Usage or Capability of Inverter

[jjrr007]

I'm working on my first small off grid installation. Did a lot of reading and testing, and ready to begin - hopefully. I am a newbie though.

I have a 12 volt 5,000 watt inverter. I only will need about 2,000 watts based on my usage. I am planning to place a fuse from the inverter to the battery. I don't see that I will ever use more than 2,000 watts based on my actual usage (the inverters can handle a spike of 10K watts on the 5K inverter and spike of 4K on the 2k inverter). I want to understand this logic; so we can just assume it's the same inverter model- one is 5k and the other 2k.

Would I save a lot of power by just using a 2k inverter or would the savings not be significant if I use upto 2K watts on the 5k inverter?

[max2k]

I'm working on my first small off grid installation. Did a lot of reading and testing, and ready to begin - hopefully. I am a newbie though.

I have a 12 volt 5,000 watt inverter. I only will need about 2,000 watts based on my usage. I am planning to place a fuse from the inverter to the battery. I don't see that I will ever use more than 2,000 watts based on my actual usage (the inverters can handle a spike of 10K watts on the 5K inverter and spike of 4K on the 2k inverter). I want to understand this logic; so we can just assume it's the same inverter model- one is 5k and the other 2k.

Would I save a lot of power by just using a 2k inverter or would the savings not be significant if I use upto 2K watts on the 5k inverter?

Welcome!

For newbie/first project you selected very high power levels which could be very dangerous if you lose control of the system. I understand the size is relative but your 'small' setup could power my entire house . While I have a feeling you mixed up Watt-hours with Watts strictly based on what you wrote:

5,000 W / 12V = 416A, you must have some mighty wires in there, can you post pics of the setup, especially fuse holder and around?

what are your batteries and what are you charging them from?

[AzRoute66]

Be careful. If all is as you say, and you are going to pull 2000W from that inverter, it will pull 167 Amps out of your 12V battery. Be prepared for blown fuse, hot wires/connectors, and/or inverter low voltage disconnect. Try to measure the 'standby power' of the inverter (no load, light load) before the 2 kW load testing.

[jjrr007]

Thanks for your responses. It's put together, but not started. I want to ensure it's safe first.

For the existing 5,000 watt inverter, I have two gauge wires connected to it. No wire is longer than 30 inches. The connections are factory made using the eye hole connectors. I have a mechanical and general contractor's license. I frequently work with electricity. I am not an electrician nor do I share your experience levels. I appreciate your advice.

My thought is to replace the 5K inverter with a 2K inverter. I came up with 2K watts as I think a small window ac units could spike to that. Is that right?

I was planning to put a 150 amp fuse from the inverter to the battery. So it shouldn't pull more than 1,800 watts (150 * 12) or a 90 amp fuse. Would I save energy with the 5K watt inverter or the 2k inverter if I pull let's say 500 watts?

[jjrr007]

My battery bank is a 12 volt 480 ah flooded lead battery. The battery could go up to 60 amps (480/8).

From the electric bill, I have pulled between 70 and 80 kWh per month. I could see it going up to 100 kWh per month which is 3,333Wh per day. I'm planning to power a small window ac unit or sump cooler, camera system, possibly a couple laptop computers.

It's a good idea to measure the amp draw. I will try that. I wanted to ask:

Would the inverter try to pull more amps than what is needed? If not, then what is the risk of putting in a 80 watt fuse to it?
Would a small window AC unit use 1,000 watts?
What do you think of this set-up using a 80 watt fuse?

[AzRoute66]

When it comes to fuses AND wire sizes, you want to be thinking in Amps, not Watts. Any voltage rating on a fuse merely refers to the fuses ability to not arc or otherwise pass current after it has blown. Try to rephrase what you were saying above in amps.

My suggestion that you do a no load or light load test on your inverter (regardless of which one is hooked up) first was to see what power they may take [idling] that is not going to be useful to you. Might help you decide which one you prefer. The inverters probably have this number in their specifications but it is always worthwhile to measure it as well if you have the equipment.

I have no idea what a small air conditioner might draw, or surge to. Wish I could help in that regard.

[max2k]

Thanks for your responses. It's put together, but not started. I want to ensure it's safe first.

For the existing 5,000 watt inverter, I have two gauge wires connected to it. No wire is longer than 30 inches. The connections are factory made using the eye hole connectors. I have a mechanical and general contractor's license. I frequently work with electricity. I am not an electrician nor do I share your experience levels. I appreciate your advice.

My thought is to replace the 5K inverter with a 2K inverter. I came up with 2K watts as I think a small window ac units could spike to that. Is that right?

I was planning to put a 150 watt fuse from the inverter to the battery. So it shouldn't pull more than 1,800 watts (150 * 12) or a 90 watt fuse. Would I save energy with the 5K watt inverter or the 2k inverter if I pull let's say 500 watts?

you meant 150A / 90A fuse? The fuse would open if you exceed that value cutting off your loads. It won't just 'limit' the current. I'm still having trouble putting this all together so it is hard to suggest anything without knowing your sources and loads. Inverters in general have low power cut off limit where they go to 'sleep' if your loads fall below that level. Type of the inverters you have would help to be more specific. I think you won't have a lot of power loss from oversized inverter (1% if at all) but I think you're short on battery capacity and by a lot.

your 480Ah 12V battery (hopefully deep cycle and not just used car battery) can hold 480 x 12 = 5,760 Wh which you can only use 50% of if you want it to last (2,880Wh). If you need any autonomy period common rule of thumb is to have 5 days period so useful daily energy available is 5,760Wh / 5 = 1,152Wh This is about 1/3 of what you're planning to have soon so you're definitely short on battery. Even 2,000 inverter requires 166A from the battery at full power so max inverter you can have with your current battery is 60A x 12V = 720W.

Have you considered going higher in battery voltage? 24V would reduce currents to half and 48V to 1/4 of what you need now.

[AzRoute66]

My battery bank is a 12 volt 480 ah flooded lead battery. The battery could go up to 60 amps (480/8). From the electric bill, I have pulled between 70 and 80 kWh per month. I could see it going up to 100 kWh per month which is 3,333Wh per day.

Slow down here, you are mixing concepts just as you did earlier with amps and watts. Please take a look at the equations for power (watts), volts, and amps and don't crank that thing up just yet.

[max2k]

Slow down here, you are mixing concepts just as you did earlier with amps and watts. Please take a look at the equations for power (watts), volts, and amps and don't crank that thing up just yet.

I think his 480/8 relates to highest current limit numerically equal to C/8. He seems to have low energy demands with those kWh.

[jjrr007]

Yes, I have written about a lot at one time. I find electricity sizing and this entire topic very interesting. Sorry for getting ahead of my self

I will try to measure the amp draw while not running anything. Thank you for that.

In case you are interested, the inverter I just purchased is this one:

2k watt Inverter

4 of these batteries in my battery bank wire in series and parallel (2 each way)

I agree that I should have increased the voltage of the battery, but I have already bought a 12 volt inverter. My solar panels are 400 watt and I'm thinking to increase them to 600 watts

[jjrr007]

To try to some things up, I wanted to ask if the following design is acceptable or what I should change


I have 400 watt generic solar panels which will be increased to 600 watts
Connected to this controller (click on controller link).
The batteries are 4 of these batteries in my battery bank wire in series and parallel (2 each way)
and the inverter is this one
A 80 amp fuse from the battery to the inverter and a 60 amp fuse from the controller to the battery. I understand that it will open the connection when tripped.

I'm planning to power a small window ac unit r, camera system and a couple laptop computers. Should I increase the battery bank from 460 ah or any other change?

[max2k]

Yes, I have written about a lot at one time. I find electricity sizing and this entire topic very interesting. Sorry for getting ahead of my self

I will try to measure the amp draw while not running anything. Thank you for that.

In case you are interested, the inverter I just purchased is this one:

2k watt Inverter

4 of these batteries in my battery bank wire in series and parallel (2 each way)

I agree that I should have increased the voltage of the battery, but I have already bought a 12 volt inverter. My solar panels are 400 watt and I'm thinking to increase them to 600 watts

I would suggest you to stop and rethink the project- it is much easier to 'replace' components on paper than in reality. Your battery looks ok from type point of view except you need to triple your bank to handle your loads. Its total capacity is 460 Ah, not 480 Ah.

Your inverter doesn't seem to have adjustable shut off / alarm voltages and according to this:https://pssurvival.com/PS/Batteries/...ltage_1993.pdfyour battery will be completely empty when it will decide to make a sound (9.8 V for alarm). I'd prefer alarm to go off at least at 20% - 40% SOC which corresponds to 11.5V-11.7V (p68 C/10 curve from the doc). I understand with your current battery/loads combination it would be daily event but that's indicator of design problem not the alarm.

400W panels over standard 5 hr sunlight in the middle of the summer in SoCal would produce 2kWh of energy. This is also low for your projected demand 3.3kWh and if your location is less than optimal or you need the system to work the same way in the winter time. What Charge Controller do you use / planning to use?

[jjrr007]

First off, thanks for your time. You guys are not being paid to do so, and it's nice of you to do so. If I can become better at this, I can try to help newbie's like myself.

So I need to increase my battery size and solar panels. I should triple my battery bank to about 1,380 ah? Also, how many more 100 watt panels? The controller I'm setting up is this one- controller (click on controller link). Are the fuse amp ratings ok?

If you prefer that I post this on another thread, feel free to let me know.

[jflorey2]

So I need to increase my battery size and solar panels. I should triple my battery bank to about 1,380 ah? Also, how many more 100 watt panels?

At 1380ah you will want at least C/13, or 106 amps, charging current. That's about 1500 watts of panels. However I would avoid the smaller 100 watt panels and use the cheaper 200-300 watt panels. Your charge controller will be able to handle the higher voltages of the larger panels.

[Sunking]

I have a 12 volt 5,000 watt inverter.

Make sure your life, medical, health, and home owners insurance policies are paid up. You going to need them to bury the dead and rebuild your home from the pile of ashes.