New System for Van Camper - 12V or 24V?

2p4d1van

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Okay, so this is my first post as a new member and I could use some help on deciding what voltage battery system to use for my house battery. I am building a camper from a 2007 Ford E350 passenger van. I intend to create an off-grid system that will sustain us for up to 5 days in remote locations. I want to do this without the use of a gasoline powered generator by using a solar system, combined with alternator charging and the ability to plug in to 110 AC when we have that available.

A good friend donated four panels to use in my build. Here's the specs;
Astronergy CHSM6610P-240
Max Power 240.0Wp
Open Circuit Voltage 37.77V
Voltage at Pmax 29.54V
Current atPmax 8.13A
Nominal Operating Temp 43C

My primary use will be traveling/camping during warm/hot months of the year. I am a resident in SW Florida, so being able to produce air conditioning is important. I am planning to utilize a Zero Breeze unit and duct it through the factory headliner vents. The Zero Breeze is a 24V DC unit, which comes with an adapter for 110 AC operation. Then there are the other items.

Refrig/Freezer, dorm size, 110 AC
Flat Screen TV, 110 AC
Single Cup Keurig coffee machine, 110 AC
Crock Pot/Pressure Cooker 110 AC

Water Pump 12V DC
LED Lights 12V DC
Phone Charger 12V DC
Laptop Charger 12V DC

So, here are my questions. If my highest usage is the Zero Breeze at 24V DC. Should I build a 24V DC battery system and convert 24V DC to 12V DC, using an inverter for the 110 AC items? Or, do I build a 12V DC battery system and convert to 24V DC for the Zero Breeze, using an inverter for the 110 AC items? Since I want to use my 12V alternator as one of my options for charging, is that going to limit me to a 12V battery system? Since all conversions come at a cost in efficiency loss, I'm thinking that a 24V battery system would be the way to go. The 12V items would be infrequent uses, but the Zero Breeze would be the heaviest use. Converting tto the 110 AC is going to come at a loss, no matter which voltage system I build.

Thanks in advance for the help.

Steve
 

rmaddy

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Tough choices.

You could keep everything 12V and power the A/C at 110 using the inverter. But between the A/C and the fridge you would need to run the inverter constantly and inverters use energy over and above the devices they power.

You could go 24V. You would need a 12V->24V DC-DC charger like the Victron Orion. You would also need a 24V->12V DC-DC converter to run your 12V items. And you need the inverter for the AC items.

There would be advantages to 24V if the A/C can be run at 24V and you used a 24VDC refrigerator. Those two items will be used the most so by both being the same voltage as the main system that would give the best efficiency. You could probably find a 24V TV as well. 24V water pumps are available too (I have one in my trailer). LED lights can be found or setup for 24V. This only leaves a couple of 12V items and only a couple of 110VAC items. This means the inverter would only have to be on when making coffee or using the cooker.

You really need to post the wattage usage of these items and an estimate of how much each item will be used each day. Things like the A/C and fridge will cycle on and off so you need to estimate how much power they actually use each hour or day. Simply looking at the wattage will be misleading if the device only uses that wattage say 20 minutes per hour.

Once you know your true power needs then you can work out the best setup, how much battery you need, and how much solar you need to meet your goals.
 

time2roll

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I would be at 12v, max out the solar and plan to double the battery. Cool air may not flow at every moment.
 

2p4d1van

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Tough choices.

You could keep everything 12V and power the A/C at 110 using the inverter. But between the A/C and the fridge you would need to run the inverter constantly and inverters use energy over and above the devices they power.

You could go 24V. You would need a 12V->24V DC-DC charger like the Victron Orion. You would also need a 24V->12V DC-DC converter to run your 12V items. And you need the inverter for the AC items.

There would be advantages to 24V if the A/C can be run at 24V and you used a 24VDC refrigerator. Those two items will be used the most so by both being the same voltage as the main system that would give the best efficiency. You could probably find a 24V TV as well. 24V water pumps are available too (I have one in my trailer). LED lights can be found or setup for 24V. This only leaves a couple of 12V items and only a couple of 110VAC items. This means the inverter would only have to be on when making coffee or using the cooker.

You really need to post the wattage usage of these items and an estimate of how much each item will be used each day. Things like the A/C and fridge will cycle on and off so you need to estimate how much power they actually use each hour or day. Simply looking at the wattage will be misleading if the device only uses that wattage say 20 minutes per hour.

Once you know your true power needs then you can work out the best setup, how much battery you need, and how much solar you need to meet your goals.
Thanks for the input on this.

I think you're right, the 110V fridge is going to have to go, in favor of a 24V unit. Makes sense, since the air conditioning and fridge would run pretty much full time. I could look at a 24V TV and 24V water pump since I haven't made those purchases, yet. I'll do some work on gathering wattage usages. My four panels should give me close to 960 watts at max operating. Coming to a decision on battery voltage and how much storage I need is what I need to resolve.

The fog is clearing and I'm getting a better idea of where I'm going with this.
 

kenryan

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Although I do not have direct experience with the Zero Breeze, I do have experience with Florida heat. The best you can expect from the Zero Breeze would be that it would keep your body cool when it is blowing directly on you. It will not work for cooling the van in such a demanding environment. Van air conditioning from battery power is a tough nut to crack. Refer to this forum: https://www.fordtransitusaforum.com/

If I were going to try to cool a van in the warm/hot months of the southeastern US I would expect to need to use either a generator, or plug into grid electric. Sure, it can be done from a gigantic battery, but remember, you still need a way to recharge the battery. If you want to recharge using solar, you will need a large solar bank and you will need to park in the sun--forget about parking in the shade. If you want to recharge from the alternator, you will need a large alternator and you will need to run it a lot.

Again, visit the Ford Transit USA forum and research AC. You will see what you are up against.

If you are willing to accept that the Zero Breeze blowing directly on your body as sufficient cooling then to answer your question, I would design a 24 volt system. I would run the Zero Breeze directly from the 24 volt system and I would look for a refrigerator that runs on 24 volts (example: Vitrifrigo). I would also get an inverter that runs on 24 volts and for regular 12 volt stuff like lights I would use a step down converter.
 

2p4d1van

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Well, it is a passenger van with the rear A/C unit. I'm not expecting the Zero Breeze to cool down a hot van. If it can maintain an already cold van and keep it relatively comfortable during the night time hours, it will do just fine. It's also a standard roof (can't stand up in it) with cabinets and a counter. There won't be much living space, so cubes to be cooled will be very little. I'm a year round resident of Fort Myers, so I'm very familiar with Florida heat. I don't know what the actual draw will be in watts, but at 24 volts, it only requires a 10 amp fuse.
 

2p4d1van

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Hey, I've got another question. If I run a 24V house system and a 12V vehicle system, wouldn't I want to keep the two totally separate? For the house system, I'm thinking that I would need a junction block for the positive leads, but also another block for individual negative leads, too. Could I still use the body as a common ground for both systems?
 

kenryan

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I don't know what the actual draw will be in watts, but at 24 volts, it only requires a 10 amp fuse.
This is your clue that the Zero Breeze is a weak system. This is a quote from the Zero Breeze website:

"Traditional portable air conditioners are more than 800w, which requires too much electricity. MARK2 is only 240w."

Ask yourself, what magic did they employ to gain so much cooling from so little power? Why doesn't every manufacturer use this magic?

For a 12/24 volt system, you would build the 24 volt system and then tap into it with a 24v-12v converter, and run the output of the converter to a 12v busbar. The two systems can share a chassis ground.

By the way, don't forget that your van will be full of little heating devices such as the refrigerator, lights, all electronic equipment (including the Zero Breeze), even your body. I doubt the Zero Breeze would be sufficient to just overcome these heat inputs.
 

100 Proof

"Please Lord, don't let me do something stupid."
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Have you considered a 5,000 BTU window air conditioner? I run one off of 750W of solar panels.
 

2p4d1van

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kenryan,

Are you referring to my question about keeping the two systems separate? My concern is my vehicle 12 volt system that provides starting and ignition. So, you're saying I would run my starting and ignition off of my 24 volt house system by using a converter to 12 volts?
 

kenryan

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kenryan,

Are you referring to my question about keeping the two systems separate? My concern is my vehicle 12 volt system that provides starting and ignition. So, you're saying I would run my starting and ignition off of my 24 volt house system by using a converter to 12 volts?
No, that is not what I am saying. I am saying that the 12 volt "house" system would be drawn off the 24 volt "house" system via the 24-12 volt converter. Yes, the 12 volt vehicle system is "separate" from the 24/12 volt house system. This presents a problem when it comes to charging the 24 volt system from the vehicle's 12 volt alternator. There are 12-24 volt battery-to-battery chargers. It is also possible to use the vehicle alternator to power a 12 volt invert, and use that inverter's output to power a 110 volt - 24 volt battery charger. But how well this will work will depend upon how powerful your alternator is and how much charging capacity you need.

Again, powering an adequate air conditioner for a van is a big ask. It is possible, but it is not easy. It requires a very robust system, because adequate cooling in a harsh environment requires a lot of energy.

As an example, I am currently planning my next camper build. My plan as it currently stands includes 2 x 240 amp alternators (Ford Transit) and some solar to charge a 5000 watt-hour lithium battery. This will be used to power a 10000 btu Midea U inverter window air conditioner drawing 890 watts to cool a very well insulated full sized van. My current camper which is very small and very well insulated with no windows has a 5000 btu window air conditioner, but the electrical system is not extremely robust. I can run the AC for an hour or so (supplementing with alternator power) to cool off the camper before I go to bed. This system would be completely worthless in an uninsulated van with lots of windows.
 

djnorth

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As others have said, try to run as many items with DC as possible - inverters consume energy even in standby.

If you want to add some hot water to your system, you could go with a small point-of-use tank and swap out the heating element for a 12 or 24V unit to match your house battery voltage.
 
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2p4d1van

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I'm going to stick with 24V for all of my appliances, with the exception of one or two 110AC items that would only be used for short intermittent periods. With four panels that are 240 watt, Pmax 29.54 volts, Pmax 8.13 amps, do you think I should wire them parallel, or series-parallel for charging a 24V battery bank?
 

rmaddy

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I would put the panels in 2S2P. Only consider 4P if you have a lot of shading issues due to things on the roof of the van. More in series is better for lower light conditions. More in parallel is better for shading issues. You could do 4S if there are no shading issues but with a Voc of nearly 38V and taking into account colder conditions you would need a SCC that can handle 180V input.
 

2p4d1van

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Got it! I was thinking along the same thing, mainly because I'm going to be stopping to set-up in places that I've never been to. So, not knowing what the shading might be, the 2S2P should cover the possible shading issues. Just needed to hear it, since most of this is new for me. I've done complete 12V vehicle wiring from front to back, and I've done house wiring to the extent of installing 100 amp sub panels, But some of the solar is new to me and made me think about some things differently. Thanks for the help.
 

2p4d1van

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If I wire these panels in 2S2P, would I be correct in assuming around 60V at 16A to the charge controller during full light conditions?
 

rmaddy

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If I wire these panels in 2S2P, would I be correct in assuming around 60V at 16A to the charge controller during full light conditions?
In theory, yes. Assuming your panels are mounted flat on the roof then you'll never see that much. But it is Voc that matters when picking a charge controller and checking its max input voltage. And Voc goes up in the cold. At 2S you have about 76Voc at STC. Add 15%-20% for cold. So you need a SCC that can handle 100V input. 4 240W panels is 960W. At 24V that's about 40A. So you need a SCC that can provide up to 40A output to the battery. Given the flat panels you can probably get away with a SCC that supports 30A output. 30A x 28V = 840W. It will be a rare day where your flat mounted panels will get over 840W.
 

12VoltInstalls

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think you're right, the 110V fridge is going to have to go, in favor of a 24V unit. Makes sense, since the air conditioning and fridge would run pretty much full time. I could look at a 24V TV and 24V water pump since I haven't made those purchases, yet. I'll do some work on gathering wattage usages. My four panels should give me close to 960 watts at max operating. Coming to a decision on battery voltage and how much storage I need is what I need to resolve.
The battery storage per watt-hour to meet your needs will be essentially the same because the loads are the same in watts.

If money isn’t a concern, buying the 24V stuff is fine. However, a few more panels and a ‘big’ charge controller may cost significantly less than a 24V fridge…

I’m running at 120V ~5CF fridge 24/7 on 12V battery bank. I did that all summer w/ 400W of panels. At 960W 12V is still an option - until you plug in the A/C maybe. Then 24V starts making a lot of sense.

Nobody mentioned that so I thought I should.
 
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