BMS advice needed for 7s8p or 7s16p solar storage


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grossy34

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thx for reply, will check connections today, will also attach pics of the battery
 

grossy34

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so problem sorted ourt, bad connections found out, welded again yesterday and today found another bad connection on another battery series, for now all running ok, gotta one question regarding two pics attached, so first is a power from pv and second is power charging battery so why there is such a difference?
 

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grossy34

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7s16p 18650(eve 26) battery, noticed that despite setting in inverter charging voltage 29.4v battery charging to only 28v, is that normal?
as two day in a row stopping charge at 28v
 

ajw22

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why there is such a difference
If the inverter output is ON, just the internal AC generating circuit will use some power, even if nothing is connected on the AC line. But this is typically only 10W~50W.
You mentioned a fridge earlier - any chance that it's drawing power?
551W from PW = 200W fridge draw + 10W~50W loss in the inverter + 194W left to charge battery.
 

grossy34

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If the inverter output is ON, just the internal AC generating circuit will use some power, even if nothing is connected on the AC line. But this is typically only 10W~50W.
You mentioned a fridge earlier - any chance that it's drawing power?
551W from PW = 200W fridge draw + 10W~50W loss in the inverter + 194W left to charge battery.
there was no fridge connected at that moment, weird things going on there, inverter not charging battery above 28v,lg fridge discharging 24v 40ah battery from 28v to 22v overnight
 

ajw22

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inverter not charging battery above 28v
There may be several charge voltage settings, such as "boost", "saturation", "equalize", "float". They're only relevant for charging lead acid batteries. For Lithium, you have to set them all to 29.4v (or whatever).
Other possibility is that the BMS is blocking the charging, because one of the cells has tripped the overcharge level (typically 4.25V). Check all seven voltages when the charging stops.
fridge discharging 24v 40ah battery [...] overnight
Maximun capacity at 24v * 40Ah = 960Wh.
And a fridge typically uses about 1~2kWh per day, more or less depending on size and quality of the fridge, as well as ambient temperature.
So the not fully charged battery not lasting one night may not be unusual.

Pictures of your setup might help spot other issues.
 

ajw22

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7s16p 18650(eve 26) battery, noticed that despite setting in inverter charging voltage 29.4v battery charging to only 28v, is that normal?
as two day in a row stopping charge at 28v
I just checked the manual. So you should have changed...
Program#05 to "USE" (User defined battery)
Program#26 from "28.2V" to "29.0V" (bulk charge phase; charging cells to only 4.14V will significantly increase cell lifespan)
Program#27 from "27.0V" to "29.0V" (float phase)
 

grossy34

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so settings changed - program 26 old setting 29.2v new 29v, program 27- old setting 28v new 29v,also for the record thats my pv setup at the moment, connected in series

1x 280w

Max Current (Imp) 10.77A

Maxes Voltage (Vpm) 26V

Short Circuit Current (Isc) 11.53A

Open Circuit Voltage (Voc) 31.46V

3x 330w

Max Current (Imp) 10.2A

Max Voltage (Vmp) 32.6V

Short Circuit Current (Isc) 10.9A

Open Circuit Voltage (Voc) 39.12V

i tried imp and isc to be as close as possible as 280w pv was discontinued, attached pic of pv A input 0.2a is it normal with this setup?
 

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ajw22

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pv A input 2.0A is it normal with this setup?
Depends. You should get a maximum of 10.2A ~ 10.77A from the panels on a sunny blue-sky day, when all panels are aligned perfectly perpendicular to the sun. On a fairly cloudy day, 2Amps would be reasonable.

Plus, the inverter will draw only as much current as it has something useful to do with. If the batteries are (close to) full and there's no AC load to drive, then the inverter will draw hardly any current from the panels.

Yep, the 280W+330W PV panel mix is fine since Imp and Isc are nearly identical.
 

grossy34

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Depends. You should get a maximum of 10.2A ~ 10.77A from the panels on a sunny blue-sky day, when all panels are aligned perfectly perpendicular to the sun. On a fairly cloudy day, 2Amps would be reasonable.

Plus, the inverter will draw only as much current as it has something useful to do with. If the batteries are (close to) full and there's no AC load to drive, then the inverter will draw hardly any current from the panels.

Yep, the 280W+330W PV panel mix is fine since Imp and Isc are nearly identical.
so 1x 280w + 3x 330w gives around 1270w so in perfect conditions i suppose to get pv input around that in the inverter?
as max i noticed was around 600w so far,


so new settings worked thx for that!
battery is charged to 29v,problem was in floating charge settings i geuss as i changed them from 28v to 29v,

time to build another battery i guess as if 40ah is not strong enough for a single fridge, considering 8x LF105, so will look for a minimum 150a bms for now, is there any other decent brand apart daly?

thx
 
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ajw22

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max i noticed was around 600w
Yes, under good conditions you should get around 1270W give or take. If you're only getting 600W, something is wrong. Post pictures of the panels, wiring, and battery. It's happened before that some innocuous oversight has had devastating effects on performance.

minimum 150a bms
The 60A BMS can power 60A*24V=1440W (realistically maybe 1kW), and thus is more than enough, if you're just powering the fridge.
 

grossy34

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Yes, under good conditions you should get around 1270W give or take. If you're only getting 600W, something is wrong. Post pictures of the panels, wiring, and battery. It's happened before that some innocuous oversight has had devastating effects on performance.


The 60A BMS can power 60A*24V=1440W (realistically maybe 1kW), and thus is more than enough, if you're just powering the fridge.
ok will post pics soon, so 60a bms is enough for 24v 105ah?, my next project is battery pack build from 8x eve LF05
new battery will be powering a lot of more than a fridge when i build it
 

ajw22

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60a bms is enough for 24v 105ah?
The Ampere rating of a BMS just sets the limit on how much current you can draw from the battery, and how quickly you can charge the battery.
So you could use the same 60A BMS for even a huge 1000Ah battery, but you'd still be limited to power just a ~1kW load - thus the (dis-)charge time extends to ~20hours.
The number should be taken with a grain of salt, as the BMS will often get uncomfortably hot when used continuously at that rate. Best to think of it as the peak rate, and limit continuous draw to maybe 75%.

ACTUALLY,
I just noticed that at least some "Daly 60A 7S" BMSs (I believe there are several versions) have a charge current limit of just 30A. That may be why you're only seeing 600W charge - the BMS keeps interrupting the charging as soon as the charge current ramps up above 30A. If so, that's not good at all. For one, the constant interruption will likely slow down the average charge rate to way below even 30A. More importantly, it may cause the BMS to overheat, possibly even damage the inverter. The best immediate action would be to set the inverter setting#02 (max charge current) to 30A or below, to at least not trigger the BMS.
 
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grossy34

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ACTUALLY,
I just noticed that at least some "Daly 60A 7S" BMSs (I believe there are several versions) have a charge current limit of just 30A. That may be why you're only seeing 600W charge - the BMS keeps interrupting the charging as soon as the charge current ramps up above 30A. If so, that's not good at all. For one, the constant interruption will likely slow down the average charge rate to way below even 30A. More importantly, it may cause the BMS to overheat, possibly even damage the inverter. The best immediate action would be to set the inverter setting#02 (max charge current) to 30A or below, to at least not trigger the BMS.
thx for explanation with bms A, now for the 600w, it was a pv input not battery charge input, so far achieved max 600w pv input and that was in cloudy day not sunny like yesterday (300-400W),so definitely is something wrong with my 4pv panels mounted on a flat roof, as far i know all of them having 30° angle and i read somewhere they should be around 38° as my latitude is 53° so will correct that over the weekend.
 

grossy34

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id like also to find out how load for example 1000w is taken from multiple 24v batteries connected, simultaneously?
or discharging one after one?
 

ajw22

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If you're thinking of mixing 7s Lithium-Ion and 8s LiFePO4 batteries... that's not impossible, but best avoided.

If you're thinking of putting in parallel your current Lithium-Ion 7s16p (40Ah capacity) and say a future 7s32p (80Ah), then both the charge and discharge current will be shared in the proportion 40 : 80, or 1 : 2.
Eg. when discharging at a combined rate of 60A (ca 1440W), the smaller battery will provide about 20A current, and the larger battery will provide 40A.
The voltages of both batteries will always be virtually the same, as will the SoC%. They'll get full together at the same time, and be depleted at the same time.

I currently have 7 batteries working in parallel. It's a good way to start small and then keep upgrading as needed.
 

grossy34

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well yea wanted to add 8s lifepo4 lf105 battery pack, why is the best to avoid them?
as far i know voltage are almost identical, 29.2v fully charged lifepo4 and lion 29.4,discharge 20v vs 21v also each battery will get its bms

regarding bms im trying to figure out if bms for 8s eve lf105 needs to be 150a at least or 100a is more than enough as my inerter max output is 2400w.
regards
 
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ajw22

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why is the best to avoid them
The fully charged voltage of 29V and fully discharged voltage of 22V works fairly well for both chemistries, resulting in cell voltage of 4.14V ~ 3.14V for 7s Lithium-Ion, and 3.63V ~ 2.75V for 8s LiFePO4. A bit conservative as I already indicated previously: cells will live much longer if you avoid the extreme high/low voltage ranges.

The issue is what happens between those extremes, as the two chemistries have different "power bands". Lithium-Ion has a more sloping discharge curve, with the bulk of the energy available between 28V~26V (4.0V ~ 3.7V/cell), while LiFePO4 has a very flat discharge curve with almost all the energy in the narrow band between 26V ~ 25V (3.25V ~ 3.13V/cell).
Which means that above 26V, a much larger proportion of current will flow into/from the 7s Lithium-Ion, while the 8s LiFePO4 will dominate between 26V~25V.

It's not impossible, just need to take care that during the "much larger proportion", you don't overtax whatever max current that that battery/BMS can handle. Also, the proportion will change over time, as LiFePO4 will degrade slower due to it's much longer lifespan.
 
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