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Dimensions Pure Sine Inverter Powering an inverter directly from the panels


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  #1  
Old 11-16-2014, 01:28:59 PM
4Strokeguy 4Strokeguy is offline
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Default Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Hi folks,
I have been wondering if being off the grid can an inverter be powered directly without any battery bank?
My thought here would to use some Ultra or Super Capacitors as a buffer between the panels and the load (inverter). I am pretty sure this could work depending on the inverters internal protection for low or over voltage.
It isn't that I am against using a charge controller and a battery bank. The primary goal is to power refrigeration while the sun is up. The Ultra caps would provide the extra capacity during compressor start up.
Any thoughts on this?
All the best, Craig
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Old 11-16-2014, 03:23:44 PM
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Could work. Might be some issues with peak current, caps will dump a ton of juice. Some stratigic use of long wires could help limit things. On thing you might also do is to use a relay and shut everything down while the panels are not putting out any power. Have the relay kick in once the caps come up to charge energizing the system.
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Old 11-16-2014, 04:39:39 PM
Thaumaturge Thaumaturge is online now
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Likely wouldn't work unless you have some VERY serious panels. At 100% efficiency -which is never acheived- a 1200 Watt load will suck 100 amps on the input to the inverter. That's a constant load. Even a big bank of super caps would only push that for a few seconds, if that.
Doc
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Old 11-16-2014, 05:01:29 PM
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

What he said. Except that small fridges don't draw much except at startup. If the panels are sized to provide the run current and the caps were sized to provide startup then it might work. It would be important to keep things shut down until the panels are producing enough to provide run current and the caps are charged. This would be a dedicated system built around keeping the fridge cold. Perhaps not the most efficient but functional given the criteria of not using a battery.
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Old 11-16-2014, 09:17:38 PM
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

When I worked at one particular RV dealer, some of the trailers that came in and had solar on the roof and a 100 watt inverter for the entertainment center. Not realizing the inverter was on, without the battery on the trailer, the electronics failed from low voltage as the solar panel could not keep up to the demand. I would not take the chance.
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Old 11-29-2014, 11:47:05 PM
4Strokeguy 4Strokeguy is offline
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Thanks to all that have replied, sorry I had not pop in to answer individually.
This project will be on hold until spring. I did get some Maxwell brand "D Cell" Caps, they are rated 350 farads at 2.7 volts DC. believe it or not you can start a 4 liter engine with these alone.
They are not much bigger than a D cell battery. So 6 in series yields 16.2 that should pack enough punch into an inverter on an inrush compressor start?
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Old 11-30-2014, 07:04:04 AM
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Elden DuRand Elden DuRand is offline
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Be careful when series connecting capacitors to increase the voltage rating.

If the caps aren't perfectly matched, one of them will always be under the most stress and could fail prematurely. If it fails in a shorted condition, there goes the string.

With smaller value capacitors, it helps to place equal value resistors across each cap to help equalize the voltage across each one.

What value of resistance depends on the leakage rating of the caps.

With those huge capacitances, the resistors would probably have to be drawing significant current to do their job, probably in the tens of milliamps.

Good luck and let us know how it goes.
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Old 11-30-2014, 03:45:09 PM
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Quote:
Originally Posted by 4Strokeguy View Post
Hi folks,
I have been wondering if being off the grid can an inverter be powered directly without any battery bank?
. The primary goal is to power refrigeration while the sun is up. The Ultra caps would provide the extra capacity during compressor start up.
Any thoughts on this?
All the best, Craig
If a 'fridge is your goal, LP, NG or Kero 'fridge would do the job and be silent. They cost more then an electric, but I have had one in my truck for going on 20 years, still works as good as new.

Also some absorbsion cycle 'fridge can be run on 12 or 120 volts, it is a straight resistance load, so would be easyer to budget for electric load, if you are set on solar power.
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Old 11-30-2014, 03:49:37 PM
4Strokeguy 4Strokeguy is offline
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

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Originally Posted by cornbinder89 View Post
If a 'fridge is your goal, LP, NG or Kero 'fridge would do the job and be silent. They cost more then an electric, but I have had one in my truck for going on 20 years, still works as good as new.

Also some absorbsion cycle 'fridge can be run on 12 or 120 volts, it is a straight resistance load, so would be easyer to budget for electric load, if you are set on solar power.
I have had a LP gas/electric absorption type refrigerator (ammonia refrigeration) and they do work quite well, most cold storage warehouse use them.
I want to be independent of the fuel cost.
I have converted a chest freezer to a fridge using a Ranco capillary thermostat. Once that box reaches the set point the compressor only runs 5 to 10 minuets per hour. I have yet to turn it off to see how well it will hold that setting over a 12 hour period
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Old 11-30-2014, 05:28:53 PM
cornbinder89 cornbinder89 is offline
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Default Re: Dimensions Pure Sine Inverter Powering an inverter directly from the panels

Well, as I said, many can be had with 12 or 120 heaters as the source of power, and with those there is no "starting factor" to think about, pure resistance. May not be as efficient (I don't know) but when you consider that they can be made to run on any heat source, you could likely replace the heater with any voltage, so no inverter nor any of its in efficancys nor any high starting amps.
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