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Psycloud

Inline fuse/breaker on Solar panel?

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Reading another thread regarding disconnecting panels from controller before disconnecting battery I am considering placing something like this inline between the panel(s) and the controller:

 

https://www.ebay.co.uk/itm/12V-24V-DC-20A-150A-Circuit-Breaker-Fuse-Holder-Inline-Fuse-Block-For-UK-stock/273117357933?hash=item3f9710276d:m:m3nrEq_Da6_jY7BUAfhoa9Q

 

s-l1600.jpg

 

Is this a good idea?  One problem is that these fuses are rated 12/24v volt but the panels can go 37v at open circuit.  Would that mean these fuses would go bang?

 

 

 

Thanks

 

David

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29 minutes ago, Psycloud said:

Reading another thread regarding disconnecting panels from controller before disconnecting battery I am considering placing something like this inline between the panel(s) and the controller:

 

https://www.ebay.co.uk/itm/12V-24V-DC-20A-150A-Circuit-Breaker-Fuse-Holder-Inline-Fuse-Block-For-UK-stock/273117357933?hash=item3f9710276d:m:m3nrEq_Da6_jY7BUAfhoa9Q

 

 

 

Is this a good idea?  One problem is that these fuses are rated 12/24v volt but the panels can go 37v at open circuit.  Would that mean these fuses would go bang?

 

 

 

Thanks

 

David

No they will not go bang. The 12/24V is related to the insulation rating although I very much doubt they would not be perfectly safe at 50 volts or more.

 

They are single pole devices do there is no "negative" close by to allow a short to develop and you will probably be mounting it on wood, another insulator.

 

The only time your fuse will go bang is if you try to put more than their rated current through them.

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Thank you - I might get one then - I figured it would be a quick way of disconnecting the power from the panels by hitting the reset button.

Edited by Psycloud

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48 minutes ago, Psycloud said:

Thank you - I might get one then - I figured it would be a quick way of disconnecting the power from the panels by hitting the reset button.

I have one of these:

 

https://www.12voltplanet.co.uk/waterproof-switchable-surface-mounted-circuit-breakers.html

 

It seems it is preferable to have a terminal ring on a nut/bolt arrangement, rather than a screw squashing the strands of a cable.

 

The circuit breaking facility is not necessary between panels and controller, but the power disconnection facility seems ideal. 

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1 hour ago, Richard10002 said:

I have one of these:

 

https://www.12voltplanet.co.uk/waterproof-switchable-surface-mounted-circuit-breakers.html

 

It seems it is preferable to have a terminal ring on a nut/bolt arrangement, rather than a screw squashing the strands of a cable.

 

The circuit breaking facility is not necessary between panels and controller, but the power disconnection facility seems ideal. 

They look good :)

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I might be corrected here but my understanding is that it's important to connect the controller to the batteries first (rather than to the panels) when the system is first installed. Subsequently, it doesn't matter which connection is made first. On my own system the inline fuse between battery and controller sometimes fails. It doesn't blow, it just seems to lose its connectivity. I've simply taken the fuse out and replaced it, without disconnecting the panels, without any problems.

 

If my understanding is right hopefully someone can explain why this is the case? 

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4 minutes ago, Gareth E said:

I might be corrected here but my understanding is that it's important to connect the controller to the batteries first (rather than to the panels) when the system is first installed. Subsequently, it doesn't matter which connection is made first. On my own system the inline fuse between battery and controller sometimes fails. It doesn't blow, it just seems to lose its connectivity. I've simply taken the fuse out and replaced it, without disconnecting the panels, without any problems.

 

If my understanding is right hopefully someone can explain why this is the case? 

No that’s not correct. 

 

The controller to the battery first ‘rule’ is so that the controller can determine what voltage system it’s connected to. However many times it’s connected it should always be in that order. For all the controller knows it might now be in a different boat. 

 

It might be fine not doing so (as you’ve experienced) but that’s more luck than judgment. 

 

Edited by WotEver
Untangling.

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I just use a standard breaker switch in the positive line from the panels.  - Needed it the other day when I had to remove them to get through the Harecastle tunnel!!

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I just use inline car type fuses between panel and controller. I find Fat fairly easy  to source fuses for these. To disconnect I just remove the fuse. 

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7 hours ago, Richard10002 said:

 

It seems it is preferable to have a terminal ring on a nut/bolt arrangement, rather than a screw squashing the strands of a cable

To meet RCD standards you need a bootlace ferrule when using a screw terminal. This is to prevent the turning screw cutting through the strands and just squashes the fertile thereby clamping the cable.

  • Greenie 1

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The fuse or breaker volt rating is also to do with arc suppression if the contacts open under a load, so whilst a 24v breaker is probably ok at 37v in case any one else is thinking of using one of these with 2 or 3 panels in series I wouldn’t.

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On 17/05/2018 at 12:44, WotEver said:

They look good :)

Only rated to 47VDC, so I'm going to rejig my 2 x 37V panels from series to parallel. I don't know how much damage would be done if it was switched at over 60VDC.

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21 minutes ago, Richard10002 said:

Only rated to 47VDC, so I'm going to rejig my 2 x 37V panels from series to parallel. I don't know how much damage would be done if it was switched at over 60VDC.

If you could cover one panel prior to switching it you’d be good. Bad idea to switch to parallel if you have an mppt controller. 

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29 minutes ago, WotEver said:

If you could cover one panel prior to switching it you’d be good. Bad idea to switch to parallel if you have an mppt controller. 

Sorry to sound thick but why would it be a bad idea? 

  • Greenie 1

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1 minute ago, Psycloud said:

Sorry to sound thick but why would it be a bad idea? 

Because when the light is low the voltage is low and might be too low to actually generate any charge. 

 

Two panels in series doubles the voltage. Three in series trebles the voltage. 

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But in parallel if one panel part shaded the other others can still give full output, in series current is limited to the weakest. If you have a trader MPPT controller they don't track below 1.5 amps and just act as a PWM panels in parallel reach that quicker. In low light and panels tend to give volts before current so you are more likely to get 30 volts at 0.1 amp than 1 amp at 12 volts.

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7 hours ago, WotEver said:

If you could cover one panel prior to switching it you’d be good. Bad idea to switch to parallel if you have an mppt controller. 

Do you know of a surface mounted switch or breaker that can handle 74VDC?

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37 minutes ago, Richard10002 said:

Do you know of a surface mounted switch or breaker that can handle 74VDC?

Surface mount, no. But there are many breakers designed for use in PV systems. Like these for instance, but it would require a box:

http://www.windandsun.co.uk/products/Other-System-Components/Fuses-and-Circuit-Protection/Circuit-Breakers#.WwCkAhbTWEc

 

Edited by WotEver
Typo

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21 minutes ago, WotEver said:

Surface mount, no. But there are many breakers designed for use in PV systems. Like these for instance, but it would require a box:

http://www.windandsun.co.uk/products/Other-System-Components/Fuses-and-Circuit-Protection/Circuit-Breakers#.WwCkAhbTWEc

 

I could use a DIN mounted breaker on a short piece of DIN rail - any reason why not? Do they have to be fitted in a consumer unit, or can they be standalone?

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22 minutes ago, Richard10002 said:

I could use a DIN mounted breaker on a short piece of DIN rail - any reason why not? Do they have to be fitted in a consumer unit, or can they be standalone?

No reason why not, no. They’re fine standalone. :)

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