(1)Drawing's of the electrical system in progress. I am a plumber by trade and this electrical has been kicking my but. I chose the Growatt 24v 3000w

Jimmynik1

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That's an option I considered. I don't know if the heat shrink that properly fits the wire insulation will also fit the bolt/nut.

A 6" lead is horribly short. Mine were 18" I believe.
Yea I know right. Oh well. I'll make due.
Give me your thoughts on this please. When initially charging my cells, in the end there are going to be 2 8s packs each with their own bms that feed my growatt. Say I make my 2 individual packs and with only one pack at a time, use the growatt through the bms to initially charge and balance my pack. Been watching many videos of people connecting 8 or 16 in parallel and using a small 10a power supply with no bms to charge and balance initially. Then saw another pretty popular guy on youtube make a 12v pack with bms and just use a charger and it took hours vs days.
Appreciate your thoughts.
 

DerpsyDoodler

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As for ampertime I'm not sure yet.
But there 24v battery is only 100ah
If you plan on series connecting lifepo4 batteries (not just cells), then you need to make sure the battery BMS supports it. Talk to the MFG (in this case, ampere time). Make sure they give a clear and no uncertain response. It would suck to be out of luck because you fried the battery BMS and the mfg refuses warranty coverage.
 

HRTKD

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Yea I know right. Oh well. I'll make due.
Give me your thoughts on this please. When initially charging my cells, in the end there are going to be 2 8s packs each with their own bms that feed my growatt. Say I make my 2 individual packs and with only one pack at a time, use the growatt through the bms to initially charge and balance my pack. Been watching many videos of people connecting 8 or 16 in parallel and using a small 10a power supply with no bms to charge and balance initially. Then saw another pretty popular guy on youtube make a 12v pack with bms and just use a charger and it took hours vs days.
Appreciate your thoughts.

1. Never charge the cells unless they are in a compression frame. This applies to regular charging and top balancing.
2. If you initially charge in series, be sure you charge do a voltage less than the maximum voltage. You're looking at something in the range of 3.55. If you can't program your Growatt for this, then don't do it.
3. I chose to top balance with all cells in parallel from the start. Yes, it takes a while. I was patient. For this process, patience is good.
 

Jimmynik1

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1. Never charge the cells unless they are in a compression frame. This applies to regular charging and top balancing.
Yes I've seen some cool ways to keep them, mostly threaded rod with plywood ends.
2. If you initially charge in series, be sure you charge do a voltage less than the maximum voltage. You're looking at something in the range of 3.55. If you can't program your Growatt for this, then don't do it.
The growatt certainly cant charge at that individual voltage but as far as I know it can do 28.4 which is 3.55 x 8. So that ok?
3. I chose to top balance with all cells in parallel from the start. Yes, it takes a while. I was patient. For this process, patience is good.
Mine were advertised as new so I'm not sure how they'll come. But if all else fails I'll just do the slow way but am still curious about #2.
 

HRTKD

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The growatt certainly cant charge at that individual voltage but as far as I know it can do 28.4 which is 3.55 x 8. So that ok?

Sorry, for the confusion. I meant to charge up to 3.55v x the number of cells in the pack. Your number of 28.4v is correct. You can always choose a lower number to charge to when the batteries are in series with the BMS on.
 

Jimmynik1

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You can always choose a lower number to charge to when the batteries are in series with the BMS on.
What does that do?
Sorry, for the confusion. I meant to charge up to 3.55v x the number of cells in the pack. Your number of 28.4v is correct
Okay so making my pack with the BMS and then charging at 28.4 would be generally safe and likely balance them?
 

HRTKD

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Okay so making my pack with the BMS and then charging at 28.4 would be generally safe and likely balance them?

No! That does NOT balance them. What it does is get your cells closer to being at a full charge so that when you put them in parallel to perform the top balance you don't have to wait as long.

When the cells are in series they are getting charged with 25v+. In parallel they are charged with no more than 3.65v. It takes longer to charge at the lower voltage.

You don't HAVE to charge the cells in series. It's simply a way to get them charged faster to a certain threshold so you can then finish the top balance. As I said earlier, you can connect them in parallel from the start, but it will take longer to get the cells to 3.65v.
 

DerpsyDoodler

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No! That does NOT balance them. What it does is get your cells closer to being at a full charge so that when you put them in parallel to perform the top balance you don't have to wait as long.

When the cells are in series they are getting charged with 25v+. In parallel they are charged with no more than 3.65v. It takes longer to charge at the lower voltage.

You don't HAVE to charge the cells in series. It's simply a way to get them charged faster to a certain threshold so you can then finish the top balance. As I said earlier, you can connect them in parallel from the start, but it will take longer to get the cells to 3.65v.
also, as an aside, the measured cell voltage doesn't actually need to hit 3.65v. for lishen cells, the spec sheet says charge @3.65v until the current drops to either 8 or 12 (i dont recall which) amps. If you stop the charge at that point, the cell voltage is actually 3.45ish and the cell is fully charged.
 

Jimmynik1

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No! That does NOT balance them. What it does is get your cells closer to being at a full charge so that when you put them in parallel to perform the top balance you don't have to wait as long.
Got it now thanks. So either way you'd still recommend getting one of those commonly seen benchtop chargers or similar that can put out up to 10a.
You don't HAVE to charge the cells in series. It's simply a way to get them charged faster to a certain threshold so you can then finish the top balance. As I said earlier, you can connect them in parallel from the start, but it will take longer to get the cells to 3.65v.
Also got it now. Ty very much.
 

Jimmynik1

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also, as an aside, the measured cell voltage doesn't actually need to hit 3.65v. for lishen cells, the spec sheet says charge @3.65v until the current drops to either 8 or 12 (i dont recall which) amps. If you stop the charge at that point, the cell voltage is actually 3.45ish and the cell is fully charged.
this is when charging in parallel? .8 .08a?
 

Jimmynik1

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No! That does NOT balance them. What it does is get your cells closer to being at a full charge so that when you put them in parallel to perform the top balance you don't have to wait as long.

When the cells are in series they are getting charged with 25v+. In parallel they are charged with no more than 3.65v. It takes longer to charge at the lower voltage.

You don't HAVE to charge the cells in series. It's simply a way to get them charged faster to a certain threshold so you can then finish the top balance. As I said earlier, you can connect them in parallel from the start, but it will take longer to get the cells to 3.65v.
Also wanted to run this by you. I don't actually have any of my components yet, just ordered the batteries. I'm out of the country til around December but I have almost everything I'll need in my amazon cart for when I do get home.
System will be 620ah @ 24v with 2 8s packs. I'd like to make each pack able to be used with or without the other. I'm thinking of making my wood or whatever material box with the bms mounted inside with a 2 post bar in that box, that'll alleviate the short bms whip we talked about earlier. Then have the - wire off the post meet the + wire in a 2ga Anderson.
So basically when its all said and done they'll look like 2 small heavy wooden boxs with 8 cells, bms, bus bar, and the Anderson connector coming off of each. Then once both made they'll sit on a wagon or handcart and meet an Anderson pigtail which will feed into the final breaker to the inverter.
 

DerpsyDoodler

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this is when charging in parallel? .8 .08a?
in parallel or serial (doesnt matter). Not . (point). 8 or 12 amps. Note that what i stated is for lishen cells. You will need to consult the spec sheet for your cells/batteries.
 

Jimmynik1

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in parallel or serial (doesnt matter). Not . (point). 8 or 12 amps. Note that what i stated is for lishen cells. You will need to consult the spec sheet for your cells/batteries.
Very good thank you.
With 2 8s packs each with their own bms, in parallel going into one inverter, will they be used somewhat evenly? Or would something like one pack going dead and then the other one starting to get used happen.
I've had batteries in parallel on my boats and whatnot and I'm sure they were drained/charged somewhat evenly but wasn't sure if that was the same with LI cells through bms's.
Thanks
 

DerpsyDoodler

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Very good thank you.
With 2 8s packs each with their own bms, in parallel going into one inverter, will they be used somewhat evenly? Or would something like one pack going dead and then the other one starting to get used happen.
I've had batteries in parallel on my boats and whatnot and I'm sure they were drained/charged somewhat evenly but wasn't sure if that was the same with LI cells through bms's.
Thanks
As long as you properly parallel them, they should get used rather evenly. see simplified diagram, below. pretend each battery is a 24v battery. all load and charger positive lines connect to the first battery positive. All load and charger negatives would connect to the last battery negative. Of course, I wouldn't put all lugs directly on the battery terminal. Use bus bars.

7BB52545-8726-4E99-8AA3-F093BFABBC4A.jpeg
 

Jimmynik1

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your approach would work, too. Just be sure that all parallel cable sets are of equal length. both batt pos to bus bar (pair) and both batt neg to busbar (pair)
Awesome thanks, I'll likely reference this later when I go to build / have additional questions.
Appreciate you.
 
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