Author Topic: 400w of panels, 150 watt freezer, not working  (Read 631 times)

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wine_guy_3

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400w of panels, 150 watt freezer, not working
« on: September 22, 2017, 10:52:17 AM »
I'm trying to debug a system in my back yard before I move it up to my cabin.
It does not seem to work for more than 2 nights or so.

The system:
4 100 watt panels
Charge controller.
2 batteries 115 amp hour each
800 watt inverter
freezer.

About 40 feet of double 12 awg wire for + and (4 wires total) from the panels to the controller.
I know this is somewhat undersized, but this is proof of concept before I move it up north.
The wiring at the cabin will be double 8 awg for + as well as -.
All other wires in the system are short pieces of 8 awg.

The panels are providing about 18 amps between 10 am and about 5 pm. 7 amps otherwise.
This seems low. I was expecting somewhere around 30 amps.

Inverter by itself draws about 150 mA when sleeping.
Freezer by itself draws about 120 Watts.
Kill-o-watt meter says 4.5 kwh in 42 hours, so about 0.17 kw per hour average.
The inverter and freezer are drawing about 15 amps from the batteries when running.

The inverter shuts off after 2 days for low voltage (just under 12 volts)
When I remove the freezer, the batteries recharge in about 30 hours.

According to the above...
During the day the panels should provide 2 amps charge current  even when the freezer is running,
and the batteries should provide 60 amp hours (20 % discharge) at night.

Sounds like I need more panels and more batteries, but
this does not seem right 400 watt input and less than 150 watt output.

Any ideas?

OperaHouse

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Re: 400w of panels, 150 watt freezer, not working
« Reply #1 on: September 22, 2017, 11:32:09 AM »
You never get out of batteries what you put into them.  When batteries are charged, no more  power can be put into them.  PWM from a panel only gets you rated current. Watts will be way less.  I figure 2.5 X panel watt rating for what you can get out of panel a day.  System seems to fall short. Your 100W panels were a big mistake, buy grid tie panels which are way cheaper.

I run a chest fridge 5 months a year and it takes me about 900W of panels to be marginal (I have 1300W and just doubled that this week so I never have to worry about rainy days).  My chest fridge only runs daylight hours (single car battery) and run close to 33F.  Cold is stored in mass amounts of liquids.  Fridge won't even start till battery is 13.4V and then only for timed interval. A temp only control is a disaster waiting to happen unless you massively oversize your system.

george65

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Re: 400w of panels, 150 watt freezer, not working
« Reply #2 on: September 22, 2017, 03:55:46 PM »
The panels are providing about 18 amps between 10 am and about 5 pm. 7 amps otherwise.
This seems low. I was expecting somewhere around 30 amps.

Too Tired to crunch all the numbers sorry but this is one place you are going wrong straight off.
Your 30A would be IF the panels were giving their rated 100W.  They won't/ very rarely will ( Bright summer sunshine perfect tilt/ angle maybe)
I ran my fridge for months playing around and had a 24V system and ran 1600W of normal house type used panels, through a cheap but effective PWM controller. Worked fine but a  few cloudy days and I was dropping volts fast.
Just note if you use household 30V approx rated panels, you have to run a 24V system because you will fry the controller if you try to input 24 and charge 12 with the cheapie controllers.  Ask me how I found out!  :-[   2x12V batteries in series for 24 is the same capacity as 2x 12v in parallel anyway. You will need a 24V inverter though.

My theroy I have come up playing with solar is you have to size not for the bright sunny days but the cloudy overcast ones. I inadvertently came up with the same practice as now being done on home solar installs, over size the array to your inverter. I also came up with the theroy that its not the peak sunshine you want to try and get max amps out of, its the morning ramp up and the afternoon wind down. Extra amps here make a big difference to the days' Kwh Yields.

If you have say a 30 amp controller and 100a of panels, the controller will just take the 30 A and discard as it were the rest. You can't go high on volts, but you can go high on amps.  By going over on the panels you get more amps in the morning and afternoon and full amps through the day. In cloudy weather you get a lot more amps to help carry you through as well.  Other thing I did was run 2 of the cheaper pwm Controllers. This way if it's available, you could put say 60A into the batteries and they will share the charging BUT, check the outputs with a multi meter and set them up that way.
the controlers I had were the same makle and model and were out by 4/10ths of a volt which will make one work harder than the other.
Check with a multi meter and I wrote the - figure on the high one so I knew how much to skew that one to match the other and which one was what.

If you are planning on leaving this running at your cabin then you'd want to massively oversize the battery's and the panels because if the inverter shuts down it will stay that way till you reset it. Least every one I have seen but there maybe something uber expensive that does it by remote control or automatically.  Still probably better to invest in more panels and batteries. 

The main thing is don't take things at rated value. They rarely work that way. Panels won't produce rated power, controllers may not provide rated charge, batteries need 50% more power in than you get back out, wiring has resistance and so it goes.

As mentioned, Filling your fridge/ freezer  ( I used bottled water) is a good idea. Gives thermal mass that will help  keep stable temps and the unit cold overnight when it's not being opened and there is no charge power.  Take the bottles out as you need to add food but basically the idea is to keep the thing full.  Put in the food you need and then fill the empty space to provide a thermal mass.  Of course Fill the thing initially in the morning when there is plenty of power to cool it all or add gradually.

wine_guy_3

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Re: 400w of panels, 150 watt freezer, not working
« Reply #3 on: September 22, 2017, 06:01:46 PM »
I'm beginning to see.
It appears that you need (for example) to put 4 kWh into a battery to replace the 2 kWh you just used.
RATS.

Looks like I will need some more panels, and more batteries.
I have a modified Gurd controller. Mosfet will allow up to 150 amps if necessary.
This is for weekend/cabin use at this time, so I will limp along at 12 volts for now.
Nowhere near the grid, so grid tie is not an option.

I plan on leaving 2 panels up all the time.
Adding 2 (or more)  panels when I use the cabin for the weekend.
I have the wiring and mounts set up so this will only take 15 minutes to install.
Should be able to recharge the batteries in the 2 weeks that I am back home.

Thanks for the quick feedback.


george65

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Re: 400w of panels, 150 watt freezer, not working
« Reply #4 on: September 22, 2017, 09:47:35 PM »

You could make up a cable and connect the batteries to your vehicle and give it a run for a bit to top them off. You can bring them up to 80% charge fairly quick, the last 20% takes some time as the charge rate you can sink into them fall quickly.

By the same token, I'd be charging them from the vehicle ON the way home. The worst thing you can do is leave them discharged. Soon as you get power back in them the better. The car alt will bring them up much quicker than a normal mains charger and when you get home you can just top them off.
For years I have had a cheap charger with a small solar controller I built in.  Turns it into an auto charger and I can keep the batteries connected and not have to worry.  At times I have had several connected together to keep them topped up.

When I was doing outdoor field events, I built myself an engine coupled to a car alternator and used an inverter on a car battery. Engine and alt were cheap and I used a 5HP motor and had it geared about 2.5:1. This allowed me to run the engine slower and quieter and still get an easy 40A.  I could run computers, lights, printers and other gear all day on a few litres of fuel.  Other thing was it made an awesome battery charger when the mrs had a habit of leaving the lights on and flattening her car battery.  Hook it up and 5 Min it was charged enough to start.

Might be an interim soloution but would also allow you to run whatever you wanted when ever you wanted without worry about battery charge levels.
I'm about to build another similar one with an aircooled  Diesel engine and 2x 80A alts.  Discovered those microgroove pulleys aren't that easy to come by here so I'm having a harmonic balancer bushed to suit the engine shaft size.
Can't think why I'll need 160A but just as easy to do a single alt as a twin.  :0)

Simen

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Re: 400w of panels, 150 watt freezer, not working
« Reply #5 on: September 22, 2017, 11:40:46 PM »
For me, it doesn't make sense to run a freezer just for the weekend - unless you mean a fridge? :)

Anyway; 4.5kWh in 42 hours would be around 2570Wh/day, which is a lot for a fridge today - even for a freezer. Newer fridges usually have a consumption of 600-1000Wh/day...
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dnix71

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Re: 400w of panels, 150 watt freezer, not working
« Reply #6 on: September 23, 2017, 09:18:57 AM »
If this is a weekend cabin and you can do without the need to re-freeze food, it would be cheaper to get a 40 quart Engel fridge. The Engel uses 36 watts running, and is small enough to fit in the back seat of your car. The marine version runs on 120vac or 12vdc. Your solar setup already is overkill for this fridge. I have owned one for 10 years. It's quiet and is a real freon compressor-based refrigerator.

The Engel will freeze food easily, but it isn't setup with internal compartments so it will freeze everything or just refrigerate everything. It has temperature controls that allow keeping meat, cheese, eggs and milk at a proper temp. The Engel is also expensive, but so is what you are trying to setup.

https://www.amazon.com/Engel-MR040F-U1-Marine-Fridge-Freezer/dp/B001SNWCFO  Stay away from the lookalike Edgestar. It has copper evaporator tubing that rots from condensation.


https://www.walmart.com/ip/Della-35-lb-Freestanding-Ice-Maker/196324784

Here is a tabletop ice maker that pulls 105 watts running and double that for a few seconds at startup. Also suitable for a solar setup. Read the review. If you only plan to stay for a weekend it's probably cheaper and easier to take ice with you.
« Last Edit: September 23, 2017, 10:56:56 AM by dnix71 »

DanG

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Re: 400w of panels, 150 watt freezer, not working
« Reply #7 on: September 23, 2017, 05:29:08 PM »
https://www.engelcoolers.com/12volt-fridge-freezers.html

Engle direct has had some huge discounts in the past, including nearly half-off their largest units...