Solar Panels

[IanD]

1 hour ago, Tony Brooks said:

 

The circuit breaker should be rated in amps and I have already told you the THEORETICAL currant (Amps) the panels will produce, BUT you will never get that theoretical maximum in the UK, so the currant the breaker needs to handle will be less, probably far less. So look up the date for whatever you choose.

 

Whether you choose circuit breakers or fuses is up to you. As long as the panels to MPPT are adequate for the maximum currant the panels produce, you do not need a fuse/breaker between panel and MPPT. However, to make life easier for you some method of isolating the panels from the MPPT for the reason I explained before. That could be a removable fuse, circuit breaker, or switch.

 

You do need a fuse or circuit breaker between the batteries and MPPT (again, explained to you before). this needs to be as close to the batteries as reasonably possible, but not in any battery box or container.

 

 

And has been said, make sure any circuit breaker is rated for low-voltage (e.g. 100V or lower) DC, not just high-voltage (e.g. 230V) AC. Many are only AC-rated.

 

As well as being easier to break because voltage/current drops to zero every 10ms, HVAC is much easier on the contacts as far as corrosion is concerned because it will break through any thin high-resistance oxidation and there's no chance of any plating electromigration, LVDC won't so there's more chance of a high-resistance contact which then gets hot -- which then increases the resistance, which makes it hotter, which... 😞

Edited May 12, 2023 by IanD

[Ingylad]

Do not use cables smaller than 16mm. If your controller will take them, I would install 25mm, especially with the 3m run. This will also give you the option to add another panel in the future. I can also recommend fitting an isolator between the panels and the controller, it makes life so much easier.

[Chewbacka]

Panels (rather than controller to batteries) only need fuses if you have several in parallel, which you probably don’t.  

 

With a VoC of 46v if you put your panels in series you will be getting some fairly high open circuit D.C. voltages, so exposed terminals etc need guarding, and a warning notice by the controller wouldn’t be a bad idea.

[Tony Brooks]

38 minutes ago, Chewbacka said:

Panels (rather than controller to batteries) only need fuses if you have several in parallel, which you probably don’t

 

Why is that then, as long as the cable is properly specified for maximum currant capacity? Shorting the panels should not do any harm, they will only produce what they can produce, and that is within the capacity of the cables to not catch fire.

.

[Andyaero]

Are these any good......

 

https://www.itstechnologies.shop/products/425w-canadian-solar-super-high-power-solar-panel

[TheBiscuits]

6 hours ago, Chewbacka said:

Panels (rather than controller to batteries) only need fuses if you have several in parallel, which you probably don’t.  

 

I think that's bad advice.

 

6 hours ago, Chewbacka said:

With a VoC of 46v if you put your panels in series you will be getting some fairly high open circuit D.C. voltages, so exposed terminals etc need guarding, and a warning notice by the controller wouldn’t be a bad idea.

 

But that is very good advice.

[LadyG]

On 11/05/2023 at 12:41, Tony Brooks said:

Assuming the solar will occasionally deliver it's rated output - a very doubtful assumption - 430W of solar equals about 33 amps at 13 volts, so on that front the circuit breaker you list will be OK. However, the fuse/circuit breaker is t protect the cable from the thousands of amps that might floe in the case of a short circuit, so you need to consider the maximum current capacity of the cable that you are using - 100 amps into a 6 sq mm CCSA cable with a 100 amp fuse could easily result in a fire.

 

The fuse/breaker between the MPPT and batteries needs to be mounted as close to the batteries as reasonably possible, but outside the battery case.

 

You should never have the panels connected to the MPPT without the batteries connected first, doing so is likely to set the MPPT to 24V. so you need a way of isolating the panels during maintenance.

 

 

[GUMPY]

Fuses are there to protect the cable run. If the cable is sized to carry the full short circuit current of the panel you do not need fuses between the panel and the MPPT as it's impossible overload the cable.

 

 

A switch however is a good idea

[blackrose]

10 hours ago, Tony Brooks said:

 However, to make life easier for you some method of isolating the panels from the MPPT for the reason I explained before. That could be a removable fuse, circuit breaker, or switch.

 

Isn't removing or connecting a fuse from cables between panels & MPPT potentially dangerous if those panels are connected in series and the sun happens to be shining?

51 minutes ago, Loddon said:

 

A switch however is a good idea

 

Yes, a properly rated one.

Edited May 12, 2023 by blackrose

[Chewbacka]

On 12/05/2023 at 22:13, Loddon said:

Fuses are there to protect the cable run. If the cable is sized to carry the full short circuit current of the panel you do not need fuses between the panel and the MPPT as it's impossible overload the cable.

 

 

A switch however is a good idea

I agree, however if you have a number of panels in parallel and one panel fails with an internal short then the conductors within that panel will have to carry all the current from all the panels.  Whilst it is rare it is a risk worth considering.

[Tony Brooks]

4 minutes ago, Chewbacka said:

I agree, however if you have a number of panels in parallel and one panel fails with an internal short then the conductors within that panel will have to carry all the current from all the panels.  Whilst it is rare it is a risk worth considering.

 

Are you sure that you have that correct. It sounds as if you are talking about panels in series. Even so I am sure that panel's internal wiring would burn open circuit just like a fuse. In fact a fuse way down the cable towards the controller would not protect from a panel's internal short. (I think)

Edited May 16, 2023 by Tony Brooks

[Chewbacka]

On 16/05/2023 at 10:20, Tony Brooks said:

 

Are you sure that you have that correct. It sounds as if you are talking about panels in series. Even so I am sure that panel's internal wiring would burn open circuit just like a fuse. In fact a fuse way down the cable towards the controller would not protect from a panel's internal short. (I think)

No Parallel.  If a number of panels are in parallel and one goes short it will present as a short for all the panels in parallel with it.  Hence if a few panels are in parallel they should have a fuse between each panel and the feed cable to the controller.  That way if one panel goes short then when it ‘takes’ all the current from the other panels it’s fuse will blow.  The internal conducts within a failed panel can ‘burn out’ like a fuse but I believe there have been instances of internal arcing and serious over heating. So if you have a few big panels in parallel I would fuse the individual panels.  Obviously not required on a single string of panels in series.

[cuthound]

If you overload a solar panel the voltage drops which in turn reduces the current from it. A complete short will result in zero volts output and hence no current.

[IanD]

2 minutes ago, cuthound said:

If you overload a solar panel the voltage drops which in turn reduces the current from it. A complete short will result in zero volts output and hence no current.

That's not how solar panels work, they are silicon photodiodes and will still source current into a short circuit -- but the output power will be zero...

Edited May 17, 2023 by IanD

[Adam1991]

On 12/05/2023 at 13:06, IanD said:

 

And has been said, make sure any circuit breaker is rated for low-voltage (e.g. 100V or lower) DC, not just high-voltage (e.g. 230V) AC. Many are only AC-rated.

 

As well as being easier to break because voltage/current drops to zero every 10ms, HVAC is much easier on the contacts as far as corrosion is concerned because it will break through any thin high-resistance oxidation and there's no chance of any plating electromigration, LVDC won't so there's more chance of a high-resistance contact which then gets hot -- which then increases the resistance, which makes it hotter, which... 😞

Hi Ian, based on your advice would this model and amperage breaker be correct for 430w of solar? 
 

https://generalpower.lk/product/tomzn-63-a-2pole-1000v-dc-mcb/

[IanD]

16 hours ago, Adam Mc Gowan said:

Hi Ian, based on your advice would this model and amperage breaker be correct for 430w of solar? 
 

https://generalpower.lk/product/tomzn-63-a-2pole-1000v-dc-mcb/

Something like that would certainly do the job, it's rated to carry and break DC -- but the voltage rating is overkill, to say the least... 😉

[Adam1991]

Hi Ian, Sorry to add another question to this thread 😂
 

I’m about to go for this breaker for our setup but the 1000v is confusing. Is that max rating dangerous on a 12v system and why is it such a high maximum voltage? 
 

thanks for your advice 

On 22/05/2023 at 12:25, IanD said:

Something like that would certainly do the job, it's rated to carry and break DC -- but the voltage rating is overkill, to say the least... 😉

 

[IanD]

10 minutes ago, Adam Mc Gowan said:

Hi Ian, Sorry to add another question to this thread 😂
 

I’m about to go for this breaker for our setup but the 1000v is confusing. Is that max rating dangerous on a 12v system and why is it such a high maximum voltage? 
 

thanks for your advice 

 

It's not a problem, if it does the job and doesn't cost an arm and a leg it'll be fine. If it's super-expensive you should be able to find a cheaper one with a lower rated voltage (but still rated for DC).

[BEngo]

The breaker is fine for what you are doing.  It is just that 1000 V is a lot more than will ever be needed.  It certainly is not dangerous.

 

The breaker was clearly  designed to handle substantial DC currents- it will break successfully with a current of up to 6000 Amps passing as the result of a fault condition in the circuit.  The breaker was probably also designed for use with large series connected solar arrays in mind.  Hence it has a high voltage rating.  Nothing to worry about though.

 

N

 

 

[Adam1991]

Great, thanks for clarifying this  

 

On 22/05/2023 at 12:25, IanD said:

Something like that would certainly do the job, it's rated to carry and break DC -- but the voltage rating is overkill, to say the least... 😉