Fuse rate and cable sizing, could you recomend something ?

[iquibalamenpau]

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 in Imagur

https://imgur.com/hn0At5C

Diagram attached in PDF


PS: i got the diagram from https://diysolarforum.com/threads/w...did-we-get-the-wire-fuse-ratings-right.20224/

 

[HRTKD]

Your fuse amperage selections look OK. I think I read somewhere on the forum that someone recommended against fuses/breakers that are oriented towards car audio. A premium, but very solid, choice for overcurrent protection is Blue Sea Systems. I don't have the conversion to AWG handy, so I can't comment on your wire sizes.

Exceptions
The breaker between the Orion and the car battery might oversized at 60 amps. 50 amps would be more appropriate. On that circuit, my preference would be to run both positive and negative cables. The resistance of the chassis is different (likely a lot higher) than the copper cable. You might have a problem with that circuit. The maximum cable size for the terminal is 16mm (6 awg). Are your distances the actual length? Did you, or your wire gauge calculator, account for the round trip distance? The calculator I use requires me to input the round trip distance. At 6 awg / 16mm you might have a problem with voltage drop. Run your calculation again with the smaller wire size and see what it says. You may have to choose a DC-DC charger that consumes fewer amps to make that work.

100 amps for the DC fuse box is probably too high, unless you plan to turn on every DC load at the same time.

A dual pole breaker is common for between the PV and the MPPT. A breaker on just the positive wire between the MPPT and the common bus bar is typical.

Your diagram says 100 amp for the inverter fuse, but your table above says 150 amp. I would go with 150 amp. I have a 1000 watt MSW inverter and I arrived at 150 amps per the owner's manual.

 

[iquibalamenpau]

Thanks for your time HRTKD,
What do you mean with "towards car audio" ?
I belive my alternator is in between 110 a 140A. If i put a fuse of 50, wolun'd blow ?

The dual pole braker isn't made for 230V sistems ? And from the PV are coming 24v only, wouldn't that afect ?

I only counted one way, because i'm using two single same sized cables. Do i have to change that ?

Only a breaker on the positive wire from the mppt to the common bus bar, is enoght ? I have it also in the negative, to facilitate future modifications. does that make sense ?

 

[HRTKD]

When you listed "auto midi" I assumed it was for auto sound. Is that an automatic resetting breaker? My preference on automatic resetting breakers is that I don't want them in my system. If a breaker trips, I need to KNOW that it tripped and then I need to figure out why.

 

[iquibalamenpau]

I wouldn't use a automatic breaker , just like you said. I want to know why things happen.
I was referaing to these

 

[HRTKD]

Looks kind of cheesy to me. But I'm not familiar with them.

 

[Just An RVer]

When you listed "auto midi" I assumed it was for auto sound. Is that an automatic resetting breaker? My preference on automatic resetting breakers is that I don't want them in my system. If a breaker trips, I need to KNOW that it tripped and then I need to figure out why.

I think "midi" fuse just refers to a particular physical size, like "mega" or "ANL". You can get midi fuses from Littlefuse or Blue Sea Systems. They look like a smaller version of mega fuses, but I've never seen one over 60 amps from those brands.

I see listings on Amazon for up to 175 amp midi fuses which may or may not be appropriate. To be clear, I've never used them, but I just assumed based on the name that "midi" fuses were typicality for smaller values than "mega" fuses.

 

[Stepandwolf]

A dual pole breaker is common for between the PV and the MPPT. A breaker on just the positive wire between the MPPT and the common bus bar is typical.

I read something rather convincing regarding how to manage the solar panels. First, a solar panel won't blow a fuse, i.e. they wouldn't have a conventional short, secondly, you only need to break one side. The person said a single pole switch was all that was needed. That is far less than you see suggested most often. I am trying to finalize my own wiring diagram and would like to have this information confirmed or validated somehow. Thanks

Why a fuse?

 

[Just An RVer]

I read something rather convincing regarding how to manage the solar panels. First, a solar panel won't blow a fuse, i.e. they wouldn't have a conventional short, secondly, you only need to break one side. The person said a single pole switch was all that was needed. That is far less than you see suggested most often. I am trying to finalize my own wiring diagram and would like to have this information confirmed or validated somehow. Thanks

Why a fuse?

Because of NEC. It's true that you only need to interrupt one side of a DC circuit, but if you're in the US, you have to have a way to simultaneously disconnect both sides of the circuit coming from a PV array. A dual-pole breaker is often the easiest way to accomplish that.

Likewise for fuses. NEC requires that if the max current of your PV string exceeds the short circuit current of a single panel, you have to fuse both the positive and negative leads at the same short circuit current of the panels . If a solar panel fails in a short circuit condition, and all of the array's current is going into that one failed panel, it will most definitely blow the fuse. Or, if there isn't a fuse, the panel itself becomes the fuse and eventually melts/catches fire.

It can sometimes be hard to find the appropriate value DC breaker to match the short circuit current of your panels, but fuses come in all kinds of values. So sometimes you end up with fuses and a dual-pole breaker between a solar array and the charge controller.

You don't hear about fusing the PV wires nearly as often as you hear about using disconnects because you don't usually need a fuse on a small array. Unless you've got several panels in series, the string current doesn't exceed the short circuit current. Whereas everyone in the US is supposed to use a dual-pole disconnect, so everyone talks about that.

My apologies if you're not in the US and don't have to adhere to NEC. Even if NEC doesn't apply to you, the US-based YouTubers are still the reason you hear a lot about certain issues.

 

[Stepandwolf]

Hello, yes, I am in the US. Isn't there a distinction between "code" and what works and a DIY can do? I can see a manufacturer or someone doing this type of work for hire having to do things in a certain way, but what about people like myself?

I have seen two people suggest a particular breaker:

2P 250V Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System 63A (also available as 16 or 32A)

The current panel design is 3 100w panels in series connected in parallel with the second set of three. Might start out two and two vs. three and three. The intended, (out of stock) panel, is 21.6v open circuit, 6.5a short circuit, optimum 5.56A. These will be connected to the charge controller with a 10GA wire factory provided. Going 24V to keep the 10ga cable useable.

Thanks!

 

[HRTKD]

The current panel design is 3 100w panels in series connected in parallel with the second set of three. Might start out two and two vs. three and three. The intended, (out of stock) panel, is 21.6v open circuit, 6.5a short circuit, optimum 5.56A. These will be connected to the charge controller with a 10GA wire factory provided. Going 24V to keep the 10ga cable useable.

With two strings you don't need fusing between the strings. If you went to three strings you would need fusing on each string. Either way, you want something downstream of the Y connection so you can turn the whole thing off. That's where I have the two pole breaker. A 20 amp breaker would be just about right for your system.

 

[Just An RVer]

Hello, yes, I am in the US. Isn't there a distinction between "code" and what works and a DIY can do?

I don't think any of us meet every requirement of every building/electrical/life-safety code all of the time. Heck, code compliance is a big part of my day job, and from time to time, I've still been known to do something that was "practical" instead of "code compliant".

That said, the requirements for wire sizing, disconnects, and fusing aren't bad at all. For example, it seems to me that with a couple portable panels plugged into the "Zamp" port on the side of an RV, pulling the plug would simultaneously disconnect both the positive and negative leads.

I doubt anyone here would get too upset over you using a single pole breaker in place of a dual pole. But the parts to do it right are so cheap and easily available, why not?

Keep in mind, if you ever do have an accident, especially a fire, your insurance company will be looking for any reason not to pay. It doesn't matter to them if it was a DIY installation or professional. Even worse, if someone else gets hurt, their insurance company will be looking to you for the medical expenses. I don't want that kind of risk.

 

[Stepandwolf]

With two strings you don't need fusing between the strings. If you went to three strings you would need fusing on each string. Either way, you want something downstream of the Y connection so you can turn the whole thing off. That's where I have the two pole breaker. A 20 amp breaker would be just about right for your system.

Thanks so much, sir....would going with a 32A be a bad thing to do, in particular, if I want to add more panels? The particular supplier has 16A, 32, and 63A.

 

[Stepandwolf]

I don't think any of us meet every requirement of every building/electrical/life-safety code all of the time. Heck, code compliance is a big part of my day job, and from time to time, I've still been known to do something that was "practical" instead of "code compliant".

That said, the requirements for wire sizing, disconnects, and fusing aren't bad at all. For example, it seems to me that with a couple portable panels plugged into the "Zamp" port on the side of an RV, pulling the plug would simultaneously disconnect both the positive and negative leads.

I doubt anyone here would get too upset over you using a single pole breaker in place of a dual pole. But the parts to do it right are so cheap and easily available, why not?

Keep in mind, if you ever do have an accident, especially a fire, your insurance company will be looking for any reason not to pay. It doesn't matter to them if it was a DIY installation or professional. Even worse, if someone else gets hurt, their insurance company will be looking to you for the medical expenses. I don't want that kind of risk.

I had already put the dual pole model in my wish list but just wanted to know if it was overkill. I am likely to goof something else up Thanks

 

[HRTKD]

Thanks so much, sir....would going with a 32A be a bad thing to do, in particular, if I want to add more panels? The particular supplier has 16A, 32, and 63A.

It depends on how you want to add panels. If you add to the existing strings (3s to 4s) then the amps won't go up. So the 16 amp breaker would work. If you're adding a new (parallel) string then the amps will go up and the 16 amp breaker will be too low. In that case the 32 amp breaker would be the next step up. But I would try to find a breaker a little closer to what you thing your max amps x 1.25 would be.

 

[eXodus]

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

Yes you should fuse a 35mm cable - further can the Orion even fit a large wire like that?

How large is your alternator?

With 6.5M cable you creating enough resistance that you can potentially omit the Orion altogether and just use a relay (solenoid) to charge from the alternator.

 

[12VoltInstalls]

Isn't there a distinction between "code" and what works and a DIY can do? I can see a manufacturer or someone doing this type of work for hire having to do things in a certain way, but what about people like myselfW

NO! There is no distinction between code and what diyers can do.

I’m very anti-government interference but the electrical code is there for a reason: to keep those whether pro or diy who don’t know the science from doing dangerous stuff. There’s just this opinion in the USA that codes are there to make your life difficult. No, they’re there to stop fires and electrocutions with an undercurrent of dependability.

BTW 100A wire/fuse is too small for a 1200W inverter. The surge current is 200A. 2/0 is 200A by ABYC while some other charts say 300A. Use 2/0 per
under 15’ (five metres canadian) and a 200A breaker or fuse.