Running household appliances off grid

[Settwach]

I have a small system that I've been putting together for about 6 months now. Its off grid. I have 520 watts of panels, 4 110ah deep cycle batteries (12volt, wired for 24). 3500watt Power Bright inverter and 60amp PWM charger (I know that's old tech). I have everything mounted in a small shed 50 feet from my house. Distance from batteries to charger and inverter s all less than 6 feet. I ran a line underground to my house and have 3 wall outlets wired up to it. It runs the TV's, lights, fans, etc all fine. Whenever I try and plug in an appliance (freezer, small ac unit, dehumidifier) it will run for a minute or so and then shut down. It should have enough beef to run these. Is there something basically wrong with my setup? Supposedly this inverter is designed to run these appliances and handle the start up loads. Is my battery bank not big enough? Any help is appreciated. Seems like I have equipment with capability, I must be missing something. Thanks.

[inetdog]

I have a small system that I've been putting together for about 6 months now. Its off grid. I have 520 watts of panels, 4 110ah deep cycle batteries (12volt, wired for 24). 3500watt Power Bright inverter and 60amp PWM charger (I know that's old tech). I have everything mounted in a small shed 50 feet from my house. Distance from batteries to charger and inverter s all less than 6 feet. I ran a line underground to my house and have 3 wall outlets wired up to it. It runs the TV's, lights, fans, etc all fine. Whenever I try and plug in an appliance (freezer, small ac unit, dehumidifier) it will run for a minute or so and then shut down. It should have enough beef to run these. Is there something basically wrong with my setup? Supposedly this inverter is designed to run these appliances and handle the start up loads. Is my battery bank not big enough? Any help is appreciated. Seems like I have equipment with capability, I must be missing something. Thanks.

1. Your batteries may be toast from undercharging. Get a hydrometer and check the SG of each cell.
2. You do not say the voltage of your panels. Also how are you wiring them to the 24 volt PWM charger? You may be losing at least half of your panel power in the charger, which would lead to undercharging your batteries.
3. Measure the voltage at the battery terminals before you turn on the appliance and watch it as it is running. I predict that it will quickly drop until you have ~20 volts and the inverter cuts off.
4. Do the same measurement over a few hours running just your light loads.
5. Get a DC clamp-on ammeter to measure your battery current when charging and when running the inverter.

[wedgeantilles]

Household appliances

Don't know if this will help, but will explain something I saw yesterday.

A 800 W petrol generator was used to test an AC line 230 V 50 Hz.

When we were testing lights, all was running ok.

But when we connected a fridge, the 800 W generator began to make a different noise, and a voltmeter reading the voltage in the AC line, it went from 230 V AC 50 Hz RMS to 180 V AC 50 Hz RMS ( we did not measure the Hertz, not sure it was 50 Hz, because don't know if when the generator changed noise it loosed speed, and maybe it loosed frequency, not sure about this matter)when the fridge was connected.

We were not able to measure the current, because we felt scared and stopped the fridge. The lights were making strange things also, I think due to the voltage drop, and maybe for a drop in frequency, but no sure for the frequency. (the lights were changing the intensity of light emitted).

When the fridge was disconnected the generator recovered its normal noise and all was running ok again.

I was not able to read the Wattage of the fridge. Next test will be to measure the amps used by the fridge and try to pinpoint the intensity used for the compressor start, in order to see if a high freq inverter of 3500 Watts will be able to start the fridge.

A little bit worried untill I can measure that.

Regards,

[Sunking]

Its off grid. I have 520 watts of panels, 4 110ah deep cycle batteries (12volt, wired for 24). 3500watt Power Bright inverter and 60amp PWM charger (I know that's old tech). I have everything mounted in a small shed 50 feet from my house. Distance from batteries to charger and inverter s all less than 6 feet. I ran a line underground to my house and have 3 wall outlets wired up to it. It runs the TV's, lights, fans, etc all fine. Whenever I try and plug in an appliance (freezer, small ac unit, dehumidifier) it will run for a minute or so and then shut down. It should have enough beef to run these. Is there something basically wrong with my setup? Supposedly this inverter is designed to run these appliances and handle the start up loads. Is my battery bank not big enough? Any help is appreciated. Seems like I have equipment with capability, I must be missing something. Thanks.

Just about everything is wrong you can possible do. Nothing is matched up to work with each other.

Starting with your panels, you did not mention the specs of th epanels, how you have them configured, how far away they are from the controller, and what size wire you used. All we know is 520 watts on a 24 volt battery. Knowing you have PWM controller you have to have 4 battery type panels each rated 130 watts and the only way they can possible be wired up is 2 panels in sereis, with 2 more panels wired in series and in parallel with the other two. Assuming you did that correctly with battery panels the panel array has a Vmp of 36 volts and Imp = 14.4 amps into the PWM Controller. On the output of the controller you have 14.5 amps x 24 volts = 345 watts if you did everything perfectly.

Now to the huge problems. Your battery capacity is 24 volts @ 220 AH. That means you need a minimum of 20 amps to charge them, you only have 14.4 amps. Ideally you would want 28 amps of charge current to maintain a 220 AH battery. You panel wattage is way below the 1000 watts needed to just maintain the batteries you have.

Next huge mismatch is your battery capacity to inverter ratio. A 24 volt 220 AH battery can only support a 650 watt inverter. How large is your inverter? Did you say 3500 watts?

Lets wrk this backwards from the 3500 watt inverter. Minimum size battery to support a 3500 watt inverter @ 24 volts is 1200 AH, you only have 220AH. Not even remotely close to what you need. The Panel Wattage required to support a 24 volt 1200 AH battery is 4320 watts and 2 60 amp MPPT Controllers. You got what? At 520 watts and PWM you are not even in the Ball Park for what is required

So what is happening is when you turn on the high power items is the battery voltage crashes and the inverter drops off line from under voltage. It will never work. GIVE IT UP I know you do not believe me now, but you will.

What it will really take to run a 3500 watt inverter, is a 3500 watt panel system using a 80 amp MPPT controller on a 48 volt 600 to 800 AH battery. Should not cost you a penny more than $13,000 to make the necessary changes to make your system work like you want. Then in about 3 to 5 years you get to replace $7000 worth of batteries at even higher cost. That brings your Kwh cost to about $2/Kwh going off grid. You can buy it for 11-cents per Kwh from the electric company.

[Settwach]

Appliances

I'll post more of my set up soon. But I have 4 50 watt 12 v panels and 4 80 watt 12 v panels hooked up in series and parallel. At the controller (in sun) they read at 25.5 volts or so. Across the battery terminals at the controller is also 25.5 and the output of controller is the same. Panels are mounted directly above the shed where the controller and inverter and batteries are. Distance from panels to controller Max 7 feet, from controller to battery bank 3 feet, from battery bank to inverter 4 feet. I have 8 gauge solar wire from panels to controller, everything else is 6 gauge. I do understand that I have a voltage drop problem. What I do not understand though is how this inverter would work in a RV or such. An RV wouldn't have a huge battery bank would it? Would it run just off a battery without the controller? I don't imagine running tools or whatever at a job site, you wouldn't even have panels involved to charge the batteries? Just trying to get a handle on this. Seems crazy I can't run a small fridge without spending a fortune. Thanks

I ran my de-humidifer on it today in the house and it shut down after 10 minutes. I took it outside and plugged it directly into the inverter and it ran fine for hours. That's only rated at 3.1 amps AC.

[Mike90250]

Across the battery terminals at the controller is also 25.5 and the output of controller is the same.

Then something is wrong, the voltage at the BATTERY terminal(s) of the controller, should never be above 15V If it's higher, the controller, is not controlling.

Seems crazy I can't run a small fridge without spending a fortune. Thanks

That's the name of refrigeration. It takes power. A small "dorm" fridge consumes about 1KWh per day. Look at the sales label on it, it will state (in the USA anyway) what the annual power consumption is. Then look at the label on a 25cf energy star fridge @ $900. It too, will be about 1KWh day average. It has better insulation, motor, and controls than the dorm fridge, but uses the same amount of electricity to keep 5x the volume cold.

I ran my de-humidifer on it today in the house and it shut down after 10 minutes. I took it outside and plugged it directly into the inverter and it ran fine for hours. That's only rated at 3.1 amps AC.

Not sure what's happening here, what is the battery bank in the house, and what's outside ? That will give the story. Do both batteries power the dehumidifier via a inverter ? Are both inverters pure sine, or mod sine ? Too many factors in play to guess.

[Sunking]

everything else is 6 gauge.

Are you telling us you ran # 6 AWG from the battery to a 24 volt 3500 watt inverter? That is one heck of a fire hazard and a source of voltage drop. At 24 volts to deliver 3500 watts requires 150 amps. That is more current than a house uses. A #6 AWG in free air is only rated for 90 amps. Minimum size required for that inverter is #2 AWG

I do understand that I have a voltage drop problem. What I do not understand though is how this inverter would work in a RV or such. An RV wouldn't have a huge battery bank would it?

Well for one a RV has a vehicle alternator to supply most of the current, and they do not have 3500 watt 12 volt inverters. Part of the problem is people will buy anything even if they do not understand how it works.

But here is the technical problem. Every battery has what is called internal resistance which limits the amount of current it can supply before excessive voltage drop is incurred. For flooded Lead Acid batteries the maximum amount of current they can deliver is about C/8 where C = the battery Amp Hour capacity. Above C/8 current the battery voltage starts to collapse quickly. So you have a 220 AH battery so the largest load current they can supply is 220 AH / 8 H = 27.5 amps. So 25.5 amps x 24 volts = 612 watts or a 600 watt inverter.

But you need to ask yourself one very simple question. Why are you taking anything off-grid if you have commercial power?

If you say to save money, forget it. Anything you take off-grid the electricity is going to cost you 10 to 20 times more than buying it from the electric company the rest of your life. So if you rreason is to save money, stop right now and sell the system immediately to recover some of your losses.