HUGE, and it should have more capacity but is it cheaper like watt-hour or something?

51.2V 100AH LiFePO4 Battery $1,099.99
12V 100Ah LiFePO4 Battery $170.99

I am guessing that W=Volts x Amps, right? Why not advertise the watts? And what if I have 4 solar panels that are 200w each but at 12v? Even if I connect them in series I can only get 48v, is that enough to charge the huge battery on this example? Do I have to always have a higher voltage than the battery in order to charge it right? So I probably have to add another panel in series to get 60v? I know panels are now coming in higher voltage also. But I just want to understand this.

Thank you in advance!

48vdc vs 12vdc allows you to run higher wattage inverters at lower amperage.

3000 watt inverter at 48v = 62.5 amps
3000 watt inverter at 12v = 250 amps.

You can run smaller gauge wire with higher voltages.

Most batteries are listed in Amp Hours (AH) or Watt Hours (WH).
AH are a measurement of charge
Wh are a measurement of energy.
51.2vdc x 100 AH = 5200WH

Divide your cost by the WH to find $ per WH.

$1099/5200= .211 per Wh
$171/1200= .144 per Wh

As far as charging them you need a charge controller. Preferably MPPT charge controller.

The controller would take your panels and convert to the appropriate voltage for charging.

 

[John117]

48vdc vs 12vdc allows you to run higher wattage inverters at lower amperage.

3000 watt inverter at 48v = 62.5 amps
3000 watt inverter at 12v = 250 amps.

You can run lower gauge wire with higher voltages.

Most batteries are listed in Amp Hours (AH) or Watt Hours (WH).
AH are a measurement of charge
Wh are a measurement of energy.
51.2vdc x 100 AH = 5200WH

Divide your cost by the WH to find $ per WH.

$1099/5200= .211 per Wh
$171/1200= .144 per Wh

As far as charging them you need a charge controller. Preferably MPPT charge controller.

The controller would take your panels and convert to the appropriate voltage for charging.

Thank you so much! so in that example the 12v is actually cheaper than the48v battery. Interesting!

 

[alcook62]

Thank you so much! so in that example the 12v is actually cheaper than the48v battery. Interesting!

Don't fixate on price alone. If you want a 48-volt system you must combine 4 of those 12-volt batteries in series to achieve the 48 volts. Each of those 12-volt batteries has its own BMS that manages its respective battery. The problem is when the 4 series battery has been cycled repeatedly the individual batteries drift out of balance from each other. The system will lose the ability to produce full power potential due to either over-voltage/under-voltage cutoff when the 4 batteries drift out of balance. This can be mitigated, however, it can also be prevented altogether by just purchasing a single 48-volt battery.

 

[Nobodybusiness]

Thank you so much! so in that example the 12v is actually cheaper than the48v battery. Interesting!

Per WH yes but that doesn’t tell the whole story as you know..

48vdc is definitely way to go..

 

[John117]

Don't fixate on price alone. If you want a 48-volt system you must combine 4 of those 12-volt batteries in series to achieve the 48 volts. Each of those 12-volt batteries has its own BMS that manages its respective battery. The problem is when the 4 series battery has been cycled repeatedly the individual batteries drift out of balance from each other. The system will lose the ability to produce full power potential due to either over-voltage/under-voltage cutoff when the 4 batteries drift out of balance. This can be mitigated, however, it can also be prevented altogether by just purchasing a single 48-volt battery.

I see!! no one explained that in the videos, thank you! I added an image of my idea, you think it will work?

Per WH yes but that doesn’t tell the whole story as you know..

48vdc is definitely way to go..

Thank you!!

 

[SoggyShoes]

If you haven't already bought the batteries, you really want the batteries to match the voltage of your system (so 48V batteries).

As @alcook62 explained, running batteries in series can work, but requires a lot more monitoring and manual baby sitting/hand holding to safety and efficiently run.
With one 48V battery one BMS is overseeing all cells, making sure they all play along with each other. When you run batteries in series it is like the right hand doesn't know what the left hand is doing.
The difference between a battery made up of cells in series is that a single BMS is monitoring every single cell individually and holistically, making sure all the cells are balanced. With four 12V batteries in series you have 4 BMSs that are making sure that the 4 cells each individual BSM is monitoring is balanced but there is no balancing between groups so each group of 4 cells could be wildly different from the other groups of 4 cells. This is the issue that @alcook62 was trying to save you from dealing with.

So to me, if building a 48V system, getting anything other than 48V batteries is a non-starter regardless of price.

Also, as far as I can tell most of the LiFePO4 or LFP batteries, the "48V" batteries are the same as the 51.2V batteries as they are made up of 16cells in series that each have a nominal (or midpoint) voltage of 3.2V. So 16cells x 3.2V/cell = 51.2V battery. So that "12V" LFP battery is really a 12.8V battery

Be careful of just getting the cheapest battery you can on Amazon. There are lots of videos of tear downs, including many by @Will Prowse that show they might not be that good of deal (or just dangerous or a rip off). Will has a webpage of brands that he recommends.

I am currently waiting on an order from Amy Wan runs Luyuan on Alibaba. She has a great reputation (for at least 5 years) with fantastic prices. Depending on where you live on Earth you could probably a 51.2V (16cell x 3.2V) with a beautiful steel case and top quality BMS for $0.12 for a 304Ah battery kit to $0.22 for a 105Ah kit - including shipping. The only downside of ordering from Amy is having the patience for shipping from China. I was pretty nervous about trusting buying anything off Alibaba, but after discussions with some longtime members of this forum and seeing how good of reputation she has consistent earned for several years, I finally felt comfortable buying almost 39,000Wh of batteries from her. I am still not comfortable buying from any other seller on Alibaba.
Here is a thread that has been active for almost 2 years about buying cases (and batteries) from Amy: https://diysolarforum.com/threads/luyuan-battery-case.44827/

Good luck with your project!

 

[Rednecktek]

Another thing to consider is that if you watch tear down videos of different batteries, you'll see that most of the 12v guys have a couple inches around all sides of the cells. That extra space adds up when you're puttimg things on shelves.

Another thing to consider is that if you get 4x 12v batteries, you're going to have to build all the short connectors between the batteries.

The $1000 option is going to be easier to wire up, take less space, and stay in balance.