diy solar

diy solar

Feedback on 24v system please

K

kenfused

New Member
Joined
Nov 2, 2022
Messages
50
Hi, I’m looking to design a small system with 4 panels, 260w each, using 24v system. Can. You please look to see if any improvements/ suggestions? Any ideas on favorite SCC, Battery, inverters as well. What gauge wires should I be using? What am I missing? Thank you!

3D53AF06-4835-4EAA-8CF9-BB3DFBB470B5.jpeg
 
That matches very oddly close to my system. I made my own battery though. I just upgrade my wiring due to a melting buss bar incident to 4 AWG welding wire for battery and inverter connections. The stuff you have pictures looks good to me.
 
You can't put those 4 panels into that MPPT, they're combined VoC is 150.4v, you'd need an MPPT capable of 200v input which you're unlikely to find. If you already have the panels then you can get 2 100v MPPTs and run them in parallel.

Edit: sorry ignore me I completely failed to see your 2P2S setup. That should be fine. It's too early in the morning still for my brain to be engaged.
 
I wouldn't bother with one of those little black breakers, they are notoriously bad, just get another DIN rail mounted one like a Tomzn. As for battery your best bang for buck will be DIY followed by a server rack battery if you can find one. I built a 280ah 24v battery for around £1050 for cells/bms and box:

diysolarforum.com

Rate my battery: 280ah 24V

Hi all, Just wanted to show off my battery as I'm quite proud of how neat it's turned out while also double checking that I haven't messed anything up as its my first go. It consists of 8x 280ah Eve B-grade cells, about £950. Bought from fogstar.co.uk they came capacity tested, batched and...
diysolarforum.com diysolarforum.com
 
Does the sizing on my breakers and fuses look OK? Any suggestions on wire gauge?
Thanks
 
MPPT to battery should be 8AWG
Battery to inverter should be 2AWG at least, 1AWG would be better.

Fuses look OK and I've got no complaints on the breaker as long as you use a decent quality breaker and not go super cheap. I've been happy with my T-Tocas breakers, have even tripped a couple a couple times on accident and they worked fine.
 
Rednecktek said:
MPPT to battery should be 8AWG
Battery to inverter should be 2AWG at least, 1AWG would be better.

Fuses look OK and I've got no complaints on the breaker as long as you use a decent quality breaker and not go super cheap. I've been happy with my T-Tocas breakers, have even tripped a couple a couple times on accident and they worked fine.
Click to expand...
Why exactly 2 AWG vs an 4 AWG? 2000W should have a max pull of 83.3A on a 24V system (not taking in account for surge). 4 AWG can handle 95A. Is it just because it doesn't meet the 1.2 to 1.25 overage for circuit ratings?
 
2000W on the AC output side of the 24VDc inverter will have DC input current of about 98A due to inverter efficiency, 85% is typical.
 
I went with 4awg for my identical setup. 2awg would be better but I'll rarely be pulling more than 600w max through the inverter. Just make sure it's pure copper and not CCA.
 
2000 ac watts / .85 conversion factor / 20 volts low cutoff = 117.647058824 inverter amps
117.647058824 inverter amps / .8 fuse headroom = 147.058823529 fuse amps
That is right on the limit of pure copper 4 awg wire with 90C insulation by ABYC rules.
If it was me I would go to 2 awg to minimize the ripple.
If you are going for NEC rules then 1/0 awg is indicated.
 
John Frum said:
2000 ac watts / .85 conversion factor / 20 volts low cutoff = 117.647058824 inverter amps
117.647058824 inverter amps / .8 fuse headroom = 147.058823529 fuse amps
That is right on the limit of pure copper 4 awg wire with 90C insulation by ABYC rules.
If it was me I would go to 2 awg to minimize the ripple.
If you are going for NEC rules then 1/0 awg is indicated.
Click to expand...
Thank you for the explanation. Do you have a source or is this just a tribal knowledge thing? Not questioning, just wanna see what other stuff I can learn as well.
 
Any name you wish said:
Thank you for the explanation. Do you have a source or is this just a tribal knowledge thing? Not questioning, just wanna see what other stuff I can learn as well.
Click to expand...
Glad you asked.

The conversion efficiency is tribal knowledge based on test reports from forum users over the years.
My own inverter tested to ~.89% efficiency but its a Samlex PST which is considered teir 1 for HF=high frequency inverters.

20 volts low cutoff should be self explanatory.

2000 ac watts should also be self explanatory.
 
Last edited:
Adding to what I've already said the .85 conversion factor is also used for top of the line LF=flow frequency inverters.
Even though they can approach .95 efficiency they also have significant surge capacity which the low conversion factor covers.
 
THanks, so 8 gauge everywhere, except 2awg from battery to inverter would be ok?
 
As your panels are on a 20A breaker you could get away with 10awg depending on the distance between them and the charge controller.

8awg between charge controller and battery will be good:


Unless you're pulling close to max from your inverter regularly then 4awg should be fine but 2awg gives a little safety margin. @John Frum gave the worst possible case which is best practice to spec to but in reality you won't hit those conditions. Your BMS low voltage cutoff should probably be well above 20v for example, and my Giandel 2kw gets 92% efficiency when I measured it.

Edit: that said if you use a 150A breaker then you should spec the cable to match, ie 2awg. I use a 125A breaker in my setup.
 
One thought about the solar charge controller connections. I believe the SCC can be damaged if live solar panels are connected to it without a battery connection first. Using a breaker from the SCC to the battery puts you at risk for that situation if you manually trip the 50 amp breaker when the din breaker is still connected. Using a 50 amp AML fuse like the type going to the inverter would limit that scenario.
 
kenfused said:
Does the sizing on my breakers and fuses look OK? Any suggestions on wire gauge?
Thanks
Click to expand...
Your MCB from SCC to Battery should be at least 20AMP, not 50 AMP. the current that will flow from the SCC to battery is almost the same from Solar Panel to SCC. and then from battery to inverter, it should be at least 90 or 100 amp. if you calculate the max current that will flow from battery to inverter it is only 83.33 max. Since you cant find 90amp you can go to the next available Amperage.
 
kianz said:
Your MCB from SCC to Battery should be at least 20AMP, not 50 AMP. the current that will flow from the SCC to battery is almost the same from Solar Panel to SCC. and then from battery to inverter, it should be at least 90 or 100 amp. if you calculate the max current that will flow from battery to inverter it is only 83.33 max. Since you cant find 90amp you can go to the next available Amperage.
Click to expand...
It's fine to have slightly larger breakers so long as the cable is specced for the amps. And the current can be different between panels and mppt and mppt to battery. Not sure where you got that idea, if voltage goes down current goes up. It's a 40a mppt so 50a breaker is reasonable.
 
You must log in or register to reply here.

Similar threads

H
First timer needing advice on shed system design for off-grid.
Replies
2
Views
235
Hellraising_Paladin
H
T
Yet another 12v vs. 24v
Replies
2
Views
476
tommywass
T
J
Feedback wanted on a proposed large residential system
Replies
5
Views
463
jp4782
J
B
System Design Feedback
Replies
7
Views
343
Solar Guppy
Solar Guppy
C
Inverters and such outside (small shed)? Or garage?
Replies
1
Views
205
hwy17
hwy17
Back
Top