Is 2P4S like this doable?

[Checkingout]

Hi everyone,
I've been waiting half a year to get all 8 panels delivered from amazon.
Got them on the tiny house roof now.
We have a few days of sun forecast (in rain I won't be on the roof, no).

I am wondering if my want-to-have array connection is doable like this? (image below)
It will be my second array, feeding my tiny house battery bank.
It would allow to stay within the 15A (wiring capacity) and below the 138V (MPPT CC's max is 138 OCV and 40A rated charge current).

b) I am also toying with the idea (wish) to wire the panels in such way that I could, alternatively, charge straight from DC the ebike battery I am going to receive soon (nominal 72V 50Ah, which comes with 87V 10A charger). For longevity, I want to limit charging voltage of this battery to 86.4V MAX (the 15A charge current, if so, would not be a problem at all, it can handle far more). Though, no one online (not here, not anywhere) seems to be successfully charging his EV battery straight from solar... (yet!). Maybe it's not sensible with EV....

Image of roof panel wiring idea:



What do you think of this?

 

[FilterGuy]

If I follow what is being suggested, it looks like this:



That is certainly unconventional.

I think the problem comes in the short circuit scenario. A panel is designed to handle the short circuit of two panels. However if there is a short in one of the panels in the above layout, there would be 2 x Isc + some amount that is going through the SCC. This would be above what the panel can handle and potentially cause a fire hazard.

Is there a reason not to do 4S2P like this:

 

[rodrick]

4s2p only requires 2 branch connectors your way uses 8 also 4s2p doesn’t need fused I think your making it more complicated than need be

 

[timselectric]

Agree with above posts.
You are making it complicated, when it's not necessary.

 

[Checkingout]

Yes, I like FilterGuy 's connection a lot.
The other is not "mine" Rodrick, the question was what you think.

FilterGuy 's connection is beautifully efficient, doesn't need more wiring, needs less connectors, maybe not even a fuse, and most importantly, it stays within the design needs, which were stated as <15A and <138V coming into the CC (while it CAN handle 40A, the available roof wiring cannot, plus, 15A keeps it cooler of course, nice).

So, that's a lot of reasons to love FilterGuy 's connection layout. You just documented you ARE a consultant, sir Kudos to you.

Now, I did notice that the idea of charging the EV battery straight from solar, has been overlooked by ya all but I already said it's a difficult topic apparently as I couldn't find it online, anywhere. (2 commercial products, yes, but unsuitable, and not just price-wise).

I hope at some point in future someone here has some ideas/ experience, how to regulate solar input down to a stable voltage (86.4V in my personal case) so as to emulate the Chinese AC>DC charger that comes with the EV battery (a standard cheap off-the-Chinese-shelf "plastic charger" - the vendor actually called it that! )

Better even (for EV charging) if the solar-charging solution would be another level up in "smart charging" by offering to limit SOC as a setting (it degrades the cells if charged to 100% SOC but isn't being used soon).

Most importantly though: The solar-charging solution should be safe for the battery (no risks like SCC, OV). While OC (over current) wouldn't be a risk in most any solar - to - EV battery scenario, those batteries can handle far more charge current than our solar arrays can produce.

By the way, I was able to order that biggie (Lifepo4 50Ah ~80V actual V) for just $700, incl. metal box, capacity display, 100A bluetooth JBD BMS, 0.7ohm resistance cells, 10A charger, and incl. delivery even. I find this is a bargain. It looks like so, if you're interested, it's tailor-made for my needs:



It will be used with a Fardriver 72360 controller.

If I follow what is being suggested, it looks like this:

View attachment 183538

That is certainly unconventional.

I think the problem comes in the short circuit scenario. A panel is designed to handle the short circuit of two panels. However if there is a short in one of the panels in the above layout, there would be 2 x Isc + some amount that is going through the SCC. This would be above what the panel can handle and potentially cause a fire hazard.

Is there a reason not to do 4S2P like this:

View attachment 183545

 

[FilterGuy]

Now, I did notice that the idea of charging the EV battery straight from solar, has been overlooked by ya all but I already said it's a difficult topic apparently as I couldn't find it online, anywhere. (2 commercial products, yes, but unsuitable, and not just price-wise).

I noticed it but I did not have anything to add that would help your search. The way most DIYers are doing it now is using the Inverter AC to charge the EV. A system that did not convert from DC to AC and back to DC would have the potential to be significantly more efficient. However, most folks will not have a PV array dedicated to charging the car so direct PV to EV chargers would be a bit of a niche product.

 

[timselectric]

I also believe that dedicating solar power to just one thing is a waste of potential production. It is not something that I would ever recommend.

 

[Checkingout]

I noticed it but I did not have anything to add that would help your search. The way most DIYers are doing it now is using the Inverter AC to charge the EV. A system that did not convert from DC to AC and back to DC would have the potential to be significantly more efficient. However, most folks will not have a PV array dedicated to charging the car so direct PV to EV chargers would be a bit of a niche product.

" A system that did not convert from DC to AC and back to DC would have the potential to be significantly more efficient. "
This bit is exactly my point, yes FilterGuy!

I'd like to refrain from converting my solar input DC to Inverter AC, and back to Bike battery DC.

"

most folks will not have a PV array dedicated to charging the car so direct PV to EV chargers would be a bit of a niche product."

For EV as in CAR, I would agree with you.
For EV as in motorbike like mentioned in my case (or the millions who have a "scooter" of various design types and performance) I would argue, this SOLAR > EV Battery straight solution would be selling like Ferrero Roche (or better even).

For the very reason that you too identified: "A system that did not convert from DC to AC and back to DC would have the potential to be significantly more efficient."

 

[Checkingout]

I also believe that dedicating solar power to just one thing is a waste of potential production. It is not something that I would ever recommend.

Who said such?
Not me.
Not FilterGuy.

We believe in "or alternatively switching it to charging the EV battery, at will".
Ideally, smart charging (fixed current, fixed voltage, SOC charge limit, ....).

Technically easy. Hence why I am surprised why I cannot find online people who have been documenting the use of such, YET.

 

[timselectric]

Who said such?
Not me.
Not FilterGuy.

We believe in "or alternatively switching it to charging the EV battery, at will".
Ideally, smart charging (fixed current, fixed voltage, SOC charge limit, ....).

Technically easy. Hence why I am surprised why I cannot find online people who have been documenting the use of such, YET.

Good luck with that.

 

[FilterGuy]

Switching PV circuits can get expensive because we are dealing with high-voltage DC. Switching high-voltage DC is very prone to arc problems so the switch needs to have arc snubbing built in, and that starts to get expensive.

A good compromise might be to do a DC-DC charger from the main battery bank to the scooter. This would not be quite as efficient as if the PV energy was directly converted to the scooter charge profile, but the loss through the 2nd converter should not be too bad.

 

[Checkingout]

Switching PV circuits can get expensive because we are dealing with high-voltage DC. Switching high-voltage DC is very prone to arc problems so the switch needs to have arc snubbing built in, and that starts to get expensive.

A good compromise might be to do a DC-DC charger from the main battery bank to the scooter. This would not be quite as efficient as if the PV energy was directly converted to the scooter charge profile, but the loss through the 2nd converter should not be too bad.

Excellent again FilterGuy
I agree with the loss ratio also. An inverter is far worse than a DC-DC converter.
But: Have you used one, or found one, that reliably converts from nominal 25.6V Lifepo4 (actual most times ~26V) UP to 86.4V?

In my (very limited) experience such BOOST converters involve more problems (and conversion losses also) than BUCK converters. Taking 26V up to 86V reliably is not an easy feat, or what would you all say?

 

[Checkingout]

Oh FilterGuy, are MC4 inline fuses recommended here?

 

[timselectric]

Oh FilterGuy, are MC4 inline fuses recommended here?

View attachment 183656

I believe that he is still asleep.
With only two strings, fuses are not required or recommended.

 

[FilterGuy]

Have you used one, or found one, that reliably converts from nominal 25.6V Lifepo4 (actual most times ~26V) UP to 86.4V?

Sorry, I am not aware of anything like that.

Oh FilterGuy, are MC4 inline fuses recommended here?

For two strings, fuses are not required.

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

However, there should be a disconnect before the charge controller

 

[FilterGuy]

I believe that he is still asleep.

Yup.... I was

 

[Checkingout]

I believe that he is still asleep.
With only two strings, fuses are not required or recommended.

Excellent, both of you.

Sorry, I am not aware of anything like that.


For two strings, fuses are not required.

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

However, there should be a disconnect before the charge controller

Absolutely yes. I run everything I have through two breaker boxes (one AC, one DC, I wired my house for dual use), and the small stuff through a fuse box.
Utility box explained:


"

I believe that he is still asleep.

Yup.... I was"

The early bird catches the worm. - But then: Who would want a worm for breakfast?

 

[Checkingout]

Excellent, both of you.



Absolutely yes. I run everything I have through two breaker boxes (one AC, one DC, I wired my house for dual use), and the small stuff through a fuse box.
Utility box explained:
View attachment 183752

"

Yup.... I was"

The early bird catches the worm. - But then: Who would want a worm for breakfast?

Now I was just wondering if solar panels in series can be wired "mid-point" like so?
As opposed to how you showed?
It would reduce my cable and conduit needs

 

[timselectric]

Yup.... I was"

The early bird catches the worm. - But then: Who would want a worm for breakfast?

He's 5 hours behind me. And it was early here. lol

 

[timselectric]

Now I was just wondering if solar panels in series can be wired "mid-point" like so?
As opposed to how you showed?
It would reduce my cable and conduit needs

View attachment 183755

I'm not sure I understand what you are trying to do.
If you have two groups of 4 panels in different places.
Put one string (top row) in one place. And the other (bottom row)in the other place.