1st off-grid adventure — need charge controller advice

AC/DC said:

Thanks, these look amazing! There is a highly educational video on the product page which I unfortunately can’t link (at least on mobile, will try on my workstation).

I’m having trouble reading the diagrams, here’s what I’m looking at:
View attachment 207235
I don’t understand the 1 & 2 versions, assuming the breaker is the part my arrow is pointing to in each diagram, I’m only seeing 2 poles. And I’m not understanding why they’re calling it 4 Poles. #1 looks like it’s connected in series, #2 is not clear to me from the diagram how that’s a drawing of a parallel setup. I’m just not getting where the 4 poles are when it shows 2 connections to the breaker, just like in the unlabeled 2 Pole version and the top? And then Max Number of Strings is 1 for all of them anyway..

I’ll be running 3S2P, the top “2 Poles” versions should be fine right? I’d just like to understand what I’m looking at in those diagrams, what I’m missing.

Click to expand...

There isn't a breaker, it is a PV disconnect engineered and designed specifically for breaking high voltage PV. It breaks both negative and positive.

The wiring for a 4 pole is 1 goes to 2, 3 to 4, 5 to 6 and 7 to 8. The reason for this is due to the arc chutes and the rotary snap action.

Johnny explains it in this video.

Brucey said:

So for a single string you'd want the two pole version, for two strings the four pole version etc. I have a 4 pole clone version so I can disconnect two strings to two different sccs.

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Yep, clear on that, just confused by the 2nd and 3rd diagrams in the pic I posted. It says 4 Poles for both, but it also says Max No. Strings: 1 for both, and also to me it looks like the switches in each drawing only have 2 poles.. why would you ever even have 4 poles for 1 string?

Brucey said:

It may be simpler for you to get an mc4 version here:

Click to expand...

That looks really good actually!

Zwy said:

There isn't a breaker, it is a PV disconnect engineered and designed specifically for breaking high voltage PV. It breaks both negative and positive.

The wiring for a 4 pole is 1 goes to 2, 3 to 4, 5 to 6 and 7 to 8. The reason for this is due to the arc chutes and the rotary snap action.

Johnny explains it in this video.

Click to expand...

Thanks, that was great to see! I won't be getting a 4 pole version, I'm just confused by their diagrams, to me what is labeled 4 Poles in the diagrams only looks like 2 poles. I'd be getting the first option anyway, these two options which I'm confused about are their special "Higher Voltage/Current Rating" versions which I don't think I need.

AC/DC said:

Yep, clear on that, just confused by the 2nd and 3rd diagrams in the pic I posted. It says 4 Poles for both, but it also says Max No. Strings: 1 for both, and also to me it looks like the switches in each drawing only have 2 poles.. why would you ever even have 4 poles for 1 string?

That looks really good actually!

Thanks, that was great to see! I won't be getting a 4 pole version, I'm just confused by their diagrams, to me what is labeled 4 Poles in the diagrams only looks like 2 poles. I'd be getting the first option anyway, these two options which I'm confused about are their special "Higher Voltage/Current Rating" versions which I don't think I need.

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They series them to get from 16 to 32A capability on some models I believe.

AC/DC said:

why would you ever even have 4 poles for 1 string?

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If string voltage exceeds what a single pole can handle, multiple poles in series take care of it. Sometimes 2, 4, even 6 poles in series.

For PV strings it is useful to isolate both PV+ and PV-, so 2 poles for up to about 300V string, or 4 poles for 600V.

Hedges said:

If string voltage exceeds what a single pole can handle, multiple poles in series take care of it. Sometimes 2, 4, even 6 poles in series.

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I apologize but I’m having a hard time understanding how the actual connections are made. Does one wire per polarity come from the single string to the switch? How is it wired then, let’s say the switch has 4 poles, 2 per polarity? Is it somehow split then fed thru to poles (per polarity), or?

I think this is the mystery and I’m close to figuring it out conceptually

Here's a breaker from Midnight Solar with four 150V poles ganged together:


It could use all four wired in series (as shown) to interrupt 600V PV string that is grounded on one end. For an ungrounded string feeding a transformerless inverter, I would use 2 poles in series for PV+, the other two for PV-.

Here's another model with 2 poles also rated 600V, each pole must be good for 300V:


That is shown with a jumper connecting the two in series, so opens a 600V string at one end.
I would remove the jumper and run PV+/PV- each through one pole for an ungrounded string.

Hedges said:

Here's a breaker from Midnight Solar with four 150V poles ganged together:

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

It could use all four wired in series (as shown) to interrupt 600V PV string that is grounded on one end. For an ungrounded string feeding a transformerless inverter, I would use 2 poles in series for PV+, the other two for PV-.

Click to expand...

I'm missing something obvious here, to my mind, the way this is shown

if the PV input would be connected on the bottom terminals, the only two available, it would create a short when the switch is thrown on.

Maybe there is some trickery where the top left goes to bottom right, like the IMO, but regardless of how it is, if you have two inputs, a positive and a negative, there should be two outputs to go to your CC, no matter how many poles and jumpers. I'm banging my head against the wall because I don't understand how this works from a wiring perspective The little diagram on the switch is very low rez, and I both can't make it out well and don't understand it.

AC/DC said:

I’m having trouble reading the diagrams, here’s what I’m looking at:
View attachment 207235
I don’t understand the 1 & 2 versions, assuming the breaker is the part my arrow is pointing to in each diagram, I’m only seeing 2 poles. And I’m not understanding why they’re calling it 4 Poles. #1 looks like it’s connected in series, #2 is not clear to me from the diagram how that’s a drawing of a parallel setup. I’m just not getting where the 4 poles are when it shows 2 connections to the breaker, just like in the unlabeled 2 Pole version and the top? And then Max Number of Strings is 1 for all of them anyway..

Click to expand...

You need to define string voltage, amperage and series/parallel.

That decides what IMO is needed. You read the guide? https://downloads.imopc.com/solar-isolator-selection-guide.pdf

AC/DC said:

I’ll be running 3S2P, the top “2 Poles” versions should be fine right? I’d just like to understand what I’m looking at in those diagrams, what I’m missing.

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Are you combining strings before the IMO, in the IMO or after the IMO?

That makes a difference. Before the IMO, you need a 2 pole IMO, just a negative and a positive. In the IMO, you need a 4 pole with jumpers in place so both negatives get combined and both positives. After the IMO, you need a 4 pole that keeps both strings separate, 2 negatives and 2 positives.

As for the reason why different offerings with different number of poles, it comes down to voltage (usually limited by SCC) and amperage (possibly limited by SCC but also panel ISC and what AWG wire will be run from point A to point B).

For example, running 2 strings of 10AWG 400 feet to an IMO that will combine those strings into parallel will be cheaper than running 1 string of 8AWG 400 feet. I know, because I've run the figures. Or, maybe the 10AWG strings will be combined after the IMO, so a larger number of poles is needed.

AC/DC said:

if the PV input would be connected on the bottom terminals, the only two available, it would create a short when the switch is thrown on.

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I see what you are seeing! looks like a trap! haha

Of course - that configuration works as a SPST switch, good for 600V. Switch PV+ only.
If you want to switch both PV+ and PV-, remove the red jumper in middle, bottom of picture.

Good news is, IF you connect polarity correctly, it is load-break rated.
(If not, be sure to make a video and post it under Up In Smoke!)

Hedges said:

If you want to switch both PV+ and PV-, remove the red jumper in middle, bottom of picture.

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Then it would be rated to 300v? Correct?

In that picture, how would a person wire that correctly given it has positive and negative clearly marked?
I know that dc is directional and having the arc snuffing bits going in the right direction is critical, but how is this intuitive?

It can still open a 600V string, because it has 4x 150V poles in series.
However, if the PV string had a short to ground near the PV- wire as well as a short to ground on the PV+ output of breaker, it would be trying to open 600V with 2x 150V = 300V and would fail. I guess that is a case of not protecting for a fault before the breaker.

The proper use of polarized breakers isn't very clear once we have sources on both sides, like PV and battery.
Most positive source (PV+) should go to terminal labeled "++", most negative (PV- if breaking both poles, SCC positive input if only breaking one) goes to terminal labeled "-".

Those four poles aren't all labeled, but must alternate between ++ at bottom of picture & -- at top, with ++ at top and -- at bottom. Internally I guess that means they have magnets flipped one way or the other.

We'd rather have non-polarized breakers. There are supposed to be some, but hard to find.

Hedges said:

It can still open a 600V string, because it has 4x 150V poles in series.
However, if the PV string had a short to ground near the PV- wire as well as a short to ground on the PV+ output of breaker, it would be trying to open 600V with 2x 150V = 300V and would fail. I guess that is a case of not protecting for a fault before the breaker.

The proper use of polarized breakers isn't very clear once we have sources on both sides, like PV and battery.
Most positive source (PV+) should go to terminal labeled "++", most negative (PV- if breaking both poles, SCC positive input if only breaking one) goes to terminal labeled "-".

Those four poles aren't all labeled, but must alternate between ++ at bottom of picture & -- at top, with ++ at top and -- at bottom. Internally I guess that means they have magnets flipped one way or the other.

We'd rather have non-polarized breakers. There are supposed to be some, but hard to find.

Click to expand...

Thank you very much for explaining this.

Zwy said:

You need to define string voltage, amperage and series/parallel.

That decides what IMO is needed. You read the guide? https://downloads.imopc.com/solar-isolator-selection-guide.pdf

Click to expand...

Yes I read that. I understand what's needed, but the diagrams and labels in the picture I posted above, which come from this very document, didn't make any sense. The two I notated as #1 & #2 say "4 Poles" but only show two connections. While I'm still a bit fuzzy, I now understand that they do indeed have 4 poles, but 2 poles are used for each polarity to handle the labeled "Higher Current/Amperage"

Zwy said:

Are you combining strings before the IMO, in the IMO or after the IMO?

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3S2P, Y combined at the panels, ran via 10 AWG. For my panels, this will be ~150V ~22A. Once 6000XP is ordered and received, it will go to 6S which will be ~300V ~11A. I would like to wire it now for the end result of ~300V ~11A, even though it will potentially be ~150V ~22A for a number of months.

Zwy said:

That makes a difference. Before the IMO, you need a 2 pole IMO, just a negative and a positive. In the IMO, you need a 4 pole with jumpers in place so both negatives get combined and both positives. After the IMO, you need a 4 pole that keeps both strings separate, 2 negatives and 2 positives.

Click to expand...

I'm a little confused, I would like to keep the disconnect at a minimum, a safe minimum. While I am not treating my project's voltage and amperage with disrespect, it seems like a rather simple setup from my time reading this forum, reddit, and other places over the past couple of months. Do I really need two layers of IMOs? I was gonna start with this:
the 1000V/30A version which is DC-only and lists "Internal Spatial: Bigger" as one of its differentiators from the lower rated and combo AC/DC version.

The IMO was just an option someone mentioned (and it looks fantastic). I was just not understanding their diagrams and logic for the "4 Poles" versions which only handle "1 String Max."

Zwy said:

For example, running 2 strings of 10AWG 400 feet to an IMO that will combine those strings into parallel will be cheaper than running 1 string of 8AWG 400 feet.

Click to expand...

Great tip, thanks!

Hedges said:

Of course - that configuration works as a SPST switch, good for 600V. Switch PV+ only.
If you want to switch both PV+ and PV-, remove the red jumper in middle, bottom of picture.

Click to expand...

So in the picture as shown, it is for a single wire coming in, and you'd use an identical switch for the other polarity? One entire switch as pictured for positive, and a separate entire unit for negative? And if you didn't want to go that entire distance, you simply remove the middle jumper and get two switches? The outputs would then be right next to eachother, if removing the red jumper in the middle which is on the bottom is the way you'd accomplish having the ability to handle both polarities coming in from your single string. This doesn't seem like the greatest idea.

I will have 3S2P with roughly 150V & 22A, and probably once the 6000XP is ordered and delivered, 6S for 300V 11A. While I'm all for safety, it seems like an extreme to get such a large switch for each polarity — but I will if that's what's needed.

Hedges said:

Good news is, IF you connect polarity correctly, it is load-break rated.
(If not, be sure to make a video and post it under Up In Smoke!)

Click to expand...

So you can throw it while it's under load? How would you normally do it with a non-load-break rated switch, try to turn the load off first? What if it's an emergency vs a planned disconnect, are you SOL with a non-load-break rated switch?

AC/DC said:

are you SOL with a non-load-break rated switch?

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No, you start praying and then grab your insulated gloves, goggles, and a large scissors like object before you switch the breaker.

AC/DC said:

So in the picture as shown, it is for a single wire coming in, and you'd use an identical switch for the other polarity? One entire switch as pictured for positive, and a separate entire unit for negative? And if you didn't want to go that entire distance, you simply remove the middle jumper and get two switches? The outputs would then be right next to eachother, if removing the red jumper in the middle which is on the bottom is the way you'd accomplish having the ability to handle both polarities coming in from your single string. This doesn't seem like the greatest idea.

Click to expand...

No, single unit with all poles ganged to disconnect PV. This one is good up to 600Voc string.

Another guy needed > 600V for a higher voltage string feeding Fronius GT PV inverters, and I was able to point him to a deal on SMA 1000V fused string combiner/disconnects.

Removing the middle jumper was to have two, 300V disconnects. Those can be used in series for PV+/- of one string rated up to 600V. Or could be used for two 300V strings, opening just one end.

Side by side is OK, there is insulation between them, and "creepage and clearance" distance.

AC/DC said:

I will have 3S2P with roughly 150V & 22A, and probably once the 6000XP is ordered and delivered, 6S for 300V 11A. While I'm all for safety, it seems like an extreme to get such a large switch for each polarity — but I will if that's what's needed.

Click to expand...

For 3s2p, no need for OCP. Can use either breaker or switch.
22A x 1.56 = 34A per NEC for thermal/magnetic OCP.
But those magnetic-hydraulic breakers are rated 100%, don't need to be derated to 80% to avoid nuisance trips.
So I think 22A x 1.25 = 27.5A is sufficient.
Assuming 22A is Isc.

AC/DC said:

So you can throw it while it's under load? How would you normally do it with a non-load-break rated switch, try to turn the load off first? What if it's an emergency vs a planned disconnect, are you SOL with a non-load-break rated switch?

Click to expand...

You can throw these breakers, and suitably rated switches, under load. Although, it is still recommended to turn off the circuit first. For GT PV inverters, that means turning off AC breaker. For SCC or hybrids, there may be other ways to shut down.

Non load break rated includes MC4 connectors and touch-safe fuse holders.
It is a safety hazard, so better to just leave current flowing until sundown unless it is starting a fire. Covering PV array should drop current low enough. Otherwise, you do what you gotta do and try not to get hurt.

Hedges said:

No, single unit with all poles ganged to disconnect PV. This one is good up to 600Voc string.

Another guy needed > 600V for a higher voltage string feeding Fronius GT PV inverters, and I was able to point him to a deal on SMA 1000V fused string combiner/disconnects.

Removing the middle jumper was to have two, 300V disconnects. Those can be used in series for PV+/- of one string rated up to 600V. Or could be used for two 300V strings, opening just one end.

Click to expand...

Soooo, you can open just one end? Duh, why didn't I consider that

Hedges said:

For 3s2p, no need for OCP. Can use either breaker or switch.
22A x 1.56 = 34A per NEC for thermal/magnetic OCP.
But those magnetic-hydraulic breakers are rated 100%, don't need to be derated to 80% to avoid nuisance trips.
So I think 22A x 1.25 = 27.5A is sufficient.
Assuming 22A is Isc.

Click to expand...

Yes, it is Isc, my panels are 45.2Voc & 11.02 Isc. I will be using this device which is rated 1000V/30A and is DC-only. Do you see any issue with doing so? It does come with MC4s, but I'm well under 30A for the connectors.

Will I have to change anything when it's switched from 3S2P to 6S and 150Voc/11A Isc becomes 300Voc/22A Isc?

Hedges said:

You can throw these breakers, and suitably rated switches, under load. Although, it is still recommended to turn off the circuit first. For GT PV inverters, that means turning off AC breaker. For SCC or hybrids, there may be other ways to shut down.

Click to expand...

Very good info. The device I will be using is able to be thrown under load correct? I will of course avoid that as much as possible (read: only not stop load first in case of emergency).

Hedges said:

Non load break rated includes MC4 connectors and touch-safe fuse holders.
It is a safety hazard, so better to just leave current flowing until sundown unless it is starting a fire. Covering PV array should drop current low enough. Otherwise, you do what you gotta do and try not to get hurt.

Click to expand...

Great to know. But if I do have the device above, I would just throw it first, right?

The Dihool looks from its label ratings like it is good. 1000V, probably means 500V/pole. Non-polarized the listing says. Never trust what retailer writes in ad, get spec sheet. But I think this is from the Dihool store.

Should be fine to use for load-break. But the suggestion is to always shut down equipment with commands or AC breakers if possible.

The Midnight breakers are also rated for load-break.

150V, 300V, 600V and 11A, 22A all fit within ratings of these devices.

Opening one end stops the current flow, but I want both ends of PV string disconnected before I grab wires. Also want capacitors discharged, and power sources to equipment disconnected. Confirm zero AC volts as well as zero DC, some superimpose AC on PV +/-.

I got shocked from an inverter chassis after I disconnected the battery. With no load capacitors kept AC output running for a while. Thrice bitten, quite shy.


(That time was only twice, read on for more.)

AC/DC said:

3S2P, Y combined at the panels, ran via 10 AWG. For my panels, this will be ~150V ~22A. Once 6000XP is ordered and received, it will go to 6S which will be ~300V ~11A. I would like to wire it now for the end result of ~300V ~11A, even though it will potentially be ~150V ~22A for a number of months.

Click to expand...

Distance? The best way to wire any PV string is higher voltage/less amps. SCC should be chosen based upon this concept. I run 420 feet one way distance with higher string voltage.

AC/DC said:

I'm a little confused, I would like to keep the disconnect at a minimum, a safe minimum. While I am not treating my project's voltage and amperage with disrespect, it seems like a rather simple setup from my time reading this forum, reddit, and other places over the past couple of months. Do I really need two layers of IMOs? I was gonna start with this:

Amazon.com

www.amazon.com

the 1000V/30A version which is DC-only and lists "Internal Spatial: Bigger" as one of its differentiators from the lower rated and combo AC/DC version.

The IMO was just an option someone mentioned (and it looks fantastic). I was just not understanding their diagrams and logic for the "4 Poles" versions which only handle "1 String Max."

Click to expand...

I mentioned it.

I use an IMO at each end so PV power can be cut away from the SCC's or at the SCC's. IMO also has a lockout feature. If you do not have line of sight to a disconnect, then you either employ a lockout lock or use a pair of switches- one at each end.

Much easier to design with 2 before construction than to add another later.

AC/DC said:

Great tip, thanks!

Click to expand...

AC/DC said:

So in the picture as shown, it is for a single wire coming in, and you'd use an identical switch for the other polarity? One entire switch as pictured for positive, and a separate entire unit for negative? And if you didn't want to go that entire distance, you simply remove the middle jumper and get two switches? The outputs would then be right next to eachother, if removing the red jumper in the middle which is on the bottom is the way you'd accomplish having the ability to handle both polarities coming in from your single string. This doesn't seem like the greatest idea.

I will have 3S2P with roughly 150V & 22A, and probably once the 6000XP is ordered and delivered, 6S for 300V 11A. While I'm all for safety, it seems like an extreme to get such a large switch for each polarity — but I will if that's what's needed.

Click to expand...

Most likely you will add more PV at a later date, planning now allows more to be added later at a minimum expense and effort.

AC/DC said:

So you can throw it while it's under load? How would you normally do it with a non-load-break rated switch, try to turn the load off first? What if it's an emergency vs a planned disconnect, are you SOL with a non-load-break rated switch?

Click to expand...

I recommend using a proper load rated switch, otherwise keep a pair of long handled wire cutters handy so you can cut the wire when the switch fails. DC is not easy to break, especially at higher voltages.

What Class-T fuse do you guys recommend? I'm going by a basic formula I saw on the forum (thanks @John Frum!), starting with inverter and working backwards:

3000W max continuous / .85 conversion factor / 20V low cutoff = 176.5A service amps
176.5A / .8 fuse headroom = 220.6A fault amps

So looking for a 250A. Interestingly, when I will move to 48V + 6000XP, calculation will look exactly the same as I double the Watts but also double the low voltage cutoff:
6000W max continuous / .85 conversion factor / 40V low cutoff / .8 = 220.6A fault amps

So this battery should be good with a 250A Class-T — this battery is becoming 51.2V 150Ah with the addition of two more units, it is currently 25.6V 150Ah battery comprised of two 12.8V 150Ah units.

I'm having a tough time location one on Amazon, some say they meet the specs (AC/DC) but the pictures fuse only lists AC — is this okay in a Class-T?

I would multiply by an additional 1.12x for "Ripple Factor".
Current coming from battery isn't the DC average power, it is rectified 60 Hz ripple.
Mean average current at 20V or 24V delivers power to inverter, but RMS average current heats the fuse and wires, and that is up to 12% higher.

The Bussman and other name brand fuses we use do have DC ratings, and AIC is 20kA vs. 200kA for AC.
Blue Sea and others resell brand names.

Hedges said:

I would multiply by an additional 1.12x for "Ripple Factor".
Current coming from battery isn't the DC average power, it is rectified 60 Hz ripple.
Mean average current at 20V or 24V delivers power to inverter, but RMS average current heats the fuse and wires, and that is up to 12% higher.

Click to expand...

Got it. 250A seems to still cover my use case with the additional +12%, which would put me at ~247A.

Hedges said:

The Bussman and other name brand fuses we use do have DC ratings, and AIC is 20kA vs. 200kA for AC.
Blue Sea and others resell brand names.

Click to expand...

Would something like this work?
Do I need a holder? Holders seem to be more expensive than the fuse.

What about something like this to kill 2 birds with one stone?
It lists an AIC of 50k @ 125VDC — not sure about reaction time?

Yes, that looks like the right fuse for your application. (Be sure to use a battery cable with at least 250A ampacity.)

Two reasons for fuse holders. One, avoid wire whipping and shorting to something while disconnected. Careful location and length should minimize risk. Another is in case fuse comes apart (but don't think it will within specs. Also easier to work a wrench, without shorting anything, if mounted.

Here's a nice fuse holder with clips to secure cover (I got snap-on cover, difficult to get of.) Costs as much as some small inverters.


Yes, the Midnight/Carling breakers are good too. And they serve as a disconnect.
Fuses are the ultimate in reliability, but especially with its higher AIC rating the breaker should be fine.


Lithium battery? Consider precharge circuit across terminals of breaker.
Figure out how you will mount it. Meant to be panel mount with two screws. Could bolt to an insulator after attaching cables, or across a pair of busbars.

Got it, thanks.

Hedges said:

Lithium battery? Consider precharge circuit across terminals of breaker.

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Where can I get more info on building something like this? I'm using a resistor as seen in Will's videos, but I see what you mean, if you manually trip the breaker, then turn it back on, you can experience the dreaded inrush.

At this pace I don't think I'll ever get my system up, there's so much to do And I'll probably run out of $ soon, too