Poll: What inverter is best to use
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Singel hybride inverter
15.79%
3 15.79%
Multiple hybride inverters
31.58%
6 31.58%
Single inverter
15.79%
3 15.79%
Multiple inverters
36.84%
7 36.84%
Total 19 vote(s) 100%
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Aim high, 100 KWh powerwall
#21
For your capacity calculations, are you taking into consideration that usable capacity may be much lower than the nominal/tested capacity? "Usable capacity" will of course depend on the needs of the user.
For my system, I'm charging to max 4.05V, since charging to the full 4.2V reportedly significantly shortens the lifespan of Lithium Ion cells. My lower limit is 3.3V, in order to reduce DOD% and as a safety buffer in case the packs should come out of balance. Combined (incl inverter inefficiency), my usable capacity of my 30kWh battery is around 20kWh AC.


Another vote for: Charging one battery by discharging another should best be avoided. That's just eating up the limited number the charge/discharge cycles the cells have. It simply is not ecological or economical. Try to charge everything when the solar panels are generating power, discharge only if there is no other way.
Modular PowerShelf using 3D printed packs.  40kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#22
(07-03-2019, 11:36 PM)ajw22 Wrote: For your capacity calculations, are you taking into consideration that usable capacity may be much lower than the nominal/tested capacity?  "Usable capacity" will of course depend on the needs of the user.
For my system, I'm charging to max 4.05V, since charging to the full 4.2V reportedly significantly shortens the lifespan of Lithium Ion cells.  My lower limit is 3.3V, in order to reduce DOD% and as a safety buffer in case the packs should come out of balance.  Combined (incl inverter inefficiency), my usable capacity of my 30kWh battery is around 20kWh AC.


Another vote for:  Charging one battery by discharging another should best be avoided.  That's just eating up the limited number the charge/discharge cycles the cells have.  It simply is not ecological or economical.  Try to charge everything when the solar panels are generating power, discharge only if there is no other way.

Interesting way thinking.

However usable capacity will be close to tested capacity. All my packs/cassettes are balanced packed using repacker. I admit is cost me some time but gives me a good feeling. And pack has his own BMS. Currently I have enough difficulties to get is below 4v / string. I get more energy the I use. I am not to worried about charge discharge cycles. It is not that you have 500 of them undependend of the size of the cycle. Small charge / decharge cycles does not take every time a cycle away. Much more important is to keep the back between 20 and 90% of capacity and not heating it up. So I can not agree that it is not ecological or economical.

The reason that I have a battery in the first place is that I use my power mostly when the sun is not shining. Secondly I have it just because I can.
Menno
Using 7S80P pack. Building 14S40P packs.
"Tell me, and will I forget. Show me, and I may remember. Involve me, and I will understand." Confucius 450 BC
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#23
Well, "keeping it between 20% and 90%" is the text book example of "usable capacity" being less than the nominal/tested capacity. In fact 70% usable capacity, which is very close to my settings.
Unless your tests were performed with the conservative 20%-90% settings of course, in which case usable capacity = tested capacity.

Sure, a small discharge/charge cycle will not affect the lifespan of the battery as much as a full cycle. But it still does affect it. And you mentioned charging an EV with your battery system. That's probably no small discharge cycle.

I think we'd all love to see some pictures of your system! Personally would love to see your workplace, and your system of sorting/cataloging cells for use with rePackr. I gave up and just used random cells to build my packs ;-)
Modular PowerShelf using 3D printed packs.  40kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#24
(07-04-2019, 01:24 AM)ajw22 Wrote: Well, "keeping it between 20% and 90%" is the text book example of "usable capacity" being less than the nominal/tested capacity.  In fact 70% usable capacity, which is very close to my settings.
Unless your tests were performed with the conservative 20%-90% settings of course, in which case usable capacity = tested capacity.

Sure, a small discharge/charge cycle will not affect the lifespan of the battery as much as a full cycle.  But it still does affect it.  And you mentioned charging an EV with your battery system.  That's probably no small discharge cycle.

I think we'd all love to see some pictures of your system!  Personally would love to see your workplace, and your system of sorting/cataloging cells for use with rePackr.  I gave up and just used random cells to build my packs ;-)

 I am currently using less then 70% is never goes below 60% as it is not connected to the grid and only used for testing batteries and charging E-bikes.

About pictures of my work place it is mostly my garage which loaded with E-bikes, my car and some work benches spread around.


Here my picture oft he 3 packs I have currently running.  I was thinking to use holders like you do. It is a need idea. It is still a bit of a mess, however I am cleaning up. Also to get a nicer work bench to work from and easier connection.

Here the 4 packs currently on the move to be filled. as soon as I have enough to fill them up the will be finalised and connected to the rest. Bu that time I think also to put a Batrium BMS in.

And of course my upgraded solar  first I was running a 7S pack 3.3KWh for charging the bikes. But when my 14S packs started to being finalised I started to do all the testing also from DC. And needed more than a 100watt solar panel. So upgraded to 590watt. The aim is to go for a Tesla roof in the future as I do not like the aesthetics of a tiled roof with flat panels.
Menno
Using 7S80P pack. Building 14S40P packs.
"Tell me, and will I forget. Show me, and I may remember. Involve me, and I will understand." Confucius 450 BC
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#25
@Memmo if I may expand on how I read what @ajw22 is suggesting... A <100% DOD need not be in the range 4.2v -> 3.5v . The evidence so far suggests that the same DOD (e.g. same usable power) is available with a much longer life if you do it in the 4.0v -> 3.3v / cell range. Check out Battery University -> How to Prolong Lithium-based batteries - https://batteryuniversity.com/learn/arti..._batteries to get an idea of how to prolong the useable life of your battery bank.
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#26
(07-13-2019, 07:39 PM)OffGridInTheCity Wrote: The evidence so far suggests that the same DOD (e.g. same usable power) is available with a much longer life if you do it in the 4.0v -> 3.3v / cell range.

Where did you get that 3.3v figure from ? - there is very little capacity below typically 3.6v

You can expect to see significant cell imbalance occuring rapidly at such low cell voltages, which is why the better engineered inverter software applications will allow a range of low voltage disconnection settings dependent on current being drawn.
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#27
(07-13-2019, 08:16 PM)Sean Wrote:
(07-13-2019, 07:39 PM)OffGridInTheCity Wrote: The evidence so far suggests that the same DOD (e.g. same usable power) is available with a much longer life if you do it in the 4.0v -> 3.3v / cell range.  

Where did you get that 3.3v figure from ? - there is very little capacity below typically 3.6v

You can expect to see significant cell imbalance occuring rapidly at such low cell voltages, which is why the better engineered inverter software applications will allow a range of low voltage disconnection settings dependent on current being drawn.

I am ware about all this. Currently I am happy is I get a couple of KW out of my pack and it is winter here. My biggest problem at the moment is to keep it on lower voltage. I have now a 15 kWh battery pack and that will keep expanding. I only hook it to the grid when I have more than 30 KWh. At that time I will have also a Batrium BMS to controller more an better. Now it is under construction. I build my pack just because it like it and I have a constant supply of cells for it.
Menno
Using 7S80P pack. Building 14S40P packs.
"Tell me, and will I forget. Show me, and I may remember. Involve me, and I will understand." Confucius 450 BC
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#28
(07-13-2019, 08:16 PM)Sean Wrote:
(07-13-2019, 07:39 PM)OffGridInTheCity Wrote: The evidence so far suggests that the same DOD (e.g. same usable power) is available with a much longer life if you do it in the 4.0v -> 3.3v / cell range.  

Where did you get that 3.3v figure from ? - there is very little capacity below typically 3.6v

You can expect to see significant cell imbalance occuring rapidly at such low cell voltages, which is why the better engineered inverter software applications will allow a range of low voltage disconnection settings dependent on current being drawn.

>Where did you get that 3.3v figure from ? - there is very little capacity below typically 3.6v
Just pulled from theoretical range to illustrate that DOD need not be top down but can be in the middle voltage range.

I do agree that 3.3v/cells (46.2v in 14s) shows wilder voltage swings among the packs.    My current battery bottoms out at 48.0v (3.43v/cell) in terms of well behaved balancing - specifically the packs diverge from 0.04 (best) to 0.08v when under load.

As a side note:  I use the Midnite Classic Aux1 feature to turn the inverter on/off so I can choose any voltage range as long as the inverter accepts it.
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#29
You really need to have the ability to cease the inverters output based on a cell voltage, rather than just overall pack voltage, when you run cells so low as their voltage will drop quickly.
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#30
(07-14-2019, 09:54 AM)Sean Wrote: You really need to have the ability to cease the inverters output based on a cell voltage, rather than just overall pack voltage, when you run cells so low as their voltage will drop quickly.

Agreed.   I do have Batrium,  and its currently set it to 3.1v as low for critical shut-off...   but as you suggest in this discussion - why not take advantage of my Batrium and set 3.4v as low critical shut-off - as a technique to keep any individual pack from going lower than it needs to for my operating expectations.      I set it at 3.1v thinking 'emergency shutoff' but why not do better than just emergency?
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