Small system questions

[James1586]

Thanks for any help you can provide. I have built a small system (180 watt) from pieces and parts. I built (3) 60 watt panels, each connected to a 7 amp controller, and paralleled the three to a battery bank. The battery bank is (3) 12v 220ah batteries. The batteries are paralleled with 2 runs of #6awg and connected to a 1200w inverter, also with double runs of the #6awg. The inverter is a modified sine wave.

My goal was to run an 8500 btu air conditioner off the system. Certainly for the cost savings, but somewhat more for the pure irony of it. I can get the unit to run, and it seems to do fine, but only if I keep the thermostat set at the lowest setting of 60F. If the unit tries to cycle, if I have it set to say 70F, the inverter buzzes, chirps and pretty much tells me that it isn't happy. The AC unit is rated for 760w and 7 amp at 120v.

So, my questions are: 1. Should I be using a true sine wave inverter? 2. Should I add an automotive type battery to the system in order to provide more starting amps?

Additional information: I have ordered and will soon install a 30 amp controller as I have noticed that the 3 separate ones don't play well together. I almost never have more than 2 providing charge and I suspect that they might be reading off one another.

The input voltage to the inverter is always above 12v, ranging from 12.4 to 13.8.

[Sunking]

[...]Well assuming this window shaker 8500 BTU AC is ran 8 hours only each day will require 2000 watt solar panel array and a 12 volt2800 AH battery (2000 pound $$5000 battery). You had better get busy building more panels because it will take you a year or two to make them. Then you might want to rethink that statement: "for the cost savings".

[billvon]

So, my questions are: 1. Should I be using a true sine wave inverter?

Yes, for any motor load. Your inverter is likely not able to handle the starting surge BTW.

2. Should I add an automotive type battery to the system in order to provide more starting amps?

No.

My goal was to run an 8500 btu air conditioner off the system.

Well, you'll probably be able to do that for a few hours at a time, say once a week.

[Sunking]

I will give you a clue. To find out how much power (watts) any Air Conditioner uses the formula is BTU/SEER = Watts.

To determine how much electrical energy any electric device uses you must know how many watts the device uses and how long it runs to find the Watt Hours consumed. The formula is Watts x Hour = Watt Hours.

Since you have a window shaker air conditioner about the the highest you can find if you can afford it is SEER= 10. So let's pretend you bough the most expensive 8500 BTU window shaker money can use and determine how much power it consumers at any given moment. 8500 BTU / 10 SEER = 850 watts.

Now how long do you want to run that window shaker each day? Let's pretend again you want to run it 8 hours every day. How much energy is that? 850 watts x 8 hours = 6800 watt hours or 6.8 Kwh.

OK you want to make that much energy with solar huh? Well off grid battery systems are at best 50 to 66% efficient depending on what type of charge controller you use being either PWM or MPPT. For PWM you get 50% efficiency, and for MPPT 66%. So let;s pretend you are going to opt for the most efficient 80 amp MPPT charge controller. That means to use 6800 watt hours per day, your panels must generate 6800 watt hours /.66% = 10,303 watt hours. Well call it 10,300 wh to work with.

OK now we are set to find the panel wattage it will take to generate 10,300 watt hours. It is very easy all we have to do is factor out the Sun Hours for your area and the formula is Watt Hours / Hours = Watts. Since we do not know your location let's pretend you live in the south where there is good Sun in the summer and you recieve a whooping 5.5 Sun Hours in May. The panel wattage required is 10,300 wh / 5.5 h = 1872 watts. Round that up to 2000 watts to make life easy and ensure you have enough to carry through some clouds.

Moving on to the batteries you should size the batteries for a 5 day capacity. This ensures you only use 20% of the capacity daily so you can carry through 1.5 days of clouds. This will extend the battery life considerably from a few months to a few years. You should never discharge the batteries more than 50% without a full recharge. So if we use 5 day reserve capacity this gives you a real 2.5 cloudy day usage before you have to shut down. To find th ebattery capacity is real easy like the rest of it. All you need to know is the nominal battery voltage and the required watt hour capacity to find the Amp Hours. So the formula is: (Daily Watt Hours x 5 ) / Battery Voltage = Amp Hours. So if the battery voltage is:

12 volts: (6800 wh x 5) / 12 volts = 2833 AH @ 12 volts
24 volts: (6800 wh x 5) / 12 volts = 1415.5 AH @ 24 volts
48 volts: (6800 wh x 5) / 48 volts = 708.3 AH @ 48 volts.

Any way you spin the numbers you are talking about a 2000 pound, $5000 battery

As for the charge controller this is where things get expensive on you because you want to run at 12 volts. with a 2000 watt panel running at 12 volt battery requires 2000 watts / 12 volts = 166 amps. That means you need 2 - 80 amp MPPT charge controllers and a large amount of copper. Those 80 amp charge controllers cost $700 each. If you knew what you were doing you would use 48 volt battery and only need 1 40 amp MPPT charge controller and a lot less copper. A good 40 amp MPPT charge controller runs around $400.

So with what you have right now 160 watt panel, 12 volt 660 AH battery, and PWM charge controller you can run that window shaker about 15 to 20 minutes per day. You OK with that? Well that is if you buy a new True Sine Wave 2000 watt inverter.

FWIW what you are asking for is not a small system, it is a giant expensive system that will cost you around $15,000 or more to make less than a dollars worth of electricity per day. Then in few years you get to replace that $5000 worth of batteries.

[James1586]

Hmmm

Thanks for the information. I'll reconsider.

[Notsuredomus]

Electrically Handicapped and need input

O.K. Sorry if this is a stupid question but up until a month ago the most complicated electrical issue I tackled was a power chord I cut in half. I have been studying but I move to a 240 acre property next week with no utility but a well for water. I am starting out with 1 - 48volt (respectively) 275watt Solar Panel that produces appx 9amps ( I do plan to get at least 2 more similar panels soon so I need room to expand) and a 800watt max wind Ghost wind turbine that has a 12v/12v PMA. The Solar Array will be appx 50ft from my battery bank and the wind turbine will need to be 100 to 150ft from the battery bank. I have a MPPT Charge controller my question is what size and type of cable and connectors should I purchase to maximize the cost/efficiency and allow for expansion.

Cable type/size + Connectors type from the panels to the battery?
Cable type/size + Connectors type from the wind turbine to the battery?
Cable type/size + Connectors type from Battery to Battery?

I should mention that my battery bank will be set up for 12v

Sorry I know I should know this but I educated myself on all the big purchases and neglected to do my homework when it comes to all the small things that are necessary to tie it all together. Cable is a costly necessity and I want to be sure I don't throw away money on more than I need or throw it away by by getting something that leaves no room for expansion. Any help would be appreciated Thanks

[Mike90250]

1) don't BUY anything yet.

2) unless you have to tie your hat onto your head, when outside, you do not have enough wind to be usefull.

3) Welcome to the forum

Before you buy anything, you HAVE to plan it all out, or risk having to buy things twice !

What size (1/2 hp, 3/4hp well pump?) How much water do you need ?

In my .sig, is a link to a great wire caculator spreadsheet. You will quickly find that 12V requires humongus wires, and 48v is much more reasonable.


Here's a great article about connecting batteries in parallel (on the diagonal)
http://www.smartgauge.co.uk/batt_con.html (connect batteries on diagonal )

and some other battery stuff:

http://www.batteryfaq.org/ (very large)

Generally, much easier to manage batteries in series, than in parallel. Same wattage.


Mike

[Notsuredomus]

Thanks for the info

lol... Hold my hat to my head. Well I live in the mountains so we do get some wind up here. The reason I chose this particular turbine is that it is made for very low wind areas. It begins to spin at 3.5mph wind speed and starts producing power at 5mph... Since I live in So Cal I do have a lot of sunny days to work with and I am sure that the panels will provide the bulk of my power but the damn things are so expensive I am going to have to put my system together a lil bit at a time.

[Notsuredomus]

Thanks for the info

1) don't BUY anything yet.

2) unless you have to tie your hat onto your head, when outside, you do not have enough wind to be usefull.

3) Welcome to the forum

Before you buy anything, you HAVE to plan it all out, or risk having to buy things twice !

What size (1/2 hp, 3/4hp well pump?) How much water do you need ?

In my .sig, is a link to a great wire caculator spreadsheet. You will quickly find that 12V requires humongus wires, and 48v is much more reasonable.


Here's a great article about connecting batteries in parallel (on the diagonal)
http://www.smartgauge.co.uk/batt_con.html (connect batteries on diagonal )

and some other battery stuff:

http://www.batteryfaq.org/ (very large)

Generally, much easier to manage batteries in series, than in parallel. Same wattage.


Mike

Well the property has no structures except 2 cinderblock sheds that were built to keep the bears out of the food storage. I will be in an RV so no water pump now but I would like to put one in when I get settled in so that I can have a lawn and wont have to carry all my water by hand.

I know I have been told that 48colt loses less power in the wire is more reasonable priced. The problem I have with it is that I will only be using an inverter when I have to I plan to use 12volt ready appliances. I am not sure how much energy a power inverter bleeds from your system but judging by the way it hums when it is turned on I imagine it is quite a bit. Also I called all over town looking into it and can't find anyone that sells components or appliances made for a 48volt system which means running an inverter all the time.

Right now all that I need the system to provide power for is enough to run continuously 1 laptop, 2 security camera 1 external hard drive and direct tv satellite dish. Plus 1 light bulb at night. Though as I said I would like to build it up to eventually be able to use all the other electronics that I have in storage. This is why I want to be sure that I buy the correct equipment. If I am misinformed about the 48volt set up please let me know what I need and where I can find the best prices because nobody that I have talked to in San Bernardino makes anything for a 48volt system.

[russ]

lol... Hold my hat to my head. Well I live in the mountains so we do get some wind up here. The reason I chose this particular turbine is that it is made for very low wind areas. It begins to spin at 3.5mph wind speed and starts producing power at 5mph... Since I live in So Cal I do have a lot of sunny days to work with and I am sure that the panels will provide the bulk of my power but the damn things are so expensive I am going to have to put my system together a lil bit at a time.

When the turbine starts to spin is meaningless and if you check the power curve the output at 5 mph is virtually nil. I looked but the description you provided is not adequate to knw what exact turbine it is.

The 800 watt rating will be at a 25 to 30 mph wind speed - a storm condition. Don't plan on it providing much power.

[LucMan]

Thanks for any help you can provide. I have built a small system (180 watt) from pieces and parts. I built (3) 60 watt panels, each connected to a 7 amp controller, and paralleled the three to a battery bank. The battery bank is (3) 12v 220ah batteries. The batteries are paralleled with 2 runs of #6awg and connected to a 1200w inverter, also with double runs of the #6awg. The inverter is a modified sine wave.

My goal was to run an 8500 btu air conditioner off the system. Certainly for the cost savings, but somewhat more for the pure irony of it. I can get the unit to run, and it seems to do fine, but only if I keep the thermostat set at the lowest setting of 60F. If the unit tries to cycle, if I have it set to say 70F, the inverter buzzes, chirps and pretty much tells me that it isn't happy. The AC unit is rated for 760w and 7 amp at 120v.

So, my questions are: 1. Should I be using a true sine wave inverter? 2. Should I add an automotive type battery to the system in order to provide more starting amps?

Additional information: I have ordered and will soon install a 30 amp controller as I have noticed that the 3 separate ones don't play well together. I almost never have more than 2 providing charge and I suspect that they might be reading off one another.

The input voltage to the inverter is always above 12v, ranging from 12.4 to 13.8.

Here is another solution to your problem with start up amp draw.
Sanyo, Fujitsu, & Mitsubishi make inverter heat pumps, they start up at low speed (low amps) and gradually ramp up to full speed (& amps). Off course these units are not cheap but they work well with off grid energy as the current draw can be limited by the thermostat settings.

[inetdog]

If the unit tries to cycle, if I have it set to say 70F, the inverter buzzes, chirps and pretty much tells me that it isn't happy. The AC unit is rated for 760w and 7 amp at 120v.

I see at least three possible explanations for the A/C not restarting happily when the thermostat signals it on again:

1. The battery bank has gone down enough in voltage far enough that the inverter cannot deliver enough surge power to start the motor. As many have said here, the LRA (Locked Rotor Amps) for a motor is usually many times the FLA (Full Load Amps) which is the maximum once the motor has started and is delivering maximum power.

2. Depending on how hard the A/C has been punishing the inverter, the protection circuits of the inverter may not let it produce the same size power surge that it did when it was cold. See point #1.

3. If there is residual pressure inside the plumbing of the A/C (it has not equalized back down from the running pressure differential, a time on the order of 5 minutes), the starting current of the motor under load will be even more than in point #1. This is why most A/Cs will not restart successfully if you cycle them off and back on too soon even when running on the grid. (The A/C on a car, on the other hand, can cycle on and off rapidly because the engine has more than enough spare torque to get it turning even under pressure load.)