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is it possible to top balance LIFEPO4 cells without a charger?


sunset1

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1 minute ago, Nexuss said:

basically no, if the voltages are the same the current transfer between the batteries will be very small. You need to parallel them and charge aswell. check out this video https://youtu.be/x5ABvbbics8

yeah i saw this, however saw another video from a different guy saying his top balances small packs without a charger in parallel.  He leaves them for a few days.

1 minute ago, Nexuss said:

 

 

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That wont work properly ,If you look at the charge curve of lifepo4 you will see that there wont be much current transfer when voltages are the same , as 2 batteries can be the same volts but have much diffrent levels of charge. Edit * Off grid garage youtube channel did quite a few videos explaining this in detail which you may find very interesting..

 

Edited by Nexuss
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Speaking from experience, you definitely need to charge them. Or they must be right near their highest voltage when paralleling them. I bought a bench power supply just for doing this, although even that is a bit low on current. My strategy in the past has been to get them as high as possible (When the most full battery hits 3.6V) while unbalanced with my inverter charger, then connect in parallel and do a final charge with the bench power supply set to 3.6V. This being said, my cells were never hugely out of balance... And a year later they are almost still perfectly balanced.

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6 minutes ago, JaseZA said:

Speaking from experience, you definitely need to charge them. Or they must be right near their highest voltage when paralleling them. I bought a bench power supply just for doing this, although even that is a bit low on current. My strategy in the past has been to get them as high as possible (When the most full battery hits 3.6V) while unbalanced with my inverter charger, then connect in parallel and do a final charge with the bench power supply set to 3.6V. This being said, my cells were never hugely out of balance... And a year later they are almost still perfectly balanced.

Thanks! 

What bench power supply do you use for this?

Hmm, maybe i can use my inverter as the bench power supply somehow.

By the way, where did you get your cells from and how do you like the VMiii 3kw inverter?

 

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8 minutes ago, sunset1 said:

What bench power supply do you use for this?

I bought a Minleaf 30V/10A PSU from Banggood - working well so far, but as I said, 10A is a bit light sometimes. But it works! And hard to beat the price.

10 minutes ago, sunset1 said:

Hmm, maybe i can use my inverter as the bench power supply somehow.

Problem is you need to accurately set the voltage to 3.6V - hard to do with an inverter I think.

10 minutes ago, sunset1 said:

By the way, where did you get your cells from and how do you like the VMiii 3kw inverter?

I've got a mix - got some from China, but that was very painful and worked out quite expensive... The rest I got from LithiumBatteriesSA. They had 120ah 2nd life cells at R750 last year which was a good price. That being said I'm busy building a DIY bank using some secondhand pouch cells I got from Mecer 12V 200ah lithiums 😅 

I've been very happy for the most part with my VMiii, considering what I paid for it. It doesn't have some of the features of the fancier systems but it's been reliable for me. I am in the process of upgrading to the 5kw though - 48V is much nicer with lower currents from the batteries and while we've made 3kw work, my wife is getting a bit irritated now when I tell her to wait for the kettle to finish before she uses the microwave! But it's been over a year and we've been fine. As of last month I have saved R4744 on electricity and been the only people in our complex not worried about load shedding 😁

One thing to note - I manage my inverter and BMS through a Raspberrypi which gives me even more control than most CAN connected batteries. Without this you're relying on the inverter to figure out SoC from the battery voltage. There are quite a few threads on this and why it can be problematic. In summary, you generally just lose out on some available battery capacity. There are some BMSes available with CAN communication but you need to make sure they work with Voltronic inverters.

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26 minutes ago, JaseZA said:

I bought a Minleaf 30V/10A PSU from Banggood - working well so far, but as I said, 10A is a bit light sometimes. But it works! And hard to beat the price.

Problem is you need to accurately set the voltage to 3.6V - hard to do with an inverter I think.

I've got a mix - got some from China, but that was very painful and worked out quite expensive... The rest I got from LithiumBatteriesSA. They had 120ah 2nd life cells at R750 last year which was a good price. That being said I'm busy building a DIY bank using some secondhand pouch cells I got from Mecer 12V 200ah lithiums 😅 

I've been very happy for the most part with my VMiii, considering what I paid for it. It doesn't have some of the features of the fancier systems but it's been reliable for me. I am in the process of upgrading to the 5kw though - 48V is much nicer with lower currents from the batteries and while we've made 3kw work, my wife is getting a bit irritated now when I tell her to wait for the kettle to finish before she uses the microwave! But it's been over a year and we've been fine. As of last month I have saved R4744 on electricity and been the only people in our complex not worried about load shedding 😁

One thing to note - I manage my inverter and BMS through a Raspberrypi which gives me even more control than most CAN connected batteries. Without this you're relying on the inverter to figure out SoC from the battery voltage. There are quite a few threads on this and why it can be problematic. In summary, you generally just lose out on some available battery capacity. There are some BMSes available with CAN communication but you need to make sure they work with Voltronic inverters.

Oh interesting. Thanks for the great info. Yes we dont want worry either about load shedding - costs us money evertime since we cant work. Luckily we dont have a micro and have a gas stove for the kettle - managed to convince my better to ditch this!😁

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"Without this you're relying on the inverter to figure out SoC from the battery voltage"

yes i was wondering how an inverter determines SOC since Volts pretty much dont say much during the flat curve part.

Are you going to be selling your 3kw? If so I would be interested.

What BMS are you using by the way?

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5 minutes ago, sunset1 said:

yes i was wondering how an inverter determines SOC since Volts pretty much dont say much during the flat curve part.

Exactly the problem with LiFePO4 - the inverter doesn't do a very good job 😂

7 minutes ago, sunset1 said:

Are you going to be selling your 3kw?

I'm still deciding - might have another project for it. But will let you know.

8 minutes ago, sunset1 said:

What BMS are you using by the way?

I have a "Smart BMS" from Ali-express (Sometimes called the 'ANTbms'). With a lot of creative programming I managed to link my rPi over bluetooth to pull the data. Then use Solpiplog to pull data from the inverter over serial and send commands.

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10 hours ago, sunset1 said:

Hi,

i would like to top balance 4 x 3.2v LIFEPO4 CELLS - A grade - new

The voltages for each cell is as follows - 3.29v

IS it possible to top balance these by connecting them in parallel for a few days.

 

 

This will balance them without charging https://www.aliexpress.com/item/4000262767165.html?spm=a2g0o.productlist.0.0.380a59b7dEGlIi&algo_pvid=4d801a03-d31a-47f1-a385-6774eca85a0d&algo_exp_id=4d801a03-d31a-47f1-a385-6774eca85a0d-16

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9 hours ago, sunset1 said:

How so? 

These balancers only work to equalize the voltage across each cell.  The resistive ones just discharge the cell with highest voltage. The capacitive ones transfer charge from the cells with highest voltage to lowest voltage. Most can achieve <10mV difference between the cells, some as low as 5mV. But none will actually perfectly match the voltage.

If you disassemble the battery and connect the cells in parallel, then they will eventually settle to perfectly matched voltages.

As others have pointed out above, at nominal cell voltages, charge level is very insensitive to voltage, so a 5-10mV difference would generally be quite a large charge imbalance (perfectly matched voltages will still have some imbalance, but less).

The easiest way to actually balance the cells is to charge them. When they are close to maximum voltage, then small charge differences lead to large voltage differences, and balancing the voltages will give you well balanced charge levels.

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10 minutes ago, JustinSchoeman said:

These balancers only work to equalize the voltage across each cell.  The resistive ones just discharge the cell with highest voltage. The capacitive ones transfer charge from the cells with highest voltage to lowest voltage. Most can achieve <10mV difference between the cells, some as low as 5mV. But none will actually perfectly match the voltage.

If you disassemble the battery and connect the cells in parallel, then they will eventually settle to perfectly matched voltages.

As others have pointed out above, at nominal cell voltages, charge level is very insensitive to voltage, so a 5-10mV difference would generally be quite a large charge imbalance (perfectly matched voltages will still have some imbalance, but less).

 

Balancing by parallel will take ages and while you might balance the voltages eventually, the cells will not magically be matched, so as soon as you discharge them they will become unbalanced again.

 

10 minutes ago, JustinSchoeman said:

The easiest way to actually balance the cells is to charge them. When they are close to maximum voltage, then small charge differences lead to large voltage differences, and balancing the voltages will give you well balanced charge levels.

The whole topic is how to balance without a charger... But yes... they balance easier while charging, but then you still need a balancer. Otherwise you have to dismantle your pack and put it in parallel every time you want to charge your batteries.

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1 minute ago, tetrasection said:

Balancing by parallel will take ages and while you might balance the voltages eventually, the cells will not magically be matched, so as soon as you discharge them they will become unbalanced again.

Correct - but it will be a lot quicker and more accurate than using a balancer board.

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13 hours ago, JustinSchoeman said:

These balancers only work to equalize the voltage across each cell.  The resistive ones just discharge the cell with highest voltage. The capacitive ones transfer charge from the cells with highest voltage to lowest voltage. Most can achieve <10mV difference between the cells, some as low as 5mV. But none will actually perfectly match the voltage.

If you disassemble the battery and connect the cells in parallel, then they will eventually settle to perfectly matched voltages.

As others have pointed out above, at nominal cell voltages, charge level is very insensitive to voltage, so a 5-10mV difference would generally be quite a large charge imbalance (perfectly matched voltages will still have some imbalance, but less).

The easiest way to actually balance the cells is to charge them. When they are close to maximum voltage, then small charge differences lead to large voltage differences, and balancing the voltages will give you well balanced charge levels.

TX but confused.

Better to put them in parallel for some days or buy a bench dc charger?

I did see on my bms daly that it balances above 3.5 or something 

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25 minutes ago, JustinSchoeman said:

The only way to properly balance cells is to charge them.  The best once-off balance is to connect the cells in parallel and charge them.

The only way to actually maintain any real balance is to permanently use a balancer board.

 

Also, the proper way to balance cells in parallel is as follows:

1. If possible - top each of the cells up to the voltage of the highest cell prior to wiring them in parallel.
2. Wire the cells in parallel
3. Set the power supply to 3.40V and the amperage to about 80% of the max it can do. (Setting it at 80% is only to prolong the life of the Power Supply)
4. Turn on power supply and charge to 3.40V
5. When the current has dropped to 0.0A at 3.40V turn off the power supply & set it to 3.50V
6. Turn on power supply and charge cells to 3.50V
7. When current has dropped to 0.0A at 3.50V turn off the power supply & set to 3.60V
8. Allow current to drop to 0.0A at 3.60V
9. Disconnect Power.
10. The Battery pack is now perfectly balanced.

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