Efficiency for 12V design questions

[Skotty2wo]

I have two projects that I am working on. Both ultimately need to run 12V equipment.

One is an RV that I want to retrofit to new LED lights etc and ditch the generator, so that it can all run off of solar. The other is my robot, which uses a mix of 12V and 5V lights, motors, and controllers.

I currently have a single 12V panel and charge controller setup to run the robot, and by redesigning the light loads and the motors and computers involved, it runs and is self sufficient until unplugged (it needs to be able to run all night long, Burning Man project)

RV is going to be designed from the ground up.

SO - My question is mostly about efficiency. Is the best solution to buy 12V panels and keep everything 12V all the time, or is there a benefit to going with 24V (or higher) panels and equipment? I want to know if down converting back to 12V is inefficient and not worth it. I know that using power inverters to get 110V AC have loss. I will use one of these for the RV for the random occasions where we need to use line voltage. Everything else that the RV would need to run off of 12V, and I know that by changing out lights and other fixtures I can lower my overall consumption.
I guess I just want some direct answers as far as overall efficiency - loss due to voltage converters - information like that. Any insight or direction to websites with more information would be greatly appreciated.
Thanks
S*

[inetdog]

I have two projects that I am working on. Both ultimately need to run 12V equipment.

One is an RV that I want to retrofit to new LED lights etc and ditch the generator, so that it can all run off of solar. The other is my robot, which uses a mix of 12V and 5V lights, motors, and controllers.

I currently have a single 12V panel and charge controller setup to run the robot, and by redesigning the light loads and the motors and computers involved, it runs and is self sufficient until unplugged (it needs to be able to run all night long, Burning Man project)

RV is going to be designed from the ground up.

SO - My question is mostly about efficiency. Is the best solution to buy 12V panels and keep everything 12V all the time, or is there a benefit to going with 24V (or higher) panels and equipment? I want to know if down converting back to 12V is inefficient and not worth it. I know that using power inverters to get 110V AC have loss. I will use one of these for the RV for the random occasions where we need to use line voltage. Everything else that the RV would need to run off of 12V, and I know that by changing out lights and other fixtures I can lower my overall consumption.
I guess I just want some direct answers as far as overall efficiency - loss due to voltage converters - information like that. Any insight or direction to websites with more information would be greatly appreciated.
Thanks
S*

You need to balance the efficiency loss in an inverter against the I²R loss in the 12 volt wiring around the house. Especially if any of the loads will be high current at 12 volts.
Any given amount of power in the form of 12V "battery" panels is likely to cost twice as much as the equivalent from GT panels. Just the way the market economics are working right now.

Against the losses in the inverter also consider the losses in the PWM charge controller. And figure that if you will need to use an inverter for AC loads, the DC wiring to the inverter will be a lot heavier and more expensive.

Finally, an equivalent amount of energy storage in a 12 volt battery system will be harder to maintain and give a shorter battery life than a 24 or 48 volt system.

You have not said how much power your loads are going to add up to, nor how large the AC loads in the RV will be.

Once potentially handy feature of going with 12 volt battery is that you have the option of using the vehicle alternator to charge the battery if for any reason the PV falls short.

[Skotty2wo]

Let me rephrase a bit...

The robot project worked last year, but drained the batteries by midnight, due to larger 12v loads and using a power inverter to run some minimal 110v computers. By redesigning the parts involved, I used the same batteries and panel, and now it can run all night no problem, while doing everything it did last year and then some. It has all been converted to run on 12v or 5v.


My bigger questions of efficiency lean towards how to best power the RV and the necessities. It has a few different 12v lights, which I would change out to lower wattage LED bulbs to decrease power consumption. The bigger load is the refridgerator, which could run on propane, but on 12v would need 15+ amps. The water pump runs at around 5 amps, but would only need to be on from time to time. The big hog is the AC unit, which runs off 110V, but would only be on midday, and probably only while getting full solar charging.

So, if I set up the coach to have a 24V solar system, what is the most efficient way to run the 12v equipment? Do I assume that at 24v I can harvest twice the amount of 12v power (more or less)? And have twice as many amp hours at 12v? I am not sure how that translates. I am thinking that if the higher voltage system is a better way to go, that I would just isolate the solar from the alternator and make it a separate system. And if I use a 24v solar setup, is there a charge controller that would allow for running 12v equipment without an external converter? Step down converter or..??

Ideally, I would think that two good sized panels on the roof would work best. There is room for a few batteries, so space is not a huge issue. Any thoughts, anyone....?

[Naptown]

I can tell you right off that 2 panels will not come close to running the AC
If you add a whole bunch of batteries and at much higher voltage and a bunch more collectors you may get an hour or two out of it.
How much exactly does the AC draw when running?

[Skotty2wo]

The AC looks like it pulls somewhere from 10-13A at 110V, so to me that basically says that it takes way too much power. I am looking at a few 24V models, which pull around 14A at 24V. A little bit more reasonable. And the AC is mostly convenience, I am not a big fan of sitting around in the AC, it would more than likely be a once in a while use.

Mainly want to look at running the fridge and the water system for a day or three. And my bigger question is still about the best way to go about it... If I run all at 24V and downconvert to run 12V appliances, what is the most efficient way to do this?

[SunEagle]

The AC looks like it pulls somewhere from 10-13A at 110V, so to me that basically says that it takes way too much power. I am looking at a few 24V models, which pull around 14A at 24V. A little bit more reasonable. And the AC is mostly convenience, I am not a big fan of sitting around in the AC, it would more than likely be a once in a while use.

Mainly want to look at running the fridge and the water system for a day or three. And my bigger question is still about the best way to go about it... If I run all at 24V and downconvert to run 12V appliances, what is the most efficient way to do this?

They do make 24vdc to 12vdc step-down converters but I have no experience with any so I can't offer any suggestions.

[Sunking]

Well I have held off on replying to see how it would play out and get a better feel for what the OP wants to do.

What I can say now even the refrigerator is not going to be possible without a generator, alternator, or shore power hookup. Does not matter if the system is 12 or 24 volts. At 24 volts just makes things less efficient because it requires a very expensive converter. There is not enough room on an RV to put up enough panels to generate the amount of power required.

[FloridaSun]

They do make 24vdc to 12vdc step-down converters but I have no experience with any so I can't offer any suggestions.

Pyle makes some decent 24:12 converters from 60W to 360W. I have a 240W, works ok but came without on/off switch so added one in on wiring to save watt drainage when not using 12v.