Thanks, I must be mistaken then, I always thought it was battery capacity divided by the number. I guess I understood it the inverse way.
Can too much battery capacity be a problem?
- Thread starter Tony_
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#1: Ah capacity and BMS discharge current are two different things. You may have 800Ah of capacity but the BMS may limit the discharge current to 150A so that's your limit. See #3 below.
#2: I selected a 2000W inverter because it is all I need to run the microwave in my trailer. I don't need to run A/C to keep cool. So I'm covered to heat my morning drink and more than enough W to run the normal loads (charging laptop, watch TV). A larger inverter will have a higher idle load so the 2000W made sense to me.
#3: A 2000W inverter would be starved if the BMS could only deliver 150A. My 3 batteries can deliver 120A each, even when I'm making 2000W, each battery is under 80A. In my thinking, I'm not taxing my BMS at all. Mine are DIY using 280A cells that were available is the reason for my capacity.
More thoughts; I think 2000W is about the limit for a 12V system. I think with 3000W, 48V would be ideal. I only have 300W of solar (that's all I could fit on the roof) so my charging is slow so I may have a net negative (use more than I make) but the capacity covers the difference until as a last resort I fire up the generator and hit them with 70A.
Thanks @TacomaJoe and @time2roll. After considering all the posts so far, I'm beginning to see what factors are important. Most importantly, I think I will choose 800Ah. Now I need to decide between the type of batteries I mentioned in the original post: two 400Ah server racks, or four 200Ah "regular" SOK batteries.
Any advice on that?
sunshine_eggo
Happy Breffast!
In each post I talk about BOTH lead acid and LFP batteries. Maybe you're missing LFP=Lithium Iron Phosphate.
You asked about ratings. My answer was in that context.
Please note the bolded portion. Those are typical limits.
One of the primary advantages of LFP batteries is the ability to be charged much faster as indicated by the "C" rates above.
I don't see how anything about the above is bewildering. I literally state the rule, and indicate a "sweet spot."
I have extensive "actual experience" with multiple battery chemistries including lead acid, NiMH, LFP, NMC and LiPo.
Again, this
Is all you need to know about LFP capacity and charging.
These things are what's needed to design a system that meets your needs:
Failure to understand or execute the above means you must be extremely lucky to design a system that actually meets your needs.
DIYrich
Solar Wizard
Which server rack battery has fewest issues: SOK, Trophy, or Jackiper?
Will says all three of these have been reliable. I ruled out EG4 variants due to customer service. Which of SOK, Trophy, or Jackiper have the least issues for everyone? (48V versions) Like random BMS errors, precharge resistor, issues with inverters, or anything else. I was leaning towards...
diysolarforum.com
It seems all that thread is about which server rack battery to choose, but that wasn't my question. I probably wasn't clear enough.Which server rack battery has fewest issues: SOK, Trophy, or Jackiper?
Will says all three of these have been reliable. I ruled out EG4 variants due to customer service. Which of SOK, Trophy, or Jackiper have the least issues for everyone? (48V versions) Like random BMS errors, precharge resistor, issues with inverters, or anything else. I was leaning towards...
My question was for advice in choosing between server racks vs. 'regular' batteries and I was referring to my original post where I wrote:
I've been looking at these from the mobile-solarpower.com site:
A) 2 of the EG4-LL Lithium Battery (12V 400AH) Server Rack Batteries or
B) 3 or 4 of the 12V 206Ah SOK Batteries
I've watched a lot of van build videos on popular youtube channels but none of them involve "server rack" type batteries. So that's why I asked, since it seems less familiar to me. I really appreciate advice from people who have actual experience, so if anyone can offer that regarding server racks vs. 'regular' battery types (not sure what to call them), or can point me to someone who does, that'd be great. Thanks again.
DIYrich
Solar Wizard
My point was picking a more reliable battery, regardless of configuration. SOK seems to be more reputable than EG4.
Can you elaborate on the BMS limitation and how it is different then 4*100 ampHr batteries with 100A BMS in an example?
For example, we have a 12v system on our truck camper, have just swapped over to an Epever 4210 AN SCC (from a 3210 AN after tripping the over voltage which resulted in the BMS shutting down the battery bank, I presume that the 400 watts of solar actually obtained the max voltage despite being flat on the roof while in coastal VA a few weeks ago, as we had recently doubled the panels from 2 up to 4*100W panels in parallel for total of 400W; and our battery bank is using (2) 260 aHr (HP) LFP SFK batteries in parallel for total of 520 aHr capacity, but … they only have the 125A BMS.
We also have a Renogy 40A dcdc charger.
We are also planning on adding a 3,000 watt inverter at some future point, and converting our A/C and our 10 cu ft 3 way Fridge/freezer to 12v, but that’s probably a few more years away.
At the moment, we haven’t really even used the batteries other than for running the fridge/freezer on 12v intermittently while we are traveling between TT campgrounds, that typically have electric hookups… We purchased the LFP battery bank as we had only been been boondocking/dry camping,
So, j/c, what is the BMS rating? 100A, 200A, etc?
We too have very limited real estate on our truck camper roof (ie- We currently have 4*100 w panels in parallel, with a 520 aHr battery bank (2*260 aHr LFP (HP) SFK batteries in parallel) an Epever 4210AN (which allows I think it’s up to 520W @12V)… But …because we are frequently moving (and lately plugged in much more frequently than we had been when we bought the LFP batteries, as a result of buying a used TT campground membership, go figure) we have not had any issues (even without the campground stays) keeping our battery bank charged and topped off with both the 400 watts of solar together with (more so it seems) the DCDC charger. And … on our recent 2 week camping trip, we actually tripped the battery bank a couple weeks ago as we only had a 3210AN Epever SCC at that point, and I’m guessing we must have went over the limitation of the solar panels, which pushed the LFP 125 aHr BMS’ to trip and shut down. Live and learn.…
So my question pertains to Zwi (and sunshine_eggo, etc) if it would have made any negative or positive difference if we had a larger rated BMS on each of the LFP batteries? Would it still have over voltage‘d and shut down the bms? …. As we had been planning to run off the 12V setting on the 3 way fridge via the battery bank and the solar panels at that point, while we went biking. But sadly we ended up putting it back to propane, just to be safe that it didn’t shut off again while we were out riding, and then lose the food in the fridge and freezer, as we didn’t have any hookups where we were at that point.
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Can you elaborate on the BMS limitation and how it is different then 4*100 ampHr batteries with 100A BMS in an example?
For example, we have a 12v system on our truck camper, have just swapped over to an Epever 4210 AN SCC (from a 3210 AN after tripping the over voltage which resulted in the BMS shutting down the battery bank, I presume that the 400 watts of solar actually obtained the max voltage despite being flat on the roof while in coastal VA a few weeks ago, as we had recently doubled the panels from 2 up to 4*100W panels in parallel for total of 400W; and our battery bank is using (2) 260 aHr (HP) LFP SFK batteries in parallel for total of 520 aHr capacity, but … they only have the 125A BMS.
If you have a 400Ah battery with a 100A BMS, you will have 400Ah of capacity but can only use that capacity at a rate of less than 100A. I need 150A or so to run my 2000W inverter and with the 100A BMS I couldn't get the full use of the inverter. If you have 4*100Ah batteries in parallel, you get to add the BMS ratings, so you can pull up to 400A from your bank which will handle up to your 3000W future inverter.
My Epever would push one cell of one battery into overvoltage protection. I have reduced my boost to 14.0V and my float to 13.8V and no longer have a problem. I have since top balanced the one battery and the cell is behaving better now. With these voltages, my batteries are full and happy.
Your 560Ah battery bank can provide up to 250A. I prefer not to push mine and the typical max draw would be about 75% of the BMS (188A for you).
TLDR everything. But assuming you have a bms on each pack and you had 2 100A bms with the packs being parallel then each bms should only be pulling about 1/2 total Amps used. But not exactly half due to wire lengths individual pack resistance etc. Anyways if you had the above scenario you could safely pull around 180 amps. If you have 1 bms and one pack then obviously you need your BMS to be large enough for your max discharge. Anyway in my opinion the more battery the better unless weight becomes a problem
I would honestly be happy with 10 days autonomy if possible obviously that is probably too much weight, space and money. And if things start to get too low you can run the van no matter weather the sun is shining or not. Bottom line I do not believe in too much storage ever.
I would honestly be happy with 10 days autonomy if possible obviously that is probably too much weight, space and money. And if things start to get too low you can run the van no matter weather the sun is shining or not. Bottom line I do not believe in too much storage ever.
Zwy
Emperor Of Solar
Not quite following but either the BMS tripped from over voltage of the cells or low voltage disconnect. The BMS is doing what it designed to do. You need to adjust charge settings and determine if it was an over voltage caused by a bad cell or just not having the correct charge settings.
Yes, the reasons can range from an unbalanced pack where one cell hits 3.65V limit for LFP or the charge settings are too high on the SCC. The BMS is doing it's job.
With the 2 batteries in parallel, you can pull 250A (125A each) according to SFK specs for the 260Ah.
3 way fridge on 12V will suck some serious power plus it usually will attempt to maintain temp, not lower it. Very inefficient. You were wise to use propane.
If you power up the inverter and have a shunt, see how many watts you pull using AC power. It will surprise you. Only time I would use AC is connected to shore power. I only used 12V when traveling on the roadway and propane when parked and not connected to shore power. We no longer use the 3 way, I have a Dometic CFX95 in the back seat area of the truck cab. I run this off the solar system.
OffGridInTheCity
Solar Wizard
Never enough battery..... I could absolutely make use of a 3000kwh battery bank to get me thru the winters 
1 cycle per year (charge in summer and discharge in winter) would do it for my system so used EV batteries should work.
This pic is just taunting me because I can imagine this if I could afford it... shows 20 x 70kwh? EV batteries in metal box. I would only (ha ha ha) need 2 of these to get near 3000kwh. Sigh.... if only 'whole EV batteries' can get down to $100 each... would be a fantastic excuse to buy a home fork-lift.
1 cycle per year (charge in summer and discharge in winter) would do it for my system so used EV batteries should work.
This pic is just taunting me because I can imagine this if I could afford it... shows 20 x 70kwh? EV batteries in metal box. I would only (ha ha ha) need 2 of these to get near 3000kwh. Sigh.... if only 'whole EV batteries' can get down to $100 each... would be a fantastic excuse to buy a home fork-lift.
I realize that air conditioning is a monster power hog. (We don’t have any real inverter currently (we only have a small 750W non sine wave inverter that handles a small crock pot we use to make chili and soups etc while we are driving between destinations/camping spots, etc) …. We actually can not use air conditioning on anything other than shore power. We do have a generator, but we haven’t attempted running it while on the generator. Plus, I hate using it as it’s so loud, but on rare occasions when it is very hot and humid, we will use it to initially cool down the small camper and then just run the fans.
I also understand the 3 way fridge/freezer is inefficient, but imho, I prefer not to travel with the fridge running on propane (for both safety reasons, as well as for cost/ frugality to extend the need to replace or refill the propane tanks any sooner than we can get away with) plus, using the propane is not allowed in tunnels, etc… as well as since we are now staying at campgrounds with shore power frequently at the moment (due to a Thousand Trails camping membership) it makes sense to use the solar and DCDC charger power generating capacity we have to run the fridge on DC over propane for however long it’s capable of keeping up on the safe temperature range limit’s, and when it starts struggling, we then transfer it back to propane to get the temps back down, and then swap it back again until the temp starts rising too high again, and repeating that cycle while we are driving around. It involves a bit more monitoring, but it’s not that difficult, and it extends the propane usage, saving us $ as well, so the ROI of monitoring the fridge temp is worth it to us as we can put such saved $s back into the fuel or grocery or maintenance budgets.
I also understand the theory of the bms limitation of amps available, but not exactly what it looks like, per se. (I guess I haven’t figured out what yet draws more than 200-250 amps … which I guess is also what was being referred to regarding clarifying what caused the battery bank to cutoff and if it was over voltage or not…. PS- Looking at the minimal bms log info I could find, it showed an over voltage error.) Also, coming from experience with a 200 aHr FLA battery bank, maybe we just have not yet used anything that surpasses that 200+ aHr BMS limitation. ?
Thanks again for your reply!!!
0truck0
New Member
More battery gives you a higher starting point, but after that initial use, then the limiter is your panels/ how much they can recharge the batteries per day. Not a lot of use having more storage than your ability to fill that storage, unless you plan more panels one day.
Zwy
Emperor Of Solar
If there is alternator charging for backup, then it is wise to have more battery. The reason? Larger battery can get a system thru days of un-ending clouds and low yield. On days with high yield, the batteries can get full or close to full. It takes a long time to run a large battery bank from full to 20%. This allows many days between necessary charging.
With alternator backup charging, when traveling the yield from solar combined with the alternator may easily get the battery full or close to full.
With occasional shore power or even generator use, the large battery will also allow more days between charging.
I run 600W of PV now on my truck camper which will be increased to 800W when I finish the inverter mini split installation. Battery is 24V 280Ah. Only once have we come close to 50% SOC and I think that was the inverter was left on while we did some activities during the day.
0truck0
New Member
That's only if you drive, and if you drive a long drive. The drive is a reset of the "starting point". Yes, I understand the bigger battery part lasting longer, but after that initial discharge then it is your solar panels that are the limiting factor. When solar cannot keep up then you either have to drive or you have to plug in or you have to run a generator. Will bigger batteries help the solar panels charge faster, no, that is my point, not how long a bigger set of batteries will last compared to smaller. This is always different for everyone and how long they want to park the vehicle before doing the reset. thanks
Yes, I agree, having more reserve battery capacity is good for no sun days or times you need a lot of power for some reason, or that time you just not going to drive for a while etc... Nobody can decide but the individual I guess what works.
Yes, I agree, having more reserve battery capacity is good for no sun days or times you need a lot of power for some reason, or that time you just not going to drive for a while etc... Nobody can decide but the individual I guess what works.
thewilliam
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Your irradiance by city link is broke.
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