12 volt vs 24 volt vs 48 volt

[Off Gridin' It]

To help people understand battery capacity as it compares to different voltages.

If you have a 400 ah - 12 volt battery bank then thats 400ah x 12v = 4800 wh

If you have a 200 ah - 24 volt battery bank then thats 200ah x 24v = 4800 wh

If you have a 100 ah - 48 volt battery bank then thats 100ah x 48v = 4800 wh

 

[Tiger666]

P(W) = V(V) × I(A)

 

[Off Gridin' It]

P(W) = V(V) × I(A)

 

[Off Gridin' It]

Ok

 

[Johncfii]

You are correct.

It is valuable to have a solid understanding of “Ohm’s Law” which says “E = I x R”, and which means that the voltage measured between any two “nodes” in a circuit is equal to the current flowing between those nodes, multiplied by the resistance (in ohms) between those two nodes.

And that power (in watts, generated or consumed) is equal to the voltage between the nodes multiplied by the current flowing between the nodes, P = E x I

The time element (hours), be it amp-hours, or watt-hours, adds the element of time to indicate how long such power be consumed or delivered. This time element is needed to know the total energy that the system can store or deliver, which indicates how much real work the system can do over any period of time.

There are many internet sources of explanation that are good. Important stuff to really solidly understand for DIY electrical projects of any kind.

 

[Deleted member 23531]

Power is measured in watts and equals voltage times current.
Current is measured in amps. This is a way to communicate the number of electrons per second passing through a wire.
Charge is measured in coulombs or amp-hours. Amp-hours equals amps times time, as the name would suggest.
Energy is measured in Joules or Watt-hours. Watt-hours equals watts times time, as the name would suggest.

Therefore:
Watt-hours equals voltage times amp-hours.

This is what you're showing in your comparisons. You can have higher voltage and lower amp-hours but they still multiply to the same watt-hours.

Think of "power" as how quickly you can do stuff. Ie: you could accelerate in a sports car faster than in a economy car. Or, you could cook your frozen burrito faster if you had a more powerful microwave (though a lower power one could do it too, just slower).
Think of "watt hours" as how much stuff you can get done. It's how much energy you have to do things. For example: one shower of hot water? That's some number of watt hours. Microwaving one burrito costs you a certain number of watt hours. Microwaving two burritos costs roughly twice as much energy.
Think of "volts" as how potent your battery (or any power source) is. Maybe it's super potent so it's higher voltage and doesn't need as many electrons to get the same amount of work done.
Think of "amp hours" as how many electrons your battery stores. That's literally what it is.

Electrons have a fixed amount of charge, but they can have different energy. Just like a baseball has a fixed weight, but it's more potent if someone throws it at 100mph.

Edited.

To anyone looking to correct this, keep in mind this is my explanation for someone who never learned ohm's law, so it's targeting a certain level of understanding; try not to nit pick it unless I made a grave error.

 

[Deleted member 23531]

Another point: usually "capacity" refers to Ah, not Wh, but that's sort of a grey area because "capacity" has no definite meaning for anything except vessels which hold liquid.

A more proper term for "Wh" or watt-hours would be "energy". That is, "I have a 4.8kWh battery" means my battery stores 4.8kWh of energy. It may be any of the capacities you listed (400Ah, 200Ah, 100Ah). Again, this is sort of debatable but usually capacity refers to amp-hours.

 

[Tiger666]

Ok, I don’t know what that means. Can you volunteer more info and give more details.

I'm sorry that was a bit short wasn't it. But the other guys have covered perfectly

 

[Steve_S]

I'll try a slightly different angle. with a simple example

I run on a 24V system. I just perked my Morning Pot of Coffee, it uses 50A for 6 minutes while perking away. On a 12V system that would be 100A draw from the Battery while with 48V it would be 25A draw. A 100AH Battery Pack can output 100A for 1 hour or 50A for two (at 1C Rate).
Pack Voltage is calculated using the LFP Nominal Voltage of 3.200VPC (Volts per cell) 12V=12.8, 24V=25.6, 48V=57.2V because the LFP Voltage Curve is from 3.000-3.450.
280AH @ 12V = 3.584 kWh (4 cells)
280AH @ 24V = 7.168 kWh (8 cells)
280AH @ 48V = 14.336 kWh (16 cells)

Hope that does not muddy things.

 

[Off Gridin' It]

.

 

[Freqz]

Watts are a *rate* like a car travels so many miles per hour. You figure watts as voltage x amps. This is power.

Watt-hours are more like distance—the car traveled so many miles after going down the road at some rate for some amount of time. Volts x Amps x Time or Watts x Time. This is energy.

Batteries store energy— watt-hours or amp-hours at a specified voltage. Like your car, they can only go so fast— go too fast and you’ll have problems. They have a range, too.

4 12V batteries in parallel will each max out at this this speed limit, say 100Amps. Amps in parallel add and volts are equal so your speed limit is 4x100 or 400 amps or 12x400 or 4800 Watts.

4 12V batteries in series each still obey this speed limit of 100A *but* amps in series don’t add. Current in = Current out. So your power is now (4 x12) Volts x 100A or 4800 Watts. You can go through a similar exercise with battery capacity (energy).

Neat, huh?

From a power perspective, the voltage of your battery bank doesn’t matter much. Voltage gets important as the system power increases because dealing with many volts is easier than dealing with many amps.

 

[Steve_S]

Batteries in SERIES increase Voltage not Capacity (Amp Hours) 4x12V/100AH in series = 48V/100AH
Batteries in Parallel increase Capacity (AH) but not voltage. 4x12V/100AH in Parallel = 12V/400AH

 

[DerpsyDoodler]

Another point: usually "capacity" refers to Ah, not Wh, but that's sort of a grey area because "capacity" has no definite meaning for anything except vessels which hold liquid.

A more proper term for "Wh" or watt-hours would be "energy". That is, "I have a 4.8kWh battery" means my battery stores 4.8kWh of energy. It may be any of the capacities you listed (400Ah, 200Ah, 100Ah). Again, this is sort of debatable but usually capacity refers to amp-hours.

It’s also important to note, in case op didn’t make this connection, kWH is kiloWATT hours. It’s the same thing as watt hours to a factor of 1000. Hope that’s not insulting, just don’t want all of the different numbers and acronyms thrown out to cause confusion.

 

[markus__]

After such detailed and understandable reviews, I realized that teachers in schools should learn from you how to interpret Ohm's law even to a monkey. thanks a lot

 

[Off Gridin' It]

It’s also important to note, in case op didn’t make this connection, kWH is kiloWATT hours. It’s the same thing as watt hours to a factor of 1000. Hope that’s not insulting, just don’t want all of the different numbers and acronyms thrown out to cause confusion.

Thanks. Yes i did know that but you never know when someone doesn’t know. It’s always nice to have a little more info then not enough. Not insulting at all.

 

[DerpsyDoodler]

Going back to the very top of the query, that is actually a correct computation based on Ohm's law which was previously explained as:

Volt * Amps = Watts

However, when it comes to battery capacity, Watts or Watt-hour is not particularly used as a metric instead Amp-hours is used. W or Wh is used to refer to the maximum energy or power that a battery can store, so to speak. Ergo the similarity in Wh on your example even though voltage increases is because of the reducing amount of capacity (indicated by the reduction in Ah).

To answer your question, they can store similar amounts of power but they have different capacities.

For example: Charging 12 V batteries is not measured by the maximum wattage that can be rendered by solar panels but is more on the amperage that the solar panels can produce to fill the Ah capacity of the chargers.

Learn more about charging 12 V batteries with solar panels here: https://favorablenergy.com/charging-a-12v-battery-with-solar-panels/

it looks like your explanation gets a little complicated and merky.

Just remember this: watts are always watts, but an amp is not always an amp. 10 amps @ 12v is not the same as 10 amps @ 24v. to make a comparison of the amount of energy (which is what watts are a measurement of) we convert to watts using ohms law. why do we convert to watts? because it is a common denominator (watts are watts). so:

10a x 12v = 120 watts
10a x 24v = 240 watts

when we convert to watts, we directly compare the amount of energy and easily see the difference between the 2.

This does allow us to do capacity planning for solar panels based on their watt rating.

 

[snoobler]

Going back to the very top of the query, that is actually a correct computation based on Ohm's law which was previously explained as:

Volt * Amps = Watts

However, when it comes to battery capacity, Watts or Watt-hour is not particularly used as a metric instead Amp-hours is used. W or Wh is used to refer to the maximum energy or power that a battery can store, so to speak. Ergo the similarity in Wh on your example even though voltage increases is because of the reducing amount of capacity (indicated by the reduction in Ah).

Not on this forum and most other places. Ah as an expression of capacity is incomplete. It's capacity depends on voltage.

Capacity comparisons via Wh are direct 1 to 1 comparisons.

To answer your question, they can store similar amounts of power but they have different capacities.

Batteries do not store power.

Batteries store energy.

For example: Charging 12 V batteries is not measured by the maximum wattage that can be rendered by solar panels but is more on the amperage that the solar panels can produce to fill the Ah capacity of the chargers.

It certainly can be. 1000W/12V = 83A deliverable to the 12V.

A Wh analysis is even more effective. A 1000W array will produce about 5000Wh on a good solar day. Based on that production, energy use and battery capacity in Wh, you know what you have at the end of the solar day.

 

[sunshine_eggo]

I need help confirming if i understand battery capacity as it compares to different voltages.

If i have a 400 ah - 12 volt battery bank then thats 400ah x 12v = 4800 wh

If i have a 200 ah - 24 volt battery bank then thats 200ah x 24v = 4800 wh

If i have a 100 ah - 48 volt battery bank then thats 100ah x 48v = 4800 wh

if im understanding this that means these battery banks all have the same capacity because they are the same watt hours even though they are different amp hours. Correct?

P(W) = V(V) × I(A)

Ok, I don’t know what that means. Can you volunteer more info and give more details.

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