Lithium Cell Balancing at Nowty Towers - Resurrections

[nowty]

I have now tested the second overvoltage board and it works exactly the same as my first one but only shunts 1.25A compared with the first one shunting about 2.1A. To parallel up the circuits, on the new board I would have to cut several tracks and link the negative rail across to each individual circuit. Its the sort of thing I would have done in the past, but to be honest I cannot be bothered with these new boards as they have surface mount components and my patience and eye sight is not what it was.

So I have ordered 3 more of the first type and I will fit 4 of them onto the new cell.

Are the boards inexpensive? My delivery date for the new battery buckboard is 28th Oct! Only excuse is that it was in Turkish when I ordered.

About a tenner each but I suspect most of the charge is the airmail fee so its a bit off that I don't get a discount on buying multiple items. I guess I could have emailed and haggled but that would just delay matters.

[Joeboy]

I have now tested the second overvoltage board and it works exactly the same as my first one but only shunts 1.25A compared with the first one shunting about 2.1A. To parallel up the circuits, on the new board I would have to cut several tracks and link the negative rail across to each individual circuit. Its the sort of thing I would have done in the past, but to be honest I cannot be bothered with these new boards as they have surface mount components and my patience and eye sight is not what it was.

So I have ordered 3 more of the first type and I will fit 4 of them onto the new cell.

Are the boards inexpensive? My delivery date for the new battery buckboard is 28th Oct! Only excuse is that it was in Turkish when I ordered.

About a tenner each but I suspect most of the charge is the airmail fee so its a bit off that I don't get a discount on buying multiple items. I guess I could have emailed and haggled but that would just delay matters.

What sort of turnaround time are you ?

[nowty]

Are the boards inexpensive? My delivery date for the new battery buckboard is 28th Oct! Only excuse is that it was in Turkish when I ordered.

About a tenner each but I suspect most of the charge is the airmail fee so its a bit off that I don't get a discount on buying multiple items. I guess I could have emailed and haggled but that would just delay matters.

What sort of turnaround time are you ?

6 days from ordering, to them coming through the door. Online tracking shows most of the time is spent going through processing centres and hubs in China.

[Joeboy]

About a tenner each but I suspect most of the charge is the airmail fee so its a bit off that I don't get a discount on buying multiple items. I guess I could have emailed and haggled but that would just delay matters.

What sort of turnaround time are you ?

6 days from ordering, to them coming through the door. Online tracking shows most of the time is spent going through processing centres and hubs in China.

That's very good, I am weeks off that sort of time line (6 maybe). No hurry, worst case in a no show I'll just voltage match the systems after paralleling the new units. I hope they work well for you.
I am interested in how much power is being dumped off in heat to keep the new cell within.parameters of the rest of the storage system. Assuming it's very small amounts?

[Moxi]

I watched this a few nights back and then the second instalment, it might answer some of your questions regarding efficiency and heat loss ? then again it might not.

Moxi

[nowty]

I am interested in how much power is being dumped off in heat to keep the new cell within.parameters of the rest of the storage system. Assuming it's very small amounts?

The amount lost should be the same pro rata to what's being lost in the Pylontechs due to their protection / comms circuitry, its only a few watts.

I did some more calculations with my spreadsheet, and based upon a new higher charge voltage of 56.4V and a low cut off at 46.5V, I will have a gross size battery capacity of 68.5 kWh and a useable size of 59 kWh.

Before this extra cell (circa 1.5 kWh), my usable battery size was about 45 kWh due to running at a lower charge voltage.

[nowty]

For those who don't understand my old and new battery configuration a picture paints a thousand words as they say,



My new cell is working well, but in addition to placing a couple of overvoltage protectors on the new cell, I am also going to have to place a 20 ohm (or so) resistor across the new cell to constantly burn off the same (well slightly lower) pro-rata overhead power of the Pylontechs.

I first thought this would not be necessary, but over a few mediocre solar days where the cell did not reach full voltage and operate the overvoltage devices to burn off excess charge, the new cell slowly increased in voltage (relative to the Pylontechs) so it is possible for the the Pylontechs to charge at say 10A or 20A near their top end when the new cell is already operating its protection devices. So even if I use 4 devices burning off 8A, that may not be enough in certain situations.

Its easy for me to calculate the Pylontech cell voltage with simple mathematics so I have been experimenting each day by running my existing 1 ohm resistor across the new cell by different time periods to see how close I can get the new cell to behave in the same way to the Pylontechs. Its between about 1.5hrs and 2hrs burning off about 11W each day to stop the voltage rising on the new cell compared with the Pylontech cells. So that's not far off 1W for the full 24 hours. So for a full stack of 8 x 2.4kWh Pylontechs, the daily overhead is about 1W x 15 cells = 15W x 24hrs = 0.36kWh.

Now as the batteries are sometimes in standby and probably using less power in that state, its a little difficult to say for certain but it will average out somewhat. So I have a few cheap power resistors on order, expecting them tomorrow and I will start with a 20 ohm resistor which will burn off circa 0.5W. If the voltage on the new cell still increases (relative to the Pylontechs) day after day, then I can try a lower value resistor, say 15 ohm or even a 10 ohm. If I find the voltage on the new cell dropping day after day (relative the the Pylontechs), then the value of resistor is too low.

I hope to find one where the voltage on the new cell rises relatively very slowly so it could be left for weeks without experiencing a full charge relatively worry free. In normal operation its only in the shoulder months that this occurs, as its either full charge most days in summer and full charge every day via the grid in winter.

[Joeboy]

For those who don't understand my old and new battery configuration a picture paints a thousand words as they say,



My new cell is working well, but in addition to placing a couple of overvoltage protectors on the new cell, I am also going to have to place a 20 ohm (or so) resistor across the new cell to constantly burn off the same (well slightly lower) pro-rata overhead power of the Pylontechs.

I first thought this would not be necessary, but over a few mediocre solar days where the cell did not reach full voltage and operate the overvoltage devices to burn off excess charge, the new cell slowly increased in voltage (relative to the Pylontechs) so it is possible for the the Pylontechs to charge at say 10A or 20A near their top end when the new cell is already operating its protection devices. So even if I use 4 devices burning off 8A, that may not be enough in certain situations.

Its easy for me to calculate the Pylontech cell voltage with simple mathematics so I have been experimenting each day by running my existing 1 ohm resistor across the new cell by different time periods to see how close I can get the new cell to behave in the same way to the Pylontechs. Its between about 1.5hrs and 2hrs burning off about 11W each day to stop the voltage rising on the new cell compared with the Pylontech cells. So that's not far off 1W for the full 24 hours. So for a full stack of 8 x 2.4kWh Pylontechs, the daily overhead is about 1W x 15 cells = 15W x 24hrs = 0.36kWh.

Now as the batteries are sometimes in standby and probably using less power in that state, its a little difficult to say for certain but it will average out somewhat. So I have a few cheap power resistors on order, expecting them tomorrow and I will start with a 20 ohm resistor which will burn off circa 0.5W. If the voltage on the new cell still increases (relative to the Pylontechs) day after day, then I can try a lower value resistor, say 15 ohm or even a 10 ohm. If I find the voltage on the new cell dropping day after day (relative the the Pylontechs), then the value of resistor is too low.

I hope to find one where the voltage on the new cell rises relatively very slowly so it could be left for weeks without experiencing a full charge relatively worry free. In normal operation its only in the shoulder months that this occurs, as its either full charge most days in summer and full charge every day via the grid in winter.

That is an excellent post Nowty. I hope to not need the info for my own extension, nonetheless. Bravo!

[nowty]

That is an excellent post Nowty. I hope to not need the info for my own extension, nonetheless. Bravo!

Don't worry Joeboy, nothing for your battery extension to worry about as your two strings will be nicely balanced.

Its just my connecting of two different battery systems together. The Growatts used to be in an OffGrid system and the Pylontechs used to be in an OnGrid system. Both were totally separate, but then I connected both together so all OnGrid now, but in doing so, had to compromise on a lower charging voltage which sacrificed overall capacity.

[nowty]

My resistors arrived about half an hour ago and earlier I bled a bit more power off the new cell with my 1 ohm resistor.

I have fitted a 10W rated 20 ohm resistor across the cell, its pleasantly warm to touch burning about 0.5W.

At 12:20 today the voltages are,

Pylontech 51.12V, so each cell is 3.408V
New Cell 3.352V

I will monitor and note the voltages again tomorrow at around the same time.