I have inverter questions hooking up to a off grid house electrical panel

[Lorenzo]

New to all of this. I have the new cabin completely wired (14 and 12 gauge) to a Eaton 10/20 grounded breaker box. I have a 7k 30amp generator wired (10 gauage) to a 30amp breaker for now, powering all of my outlets, switches, and lights. They all work. The country inspector okayed my progress but I want the generator to eventually charge only the battery farm I have planned. Then it in turn, will power an inverter with hardwire capability to supply 110 AC power (no 220) to my grounded main breaker panel. Sounds like I know what I'm talking about? Well, no, I don't. I have a 4k power spike needs cabin if everything is turned on at once. Normal use, about 2k. No electrical dryer, oven, stove,or water heater. No AC pumps. Propane for oven, stove top, and water heater.

I don't have a clue about the size of an inverter I'll need, the size of the single pole circuit breaker I'll connect it to, or the battery farm amps I'll need.


Eventually, I want to go solar but as my generator will charge my batteries (yes, I know, through a charger) for now, that's a whole other discussion for now.


Any ideas????

[inetdog]

1. An inverter to handle 4kW at one time is a very large inverter. Even if you use a 48V battery bank you will need to be able to feed it more than 100A DC. And your battery bank will have to be 48V at 500Ah or more to handle that current, if you choose to use Flooded Lead Acid (FLA).
2. So consider instead using the generator to assist the inverter when you need to run large loads. (Or simply manage your usage so that you never turn everything on at once!)
3. You can also find what is called a hybrid inverter with generator support that can automate that process to some extent. They are expensive, but may be the best way for you to go.
4. If you do decide to go with just an inverter capable of 5kW or more, you should plan on also having a smaller inverter, with lower idling power losses, to use most of the time. The 5kW inverter will suck a lot of power just sitting there waiting for loads.
5. There are some tricky points involved with wiring up your panel to accomodate both a 240V generator and a 120V only inverter. You may need to add an autotransformer to the mix or find an inverter with 120/240V output.

Most important: read the sticky threads in the Off Grid section to get basics on sizing your system and designing your battery bank, then come back with questions about things you do not understand or feel comfortable with.
In particular also look for threads from member Chris Olson about "generator support". He is not active here at this time, but he has contributed some very good information.

[karrak]

I have a 7k 30amp generator wired (10 gauage) to a 30amp breaker for now

Is the generator 240 AC?, 7kVA would be 60A (amp) at 120V.
Do you have at least two separate power circuits in the house? again 4kVA is more than one 20A circuit.

The criteria that I used when selecting my 4kW inverter was that it had to be able to power any device that I could buy off the shelf that would plug into our standard 240V 16A power circuits here in Australia. The peak usage that I have recorded is ~6kW. The 4kW inverter is able to cope with this load for short periods of time.

Have you thought about looking at a lithium iron phosphate (LFP) battery rather that a lead acid battery. To run a 4kW 48V inverter you only need a 150Ah LFP battery rather that a 500Ah lead acid battery. It is also much quicker and uses less fuel to charge an LFP battery from a generator as you can charge it around five times the rate that you can charge a flooded lead acid (FLA) battery. They are also much more efficient at around 95% than an FLA battery. There are many other advantages which I won't go into here. Only downside as far as I can see is that they are more complex to set up.

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[Logan5]

If you have not purchased any of this as of yet, DON'T, you are going to make a big mistake, to go off grid you must first reduce your loads, then calculate your revised needs/usage. Why run an inverter at all? a small off grid cabin may best be served by a DC voltage micro grid.

[Lorenzo]

All good thoughts but let me restate my situation. I have a new, grounded, off grid, weekend cabin that I built. To date, I have completely wired the cabin to support a 'county inspected' 110 AC electrical system. I also have a dual fuel 7k generator. I use its 30amp side to plug into the cabin, wired to the electrical panel on a 30amp breaker that supplies power to the cabin on a 30amp basis. It functions perfectly but with gasoline prices a variable, I need a more permanent solution. I have calculated my peak power requirements at 4kW but the steady requirements are 2kW at most. While I want a solar charging solution eventually, the Arizona sun is pretty steady most of the time, I cannot afford that expense right now as I am retired. So I am stuck with using the generator to charge a battery farm for now when I change my setup to include a charger and inverter.

So even with the battery amp hours and inverter sizing problem solved to support a 2kW electrical requirement, I still have the question of the circuit breaker size needed when I hardwire my grounded electrical panel from the inverter.

So with a generator handy when the batteries need charging, how many amp hours will my battery farm need and what inverter will I need to keep my grounded 2kW cabin going for, say, 24 hours between charging cycles. I don't even know if that's reasonable on a limited budget. Is 12 hours more reasonable?


I've gone to many forums and read what they had to say but they never seem to address my situation or needs directly. So to get some suggestions that may apply to my setup, I joined this forum with some very specific questions given my situation before I buy batteries and inverter. Am I asking too much?

[Mike90250]

Welcome. There are several "stickies" that answer the most frequently asked questions like yours, in the
https://www.solarpaneltalk.com/forum...-panel-systems forum. Read them, make notes, and then
when you have your daily KWh load figured out, we can advise you better,
There are 2 specs we need, the max load (when both the toaster and microwave are on) and the total KWh consumed in a 24 hour period.

[Lorenzo]

2kW is my estimated daily use. The 4kW is the max load if I am stupid enough to turn on the microwave, space heater, and coffee maker at the same time.

[Mike90250]

BATTERIES
So, for a 2Kwh daily load (2,0000wh), you at least 3 days bad weather capacity, before you have to start the generator @ 50% full (you can make it fewer days, if you like running the generator more)

3 days x 2Kwh = 6Kwh = 50% so 12Kwh is battery bank size. I'm going to try to attach a table with battery choices,

Keep in mind, it's better to put batteries in SERIES instead of parallel (and you thought this would be cheap)

If I was in your shoes, I'd choose the 8 flooded golf cart batteries @ 9.1Kwh, and save a bit of money. You will be hitting the batteries a bit harder and may need to run the genset on day 2

You could do it with 4, 12V deep cycle batteries, and you would be draining them 50% daily, but that would be the cheapest possible way to get your feet wet.

---

Battery style	est co$t	Volt	Ah	Wh each	Qty in Series	Bank V	Total Wh	Useable 50%	3 day Res. Allowed daily drain	est total co$t	cost/wh	Cells to check levels	Interconnects required @ $8 ea	Weight ea
"Marine" flooded	$ 95.00	12	90	1080	1	12	1080	540	270	$ 95.00	$ 0.09	6	0	~70
"Marine" flooded	$ 95.00	12	90	1080	2	24	2160	1080	540	$ 190.00	$ 0.09	12	1	~70
"Marine" flooded	$ 95.00	12	90	1080	4	48	4320	2160	1080	$ 380.00	$ 0.09	24	3	~70
Golf cart, flooded	$ 95.00	6	190	1140	2	12	2280	1140	570	$ 190.00	$ 0.08	6	1	~70
Golf cart, flooded	$ 95.00	6	190	1140	4	24	4560	2280	1140	$ 380.00	$ 0.08	12	3	~70
Golf cart, flooded	$ 95.00	6	190	1140	8	48	9120	4560	2280	$ 760.00	$ 0.08	24	7	~70
AGM, Carbon Foam	$ 400.00	12	116	1392	1	12	1392	696	348	$ 400.00	$ 0.29	0	0	~90
AGM, Carbon Foam	$ 400.00	12	116	1392	2	24	2784	1392	696	$ 800.00	$ 0.29	0	1	~90
AGM, Carbon Foam	$ 400.00	12	116	1392	4	48	5568	2784	1392	$ 1,600.00	$ 0.29	0	3	~90
Rolls "L-16"	$ 861.00	6	546	3276	2	12	6552	3276	1638	$ 1,722.00	$ 0.26	6	1	221
Rolls "L-16"	$ 861.00	6	546	3276	4	24	13104	6552	3276	$ 3,444.00	$ 0.26	12	3	221
Rolls "L-16"	$ 861.00	6	546	3276	8	48	26208	13104	6552	$ 6,888.00	$ 0.26	24	7	221
Trojan L16RE-A	$ 305.00	6	325	1950	2	12	3900	1950	975	$ 610.00	$ 0.16	6	1	115
Trojan L16RE-A	$ 305.00	6	325	1950	4	24	7800	3900	1950	$ 1,220.00	$ 0.16	12	3	115
Trojan L16RE-A	$ 305.00	6	325	1950	8	48	15600	7800	3900	$ 2,440.00	$ 0.16	24	7	115
CALB -400	$ 525.00	3	400	1200	4	12	4800	2400	1200	$ 2,100.00	$ 0.44	0	3	30
CALB -400	$ 525.00	3	400	1200	8	24	9600	4800	2400	$ 4,200.00	$ 0.44	0	7	30
CALB -400	$ 524.00	3	400	1200	17	51	20400	10200	5100	$ 8,908.00	$ 0.44	0	16	30

[Mike90250]

Inverter

This depends on how the power box at the house is designed, if it's single phase, or split phase NA standard. Single phase, you could use any pure sine, 120V inverter. BUT, if it's split phase, you need to use a 240V split phase inverter. You could replace a split phase box with a single phase box too.
But if you try to use a single phase to feed a split phase box, you can overload the neutral wire in the house wires.
When looking at an inverter, look closely at the Surge Capacity (which is what starts a fridge motor or a blender) and it's standby loss or idle loss. The larger inverter (to handle the larger loads) have larger losses. Most good household class pure sine inverters will be >90% efficient.

[Sunking]

2kW is my estimated daily use. .

No that is power, not energy.

Power or watts is the rate at which energy is used.

Energy is Watt Hours, not watts.

Watt Hours = Watts x hours.

All you have given us is watts.

FWIW if you wired to code you wired it 240/120 single phase

[Lorenzo]

No that is power, not energy.

Power or watts is the rate at which energy is used.

Energy is Watt Hours, not watts.

Watt Hours = Watts x hours.

All you have given us is watts.

FWIW if you wired to code you wired it 240/120 single phase

I gave you watt hours. 2kW over 24 hours (as in 'daily use') as I stated. I also stated I wired the cabin 110 AC, needing a 'single pole circuit breaker' to connect the inverter.

[Lorenzo]

Mike90250, thank you for the battery info based on my 2000 watts of daily use. It does sound like 4 12s with 90Ahs would suit my needs.

My panel is currently powered by a 30amp, single pole breaker, from the 30amp side of my generator. It is a single pole wired 110 AC panel suppplying house power to all my outlets, switches, and lights. No 220 requirements. So I am looking to replace the source of that power and the 30amp single pole circuit breaker with the inverter and circuit breaker appropriate for a 4000 watt surge.

And remember, it is a grounded panel which I understand is important in inverter selection. One other thing, the country inspector has approved my panel, circuits, and generator connection. You mentioned a pure sine wave inverter. Is that necessary? My generator is not an inverter generator but a 7K construction generator that I use for my travel trailer. And all of my electronics work fine with it; TV, DVD player, chargers for my computers let alone my air conditioner and microwave. So is a pure sine wave inverter really needed? They are way more expensive.

[J.P.M.]

I gave you watt hours. 2kW over 24 hours (as in 'daily use') as I stated. I also stated I wired the cabin 110 AC, needing a 'single pole circuit breaker' to connect the inverter.

And Watt-hours is energy or work, not power. Watts or kiloWatts (kW) is power - the time rate of doing work.. You gave incorrect and confusing terms. Learn the difference and you'll understand SK's post.

If you mean 2 kilowatt-hours used continuously and at a constant rate over a 24 hour period, that's an average power draw of 2,000/24 = 83.3 Watts. If you mean 2 kilowatt- hours continuous over 24 hours, which is how your statement could be interpreted, that's (24) X (2,000) = 48,000 Watt-hrs. or 48 kWh.

You want good information back, start by providing information that's correct for the situation, or at least not confusing.

As you may have noticed by the responses , folks around here can be helpful, but they need to start with correct information. A few may be engineering savants, but few are mind readers. GIGO. It's a real PITA trying to give useful information, in effect, doing what amounts to some pro bono work, and then finding out it's all for naught because of someone's ignorance and/or poor understanding of what they were asking. Hence, the qualifying questions/comments.

[Sunking]

I gave you watt hours. 2kW over 24 hours (as in 'daily use') as I stated. I also stated I wired the cabin 110 AC, needing a 'single pole circuit breaker' to connect the inverter.

No you have not KW = Kilo Watts.How many watt hours.

WATT HOURS = Watts x Hours,

You are implying you use 2000 watts x 24 hours = 48 Kwh. That requires a 10,000 watt solar panel and a 15,000 pound $50,000 battery. Do you have $100,000 to pay for that?

[Lorenzo]

And Watt-hours is energy or work, not power. Watts or kiloWatts (kW) is power - the time rate of doing work.. You gave incorrect and confusing terms. Learn the difference and you'll understand SK's post.

If you mean 2 kilowatt-hours used continuously and at a constant rate over a 24 hour period, that's an average power draw of 2,000/24 = 83.3 Watts. If you mean 2 kilowatt- hours continuous over 24 hours, which is how your statement could be interpreted, that's (24) X (2,000) = 48,000 Watt-hrs. or 48 kWh.

You want good information back, start by providing information that's correct for the situation, or at least not confusing.

As you may have noticed by the responses , folks around here can be helpful, but they need to start with correct information. A few may be engineering savants, but few are mind readers. GIGO. It's a real PITA trying to give useful information, in effect, doing what amounts to some pro bono work, and then finding out it's all for naught because of someone's ignorance and/or poor understanding of what they were asking. Hence, the qualifying questions/comments.

Ummm, I clearly said my use for my 360sf cabin is 2kw over a 24 hour period; with a surge potiental of 4kW at any one time. That was my story to begin with and my story now. I don't understand the need to belittle someone that does not know as much as most here. I have supplied all I know about my electrical environment. I have received some valuable suggestions based on my input so far but apparently I do not have the background to provide my input exactly in the format you need it. Sorry but this is why I asked for help. I have stated everything about my setup I know about. I do not know what I do not know. I do not know how to say what I do know any other way.


I have a good start on my battery needs. Still not sure about the Inverter yet nor the circuit breaker needed for the inverter in the panel. I have a 30amp breaker for the generator connection now but if say I need a 5000 watt inverter, will it need something larger than a 30 amp breaker?