12v vs 12v related

[DavidRoss]

Hello,
I'm building out a new system for a sailboat. Most all of the components in question are 12 volt.
The 12 volt users are Autopilot, chart plotter, lights, water pump...standard stuff.
Except for the largest draw - the air conditioners are 24 volt. They are the new Zero Breeze units which use 250watts each.
The Air Conditioners draw more power than everything else on the 12 volt side when they are on.

Would it be more efficient to
1. build out a 12 volt system and convert to 24 for the AC units
OR
2. build a 24 volt system and convert to 12 for the rest of the house

AND why?

The whole system is not terribly large. I was planning on 400 watts solar using a 200 amp hour battery. Not bad considering the high Air Conditioner loads will be in the middle of the day when the sun is strongest.

We will also have a 2000 watt inverter consuming DC as well but all the components will be within five feet of eachother.

Thanks

 

[Diysolar123]

is that a 200ah 24v battery?
if you have two 250W AC units thats 500W / 24 = so you are pulling 20A from your 24v pack which is a nice manageable current.
When you double that current if usiing 12V, well, 40Amps is certainly some serious amperage that requires larger connectors, wire, etc..

fyi, when I looked at the zero breeze info sheet it states that it runs on its own battery...and you need 5hrs to recharge it..also I see a bullet that says:
"The Zero Breeze Smart Battery cannot be used with other products like other 24V batteries"

 

[DavidRoss]

But is the 20 amps vs 40 amps worth converting the whole system to 24 and running a step down converter for the rest of the house?

 

[DavidRoss]

It would likely 100ah 24v or 200ah 12 volt start and adding capacity as time goes on.

 

[Jasgeer]

Hello,
I'm building out a new system for a sailboat. Most all of the components in question are 12 volt.
The 12 volt users are Autopilot, chart plotter, lights, water pump...standard stuff.
Except for the largest draw - the air conditioners are 24 volt. They are the new Zero Breeze units which use 250watts each.
The Air Conditioners draw more power than everything else on the 12 volt side when they are on.

Would it be more efficient to
1. build out a 12 volt system and convert to 24 for the AC units
OR
2. build a 24 volt system and convert to 12 for the rest of the house

AND why?

The whole system is not terribly large. I was planning on 400 watts solar using a 200 amp hour battery. Not bad considering the high Air Conditioner loads will be in the middle of the day when the sun is strongest.

We will also have a 2000 watt inverter consuming DC as well but all the components will be within five feet of eachother.

Thanks

Diysolar123 brought up the issue of the bullet point which you will need to address..
My approach is perhaps a little unorthodox but I would encourage you to configure a 24V solar system where you can pull power from each of the two 12V batteries. You could distribute the loads to try to balance the current drain in the two 12V systems I would try to avoid DC-to-DC converters due to loss in efficiency compared to running from 12V directly. The question in my mind is whether someone has a device to balance the charge on the two 12V batteries which are in series. In theory a BMS would control this function by shunting charge current selectively around one of the 12V batteries.

 

[time2roll]

Go 24 volt battery at 200+ Ah. Save room for more battery if you like the cool A/C.

 

[DavidRoss]

is that a 200ah 24v battery?
if you have two 250W AC units thats 500W / 24 = so you are pulling 20A from your 24v pack which is a nice manageable current.
When you double that current if usiing 12V, well, 40Amps is certainly some serious amperage that requires larger connectors, wire, etc..

fyi, when I looked at the zero breeze info sheet it states that it runs on its own battery...and you need 5hrs to recharge it..also I see a bullet that says:
"The Zero Breeze Smart Battery cannot be used with other products like other 24V batteries"

• 
  The Zero Breeze Smart Battery cannot be used with other products like other 24V batteries

Meaning their battery can not be used with other products.
However their product can be used with other batteries - which is what I will be doing.

 

[12VoltInstalls]

I hate split voltage systems for a couple of reasons. But your case seems to warrant it.

Did I miss your 12V sum Watts/amps? Plus you mentioned plural “air conditioners” which is ~500W, a losing game with 400W solar input.
You have to provide for recharging the battery fully for sunset use plus the full-sun continuous use simultaneously.
Sorta figuring 10hours dark run time and 10hours charge time you have to replace 12kWh daily, right? Yes, I know I left out that four hours but: 400W x 10hrs is only 4kWh

Unless coffee hasn’t fully uploaded and I missed something : the numbers don’t work.

Anyway, my opinion is give the AC the 24V it wants, run a DC2DC 12V supply with a tiny 12V battery, and use a 24V inverter for whatever 120V you need. But you need more panel for those AC units imho.

 

[John Frum]

They are the new Zero Breeze units which use 250watts each.

Please provide a product link to your exact units.

 

[DavidRoss]

Thanks for all the replies but none of them really addressed the question I had. Im not asking if my battery or solar panels are sufficient for running the AC unit for a given period.
I am simply asking if it is more efficient to store power as 24volts to serve the one 24 volt load (the AC) and convert to 12 for everything else.
Or should I store power at 12 volts and convert to 24 for this one load.

Perhaps I gave too much information in my first post which made folks fixate on solar panels and amp hours when that had nothing to do with the question.

 

[12VoltInstalls]

I answered. The inefficiency of the biggest watt consumer will have theoretically the largest ‘waste.’ 12V-24V converting costs more money. So you build for that 24V and make the ‘waste’ on the discretionary use side, 12V.
Me? I’d probably just make a second 200W system at 12V. Dunno if you prefer the cost to be in dollars or watts. Though both approaches cost money