I am very new here. I just bought some lithium battery banks ready to be used for my solar application. I have 4 banks of 24v battery system ready to connect. My inverter is 3000w. I am looking at buying one of those BMS on Ali Express. I have seen one that is 8s 24v100a commom, and also 8s 24v 60a. Can anyone please advice how to go about connecting the BMS to the batteries and if 100a for each bank is something to go for or 60a for each bank can do the Job.
Can I connect BMS in parallel or series?
- Thread starter Kwame
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It really depends on your load. Do you expect to pull 400 amps from the battery at one time?
OverKillSolar has an 8s BMS, but I don't see it on Amazon. Here is a link to his 4s BMS, however it is 12v not 24v. He is active here on the forum so you can get in touch with him that way and as about 24v.
OverKillSolar has an 8s BMS, but I don't see it on Amazon. Here is a link to his 4s BMS, however it is 12v not 24v. He is active here on the forum so you can get in touch with him that way and as about 24v.
A bank is considered to be a group of 1 or more batteries. Four batteries wired in parallel into a (single) battery bank would be capable of four times the Ah rating of each battery, assuming that all four batteries are the same.
If you used a 60A BMS on each battery and the batteries are wired in parallel then you get a battery bank that is - effectively - 240 Ah. I wouldn't size my battery bank on the inverter alone. It's all the appliances that the inverter will be powering that I base my battery bank on.
If you used a 60A BMS on each battery and the batteries are wired in parallel then you get a battery bank that is - effectively - 240 Ah. I wouldn't size my battery bank on the inverter alone. It's all the appliances that the inverter will be powering that I base my battery bank on.
GXMnow
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From the reading I have done, it seems most BMS units do not work properly when wired in series. If one does have to go into protect, it will need to open the entire string voltage. That can cause the unit to fail as most are only designed to open their rated voltage, not 2 or 4 times it's nominal voltage. There is also no way for 2 separate BMS units to balance the cells between the other series banks.
BMS units do work in parallel, but can still cause some issues if you run near the maximum loading. For example, if you have two 60 amp units running a 100 amp load, it should all work fine, but if one bank happens to have a cell reach the low voltage limit, it will open to protect that cell. And then the full load current of 100 amps will be on the other 60 amp BMS which will then trip in an over current situation. You need to keep the banks balanced. You should make sure all the cables are the same length so the banks evenly share the load current. At lighter loads, they will self balance to a point, but if your system needs all of the current, it may not stay in balance.
BMS units do work in parallel, but can still cause some issues if you run near the maximum loading. For example, if you have two 60 amp units running a 100 amp load, it should all work fine, but if one bank happens to have a cell reach the low voltage limit, it will open to protect that cell. And then the full load current of 100 amps will be on the other 60 amp BMS which will then trip in an over current situation. You need to keep the banks balanced. You should make sure all the cables are the same length so the banks evenly share the load current. At lighter loads, they will self balance to a point, but if your system needs all of the current, it may not stay in balance.
caglar gediksiz
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GXMnow
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What is your load? There are quite a few good 13S BMS units available. But most are good for about 100 amps continuous. I have a Ji Kong BMS rated for 200 amps, but I would not trust that for long term at that power level. My 14S 48 volt system runs from 15 to 85 amps. 80 amps at 50 volts is 4,000 watts. That is still a lot of power.
DALY has some new BMS units rated for 250 amps with thick copper rails to handle the current. Orion and Overkill also get good reviews. Whatever it is rated for, run it at half that current and you know it will hold up. You can run BMS units in parallel. If one does go into protect, the other will likely go into over current protect fairly soon after. Be sure to check their calibration and set them to the exact same shut off points.
there are some benefits to building the system as 2 or 3, or even 4 separate batteries. With 4, and any two being able to run the load, you can keep running with no worries even with one module down. I may be doubling up my battery bank. I plan to set them up on separate BMS units and fuses. I know one can run my system, the second is for more time without power and to maybe time shift power to run my A/C off solar in the evening. My current battery bank is 360 AH.
DALY has some new BMS units rated for 250 amps with thick copper rails to handle the current. Orion and Overkill also get good reviews. Whatever it is rated for, run it at half that current and you know it will hold up. You can run BMS units in parallel. If one does go into protect, the other will likely go into over current protect fairly soon after. Be sure to check their calibration and set them to the exact same shut off points.
there are some benefits to building the system as 2 or 3, or even 4 separate batteries. With 4, and any two being able to run the load, you can keep running with no worries even with one module down. I may be doubling up my battery bank. I plan to set them up on separate BMS units and fuses. I know one can run my system, the second is for more time without power and to maybe time shift power to run my A/C off solar in the evening. My current battery bank is 360 AH.
timber1111
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getting 2 of the https://signaturesolar.com/eg4-8-cell-pack-lithium-cells-25-6v-100ah/, 24v bank, putting in parallel for 200ah capacity.....
Do I use 1 BMS or 2? If 2 how are they wired? https://overkillsolar.com/product/bms-100a-8s-lifepo4-12/
Thanks
Do I use 1 BMS or 2? If 2 how are they wired? https://overkillsolar.com/product/bms-100a-8s-lifepo4-12/
Thanks
Based on the picture of those cells, the bus bars between cell terminals are welded. Performing a top balance would be a bit challenging since you can't take the cells apart and rearrange them in parallel instead of series. But maybe they come top balanced? I wouldn't count on that. I would call to confirm the bus bars.
One BMS for each set of eight cells. Wire each battery to a common bus bar using equal length cables. You're going to want a Class T fuse on the positive leg, so run the positive battery cables to the fuse, then the fuse to the positive common bus bar. A switch would be good to have also and it would be installed between the fuse and the positive common bus bar. If you have a shunt, it goes on the negative leg. Run the negative battery cables to the shunt, then a cable from the shunt to the negative common bus bar.
timber1111
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Thanks for the info, these batteries are featured here ...
So you are saying 2 bms's, but how are they connected to the main negatives (and then on to the inverter/charge controller) when the (2) 24v banks are in parallel?
Thanks!
A quick drawing. The lines aren't quite right because the cables are expected to be equal lengths. The BMS and the cells are considered one unit because the BMS must be located on or near the cells.
Does anyone know the internal resistance of these batteries? A class T fuse would be have an AIC rating of 20,000 amps where a MBRF fuse is 10,000 amps. An internal resistance over2.5 milliohms (.0025 ohms) would allow for a MBRF fuse. Under that requires a T fuse. Thanks in advance.
John Frum
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I've been working on the same concept.
Don't forget the resistance of the rest of the battery.
Include busbars, bms, main terminals, mrbf fuse.
I think the bms resistance will be the big one.
my sense is the internal resistance of the battery is the IR of each cell times 8. The bus bars and bms may add more, but don't you want to use the base level for figuring out your fuse? Any additional resistance from the other stuff adds a level of safety.
jps
jps
John Frum
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You might, but I don't.
For a 4s battery at 14.6VDC just considering the internal resistance it can be as low as low as 0.37 milli-ohms and still get a dead short ampacity of 9865 amps which is in spec for an MRBF fuse.
At least that is what the math tells me.
John Frum
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Which would give a 4s battery a dead short ampacity of 24333 amps.
I'm looking at an 8s battery at 25.6 V at 100 ah. With no idea of the IR at this point. My 280 AH 4s EVE battery spec chart says .25 milliohms per cell; or 1 milliohm for 4 cells? That gives me a dead short of 14,600??? (14.6 divided by .001) I use a T fuse on that battery.
I suspect these 100 ah batteries have a higher IR due to their smaller capacity, but I can find zero specs. If i use the EVE specs on thes batteries, I'd get 25.6 divided by .002) 12,800 which still puts me in T fuse land. . . . .
I suspect these 100 ah batteries have a higher IR due to their smaller capacity, but I can find zero specs. If i use the EVE specs on thes batteries, I'd get 25.6 divided by .002) 12,800 which still puts me in T fuse land. . . . .
But these CATL batteries are .39 mOhms. So, I'm thinking I need a 125 amp T fuse. So far, no luck at finding a holder for that . . .
Module:001CB270
Nominal Voltage:3.2V
Nominal Capacity:100Ah
Internal Resistance:0.39±0.05mΩ
Dimension: 200.33*172.2*33.22mm±0.5mm
Weight:2.27±0.30Kg
3.2V 100Ah CATL LiFePO4 Battery cell with screws for easy connection
Module:001CB270
Nominal Voltage:3.2V
Nominal Capacity:100Ah
Internal Resistance:0.39±0.05mΩ
Dimension: 200.33*172.2*33.22mm±0.5mm
Weight:2.27±0.30Kg
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