24 or 48 volt battery bank

[asdex]

Hi seems like a 48 volt battery bank would be best for my 2kw PV array but other than running an inverter how else do you utilize 48 volts? I run a 12 volt car stereo, 12 volt LED lighting, 12 volt USB charger for weather station and charging mp3 players etc and a 12 volt pump for the water header tank off my existing 12 volt battery bank. I have never seen the equivalents in 48 volts. Even the Danfoss fridge unit I am looking at is 12 and 24 volts.
Do I use a dc-dc step-down converter?
Thanks,

[bcroe]

Hi seems like a 48 volt battery bank would be best for my 2kw PV array but other than running an inverter how else do you utilize 48 volts? I run a 12 volt car stereo, 12 volt LED lighting, 12 volt USB charger for weather station and charging mp3 players etc and a 12 volt pump for the water header tank off my existing 12 volt battery bank. I have never seen the equivalents in 48 volts. Even the Danfoss fridge unit I am looking at is 12 and 24 volts.
Do I use a dc-dc step-down converter?
Thanks,

Seems like an efficient way to do this would be to build in a 48V to 12V DC-DC converter into
or attached to each item. Distributing 48V will be efficient, and the output 12V regulated
regardless of the battery voltage. Use a switch on the 48V side to avoid loss if not in use.
You will not be running a very large converter in an inefficient, underutilized mode all the time.
This is done in phone offices all the time. Bruce Roe

[Mike90250]

I designed and built a 48V DC buss for a lighting trailer, where I used about 15 distributed DC-Dc converters, to power banks of 12V LEDs. To run enough copper to carry the total power at 12V, would have popped the tires. If you can stay with >90% DC-Dc converters, it will work, otherwise, you are better off getting a efficient 120VAC sine inverter to power conventional gear.
Since we don't know what all the loads are, it's hard to be exact with advice.

[asdex]

I designed and built a 48V DC buss for a lighting trailer, where I used about 15 distributed DC-Dc converters, to power banks of 12V LEDs. To run enough copper to carry the total power at 12V, would have popped the tires. If you can stay with >90% DC-Dc converters, it will work, otherwise, you are better off getting a efficient 120VAC sine inverter to power conventional gear.
Since we don't know what all the loads are, it's hard to be exact with advice.

Hi, thanks for the advice. We don't use much power. The pump is 9amp 12v and runs for about 20 minutes every second day. The 5 LED lamps are 4 watt each I think. Not sure what a car stereo takes which we use about 4 or 5 hours a day.The other things are a laptop which I run from a 200watt inverter and an AA battery charger.
It soulds like I can run all this ok from a dc-dc convertor. I also have a 1000w invertor which I use for small power tools like a jigsaw and renovator tool.
I take it you would get as much power or have the same battery capacity with 800AH @12 volts as you do with 200AH @48 volts?
Thanks,

[Mike90250]

....
I take it you would get as much power or have the same battery capacity with 800AH @12 volts as you do with 200AH @48 volts?
Thanks,

Both have the same wh storage (9,600wh) but the 48V bank is more efficient because it's running less amps through the wires, and so there is less loss.

[asdex]

The dc convertors for 48 volts to 12v and 24v I've seen to have an efficiency of 80% to 90% which isn't great. Plus the addition of an extra piece of electronics to rely on, I think I'll stick with 24 volts. I'n not concerned with voltage drop as everything is pretty close and I have plenty of 16mm cable (5 AWG I think.)
Cheers,

[Sunking]

The dc convertors for 48 volts to 12v and 24v I've seen to have an efficiency of 80% to 90% which isn't great. Plus the addition of an extra piece of electronics to rely on, I think I'll stick with 24 volts. I'n not concerned with voltage drop as everything is pretty close and I have plenty of 16mm cable (5 AWG I think.)
Cheers,

If you go with 24 volts, you have limited your system size to 2000 watts with a 80 amp MPPT controller. To go any higher requires you to either convert to 48 volts, or add another controller.

[bcroe]

The dc convertors for 48 volts to 12v and 24v I've seen to have an efficiency of 80% to 90% which isn't great. Plus the addition of an extra piece of electronics to rely on, I think I'll stick with 24 volts. I'n not concerned with voltage drop as everything is pretty close and I have plenty of 16mm cable (5 AWG I think.)
Cheers,

The efficiency of converters with isolated input/output is less. If you have a simple
load like an LED light, you you could a non isolating buck type converter which will
greatly reduce losses. Typically the input and output will share a negative lead.
Something like a computer input, better be isolated. Bruce Roe

[asdex]

The efficiency of converters with isolated input/output is less. If you have a simple
load like an LED light, you you could a non isolating buck type converter which will
greatly reduce losses. Typically the input and output will share a negative lead.
Something like a computer input, better be isolated. Bruce Roe

Thanks for that information. I'll have a look at the buck convertors. I have decided to stick to 24 volt and if I ever need more panels, I'll get another controller. All the same I would feel if we can't live on 2 kw there is something wrong with our off-grid lifestyle. We have lived in a bus for two years and then on a yacht for two and a half with young family so I have a good idea of this sort of lifestyle.
Cheers,

[reed cundiff]

There is supposed to be a good 48 V DC A/C that uses only 750 W. The Aussies are using Fujitsu DC A/Cs of various voltages. Primary reason for 48 V is probably less voltage/power loss. The voltage from our 6 panels (3 each in series) is about 90 V to TriStar MTTC-45. 1300 W is then only 14 amps and uses smaller cabling and much less power loss. Son designed and fabricated system. He is in commercial building/power plant solar with long cabling and the higher voltages is just part of his paradigm.
Reed and Elaine

[asdex]

There is supposed to be a good 48 V DC A/C that uses only 750 W. The Aussies are using Fujitsu DC A/Cs of various voltages. Primary reason for 48 V is probably less voltage/power loss. The voltage from our 6 panels (3 each in series) is about 90 V to TriStar MTTC-45. 1300 W is then only 14 amps and uses smaller cabling and much less power loss. Son designed and fabricated system. He is in commercial building/power plant solar with long cabling and the higher voltages is just part of his paradigm.
Reed and Elaine

Hi, thanks for your reply but we don't need an air conditioning unit. Our pv array voltage will be 73 volts and 1920 W which is 26 amps. The panels are 15 meters from the controller and batteries and I have 16mm sq 2 core cable (5 AWG). I have about 100 meters of this cable I got cheap so aren't too worried about voltage drop. I'm hoping the 24v bank will be fine.
Cheers,