Question about Inverter distance to breaker board and PV distance to inverter

[Offgrid]

Hi everyone, well sh#t its only been 10 years since I've been on lol. Is Sunking still here? bud I finally understand amps and voltage mean nothing,its the power that has most meaning. lol... I also converted a motorcycle to electric during my absence from the forum, thanks a lot for all your advice all those year ago. Anyway... I digress.

So I am about to start my DIY powerwall but just have a question about distances between AC that goes into the inverter from the grid (If the inverter cant handle the load/charge the battery) and the distance of the power coming back from the inverter to the breaker board to power the house. I have put all my equipment in a power shed away from the house due to safety as the battery is made of recycled laptop cells. This unfortunately has led to a long run from the inverter to the breaker board and vice versa (~100 feet). I will be using either 8 awg cable for these runs, which should give me about 40 amps. The inverter is only 5kw at 220volts but this should give me room for growth. Sooooooo do you think the 100 feet to and from the breaker board will be a issue with voltage drop at 220 volts?

Lastly the distance between the PV combiner box and the inverter is about 32 feet. The array is 137 volts and 40 amps. Will the standard size solar wire be fine for this distance?


Oh if you want to see the electric bike, you can check it out on youtube. thanks everyone! https://www.youtube.com/channel/UCio..._as=subscriber



Solar.jpg

[bob-n]

Here is a calculation for the 240VAC run from house to garage. The calculation for the other runs is similar.
8 AWG wire is 0.0006282 ohms per foot at 20C.
Voltage loss is ohms x amps.
40 amps x 100 feet x 2 wires x 0.0006282 = 5 volts drop. That means 2% energy loss, and also voltage drops that can cause the system to malfunction. I would engineer to stay under 1 volt drop.

Copper wire resistance tables here:

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html

Note that copper resistance goes up roughly 0.4% every degree C above 20C, so if you are in a hot climate, you need slightly more copper.

[Ampster]

What kind of inverter are you using? How many kWhrs of batteries?

[Offgrid]

Here is a calculation for the 240VAC run from house to garage. The calculation for the other runs is similar.
8 AWG wire is 0.0006282 ohms per foot at 20C.
Voltage loss is ohms x amps.
40 amps x 100 feet x 2 wires x 0.0006282 = 5 volts drop. That means 2% energy loss, and also voltage drops that can cause the system to malfunction. I would engineer to stay under 1 volt drop.

Copper wire resistance tables here:

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html

Note that copper resistance goes up roughly 0.4% every degree C above 20C, so if you are in a hot climate, you need slightly more copper.

What I dont understand then is if you use that calculation with thicker wire that can carry more amps, the voltage drop is more.
eg
6awg which can carry 78 amps:
78x100x2x0,0003951 = 6 volt drop. Surely the thicker the cable the less the drop?

[Offgrid]

What kind of inverter are you using? How many kWhrs of batteries?

15kwh Axpert King 5kva 5kw https://www.sustainable.co.za/axpert...-inverter.html

[bob-n]

Thicker wire = Less drop for the same current
The key is to enter the actual current flowing in the wire, not the maximum rating of the wire.

[Mike90250]

Consider, that one day, you may want a larger inverter, and not have to pull wires. Again.
Personally, I would use 2AWG Aluminum wire. It will perform like 4awg, and pull nicely like 8awg.

You are going from Main to Main, as a non-spliced run and will have little hazard if you properly use anti-ox and the right torque on the wire ends
Make sure your components are rated AL or AL/CU and #2 will fit the terminals.

You can "under breaker" the wire and use 40A breakers, to protect the inverter (which should have it's own protection) or use breakers rated for the full amps of the wire. (easier upgrade to larger inverter later)

I worry about using dozens of small batteries and the method used to tie them together into giant strings for big amps. The battery connections (hundreds of connections) will likely be your failure points. "dangerous off-grid solar house burns down" headlines hurts us all. don't be that person. Get advice and be sure to do it right.

[Offgrid]

Aaaah ok makes sense. What is a acceptable voltage drop? 5% and less? I found this online calculator to just speed up the calculation a bit because I'm new to this. https://www.calculator.net/voltage-d...s=40&x=47&y=1

With the 8awg and my 5kw inverter that will max do 22amps, I get the following

Voltage drop: 2.72v
Voltage drop percentage: 1.18%
Voltage at the end: 227.28

If I had to upgrade my inverter to 10kw then my max amps at 230v would be 43 amps. With this I get

Voltage drop: 5.32v
Voltage drop percentage: 2.31%
Voltage at the end: 224.68

Surely less than 5% is acceptable? Unless I am missing something, thanks for your patience explaining.

[Offgrid]

Consider, that one day, you may want a larger inverter, and not have to pull wires. Again.
Personally, I would use 2AWG Aluminum wire. It will perform like 4awg, and pull nicely like 8awg.

You are going from Main to Main, as a non-spliced run and will have little hazard if you properly use anti-ox and the right torque on the wire ends
Make sure your components are rated AL or AL/CU and #2 will fit the terminals.

You can "under breaker" the wire and use 40A breakers, to protect the inverter (which should have it's own protection) or use breakers rated for the full amps of the wire. (easier upgrade to larger inverter later)

I worry about using dozens of small batteries and the method used to tie them together into giant strings for big amps. The battery connections (hundreds of connections) will likely be your failure points. "dangerous off-grid solar house burns down" headlines hurts us all. don't be that person. Get advice and be sure to do it right.

Wow Mike only like 9 years later, you wont remember me but like Sunking, you helped me stacks back in the day!. In terms of wire, we have plain old copper. 4awg will cost the same as my house in this country unfortunately, was hoping I would get away with 8awg. In terms of saftey of the batteries, this is ecactly wht I want to put everything AWAY from my house in a shed.

Hope you well bud.

[Mike90250]

Aluminum wire is much less expensive than copper, for the same amp capacity
4ga copper $1.01 FT
2ga AL $0.65 FT
When you get 200' of it, it's a big difference

[Offgrid]

Got you, is this the stuff Mike?

http://unitycables.co.za/ACSR.html

[Mike90250]

Close, but way overkill. What you want is 600V - 1000V range ( called low voltage ) and simply a aluminum wire. It may be that SE (service entrance cable) with a pair of #2 wires and a third ground wire is more available. When I did power to my pumphouse, I called the local cable vendor, and asked for 3 spools, 1,000 feet #2 (or was it #4) aluminum. I spray paint marked them on the spool before pulling, and had 3 helpers at 3 pull stations to haul the thousand feet of cable, 200' up hill to the pump and tanks.....

Wire spools.jpg


LeftoverWire.jpg

[Offgrid]

That looks great man. all I can find in the smaller sizes is the multicore. Single core starts a 0awg. On the multi-core its mostly armored.I did find one place that wasnt bad on pricing (if I remember correctly but if a 2AWG multi-core cable has 4 cores, surely then each conductor is much less than 2awg. This would mean I would need like a 0 awg or whatever the size required to get each core to 2 awg if that makes sense? This then pushed the price up nearer to copper prices. I'm in a bit of sh1t now lol.

[Offgrid]

example of what I mean above. overall cable is 35mm2/2awg but each core then is obviously thinner so not true 35mm2 if I use 3 of the 4 cores for L,N,E
https://www.actomep.co.za/pvc-mains-...ded-cable-35mm

[Offgrid]

That's its, I am going back to school and selling everything. Well this is embarrassing. See screenshot. So while overkill this will work and get it for slightly over a dollar per foot https://www.actomep.co.za/pvc-mains-...ded-cable-35mm

Capture.JPG