Fuse rate and cable sizing

Question

question

pau-farreny asked May 27, '21

Fuse rate and cable sizing

Hi,

I have very little knowledge of electronics but these diagram has been very helpful to represent it in a simpler way.

I hope that somebody could give me a recommendation on my design, fuse rate and wire size. I’m open to any recommendations and adjustments.

Thanks to everyone

Wire Location	Max Length (meters)	Wire, mm2	Fuse/Breaker Rating (Amp)
Solar Panels to MPPT	5	10 - 16 ???	20
MPPT to (+) Bus Bar	0.5	6	40
(+) Bus Bar to Second Battery	0.5	25	100
(+) Bus Bar to DC Fuse Box	0.5	25	100
(+) Bus Bar to Alternator	0.5	25	100
(+) Bus Bar to Orion DC-DC	0.5	10 ?	45 ?
Orion to main car Battery	6.5	35 ?	60
(+) Bus Bar to Inverter	0.5	35	150
Inverter to loads 220	5	2.5	-

Components Used:

1 x 370 W, 24 v, Mono Solar Panels by Jinko ( Link )
Smart Solar 100|30 MPPT by Victron ( link )
Orion tr DC-DC 30A Isolated by Victron ( link )
4 x REPT 3.2 280 AH Lifepo4 Battery cells ( link )
Smart BMS 4S cells 12V 120A (link)
300 A Shunt by Mictuning ( link + link shunt )
1000 W, 12V, Pure Sine Inverter ( link )
Main switch 300A ( link )
Auto midi Fuses (50A to 100A) (Link)

I am living in Europe and I am using this table to guide me in the current withstand in amperes of the cables

Doubts:

1- I am going to use the Inverter to power 2 laptops and a 50L fridge (which opens three times a day). Is it necessary to increase the 25mm2 cables and the 100A fuses?

2- In the MPPT Smart Solar manual, it indicates that it is optional to connect the ground (chassis), is it recommended?

3- Can I connect the negatives (-) of both batteries through the chassis ? Instead of two negative cables from the Orion DC-DC to each battery.

4- Do the negatives (-) have to be connected to the chassis in a lifepo4 system?

5- Should I fuse the positive (+) cable of the main battery to Orion tr?

Diagram attached in PDF
Planol imitacio angles..pdf

Diagram in Imagur
https://imgur.com/hn0At5C

PS: i got the diagram from https://diysolarforum.com/threads/what-do-you-think-of-our-diy-wiring-diagram-did-we-get-the-wire-fuse-ratings-right.20224/

Lithium Battery fuses

planol-imitacio-angles.jpg (1.8 MiB)

planol-imitacio-angles.pdf (1.3 MiB)

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Modifications Space

Node Red Space

Answer 1 · 2021-05-28T04:37:18Z

greendovefarms answered · May 28, 2021 at 04:37 AM

Have you downloaded the victron toolkit as it has a great cable calculator in there that will be able to help you with your cable sizing

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Answer 2 · 2021-05-28T11:32:30Z

Vance Mitchell answered · May 28, 2021 at 11:32 AM

A few things stand out immediately.

1. The Orion 12/12-30 can only accept 16mm cable so that is what I would use for both sides of it.

2. The solar panels only have 4mm cable attached, 4mm would be suitable to connect it to the MPPT but upgrading to 6mm wouldn’t be a bad idea.

3. I would make All the cables between the battery and the busbar at least 35mm and you might as well change the inverter cable to 35mm while you are at it.

4. I would reconsider the inverter, Once you are converting into dangerous voltages, a good brand with a known reputation and warranty is worth it for your safety. If need be a smaller inverter might handle your loads (depending on the starting current of your fridge).

5. Definitely add a fuse as close to the main battery as possible.

I hope this helps a bit.

3

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

pau-farreny commented · May 30, 2021 at 03:54 PM

Thank you, it helped alot

1- Thank you for telling, I didn't knew that.

2- 4mm2 or 6mm2 wold be enought if didn't take in consideration the lenght betwen PV and MPPT. 5 meters

3- would you alse increase the fuse ?

thanks for your time !

0 ·

pau-farreny commented · May 30, 2021 at 03:56 PM

I forgot last one,

5- what fuse wolud you use there ? 50 or 100 ? My alternator is 110 or 140. and my batery 100Ah

0 ·

Vance Mitchell pau-farreny commented · May 31, 2021 at 12:31 AM

2. 6mm will still be fine even up to twice that distance, At that distance it will still be less than 2% loss in the cabling and can safely carry more than twice the current that the solar panel will output.

3. With 35mm cable you could upgrade to 150A. For the battery fuse I would upgrade to 150A, the Inverter I would also use 150A unless the inverter manual recommends smaller.

5. The Orion manual recommends a 60A fuse which is within the safe range for 16mm cable.

0 ·

question