My understanding was that all Lithium batteries, when connected in parallel, double the discharge current capacity. Is that true? E.g. if I combine two US5000, then max continuous discharge current is 200amps @ 48v?

However, was looking at datasheet of Narada NESR batteries about Parallel expansion. According to it, 1 battery supports 100amps discharge, but 2 batteries support 120amps discharge and 3 batteries 150amps? Does anyone know why 2x doesn't support 200amp and 3x doesn't support 300amps discharge? Is the same true for NPFC & pylontech batteries?

Edited January 8, 20241 yr by LionKing

49 minutes ago, LionKing said:

My understanding was that all Lithium batteries, when connected in parallel, double the discharge current capacity. Is that true? E.g. if I combine two US5000, then max continuous discharge current is 200amps @ 48v?

However, was looking at datasheet of Narada NESR batteries about Parallel expansion. According to it, 1 battery supports 100amps discharge, but 2 batteries support 120amps discharge and 3 batteries 150amps? Does anyone know why 2x doesn't support 200amp and 3x doesn't support 300amps discharge? Is the same true for NPFC & pylontech batteries?

 When you parallel multiple batteries, you can't ever expect to get the full current. My own personal rule is two batteries, 150% current of one battery. So with two batteries each capable of 100 amps, with 2 in parallel, you can pull 150 amps, so even if there is a 50 amp difference, the high battery is only at 100 amps, and the low one is providing the other 50 amps. Go to 4 batteries, and now you should be safe pushing 225%. This is again getting 50% more current when you double the batteries. If the balance is perfect, then you would only have 56.25 amps from each battery, but if one is weak, and another it strong, you could have one pulling 85 amps, and one pulling just 20 amps, while the other two are at 60 amps. That goes for all batteries in parallel. Any tiny difference in the internal cell voltages, state of charge, cell resistance, BMS resistance, and even the voltage drop of the mosfets and different cable lengths will cause the two separate battery strings to carry a different amount of current.

Edited January 8, 20241 yr by TaliaB

Good morning, I'm very interested in the discussion, I have 4 TAICO 51.2V 100ha batteries in this period which in Italy we have little sun, they charge and discharge differently, I can even have a difference of 10%, is it possible to balance the batteries with something?

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That is strange, the Discharge and Charge rates reported on my inverter by my BSL batteries is directly in proportion to the number of batteries installed. 

i.e. 4 batteries = 4 x a single batteries charge and discharge rate. 

You obviously will also need to have the necessary cables and fuses to carry the extra current and they recommend bus bars for installations of more than 4 batteries. 

This original question is solely based on the C rating of the battery in question. Simple example, some batteries are 0.5C & some are 1C. The Pylontech family of batteries are usually rated at 0.5C. eg you have 2 x us3000. One is capable of 1.75kW continuous rated. So adding 2 of them unlocks 3.5kW continuous. 

Another example the FreedomWon 20/16 is 1C. So adding 2 of them gives you 40kW continuous. 

The C rating is a very important aspect when you buy a battery. It will determine a lot in the operations of your inverter. Choose wisely. 

24 minutes ago, Steve87 said:

This original question is solely based on the C rating of the battery in question.

The C rating of Narada NESR battery is 100amps. So two should have been 200amps. If you look at Parallel Expansion chart provided by Narada, the discharge amps increase isn't linear - when you add more batteries. 

Do these batteries have snap on connectors like Pylontech? If so what is the diameter of the cables? 

3 hours ago, Steve87 said:

Do these batteries have snap on connectors like Pylontech? If so what is the diameter of the cables? 

I haven't purchased these yet, still deciding between pylons and these. AFAIK, these dont come with cables at all, but cable mounting screws are M8. 

Key differences between Pylon UP5000 (only have that available locally) and Narada NESR:

NESR is cheaper, uses 16 cells vs pylon's 15s, has 6000 cycles (15year design life) vs pylon's 4500.

One should not even dare to plan to use 1C discharge current. It is very damaging to the cells and creates lots of losses due to heating the cells. Size your battery capacity such that with your practical max load you do not exceed 0.5C. Battery live will reward you. Anyway the most benefit of increasing battery capacity is not the increased discharge current, but the increased storage capacity of harvested solar energy. As a side effect it increases live expectancy due to lower stress on the cells.

By the way, according to my observations parallel packs do equalize themselves when reaching bulk or floating charge voltage. Provided the BMS comms do not prevent the inverter charger to properly charge up to that level.

Edited January 9, 20241 yr by Beat

23 hours ago, TaliaB said:

 When you parallel multiple batteries, you can't ever expect to get the full current. My own personal rule is two batteries, 150% current of one battery. So with two batteries each capable of 100 amps, with 2 in parallel, you can pull 150 amps, so even if there is a 50 amp difference, the high battery is only at 100 amps, and the low one is providing the other 50 amps. Go to 4 batteries, and now you should be safe pushing 225%. This is again getting 50% more current when you double the batteries. If the balance is perfect, then you would only have 56.25 amps from each battery, but if one is weak, and another it strong, you could have one pulling 85 amps, and one pulling just 20 amps, while the other two are at 60 amps. That goes for all batteries in parallel. Any tiny difference in the internal cell voltages, state of charge, cell resistance, BMS resistance, and even the voltage drop of the mosfets and different cable lengths will cause the two separate battery strings to carry a different amount of current.

Interesting and my understanding was different to this.

 

A single battery, if capable of 100A would mean that 2 of those batteries in parallel would therefore be capable of 200A.

I guess the way you have the batteries installed and wired would make a big difference too.

 

With my setup, all batteries are connected to busbars and then the inverters connect to the busbars. I have tried to keep cable lengths as similar as possible between the batteries & busbars 

When I charge or discharge the batteries, if I view the current on the battery BMS screen the current is almost identical between each battery.

For example I may have the following current per battery:

Battery 1 = 20.42A

Battery 2 = 20.26A

Battery 3 = 20.01A

 

I would assume that if I were to increase the draw from the batteries that the discharge current would remain split fairly equally between each battery? I would not expect the small difference / imbalance to be a big issue.

 

I could understand that if one battery were weaker / older and perhaps had very different sized cables that the discharge / charge current on that battery may differ more compared to the other batteries and if you are running the batteries near their max discharge / charge rate it is possible for one battery to maybe exceed the limit and lead to the BMS kicking in and stopping all charge / discharge to that battery temporarily and this would lead to other issues - such as the remaining battery BMS kicking in and stopping charge / discharge, comms to the inverter may be interrupted as well and then the inverter thinks that no batteries are connected and if there is no grid then your system may be offline until the BMS fault clears.

On 2024/01/08 at 3:41 PM, TaliaB said:

 you could have one pulling 85 amps, and one pulling just 20 amps, while the other two are at 60 amps. That goes for all batteries in parallel. Any tiny difference in the internal cell voltages, state of charge, cell resistance, BMS resistance, and even the voltage drop of the mosfets and different cable lengths will cause the two separate battery strings to carry a different amount of current.

My take on this is if you control the items you have control over like age, cable size and length, SOC there will be little chance that one will deliver 85A at a high and another 20A at the low. 

Due to the items out of control there might be about a 5% difference as a guess. 

Here is a interesting read about Parallel of lifep04.

https://www.master-instruments.com.au/tech-talk-article/3/Explaining the limits of LiFePO4 batteries in parallel.html#:~:text=First%2C we need to understand,is unlikely to be equal.

1 hour ago, TaliaB said:

Here is a interesting read about Parallel of lifep04.

https://www.master-instruments.com.au/tech-talk-article/3/Explaining the limits of LiFePO4 batteries in parallel.html#:~:text=First%2C we need to understand,is unlikely to be equal.

Thanks for the link. I think the key take away is could. Also indicated they won't provide exactly the same. This means if 25.05A and 24.95A it is close enough to equal for me. 

The exact example is 22A and 28A with the wording COULD. 

Hi, I would go for Freedom Won eTower and buy it from Solarways for just under R26k each. Here are the specs. Good max and continous discharges.

It's also a 16cell battery 

Just a suggestion. 

 

The end of the article mentions the distributed BMS, with a master unit controlling the combined current intelligently during parallel operation. 

Freedomwon does exactly that with great success on the orion BMS, and you get the full current rating of your batteries when paralleling. On the orion BMS software you can see a lot of detail, the individual currents etc of each battery for a start , and the  combined current rating the BMS will allow for the combined entire pack, etc. Works well. 

Edited January 9, 20241 yr by abd7

10 hours ago, Jakac said:

Hi, I would go for Freedom Won eTower and buy it from Solarways for just under R26k each. Here are the specs. Good max and continous discharges.

It's also a 16cell battery 

Just a suggestion. 

 

Thanks for the detail around how in this case parallel batteries behave and provide power. 

The reduction seems around 10% which is a good ball park figure. It is assumed in some cases it is the BMS preventing full use of power. 

My own tests with 2 x 200Ah 12V Mecers in parallel being charged from the car while driving do charge at less than 5% delta. I had enough time to see the readings while to work and back. About the same small delta during discharge. These 2 batteries were more than a year old and they are now over 2.5 yrs old. 

In the case above no interaction between each BMS.