Have we painted ourselves into a corner?

[Batonage]

Hi All,

I have a bit of a dilemma with our off grid set up...

We have a nice setup (12 x 410w PV, MPP Solar 5kW inverter, 3 x Pylontech US3000), but are looking to expand to add capacity for another build close by. The new build will increase roof area to allow for more panels (12 more 410W), and swapping in a MPP 11Kw will handle the extra input, all good so far.

However storage is the issue. In NZ batteries are not getting cheaper (small market, high freight costs) and we seem to have bought batteries of an unusual size. Are our batteries 75Ah (3500Wh/48V)? Are they incompatible with 100Ah? It seems like only Pylontech make 75Ah units, so we're stuck using these (pricey!) to expand our storage.

Do I understand this correctly or am I confusing my self? All advice welcome, no matter how basic!

Cheers from the best summer in years...

 

[alcook62]

Hi All,

I have a bit of a dilemma with our off grid set up...

We have a nice setup (12 x 410w PV, MPP Solar 5kW inverter, 3 x Pylontech US3000), but are looking to expand to add capacity for another build close by. The new build will increase roof area to allow for more panels (12 more 410W), and swapping in a MPP 11Kw will handle the extra input, all good so far.

However storage is the issue. In NZ batteries are not getting cheaper (small market, high freight costs) and we seem to have bought batteries of an unusual size. Are our batteries 75Ah (3500Wh/48V)? Are they incompatible with 100Ah? It seems like only Pylontech make 75Ah units, so we're stuck using these (pricey!) to expand our storage.

Do I understand this correctly or am I confusing my self? All advice welcome, no matter how basic!

Cheers from the best summer in years...

I'm admittedly not familiar with the Pylontech batteries, however, that being said, generally any battery of corresponding chemistry (ex. LiFePO4 with LiFePO4) added to the system will work. They should be similar in amp-hour capacity, but that can be stretched somewhat. I have two separate batteries, one 280ah and one 230ah. They have lived happily together for two years now.

 

[Warpspeed]

At the moment I have thirty 50Ahr Winston cells (in a 100v system) which is 5Kwh storage.
Planning to upgrade to thirty 280Ahr Chinese cells soon.
I already have thirty two of these larger cells, they are not yet installed.

One of my Winstons finally died after six years.
Replaced it with one of the 280 Ahr Chinese cells and it works fine.
While the Winstons charge and discharge over their normal voltage range, the voltage on the much larger cell hardly changes.
I still only have 50Ahr of storage.

Yes you can mix cell sizes, but the smallest weakest cell in the whole string, will set the limit for the whole bank.

 

[Andrewr05]

I suppose you could also run part of your home off of your existing setup and then the new larger setup would run another part of the house?

Or wire the batteries in parallel to turn them into a 150Ah setup and then connect them up with some 150Ah batteries.

Although they're less common-
Cloudenergy Cabinet Type 48V 150Ah LiFePO4 https://a.co/d/5cW9FK9

 

[LydMekk]

Btw. Pylontech are 15s configs, not 16s. If you are going to buy more batteries do select the same 15s config on the new ones. No matter what brand they are.
This way they will be compatible and run on the same voltage for the whole combined pack.

 

[OffGridForGood]

you can spend some time over on the DIY - battery build subforum - building your own packs 15s 75Ah if you like, or upsize a bit to 100Ah packs (I would do this if I were you) but as LydMekk says, keep to 15s would be best.
shipping is not too bad with separate cells, since each box is lighter and they can ship courier (instead of freight) - should save $$
Typically DIY packs will be about half the cost of ready-made server rack type packs. For your situation perhaps even less expensive.

 

[Batonage]

I'm admittedly not familiar with the Pylontech batteries, however, that being said, generally any battery of corresponding chemistry (ex. LiFePO4 with LiFePO4) added to the system will work. They should be similar in amp-hour capacity, but that can be stretched somewhat. I have two separate batteries, one 280ah and one 230ah. They have lived happily together for two years now.

thanks for the feedback!

 

[Batonage]

you can spend some time over on the DIY - battery build subforum - building your own packs 15s 75Ah if you like, or upsize a bit to 100Ah packs (I would do this if I were you) but as LydMekk says, keep to 15s would be best.
shipping is not too bad with separate cells, since each box is lighter and they can ship courier (instead of freight) - should save $$
Typically DIY packs will be about half the cost of ready-made server rack type packs. For your situation perhaps even less expensive.

great suggestion, thanks!

 

[Batonage]

Btw. Pylontech are 15s configs, not 16s. If you are going to buy more batteries do select the same 15s config on the new ones. No matter what brand they are.
This way they will be compatible and run on the same voltage for the whole combined pack.

ah, hadn't though about that, thanks

 

[rustyrotors]

it will be fine, check it by measuring the charge current to each battey with a clamp meter and see if it is proportional to battery size. i am parallel mixing 100Ah and 300Ah batteries, and they naturally share the current proportionally. when i charge at 40A (0.1C), the 100Ah pulls about 12A, the 300Ah pulls 28A, both individually pulling roughly 0.1C

 

[jgh]

I realise you're thinking of not using more Pylontech,
but they do make (at least) 3 models in that range, with different capacities. US2000, 3000, 5000.
The current submodel seems to be "C". They interwork in a parallel power, serial control string.

Put the newest one as the first on the control string (I assume this is just for BMS software compatibility issues).

All 48V nominal, 15S internal.

 

[Steve_S]

You can pot batteries in Parallel that have a different AH Capacity without issues BUT it's generally best to not have to much difference, over 100AH difference and there is some serious math & config required.

PylonTech batteries are 15S as others pointed out, that is NOT common but still works. Several aftermarket BMS' have P{ylontech protocol support & some will support a 15S battery Pack. I would NOT place 15S Packs with 16S Packs because the hi & lo voltages are not in synch and that will cause a lot of trouble.

MPP and many other AIO's support the PylonTech protocol if you wish to have a closed loop system BUT this is not necessary if a proper charging profile is used.

OPTIONS:
Stick with the Pylontech packs nd get more...
Replace the PylonTech packs with an alternate (DIY or other) and sell off the ones you have.
Build (DIY) larger 15S Packs to go in parallel (cases etc will be difficult and you will have limited BMS choices).

We now have access to very respectably priced 280/304AH Cells and some pretty good BMS and when you work out the math - you really have to consider the pathway forward.

 

[Batonage]

I realise you're thinking of not using more Pylontech,
but they do make (at least) 3 models in that range, with different capacities. US2000, 3000, 5000.
The current submodel seems to be "C". They interwork in a parallel power, serial control string.

Put the newest one as the first on the control string (I assume this is just for BMS software compatibility issues).

All 48V nominal, 15S internal.

Thanks, US5000 is a bit better value so that is an option

 

[Batonage]

You can pot batteries in Parallel that have a different AH Capacity without issues BUT it's generally best to not have to much difference, over 100AH difference and there is some serious math & config required.

PylonTech batteries are 15S as others pointed out, that is NOT common but still works. Several aftermarket BMS' have P{ylontech protocol support & some will support a 15S battery Pack. I would NOT place 15S Packs with 16S Packs because the hi & lo voltages are not in synch and that will cause a lot of trouble.

MPP and many other AIO's support the PylonTech protocol if you wish to have a closed loop system BUT this is not necessary if a proper charging profile is used.

OPTIONS:
Stick with the Pylontech packs nd get more...
Replace the PylonTech packs with an alternate (DIY or other) and sell off the ones you have.
Build (DIY) larger 15S Packs to go in parallel (cases etc will be difficult and you will have limited BMS choices).

We now have access to very respectably priced 280/304AH Cells and some pretty good BMS and when you work out the math - you really have to consider the pathway forward.

Yeah, lots of options and thinking to do...just wish I'd done a bit more research back in the day...story of life I guess

 

[JoeHam]

Here is an extreme example that suggests don’t worry about it :

Personally I have 48V 100Ah in parallel with 50Ah running 24/7/365. I also had a 13Ah in the mix before taking it to another application.

I did match the voltages prior to parallel connecting them but that’s it.

 

[OffGridForGood]

When I started to DIY 280Ah and 304Ah packs, I wondered what to do with my original two 100Ah Factory Server Racks due to the different capacities.
I ended up putting the two 100Ah in parallel on their own small bus and then connected the small bus to the main server rack bus using 4AWG wire, while the 280's and 304's are connected with 1AWG to the main bus. I could play with the length of the 4AWG but it runs pretty close to the bigger packs now. (Thanks @Solarod)

 

[pinkie]

Expansion of storage, it is best to use the same brand with the same batch of batteries for expansion, because the most critical part of the battery, the cell with the same batch of differential pressure, internal resistance, capacity are the most consistent, and to be connected in parallel to the old and new batteries are full of parallel connection, and then static for 12 hours before use!