48 to 12v converter or battery?

[skeeter_ca]

Designing my Solar system. I will be using 2-3 48v 100ah EG4 batteries. Have a wiring diagram planned out but still not sure on how i want to power the RV's 12v system. My current plan is to use a 48v to 12v 50a converter. However, now also considering using one 12v lead acid battery and utilizing the rv battery charger. Or replace the stock rv charger and get a LiFePo battery but that would be a large price increase. I understand there would be an efficiently loss but think it would be small. I am concerned about a higher idle consumption. The battery would work as a buffer for voltage spike demands. I am worried about the 48v to 12v 50a converter not being able to handle the voltage spikes from the electric leveling system. Would a large converter be better or a battery buffer system.

skeeter

 

[John From Detroit]

There are advantages to both systems but DC/DC converters. if properly dedsignedf are more efficient then Converting from DC to AC and back to DC.

 

[rvlifer]

I dont know enough about all that to say what is best but here is how mine is set up. They set up my system to run 72v from the panels to the solar charge controller and 12v to the batteries. My solar charge controller is a midnite. Replaced the onboard converter with a magnum inverter charger to charge the batteries from shore power.

When we were talking about what solar controller to go with they had to be careful to get one that would handle all the panels we planned.

I understand why they set it up to run higher voltage from the panels. Not sure of the benefits of highe voltage batteries

 

[DonTom]

Not sure of the benefits of highe voltage batteries

One will be that the current is less for the same power and can run thinner wires. Or can run longer wires with less loss from the battery.

If there are other advantages, I do not know what they could be.

-Don- Reno, NV

 

[Primerump]

Designing my Solar system. I will be using 2-3 48v 100ah EG4 batteries. Have a wiring diagram planned out but still not sure on how i want to power the RV's 12v system. My current plan is to use a 48v to 12v 50a converter. However, now also considering using one 12v lead acid battery and utilizing the rv battery charger. Or replace the stock rv charger and get a LiFePo battery but that would be a large price increase. I understand there would be an efficiently loss but think it would be small. I am concerned about a higher idle consumption. The battery would work as a buffer for voltage spike demands. I am worried about the 48v to 12v 50a converter not being able to handle the voltage spikes from the electric leveling system. Would a large converter be better or a battery buffer system.

skeeter

I would ask what are your anticipated loads ?
generally for boondocking, 12 Volt useage should be minimal so I would question the use of 48 Volts.
however, if you plan to supply 120V or 240V power for a/c microwave and other high consumption appliances then the voltage is usually defined by power first and capacity second and reducing the current load to something reasonable.

My suggestion, based on many years of professional design woud be to sum all your power requirements and then divide the total power by 100 Amps, that should give you a good starting point for voltage.

for example, a good practice is not to exceed a current of 100 Amps. if your total wattage load is say:
a/c = 1500 W, Microwave = 1500W and a TV and other small loads then you could have concurrent loads of approx. 3200 Watts, 3200 watts at 12 V = 266 A. at 24V = 133A and 48V = 66 A.

My choice here would be 24 or 48V..
for 24V, panels should have a Vmp of at least 33V, at 48V one requires 96cell panels with Vmp at 58 V or higher or you can series 60 cell panels..

as for the 12V system, that's easy, just use the existing converter and a small 12V battery.

For my own travel trailer, I replaced the stock 12V 100Ah battery with a heated lithium drop-in and left it on the tongue in a box. It powers the trailer system and the emergency brake away system. The solar system is 24 Volts ( 19,200 W/hr ) or 24 V @ 800Ah feeding a 3000W charger/inverter. It is designed to act as a UPS system and power the a/c overnght and also other appliances.
The 12V system is charged from the 120V from the inverter so nothing else has to be done to provide 12 V.

 

[Primerump]

I understand why they set it up to run higher voltage from the panels. Not sure of the benefits of highe voltage batteries

it's all to do with power and balancing cable cost with voltage drop.

 

[Primerump]

One will be that the current is less for the same power and can run thinner wires. Or can run longer wires with less loss from the battery.

If there are other advantages, I do not know what they could be.

-Don- Reno, NV

quite correct.. cost is also a factor, why run 20 feet of 4/0 when 2AWG could be used.
cost difference on a large project is considerable.

 

[DonTom]

quite correct.. cost is also a factor, why run 20 feet of 4/0 when 2AWG could be used.
cost difference on a large project is considerable.

I think I recall hearing something about cars in the future using a higher voltage battery. The problem is most of the car will need to be redesigned. It was a mistake to use 12V to begin with.

IMAO, we made the same mistake by making 120 VAC the norm in houses, unlike in Europe where 240 VAC is the norm. Most USA houses have 240 VAC anyway, just not used as much as it should be.

-Don- Reno, NV

 

[Larry N.]

It was a mistake to use 12V to begin with.

Much better than the 6V systems it replaced, and they could hardly anticipate all the things that make higher voltages more desirable to day. If I recall correctly the military went to 24V systems on most of their special built vehicles.

 

[DonTom]

Much better than the 6V systems it replaced,

That would have been a great time to redesign cars for 48 VDC. 48 VDC seems kinda high for today, but lets not make the same mistake again. Get ready for whatever could happen in the future unless there is some disadvantage. Perhaps a possible shock hazard from handling the battery? Where that starts isn't exactly a clear number.

Even modern EVs are stuck on the 12-volt systems for just about everything except for the motors.

-Don- Reno, NV

 

[John From Detroit]

quite correct.. cost is also a factor, why run 20 feet of 4/0 when 2AWG could be used.
cost difference on a large project is considerable.

Yup. No matter what the system voltage to hold 10KWH of power you need the same amount of battery.. (Roughly 1000 amp hours at 12 volt after losses) iir 250 amp hours at 48 volts So the battery weight and cost.. Identical..

But the cost and weight of the expensive and heavy copper wire reduced by 75%.
Hence the 48 Volt system.. I've heard there are regulations about higher voltages (prohibited) but I'm not sure on that.

 

[Primerump]

Yup. No matter what the system voltage to hold 10KWH of power you need the same amount of battery.. (Roughly 1000 amp hours at 12 volt after losses) iir 250 amp hours at 48 volts So the battery weight and cost.. Identical..

But the cost and weight of the expensive and heavy copper wire reduced by 75%.
Hence the 48 Volt system.. I've heard there are regulations about higher voltages (prohibited) but I'm not sure on that.

50 Volts is the accepted max dc voltage for consumer goods.

NEC does not specify the voltage, it all depends on the installation and power.
so some people might call 600 Volts "low".. others 2000 Volts.

another aspect of 48V systems is the solar panel side, having a higher voltage at the controller
reduces the currents and therefore cabling. the lower current also reduces the cost of the controller too..

amperage and wattage usually defines the cost basis for a controller.

Typical cost for 1200 Watt controller.

12V 100A typically $500
24V 50A typically $160
48V 25A typically $90

additionally, high voltage residential panels are also much more efficient than these so called "12V panels"

 

[rvlifer]

50 Volts is the accepted max dc voltage for consumer goods.

NEC does not specify the voltage, it all depends on the installation and power.
so some people might call 600 Volts "low".. others 2000 Volts.

another aspect of 48V systems is the solar panel side, having a higher voltage at the controller
reduces the currents and therefore cabling. the lower current also reduces the cost of the controller too..

amperage and wattage usually defines the cost basis for a controller.

Typical cost for 1200 Watt controller.

12V 100A typically $500
24V 50A typically $160
48V 25A typically $90

additionally, high voltage residential panels are also much more efficient than these so called "12V panels"

What is factored into the efficiency of an electrical panel?

 

[Primerump]

What is factored into the efficiency of an electrical panel?

ambiguous question...

I will assume you mean the RV's panel and charger ?
if so, then the charger will be some 80% or better efficiency at charging.
I added a few percent on my panels to account for it.. I don't notice it in practice.

 

[rvlifer]

ambiguous question...

I will assume you mean the RV's panel and charger ?
if so, then the charger will be some 80% or better efficiency at charging.
I added a few percent on my panels to account for it.. I don't notice it in practice.

I may have heard the term once or twice but didnt know what it meant in relation to a breaker box. Was asking what you meant when you used the term

 

[John From Detroit]

What is factored into the efficiency of an electrical panel?

Eelctrical panels are like 99.99999% (Basically 100%) efficient (Some slight heating of the breakers happens)

CONVERTERS (Often attached to ther rear of the panel.) have both an effiency (As someone pointd out 80% is common) and a Power factor (Difference between WATTS and Volt-amps is Power Factor VA is always higher on inductive circuts.. Pure resistive always the same (PF of 1)

 

[DonTom]

As someone pointd out 80% is common) and a Power factor (Difference between WATTS and Volt-amps is Power Factor VA is always higher on inductive circuts.

80% sounds extra poor to me. And I discovered here, thanks to Lou, how poor the power factor is in RV Converters. Power factor is 78.25. 269 VA wasted in heat reflected back to the source doing nothing useful.

It sounds poor to me because EV chargers (inside the EV)are better than 90% efficient and the power factor is normally very close to one. And I am more used to seeing those specs, where the PF can normally be ignored and just think in watts.

Here is an example. I got my external motorcycle chargers from there. Note efficiently is 93% and the power factor is better than 0.98.

To make electric motorcycle chargers small enough, they cannot afford to waste much power. A 13.2 KW charger (really is two 6.6 KW chargers) will fit in my Zero DSR/X motorcycle, that is a little larger than the charger in my Tesla. However, I only have the 6.6 KW charger in mine for several reasons. One is that most places I charge it at cannot do anything near the 13 KW. A few cannot even do the full 6.6 KW, but are close enough. The other reason is I have extra storage space this way. A 6.6 KW charger is still fairly large for a motorcycle. Another reason is less top heavy and I find the charge times are just right for my breaks as is. If I am out on an electric motorcycle, I am not in a big hurry to get anywhere fast. And I have made several 300 mile day trips on electric motorcycles as it is. A few have done a thousand miles per day (24-hour day) on an electric motorcycle.

-Don- Reno, NV

 

[Primerump]

80% sounds extra poor to me. And I discovered here, thanks to Lou, how poor the power factor is in RV Converters. Power factor is 78.25. 269 VA wasted in heat reflected back to the source doing nothing useful.

typical RV equipment.. what did you expect ? LOL

 

[John From Detroit]

80% sounds extra poor to me. And I discovered here, thanks to Lou, how poor the power factor is in RV Converters. Power factor is 78.25. 269 VA wasted in heat reflected back to the source doing nothing useful.

Power factor is a percentage though I usually see it expressed as a decimil number 1 is o f course Perfection so the PF you cite is .7825 or 78.25% It is the cosine of the phase angle between voltage and current which is why it is expressed as 1 or less.. I've seen, or rather heard of Machines with power factors of zero.. Ate lots of Volt-amps but the motor shaft.. just sat there A small adjustment in the phase angle and... Like magic. it worked

now Efficacy.. that's 120)% times wats out/watts in .. and a whole differnet calculation.

Many RV converters are still Transformer based.. Though more and more now days are switching (Switching is USUALLY Better) Some are a combination of both.. Your EV charger is likely pure switching .. Filtering (needed for the RV but not for the EV charger) also adds in losses.

 

[DonTom]

I've seen, or rather heard of Machines with power factors of zero.

It's easy to get a zero power factor. Just use a capacitor as a load. If you want a PF of 1, that is just as easy. Use a carbon resistor instead of a capacitor. Use both and get any power factor you want by changing values or frequency.

Power factor is a percentage though

Makes no difference. "percentage" means "per cent" or "per 100". Note that my EV charger link said:

• "Greater than 0.98 power factor minimizes utility surcharges and maximizes AC power utilization."

No percentage mentioned for power factor in above.

But they did for efficiency:

• "93% typical efficiency"

-Don- Reno, NV