Power Outage & Use of Inverter with Batteries for AC Power

Your starting watts will be at least 1200 and you should have 2000 ...and I would recommend a pure sine wave inverter....it might work on a modified sine wave, but not well and not long....

http://www.nationallibertyalliance.org/files/survival/HOW%20MANY%20WATTS%20DO%20YOU%20NEED.pdf

http://www.theinverterstore.com/2000-watt-pure-sine-inverter-12-volt.html

http://www.circuitsgallery.com/2012/09/sg3524-pwm-inverter-circuit2.html

Series connect one 1MFD450 Capacitor and a 10 watt filament lamp at the out put of the PWM inverter; this may solve your problem.

What?

That should shed a little light on the problem!

Us knowing what brand and model of power inverter would be helpful being not all 3000 watt rated power inverters are the same.

Many are grossly overrated and underbuilt whereas others are well designed and built.

A good example of that is a 2500 watt (suposedly continuous) 5000 watt surge rated Cobra brand inverter I picked up cheap that didn't work. By design and all around internal layout it's a total overrated POS. To be honest it's such a low end peice of crap I never bothered to get the parts to fix it let alone put it back together and just tossed it in my parts bin.

In its design the actual semiconductors that do all the power conversion work are at their spec design voltage and current limits while producing the 2500 watt output and way too small for the 5000 watt surge capacity to be real plus it has no appreciable degree of output stage filtering to clean up it's output power harmonics either.

Now on the other hand I have been picking up broken Whistler brand units due to their incredibly overbuilt designs. Their 2500 watt rated 5000 watt peak units have semiconductors that even at the 5000 watt peak output are only running at ~1/2 - 2/3's their as spec'd maximum capabilities plus they have large toroid core inductors along with good low ESR rated snubber capacitors to clean up their output power.

So given that, what did you buy? A low end as cheap as you could possibly find one or a good but more costly quality one? My guess is you let your cheapness do the shopping and you got the crappiest one you could find that had the biggest flashiest numbers on the box you could relate to.

You might also check the wire size feeding the inverter from the batteries for capacity...and battery charge level and capacity...You probably need a 1/0 wire size min...but you can get 2/0 for the same price....

That's a good point. At 12 volts, 600W will be 50 amps and starting current will be more. A bad connection (0.1 ohms) at 50 amps would drop 5 of the 12 volts.

You can do the math Calculate Size of Inverter & Battery Bank.

For such an application I´d rather go for a genset, preferably using LPG for fuel (no "Old" fuel in the tank, no need to crank it weekly, etc), cause maintaining a battery bank is expensive as the batteries will be probably dead within 5 years or so. Inverters are also an expensive piece of equipment that can get ruined when manipulating cable connections, by overloads, lightnings, etc Depending on the length of the outages, your batteries may be empty before the electricity returns, just postponing the moment you will have no electricity at all

How long are your power outages?

An unpowereed full freezer should keep foods adequately frozen for around 48 hours if unopened.

I regularly use Giandel brand PSW inverters.

They hold a good steady voltage and a sine wave quality equal to mains - in my case 240v 50Hz - over their entire load range (personally verified by myself with a scope), and are cheap compared to many others available.

I have one of these in my RV, and can concurrently run the 1000W microwave (1500w on high) and the rooftop AC (1200w on start) off it. The caveat here is that I use LFP batteries which will better allow this than will lead acids.

Outage might run max of 3 days.
My freezer will stay well above freezing for about 2 days if unopened.
See response to Solar Eagle for current status of my system. Got her working.

In general, your freezer and inverter match is fine, (modified will work for this purpose; it is not so much that it is not pure sine, it is that modified wave inverters are usually of much lower build quality, so don't last).

It is possible that you have an insufficient discharge rate or capacity from your battery bank (you don't give any details, but for each day of autonomy, with agm batteries, you should probably plan on about 12 x operating wattage. 600 watts is a pretty good size freezer, so 12 x 600 = 7200 watts x per day x 2 days = 14,400 watts. Then you need that doubled, so you don't discharge your bank to more than 50% state of charge. So first, start up issues may be wire sizing issues, second discharge rate, (less likely, if you have a well designed battery bank). I find that almost everyone who DIY's a battery back up significantly underestimates load and battery capacity requirements. See below.

So, if you want two days autonomy without grid, genset, solar or other recharge, you will need a battery bank with 28.800 WH capacity, or a 28.8KHW bank.

A nominal voltage in a 12V bank might be 13 volts. 28,800/13V = 2215 amps.

A trojan *D is a good battery you can get for $500 and packs 254 AMPS at a 24 hour rate, which will work for you fine for a consistent low demand use like a freezer. That means you need 8 or or 9, wired in parallel, with high quality conductors sized for max discharge (inverter max demand) and max charge (you did not mention your charging regime). You need very good conductors and connectors, good overcurrent protection, You need to figure it all out before you buy anything. With racks, batteries, fusing, conductors, connectors, a decent inverter/charger, this is a $6000 material cost system. You can build one for less, ( I am guessing you did) but it will not last or work as you need it to the one time you need it to work the most, in an emergency. I hope you read a bit more, and are successful.

I personally would look to build a 24V or 48 V system, which will reduce amps in most conductors, making it a bit safer, more economical, and open up a wider universe of equipment, especially inverters and chargers.

Bear in mind that the run time for this freezer is probably less than 2 hrs per day...depending on design....

says who?

Being a user of both: battery bank and a genset on my boat (which of course is mainly off the grid) and without having your knowledge in this field, my experience is that there is no better cost / benefit combination than a small deep cycle battery bank (like 500 Amps x 12 V), a 2000 W inverter and a 10 KVA Kohler generator: this allows me to use any of the appliances / tools on board during daytime, and to switch the genset on during the late evening to replenish the batteries and having plenty of electricity for whatever use is needed. Unless living on a remote island and having no access to fuel, it makes no sense to me to go only for batts and inverters.

absolutely the right approach.

People often see a battery bank as an option to provide backup power, when a more effective and efficient design program would be to integrate power production so that the bank buffers and conditions various supply options, which in my case, is often grid, solar and genset. We often install gensets, and manage state of charge with the genset as a backup, thereby significantly reducing autonomy requirements. That means a smaller, easier to mange and cheaper bank, all good in my book. The OP wants to backup a freezer with batteries. A four stroke Honda 2000, or Hyundai clone for 600$ is a very cost effective 1 week a year solution. But storage is fun.

He could just go with a inverter generator....2000kw remote start $620

https://www.amazon.com/gp/product/B004RCQ05Q/?tag=trgen54355-20

Your response is appreciated very much.
I read responses and at this point have configured a 12 volt system (I already had two batteries - both AGM, a Duracell 80 Ah and an X2Power 90 Ah) and have set up the system (it works) with a 2000 Watt Pure Sine Wave Inverter made by Go-Power ($699).
Ran it with only the X2Power battery for a couple of hours.
Will hook these two batteries in parallel and test again tomorrow. (purchased 20 inch cables today).
I probably need to add additional batteries, but will know after testing.
I like your suggestion of the 24 or 48 V system. Wish I'd started there.

Years ago I set up a former coworker (Y2K preping to give you a timeline) with what turned out to be a surprisingly reliable backup power system based on a mid range 2000 or 3000 watt inverter powered by two 100 Ah deep cycle batteries and a 130+ amp alternator we refitted into his old 1/2 ton pickup.

The thing is realistically there are very few times a person needs long duration backup power and when the do if they use the least bit of rationalization they can easily get by on very minimal power for some time.

In my old coworkers case the fair sized inverter was more than enough to keep critical devices running indefinitely being it was backed up with a adequately sized battery set plus the oversized alternator as well.

The system was more than good enough to handle short term peaks like running one or two larger things like his well pump, furnace or refrigerator and freezer along with basic lighting then keep the batteries up well enough with the big alternator.

For light load stuff I think we figured that it could have easily ran 12+ hours before needing to start the engine to bring the batteries back up.

Odds are he used it far more for running power tools and camping than he ever did for any real power outage emergency but either way being the batteries were in a regularly used vehicle they were always keep at full charge and ready to run at any time and it was portable!

Total cost was around $500 and as far s I know he still has it.

In the OP's case that's what I would recommend setting himself up with. Get a good inverter and set up a regularly used vehicle to be the backup power base station.

Larger battery set and alternator recommended but not necessarily required unless there is a fairly high average load and needing to run for hours to days or more is likely.