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SunSynk battery questions


Kalahari Cruiser

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Hi all, am newly on the path to installing power backup at home, and solar shortly as well.

The still boxed Inverter is a 8kw Sunsynk, and battery for now is a 5kw SunSynk (L5.1). Intention was to add a second similar-sized SunSynk battery a little later. 

I have some doubts now whether this is the best path to take, or whether I should have gotten a single 10KW Sunsynk (not sure if there's stock) - in lieu of 2x 5KW. The reason is the discharge specs of the two batteries. 

The label of the 5kw battery (with production date September 2022) simply / only mentions a nominal discharge current of 50A. The SunSynk website for this particular battery states the following (see below attachment): 

Recommended discharge current 50A, max 100A, and a peak (2min) of 150A. The max is sometimes also referred to on the SunSynk website as "Max. Continuous Discharging Current" i.e. 1C. I don't see a time limit on this discharge current.  I assume at 50V this translates into approx. 2.5KW, 5KW and 7.5KW concurrent and/or continuous power usage (peak power), respectively. 

-> The 10KW Sunsynk seems to have double the ratings in terms of discharge, i.e. 100A Recommended, etc. 

The crux of the question is:

  • If I add a second Sunsynk L5.1 battery in parallel shortly, will this simply double the capacity (i.e. length of discharge / amount of power in the "tank") rather than increase the peak KW that my loads can consume concurrently? 
  • If I rather opt to get a single 10KW Sunsynk battery, I'll have the same capacity as 2x5KW but can double the amount of peak loads? I'm not so much concerned about overall capacity here (or understand those limitations and benefits), but don't want to have a situation where (with 10 KW of batteries spread across two units) I'm still limited to the discharge current of only a single battery, especially if this is only relating to 2,500W peak power. 
  • And finally, with one (or two) of the 5KW SunSynks installed, am I limited by the discharge current of 1 battery (since they're in parallel), and how many watts can I concurrently use during load-shedding (is it 2,500W, is it 5,000W?). 

With a couple of fridges/chest freezer in the house, coffee machine, 2,000W airfryer, TV, lights etc, I definitely need to be able to comfortably have concurrent peak power of say 4,000W during load-shedding, even if most of the time it might well be less bearing in mind the limitations of my stored battery energy. I realise that at say 90% discharge, my effective KW availability of stored power is 90% of 5.12KW. 

 

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And one further unrelated question: this battery is the wall-mounted IP65-enclosure battery (5.12KW) like the one on the right in attached picture, with on-off button at base (Manuf. Sept 2022). Is this older tech versus the standard current indoor models, in terms of cells etc.? Would it be fully compatible with a second SunSynk battery (5.32KW?) added in parallel?

Thanks in advance for input - sorry if above is a bit long-winded, but trying to provide enough context. 

 

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28 minutes ago, Kalahari Cruiser said:

 

  • If I add a second Sunsynk L5.1 battery in parallel shortly, will this simply double the capacity (i.e. length of discharge / amount of power in the "tank") rather than increase the peak KW that my loads can consume concurrently? 

It will double current dis- & charge capability

29 minutes ago, Kalahari Cruiser said:

If I rather opt to get a single 10KW Sunsynk battery, I'll have the same capacity as 2x5KW but can double the amount of peak loads?

this would be the same as the two 5kW batteries in parallel. I don't know the current limits for the 10kW battery, but I'd imagine it should be 200A max current in & or out

31 minutes ago, Kalahari Cruiser said:

And finally, with one (or two) of the 5KW SunSynks installed, am I limited by the discharge current of 1 battery (since they're in parallel), and how many watts can I concurrently use during load-shedding (is it 2,500W, is it 5,000W?)

as stated above the two 5kW batteries in parallel double up the current potential and are effective a 10kW battery once paralleled up...

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Thanks very much, Meerkat. 

Yes the 10KW battery seems to have a nominal discharge current of 100A and maximum of 200A (presumably continuous). 

On the 5.12KW units: Is the current continuous discharge rate on a single battery then 100A (even if in practice it may only operate at this level periodically)? What does that equate to - approx 5,000W of peak power? Why then have a recommended 50A discharge spec - is this more something to keep in mind (i.e. try limit power use to 2500W, but no problem if it goes to 5,000W?) and to maximise battery life?

The doubling of discharge rates when adding a second same-spec battery is good news then. Would 2x 5.12KW SunSynk batteries then allow me to have a peak power of 10,000W then (at least from time to time), while the recommended continuous current draw would be 100A (equivalent to 5,000W?) of these two parallel units?

In summary: having one battery allows continuous use of up to 5,000W peak power (even if less is "recommended"), and having 2 batteries in parallel allows me to have 10,000W peak power then? 

(Important considerations as wouldn't want to start using the 5KW unit if it wont meet my needs, ultimately). 

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2 hours ago, Kalahari Cruiser said:

Why then have a recommended 50A discharge spec - is this more something to keep in mind (i.e. try limit power use to 2500W, but no problem if it goes to 5,000W?) and to maximise battery life?

No battery will do better lifespan wise when its hit pretty hard, so ideally for long life, try and limit the power draw to .5C or less, in other words, if you expect to peak around 8kW power draw a 16kWh battery would be great and basically allow for .5C, in your case, 3 * 5kW batteries would come close to this 8kW (actually 15kW * .5C = 7.5kW).

I run a 8k2Wh battery on a 5kW inverter, the battery is specced at 1C, thus 8kW, but we obviously never get there and I expect the battery to do quite well, lifespan wise, because of this.

2 hours ago, Kalahari Cruiser said:

The doubling of discharge rates when adding a second same-spec battery is good news then. Would 2x 5.12KW SunSynk batteries then allow me to have a peak power of 10,000W then (at least from time to time), while the recommended continuous current draw would be 100A (equivalent to 5,000W?) of these two parallel units?

Yes

2 hours ago, Kalahari Cruiser said:

In summary: having one battery allows continuous use of up to 5,000W peak power (even if less is "recommended"), and having 2 batteries in parallel allows me to have 10,000W peak power then?

Yes, actually since the peak discharge for the 5kW is supposedly give as 150A, 7k5W, the two of them in parallel would allow for 15kW peak, but since your inverter is an 8kW units, you should never actually get there...

Are you planning to add solar panels? If you are, you are in for potential longer term habit changes, like running things more during sunshine and daylight hours and keeping the batteries mostly for overnight and aiming to live without commercial power, we are, but I still need a tad more battery capacity...

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16 hours ago, BritishRacingGreen said:

That a good equation,  one i try to impose on my system since day one. 

My daughter has recently installed the 8kW Sunsynk with the 10 KW battery. Should you wish to add further battery capacity, you will be limited to doubling up with the 10kW unit, whilst the 5 kW will allow you to go up in increment of 5 Kw. This may be a consideration for future system expansion.

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7 minutes ago, Peter V said:

My daughter has recently installed the 8kW Sunsynk with the 10 KW battery. Should you wish to add further battery capacity, you will be limited to doubling up with the 10kW unit, whilst the 5 kW will allow you to go up in increment of 5 Kw. This may be a consideration for future system expansion.

Well, no, if you run in voltage mode, there's no reason that you can't mix 5kW 16cell battery with 10kW 16cell battery in parallel, a 6kW draw would automatically draw 2kW from the 5kW battery and 4kW from the 10kW battery, of course in BMS communications mode, the 2 batteries' BMS' may not talk the same protocol and you may not be able to use LiBMS mode on the inverter, but the point that different capacity batteries can be paralleled up and there should be no real issues, as long as they have the same amount of cells and thus the same Voltages... one more point to consider, the batteries' internal resistances should be similar, an old 10kW battery with fairly high internal resistance paralleled with a new 5kW battery with very low internal resistance, would allow more of the work to be done by the 5kW battery...

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38 minutes ago, Kalahari Meerkat said:

.. one more point to consider, the batteries' internal resistances should be similar, an old 10kW battery with fairly high internal resistance paralleled with a new 5kW battery with very low internal resistance, would allow more of the work to be done by the 5kW battery...

Please correct me if I'm wrong.

My understanding is that a 10 kWh battery made up of 2x5 kWh will have a resistance of half of a 5 kWh battery. (2 resistances in parallel) If the 10 kWh is older and the resistance has increased slightly it will still have a resistance lower than a new 5 kWh. This makes me think the 10 kWh will still provide substancially more current than a new 5 kWh.

Good point you raised of using voltage when using different sizes vs via BMS where you need the same battery size and voltage. I am using voltage and its working fine for me as I have to with my non comms Axpert clone. BMS is like having speed control and using voltage mode you have to just look what the speed is like and adjust.

Great point raised by @Peter V

Edited by Scorp007
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Information based on a telecon I had with the Sunsysk call centre in the UK that different size batteries cannot be mixed.. Please bear in mind that not all are technically inclined and I would venture to say that the average installer out there is not going to get a different capacity battery installation right.

I would also assume that if you mixed sizes, Sunsynk could well invalidate your warranty.

Edited by Peter V
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5 hours ago, Scorp007 said:

My understanding is that a 10 kWh battery made up of 2x5 kWh will have a resistance of half of a 5 kWh battery. (2 resistances in parallel) If the 10 kWh is older and the resistance has increased slightly it will still have a resistance lower than a new 5 kWh. This makes me think the 10 kWh will still provide substancially more current than a new 5 kWh.

A 10kWh battery could be made up of 100Ah cells in 16S2P configuration or 200Ah cells in straight 16S configuration, also, I suppose out of 50Ah cells in 16S4P configuration and more permutations exist, either way, when new A grade cells are in place the total internal resistance for a 10kWh battery should be roughly half that of for a 5kWh battery, again, though it depends if the cells are rated for .1C or 1C etc.

The point is and was if you have a 3 year old 10kWh battery that's been abused (cycled 3 times a day, down to SOC of 5% for these 3 years) and subsequently the cells are somewhat the worse for wear and you add a new 5kWh battery, the new 5kWh battery may end up carrying more than its share of the load.

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12 minutes ago, BritishRacingGreen said:

how to you entertain the measurement of overall accurate SOC? 

The only accurate way would be to chat to the two BMS' with a computer (EMON/HASS/whatever), but keep the inverter on Voltage mode... I reckon since Voltage in LiFePO4's is a poor indicator of SOC, but knowing ones overnight load and usage patterns can give one a pretty good idea of where one stands... to a degree I have come to the conclusion that the SOC on the discharge end can be of use *** but on the charging end a detriment, I have seen the battery's BMS report 100% SOC but since the battery was still accepting current & presumably balancing the cells, it could have been at 80% or up to near 100% and this can be a real problem, looking at reported SOC is a crapshoot which can, if you're sailing close to the wind in terms of total battery capacity, bite you.

*** where this can be a problem is where the SOC was reported to be 100% near sunset with no grid power available and then in the morning 3 hours to sunrise the SOC goes from 30% to 0% in seconds and without grid, you start polishing off the expanded vocabulary and put it to some use, not that, that helps...

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2 hours ago, Kalahari Meerkat said:

A 10kWh battery could be made up of 100Ah cells in 16S2P configuration or 200Ah cells in straight 16S configuration, also, I suppose out of 50Ah cells in 16S4P configuration and more permutations exist, either way, when new A grade cells are in place the total internal resistance for a 10kWh battery should be roughly half that of for a 5kWh battery, again, though it depends if the cells are rated for .1C or 1C etc.

The point is and was if you have a 3 year old 10kWh battery that's been abused (cycled 3 times a day, down to SOC of 5% for these 3 years) and subsequently the cells are somewhat the worse for wear and you add a new 5kWh battery, the new 5kWh battery may end up carrying more than its share of the load.

Yes again spot on. This is the problem when calling old - it is a vague indicator of use/abuse/SOH. Debating this point I looked at the OP using words like adding another later and also shortly. This will then be very different from abusing and battery down to 5% SOC for a long 3 years. At least I think the take away is one can use different sizes together and using volts as a very rough indicator. I am forced to use volts but over time one learns what estimated SOC is left if you run a constant load through the night. My load during the night is 3 fridges at bed time and if below 25.9V under this load I know I have to set a timer to use bypass say at 04h00. This is affected in a big way if we have LS after 22h00. I set the timer for bypass for a time after LS. Luckily for me our power comes on before the end of the period for 99% of the LS cycles. It's working for me as my inverter has not cut out/tripped in over 9 months. I mostly charge from PV so a lot more running on bypass the last few days due to the weather.

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Thanks all for valuable inputs and advice - much appreciated. 

On 2023/01/01 at 8:43 PM, Scorp007 said:

I looked at the OP using words like adding another later and also shortly

Yes, thinking is to source one soon, be it in weeks or a few months at most, since I realise that with only 1x 5KW battery I'm going to be short - but more importantly, would like higher peak current draw than what only one 5KW battery would be able to provide (and have it more in line with having a 10KW battery). 

 

On 2022/12/31 at 3:17 PM, Kalahari Cruiser said:

And one further unrelated question: this battery is the wall-mounted IP65-enclosure battery (5.12KW) like the one on the right in attached picture, with on-off button at base (Manuf. Sept 2022). Is this older tech versus the standard current indoor models, in terms of cells etc.? Would it be fully compatible with a second SunSynk battery (5.32KW?) added in parallel?

Just want to get back to this question. I see my IP67 battery is 5.12KW but the standard indoor ones are 5.32KW. Can I freely mix these two SunSynk batteries in terms of sourcing a second battery to my 5.12KW? Are they de facto the same?

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1 hour ago, Kalahari Cruiser said:

Thanks all for valuable inputs and advice - much appreciated. 

Yes, thinking is to source one soon, be it in weeks or a few months at most, since I realise that with only 1x 5KW battery I'm going to be short - but more importantly, would like higher peak current draw than what only one 5KW battery would be able to provide (and have it more in line with having a 10KW battery). 

 

Just want to get back to this question. I see my IP67 battery is 5.12KW but the standard indoor ones are 5.32KW. Can I freely mix these two SunSynk batteries in terms of sourcing a second battery to my 5.12KW? Are they de facto the same?

I would rather bounce this of Synsynk support and not run the risk as you will be using comms between the 2 batteries and the inverter. 

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Thanks.

I did call SunSunk via the support line (very friendly and helpful!) - but according to them, the SunSynk 5.12KW (IP67) battery I have is not compatible with the SunSynk 5.32KW (IP40 housing). Which suggests that I'd need to try source another 5.12KW in the IP67 housing with same connections. 

I'm a bit confused by the fact that even the "standard" 5KW batteries in the IP40 housing (switch and lights top right corner) seem to come in 5.12KW and 5.32KW capacities, per different online sites. The SunSynk site itself isn't particularly good with providing specs, certainly can't find any for the standard battery, only for (mine) in the IP67 housing. They mention that "specs for the 5.32KW are coming soon". 

With all the info floating around - some contradictory - and not entirely sure what to trust (especially online vendor sites), I'm still a bit unclear about which second SunSynk battery will work seamlessly in parallel with my 5.12KW/IP67 battery. 

(they did confirm - as per earlier in this thread - that adding a second battery will double the max current draw and power on the load side, rather than just doubling the available amp hours i.e. usage time; of course same consumption rate would double the time). Lingo may not be 100% technical :)  

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2 hours ago, Kalahari Cruiser said:

Thanks.

I did call SunSunk via the support line (very friendly and helpful!) - but according to them, the SunSynk 5.12KW (IP67) battery I have is not compatible with the SunSynk 5.32KW (IP40 housing). Which suggests that I'd need to try source another 5.12KW in the IP67 housing with same connections. 

I'm a bit confused by the fact that even the "standard" 5KW batteries in the IP40 housing (switch and lights top right corner) seem to come in 5.12KW and 5.32KW capacities, per different online sites. The SunSynk site itself isn't particularly good with providing specs, certainly can't find any for the standard battery, only for (mine) in the IP67 housing. They mention that "specs for the 5.32KW are coming soon". 

With all the info floating around - some contradictory - and not entirely sure what to trust (especially online vendor sites), I'm still a bit unclear about which second SunSynk battery will work seamlessly in parallel with my 5.12KW/IP67 battery. 

(they did confirm - as per earlier in this thread - that adding a second battery will double the max current draw and power on the load side, rather than just doubling the available amp hours i.e. usage time; of course same consumption rate would double the time). Lingo may not be 100% technical :)  

This is why my next batteries will be Pylontech

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