diy solar

diy solar

Planning to post pictures when it's done, need some help first.

Firesky567

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Apr 19, 2022
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I would really appreciate any constructive criticisms / inputs / suggestions for my first system.
I have taught myself the fundamentals in so far and I now feel I have a decent grasp on the terms used in Solar I could use some feedback.

- 4x Roof mounted 270W Trina solar "24v" panels in 2S2P, providing 70V @20A. (6AWG tinned copper cable)

- Victron 100/50 MPPT (Board mounted)
- Victron 24/800 PSW Inverter (Board mounted)

- 3x 2P DC Breakers (40A, 50A & 125A) in 8 way mini consumer unit (Board mounted) Do I need to swap the 50A for a 65A?)

- Victron Smartshunt 500A
- Kepworth 24v/100Ah LiFePo4
- 8AWG leaving the 40A breaker and throughout entire system
- 2.5mm Flex spliced into A/C Breaker from Inverter UK Socket & Plug
- SC10-8 Copper lugs & Heat shrink on Battery & Shunt (Using a cheapo hammer / vice punch for cold welds, seems decent for the price though)

Planning to mount the battery on a shelf on a timber stud wall to reduce cable distance, is this a bad idea? (Will be firmly secured)
Also planning to build an enclosure for the battery out of an ammo case, with pc fan, heat mat and ITC (batt. has no U/T probe) will this be ok?

Thankyou for any input you may have.
 
Post an actual planned schematic showing all components, wires (and their sizes), breaker/fuses (and their sizes).

Post the full specs of your 270W solar panels.
Why 2P DC breakers?
Why metric and AWG wire?
 
Post an actual planned schematic showing all components, wires (and their sizes), breaker/fuses (and their sizes).

Post the full specs of your 270W solar panels.
Why 2P DC breakers?
Why metric and AWG wire?
2P DC Breakers seem to be the better and more reliable form breaker that I can get my hands on for a reasonable price.
Still getting used to dealing with AWG.
I come from a carpentry background, always used millimeters but I'm getting used to it lol

Here's the PV Datasheet and my diagram, as asked.

 

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The breaker between the SCC and the battery needs to be 60A. The SCC can output 50A so a 50A breaker will likely trip needlessly. You also only need a 1P breaker on the positive wire. To safely carry 50A you need at least 6AWG or 16mm² wire. 3mm² is way too small for 50A.

The 24V 800W inverter won't use anywhere near 125A. 800W / 24V / 90% efficiency = 40A. So wire for 40A. 40A x 125% = 50A breaker. I would use the same 6AWG or 16mm² wire for the inverter to the battery that you use for the SCC.

Remember that fuses/breakers are there to protect wire. You have a 125A breaker on 3mm² wire. That size wire must never be fused higher than 50A. The 125A breaker would sit there all nice and happy while the 3mm² wire burst into flames.

In your original post you mentioned using 6AWG wire with the solar panels but your diagram shows 4mm². 6AWG is roughly equal to 16mm². 4mm² is roughly the same as 12AWG.

How long is the wire from the solar panels to the SCC? 4mm² is likely too small unless the wires will only be about 40' round trip. I suggest using 6mm².

On the AC side, 2.5mm² is too small for a 40A breaker. For such a breaker to be safe you would need at least 4mm².
 
The breaker between the SCC and the battery needs to be 60A. The SCC can output 50A so a 50A breaker will likely trip needlessly. You also only need a 1P breaker on the positive wire. To safely carry 50A you need at least 6AWG or 16mm² wire. 3mm² is way too small for 50A.

The 24V 800W inverter won't use anywhere near 125A. 800W / 24V / 90% efficiency = 40A. So wire for 40A. 40A x 125% = 50A breaker. I would use the same 6AWG or 16mm² wire for the inverter to the battery that you use for the SCC.

Remember that fuses/breakers are there to protect wire. You have a 125A breaker on 3mm² wire. That size wire must never be fused higher than 50A. The 125A breaker would sit there all nice and happy while the 3mm² wire burst into flames.

In your original post you mentioned using 6AWG wire with the solar panels but your diagram shows 4mm². 6AWG is roughly equal to 16mm². 4mm² is roughly the same as 12AWG.

How long is the wire from the solar panels to the SCC? 4mm² is likely too small unless the wires will only be about 40' round trip. I suggest using 6mm².

On the AC side, 2.5mm² is too small for a 40A breaker. For such a breaker to be safe you would need at least 4mm².
Some amendments are definitely in order then. Thankyou for the information; Glad I posted this.


- 40A is only for my reference, there's a Board, B12 breaker and a socket not shown on diagram.

- Cable run from panels is 4mm diameter (Measured with calipers) and about 2m, fed into branch connectors. It came preinstalled on the panels. Leads into the panels' diode boxes, not designed for rewiring afaict)

- The metric sizes in the diagram are referring to cross section not area²

- The 125A breaker is just straight up the wrong thing, no excuses for that tbh, I thought I was sizing off the battery. No harm done as I've yet to install anything, still waiting for bits to show up.

- I will swap the 125A for a 60A breaker to use between SCC & Battery, and use the 50A I already have between the Battery and Inverter. The 40A is for between the panels and the SCC as a disconnect and fuse rolled into one (that's the idea)

- Is the 40A 2P breaker ok to use in the stead of a solar disconnect & fuse?

-Can I use the 2P breakers or is there a disadvantage compared to 1P?
I used 2P over 1P as they seem safer and more reliable as far as I'm aware, Plus they eliminate the need for a busbar in my system keeping things tidy on the board.
I can go the 1P route if need be, I didn't want to as it seemed like unnecessary work installing to busbars and they're not much cheaper really. I want it to be as safe as possible, don't mind paying a bit more for simplicity & safety.

- Final question; is the 8AWG cable I plan on using going to be fit for use (given all measurements are cross section not area²) - datasheet says it can handle 60A, it's pure tinned copper, jacket reads 600v rated. (Link below)

Sorry for the long reply. I want to be extra sure I know what I'm doing this time.

ps love the setup description in your blurb, sounds awesome, I am planning to do something similar. Must be a great way to live
 
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Cable run from panels is 4mm diameter (Measured with calipers)
Is that measuring just the copper or the insulation?

The metric sizes in the diagram are referring to cross section not area²
OK. I hadn't seen wires labeled with diameter. I'll update my comments based on this info.

Is the 40A 2P breaker ok to use in the stead of a solar disconnect & fuse?
Using a 2P DC breaker is commonly used for a PV disconnect. Just make sure it is rated for the Voc of your panel array and the amperage is higher than the max current of your panel array. The disconnect is not meant to protect the wire (unlike all other breakers/fuses). 40A is plenty for your 20A array.
Can I use the 2P breakers or is there a disadvantage compared to 1P?
I've never seen 2P breakers be used for DC circuits. The PV disconnect breaker is the only exception. Normally only the positive wire needs a fuse or breaker. I honestly don't know if there is any issue using a 2P DC breaker.

Plus they eliminate the need for a busbar in my system
Can you explain how using a 2P DC breaker eliminates the use of a bus bar? That makes no sense to me.

is the 8AWG cable I plan on using going to be fit for use - datasheet says it can handle 60A
Your diagram shows no use of 8AWG wire. Where were you thinking of using it?

You should not use 8AWG for anything over 40A. It can handle 60A but you will have far too much voltage drop.
 
Since I'm not as familiar with metric wire measured by diameter I'll leave my comments above using cross-sectional area in mm². I'll let you work out my recommendations in your preferred measurement. I want to avoid giving the wrong answer.
 
Is that measuring just the copper or the insulation?
4mm stranded Core, ignoring the insulation (1mm jacket I believe)

I honestly don't know if there is any issue using a 2P DC breaker.
Found this discussion, consensus seem to be they're ok across the board, provided they don't interrupt negative ground (?)

https://community.victronenergy.com...dual-pole-breaker-between-pv-array-and-m.html

"In this case, you CAN interrupt the negative of the PV array - IF it is a 2 pole breaker that also interrupts the positive at the same time. You must also ensure that the ground connection to the FRAME of the PV array is NOT interrupted by the operation of this breaker."

I can earth the inverter SCC & battery on a ground bus going to earth rod if need be. (All have earth points)

Can you explain how using a 2P DC breaker eliminates the use of a bus bar
It doesn't after re thinking it .. I'm used to using 2 core and hadn't considered I can just run the negative from one device to another, round the back of the CU and just feed the live into & out of a 1P.
If it's ok to use the 2P breakers I still plan to, I prefer the design and the fact that it's protecting parts from each others potential internal faults (Unlikely as I'm using bluepower but it's still a nice measure I think)

8AWG wire. Where were you thinking of using it?
I was planning to use the 8AWG throughout the entire system (SCC - Battery - Inverter) as the inverter is 800w / 33A max draw @24v and the battery can charge at 50A max, both of which I predicted should be covered by 8AWG, "max bear current" is 60A on the product info (already posted the link in previous reply)

Don't understand the voltage drop point you made, surely that's only affected over long runs?

Thankyou again for your answers. May have saved me some serious grief.
 
Wire size in metric is sized by squared mm. On quality cable that number is printed on the insulating sheath.
 
I was planning to use the 8AWG throughout the entire system (SCC - Battery - Inverter) as the inverter is 800w / 33A max draw @24v and the battery can charge at 50A max, both of which I predicted should be covered by 8AWG, "max bear current" is 60A on the product info
In post #4 I gave my recommendations for wire size. 6AWG is the minimum size you should use for many of the wires. 8AWG is too small. It might technically carry the loads but the wire will be getting really hot and you will have voltage drop. You don't need long runs to experience voltage drop. It's always better to use slightly bigger wire than you think you might need. Think of it this way. Marine grade copper wire can have insulation rated at 105ºC. So you lookup the needed wire size for a given current based on that kind of wire. You install it and run your system at max loads. The wire works just fine. But the wire could be hot enough to boil water while it sits there all nice and happy. Do you want wire that gets that hot even if it is electrically safe? I'd rather choose wire that won't give me 2nd and 3rd degree burns.
 
I'm not sure that is how wire ampacity ratings work. I'm will have to look into that. OWT

We select the wire gauge using voltage drop tables. The wire should not ever get close to it's ampacity. The fuse is an emergency disconnect.
 
Found on Anchor web site. Emphasis is mine.
quote; "*******tors under 50 volts. The values shown on the ampacity table are the maximum safe amperages which the conductor can carry on a continuous basis. They do not apply to intermittent starting loads such as motor start currents. Since all ANCOR*****"

That reads to me as safe continuous means not as hot as to be unsafe. Boiling water is not safe.
 
I'm not sure that is how wire ampacity ratings work.
Look at any ampacity chart. It will have different values depending on the wire's insulation rating. Uninsulated copper wire in free air can carry a lot more amperage than insulated wire. Such high amperages are "safe" as in the wire won't melt and start a fire. Once you start adding insulation the amperage needs to go down so the insulation doesn't melt. Obviously 60ºC rated insulation can handle less amperage than 105ºC rated insulation.

Of course you don't want your wires getting so hot that it will burn you. That is why it's a good idea to oversize wires a bit.

And none of the above takes into account voltage drop. All of that heat is coming from resistance which in turn is causing the voltage at the other end of the wire to be lower than the beginning.

A good wire chart takes into account amperage and voltage drop. Then you can look at the recommendation and choose the next size bigger to keep things cooler.

Here's one example of many for a wire amperage chart with different columns for insulation rating:

 
Found on Anchor web site. Emphasis is mine.
quote; "*******tors under 50 volts. The values shown on the ampacity table are the maximum safe amperages which the conductor can carry on a continuous basis. They do not apply to intermittent starting loads such as motor start currents. Since all ANCOR*****"

That reads to me as safe continuous means not as hot as to be unsafe. Boiling water is not safe.
I'd rather avoid anything even getting warm, let alone boiling ?I'll be going around the system with an IR gun when it's installed and running to find hot spots, will have the victron app immediately available within seconds etc etc. Definitely doing everything I can to avoid anything grim from happening. I underestimated how difficult it'd be to make it fully 100% safe though.
Definitely some Dunning Kruger Effect at play here lol

In post #4 I gave my recommendations for wire size. 6AWG is the minimum size you should use for many of the wires. 8AWG is too small. It might technically carry the loads but the wire will be getting really hot and you will have voltage drop. You don't need long runs to experience voltage drop. It's always better to use slightly bigger wire than you think you might need. Think of it this way. Marine grade copper wire can have insulation rated at 105ºC. So you lookup the needed wire size for a given current based on that kind of wire. You install it and run your system at max loads. The wire works just fine. But the wire could be hot enough to boil water while it sits there all nice and happy. Do you want wire that gets that hot even if it is electrically safe? I'd rather choose wire that won't give me 2nd and 3rd degree burns.
My SCC & Inverter will take 6AWG Max so it'll have to be ok. I'm sure they wouldn't limit the port size if doing so was dangerous.

I do however have to accept that I already cut up a length of 8AWG .. and got another in the mail today which will be going back alongside the 125A breaker and a dodgy LAN coupler that gave me so much grief you wouldn't believe .. Buried it, then completely un buried it, and re buried it again..

Mad gratitude for the help. If there's anything else you see in my plan that's iffy please let me know asap. I'll go about making these corrections and post promised pictures when all's said and done.
 
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Look at any ampacity chart. It will have different values depending on the wire's insulation rating. Uninsulated copper wire in free air can carry a lot more amperage than insulated wire. Such high amperages are "safe" as in the wire won't melt and start a fire. Once you start adding insulation the amperage needs to go down so the insulation doesn't melt. Obviously 60ºC rated insulation can handle less amperage than 105ºC rated insulation.

Of course you don't want your wires getting so hot that it will burn you. That is why it's a good idea to oversize wires a bit.

And none of the above takes into account voltage drop. All of that heat is coming from resistance which in turn is causing the voltage at the other end of the wire to be lower than the beginning.

A good wire chart takes into account amperage and voltage drop. Then you can look at the recommendation and choose the next size bigger to keep things cooler.

Here's one example of many for a wire amperage chart with different columns for insulation rating:

How does this look? Same flexible silicone style, easy to work with and 200C rated. 6AWG
https://amazon.co.uk/Bryne-Flexible-Silicone-Temperature-Resistance/dp/B08LT7W5LQ/ref=sr_1_18?crid=HCUTDICEDP0K&keywords=6%2Bgauge%2Bcopper%2Bcable&qid=1652048183&sprefix=6%2Bgauge%2Bcopper%2Bcable

Or would this be better for another £5 ish? also 6AWG
https://amazon.co.uk/WINDYNATION-Welding-Battery-Copper-Flexible/dp/B01N5GMXJX/ref=sr_1_5?crid=HCUTDICEDP0K&keywords=6%2Bgauge%2Bcopper%2Bcable&qid=1652048183&sprefix=6%2Bgauge%2Bcopper%2Bcable%2Caps%2C137&sr=8-5&th=1
 
I don't see the point of 200ºC silicone wire. Sure, the insulation won't melt under pretty extreme wire temperatures but you should never get anywhere near that point.

I used some 1/0AWG wire from Windy Nation. I've had no issue with it.

As long as you get quality pure copper (optionally tinned) stranded wire of the correct size you will be fine. Be careful of the wire seems too cheap. Copper isn't cheap. Cheap wire being sold as copper is sometimes copper clad aluminum. You do not want that.
 
Look at any ampacity chart. It will have different values depending on the wire's insulation rating. Uninsulated copper wire in free air can carry a lot more amperage than insulated wire. Such high amperages are "safe" as in the wire won't melt and start a fire. Once you start adding insulation the amperage needs to go down so the insulation doesn't melt. Obviously 60ºC rated insulation can handle less amperage than 105ºC rated insulation.

Of course you don't want your wires getting so hot that it will burn you. That is why it's a good idea to oversize wires a bit.

And none of the above takes into account voltage drop. All of that heat is coming from resistance which in turn is causing the voltage at the other end of the wire to be lower than the beginning.

A good wire chart takes into account amperage and voltage drop. Then you can look at the recommendation and choose the next size bigger to keep things cooler.

Here's one example of many for a wire amperage chart with different columns for insulation rating:

I updated the Diagram according to suggestions made. DC cable measurements are cross sectional, AC cable measurements are Area squared, just to add to the confusion :LOL: my bad
 

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I don't see the point of 200ºC silicone wire. Sure, the insulation won't melt under pretty extreme wire temperatures but you should never get anywhere near that point.

I used some 1/0AWG wire from Windy Nation. I've had no issue with it.

As long as you get quality pure copper (optionally tinned) stranded wire of the correct size you will be fine. Be careful of the wire seems too cheap. Copper isn't cheap. Cheap wire being sold as copper is sometimes copper clad aluminum. You do not want that.
Probably just a marketing tactic to fool mugs like me. lol. I'll use the windy nation cable. seems intended for the purpose and yeah, I'd rather smell the cables burning at a lower temp than operating at a higher temp.
 
I was just looking at the spec sheet for Victron's 24V/800VA inverter. The max wire size it says it can take is 10mm²/8AWG. I had suggested 6AWG as a convenience since you need 6AWG for the higher amperage charge controller. So it turns out you may need to keep some of the 8AWG for the inverter. But still use 6AWG for the charge controller. Sorry about that.
 
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