PV Panel Disconnect

[littleharbor2]

Imagine combining two different songs on one set of speaker wire then thinking you can split it apart and get the tunes to come out sounding right. Something like that....

 

[Zwy]

I would never recommend doing that. If, something happens to one mppt, the other will be way overloaded. Which could leave you with nothing.
Just because it seems like it will work, doesn't make it right or safe. But as I said, it's a free world.

I'm just the messenger at this point. kromc5 did this with the input from Signature Solar. Go ask them about it. It was their idea and it does work.

As for one mppt failing, if the input is fused properly, the other mppt would not be overloaded.

 

[Zwy]

Imagine combining two different songs on one set of speaker wire then thinking you can split it apart and get the tunes to come out sounding right. Something like that....

Actually, you have no idea how the audio travels down a single pair of speaker wires, yet can produce sound. Proves the point actually.

As for whether the algorithms will adjust to each other and produce max power point tracking, I actually think they will. No different than cloud cover passing over an array.

 

[timselectric]

It saves me money, when I learn from other people's mistakes. So, I have no problem with others trying things out.

 

[Zwy]

It saves me money, when I learn from other people's mistakes. So, I have no problem with others trying things out.

I agree, that's why you should try it first.

I've been waiting for kromc5 to say he has had a SCC failure but it hasn't happened yet. If one fails 5 years from now, will it be due to the parallel connection from PV or attributed to something else? What about 10 years, 20 years?

People say things can't be done, yet we find where someone has done it. Just throwing it out there, your results may vary. Considering some here believe Sig Solar walks on water, drink the Kool Aid they mix and recommend buying the ES5000 inverter with an auto transformer, yet question the fact James told kromc5 to wire Y's to run parallel SCC's seems a little strange.

I take everything they recommend with a grain of salt, actually throw large handfuls over my shoulder, but they may or may not be correct on this one. Time has a way of correcting mistakes or proving myths unsubstantiated.

 

[timselectric]

I agree, that's why you should try it first.

I've been waiting for kromc5 to say he has had a SCC failure but it hasn't happened yet. If one fails 5 years from now, will it be due to the parallel connection from PV or attributed to something else? What about 10 years, 20 years?

People say things can't be done, yet we find where someone has done it. Just throwing it out there, your results may vary. Considering some here believe Sig Solar walks on water, drink the Kool Aid they mix and recommend buying the ES5000 inverter with an auto transformer, yet question the fact James told kromc5 to wire Y's to run parallel SCC's seems a little strange.

I take everything they recommend with a grain of salt, actually throw large handfuls over my shoulder, but they may or may not be correct on this one. Time has a way of correcting mistakes or proving myths unsubstantiated.

Agreed
Also,
What works for one person, doesn't always work for another.

 

[pellicle]

@pellicle , those circuit breakers look very similar to one that a forum member posted about last year. It was causing havoc in his system. Those breakers may be good for car audio but I would never use them in a PV/LiFePO4 system.

well I don't see why (and I've tested them) ... as it happens I have a background in electronics which goes back some decades (doesn't exclude me from making mistakes) and I can't see what it is that might be considered a problem with carrying up to their rated current and then (appropriately) disconnecting when exceeding it.

In my testing they either provided consistent conduction of power or disrupted it until reset.

What voltage were they being used at? Can you point me at a thread?

 

[pellicle]

What works for one person, doesn't always work for another.

this is often said, but without context its hard to accept. Now if we are talking about planning based "that won't work for me" caused by specification issues then sure, but if one argues that it doesn't work one should be able to provide some rationale for why.
Maybe they did ... ?

PS: to give an example I have a 250W panel and 90Ah of 24V FLA powering my shed, if someone says "that won't work for me" and they have an industrial premise doing welding and whatnot then "of course it won't" ... but then that's context.

 

[timselectric]

this is often said, but without context its hard to accept. Now if we are talking about planning based "that won't work for me" caused by specification issues then sure, but if one argues that it doesn't work one should be able to provide some rationale for why.
Maybe they did ... ?

PS: to give an example I have a 250W panel and 90Ah of 24V FLA powering my shed, if someone says "that won't work for me" and they have an industrial premise doing welding and whatnot then "of course it won't" ... but then that's context.

There was context, in the conversation.

 

[littleharbor2]

My first question would be, are the rated to carry DC current?

 

[littleharbor2]

I see that some seem to be rated for up to 42 vdc. But also look to be intended for car audio.

 

[WYtreasure]

Thanks for all of the replies. I have 4 100w panels connected in series/parallel.

Hey MarcM...
I have 100w panels as well, 8 of them 4S2P. My panel specs are: 60 cells, 100w, Monocrystalline Silicon, 14.55 pounds, Vmp 16.77, VOC 19.83, IMP 6.26A, ISC 6.56A. Do these numbers sound familiar?

 

[TorC]

Power is power, modulo some variant wrinkles when dealing with DC, AC, audio, or even RF/microwave. DC arc extinguishing is DC arc extinguishing, and if can interrupt the current it can do so. Doesn't matter why the current is flowing. Large batteries can, however, produce scary current most fuses/breakers can't interrupt. 10kA+ expected short circuit current has been calculated for solar batteries here on this forum. That's why battery fuses are class T, with 20kA interrupt. If you check the datasheet for amps interrupting you can determine whether it's safe or not.

ETA: for panel fuse/breaker I'd be comfortable with much smaller Aic, but audio designed equipment is relatively unlikely to be rated for the DC voltage required. Datasheet is king here.

 

[Browneye]

I see that some seem to be rated for up to 42 vdc. But also look to be intended for car audio.

They are. The experienced guys will tell you those type of cheapo breakers can create a lot of heat and resistance, and are prone to fail.
If you want a cheapo switchable breaker the Eaton Bussman ones are recommended. Sure they cost twice as much, but they also work better. But yeah, for main feed to lifepo4, using a class-T has been implored for safety.

 

[Zwy]

this is often said, but without context its hard to accept. Now if we are talking about planning based "that won't work for me" caused by specification issues then sure, but if one argues that it doesn't work one should be able to provide some rationale for why.
Maybe they did ... ?

PS: to give an example I have a 250W panel and 90Ah of 24V FLA powering my shed, if someone says "that won't work for me" and they have an industrial premise doing welding and whatnot then "of course it won't" ... but then that's context.

It is interesting that many claim this or that won't work but won't push the envelope to see for themselves if the "myth" is true or not.

We would all be sitting in the dark if Edison believed what was said, " that won't work".

 

[pellicle]

It is interesting that many claim this or that won't work but won't push the envelope to see for themselves if the "myth" is true or not.

agreed ... and if the magic smoke doesn't come out then "it worked" ;-)

 

[littleharbor2]

They are. The experienced guys will tell you those type of cheapo breakers can create a lot of heat and resistance, and are prone to fail.
If you want a cheapo switchable breaker the Eaton Busman ones are recommended. Sure they cost twice as much, but they also work better. But yeah, for main feed to lifepo4, using a classT has been implored for safety.

View attachment 86825

Personally, I have never used the cheapo car audio breakers in any PV/battery system. I was going through some stuff yesterday and came across 4 of them that somehow I ended up with. I was trying out the action of them and found not one acted the same as another one. Hitting the test button only released one lever, the others wouldn't snap open. Another wouldn't lock closed. They have an overall cheap feel to them.

 

[Supervstech]

Personally, I have never used the cheapo car audio breakers in any PV/battery system. I was going through some stuff yesterday and came across 4 of them that somehow I ended up with. I was trying out the action of them and found not one acted the same as another one. Hitting the test button only released one lever, the others wouldn't snap open. Another wouldn't lock closed. They have an overall cheap feel to them.

Bottom line with these breakers is they are RARELY rated over 32V… so, useless for any but the smallest 12V PV wiring…

 

[Browneye]

Summary: forum members don't let forum members use cheap-crap circuit breakers from the car-stereo industry in their PV systems.
But it's a free country, you do what you want, at your own risk.

I just replaced all of my brass/gold plated 'car stereo' ANL fuses with Eaton Bussman tin-plated copper blade fuses. Yeah, they're three to five times the cost but well worth it. There IS a big difference. An electrical fire will ruin your entire day, we promise!!

Here's a recent thread on a burnt fuse and general fuse discussion that has a lot of information, links, and value:

burning fuse

another solar headache,positive battery wire going from cc to battery getting hot enough to burn the fuse,at the time controller read 339w 24amps,inverter draw 290w,two 6v batteries in series 230ah lead acid,watts going on now lol,30a fuse 10 gauge wire,13.7 float and stayed there all day

diysolarforum.com

 

[pellicle]

Personally, I have never used the cheapo car audio breakers in any PV/battery system. I was going through some stuff yesterday and came across 4 of them that somehow I ended up with. I was trying out the action of them and found not one acted the same as another one. Hitting the test button only released one lever, the others wouldn't snap open. Another wouldn't lock closed. They have an overall cheap feel to them.

Morning

well of the 6 I bought (not much of a statistically valid sample) all worked perfectly and tested fine. If they hadn't, well I'd just send them back.

Mine didn't have an overall cheap feel any more than the typical "cheap plastic" feel that ones I see in service in almost every situation (compared to older heavy duty or current military grade stuff).
Mine are in service now and I'll be sure to post back if they fail. I'm not in the habit of recommending crap that falls apart. I am however in the habit of reading specs and the specs I have suggest that for the panel side there might be a bit much voltage for them on my application, but for the DC side between my controller and my 24V battery the ones I've bought would appear adequate.

Lastly I didn't say "buy these they're great" I said:

I agree with all the answers, but my question is "why wouldn't you"

I put in a 20A DC circuit breaker which can also be manually tripped (this one) on each of my DC circuits (panel to SCC, SCC to battery). I'm in Australia so I bought that one, but you must be able to find something similar.

perhaps people are unable to read "find something similar" and instead read it as "you should totally buy these"

meanwhile we drift from the actual question asked which was "should I build in a disconnect switch or fuse..."

to which I still say "why wouldn't you"