Reliable PV DC disconnect?

[ns31]

Hi all, I wired up 2x strings to a DC disconnect made by Dihool (Chinese)... https://www.amazon.co.uk/Isolator-Disconnect-pre-wired-connectors-Waterproof/dp/B0B8YRBHHZ/

However, I'm aware that the cheap brands of DC disconnect increase the risk of fire. Even if the fire risk is low I'd like to make sure I use a very reputable/reliable disconnect, does anybody have any recommendations? Is the likes of the following ok, or still a bit cheap? https://www.tlc-direct.co.uk/Products/CMDX032DC.html

 

[Zwy]

IMO only. https://imoautomation.com/imo_us_usd_view/catalog/category/view/s/si-series/id/294/

For what these cost, you would be insane to use anything else. The switch was designed for PV.

 

[Kenny_]

Interesting. I used breakers.

https://www.amazon.com/gp/product/B0CGX6XPF9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

 

[marionw]

"Disconnects" are just that, normally an on/off switch, while "Breakers" can also be disconnects while providing overcurrent protection. Regardless, they need to be able to handle the voltage (upwards of 350 t0 400 vdc depending on your panel wiring) without arcing when opening or closing.

 

[Neil H]

Interesting. I used breakers.

https://www.amazon.com/gp/product/B0CGX6XPF9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

View attachment 187779

I used similar din rail mounted DC breaker BUt used a metal consumer box so if there was a fire it should be contained within the box

 

[efficientPV]

I've actually tested those Jotta breakers. The problem with all these DC breakers is that they don't have a snap turn on. I'd be careful using them as a switch. You can push one on very slowly and they will sizzle. I don't know why that is considered ok. Turn on isn't usually a problem. Initial voltage is 100V and you can see the arc for 172 microseconds. Arc stops at 40V.

 

[ns31]

I've actually tested those Jotta breakers. The problem with all these DC breakers is that they don't have a snap turn on. I'd be careful using them as a switch. You can push one on very slowly and they will sizzle. I don't know why that is considered ok. Turn on isn't usually a problem. Initial voltage is 100V and you can see the arc for 172 microseconds. Arc stops at 40V.
View attachment 187794

Interesting this, I'm assuming the PV disconnects can be quicker and built with arcs in mind?

 

[Kenny_]

I used similar din rail mounted DC breaker BUt used a metal consumer box so if there was a fire it should be contained within the box

Yep. Agree. Likely will redo all of this at some point.

 

[Zwy]

Interesting this, I'm assuming the PV disconnects can be quicker and built with arcs in mind?

The IMO has a snap function plus proper arc chutes for DC. It was designed for a PV disconnect. It is a knife switch that is spring loaded.

Yep. Agree. Likely will redo all of this at some point.

Ever heard the saying "you can lead a horse to water but can't make it drink"?

I responded to you in this post when you asked what an IMO was. https://diysolarforum.com/threads/2-mwh-srne-asf48100u200-h-10kw.67809/post-913658

 

[ns31]

The IMO has a snap function plus proper arc chutes for DC. It was designed for a PV disconnect. It is a knife switch that is spring loaded.

Just what I was looking for thank you

 

[efficientPV]

If you hold a compass near the base of a DC breaker you will notice it has a magnet. Current produces a magnetic field and the magnet pulls the arc into a longer path causing it to extinguish sooner. That's why they have polarity. I have tried some DC breakers and they quench the arc better backwards. What can I say, CHINA.

 

[Kenny_]

The IMO has a snap function plus proper arc chutes for DC. It was designed for a PV disconnect. It is a knife switch that is spring loaded.



Ever heard the saying "you can lead a horse to water but can't make it drink"?

I responded to you in this post when you asked what an IMO was. https://diysolarforum.com/threads/2-mwh-srne-asf48100u200-h-10kw.67809/post-913658

Yeah and ....

 

[Kenny_]

P.S. there is nothing on my rooftop but squirrels and birds and pine needles.

 

[Kenny_]

If you hold a compass near the base of a DC breaker you will notice it has a magnet. Current produces a magnetic field and the magnet pulls the arc into a longer path causing it to extinguish sooner. That's why they have polarity. I have tried some DC breakers and they quench the arc better backwards. What can I say, CHINA.

Yes, DC vs AC breakers for the win!

 

[Zwy]

P.S. there is nothing on my rooftop but squirrels and birds and pine needles.

I wouldn't put the IMO on the roof, much harder to turn the knob.

Like this is much better.



If women don't find you handsome, at least they might find you handy.

 

[ns31]

Can I just check, is the following 600V per series string? So 1200V in total? https://www.solartradesales.co.uk/imo-dc-isolator-25a-4-pole-600v-two-strings

 

[Zwy]

Can I just check, is the following 600V per series string? So 1200V in total? https://www.solartradesales.co.uk/imo-dc-isolator-25a-4-pole-600v-two-strings

600V total. You most likely won't be near that voltage due to charge controller max VOC rating.

The amps will be 25A per string.

If you use the IMO, be sure you understand how to wire it. It isn't a straight down type of wiring arrangement. If you don't understand, just ask.

 

[ns31]

600V total. You most likely won't be near that voltage due to charge controller max VOC rating.

The amps will be 25A per string.

If you use the IMO, be sure you understand how to wire it. It isn't a straight down type of wiring arrangement. If you don't understand, just ask.

Thanks. Each string is 446.76v as the voc is 37.23v and there's 12 panels per string. Do IMO offer a product that will handle 2x strings at this rating? I'm assuming it needs to be >1000V rated

 

[Zwy]

Thanks. Each string is 446.76v as the voc is 37.23v and there's 12 panels per string. Do IMO offer a product that will handle 2x strings at this rating? I'm assuming it needs to be >1000V rated

No, it needs to be rated only over 446.76V DC. The IMO is rated at 600V DC. It will work just fine.

You didn't say what you are using for a charge controller but you need to run the VOC calculations for the strings at the lowest ambient temp you will see in your area. Many operate in the range of 150V to 450V with a VOC limit of 500V. Use the Midnite Calculator and input your system specs. Then find the max VOC rating of the MPPT. The strings need to stay under that VOC rating at the coldest ambient temp for your area.

 

[ns31]

600V total. You most likely won't be near that voltage due to charge controller max VOC rating.

The amps will be 25A per string.

If you use the IMO, be sure you understand how to wire it. It isn't a straight down type of wiring arrangement. If you don't understand, just ask.

It arrived, it's a lovely piece of kit. I usually figure out wiring with a combination of a multimeter, and the instructions, but can I just sanity check something that appears to be a confusion in the design?...



The terminals on the top appear to be indicated with a negative symbol. Yet this does not reflect the instructions which show one of the outer terminals as +ve. Therefore I assume these '-' symbols are infact just the design and not an indication that a negative lead should be connected?

Im also making an assumption that the input terminals are top, and output terminals bottom? thanks

 

[SeaGal]

No, it needs to be rated only over 446.76V DC.

Sadly it's not always over 25C in the UK, so I'd go for at least 500V

 

[Solarholt]

I wouldn't put the IMO on the roof, much harder to turn the knob.

Like this is much better.

View attachment 187869

If women don't find you handsome, at least they might find you handy.

Where did you find those waterproof box connectors between the junction box and disconnect.

 

[Bkord]

Where did you find those waterproof box connectors between the junction box and disconnect.

That is a Myers hub.

 

[Zwy]

Where did you find those waterproof box connectors between the junction box and disconnect.

Myers hub and chase nipple. The Myers hub have an oring seal. You can find the Myers hub and chase nipples at Menards, or Home Depot, and I'm sure Lowes carries it. Online too.

Chase nipple from Home Depot and Menards.

Chase nipple is screwed from inside the disconnect thru the hole into Myers hub. Then Myers hub thru hole with it's nut in the inside of the junction box.