Question about the battery extension

Walde

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May 18, 2018
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131
Have at the moment already a 14er package with 7.5KW (60P14S) on the run.

Would like to switch now also a second set of Akkus also 7.5KW (60P14S) in order
to come to 2x 7,5KW (60P14S).

How should the state of charge of the first sentence be.
The new set is loaded at about 4.15 V per pack.
 
All voltages should be fairly close to each other before you connect them. I'd aim for max +/- 0.1V per cell difference.
The higher the voltage difference, the more current will rush in as you connect them, possibly triggering the breaker.
You can charge the first battery up to close to 4.15V, or discharge the new battery to the level of the first battery, or a combination of both - it does not matter.

Have you considered going 14s120p instead of 2p(14s60p) ? With your current plan, you need a second set of BMS, wiring, and breaker. I think most people expand to about 14s200p before adding a new parallel battery.
 
Ok, something was misunderstood.
I would like to extend the 60p to 120p.
The new 60p are to be switched parallels to the first 60s packages.
And will completely use the BMS of the first packages.

Construction as in the photo



image_zoicks.jpg



Now the only question is how the condition should be from the first package.
Since the new is the second package at 4.15v.
or does it matter anyway from the first packet ... 3.5-4.15v
 
Walde said:
Ok, something was misunderstood.
I would like to extend the 60p to 120p.
The new 60p are to be switched parallels to the first 60s packages.
And will completely use the BMS of the first packages.
ajw22 said:
All voltages should be fairly close to each other before you connect them. I'd aim for max +/- 0.1V per cell difference.
The higher the voltage difference, the more current will rush in as you connect them, possibly triggering the breaker.
You can charge the first battery up to close to 4.15V, or discharge the new battery to the level of the first battery, or a combination of both - it does not matter.

As ajw22 states, these need to be very close to the same voltage as possible before hooking them up.

Walde said:
Now the only question is how the condition should be from the first package.
Since the new is the second package at 4.15v.
or does it matter anyway from the first packet ... 3.5-4.15v

Refer to the previous statement. They need to be equal voltages, all packs & full string.
 
Very neat construction!
But I don't quite understand what I'm looking at.
Is this the new 14s60p (looks more like 90p, if not more) charged to 4.15V, and you want to insert the packs of your old battery (now at 3.5V) into the empty slots on the far left and far right?

If so, definitely equalize the voltages before connecting! If you don't, you will fry your old packs.
I suggest you get a "Laboratory Power Supply" such as this one:

https://www.amazon.de/KKmoon-Schalt...netzgerät+60v&qid=1566004307&s=gateway&sr=8-5

With this, you can easily set the output voltage as well as limit the max current. Very useful when you need to slowly charge something (eg. your Battery#1) to a specific voltage.
Also order the banana clips - they are not included in the package.

How to use:


Just a little nitpick regarding the units/spelling/capitalization in the interest of education. A lot of people seem to be confused by this, but it's not that difficult.

KW <- this would be "Kelvin Watt" - not what you mean
kW <- this is "kilo Watt", a unit of power. Eg. the power output of an inverter is measured in this

kW/h <- this would be "kilo Watt per hour" - not what you mean
kWh <- this is "kilo Watt hour", a unit of energy. Eg. if an inverter outputs 0.5kW for 3 hours, you get 0.5kW*3h = 1.5kWh of energy.
 
Its a photo of my setup ... how dit that get here ? :)

there are 3 strings of 14s90p ... kind of ... becourse all the packs are in paralelit is realya 14s270p setup made with 90p packs.
it is all in my build : https://secondlifestorage.com/t-Instant-powerwall

The free slot is for future expansion.

If you add packs, they need to be very close in voltage...
 
wim said:
Its a photo of my setup ... how dit that get here ? :)

there are 3 strings of 14s90p ... kind of ... becourse all the packs are in paralelit is realya 14s270p setup made with 90p packs.
it is all in my build : https://secondlifestorage.com/t-Instant-powerwall

The free slot is for future expansion.

If you add packs, they need to be very close in voltage...

Have your system as in the photo as a model.
Mine is still under construction and not quite finished.
Was so free and took your photo so that the others understand what is meant by extension.
Because it seems to have given misunderstandings.
 
For what its worth - when I add a new 'battery' in parallel to the others... (each row in my picture to the left is 14s 'battery')
1) As prep - all 14packs are parallelized with each other (using 28 alligator clip wires) for several days to balance all the packs with each other.
2) Then use 'the system' to raise (PV input) or lower (inverter drain) the overall battery bank to match the voltage of #1
3) Turn things off / hook in the new 'battery'

and resume normal operations.
 
Would be glad if you just as know as you do that.
There will be more than one way or approach for enlargement.
I'm sure other people would be interested.
 
Exactly as OffgridInIheCity says, exept the first point...

Just charge/discharge the packs already in useto the samevoltage as the new ones beforeinstalling them.
There is no simpler way to do this.

Not difficult, or are we missing something in your question ?
 
plus one on Wim.
Just charge your packs up to the voltage of your wall.
https://www.aliexpress.com/item/32872607362.html?spm=a2g0s.9042311.0.0.27424c4dmyUPhn

No need to rush.
Check every morning what the average voltage is of your wall in use, take that as a guideline to charge your add ons.
Let's say you have a average of 3.6v, in the mornings, make sure your add ons will be in that range.
If the voltage of your wall in use is higher on the day you want to add, just switch off your pv array, till they match.
If the voltage is lower, just take the house off line till it matches.
This would be "my method."
I am planning to add on a frequent base, when my wall is finally running.

You can also equalize with a light bulb or a big watts resistor.
To speak frankly: my knowledge is to short to explain this properly.
I read a lot on this million dollar forum, there are some very interesting topics about this.
"My Method" is the one i like the most, but that is personal.

Best
 
have today extended to 15kw / h.

Have the system running until noon today, Batteries were full and have the inverter from the network taken (switching to shore power).
Have left one of the solar charger 60min Nachlauf. Batteries were so far full at 4.10 +/- 0.03.
Then I started to switch the new battery set in parallel +/- 4.15 volts.
Then everything back to the network and until now everything ok ....
 
OK you did it correctly :)
Like everyone has said, when you join two battery packs, they need to be at the same voltage.
 
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