Off grid inverter issues

Tradiscantia

We had a Cobra 800 watt inverter in our trailer when we installed our solar equipment, which consists of 490 watts of panels, Tristar MMPT 45, and 4 Trojan batteries, plus big (2/0) cables to the inverter. We're having some problems despite having battery amps to spare.

The inverter mostly runs a dorm-room sized Danby refrigerator that draws close to the rated max for the inverter (800 continuous watts, 1600 surge) When the temperature outdoors dropped, the inverter went off during the charging period in the morning. We reset the Tristar program to a lower voltage to match the maximum rating for the inverter and 'solved' that problem.

Now we're having another problem at night. When the refrigerator cycles on, the motor (inverter? fridge?) strains and sounds a little bit like a mooing cow. If we get up and switch off the fridge, the inverter quiets. Then, when we turn on the fridge again, even if it's only a few seconds later, it quiets and runs normally. But within a short while, it strains again. At night we don't have any other load on the inverter except the refrigerator.

2. We are also having issues when we plug in an ipad or iphone to charge from any of the 110 sockets, either the phone beeps or the inverter freaks out. Is this because it's a modified sine wave? We are charging our devices through the cigarette lighter in the power conrol center or in our cars. This seems to work okay.

3. My laser printer and my nebulizer compressor don't work at all.
Will having a pure sine wave inverter solve the electronics issues? If so, can we have a small inverter wired into the 100 sockets and get the Cobra to work for the fridge?

KnowledgeSponge

Re: Off grid inverter issues

WAG.....

Dirty Power is causing the problem

Do you know if this is a MSW inverter?

Yes, I can tell you a Pure Sine Wave Inverter is MUCH more likely to operate a refrigerator and certain delicate electronics "properly".

Any inverter that is not Pure Sine Wave, is (in my opinion) for devices like light bulbs (although not sure about the new LED ones)
and such...but not necessarily Microwaves

I only use "Dirty Power" inverters (MSW or less) for basic incandescent lighting

Tradiscantia

Re: Off grid inverter issues

What does 'dirty power' mean?

KnowledgeSponge

Re: Off grid inverter issues

Tradiscantia wrote: »

What does 'dirty power' mean?

Sorry,

Dirty Power refers to power that is not of the high quality that you'd get from the Grid.

If you want to know more, Google the terms "Modified Sine Wave Inverter" and "Pure Sine Wave Inverter".

Basically AC devices in the US are designed to operate at 60Hz. "60 Hz" referes to oscillation or the number of times the "cycle" repeats in a given time. In this case, 1 second.
That means if you saw a graph of the power, it would look like a very, very SMOOTH rise and fall on a graph.
60v Negative, then back to 60v Positive. The smoother this happens, the "Cleaner" the power.

Here's what Grid Power looks like....

.
.
And here's what a Modified sine Wave looks like....(for 220v)


The circuit to produce a Pure Sine Wave costs more. That's why Pure Sine wave Inverters are more expensive.

Unfortunately, Only Pure Sine Wave Inverters are capable of mimicking Grid power.
An inverter that is NOT Pure Sine Wave will still have the rise and fall, but it will be less smooth and more "choppy"

That "choppiness" is what causes the problem with the sensitive electronic devices such as computers and refrigerators.
(Although some refrigerators work fine with Modified Sine Wave inverters.)

Perhaps I confused you even more. If so, I apologize.
But, I Hope that helps

westbranch

Re: Off grid inverter issues

think of a set of stairs, the number of 'stairs' going from Zero volts to 120 volts determines the choppiness refered to.
More stairs = less deviation from a 'true sine wave' pattern like this symbol '~' which represents a full cycle ie 60 Hz = 60 cycles per second.
https://en.wikipedia.org/wiki/Utility_frequency

Tradiscantia

Re: Off grid inverter issues

I understand that this is why the printer doesn't work, and why the electronics are not so happy getting AC through their transformers.

But, the refrigerator has been very happy with this square wave inverter for over two weeks. Also, it works fine all day long, waiting until nightfall to act up.

If dirty power were the cause, I'd expect the problem with the fridge to be intermittent, not just at night.

Is there another explanation out there?

icarus

Re: Off grid inverter issues

The fridge may have seemed happy, but if we running it on MSW it is (has been) working very hard, and may be on the road to failing.

It may be acting up t nit because the battery voltage is low enough to make the inverter not work well as well.

Tony

harry

Re: Off grid inverter issues

I have a small system which started off with a similar 400 watt inverter as yours. I put a kill-a-watt meter with the following results.

TV : 40+ watt draw.
LED lights : 30+ watt draw.
I could only use one of the above at a time. Both together would stop the TV or flicker the lights. Even the TV running alone would loose it's channel scan settings and other strange things. Cutting the power to the TV for a few minutes would restore the channel scan settings.

With my new Morningstar SureSine 300 watt all that changed. First thing I noticed was the watt draw was cut in half.
TV : 18 watt draw.
LED lights : 10 watt draw.
All items work like a charm. Can also use the laptop, charge the Bissell vacuum all at the same time. Chargers work perfect.

My conclusion, MSW inverters don't cut it. That's where I would start.

mike95490

Re: Off grid inverter issues

Fridges don't like mod-sine inverters either! But pure sine inverters large enough to start the fridge, are pretty pricey. And you've discovered several other things that don't like the mod sine either! And mod-sine inverters don't like a variety of loads either.

MorningStar makes a nice pure sine wave inverter, 300W cont, 600w for 10 min. Very beefy design, but not quite enough to start most fridges. It's also advanced enough to consume little overhead, has a stand-by/search mode, and a remote ON-OFF switch. Look for the SureSine 300.

waynefromnscanada

Re: Off grid inverter issues

Re your system acting up after you adjusted down the charge voltage level of your controller, two things come to mind right away.
1) Your inverter is probably not designed for off grid solar use. Meaning, it's high voltage input cutoff is likely around 14.5, the normal max for automotive 12 volt systems, so it's shutting down when the charge controller tries to get the voltage up far enough to properly charge the batteries. That's a common thing with "automotive" inverters. Been down that road, learned the lessons. My cousin has that problem at his camp, so when he needs power on a sunny day, he shuts off the power coming from the panels. Luckily he has very little load on his system, so his batteries get a full charge later - - or the next day.
2) I strongly suspect that when you adjusted down the charge voltage to prevent the inverter shutting down on over voltage, the batteries are no longer getting properly and fully charged during the daytime, thus are running low at night, causing problems. Hopefully your batteries have not been damaged or ruined from undercharging.
Cure? A good quality off grid pure sine wave inverter with a high voltage limit of at least 15.5 to 16.5. This will prevent shutdown when the controller is charging the batteries at the proper voltage. It will also make the fridge compressor operate more efficiently, and thus cooler, and last longer. It will also properly charge your phone and operate your other items properly.
Good luck.

NorthGuy

Re: Off grid inverter issues

An important question is:

Did you experience all these problems with the inverter before you installed solar?

vtmaps

Re: Off grid inverter issues

I agree with the others about upgrading to PSW. Just because your fridge can work on MSW doesn't mean it can work efficiently, and the inefficiency of the motor on MSW means more heat in the motor and a shorter lifespan.

Tradiscantia wrote: »

Also, it works fine all day long, waiting until nightfall to act up.

But this sounds like low voltage... battery getting old. Also check your connections between battery and inverter... you could be losing some voltage with a bad connection.

--vtMaps

waynefromnscanada

Re: Off grid inverter issues

vtmaps wrote: »

But this sounds like low voltage... battery getting old. Also check your connections between battery and inverter... you could be losing some voltage with a bad connection.

--vtMaps

True, but also note that his night time problems only showed up after he reduced the charging voltage to prevent the inverter shutting down while batteries were charging.