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If you don't mind me asking, what was your OTD price? Looking to buy a 16s system myself
$5639 shipped. $0.13/Wh.
Have yet to order a BMS. I do have some Electrodacus BMSes laying around, but I may get a 250A Daly 16S LFP BMS.
That'd be about $130/kwh, which is a really good price.
I would seriously recommend checking the balance current on any BMS system. While we want to offer a high-current BMS solution at Genetry Solar (5A balance current) ideal for large off-grid battery banks, things keep getting on my plate that are a bit more pressing than launching a new product.
The 250A Daly BMS has a rated balance current of 0.2A. More than the 0.03A typically offered...but even so, Sean tested a BMS with a 1A rating (Chargery) and it wasn't sufficient to keep his Li-Ion powerwalls in balance (>400Ah). YMMV.
Electrodacus SBMS0 balance current is 0.14A.
4 minutes ago, Sid Genetry Solar said:That'd be about $130/kwh, which is a really good price.
I think so.
4 minutes ago, Sid Genetry Solar said:I would seriously recommend checking the balance current on any BMS system. While we want to offer a high-current BMS solution at Genetry Solar (5A balance current) ideal for large off-grid battery banks, things keep getting on my plate that are a bit more pressing than launching a new product.
The 250A Daly BMS has a rated balance current of 0.2A. More than the 0.03A typically offered...but even so, Sean tested a BMS with a 1A rating (Chargery) and it wasn't sufficient to keep his Li-Ion powerwalls in balance (>400Ah). YMMV.
Electrodacus SBMS0 balance current is 0.14A.
I found a balancer that did 2A at one point. Honestly I'm not sure more is going to be better in this case. LFP has a very flat voltage curve especially in contrast to LiCoO2, and current BMSes can only balance based on voltage even though we know its a horrible indicator of SoC.
I think every few years if one wants their LFP pack to last, its going to need to be disassembled and top balanced manually.
I've seen no data on expected cell drift in LFP banks either...
I think every few years if one wants their LFP pack to last, its going to need to be disassembled and top balanced manually.
So as someone who personally has a 12kwh 16S LFP bank, I do have a few comments 😉
I've had it for roughly 4 years with absolutely no issues whatsoever. I do have 3A home-made (hand-soldered) balancers on it, and I also do not regularly cycle the battery to a very low SOC (been twice in 4 years that I'm aware it's gotten down to the "falloff knee" on the discharge curve).
One serious risk with LFP and balancers, is that when they reach a full SOC, the voltage immediately begins to rise--meaning that the balancers have next to zero warning before they get slammed with full load work. If they can't keep up, then cell voltages will go out of range, hurting longevity.
With that in mind, it may be wise to charge the batteries the first time with a bench supply, watching the cell voltages to make sure the balancer can keep up. If an imbalanced Li-Ion bank is connected to full solar on day 1, the cells very well could sustain damage due to overvoltage...and if the BMS is set up to disconnect the batteries in event of a cell voltage issue, you likely will end up with a smoked MPPT, as it seems that most of them will blow up if the battery is disconnected while solar is present. (I digress!)
In my case, it took 3-4 days (with a time-limited "absorption" cycle, which is why it took so long) before the batteries were fully balanced. Ever since then, I've checked the battery voltages about once per year just to make sure the hand-assembled balancers are functioning...and have never had reason to manually balance the cells. The balancers each have a little "active" LED on them--and every day during the "absorption" cycle, some cell LEDs will barely light (indicating a very low balance current. How much, I have no idea.)
With that in mind, I would conclude that LFP batteries should do better with a (comparatively) low-current balancer, than, say, Li-Ion batteries. That is, providing you aren't deep-cycling the batteries every day--if that's the case, you're going to need one huge balancer. I know someone who burned through several sets of LFP batteries in about a year's time--but they were running 80-100% DOD cycles on a daily basis, and only had a cheap 0.03A eBay balancer to try to hold them together. Which it...didn't.
Yeah, I'll be sticking between 20% and 80%, using a very very conservative charging profile. Even doing so I'll have between 4x and 5x the capacity I have now.
I actually have another problem I'm trying to solve... 3000W of solar was enough to charge my bank to full from zero in half a day of good sun, it wont be after this upgrade. So I'm working on trying to double up on panels (~6200W). Without any remaining roof space, that means designing a stacked panel slide out system.
Well, much as I admire you guys buying new battery cells, I just can't spend that much. Last fall, when my lead acid batteries started faltering, I bought used Byd modules from battery hookup. It was the only way I could afford a sizeable bank in Lifepo4. My 48v bank is (8) 24v byd modules arranged in (4) 48v sets. Because they are not new, battery hookup suggests only using a 24v-27v range (in my case 48v-54v).
I wanted more batteries but that was all I could afford at the time. So, do they stay balanced? Pretty much, that is until they get above 54v. Then they drift a bit. Not intolerably much, but I'm still trying different active balancers. The daly bms' can't keep up, obviously at .2a. Trying an active 1.2a balancer currently. Without changing wire size can't go much higher in amp ratings. Don't really want to take down the batteries to increase wire size. Those things weigh 125lbs each!
I just ordered 8 more byd modules, this time from Battery Clearing house. (Battery hookup hasn't had these for some time, except for a few 'bad-cell' modules - why would you want those?). That will double my 48v bank size, which, for my needs should be a lot of overkill most of the time. Short Idaho winter days and many of those with little to no sun motivates the increase in bank size. The rest of the year is full off-grid time with the current bank being plenty!
So before I mount the new additional modules, I will add larger balance wires, parallel all the cells and use a 5a active balancer for the whole set. Hoping to do much better going that route. If the results are good enough, I'll eventually take the original 8 down and do the same for them.
The link to what I just ordered;
They are $295 each and flat $297 shipping for 1 to 12 modules.
So if anyone else is cheap like me, its the best deal I found for lots of capacity at a good price. Just not new....
Yep, same here on my battery bank, 20 to 80%. That is one thing I'm worried about is if these batts decide to cut off all at once, dang the poor mmpr ain't going to like it. So far, its not done that with the three batt bank I got hooked up on it right now, but I've not been able to pull the batts down since I don't have anything 24v. . . .
7 minutes ago, dochubert said:The link to what I just ordered;
They are $295 each and flat $297 shipping for 1 to 12 modules.
So if anyone else is cheap like me, its the best deal I found for lots of capacity at a good price. Just not new....
Really not bad at all...$112/kwh considering worst-case of 3kwh/pack. If they're 4kwh/pack, that's $85/pack.
You did really good 😉.
8 minutes ago, dochubert said:Not intolerably much, but I'm still trying different active balancers. The daly bms' can't keep up, obviously at .2a. Trying an active 1.2a balancer currently.
Have to say that while I like the "active balancer" concept, I have yet to see a favorable in-depth review of them anywhere. I've seen videos of them blowing up if not connected in the right sequence...or others where they further increase the cell imbalance (very hard to detect on LFP due to the sharp SOC curve). Not saying they don't work, though.
Gotta love the charge-pump style with electrolytic caps...now THAT might last a brief minute 😉.
Uhm, I'm kind of stump, well, probley could find it on google if I loook, but what would be the voltage level of 24V at 20% to 80%?
56 minutes ago, Sid Genetry Solar said:Gotta love the charge-pump style with electrolytic caps...now THAT might last a brief minute
Sid, since I'm learning as I go with the balancer thing, could you expand on what's not good about these? Thanks!
Have to say that while I like the "active balancer" concept, I have yet to see a favorable in-depth review of them anywhere.
I can't give you an in depth review and the setup I've used one in is quite different but it worked. I bought a cheap 4s active balancer rated at 10amps for a 36v hydraulic system using 3 standard lead acid automotive batteries and it worked great. The system is constantly connected to 120v and a golf cart charger and I was having issues with them getting horribly out of balance and this did the trick. I did test the 10amp claim with a clamp meter and a load tester and it actually did it.
But apples and oranges here. Flooded lead acid is anything but flat with SOC so an active works great on them.
11 hours ago, The Blind Wolf said:Yep, same here on my battery bank, 20 to 80%. That is one thing I'm worried about is if these batts decide to cut off all at once, dang the poor mmpr ain't going to like it. So far, its not done that with the three batt bank I got hooked up on it right now, but I've not been able to pull the batts down since I don't have anything 24v. . . .
The BMS shouldn't be cutting while your MPPT is charging under any (normal, recoverable) circumstances, really. The MPPT should be set so conservatively as to never reach the over voltage protection threshold. Also, and this is really a design decision, for low voltage cutoff I'd place the MPPT leads upstream of the cutoff mechanism, set low voltage cutoff somewhat conservatively, and use something like a Victron Battery Protect to cutoff appliances at an even more conservative threshold. That would allow for the batteries to be protected, the MPPT to recharge the cells from a safe low voltage threshold, and the restoration of power to appliances after a second more safe threshold was reached.
Electrodacus, the over voltage protection uses the MPPT's remote port to shut off charging and the remote port on the battery protect to shut down appliances/draws. Both are programmable to whatever cutoffs you want.
10 hours ago, dochubert said:Sid, since I'm learning as I go with the balancer thing, could you expand on what's not good about these? Thanks!
Using electrolytic caps in a charge pump method is great for high currents...but not for longevity. I seriously doubt the caps have a 5 amp ripple current rating (you have to get physically huge caps to get that level of rating)--and even if so, most electrolytic caps are only rated for 2,000 hours (that's 3 months!) at max voltage/temp/ripple current ratings. With that in mind, I don't see them lasting very long before the caps dry out and fail.
If they used ceramic caps (usually much smaller though), they'd be fine.
Thanks Sid. That makes sense. There seem to be a lot for sale on ebay using electrolytic caps. Guess when they blow up in 3 or 4 months and people raise heck, those type will disappear from ebay....
The fundamental issue with "active balancers"...at least as far as I know, the "active" units "dump" power into the next cell up. Which is all great and roses...until you consider what happens...
Let's start with a charge scenario, 4S LFP battery, 5A active balancer, 5A charge current.
[all cells have equal charge current, they're charging]
...3.4v/5A...3.4v/5A...3.4v/5A...3.4v/5A...
[one cell reaches full charge, the charge current plummets and voltage rises past the threshold. Balancer starts "dumping" power into the next cell]
...3.65v/0A [balancer 5A->]...3.4v/10A...3.4v/5A...3.4v/5A...
[this will very quickly fill the 2nd cell...BUT now because 5A is being dumped into it ABOVE the 5A charge current...]
...3.65v/0A [balancer 5A->]...3.65v/5A [balancer 5A->]...3.4v/10A...3.4v/5A...
Notice that we need 10A of balance current to pass the power up and prevent overcharging the 3rd cell. Immediate problem.
When the 3rd cell gets fully charged (hypothetically assuming the balancer can run 10A balance current into the 4th cell)...now we have to "lose" 15A of current...
4th cell has to lose 20A of current...and it only gets worse the farther up you go. You can see how an "ideal" active balancer situation gets very quickly out of hand.
I really like the active balancer concept. But unless it's under microprocessor control and "gated" one cell at a time (a la Chargery I believe), it really can cause more trouble than it's worth.
Conversely, while shunt balancers are quite wasteful, burning up all the excess power in heat--they aren't "passing the buck", preventing that problem.