12v versus 48v

[ricardocello]

It if load is just 500 watts, is there a concern of fire? Or 500A fuses?

If that is the maximum load wattage (ever), then a 12V system fits very very well.
In fact, lots of people here have 12V systems like this.
You could go with an 80A fuse and AWG 4 wire to give it a little room (960W DC should cover 500W AC).

I didn't mean to imply 48V is always better.
But if you are planning for the future (more than 500W loads), 48V is optimal in the current market.

 

[Supervstech]

Think of it in terms of what makes a battery.
Cells.

Use 100Ah cells 3.2vx100 is 320Wh
For a 12v 1000Ah battery ya need 40 cells. 40x320Wh is 12800Wh divide by 12.8V is 1000Ah
For a 250Ah 48V battery ya need... 40 cells. 40x320 is STILL 1280Wh divide by 51.2V is 250Ah

It is all the same Wh storage capacity.
So the same 500W drain would last just as long.

However.
41A at 12v will require #8 minimum, and still be wasting watts and voltage drop.

10A at 51.2V would easily flow on #14 wire with little voltage drop or wattage loss. Also, even assuming you have the same heating and voltage drop, since the drop is from a higher base voltage, less watts are lost, and the drop in voltage is less of a loss.

 

[WorldwideDave]

So you are saying that in a 12 V system even with 4/0 AWG wire running only 500 W direct current that there will still be losses, and those losses are so significant that a 48 V system would be better?

I appreciate the post above about cells. That was very educational.

I am also understanding that with a 12 V battery. There will be higher amps flowing through the conductors than with a 48 V system. It is all starting to come together in my mind. I think testing systems with my Victron smart shunt and smart solar has been very educational.

Help me understand things on the charging side. While I understand that with a 48 V battery, you can have more PV than a 12 V battery and that the conductors can be smaller. By the very nature of having more amps and volts that will enable you to charge a battery faster. So is the theory that by having a 48 V system, if the PV array was the same size, would it actually charge the battery any faster?

Additionally, does a 15 amp 12 V battery charger take longer to charge a battery than a 48 V 15 amp charger? My guess is the answer is yes.

 

[Rednecktek]

So you are saying that in a 12 V system even with 4/0 AWG wire running only 500 W direct current that there will still be losses, and those losses are so significant that a 48 V system would be better?

No, a 500w load is so insignificant that going up to 48v would be a waste of time and money. The losses on such a small load are so insignificant it wouldn't be worth paying for a $1500 battery to save $3 in copper wire and gain that 0.00001% efficiency.

Help me understand things on the charging side. While I understand that with a 48 V battery, you can have more PV than a 12 V battery and that the conductors can be smaller. By the very nature of having more amps and volts that will enable you to charge a battery faster. So is the theory that by having a 48 V system, if the PV array was the same size, would it actually charge the battery any faster?

It comes down to the capacity. If you have a 100ah 12v battery charging at 10a, it will take 10 hours to charge. If you had a 100ah 48v battery charging at 10a, it would still take 10 hours.

Inversely, if you had a 1200w array charging a 12v, 100ah battery (1280wh) that would take a little over 1 hour to charge (1280wh ÷ 1200w = 1.06 hours) and need a 120a charge controller $$!! But that same 1200w array on a 48v, 100ah batteri (5200wh) would take about 4.5 hours (5200wh ÷ 1200w = 4.33 hours) but it would only need a 25a charge controller because 1200w ÷ 52v = 23 amps.

Where you get the array size benefit is that a 50a charge controller charging a 12v battery (at 14v) can only use (50a × 14v = 700w) 700ish watts of panel where that same controller on a 48v battery (charging at 53v) can handle (50a × 53v = 2650) about 2700w of array. Granted you could put 1.21Jiggawatts of panels on a 50a controller to a 12v battery, but anything over about 700w wouldn't do anything because the controller can only use 700-ish watts because the charge controller is the limiting factor. Think of it like putting a garden hose sprayer on a fire hose. Sure, you've got a fat pipe full of high pressure water, but you can only get so much through that little plastic nozzle.

Additionally, does a 15 amp 12 V battery charger take longer to charge a battery than a 48 V 15 amp charger? My guess is the answer is yes.

Tl:Dr ; A 100ah battery charging at 10a will take 10 hours, regardless of what the voltage is. A 15a charger will charge a 12v 100ah capacity battery just as fast as a 15a charger will charge a 48v 100ah battery.

 

[Supervstech]

No, a 500w load is so insignificant that going up to 48v would be a waste of time and money. The losses on such a small load are so insignificant it wouldn't be worth paying for a $1500 battery to save $3 in copper wire and gain that 0.00001% efficiency.




It comes down to the capacity. If you have a 100ah 12v battery charging at 10a, it will take 10 hours to charge. If you had a 100ah 48v battery charging at 10a, it would still take 10 hours.

Inversely, if you had a 1200w array charging a 12v, 100ah battery (1280wh) that would take a little over 1 hour to charge (1280wh ÷ 1200w = 1.06 hours) and need a 120a charge controller $$!! But that same 1200w array on a 48v, 100ah batteri (5200wh) would take about 4.5 hours (5200wh ÷ 1200w = 4.33 hours) but it would only need a 25a charge controller because 1200w ÷ 52v = 23 amps.

Where you get the array size benefit is that a 50a charge controller charging a 12v battery (at 14v) can only use (50a × 14v = 700w) 700ish watts of panel where that same controller on a 48v battery (charging at 53v) can handle (50a × 53v = 2650) about 2700w of array. Granted you could put 1.21Jiggawatts of panels on a 50a controller to a 12v battery, but anything over about 700w wouldn't do anything because the controller can only use 700-ish watts because the charge controller is the limiting factor. Think of it like putting a garden hose sprayer on a fire hose. Sure, you've got a fat pipe full of high pressure water, but you can only get so much through that little plastic nozzle.


Tl:Dr ; A 100ah battery charging at 10a will take 10 hours, regardless of what the voltage is. A 15a charger will charge a 12v 100ah capacity battery just as fast as a 15a charger will charge a 48v 100ah battery.

I actually disagree here.

500W, if it is the maximum you use, and if you install only a 500W inverter, sure, 12V would be the way to go.

But.
A 12V 500W load on copper properly sized would be say #6 and there will be a conductor loss ALWAYS , and the inverter will have its losses as well. At 12V those losses will be minor to be sure, but they will be larger than on a 48V setup.
Keep in mind a 500W inverter at 12V will likely be a low dollar inverter, so you will likely have a 100W or 2000W inverter. Low cost inverters have high standby losses that always draw watts on top of the load, as well as whenever the load is not present.

500W sounds insignificant until you realize that at 12V it is over 40Amps of drop. Higher amps equals higher voltage drop and increased wattage lost. The drop can be offset with larger copper conductors, meticulous cleaning and torque etc, but that takes skill, time and money.

A 2000W 12V inverter should have a 4/0 cable feeding it. 500W max would be #6 for comfort, #4 for lower loss...

In 48v land high end inverters can have much lower standby/constant losses and be larger to handle additional loads when needed, and the voltage drop and wattage waste will be lower.

 

[Mattb4]

Keep in mind that batteries are chemical devices. Yes use the math (W=VA) to get a approximation of how they can store and output power. However being a chemical device they are not a direct 1 to 1 relationship. There is a loss involved in charging and discharging batteries. Different chemistries react differently based on how that charge/discharge occurs. For instance you might bulk charge a 100ah battery at 10a but when it gets near full charge the charge controller will back off amps and take longer time to finish charging it. So what might appear by the math to be 10 hours could actually be 12 hours.

Is 48vDC better than 12vDC? Is a Semi better than a Tesla?

Lucky for me I avoid the controversy and just use 24vDC .

 

[Rednecktek]

@Supervstech : Napkin math buddy, napkin math.

He's just getting started on the whole W=V×A so let's keep the minutia and fine details to where I can keep track.

 

[WorldwideDave]

No, a 500w load is so insignificant that going up to 48v would be a waste of time and money. The losses on such a small load are so insignificant it wouldn't be worth paying for a $1500 battery to save $3 in copper wire and gain that 0.00001% efficiency.




It comes down to the capacity. If you have a 100ah 12v battery charging at 10a, it will take 10 hours to charge. If you had a 100ah 48v battery charging at 10a, it would still take 10 hours.

Inversely, if you had a 1200w array charging a 12v, 100ah battery (1280wh) that would take a little over 1 hour to charge (1280wh ÷ 1200w = 1.06 hours) and need a 120a charge controller $$!! But that same 1200w array on a 48v, 100ah batteri (5200wh) would take about 4.5 hours (5200wh ÷ 1200w = 4.33 hours) but it would only need a 25a charge controller because 1200w ÷ 52v = 23 amps.

Where you get the array size benefit is that a 50a charge controller charging a 12v battery (at 14v) can only use (50a × 14v = 700w) 700ish watts of panel where that same controller on a 48v battery (charging at 53v) can handle (50a × 53v = 2650) about 2700w of array. Granted you could put 1.21Jiggawatts of panels on a 50a controller to a 12v battery, but anything over about 700w wouldn't do anything because the controller can only use 700-ish watts because the charge controller is the limiting factor. Think of it like putting a garden hose sprayer on a fire hose. Sure, you've got a fat pipe full of high pressure water, but you can only get so much through that little plastic nozzle.


Tl:Dr ; A 100ah battery charging at 10a will take 10 hours, regardless of what the voltage is. A 15a charger will charge a 12v 100ah capacity battery just as fast as a 15a charger will charge a 48v 100ah battery.

Very educational and helpful thank you. Greatly appreciated your response.

 

[WorldwideDave]

I actually disagree here.

500W, if it is the maximum you use, and if you install only a 500W inverter, sure, 12V would be the way to go.

But.
A 12V 500W load on copper properly sized would be say #6 and there will be a conductor loss ALWAYS , and the inverter will have its losses as well. At 12V those losses will be minor to be sure, but they will be larger than on a 48V setup.
Keep in mind a 500W inverter at 12V will likely be a low dollar inverter, so you will likely have a 100W or 2000W inverter. Low cost inverters have high standby losses that always draw watts on top of the load, as well as whenever the load is not present.

500W sounds insignificant until you realize that at 12V it is over 40Amps of drop. Higher amps equals higher voltage drop and increased wattage lost. The drop can be offset with larger copper conductors, meticulous cleaning and torque etc, but that takes skill, time and money.

A 2000W 12V inverter should have a 4/0 cable feeding it. 500W max would be #6 for comfort, #4 for lower loss...

In 48v land high end inverters can have much lower standby/constant losses and be larger to handle additional loads when needed, and the voltage drop and wattage waste will be lower.

I use 4/0 wire and it’s a pain in the butt but only runs 2 feet or so. Very hard to bend.

The inverter is a Giandell 2000w 12v but as pointed out going to 48 V to save three cents or five minutes or whatever the return on investment is not there.

However, because I have bigger ambitions with a larger hybrid inverter, I am enjoying this discussion a lot.

Today I’m adding a lot more panels to my existing 12 V system to see what that does for me. It is a 100v 20a victron which supports 12 V all the way up to 48 V. I will be over paneling it and it is very cloudy so let’s see what happens. I will have 1200 W of panels but with losses and any efficiencies and where I’m mounting stuff I’ll be lucky if I get 600 to 800 on a good day. Also panels are used.

 

[Glock24]

Another consideration is the inverter efficiency. If on 12V you'll have a small load (eg. 500W) a 2000W inverter will probably have a high self consumption and will operate at low efficiency. Most cheap inverters are inefficient and in general inverters usually opera at their highest efficiency between 50 and 80% load.

 

[WorldwideDave]

Another consideration is the inverter efficiency. If on 12V you'll have a small load (eg. 500W) a 2000W inverter will probably have a high self consumption and will operate at low efficiency. Most cheap inverters are inefficient and in general inverters usually opera at their highest efficiency between 50 and 80% load.

I ran the pool pump at 3000 rpm yesterday for 2 hours and the fans kicked on the inverter but it never stopped outputting power. Maybe the 4/0 AWG wires are working too well

 

[Supervstech]

I ran the pool pump at 3000 rpm yesterday for 2 hours and the fans kicked on the inverter but it never stopped outputting power. Maybe the 4/0 AWG wires are working too well

More likely, the lower ambiant temps are allowing heat dissipation without the need for fans.

 

[Mattb4]

...

Today I’m adding a lot more panels to my existing 12 V system to see what that does for me. It is a 100v 20a victron which supports 12 V all the way up to 48 V. I will be over paneling it and it is very cloudy so let’s see what happens. I will have 1200 W of panels but with losses and any efficiencies and where I’m mounting stuff I’ll be lucky if I get 600 to 800 on a good day. Also panels are used.

You can only get 20A at battery charging voltage from the Victron. Thus if you have a 12vDC (nom) battery (say 14.4v charging) 14.4vDC X 20A = 288w. With over paneling you will likely get max watts a lot longer through the day and thus more harvested watt-hours.

 

[xjaw4]

All costs aside and conductor thickness aside…a hypothetical question:
Pretend you had a 1000 amp
Hour 12 volt battery and a 1000 amp hour 48 volt battery.
The load remains the same - 500 watts constant dc load.
The solar panel array is the same in both test environments.

Question 1: Would the 48v battery take longer to reach 0% state or charge than the 12v battery?

Question 2: if a 48v battery and 12v battery have the same features, why would 48V be better (all costs aside)?

Question 3: Will having 4 batteries at 250 Amp Hours each reach 0% state of charge faster than a single 1000 amp hour battery? The voltage doesn’t matter-12V or 48V. Just trying to learn. Four 12v 250 AH 2v batteries in parallel would be 1000 AH. The same batteries wired in series the voltage would be 48. In either case the total energy stored stays the same.

 

[xjaw4]

Another consideration is the inverter efficiency. If on 12V you'll have a small load (eg. 500W) a 2000W inverter will probably have a high self consumption and will operate at low efficiency. Most cheap inverters are inefficient and in general inverters usually opera at their highest efficiency between 50 and 80% load.

What seems to happen is folks buy a 3000 watt 12v inverter one battery and one solar panel connected by a cheap pwm charge controller. The large inverter can drain the small battery in minutes and it will take a 100 w panel days to recharge even a trolling motor battery. Disappointment follows... Upgrades can be made incrementally but the resulting 12v system is more expensive and less good than a well planned system from the start. There is nothing wrong with a 12v setup and it makes sense in some cases say a service truck where the alternator keeps the battery charged. Just make sure you understand what you want your system to do and what the system can actually do before you spend money.

 

[HRTKD]

I use 4/0 wire and it’s a pain in the butt but only runs 2 feet or so. Very hard to bend.

What kind of wire? I use 2/0 welding wire and it's fairly flexible.

 

[WorldwideDave]

What kind of wire? I use 2/0 welding wire and it's fairly flexible.

Whatever Will recommended. That threaded tMnn or whatever it’s called. It cheap. Have a lot of it. Plan to do more than the three separate projects I’m doing right now.

 

[HRTKD]

I'm not familiar with that wire. All my (bigger) wire came from TEMCo Industrial. Made in the USA, very good customer service and good prices/inventory.

 

[WorldwideDave]

I'm not familiar with that wire. All my (bigger) wire came from TEMCo Industrial. Made in the USA, very good customer service and good prices/inventory.

Thermoplastic High Heat Nylon Wire - THHN​

THHN wires have a thin flame-resistant PVC insulation that is covered by an abrasion-resistant nylon jacket. THHN wires are suitable for applications up to 90ºC in dry locations and 75ºC in wet conditions. Although THHN wire can perform in high temperature environments, you must correct the wire's ampacity at high ambient temperatures and when bundling cables together in a raceway or conduit.

The maximum voltage rating of the THHN cable is 600 volts. All THHN cables meet the UL 83 standard for safety thermoplastic-insulated wires and cables as well as the UL 106 Standard for safety machine-tool wires and cables.

I am running 12V. and at 4/0 AWG, copper THHN, it can support 260 amps. My entire house has a 100 amp panel and isn't running wires as thick as I am between my battery and inverter, battery and bus bar, etc. I am over-wired for sure. So all this talk about losses due to wires, which I had hoped to avoid discussing in this thread, seem to be a non-issue for my application. Costs? Don't care about wire costs. I have probably 60 feet of this, and used about 3 feet so far, cut into two 18" wires.
76 Celsius to Fahrenheit is 167 degrees. I'm not aware of anywhere along the california coastline that gets this hot. I think I'm good.
But I do appreciate you taking the time to read and respond. Honestly I do.

 

[Rednecktek]

I'm not aware of anywhere along the california coastline that gets this hot.

Waaaait forrr iiittt....



Oddly, wire is rated for lower temperatures when it's wet, but made of water proof materials. With the heat transfer ability of water, shouldn't it be rated for MORE amps when wet?

 

[ricardocello]

I am running 12V. and at 4/0 AWG, copper THHN, it can support 260 amps.

Ampacity of the wire isn’t the issue.

THHN/THWN2 uses rather thick individual wires making it less flexible than welding wire or silicone jacketed wire.
This wire is typically used inside conduits, junction boxes, and electrical panels, not typically used in free air
because the insulation isn’t rated for abuse.

 

[Glock24]

My entire house has a 100 amp panel and isn't running wires as thick as I am between my battery and inverter, battery and bus bar, etc.

At 12V the amp draw is 10x the amp draw at 120V. For a 1500W load at 12V you are already above the 100A rating of your panel. 120V AC wiring is not comparable to a 12DC wiring.

 

[WorldwideDave]

At 12V the amp draw is 10x the amp draw at 120V. For a 1500W load at 12V you are already above the 100A rating of your panel. 120V AC wiring is not comparable to a 12DC wiring.

But once again, I have a 500 W DC load.
I’m not sure what panel you’re referring to. I do not have a panel in this 12 V system. Are you telling me that my wires aren’t good enough?

 

[wpns]

But once again, I have a 500 W DC load.
I’m not sure what panel you’re referring to. I do not have a panel in this 12 V system. Are you telling me that my wires aren’t good enough?

OK, I'll bite, what is your load? I'm gonna back up and try your original question again, this has drifted far afield into AC inverters, which you apparently don't have.

 

[HRTKD]

That threaded tMnn or whatever it’s called.

Thermoplastic High Heat Nylon Wire - THHN

No wonder I had no idea what that wire was.

THHN is just like welding cable, if THHN was on the little blue pill. Seriously, THHN is very stiff and challenging to work with in an RV with the cramped space and difficult corners. I'm going to be installing some 8/2 THHN tonight in my camper for the run between the inverter and the camper's main distribution panel (AC side, not DC) and I'm not looking forward to it.

None of the DC circuits in my camper use THHN, it's all welding cable.