Design questions for a solar system

Firetodd

Solar Enthusiast
Joined
Aug 24, 2020
Messages
147
Location
Arvada, CO
I ordered the LV6548 from Ian at watts247.com on Sunday and it shipped on Monday. As I was typing, Fedex just dropped it off!
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
7,943
Location
Somewhere South of Denver
Fusing for more than two parallel strings is a gray area for me since I don't have parallel strings. Almost every source on fusing PV says no fuse is required when two strings are involved. If you use three or more strings then fusing is required.

According to the article below, the fuse formula would be this. But only for three or more strings.
Imax = (ISC1 + ISC2 + ISC3 + ... + ISCn) x 1.25

 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
My family are avid campers who spend 50-60 days per summer at a lake. Our land at the lake has no facilities and so we “boondock” for 4-6 days at a time and generally have used portable generators. Our power needs are small as we rarely if ever have used air conditioning. We can swim or boat to cool down and entertainment can be found in front of a campfire!


I am getting a new 5th wheel camper and want to go solar to limit or even eliminate the need to fire up portable generators (the lake has rules against generators after 10pm too). The 5th wheel RV will come with a 50 watt solar panel on the roof, connected to a solar port, and run down to a cheap charge controller in the battery compartment. I plan on discarding the 50 watt panel and charge controller and putting in my own system. My hope is that the wires from the solar port are 10-12 gauge at the minimum. The RV has a 50 amp power cord….


So I have looked at a million systems and watched every video on youtube and am struggling to decide on exactly what to do. I had pretty much decided on going with a Growatt SPF3000 24V all in one, with two 24V-A123 LifePO4 batteries from bigbattery.com with 240ah of storage, and (6) 310 watt panels from santansolar.com wired in 3s2p. As the storage compartment and electrical systems are not remotely near each other, I was planning on placing the batteries and Growatt unit in the compartment and wire the AC output of the Growatt to a new boxed 50 amp outlet in the compartment. Then when I arrived at the lake, I will take the shore power cord from the RV and plug it into the outlet. I understand it would be under powered, but I really only need it to power some tvs, charge phones, and charge the separate house batteries. As I don’t use A/C, that system should allow me to eliminate the need to fire up a generator for the most part and to flip on a TV at night. But that system with shipping would be about $5000 with wiring, Victron Bluetooth shunt, and materials.


Then I went down the rabbit hole of building my own batteries. I had watched Will Prowse and others build their own LifePO4 batteries by ordering cells and a BMS and decided that I could do that! So I looked at 280 AH cells and thought that I should buy 16 cells and matching BMS unit and depending on pricing and time of shipping from Alibaba, I could cut my battery prices down $600 and increase storage to 280ah! But I worried that I’d get grade B cells or make a mistake and burn down the whole thing, plus I would need to spend money on power supplies and materials to balance and charge the units and build enclosures. So I may be back to looking at the Big Battery premade units, although I ‘m not sold on the Anderson connectors…


And then I saw the MPP LV6548. It can provide more than twice the power of the Growatt unit and provide power from solar panels even without any batteries connected! If I were to wire the two 24V-A123 LifePO4 batteries from bigbattery.com in series for 48V, I would have 120 ah of storage. The larger MPP LV6548 would also allow me to wire my panels in a 6s configuration as well. Having more power available would be nice for two reasons. One, not having the noise of a generator is nice, but even if I do this system, my in-laws will still need to fire one up to power their camper to watch tv at night in their camper. Having more power will allow me to run an extension cord to them as well. The Second reason the MPP LV 6548 appeals to me is that because the charge controller in it allows up to 250V input, I can run the solar panels in series and lower the amperage on those unknown solar wires routed down from the roof. Total price for this system is $5600.

Here are the panels: https://store.santansolar.com/product/csun-310w/

Here is the MPP LV6548 all in one: https://watts247.com/product/2-x-lv...kw-250v-mppt-bms-ul1741-listed-built-in-wifi/

Here are the batteries: https://bigbattery.com/products/24v-a123-8s5p-lifepo4-battery-box-3/

RV outlet: https://www.amazon.com/GE-Unmetered-Circuit-Protected-Receptacles/dp/B00FI6TKK2/ref=sr_1_36

My RV: https://www.rvwholesalers.com/desig...fth+wheel&brand=heritage+glen&floorplan=378fl



What do you think? Base it on a 3kw 48v system which is a standard 30amp RV system. 16 Lifepo4 3.2v 280ah cells, BMS, 8x200w 12V 4s2p panels (dont put residential panels on an RV)
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
My family are avid campers who spend 50-60 days per summer at a lake. Our land at the lake has no facilities and so we “boondock” for 4-6 days at a time and generally have used portable generators. Our power needs are small as we rarely if ever have used air conditioning. We can swim or boat to cool down and entertainment can be found in front of a campfire!


I am getting a new 5th wheel camper and want to go solar to limit or even eliminate the need to fire up portable generators (the lake has rules against generators after 10pm too). The 5th wheel RV will come with a 50 watt solar panel on the roof, connected to a solar port, and run down to a cheap charge controller in the battery compartment. I plan on discarding the 50 watt panel and charge controller and putting in my own system. My hope is that the wires from the solar port are 10-12 gauge at the minimum. The RV has a 50 amp power cord….


So I have looked at a million systems and watched every video on youtube and am struggling to decide on exactly what to do. I had pretty much decided on going with a Growatt SPF3000 24V all in one, with two 24V-A123 LifePO4 batteries from bigbattery.com with 240ah of storage, and (6) 310 watt panels from santansolar.com wired in 3s2p. As the storage compartment and electrical systems are not remotely near each other, I was planning on placing the batteries and Growatt unit in the compartment and wire the AC output of the Growatt to a new boxed 50 amp outlet in the compartment. Then when I arrived at the lake, I will take the shore power cord from the RV and plug it into the outlet. I understand it would be under powered, but I really only need it to power some tvs, charge phones, and charge the separate house batteries. As I don’t use A/C, that system should allow me to eliminate the need to fire up a generator for the most part and to flip on a TV at night. But that system with shipping would be about $5000 with wiring, Victron Bluetooth shunt, and materials.


Then I went down the rabbit hole of building my own batteries. I had watched Will Prowse and others build their own LifePO4 batteries by ordering cells and a BMS and decided that I could do that! So I looked at 280 AH cells and thought that I should buy 16 cells and matching BMS unit and depending on pricing and time of shipping from Alibaba, I could cut my battery prices down $600 and increase storage to 280ah! But I worried that I’d get grade B cells or make a mistake and burn down the whole thing, plus I would need to spend money on power supplies and materials to balance and charge the units and build enclosures. So I may be back to looking at the Big Battery premade units, although I ‘m not sold on the Anderson connectors…


And then I saw the MPP LV6548. It can provide more than twice the power of the Growatt unit and provide power from solar panels even without any batteries connected! If I were to wire the two 24V-A123 LifePO4 batteries from bigbattery.com in series for 48V, I would have 120 ah of storage. The larger MPP LV6548 would also allow me to wire my panels in a 6s configuration as well. Having more power available would be nice for two reasons. One, not having the noise of a generator is nice, but even if I do this system, my in-laws will still need to fire one up to power their camper to watch tv at night in their camper. Having more power will allow me to run an extension cord to them as well. The Second reason the MPP LV 6548 appeals to me is that because the charge controller in it allows up to 250V input, I can run the solar panels in series and lower the amperage on those unknown solar wires routed down from the roof. Total price for this system is $5600.

Here are the panels: https://store.santansolar.com/product/csun-310w/

Here is the MPP LV6548 all in one: https://watts247.com/product/2-x-lv...kw-250v-mppt-bms-ul1741-listed-built-in-wifi/

Here are the batteries: https://bigbattery.com/products/24v-a123-8s5p-lifepo4-battery-box-3/

RV outlet: https://www.amazon.com/GE-Unmetered-Circuit-Protected-Receptacles/dp/B00FI6TKK2/ref=sr_1_36

My RV: https://www.rvwholesalers.com/desig...fth+wheel&brand=heritage+glen&floorplan=378fl



What do you think?
Get the Eve 280ah 3.2v cells, no-brainer. Grade B will still last thousands of cycles. I got 16 cells including taxes, shipping and duty for $1800.
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
Weird how that happened...I was suggesting he get the lifepo4 Basen cells and go 48V. Nothing wrong with grade B cells for $80 usd.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
11,561
Fusing for more than two parallel strings is a gray area for me since I don't have parallel strings. Almost every source on fusing PV says no fuse is required when two strings are involved. If you use three or more strings then fusing is required.

According to the article below, the fuse formula would be this. But only for three or more strings.
Imax = (ISC1 + ISC2 + ISC3 + ... + ISCn) x 1.25


That's the equation the paper gives to compute Imax, not fuse size. It goes on to say an additional x 1.25 to determine minimum fuse size.

But with 3 or more strings, each should have a fuse. String #1 has ISC1, so should have fuse ISC1 x 1.25 x 1.25 which is ISC1 x 1.56
With fuse or breaker per string, you don't need another one for the home run wire carrying combined current. It just needs sufficient ampacity.
 

Firetodd

Solar Enthusiast
Joined
Aug 24, 2020
Messages
147
Location
Arvada, CO
That's the equation the paper gives to compute Imax, not fuse size. It goes on to say an additional x 1.25 to determine minimum fuse size.

But with 3 or more strings, each should have a fuse. String #1 has ISC1, so should have fuse ISC1 x 1.25 x 1.25 which is ISC1 x 1.56
With fuse or breaker per string, you don't need another one for the home run wire carrying combined current. It just needs sufficient ampacity.
I ended up getting an overkill 16s BMS and ordering 16 280ah cells from Micheal Caro. Cells have been a little delayed but I may be getting them soon. My new camper gets here next week. And the it’s install time!
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
I ended up getting an overkill 16s BMS and ordering 16 280ah cells from Micheal Caro. Cells have been a little delayed but I may be getting them soon. My new camper gets here next week. And the it’s install time!
Good call on the cells...I can tell you're excited...lol. I came up with an interesting way to mount them in an 8x2 pattern using a ratchet strap for tension and a "floating wall" box design.
 

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Firetodd

Solar Enthusiast
Joined
Aug 24, 2020
Messages
147
Location
Arvada, CO
Good call on the cells...I can tell you're excited...lol. I came up with an interesting way to mount them in an 8x2 pattern using a ratchet strap for tension and a "floating wall" box design.
I’ve been looking at lots of battery box designs. Your box looks very nice!
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
I’ve been looking at lots of battery box designs. Your box looks very nice!
The back and base are bolted to the RV with a channel on the back for the ratchet strap to slide, the front and sides are floating also with channels for the ratchet strap. What cool is you can compress for travel, and loosen to take the cells out!
 

Boondock Saint

Solar Addict
Joined
Apr 8, 2021
Messages
658
I came up with an interesting way to mount them in an 8x2 pattern using a ratchet strap for tension and a "floating wall" box design.
It took me forever to re find your post and pic. I've been interested in doing this floating style too, but with a 2P16S bank that has to be placed together in two 200lb pieces then re-strapped.

My concern is the weight of the 3/4" plywood and the heat of the batteries, not being able to breath.

Have you made any modifications to this design since you made this post?

I'm thinking more of a tray with a lip around the bottom to hold the cells in place, and a straps(s) going around two end pieces like yours.

I think a snug 2P16S placement in a lip is not going to HOP out, the lip keeps all the cells perfectly aligned without the need for a full wall.

Tension would be "tight enough" which is how mine are in a long parallel string and I have no deformation or expansion at all.



.
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
Go 48V if you can. Even with 24v the inverter/charge controller supplies your panel with 120v which feeds/charges your 12v system. No need for transformers. All in ones are great growatt/mpp etc. For batteries you cant beat eve 280AH 3.2v cells I have a 16s 48v system and a MPP3048MK-LV with 8x200w panels in 2P4S config, no need for fusing because the string amperage doesnt exceed the max fuse rating of the individual panel. This gives me a 90V 20amp solar feed.
 

Gadgetnerd

Solar Enthusiast
Joined
May 1, 2021
Messages
70
It took me forever to re find your post and pic. I've been interested in doing this floating style too, but with a 2P16S bank that has to be placed together in two 200lb pieces then re-strapped.

My concern is the weight of the 3/4" plywood and the heat of the batteries, not being able to breath.

Have you made any modifications to this design since you made this post?

I'm thinking more of a tray with a lip around the bottom to hold the cells in place, and a straps(s) going around two end pieces like yours.

I think a snug 2P16S placement in a lip is not going to HOP out, the lip keeps all the cells perfectly aligned without the need for a full wall.

Tension would be "tight enough" which is how mine are in a long parallel string and I have no deformation or expansion at all.


Hey Saint you can "vent" the sides if you want but it's a waste of time lifepo4 cells don't "breathe" Havent change my setup, working great. Cheers.
 

Boondock Saint

Solar Addict
Joined
Apr 8, 2021
Messages
658
Your tooo late! Someone already pushed the self destruct button! 🙂

I put together a tray with floating ends and rounded the corners for the straps.

This is the bare wood form of the two pieces and two end-plates.

Each half will hold 2P8S in order to move into place next to the bed pedestal in my RV as indicated.

Both pieces total length is slightly shorter than the length of 16 cells and the insulating material so the plates will cause compression.

It has a generous amount of wood glue and a buttload of nails from both directions holding the footings.

I'm thinking of priming and painting it all gloss black. Except that will really show up the dust bunnies.


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