diy solar

diy solar

DIY 24-volt 560Ah LiFePO4 battery (272x2=544Ah) with Electrodacus SBMS0 and Electrodacus DSSR20

2 more 500amp 50 MV shunts (Deltec) ready & attached to 4/0 copper cables with crimped Selterm lugs. An upgrade for redundant system.
should have sense wiring in a few days.
class t fuses for each inverter on the positive cable. ?
used wood spacer blocks to get the Deltec shunts in the same plane as the large busbar. I have about 90 extra red insulator and black insulator busbars. I ordered 100 of them.
 

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February 13th, 2021 update:
2nd 24volt 2P8S battery charged with second Electrodacus SBMS0. used 2 south-facing 250-watt 60 cell PV panels and 2 west-facing 250-watt 60 cell polycrystalline PV panels (in parallel of course). 2 Electrodacus DSSR20 --- one for each pair of panels.
the DSSR20 is the solar charger --- they work great.
had to rearrange shunts and cables a bit to make it fit. used all 4/0 cables for the second battery. and had to seek out solid strand cat 5 24awg cable yesterday for the sense wires. lots of new connections today.
272Ah x16cells x 3.2 volts per cell = 13,926.4 watts per battery; so now have 2 working. waiting on the second inverter for the redundant system.
maybe I will try a 3P8S on the next battery for 272 x 3 = 816Ah 24-volt battery 24 cells would be 272Ah x24cells x3.2volt/cell = 20,889.6 watt-hour battery potential.
solar PV trickle charger works great -----????!
 

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you will want to get double the bus bars to top balance in parallel. I bought some 6 gauge lugs with 1/4 inch holes to make cable interconnects so I can balance more cells. my Lishen cells came with 4 busbars per 4 cells. also if you get the 6mm diameter x 20mm long set screws/ aka grub screws with flange nuts that is the way to go.
my 1st 32 Lishen 272Ah cells came with 16mm long grub screws and flange nuts. the 16mm is not long enough for some connections so you want 20 mm long ones. the second set of 32 Lishen 272Ah cells came with bolts and washers.--- they did not fit good or tighten well -- I replaced all of those bolts with 20mm x 6mm grub screws. you will find that the grub screws sticking up are better for mounting the busbar interconnects together with fewer problems of accidental arc-ing between cells. do not over tighten the set screws!!!!!! snug them down carefully -- they are only 6mm which is 1/4 inch approximately and you will hate yourself if you strip one out. I plan to use lock-tite on the threads also.
Where did you get the 20mm M6 Grub screws and bus bars from?
 
Where did you get the 20mm M6 Grub screws and bus bars from?

Here:



 
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Where did you get the 20mm M6 Grub screws and bus bars from?
I bought mine on amazon. 100 pieces for the 20mm long x 6mm diameter grub screws with a 3mm hex key needed to tighten them. 100 cost 12.80 with free prime delivery the brand is Sscon --- This item Sscon 100 PCS M6 x 20mm Grub Screws 201 Stainless Steel Hex Allen Head Socket Set Screw Bolts. the copper bus bar I bought a 1/4" x 3/4" x 6-foot piece solid copper bus bar from online metals also on amazon but w/o free shipping and a bit expensive at about 83 dollars with delivery and tax.
 
10:51 AM (2 minutes ago)

how to keep you batteries above freezing:
I use a 250-watt heat lamp bulb to heat my 8-foot x 8-foot x 8-foot (512 cubic feet) insulated solar power shed. today February 15th, 2021; it is 25 degrees below zero Fahrenheit. I do not have any thermostat control at this time. it is 57 degrees inside right now so this is the ultimate test for cold temperature. I think insulating your battery space would be the 1st thing to do and then use an incandescent light bulb is likely the most inexpensive option. for 64 cells I would need 64 heating mats at 4 dollars each = 256 dollars plus thermostatic controllers. the light bulb in the well pit in the winter to keep things from freezing is still the most economical method (that is how we kept the well from freezing when I was growing up). the heat lamp bulb is running on the solar electricity generated from the PV panels. which charges a 16 cell Lishen 272Ah per cell battery 2P8S configuration at 24 volts. presently 4 260 watt panels facing south connected to 2 Electrodacus DSSR20's via the Electrodacus SBMS0. I have the 24-volt inverter running 24/7 for the light bulb etc as I build assemble inside the solar power shed. I also use some dc directly connected to the battery lights some but only the heat lamp bulb and 3 dc direct connected light bulbs used overnight to keep it at a balmy 57 degrees Fahrenheit even though it is 25 degrees below zero outside. just a thought on economics. cheers from South Dakota USA
 
Solar Power Shed:
I built it with 2x6 walls floor and roof. I used 5/8 plywood sheathing on the outside and 3/4 plywood floor. I used precut Fiberglas batts with the paper backing and stapled in place on inside walls and ceilings. I sheetrocked with 1/2 inch sheetrock on inside ceiling walls and ceiling. I installed a 36-inch prehung entry door. have a storm door but not yet installed. I put 2x4 purlins flat on the outside and then used a solid insulation board between the 2x4s on 16-inch spacings. oh, I also used black tar paper on the outside and covered all plywood with the black 30-pound roofing felt. the 2x4 purlins/laid flat on the outside allowed me to have a good solid place to screw down the final layer of white sheet steel. it is 38 inches wide but covers 36 inches when overlapped correctly. I used plenty of caulk in places until each layer was completed. I am a little slow when working by myself. On the inside, I put 2 layers of the solid insulation board on top of the 3/4 inch plywood floor and then covered that with 5/8 inch plywood. I have insulation for underneath the building 6-inch fiberglass but have not put that in yet.
so essentially 6-inch walls with another inch of Celotex/iso-urethane type insulation on the outside. I got it (the rigid board insulation)second hand from a roofing company for about 2 dollars per sheet to cut up to insulate some projects.
I like the white steel 36/38 inch steel siding mounted vertically as I have some I installed 32 years ago that still looks like new.
I still like paint for good wood siding but hard to beat the durability of the white steel siding.
insulation is the key to energy conservation. insulation has the fastest payback for the long term.

I used construction screws (get the Torx type - star 6-point screws) for all the wood assembly, and used the rubber washer screws for the steel insulation. makes a good secure rodent and weatherproof building. I will insulate the floor from underneath after all the wires are installed and the weather is a bit more human tolerable.
thanks for asking.
This is a stationary build and a major concern was protecting the batteries from freezing and using the BMS to not overcharge etc.

t says minus 24 degrees Fahrenheit here this morning at 8 am February 16th, 2021; but it is still 57 degrees inside the solar power shed with one 250 watt heat lamp bulb and 3 dc direct-wired led lights (about 27 watts total for the LEDs). so 280 watts for heat

houses the 64 272Ah cells in 4 batteries (5.3x16x4x2.2=746pound lifepo4) configured to 2P8S each. plus 4 other 200-pound each lifepo4 battery boxes. plus tools workbenches shelves, etc so I can assemble all in any weather. SBMS0's, DSSR20's, AC load centers, inverters etc, wire etc
no lead-acid batteries in here.

the next problem will be keeping it cool in summer heat of June July August. can't wait -- I do not like this cold weather.
 

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the 3 led lights that are wired directly to the LiFePO4 battery #2 show as a 24.7-watt load on the SBMS0 2. I put in a 10 amp breaker in between just for safety and it also works for the on-off switch, so no inverter needed at all for the LED lights. the LED lights have 16 leads each and are rated 24-48 volts. the SBMS0 maybe uses 1 watt if that. the 6000-watt inverter also wastes a few watts and I am leaving it on all the time. I use it to solder and heat shrink cables as I build all on PV-generated solar power. 4 250-watt 60 cell polycrystalline PV panels (used 8-10 years old) on SBMS0 number 1; and 2 250-watt 60 cell polycrystalline PV panels (used 8-10 years old)on SBMS0 number 2 that face south at a 45-degree angle.
too cold to mount more panels...maybe later this week, or early next week?
supposed to get up to 0 degrees Fahrenheit today.... heatwave ya know...???
time to jump in the icy artesian pond --- not!
the otters do but only to rob the fish...
 

Dacian Todea​

Feb 16, 2021, 10:56 AM (21 hours ago)

to electrodacus

Peter,

Sorry but you can not use voltage as an indication for SOC with LiFePO4 not even a rough estimation. The only thing voltage can be used is to say if battery is full or empty and nothing in between.
I think you refer to the graph below that I shown a few times on the forum. You can have the battery at 90% or at 30% SOC and see the same battery voltage (so it will be completely useless to try and guess the SOC).
Answering the question of the charge/discharge rate in that graph will be fairly mining less unless you also know the capacity and internal resistance of the cells (cell resistance also fluctuates significantly with temperature).
The top point on SBMS0 is 3.55V default and SOC will be reset/corrected to 100% on the 2.8V all loads will be stopped so that will be the 0% SOC point but SBMS0 will not make any SOC corrections at 0% SOC so if you did not set the capacity correctly the SOC indication may be 0% before the battery is actually at 2.8V or if you set the capacity higher than it actually is then it will show some higher than zero SOC value even if a cell got to 2.8V and all loads where disconnected so then you can see that value say 10% and correct your real capacity setting as SBMS0 will not do anything to SOC when battery is fully discharged (not to mention that battery will likely never be fully discharged but will almost every day be fully charged).

Yes chargers should be set around 3.55V or slightly more and they should stop when the SBMS0 say so.
Inverter can be set at 2.8V to 2.9V per cell as one cell will always be the first to fully discharge and get to 2.8V while most other cells will still be around 3V
As mentioned the charger will be set at >3.55V for bulk charge and since there will always be a cell to get there first while others will be around 3.4 it is unlikely charger will ever get in to absorption let alone float and even if by any chance it gets in to absorption current will still be higher than cell balancing current so highest cell will continue to increase in voltage and get to 3.55V terminating the charging.
Yes you can set all values to 3.6V as they will have no meaning since SBMS0 will stop the charging.
One charge to 100% per day will not do any harm to battery as that will be considered a light normal use and battery should last 10 to 20 years in normal even heavy duty operation. After that charge battery will not be charged again for 24h if you set a low SOC for recovery. Low enough that the small DC loads you may have do not discharge the battery to in 24h period.

the graph above was in Dacian's explanation and is good information to help all understand the LiFePO4 chemistry and charging. really a big thank you to Dacian for the above information.
 
voltage drop with 10 awg pv wire:
example55 ft of 10 awg pv wire will have a 2.13% voltage drop at 7 amps 36 volts
55 ft of 10 awg pv wire will have 2.41086 percent voltage drop at 8.27 amps 37.6 volts
55 ft of 10 awg pv wire will have 4.82173 percent voltagedrop at 16.54 amps 37.6 volts2 250 watt 60 cell panels in parallel - the amperage doubles to 16.54 amps
4.821% voltage drop
so 37.6 volts - (.04821 x 37.6) = 35.787 volts
60 ft5.25% voltage drop
so 37.6 volts - (.0525 x 37.6) = 35.626 volts
30 ft2.63% voltage drop
so 37.6 volts - (.0263 x 37.6) = 36.61112 volts


 
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so as it is the amps that change the battery --- the 16.54 amps run through 30 feet or 55 feet or 60 feet will still be 36.61112 volts, 35.787 volts, or 35.626 volts and more than adequately charge the 2P8S LifePO4 batteries. the LifePo4 battery is 99 percent at 3.55 volts (3.55X8=28.4 volts) but will likely never get to 28.4 volts but the voltage and amps are greater so it will charge until one cell goes above 3.55 volts for too long of a preset time.
my battery banks get up to 27.2 or a bit more at full charge. 27.2/8=3.4 volts per cell.
the SBMS0 (the BMS) prevents the permanent damage overcharging will cause.
the SBMS0 shuts the DSSR20's off at 100 percent full ie 99% when any cell reaches 3.55volts for too long of a time.
then after using some of the stored power either by inverter loads or in my case I also use direct-wired LED lights as a small load the charging from the DSSR20's will again be started to put more power back into the 2P8S 272Ah Lishen cells (24-volt battery).
this trickle charger works great.

the SBMS0 balances the cells while charging from the used 250-watt polycrystalline 60 cell PV panels wired in sets of 2(parallel) to each DSSR20.
???


 
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right I agree space limitation applies to anyone's decision for sure. 58 dollars divided by 250 watts = 23.2 cents per watt that is what the used 60 cell 250-watt solar panel cost that I purchased in 2020. so a few more solar panels make the most sense to me. I plan to use excess solar production for heat storage and water pumping in the garden etc. if you are limited to an RV roof then real estate mounting space is critical. probably then they could increase the DIY LiFePO4 battery storage. or put in a foldable array to increase the array wattage. and the DSSR20's are less than 37 dollars to control each additional 2 60 or 72 cell panels. newer panels may be more efficient. so in my stationary build, a 37 dollar DSSR20 controls 500 watts and makes a lot more sense than the outback 80 for 453 dollars each.
there are a million ways to do the same thing depending on what solar charge controller one chooses.
i have a set of 4 flexmax 80's but think the sbms0 and DSSR20's are going to outshine the MPPT's in the long haul.
again I am talking the most bang for the buck.
i do not think anyone's way is the only way to go.
the problems arise with compatibility just as the computer industry struggled to make compatible products for years.
the dssr20 is not a PWM or MPPT -- it is a digital solid-state relay --- it functions great as the solar charge controller. I have 5 of them running right now. and 5 more waiting for better weather to connect to more solar panels. it is a balmy 0 degrees Fahrenheit with a wind chill lower than that today. February 17th 2021
space limitation is not an issue to me for this off-grid build on the farm. cheers all ??? from pilgrim valley --- South Dakota USA

the federal solar income tax credit is 26 percent until 2023 is what the internet says for 2020 and 2021 installation in the USA!

Any US taxpayer, business or consumer who commences construction of a solar or solar + storage system before January 1, 2023 is eligible to receive the full 26% solar ITC.
likely the wise investment for anyone with taxable income!

all ground mount but I may rearrange some to make use for shelter for truck or lawn mower or car or other things to get double duty out of the solar panel square footage.
 
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ferrules are good to use on the 10 AWG PV wires connecting the circuit breakers and DSSR20's see attached pictures. I strip the 10 AWG PV wire back about 5/8 of an inch using the Klein catapult wire stripper. it is aptly named catapult as it ejects the wire insulation with a bit of force.
just a tip for those assembling your own system! ?
 

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i also like and used the temco branch connectors as they are easy to use. plug and play to connect 2 250-watt PV solar panels together right at the array location. see the picture below. ?
 

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inverter size --- 6000 watts /24 volts = 250 amps.
so the load through the inverter could max out at 250 amps.
has nothing at all to do with the SBMS0.
no large current goes through the SBMS0.

voltage drop is between 2.63% for a 30 foot run in the dc circuit to the DSSR20, up to 5.25% voltage drop on a 60 foot run using readily avaliable standard 10 AWG PV wire.
so if you are only looking at the 5.25% voltage drop to get the same voltage you would have to add another 250 watt PV panel for every 20 panels installed.
i bought used 250-watt polycrystalline panels for 58 dollars delivered. so 58 divide by 20 = less than 3 dollar efficiency loss on the 60 feet of PV wire run in the dc circuit. insignificant expense in the big picture. less if one uses shorter wire runs to the solar charge controller (DSSR20 is the solar charge controller I am using)
the wire cost is about 30 dollars for every 2 250-watt panels installed for the 10 AWG PV wire.
or 90 dollars for every 6 250-watt panels and 3 DSSR20's at less than 37 dollars each for every 6 panels (1.5Kw array).
no soldering - except I installed a 1-watt fuse inline on the positive side of the DSSR20 to the positive bussbar I think this is standard 20 AWG automotive wire and fuse. if you position it closer then no soldering would be needed at all. a person probably could use crimp connectors but I soldered because I think the wires were not exactly the same AWG that I used there.
I color code and use red PV wire for the positive side and black PV wire for the negative side on all DC wiring. less confusion and easily identify circuits. The Dymo label maker also helps to keep it organized.

Again this is an off-grid DIY solar build. easily done in small increments by almost any handyman or woman.
For me, the most difficult part is installing the 41 pound 250-watt panels onto the array support structures. wish I had a second person for that task.

the LIshen 272Ah cells cost 95.74 dollars per cell delivered. for the 1st 32 that I purchased;
and only cost 90.73 dollars delivered for the second 32 Lishen 272Ah cells I ordered in 2020.

the SBMS0 is the BMS I specifically chose for this 24-volt off-grid DIY build.

Dacian the engineer/designer has been helpful whenever I asked him any questions. so personally I like the service after the sale and the functionality of the SBMS0 and DSSR20's.

the solar panels easily charge the batteries by noon or before on any good sun day using the DSSR20's and are shut off by the SBMS0 when any cell reaches 3.55 volts for a preset time I did not change any of the preset values that Dacian already had input to the SBMS0. I put in 544Ah for 8 cells as each 2P acts and functions as one cell. 2P8S configuration....

All is working great --- ya ya ya - no number as that is an adjective.?

the SBMS0 turns off the charging with the DSSR20 via small sense wires I use 24 AWG solid strand cat 5 cable which is very inexpensive and readily available. the supplied ribbon cable that monitors the individual cells in the 24-volt battery is 28 AWG. there is no real amount of voltage going through the SBMS0.
I paralleled the DSSR20's with 20 AWG solid strand thermostat wire. only one wire is needed per DSSR20 for that part. again insignificant wire cost. I paralleled them into Dinkle terminal blocks with a cost of 50 cents per terminal block. this simplifies the wires some. I use a different color 20 AWG solid strand thermostat wire for each one (4 colors to choose from in my 20 AWG thermostat wire).

my understanding is the SBMS0 balances the cells with some small number like 300mA or something through the 28 AWG ribbon cable that is direct wired to each cell. the balancing works great as my cells run about 30 to 120 mA differences and often down to 8 mA (delta between cells).

I have 2 SBMS0 set up and functioning correctly they are the newest version 03d.
if any mistakes are made they are mine - ???
I purposely make a mistake everyday so I can learn from my errors.

I was a chemistry major chemist in the honors program and have extensive 10 years of college. 3 years undergrad college, and 7 more years graduate-level education at the state university but still learning. I graduated in 1987.
 
49 amps charging with 6 250-watt used polycrystalline panels. panels are in parallel pairs facing south. 3 DSSR20's are used as the solar charge controller. the SBMS0 is the BMS and will turn them off when the battery is full.
just a small update so people can hopefully get a better understanding of how it all works.
the battery is 2P8S 16 cell Lishen 272Ah battery so 13926.4 watt-hour potential capacity. February 20th, 2021 picture so real-time. no fake news here
 

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If you care about the look then there is no harm in using 72 cell panels is just that the extra 12 cells you will pay for will have no impact of charge current but it is extra roof space and it looks better.
MPPT will be more expensive even if you consider the small savings on cables to have the battery inside the house. But if you decide to use an MPPT then Victron ones have remote ON/OFF either with a cable you get separately for the smaller models or directly included in the larger models.
info from Dacian above

I purchased and I am using the 60 cell 250-watt panels as they were very inexpensive at 23 cents per watt (delivered price to my site). I think the possible small advantage of a 72 cell panel would be a higher voltage for longer wire runs but if you keep the 10AWG runs to 60 feet or less the 60
cell panels in parallel work fine.

C-rate for 544Ah 24volt battery LiFePO4 using 272Ah Lishen cells 2P8S configuration:
Optimum is around a 0.2C charge rate so if you have a 2p 272Ah so that will be 544Ah x 0.2 = 108.8A so that will be about 10 panels but 12 panels should also work if you prefer that.
The SBMS0 will not interfere in the charge current unless you use a dual PV array setup and that will allow you to have a PV array 3x larger made of two separate arrays say one with 10 panels and another one with 20 panels in total 30 panels and in that case the SBMS0 will control with array will be used for charging can be just the small 10 panels array if is sunny and you set limit to 100A or it can be the 20 panels array if amount of sun is about half and if is cloudy the SBMS0 will connect all 30 panels so you can still get a good charge even with bad weather.
my thanks and compliments to the electrical engineer DT

a few more answers for my off-grid DIY solar PV >>>> long-life span system!!!!!???

60.99 amps 1674 watt from 6 250-watt used 60 cell polycrystalline panels charging right now through 3 DSSR20's. about 55 to 60 feet of 10 AWG PV wire. woohoo! ???
I can't wait until I can show ya all 12 panels charging at 120 amps!
 

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You can see the DSSR20 as an ideal diode plus a solid-state switch in series so there will be almost no voltage drop on the DSSR20 (just a few mV) The important part is your battery that is 25.6V nominal but most of the time it will be around 26.5 to 27V and so the panel when hot needs to have at least this 27V + depending on cables 2 or 3V drop on those so around 29 to 30V max power point voltage with a 60 to +70C panel. The max power point for 60 cell panels is around 32 to 33V at STC meaning panel at +25C but for the panel to be at +25C ambient needs to be around -10C.
But PV panels are constant current sources so the voltage of the panel if connected to the battery will be the same as battery voltage plus the voltage drops on the wires. So in most cases (mostly dependent on PV panel temperature) the 60 cell panels + DSSR20 + 8s LiFePO4 battery will result in a 90 to 100% efficiency so an average of around 95% and thus it is an ideal match.
If you go for a panel with exact same cells but 72 of them then those extra 12 cells will not contribute with anything but the open-circuit voltage of 72 cell panels is below 51V so it is not a problem for the DSSR20 is just that a 72 cell panel has 20% more cells and so 20% higher power rating than a 60 cell panel and also a 20% higher cost but charge current will be the same so will be the charge power thus there is no advantage other than aesthetics (in your case) to pay 20% extra.
So DSSR20 can handle 60 cell and 72 cell panels with no problem is just that there will be no difference in power provided to the battery.

more thanks to Dacian the Electrical Engineer and designer of the Electrodacus DSSR20 and Elecrodacus SBMS0 for all the information above.
???
 
ferrules are good to use on the 10 AWG PV wires connecting the circuit breakers and DSSR20's see attached pictures. I strip the 10 AWG PV wire back about 5/8 of an inch using the Klein catapult wire stripper. it is aptly named catapult as it ejects the wire insulation with a bit of force.
just a tip for those assembling your own system! ?
Enjoying the thread of your build. I’m getting ready to install a SBMS0 and need to order the DSSR20 for my skoolie. And I just bought a ferrule kit.
Where did you get the circuit breakers?
 
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