Author Topic: Running a large 12v system with high efficiency  (Read 2522 times)

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fabieville

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Running a large 12v system with high efficiency
« on: November 01, 2016, 12:21:11 AM »
Is it possible to have a 12v system for example a solar array at 2000watt at 12v with a 2500watt 12v inverter  operate with the same efficiency like a 24v system with the same system specs by just over sizing on your cables only so that you have 1% or less voltage drop at all of your connections at all times regardless of your loads?

In other words is it possible to have a large 12v system operate with similar efficiency like a large 24v or 48v system?

If yes what should you add or adjust to get the same efficiency? is it just oversizing on your cables to have very minimum voltage drop or is there some other issues that would need to be address. Please expound on this matter. I really love using 12v and would hope to can still use it with a 2000 or maybe a 3000watt system.

tanner0441

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Re: Running a large 12v system with high efficiency
« Reply #1 on: November 01, 2016, 09:35:31 AM »
Hi

I put a 12V system in when I first started with a 1Kw PSW inverter, because of cost plus I had access to 113Ah 12V deep cycle batteries.. It didn't take me long to realise that a 1KW inverter was about the limit. Not only the cable sizes but the actual current you could pull from the battery. It was pointed out that if12V was efficient fork lift trucks wouldn't have 36 and 48V systems.  2500W  inverter is only the running current when you switch things like electric motors the initial load before the motor reaches the operating speed can be several times the running current.

I used to fit bow thrusters to boats 2 to 7 Kw when the power was applied the cabled would physically jump and that was 50mm2 cable over 10 to 15 ft, the only way to reduce it was by fitting another battery next to the motor.

Plus if you read back through some of the posts on here there are plenty of accounts of high current inverters that failed when run at or near their rated output.

Brian.

OperaHouse

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Re: Running a large 12v system with high efficiency
« Reply #2 on: November 01, 2016, 01:33:50 PM »
I run about 1.6KW array into just a 12V car battery, but that us just to run everything real time and only to use the battery for high starting currents. Just the 140W fridge draws 120A at startup.  2KW inverter though the load is so small I don't even have the fans connected.  The legacy mismatched panels are 12V, but the majority of the power is 36V brought down to 12V with a 300W power point converter.  There is no need for any higher power.  Using a power point converter is a waste of money with a 12V array.  Go as high a voltage as you can on the array even if you stay at 12V.  I use the excess power to heat water and there is always plenty.  I'd run at 24V if I didn't have to buy a second battery.  As it is my power needs are minimal even though I live at the camp for 5 months a year.

kitestrings

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Re: Running a large 12v system with high efficiency
« Reply #3 on: November 03, 2016, 11:11:29 AM »
I'm not sure of your system, limitations or goals, but another option is to have the inverter running at 24V, center tap your bank and employ a battery balancer/equalizer to keep them even.  Solar Converters (CA) makes a number of buck/boost DC converters for this purpose.  They do introduce their own losses (~93%), but the benefit is you can have a heftier inverter and still run your DC loads, and because you are tapping the batteries, as opposed to putting all the load through an step-down converter, you have more robust short-term load capabilities.  I think of it as being similar to a single-phase 120/240VAC system.

Looks like their website is being revamped, but here's an example:
https://www.altestore.com/store/charge-controllers/battery-to-battery-dc-chargers/solar-converters-eq-1224-20a-dc-to-dc-updown-converter-p1284/

We've used these converters on a number of configurations as our system has grown.  They've been very reliable and have good support.  We still have predominantly 12VDC lighting, but we have a 48V bank.

Kindly, ~ks
« Last Edit: November 03, 2016, 11:29:30 AM by kitestrings »

ChrisOlson

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Re: Running a large 12v system with high efficiency
« Reply #4 on: November 18, 2016, 12:15:37 PM »
In other words is it possible to have a large 12v system operate with similar efficiency like a large 24v or 48v system?

I would say a large 12V system would be 2,000 watts.  A large 24V system would be 4,000.  A large 48V system would be 6,000 or more.

In theory you can achieve close to the same electrical efficiency with 12V, just that it takes more equipment.  An example; say you have two 12V batteries on a 12V system operating at 1,200 watts.  The batteries will obviously be in parallel, total amp draw on the system will be about 100 amps with no inverter losses, each battery must deliver 50 amps.  Use those same two batteries in series on a 24V system @ 1,200 watts and the amp draw of the system is now 50 amps.  However, each battery is still delivering the same 50 amps to the inverter that they do on 12V.

So hopefully you can see from the example above that building a large 12V system requires using more parallel components, including charge controllers, wiring, and inverters.  And it is easily doable - most RV's are 12V and some of those rival many off-grid homes.  I like 12V systems for off-grid cabins and smaller off-grid homes because the parts for it can be economically sourced from the thousands of RV dealers and automotive parts warehouses scattered across the country - especially lighting.  Once you go to 24 or 48V you need less equipment, but it's unproportionately more expensive equipment.  Even something as simple as a circuit breaker or relay for 24V is not commonly available and costs 4x what one will cost for 12V from the automotive or R/V industry.