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So out of my element... help an IT guy figure it out?

L

Lord Doa

New Member
Joined
Jun 13, 2023
Messages
21
Location
Backwoods, Texas
I'm looking to add solar to a small cabin in the woods and I need some help confirming I'm on the right track before I order kit that's not gonna work for my application. Doing a quick inventory of items I'll be running gives me a total of 5.2 kWh (
https://imgur.com/ObNTLn3
).

I was looking at the EG4 6500EX-48 + 2 x EG4-LifePower 48v 100AH batteries but the more I think about it, I'm starting to think I don't need such a huge inverter (6500w.) At least if I'm understanding it correctly and the inverter should match maximum concurrent usage at a point in time (1323.50 watts / 1654.375 @ 80%) in my example screenshot.) If that's so, and I have no plans to add any type of major electrical devices in the future, would the EG4 3000EHV-48 serve me better since the inverter is almost twice what I'll need at any given point in time?

Additional Thoughts:
  • Panels - I haven't thought about these yet; I'm hoping they're interchangeable enough to not be a problem
  • Surplus storage - I'm aware 2 batteries only gives me 1.5 days of storage; I'll be adding a pair of additional batteries in the future. I understand this leaves very little room for cloudy days and such and I can live with that until I add two more batteries.
  • Use - This is an off grid cabin that will have very few electrical items in it with max 4 hours inside (awake) on an average day
  • Modular - I'm a big fan of modular and being able to add more things to expand (ie batteries/panels)
 
It could go either way. I didn't see anything about water in your load analysis. Any pump? Microwave oven?

I would probably go with the larger inverter. It will have more upfront cost with larger wiring, but at least you can grow your loads as life happens! Probably better to do it now than replace and redo later.
 
The 6500W inverter, loaded lightly, won't be as efficient as it would be more heavily loaded and the idle consumption may be higher than the 3000W unit, but those issues can largely be overcome with adding an additional panel, particularly since they are inexpensive.
 
Madco said:
The 6500W inverter, loaded lightly, won't be as efficient as it would be more heavily loaded and the idle consumption may be higher than the 3000W unit, but those issues can largely be overcome with adding an additional panel, particularly since they are inexpensive.
Click to expand...
Yes an additional solar panel can be inexpensive to cover the inverter idle consumption but my concern would be the inverter high idle consumption / inefficiency on a series of cloudy days where solar production can be 5-10% of a sunny day and every night where adding panels is of no help and extra battery storage is more expensive.

Knowing what I know now, I am very glad my inverter had has a very low idle consumption of 16 watts or much less if placed in Search mode.
 
Madco said:
It could go either way. I didn't see anything about water in your load analysis. Any pump? Microwave oven?
Click to expand...
Nah, I got a hand pump and outhouse for water and no need for a microwave. I've tried to think of everything I'd ever even think of adding which is why I added the AC/Fridge.
 
E. Cho said:
Yes an additional solar panel can be inexpensive to cover the inverter idle consumption but my concern would be the inverter high idle consumption / inefficiency on a series of cloudy days where solar production can be 5-10% of a sunny day and every night where adding panels is of no help and extra battery storage is more expensive.

Knowing what I know now, I am very glad my inverter had has a very low idle consumption of 16 watts or much less if placed in Search mode.
Click to expand...
Ide consumption... is that what the spec sheet is referring to as "Battery to Inverter" (94%) and "PV to Inverter" Efficiency? (97%)? Also, which "side" do I need to calculate that into? Battery size, inverter, or both?

Also, I won't be adding the AC/Fridge for a while so I'm looking at <800 watts / 2.2 kWh to begin with. A pair of batteries (8,192 kWh) will give me 3.6 days of power storage.
 
Those electronics have phantom loads unless they are on a power strip that you turn off, or unplug the adapters.
For your Internet, you have "Watts Device On" and hours for it. You don't have any hours for "Watts Device Off".

I would install the larger inverter. The power you save with the smaller one is nominal, but it makes the system much easier to expand. Also, you might need the higher power for "surge" (AC and fridge). AC can easily be 3x running amps.
 
No, idle consumption is what the inverter needs to operate. The spec sheet shows it towards the bottom. It states "<50w". So let's say 49w x 24hrs = 1,176 watt hours, just to run the inverter. This comes from the sun, if it's shining, otherwise batteries.
 
Go down the spec sheet. It lists the "Idle Power Consumption" as 50 Watts. So the inverter is always using 50 Watts continuously, whether inverting or not, unless in Eco mode or Off. Some inverters warn not to frequently cycle them On/Off. Eco mode may not start all devices or appliances but would be a good mode if away and not wanting to shut it down.

50 watts continuous is for me quite a bit during cloudy days or at night.

Also note that the Peak Surge is only 5 seconds, which may not be long enough for some tools or appliances with inductive motors. Might be worth searching the forum or seller for real world use with a variety of appliances or tools. This is a high frequency inverter which has compromises vs a higher quality Low Frequency inverter like a Victron or Samlex. Again may be worth searching the forums on Inverter Frequency differences.

I have also read that these type of inverters can be quite loud, especially under bigger loads. Might be worth looking into unless it will be sound isolated.

Also you have your laptop consumption listed twice.
 
How close is the all in one going to be to your living space. They generally tend to be have small rack server type fans and can start making a lot of noise. Perhaps consider Schneider or Victron low frequency (old school big transformers) inverter/chargers. Lightly loaded my understanding is they are much quieter than an all in one. And very impressive sustained surge capabilities. You will need a seperate SCC but you said modular is a bonus.
 
My recommendation would be a Victron Multiplus II 48/5000.
Very low idle draw - plenty of power - modular, Lots of Surge, (if you get another in the future you can either get 240v or twice as much 120v).

The low idle draw is 15w or 3w if in search mode- very low!

Although the Victron path will be more expensive.

With a Cerbo and Starlink, you can monitor all the Victron equipment from Home (or anywhere on the internet) and make changes to the equipment remotely.

Because it’s not an all-in-one, you will need
The Solar Charge Controller too - that will depend on how much solar you install - my guess - SmartSolar mppt 150/35.

Good Luck with your project.
 
E. Cho said:
Go down the spec sheet. It lists the "Idle Power Consumption" as 50 Watts. So the inverter is always using 50 Watts continuously, whether inverting or not, unless in Eco mode or Off. Some inverters warn not to frequently cycle them On/Off. Eco mode may not start all devices or appliances but would be a good mode if away and not wanting to shut it down.

50 watts continuous is for me quite a bit during cloudy days or at night.

Also note that the Peak Surge is only 5 seconds, which may not be long enough for some tools or appliances with inductive motors. Might be worth searching the forum or seller for real world use with a variety of appliances or tools. This is a high frequency inverter which has compromises vs a higher quality Low Frequency inverter like a Victron or Samlex. Again may be worth searching the forums on Inverter Frequency differences.

I have also read that these type of inverters can be quite loud, especially under bigger loads. Might be worth looking into unless it will be sound isolated.

Also you have your laptop consumption listed twice.
Click to expand...
That’s the “heads up” that I’m here for. I just did a quick look into low vs high frequency inverters and I think I’ll be ok with the high frequency inverter because I won’t be using anything with motors that would cause a surge. Most of the tools I have are battery powered and for the occasions that I need to use power tools I do have a generator. Though I do want the option of an AC/Fridge… which do have motors.

Is there a standard calculation for surge (Ie. an item using 500 watts would use a max of XXX watts when turned on) or is it item dependent? I can just build the surge into the calculation of the system, right? Without the AC/Fridge I’m just under 900 watts usage which leaves 2100 watts on the inverter before even entering surge.

One thing that matters, I think… this is a low-tech, off grid solution that will have very little utilization. I don’t expect anything other than the internet section staying plugged in all the time though it wouldn’t hurt my feelings to have to turn it on each night for a few hours. The point of the solar isn’t to replace my incoming power as much as to address minor electronic needs.
 
Rocketman said:
My recommendation would be a Victron Multiplus II 48/5000.
Very low idle draw - plenty of power - modular, Lots of Surge, (if you get another in the future you can either get 240v or twice as much 120v).

The low idle draw is 15w or 3w if in search mode- very low!

Although the Victron path will be more expensive.

With a Cerbo and Starlink, you can monitor all the Victron equipment from Home (or anywhere on the internet) and make changes to the equipment remotely.

Because it’s not an all-in-one, you will need
The Solar Charge Controller too - that will depend on how much solar you install - my guess - SmartSolar mppt 150/35.

Good Luck with your project.
Click to expand...
When I started in computers 35 years ago I built everything from individual parts, but now I’m old and tired I see benefit in paying someone else to do so of the heavy lifting for me when it makes sense. I started building a solar system from individual parts and then saw the all-in-one and said to myself, “Self, you have more money than time… that looks like a good idea!” But of course, there are trade offs when you have someone else build your system for you.

I have a rudimentary knowledge of electricity and can understand English… let’s see if I’m smart enough to build out a system :)
 
Brucey said:
How close is the all in one going to be to your living space. They generally tend to be have small rack server type fans and can start making a lot of noise. Perhaps consider Schneider or Victron low frequency (old school big transformers) inverter/chargers. Lightly loaded my understanding is they are much quieter than an all in one. And very impressive sustained surge capabilities. You will need a seperate SCC but you said modular is a bonus.
Click to expand...
Hmm… I haven’t thought about this. It’s a small cabin so it would basically be in the same room with me. However, I’m in IT and have had a 22U server rack in my room forever with UPS, servers, workstation, and a full network stack running so fan noise isn’t an issue.

However, I may bail on the all-in-one if I’m smart enough to build a comparable system. I love the aesthetics of the all in one, but it’s starting to look like the trade off for looks might not be worth it.
 
One other thought for this. Your starlink power consumption does not factor in the antenna heaters running. I do understand that it is not likely to need them in Texas most of the time, but should they go on that 70W goes to more like 200-300w. That basically quadruples the power it uses and drives up your total planned consumption by 15% if they come on
 
Lord Doa said:
Is there a standard calculation for surge (Ie. an item using 500 watts would use a max of XXX watts when turned on) or is it item dependent?
Click to expand...
There is not a calculation. Not only is it item dependent, it is inverter dependent.

Shopping for my inverter for my Air Conditioner, which uses 1700 watts and surges a bit, I felt like this info should be readily available, but the best you can do is see if anyone else ran a similar device off it and look at charts that sometimes have a broad range like “2 time to 5 times the wattage rating of the device”.

This is an example from a better inverter about SAMLEX documentation and inverter sizing:

IMG_1332.jpeg
My 3000 watt Samlex inverter is 2X the wattage of the device and has a soft start. This chart says I’d need a 5000 watt inverter to run my AC.

There’s also YouTube videos out there about inverters with the same wattage rating not running the same device, and I saw a video of a couple of the cheaper inverters catching fire.
 
zcskywire2 said:
One other thought for this. Your starlink power consumption does not factor in the antenna heaters running. I do understand that it is not likely to need them in Texas most of the time, but should they go on that 70W goes to more like 200-300w. That basically quadruples the power it uses and drives up your total planned consumption by 15% if they come on
Click to expand...
You bring up a good point, thank you! I see I need to do some more calculations on my needs
 
Sort of. The Charge Controller is separate from Solar vs Generator/Turbine. Each will have it's own charge controller. They are separate components. I also don't get why there is a "Battery Charger" just before the Batteries? It is usually part of the Charge Controller. The "12V Converter" is also part of the Inverter, unless it's a system that is really cobbled together of entirely separate components. Personally, I would not follow that diagram to put together a system.

For solar, a MPPT Charge Controller is recommended (vs PWM) and for a Generator/Turbine a good quality Low Frequency Inverter usually has a Charger / Controller function that a generator can be wired into. But it's not a given, so you need to read the Inverter specs and look for one that has the Inverter/Charger combo.

You can research Off Grid "Kits" with the functions that you want (excluding AiO's) and it will help guide you and inform you of the components required. After that, it depends on your budget to cobble the desired components together.
 
Last edited:
Lord Doa said:
You bring up a good point, thank you! I see I need to do some more calculations on my needs
Click to expand...
Another point on power needs, 130w for a chainsaw seems very low. Consider 1hp ~= 750w of energy. No chain saw is 100% efficient there either. So I don't imagine you have a 1/6th or so hp chainsaw.

Instead I'd immagine you've measured the free speed power draw of the chainsaw, rather than the power draw while cutting a log. This again will throw your numbers off by a very good amount if I'm correct. Apologies if I'm wrong
 
zcskywire2 said:
Another point on power needs, 130w for a chainsaw seems very low. Consider 1hp ~= 750w of energy. No chain saw is 100% efficient there either. So I don't imagine you have a 1/6th or so hp chainsaw.

Instead I'd immagine you've measured the free speed power draw of the chainsaw, rather than the power draw while cutting a log. This again will throw your numbers off by a very good amount if I'm correct. Apologies if I'm wrong
Click to expand...
It's just a little battery operated saw that is basically the limb trimmer. Anything of significant diameter and I pull out the gas saw.
 
E. Cho said:
Sort of. The Charge Controller is separate from Solar vs Generator/Turbine. Each will have it's own charge controller. They are separate components. I also don't get why there is a "Charge Controller" just before the Batteries? It is usually part of the Charge Controller. The "12V Converter" is also part of the Inverter, unless it's a system that is really cobbled together of entirely separate components. Personally, I would not follow that diagram to put together a system.

For solar, a MPPT Charge Controller is recommended (vs PWM) and for a Generator/Turbine a good quality Low Frequency Inverter usually has a Charger / Controller function that a generator can be wired into. But it's not a given, so you need to read the Inverter specs and look for one that has the Inverter/Charger combo.

You can research Off Grid "Kits" with the functions that you want (excluding AiO's) and it will help guide you and inform you of the components required. After that, it depends on your budget to cobble the desired components together.
Click to expand...

Thanks for the replies. They made me realize that I don't have a full grasp on the theory so I've decided to take a step sideways and get a handle on that before continuing this. I would appreciate your input in that thread if you're willing to continue the conversation. Thanks!

diysolarforum.com

Is my basic understanding of the theory correct in this image?

I realized I didn't have a full understanding of the theory behind solar so I'm trying to get that locked down. My idea being the more I understand how the system works the better I'll be able to troubleshoot and optimize it. First off, are my following assumptions correct? Solar panels -...
diysolarforum.com diysolarforum.com
 
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