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Nobadays
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# Posted: 30 Jun 2020 07:01pm
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BMS.... Battery Management System. These are either built into the lithium battery ( Battle Born, etc) or are an external unit that, to put it simply controls the SCC/and or inverter... as in disconnects the batteries from the SCC to prevent over charge, shuts off the output in case of under voltage, again disconnects the SCC from charging in case of low temp.... and often balances the cells that generally make up a lithium battery pack.
I don't know of a SCC with an integrated BMS, but that doesn't mean there isn't one out there!
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ICC
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# Posted: 30 Jun 2020 08:15pm
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A BMS needs to be matched to the number of cells it is controlling. They do not just read total voltage as a charge controller does in order to set the charge voltage for the battery bank. A lithium battery bank/pack could be built with cells that are 3.2 volt or 3.6-3.7 volts. There are balancing circuits connected to the cells that are supposed to redistribute or balance, the current between cells in order to stop the voltage rise when a cell has reached full charge before other cells in the battery. So, I don't see how a BMS could be built into a CC.
As well there should be a low voltage and a high voltage automatic disconnect of the entire battery from the system, or at least from the discharge side of the system. That is designed to be able to cover the needed maximum charge and discharge amperages, which can vary and gets more costly as the max amps increases.
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paulz
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# Posted: 3 Jul 2020 11:00am
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Quoting: ICC Myself, I wouldn't spend serious money if it was not usable with lithium
Still poking around for a controller. If I get one with lithium compatibility can it be used for lead? If so do they sense what battery or do you program it it?
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Nobadays
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# Posted: 3 Jul 2020 02:28pm
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Though there are some lithium only chargers..... when it comes to SCC's all that are lithium compatible (to my knowledge) can be used with LA as well. It comes down to being able to set the charging parameters to accommodate lithium charging needs. Some are set up now to choose lithium in the menu and possibly then just plug and play. That said I bet you will have to make a few adjustments whether it be flipping dip switches or manually programming the controller. Some like Victron.... likely others... have phone aps/bluetooth so you can just zip through the setup.
You dont do Absorption or equalizing charges on lithium. The Schneider SCC I use does have a lithium setting, however the charge parameters in it's little brain are for LiFePo and since I use a different lithium battery (Chevy Volt MNC cells... different lithium chemical) I had to adjust manually through the SCP all the parameters, which once done has work exceedingly well. Not so with the Schneider inverter/charger. It wants to always do an Absorption charge.... and can't set that less than 53vdc..... not good for the lithium cells! If I charge with the generator through the inverter I have to watch it like a hawk!
There are plenty of options out there and getting better all the time. On the DIY solar site they seem to like the Epever SCC's. Relatively cheap and pretty reliable it seems. I might go for one of those on my shop. Using LA out there so I have a source of power all winter to run satellite internet/security camera when we are gone.
Good luck in the search!
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paulz
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# Posted: 3 Jul 2020 07:54pm
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Well I bought a controller that popped up local today. Only 40 amp 12/24 volt but LA/Lithium programmable and 150v pv voltage capable so I can hook up my panels wired as they are. My plan, or thought at least, is to split my array in two and point them in different directions, since I get morning sun, then it goes behind the trees and comes back in the afternoon. At least it will give me some experience for a more elaborate setup later.
So I got:
Epever Tracer 4215BN controller. Seems to have a good rep.
Epever MT50 remote meter
Victron 100A battery protector
Drock battery monitor
fuse panel, cutoff switch..
All new in boxes. Well over $300 I think, paid $150. So for under $500 with panels I should have enough juice to keep me happy, for awhile..
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Nobadays
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# Posted: 3 Jul 2020 08:09pm
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Wow....Good score! You're set!
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paulz
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# Posted: 3 Jul 2020 08:33pm
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Thanks Noby, and thanks for the help.
Lots of instructions to wade through. Should I make my long wire runs from the panels to the SCC? At 110v I can use smaller gauge wire than the 12/24 Controller output, right?
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Nobadays
Member
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# Posted: 3 Jul 2020 09:06pm
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Yep.... panels to the SCC for the long run.
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Brettny
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# Posted: 4 Jul 2020 02:11pm
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Well you suck Paulz....that is the exact controller I'm going to buy for my setup, but il have to pay full retail.
Yes higher voltage can run longer distances with thinner wire and have less loss. That can be a major benefit to this 150v input controller you got.
Since your going to aim pannels in different directions you may want to series and parallel them. I'm sure theres a youtube video to explain this.
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paulz
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# Posted: 4 Jul 2020 03:12pm
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Thanks Brett. Don't know where to get the best deal on one. I just checked briefly to see if this one was a good deal. Prices did seem to vary some from what I saw.
My array of 12 panels is currently wired in two 6 panel series groups, each about 110v. I could hook them both up in parallel but I think that might exceed the 40 amps, or is that 40 amps just the output?
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Nobadays
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# Posted: 4 Jul 2020 07:48pm
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Though the amps of the SCC does relate to the output, I don't believe you can go higher on the input. Someone smarter will chime in if I'm wrong...
The simple equation for sizing SCC is:
total watts ÷ battery voltage = input amps
So for your panels: 75 watts × 12 = 900 watts -
With 12v system: 900÷ 12 = 75 amps
With 24v system: 900÷ 24 = 37.5 amps** you would be ok here.
With 48v system: 900÷ 48 = 18.75 amps** or here
Or to look at it another way...
40 amp charge controller -
40 × 12v battery voltage = 480 watts solar
40 × 24v ..... = 960 watts
40 × 48v ..... = 1920 watts
Hope that helps!
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paulz
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# Posted: 4 Jul 2020 09:35pm
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Trying to understand how the output voltage affects input side... does it affect wire gauge for pv to scc as well?
Pretty sure both my inverters are 12v only (2k and 5kw). If I wire my batteries in series for 24v, can I tap off one battery for 12v inverters?
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ICC
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# Posted: 4 Jul 2020 10:37pm
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Quoting: paulz array of 12 panels is currently wired in two 6 panel series groups, each about 110v.
That output voltage will change with the amount of sunshine hitting the cells, and on whether or not the wires are open circuit or connected to a charge controller and batteries. So, maximum voltage could be higher. Or less on a cloudy but hot day with a load of dirt on the panel surface.
Quoting: paulz If I wire my batteries in series for 24v, can I tap off one battery for 12v inverters?
Do NOT do that! If you did that you will be guaranteed to end up with one of those 12 volt segments of the 24 volt series string at a charge that is less than the other segemnt. The charge controller will sense the total series voltage of the series battery string. It will charge the battery string at a rate appropriate as if each cell of each battery was at the same charge. When the highest cells or batteries reach full charge before the lower charged ones they will then be overcharged for as long as it takes for the charge in the lower cells to reach full. That is all assuming lead-acid type batteries.
If the cells or batteries are a lithium type with their own BMS the BMS may try to balance the cells and prevent overcharge but the BMS may not be able to handle the required amounts of balancing current. I have no idea on that; probably varies between different BMS. If the system has two series connected 12 volt lithium batteries such as those green ones (I forget the name off hand) there are two separate BMS if I understand them, and I do not know how they would react to an imbalance between batteries. You'd have to do some research on that. Might be okay and maybe not.
Quoting: paulz Trying to understand how the output voltage affects input side... does it affect wire gauge for pv to scc as well?
Wire is sized by how much current (amps) it must safely pass. Virtually any NEC approved wire will be certified to up to 600 volts. IF the wire gauge is too small, the resistance to the current flow will be too high and result in (a) the wire heating up too much, and (b) dropping the voltage at the end of the run by a significant amount. PV systems do not usually operate at maximum amps for hours on end though, due to the changing angle of the sun, so skimping on wire gauge a little is not necessarily a death knell. I do like to be on the conservative side when it comes to power loss and wire heating and tend to err on the side of using the largest theoretical need.
Quoting: Nobadays Though the amps of the SCC does relate to the output, I don't believe you can go higher on the input.
Charge controller amp ratings almost always are the maximum amps that the CC can put out. Some are made to simply waste any excess as heat, but that can vary. I have no idea about this CC.
Note that charge controllers, like this one, that can also be used as a load controller will have the maximum charging amps reduced by whatever amps the load controller portion can handle IF the load controller is turned on. That feature is selected with dipswitches or firmware. No idea how this one has the load controller selected.
The INPUT wattage total of the PV panels is limited by the VOLTAGE of the battery bank that is being charged. Page 13 of the manual I looked at online lists the rated charge power as 520 watts for a 12 volt battery bank. Maximum PV array is listed as 1560 watts for a 12 volt battery system. There are damage warnings listed there as well.
Also note on that page 13 table the column named Max. PV open circuit voltage. Read the footnote where it states the 138 maximum voltage is at 25 C (77 F). The 150 volt figure is for colder temperature.
Those panels are factory rated at 21.7 volts Voc. Those factory ratings are at STC which is 25 C (77 F). Six of those in series at STC would have a factory Voc total of 130.2 volts. Quite close to the 138 maximum. Is that a problem? Hard to say for certain; close is okay but over that could be a problem. I don't know what this controller does if the max. value is exceeded. Some brands like Midnite have protection built-in and will simply shut down until the voltage drips. Others....?
The cold weather 150 volts could easily be exceeded on a frosty day in winter. (PV voltage increases with cold and voltage drops with higher temperatures. The rule of thumb is to multiple the Voc x 1.25 to get the theoretical maximum voltage. That is the NEC metod. The true cold weather maximum in any one location may not rise by the full factor if the coldest is only around freezing temperature for example. But "rules of thumb" take the worst case into account as a rule. 
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ICC
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# Posted: 4 Jul 2020 10:52pm - Edited by: ICC
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I forgot to add one thing.... You mentioned two series strings of 6 panels each and then connecting those in parallel and facing different directions. That should be okay as long as the total watts making it from all the PV to the CC is within the allowable values. What is the high noon output going to be when the sun doesn't hit any panels straight on, but does hit them all? ??? On the other hand, any shading between the panels connected in series will be noticeable.
The solution that will provide maximum charging is to use a separate CC for each section of the array. I used to have panels facing E, S and W and each used its own CC.
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Brettny
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# Posted: 5 Jul 2020 06:12am
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Paulz your useing 4 group 24 batteries? Those are pretty small for a 5kw inverter. They may not even physically be able to output that amount of amps at 12v.. that would be 100a per battery in parallel.
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Nobadays
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# Posted: 5 Jul 2020 08:36am
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Good write up ICC..... I think the simple rule of thumb equation I have been using errors on the safe side according to the numbers you found for that particular SCC...
Quoting: ICC online lists the rated charge power as 520 watts for a 12 volt battery bank. Maximum PV array is listed as 1560 watts for a 12 volt battery system.
I'm pretty sure the Maximum listed at 1560 is for 24v battery system? That still seems WAY high.
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paulz
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# Posted: 5 Jul 2020 08:50am
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Sheesh what a learning curve. I guess it's worth it..
Yes I currently have 3 of those green Valance 140ah Li batteries. Two are in my truck, in parallel, and plug into/power the cabin when we arrive. We don't stay more than 4 days at a time, which they easily handle, and get recharged off grid power back at the house. The third one sits in the cabin and sometimes get used to keep the cooler and wifi up if we take the truck someplace. It's pretty dialed in, though wife would love to use the small microwave on the shelf. Haven't ever tried it off an inverter, or these batteries.
The new shop has the 5k inverter hooked to two group 24 la batteries hooked to the Harbor Freight 130w solar kit. I've been running saws and drills which do take the batteries down but they recover. Poor lighting now, 3 LED bulbs. The shop is really where the new juice would be welcome.
Back to the SCC. ICC, yes that is the manual. I just noticed this blurb, which sounds like you can't hurt it by to much PV power:
ï‚Ÿ Reliable automatic limit function of maximum PV input power, ensuring no overload under any circumstance.
And this, what is all this polarity reversing stuff?
WARNING: Controller will be damaged when the PV array straight polarity and the actual operation power of the PV array is three times greater than the rated charge power!
WARNING: Controller will be damaged when the PV array reverse polarity and the actual operation power of the PV array is 1.5 times greater than the rated charge power!
The chart on page 13 shows:
Max PV power
1560W/12V
3120W/24V
Does this mean my 900w array cannot harm it, even at 12v, as long as series voltage is under 138?
There is also a chart for Max PV wire size, 6awg for mine. Why max?
Is there a way to use my 12v inverters with a 24v battery setup? Tranformer, 2 iverters in series? If the SCC is mounted at the batteries, what is the advantage to 24v again?
As always, thanks for the help!
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ICC
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# Posted: 5 Jul 2020 10:44am
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Quoting: Nobadays I'm pretty sure the Maximum listed at 1560 is for 24v battery system? That still seems WAY high.
Read the manual, page 10 is the correct page.
https://www.epsolarpv.com/upload/cert/file/2003/Tracer-BN-SMS-EL-V1.2.pdf
That is the MAX, maybe not the best. Rated is 520watts at 12 volts
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ICC
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# Posted: 5 Jul 2020 11:04am
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Quoting: paulz ï‚Ÿ Reliable automatic limit function of maximum PV input power, ensuring no overload under any circumstance.
In theory there should be no danger. But then they do list the rated watts and a maximum watts. Rated is probably safest. Max usually means the components, or some of them, can handle up to this higher amount, but they will last longer when not pushed.
Quoting: paulz And this, what is all this polarity reversing stuff?
Means connecting + to the - and - to + which will instantly kill many electronic components. There is a built-in polarity protection system but it has limits. Connection polarity errors may not instantly destroy the electronics that are polarity sensitive.
Quoting: paulz Is there a way to use my 12v inverters with a 24v battery setup?
No.
Quoting: paulz chart for Max PV wire size, 6awg for mine. Why max?
The terminal blocks probably cannot accept anything larger. My experience has been that the stated max size of wire may be difficult to insert at times unless the wire end is cut perfectly with no distortion of the cut end. YMMV.
Quoting: paulz If the SCC is mounted at the batteries, what is the advantage to 24v again
The wires to the inverter are smaller.
If one is building the battery bank from cells (2 or 3 volts each for example) rather than a multi-cell battery, one can build a larger capacity bank when connecting in series and if parallel connections can be avoided altogether that makes for a better battery bank. That is one reason prismatic LiFePO4 cells are made in large capacities, such as 200 Ah and even higher. Put 8 of the 3.2 volt LiFePO4, 200 Ah in series and you have a simple configuration that has minimal connections and loads of capacity.
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Brettny
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# Posted: 5 Jul 2020 03:07pm
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I think if your going to push that 40a CC with more solar than in can Input to the batteries you should have a dummy load on the load side of the CC.
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ICC
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# Posted: 5 Jul 2020 03:58pm
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Quoting: Brettny I think if your going to push that 40a CC with more solar than in can Input to the batteries you should have a dummy load on the load side of the CC.
I don't follow why you would think there would be a benefit to that.
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Brettny
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# Posted: 5 Jul 2020 08:08pm
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That in high sum times the power could be used for something. But personally I wouldn't use a cheap CC at max amps any way. There just to fragile.
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paulz
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# Posted: 7 Jul 2020 07:48pm
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I have a new plan! I made a solar rickshaw with a couple of my wife's old wheelchair wheels. Now if I can teach Buddy to keep the panels in the sun I should have plenty of power.
I got them in full afternoon sun today, still 112-114 volts open circuit.
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paulz
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# Posted: 9 Jul 2020 09:23pm - Edited by: paulz
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Got the panels up on my shop roof. Been playing the Renogy wire calculator
https://uk.renogy.com/calculators/
I'll have a 20-40 ft. run to the SCC. I have enough 10 awg sold copper wire to make two runs, one for each pair of 6 panels. 115 volts, 26 amps, says it's OK?
I'm thinking the 4 LA batteries will be 10 ft. from the SCC, other side of the wall on the outside. I have a bunch of auto jumper cables, would some heavy gauge ones work with new copper ring terminals? Same thing between the batteries? (4 in parallel)
Inverter will be within 10 feet of SCC. Same thing?
If I want to get AC up to the cabin it's a 150 ft run.
I'll probably only hook up one pair of panels to start with, and see what the meter says is going on.
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Nobadays
Member
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# Posted: 10 Jul 2020 08:27am
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Most jumper cables are #4 or #6 cable. You can use the chart to see if that will carry your anticipated loads. Likely will work... check though.
From the batteries to to the inverter is a different situation entirely! If you plan to use the 5000 watt 12vdc inverter you are looking at incredible amperage draw!
Wattage ÷ Voltage ÷0.85(inverter efficiency) = Amps
5000W ÷ 12V ÷ 0.85 = 490 amps No battery jumper cable will handle that kind of amperage! Again.... this is where increasing battery voltage can decrease wire sizes.
5000 ÷ 24 ÷ 0.85 = 245 amps
5000 ÷ 48 ÷ 0.85 = 123 amps
ICC.... ?
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paulz
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# Posted: 10 Jul 2020 09:57am - Edited by: paulz
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Thanks Noby. I don't ever foresee using 5000 watts, it's just the inverter I have and have been using. I have it hooked up with jumper cables now to run power tools but will probably add some LED shop lights. That's about it for simultaneous. I have a 110v 15a air compressor but probably best run off a generator.
I'd like to run the panel to SCC wires this weekend, two #10 wires runs should do I hope. I have both solid copper (Romex) and a 100' #10 extension cord I could cut in half and use, which might be better for moving the panels around.
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ICC
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# Posted: 10 Jul 2020 10:00am
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What is the maximum continuous discharge rate of the valence battery? That should not be exceeded to prevent damage / overheating of the cells in the shell.
Two 12 volt batteries in parallel will double the amps that can be drawn from the batteries but you still have the wire size problem. That is one reason to go 24 or 48 volts for storage.
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paulz
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# Posted: 10 Jul 2020 02:23pm
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I plan to keep the Valence batteries mounted in my truck and charge them from home as I do now, at least for the time being. I have 4 lead acid batteries to use with the solar, Group 24 Delco Marine.
Here's probably a dumb question: If the SCC can take varying input voltages, why can't the load voltage be set different than the battery voltage?
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paulz
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# Posted: 16 Jul 2020 10:42am
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My solar project is on hold for a week, because.. I was telling the local gang about it last weekend, when one of them says "You want a huge system, free? A friend has bought a big house. There was a dispute over the solar (leased or something) and the solar company gave up and washed their hands of it. The house needs a new roof and the homeowner wants the solar gone."
I said yes, there are workers coming next week to remove it, I just have to load my trailer. Haven't seen it, nor photos. It's in a gated community 30 miles away. There are 2 'Sony Boy' inverters, I know that much. It is a grid tie system.
I wasn't going to mention it yet but now I'm wondering if a grid system is usable off grid? The panels at least, right?
If I can use it I will put it on the shop roof and put my current stuff up at the cabin.
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Brettny
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# Posted: 16 Jul 2020 11:48am
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Geez paulz..you suck again. That's alot of free pannels.
As for wire gauge/volts/run and amps there are many good calculators. This is the one I like the most. Usualy you want to stay under 5* drop. If it's for a 12v system to run your inverter stay way less than 5*
https://www.calculator.net/voltage-drop-calculator.html
For the 150ft run of 120vac with 30a 6ga should be fine. But for the 14.7v run from the batteries and 10ft to the inverter at 24v you will need 1/0ga for 210a.
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