Solar panel wiring sanity check

[djgriff]

Hello, not sure this is the best place to discuss, I have bought a Victron 100/30 mppt smart solar controller to go with my 360w panel. I am looking at the wiring required and breakers and not 100% confident i have it correct. So any feed back would be greatly appreciated. I am looking to buy solar panel extension cables 6mm2 10awg cable to run 3/4 meters from the back of the van to the controller. The position of the controller will be placed mid way in the van (vw t6 lwb). So plan to run the cable along the top of the van, down the pillar behind the driver then along the floor to the controller. Then from the controller I will be running 8AWG wire approx. 2 meters to the battery. I would then be looking to ad d a 40amp breaker switch between the battery and the mppt controller. (in the manual it states max pv short circuit current 35A) but i can't locate a 35a breaker like this. Would 40 amp be ok? or should i go for a 30 amp breaker?
Also do i need to add breakers from the solar to the MPPT controller?

Sorry for the questions and hope someone can point me in the right direciton.

Cheers
Daniel

 

[Samro]

I would add a midi fuse on the battery side of the mppt and a 40A breaker on the panel side of the MPPT.
This is because the MPPT will come up with a fault if the battery is isolated without the panel voltage being cut.
If you use a breaker, it will enable you to cut the PV power without the faff of removing a fuse.

 

[djgriff]

awesome thanks so much, will do as you have suggested.
cheers
Daniel

 

[Grim Reaper]

I used some small battery cut off switches to isolate the panels before the charge controller.

Panel Mount Miniature Battery Isolation Switch With Removable Actuator - 50A

Miniature panel mount battery isolation switch with removable actuator. 50A continuous, 75A intermittent. Ideal for campervan fuse box isolation.

www.12voltplanet.co.uk

You only need it in the positive side.
As above, midi fuses are better than those resettable breaker devices as there have been instances of them not disconnecting when they should.
I don’t have a fuse on the solar input side but there’s no reason why you shouldn’t, just size it appropriately to the max output of the panels.
Always connect the battery to the solar charge controller first, some charge controllers can be damaged if connected to solar panel before the battery as the current has nowhere to go and some need the battery voltage in order to self set the output voltage.

 

[djgriff]

I used some small battery cut off switches to isolate the panels before the charge controller.

Panel Mount Miniature Battery Isolation Switch With Removable Actuator - 50A

Miniature panel mount battery isolation switch with removable actuator. 50A continuous, 75A intermittent. Ideal for campervan fuse box isolation.

www.12voltplanet.co.uk

You only need it in the positive side.
As above, midi fuses are better than those resettable breaker devices as there have been instances of them not disconnecting when they should.
I don’t have a fuse on the solar input side but there’s no reason why you shouldn’t, just size it appropriately to the max output of the panels.
Always connect the battery to the solar charge controller first, some charge controllers can be damaged if connected to solar panel before the battery as the current has nowhere to go and some need the battery voltage in order to self set the output voltage.

thanks for the info appreciated
best daniel

 

[t0mb0]

Those breakers are generally awful and seem to be the culprit in issues raised in a few threads here because of the huge voltage drop over them, use an appropriate fuse instead to protect circuits.

 

[Samro]

Those breakers are generally awful and seem to be the culprit in issues raised in a few threads here because of the huge voltage drop over them, use an appropriate fuse instead to protect circuits.

Which breakers are you referring to as being awful?
I regularly use surface mount Bluesea breakers with zero issues to date?

https://www.bluesea.com/products/7138/187-Series_Circuit_Breaker_-_Surface_Mount_40A

 

[Grim Reaper]

You get what you pay for.
However, a 360W solar panel only puts out about 10A max, putting a 40A breaker in the line would be pointless.
Solar panels can withstand short periods of short circuiting so even a 10A fuse on the feed from the panel would not be of any use.
What fuse rating would you install and what would it protect? Any lower than 10A and you risk blowing it when the panel gets full sunlight, any higher and it is unlikely to blow ever.

 

[t0mb0]

Which breakers are you referring to as being awful?
I regularly use surface mount Bluesea breakers with zero issues to date?

https://www.bluesea.com/products/7138/187-Series_Circuit_Breaker_-_Surface_Mount_40A

The kind linked to in the original post. Maybe Bluesea breakers are fine but those cheap ones often seem to be the cause of trouble in a few threads I’ve seen on here because of the huge voltage drop across them.

 

[Dellmassive]

The thermal breakers are the ones with issues..... The Chinese cloan ones.

Blue sea make the original ones and are top quality.

The mechanical isolator switches are normally all ok..... But if getting the cloan / copy version I would down rate the capacity by 50%.

For example I had a (eBay cheaper version) 300A islotor switch that got hot when running 80A through it.... When swapped for a better quility 200A unit it was cool.

......

As above use a midi style fuse for the battery connection (at the battery connection point).... And fit an isolator switch on the PV side...

Fusing the PV line isn't exactly necessary on low wattage systems.... Ie below 500w or about 50v.

 

[Samro]

You get what you pay for.
However, a 360W solar panel only puts out about 10A max, putting a 40A breaker in the line would be pointless.
Solar panels can withstand short periods of short circuiting so even a 10A fuse on the feed from the panel would not be of any use.
What fuse rating would you install and what would it protect? Any lower than 10A and you risk blowing it when the panel gets full sunlight, any higher and it is unlikely to blow ever.

That's not quite right in that the 360W panel has the ability to potentially operate at a max of around 20A.
Whilst a breaker is not necessary, an oversize breaker which can act as a switch, will operate with negligible volt drop and be able to operate as a switch to isolate the solar in the event of a disconnection from the battery to the solar controller.
Oversizing a breaker has the benefit of being able to add to the PV array in the future, but also provide protection in the event of a stray positive on the panel side.
This is unlikely and a switch will do, but I'd rather an oversize breaker than a simple switch to ensure maximum safety without risking high resistance which will lead to charging issues.
I have used the exact cheap and nasty breaker referred to original thread on my own van and found it useful as a way of isolation. (Don't tell anyone though!

 

[djgriff]

ok thanks for all the details and insights. Did know there were issues surrounding the breakers. i noticed @Dellmassive that you have one of these in you' how i done it' examples: DC isolator, would this be over kill or could i get away with one of these: 10 Amp breaker

cheers for all the help and comments, appreciated

best
Daniel

 

[djgriff]

That's not quite right in that the 360W panel has the ability to potentially operate at a max of around 20A.
Whilst a breaker is not necessary, an oversize breaker which can act as a switch, will operate with negligible volt drop and be able to operate as a switch to isolate the solar in the event of a disconnection from the battery to the solar controller.
Oversizing a breaker has the benefit of being able to add to the PV array in the future, but also provide protection in the event of a stray positive on the panel side.
This is unlikely and a switch will do, but I'd rather an oversize breaker than a simple switch to ensure maximum safety without risking high resistance which will lead to charging issues.
I have used the exact cheap and nasty breaker referred to original thread on my own van and found it useful as a way of isolation. (Don't tell anyone though! View attachment 167926

ok interesting, i have a spare 60Amp break exactly like that, guessing i could use this as it is literally to just break the circuit as and when?
Cheers
Daniel

 

[t0mb0]

You can use a fuse to break a circuit too - just pull it out. It doesn’t have all the issues associated with cheap breakers and it’s about 10x cheaper than a decent breaker.

 

[Grim Reaper]

That's not quite right in that the 360W panel has the ability to potentially operate at a max of around 20A.

?? What is the Short Circuit Current figure for the panel? None of the 360W panels I have seen have an Impp or Isc of much more than 10-11A

 

[djgriff]

This is the panel i purchased : 360w -photonicuniverse

• Peak power: 360W
• Maximum power voltage: 41.2V
• Maximum power current: 8.9A
• Open circuit voltage: 49.6V
• Short circuit current: 9.3A
• Dimensions: 2035 x 1020 x 2 mm
• Weight: 6.82 kg

cheers
Daniel

 

[Grim Reaper]

Yeah, so as far as I can tell, the max output current from that panel would be 9.3A if it were short circuited.
If you wanted to fuse it you would be looking at a fuse between 8.9A (Impp) and 9.3A (Isc) so ideally 9.2A to account for a cold panel on a sunny day, but the nearest you can get is a 10A (because you can't get a value any closer than that) but if the panel were to be shorted out, the 10A fuse may not blow anyway, so there's no point.
There's also no point putting the fuse at the end of the wiring closest to the charge controller because that won't protect the wiring from the current source, it would have to be right at the output from the panel.

 

[t0mb0]

Those specs make it very clear why fusing a solar panel isn't actually necessary - it's designed to produce 8.9A but even short circuited it can only ever produce 9.3A so your fuse will either blow in normal operation, or never blow...

There maybe is an argument for fusing at the controller end if you're really into a belt and braces approach to safety as it will protect you from mis-wiring, some undue contact between wires/terminals or the (extremely unlikely!) event that your controller malfunctions to the extent that it produces current at its input.

 

[djgriff]

cheers, i'm not to worried from a fire perspective, i guess its just having a convenient way to break the circuit if need. This in mind i think i will just drop the 60A spare break that i have in, then a 40Amp mini fuse between battery and Mppt controller.

Thanks for all the discussion, been insightful and very helpful.
Cheers
Daniel

 

[Oceanis]

Have a similar setup .... looks like this


The breaker on the panels is purely to isolate the MPPT and stop it producing current (30A) if I need to work on the wiring. A dual-circuit breaker in this position is mandated for solar installations on vehicles in the US.

The fuses are fuses because circuit breakers work on a cumulative build-up of heat and over long periods of use they can heat up considerably before they trip, particularly if attached to heavy gauge wires.