Need help with wire gauge/fuse amperage

[manamongtheruins]

So I finally got the inverter I think we'll need. Now I need to get another 100 ah 12v battery and the wiring/fuses and I think we'll finally be able to get this going. I have been doing a lot of research on what we need and it's just really confusing to try to find what's relative to our specific components so I figured I'd just try to find someone that knows this stuff and can maybe explain the why and how so I can better understand it.

To start off, let me say what we're trying to power:

The absolute required loads are two small Criterion 5 cu ft chest freezers from Menard's. The thing is, one is going to be overridden with a temp controller and used as a fridge so it shouldn't eat as much watts as the actual freezer one. Aside from that, we might use the batteries for a strip of lights (30 watts) for a few hours a day or a small fan (5 watts) for a few hours a day as well. We run a gas generator for our usual stuff (a/c, internet, projector, Bluetooth speaker, etc) so as far as trying to run something 24 hours a day like a freezer, solar is going to be the way to go so it's gonna be sort of dedicated to that.

Now on to what components we have:

- 2 x 200 watt Grape Solar panels (however 1 got shattered and I'm in the process still of testing it for its efficacy)
- 40a Grape Solar Comet PWM charge controller
- 1 (only 1 right now but the goal is to have 2 and then probably 4 later on but them being $180 each is a bit hard on the budget) Universal Power Group 100ah 12v SLA AGM (UB121000)
- GoWise Power 1500w PSW inverter (PS1005)
- 15' of 10 ga wire with MC4 connectors
- 2 x 20a inline MC4 fuses

Now for my questions/concerns:

I understand that there are four connections we need to make:
Panels - charge controller
Charge controller - batteries
Battery - battery (in parallel)
Battery bank - inverter

So far I'm about 99% sure that I have the panels to charge controller figured out. The panels and controller came as a kit and included the 15 ft of 10 ga wire as well as the 2 20a inline fuses. It said in the manual to cut the cable in half which would be 7 1/2 ft and to hook it all up with the inline fuses on the positives from the panels so I'm hoping that that is correct. The other connections however, I can't figure out. I don't know what wire gauge to go with as well as what fuse amperage to get. As far as wire distance and what not, I plan to have all the components within 5 ft of each other except for the panels to controller which will be the provided 7 1/2' most likely.

Any help or information to finally get this done would be extremely appreciated. This whole pv stuff has been something I've slowly been trying to research for the past year due to money issues and time issues (as always). The wife needs a freezer already and for the past couple years we've been living out of a little cooler having to buy bag after bag of ice especially in the summer (we live off grid). Really eats up the wallet and we also have our first baby on the way so I'm trying to get this figured out! Thanks guys!

 

[Diysolar123]

first thing to do is figure out your actual load...that means add up the watts.
a 100Ah 12v sla is good for about 50Ah * 12v or 600Whours of power.

if i just go to an offgrid calculator such as: https://unboundsolar.com/solar-information/offgrid-calculator
and toss in one 16cuft fridge, a laptop, and an led light for a couple hours a day I get 1600Wh/day.
Also from same site you can see you will need probably around four 200W panels and at least three batteries.
There are other sites and off-grid calculators so give them a try and make sure you are starting out with an accurate assessment of what your power demands will end up being.

 

[manamongtheruins]

first thing to do is figure out your actual load...that means add up the watts.
a 100Ah 12v sla is good for about 50Ah * 12v or 600Whours of power.

if i just go to an offgrid calculator such as: https://unboundsolar.com/solar-information/offgrid-calculator
and toss in one 16cuft fridge, a laptop, and an led light for a couple hours a day I get 1600Wh/day.
Also from same site you can see you will need probably around four 200W panels and at least three batteries.
There are other sites and off-grid calculators so give them a try and make sure you are starting out with an accurate assessment of what your power demands will end up being.

View attachment 55068

Well, I tried several times to figure out the wattage for what we're trying to do but I don't think it's something that can just be calculated at least not easily and definitely not easily for me. The freezer that's going to stay a freezer might be possible but as far as trying to figure out the freezer I'm turning into a fridge, I don't know how that can be done.

As far as your calculator suggestion, a 16 cu ft is a bit bigger than the freezers we have so I can understand how it needs more than we'll need.

As far as what you're saying goes though, any idea how to figure out the load for each of our appliances? I can try to get whatever info you think will help off of the manual/box of them. Thanks

 

[Diysolar123]

if you check the calculator it actually has not only the size of the device, but the HOURS it may run per day...
using a freezer as a fridge is not that big of a deal; a freezer is just a fridge with more insulation and a compressor that runs a bit more.

Do not get to caught up the specific device itself, focus on the watt hours.
Your, lets call them "coolers", will cycle on and off many times per day, however, in the end it is a watthour load.
To get a simple idea of a device you can pick up one of the cheap kill-a-watt-hour meters that you plug something into.
Also, you can just lookup your model online and find its power label.
A small standard refrigerant (r134a) compressor for a 5cuft fridge or freezer is probably going to pull 300-600w when its running.

I really would not want you to get caught going down the rabbit hole of wiring, and panels, and all that when you have not done the most important part before starting ANY of that...if you do not have a good handle on your real anticipated load, you will be very disappointed.

worst case you could just look at the manfuacturers specficiation for the MOST energy efficient model there is in the size you plan on using. FYI, it will cost a fortune so do not look at that hehe... but you can know with a certainty that your units WILL use more power so that will set the absolute minimum sizing.
I just went to bestbuy website and looked up a 5cuft fridge which showed an annual power usage of 327kwh...so...
327000wh / 365day is around 900wh of power a day. Hey look at that, thats a 300W fridge running about 3hours a day hehe

You do not want to go thru all this trouble and end up on day one at 7pm with a dead battery bank and fridge of warming food!!
Good luck and do not let it get you to overwhelmed!

 

[manamongtheruins]

if you check the calculator it actually has not only the size of the device, but the HOURS it may run per day...
using a freezer as a fridge is not that big of a deal; a freezer is just a fridge with more insulation and a compressor that runs a bit more.

Do not get to caught up the specific device itself, focus on the watt hours.
Your, lets call them "coolers", will cycle on and off many times per day, however, in the end it is a watthour load.
To get a simple idea of a device you can pick up one of the cheap kill-a-watt-hour meters that you plug something into.
Also, you can just lookup your model online and find its power label.
A small standard refrigerant (r134a) compressor for a 5cuft fridge or freezer is probably going to pull 300-600w when its running.

I really would not want you to get caught going down the rabbit hole of wiring, and panels, and all that when you have not done the most important part before starting ANY of that...if you do not have a good handle on your real anticipated load, you will be very disappointed.

worst case you could just look at the manfuacturers specficiation for the MOST energy efficient model there is in the size you plan on using. FYI, it will cost a fortune so do not look at that hehe... but you can know with a certainty that your units WILL use more power so that will set the absolute minimum sizing.
I just went to bestbuy website and looked up a 5cuft fridge which showed an annual power usage of 327kwh...so...
327000wh / 365day is around 900wh of power a day. Hey look at that, thats a 300W fridge running about 3hours a day hehe

You do not want to go thru all this trouble and end up on day one at 7pm with a dead battery bank and fridge of warming food!!
Good luck and do not let it get you to overwhelmed!

If I remember correctly, I tried researching the wattage per day that the both of them would use and I came up with 50 watts on average so that would be 1.2 kwh/day. Then I thought that with two 100ah batteries at a 50% DoD that would give us a day or so of storage so that's why I want to get 4 batteries so we can go longer if it's real cloudy and stuff. Does that seem right?

 

[manamongtheruins]

Anyone else have anything to offer as far as what wire and fuse are appropriate for our components? Seems like it would be simple for someone in the know but I'm stumped

 

[Just John]

Well, I tried several times to figure out the wattage for what we're trying to do but I don't think it's something that can just be calculated at least not easily and definitely not easily for me. The freezer that's going to stay a freezer might be possible but as far as trying to figure out the freezer I'm turning into a fridge, I don't know how that can be done.

As far as your calculator suggestion, a 16 cu ft is a bit bigger than the freezers we have so I can understand how it needs more than we'll need.

As far as what you're saying goes though, any idea how to figure out the load for each of our appliances? I can try to get whatever info you think will help off of the manual/box of them. Thanks

Get a Kill-a-Watt meter and plug one into grid power for a day to figure out how much you need. If no grid power, use the generator and multiply accordingly.

Using one as a fridge won't save you as much power as you think. It is much more likely to be opened frequently.

Starting off buying an inverter and battery is going backwards and will likely cost you more in the long run. Figure out how much you need, then figure out how to get it. I bought 8 cells (105 amp hours) for $500 including shipping, add a BMS and you are at $600 and usable capacity would be about 4 times a single AGM you have.

 

[Just John]

Anyone else have anything to offer as far as what wire and fuse are appropriate for our components? Seems like it would be simple for someone in the know but I'm stumped

Knowing for the components you have is indeed easy. Knowing for what you will actually need is more difficult. 1500 watt inverter will be over 125 amps, likely safer to go with 200 amp fuse and wiring rather than 150 amps. 2 gauge wiring and 200 amp circuit breaker or fuse. You actually size the fuse or circuit breaker to protect the wire. The inverter should handle this, the real question is how much storage you need, and how much solar you will need to recharge the storage. You are building your system backwards.

 

[manamongtheruins]

Knowing for the components you have is indeed easy. Knowing for what you will actually need is more difficult. 1500 watt inverter will be over 125 amps, likely safer to go with 200 amp fuse and wiring rather than 150 amps. 2 gauge wiring and 200 amp circuit breaker or fuse. You actually size the fuse or circuit breaker to protect the wire. The inverter should handle this, the real question is how much storage you need, and how much solar you will need to recharge the storage. You are building your system backwards.

Ah thank you very much, finally getting some proper information on what I need. Like I said in post #5, "I came up with 50 watts on average so that would be 1.2 kwh/day. Then I thought that with two 100ah batteries at a 50% DoD that would give us a day or so of storage so that's why I want to get 4 batteries so we can go longer if it's real cloudy and stuff."

Anyway, as far as your 2 gauge wiring and 200 amp circuit breaker or fuse, you are referring to the connection between the inverter and the batteries right? What about the other connections: from panels to charge controller (was I right in my op to go with what was implied in the manual), from charge controller to batteries, and from battery to battery? Thank you very much for answering my questions!! It seems very difficult to get this stuff answered.

 

[Just John]

Anyway, as far as your 2 gauge wiring and 200 amp circuit breaker or fuse, you are referring to the connection between the inverter and the batteries right?

Yes. Assuming 100% efficiency (never going to happen), 125 amps would be the current. You need to wire and fuse for 150 amps, and add in any surge (like for starting compressors) and call it 200. A critical factor in wire ratings is also "how long is it?"

What about the other connections: from panels to charge controller (was I right in my op to go with what was implied in the manual)

For the panels, use 10 gauge photovoltaic wire (UL 4703). Although you can buy it in 12 gauge and 8 gauge, 10 is the most common. The industry standard MC4 connection is rated for 30 amps, thus the 30 amp rated 10 gauge photovoltaic wire is most common.
Use anything other than photovoltaic wire at your peril. It's rated for Sunlight, ozone, UV, flame, and moisture. Using anything else is against the law (fire code) in most locations.

Solar Wire Guide

temcoindustrial.com

, from charge controller to batteries

Depends on how many amps you are going to run through it. Size the wire accordingly and use a breaker as well. A breaker is easier because it also serves as an on/off switch, but fuses work. 40 amp charge controller use 8 gauge and 50 amp breaker. FYI, your battery should not exceed 30 amps charge, so be careful when you hook up that second panel. You will likely find you need more panels, and a second charge controller.

50 watts per hour, go with 12 gauge through the entire system. What, you mean it isn't that easy?
Lots of examples on this board of people saying "that's what you told me to use". That occurs when people don't know the correct questions to ask.

Circuit Wizard - Blue Sea Systems

, and from battery to battery? Thank you very much for answering my questions!! It seems very difficult to get this stuff answered.

Battery to battery, use 2 gauge (or better). It should be at least the size going to your inverter.

Answering your perceived question is indeed easy. Getting the right answer for reality is harder.

 

[manamongtheruins]

Yes. Assuming 100% efficiency (never going to happen), 125 amps would be the current. You need to wire and fuse for 150 amps, and add in any surge (like for starting compressors) and call it 200. A critical factor in wire ratings is also "how long is it?"

For the panels, use 10 gauge photovoltaic wire (UL 4703). Although you can buy it in 12 gauge and 8 gauge, 10 is the most common. The industry standard MC4 connection is rated for 30 amps, thus the 30 amp rated 10 gauge photovoltaic wire is most common.
Use anything other than photovoltaic wire at your peril. It's rated for Sunlight, ozone, UV, flame, and moisture. Using anything else is against the law (fire code) in most locations.

Solar Wire Guide

temcoindustrial.com

Depends on how many amps you are going to run through it. Size the wire accordingly and use a breaker as well. A breaker is easier because it also serves as an on/off switch, but fuses work. 40 amp charge controller use 8 gauge and 50 amp breaker. FYI, your battery should not exceed 30 amps charge, so be careful when you hook up that second panel. You will likely find you need more panels, and a second charge controller.

50 watts per hour, go with 12 gauge through the entire system. What, you mean it isn't that easy?
Lots of examples on this board of people saying "that's what you told me to use". That occurs when people don't know the correct questions to ask.

Circuit Wizard - Blue Sea Systems

Battery to battery, use 2 gauge (or better). It should be at least the size going to your inverter.

Answering your perceived question is indeed easy. Getting the right answer for reality is harder.

Thanks a ton!! And that calculator page you sent is really helpful as well. Well I think I finally have something to work with here and can go forward, thanks again. I do have a question concerning distance. Like you said, "how long is it?", well how does that relate to losses? Do losses occur at a set distance or does it depend on what the current is at what point in the distance the loss occurs? Confused...

 

[Just John]

Thanks a ton!! And that calculator page you sent is really helpful as well. Well I think I finally have something to work with here and can go forward, thanks again. I do have a question concerning distance. Like you said, "how long is it?", well how does that relate to losses? Do losses occur at a set distance or does it depend on what the current is at what point in the distance the loss occurs? Confused...

All wires have resistance. The longer the wire, the more the resistance. Higher resistance means voltage drop. So "how long is the wire" is always a consideration, as well as how your equipment handles the voltage drop.

 

[manamongtheruins]

All wires have resistance. The longer the wire, the more the resistance. Higher resistance means voltage drop. So "how long is the wire" is always a consideration, as well as how your equipment handles the voltage drop.

Right I understand but is there maybe a way to figure out the distance at which it starts to drop dramatically or is it just exponentially continous?

 

[JoeHam]

Just use an online calculator that inputs distance. Make sure it accounts for “round trip” distance and stay under 3% loss.

Lower than 3% is better.

See here for one example :

http://circuitwizard.bluesea.com/#

 

[Just John]

Right I understand but is there maybe a way to figure out the distance at which it starts to drop dramatically or is it just exponentially continous?

If you double the wire length, you double the resistance. It's linear, not exponential. Use Google, there are all kinds of charts to tell you how much resistance a kilometer of wire has.

 

[manamongtheruins]

Just use an online calculator that inputs distance. Make sure it accounts for “round trip” distance and stay under 3% loss.

Lower than 3% is better.

See here for one example :

http://circuitwizard.bluesea.com/#

Thank you!

If you double the wire length, you double the resistance. It's linear, not exponential. Use Google, there are all kinds of charts to tell you how much resistance a kilometer of wire has.

Thank you!