DC Isolator on solar

[Manxcat54]

So what is the thoughts on having a DC Isolator on the incoming +/- of the solar just before the controller, I read somewhere that it could be a fire hazard??

[GUMPY]

An isolator could be useful if you need to work on the system with no solar input.

I have them on the system at home but never bothered on the boat or in the van I just covered the panels with a blanket when I needed to work on them.

[Tony Brooks]

49 minutes ago, Manxcat54 said:

So what is the thoughts on having a DC Isolator on the incoming +/- of the solar just before the controller, I read somewhere that it could be a fire hazard??

 

It should not be a fire hazard any more than the battery isolators or any other switch that is:

 

a. having a high enough current rating

b. not some no name piece of kit made in the Far East.

 

Some people use a fuse they can pull out instead of the switch, but electrically it is not vital.

 

Having one will make diagnosing things like alternator or battery faults easier, covering the panels is far enough, but things get a bit more complicated if there is a lot of wind about. Also, with panels connected in series may push the voltage towards a dangerous level, so a switch saves trying to disconnect a high voltage connection.

[blackrose]

1 hour ago, Manxcat54 said:

So what is the thoughts on having a DC Isolator on the incoming +/- of the solar just before the controller, I read somewhere that it could be a fire hazard??

 

It's only a fire hazard if it's not properly rated. I have a DC isolator fitted because my two panels in series can put out about 90v. How else would one isolate the panels safely? If you disconnect solar cable connectors they're not rated to be make & break connectors and neither are most small fuse holders. . 

Edited May 20 by blackrose

[Alan de Enfield]

28 minutes ago, blackrose said:

I have a DC isolator fitted because my two panels in series can put out about 90v. How else would one isolate the panels safely?

 

My panels are rated 120v - if I need to work on them I simply take the + wire out of the MTTP feed.

[Manxcat54]

9 hours ago, Tony Brooks said:

 

It should not be a fire hazard any more than the battery isolators or any other switch that is:

 

a. having a high enough current rating

b. not some no name piece of kit made in the Far East.

 

Some people use a fuse they can pull out instead of the switch, but electrically it is not vital.

 

Having one will make diagnosing things like alternator or battery faults easier, covering the panels is far enough, but things get a bit more complicated if there is a lot of wind about. Also, with panels connected in series may push the voltage towards a dangerous level, so a switch saves trying to disconnect a high voltage connection.

I bought this one, it feels like a good bit of kit and I have seen other boaters use them.

[Tony Brooks]

I note that it has no obvious current rating, which is one thing that may cause a fire if it is insufficient. You really should calculate the maximum likely current your panels can produce and compare that with any switch's current rating.

[Jen-in-Wellies]

If you are working on the boat batteries and have effectively disconnected the solar controller from the batts, then it is a good idea to also have a way of disconnecting the panels from the controller too. Many solar controllers can run in to problems if the panels are connected before the batteries. Particularly if they sense battery voltage to automatically set themselves to 12, or 24V. Check your controller manual. If it says connect batteries, then panels, then a switch to the panels is a good idea.

[blackrose]

9 hours ago, Alan de Enfield said:

 

My panels are rated 120v - if I need to work on them I simply take the + wire out of the MTTP feed.

 

MTTP? What's that? I don't have that bit of kit. 

 

I'd rather isolate my panels with a switch than disconnecting cables.

31 minutes ago, Tony Brooks said:

I note that it has no obvious current rating, which is one thing that may cause a fire if it is insufficient. You really should calculate the maximum likely current your panels can produce and compare that with any switch's current rating.

 

It's 32A

[Manxcat54]

32 minutes ago, Tony Brooks said:

I note that it has no obvious current rating, which is one thing that may cause a fire if it is insufficient. You really should calculate the maximum likely current your panels can produce and compare that with any switch's current rating.

TRUE DC ENCLOSED ROTARY ISOLATOR IP66 SOLAR/PV - 32A 2 POLE/4 POLE 1000VDC

The V-Switch is a configurable DC isolator for a photovoltaic system with PV string voltage from 300V to 1000V. The switch is a piece of essential equipment for any PV installation and should be connected between the solar panels and inverter.

Features ;

— IP66 water proof with UV resistance

— Arcing time <3ms

— Earth connection

— IEC60947-3, AS60947.3 compliant

— 2 poles, 4 poles available for single and double string

— 32Amps up to 1000V configurable

IP66 1000V 32A true DC isolator switch BYH-32, shall be installed between the solar arrays and solar inverter.

For isolation the PV array during system installation or any maintenance.

The switch must be rated for system voltage ( 1.15 x string open circuit voltage Voc ) & current ( 1.25 x string short circuit current ISC ). Recommend as a standard isolator to solar installers.

 

 

 

 

 

 

 

 

[Alan de Enfield]

16 minutes ago, blackrose said:

MTTP? What's that? I don't have that bit of kit. 

 

Fat finger brain fart !

 

MPPT not MTTP

[Chris John]

MPPT is basically what you’ve called the controller. 
Unfortunately some posters prefer to take the mick rather than answer questions 

[Russ T]

11 minutes ago, Chris John said:

MPPT is basically what you’ve called the controller. 
Unfortunately some posters prefer to take the mick rather than answer questions 

Which part of the question do you think @blackrose didn't answer?

 

I have isolators on both sets of my panels 2 in series (80V), two in parallel. I find it very useful to be able to isolate them from the controller without having to disconnect MC4's. I don't regret installing them.

[blackrose]

39 minutes ago, Chris John said:

Unfortunately some posters prefer to take the mick rather than answer questions 

 

Isn't it possible to do both? I have been asking and answering questions on this forum for nearly 20 years.

 

I'm not sure what your issue is? I wasn't being nasty or aggressive and I have no problem with Alan who is also known to indulge in gentle piss-taking when the opportunity arises.

[Llamedos]

Never ever fit an AC isolator in a DC circuit.

 

There's one chap who calls himself a professional solar panel fitter on YouTube who fits AC ones he get's from Screwfix! There is a significant fire risk as DC causes a huge spark across the contacts which you don't get with AC, so you need an isolator with both a greater distance and faster closing and opening than AC. The one @Manxcat54 has fitted is spot on.

 

Here's a rather scary video if anyone doesn't believe me...

 

The jaw dropping difference between AC and DC isolators

[nicknorman]

36 minutes ago, Llamedos said:

Never ever fit an AC isolator in a DC circuit.

 

There's one chap who calls himself a professional solar panel fitter on YouTube who fits AC ones he get's from Screwfix! There is a significant fire risk as DC causes a huge spark across the contacts which you don't get with AC, so you need an isolator with both a greater distance and faster closing and opening than AC. The one @Manxcat54 has fitted is spot on.

 

Here's a rather scary video if anyone doesn't believe me...

 

The jaw dropping difference between AC and DC isolators

The arcing on the DC only arises due to inductance in the circuit. The heater in the video has a lot of coiled wire inside which I guess gives it plenty of inductance. I don’t know what the inductance of a solar panel itself is, not much I’d have thought. And the wiring is in straightish lines so again very little inductance. So I think the video rather over-eggs the issue as applicable to solar panels.

Whilst of course it’s true that a switch rated for ac will have a different (much lower) current rating for dc, that is only an issue when interrupting a high current with significant inductance in the circuit. It has no bearing on the current rating whilst the switch is on. And if you only switch it off when the current is low (batteries fully charged, darkish etc) then again no problem.

 

So yes of course the correct answer is to ensure that the dc rating of the switch is adequate, but in practice let’s not over scare-monger!

[Gybe Ho]

2 hours ago, blackrose said:

 

Isn't it possible to do both? I have been asking and answering questions on this forum for nearly 20 years.

 

I'm not sure what your issue is? I wasn't being nasty or aggressive and I have no problem with Alan who is also known to indulge in gentle piss-taking when the opportunity arises.

 

His problem is that he is a normal human being whose sense of civilized behaviour has not been debased by "nearly 20 years" of interaction with this forum.

 

In your specific case I genuinely thought a 21st century piece of boating technology was unknown to you, aren't you the character who has spent 6 months trying to install and properly charge a drop-in lithium battery?

 

Reading this forum thread you were never think the household solar installation industry is currently in a panic over house fires triggered by failing isolators. There is a case to be made that the occasional utility of a solar isolator is negated by the fire risk, cost and the ridiculous size of these DC isolators that seem to be produced in a garden shed manufacturing facility using diy project box casings. 

Edited May 21 by Gybe Ho

[Russ T]

29 minutes ago, Gybe Ho said:

 

His problem is that he is a normal human being whose sense of civilized behaviour has not been debased by "nearly 20 years" of interaction with this forum.

 

In your specific case I genuinely thought a 21st century piece of boating technology was unknown to you, aren't your the character who has spent 6 months trying to install and properly charge a drop-in lithium battery?

 

Reading this forum thread you were never think the household solar installation industry is currently in a panic over house fires triggered by failing isolators. There is a case to be made that the occasional utility of a solar isolator is negated by the fire risk, cost and the ridiculous size of these DC isolators that seem to be produced in a garden shed manufacturing facility using diy project box casings. 

Blackrose has mentioned the term MPPT approx twenty six times in the last six months. It seems strange that you know details about his batteries, but neglected to notice this.

Edited May 21 by Russ T

[Chris John]

2 hours ago, Russ T said:

Which part of the question do you think @blackrose didn't answer?

 

I have isolators on both sets of my panels 2 in series (80V), two in parallel. I find it very useful to be able to isolate them from the controller without having to disconnect MC4's. I don't regret installing them.

Where did I say it was that poster?

[Russ T]

2 minutes ago, Chris John said:

Where did I say it was that poster?

Apologies. Which poster were you referring to?

Edited May 21 by Russ T

[Llamedos]

54 minutes ago, nicknorman said:

The arcing on the DC only arises due to inductance in the circuit. The heater in the video has a lot of coiled wire inside which I guess gives it plenty of inductance. I don’t know what the inductance of a solar panel itself is, not much I’d have thought. And the wiring is in straightish lines so again very little inductance. So I think the video rather over-eggs the issue as applicable to solar panels.

Whilst of course it’s true that a switch rated for ac will have a different (much lower) current rating for dc, that is only an issue when interrupting a high current with significant inductance in the circuit. It has no bearing on the current rating whilst the switch is on. And if you only switch it off when the current is low (batteries fully charged, darkish etc) then again no problem.

 

So yes of course the correct answer is to ensure that the dc rating of the switch is adequate, but in practice let’s not over scare-monger!

Well I'm sure you're right but I'm not taking any chances. I've probably over engineered my setup but better safe than sorry.

[Chris John]

1 hour ago, blackrose said:

 

Isn't it possible to do both? I have been asking and answering questions on this forum for nearly 20 years.

 

I'm not sure what your issue is? I wasn't being nasty or aggressive and I have no problem with Alan who is also known to indulge in gentle piss-taking when the opportunity arises.

Did I say it was you?

read the page  and you’ll see someone comment that the poster has made a typo and has made zero attempt to answer the question even though he knows the answer I have no doubt 

[Russ T]

4 minutes ago, Chris John said:

Did I say it was you?

read the page  and you’ll see someone comment that the poster has made a typo and has made zero attempt to answer the question even though he knows the answer I have no doubt 

Neither have you (or I) answered the question asked by the OP.  It's a discussion forum. One person says, I do it this way, someone else says I do it another way. It prompts discussion about the pros and cons of each.

 

Thoughts on isolators differ. Are they required? no. Are they useful? yes. Are they dangerous? All things electrical, are potentially dangerous.

[Llamedos]

Back on the original topic...

 

There has been a big debate going on in Australia about the use of isolators on solar circuits. Australia, of course, being the country with a lot of powerful sunshine.

 

Isolators are no longer recommended there because of the amount of fires they were causing probably down to them being under specified or the wrong type being fitted by poorly qualified installers. Doesn't mean they're a bad idea in my book, just that if you're fitting one fit the correct one.

[Tony Brooks]

12 minutes ago, Llamedos said:

Back on the original topic...

 

There has been a big debate going on in Australia about the use of isolators on solar circuits. Australia, of course, being the country with a lot of powerful sunshine.

 

Isolators are no longer recommended there because of the amount of fires they were causing probably down to them being under specified or the wrong type being fitted by poorly qualified installers. Doesn't mean they're a bad idea in my book, just that if you're fitting one fit the correct one.

 

Precisely, and choosing the correct one, involves assessing the competence/good standing of the manufacturer and inspecting and understanding the specifications and what is needed. It seems to me that the OP justified his choice on the grounds that lots of boaters use that type he selected, rather than the specifications and the current it was needed to handle.