Poll: 14S or 15S?
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14S
66.67%
6 66.67%
15S
33.33%
3 33.33%
Total 9 vote(s) 100%
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14S... or 15S?
#1
I am about to solder up my first few packs, and I have already decided I want to build 14S8P packs and have them completely wired into a common BMS/balancer. So there'll be 15 wires connecting each pack to the system. For all the arguments for and against this method, the one that tipped the balance for me is the ability to grab a pack or 2 and use them for a portable power source. It also has a few other advantages, but the purpose of my post is not to justify the paradigm, but rather to ask a simple question.

I am all set to build packs of 14S, but yesterday I read a thread regarding the benefits of 15S. The need to only charge up to 3.92V per cell to get 58.8V, and then discharging to 3.2 (48V) must surely be a significant boost to cycle life. It also means that in a pinch, I could run the packs down a bit more if I had to.

So what are people's thoughts on 15S over 14S?
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#2
I mostly use 16S .... you just need to make best use of your inverters/chargers input voltage range while being kind to your cells.
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#3
You dont define cycle life like that by going 14 or 15. You set charging voltages!!

Stressing out the inverter or charging by maxing its max voltage is stupid. Most chinese or cheaper inverters can even blow up and have happened many times due to how it was designed. Look at the gears optimal voltage range and use that!

Also limiting so you cant charge above 3.9V is also waste.. The day you need more you are screwed. Instead go 14s and set the limit in the charger and you will be happier.

Some people say its less waste being at highest voltage but its not true. Yes if you have way to small wires that may be such but generally not. A device is optimized at a certain voltage and its for sure not its maximum Tongue

I go 14s. Its well within limits of my gear. My gear only go towards 60VDC. If I would have had 64 or even 68vdc gear i would have choosen otherwise.

Note that I also run 16s in conjunction with 14s.. So perhaps you need to look into how to reprhase your question.

Lastly. Dont base your decision on the result here. It may even end up in a setup that doesnt work very well....
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#4
What inverter and charger do you have so we can all make a more informed suggestion?
If it's not a common familiar unit, please include url as well
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#5
I used 14s as well because most common controllers/inverters can't handle the full charge voltage of 15s.
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#6
The entire conversation should be governed by the equipment selection and design of the system. My solar charge controller and inverter are both Victron items with a wider voltage range and manual control over voltage set points.

I decided to use 15s because my equipment chain supports it very well. I could have used 14s as well, but keeping the voltage on the higher end of the input range will also help with power conversion efficiency; and while it may be small, it would still be measurable.
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#7
(06-26-2019, 02:05 PM)Korishan Wrote: What inverter and charger do you have so we can all make a more informed suggestion?
If it's not a common familiar unit, please include url as well

At the moment, I have not committed to anything. I was kinda looking at it the other way around... Batteries first as they take the longest, then get the expensive stuff.
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#8
(06-26-2019, 07:10 PM)Grumplestiltskin Wrote:
(06-26-2019, 02:05 PM)Korishan Wrote: What inverter and charger do you have so we can all make a more informed suggestion?
If it's not a common familiar unit, please include url as well

At the moment, I have not committed to anything. I was kinda looking at it the other way around... Batteries first as they take the longest, then get the expensive stuff.

Ok, good. That allows for a much broader response from others.

Now, the thing to look at is what inverters have what voltage ranges, and then compare that to princes between devices. This would help in the deciding factor.
I would recommend putting all the inverters into a spreadsheet with prices and voltage ranges so that it'd be easier to compare. If 1 inverter costs $300 less than another and they are just as good as the other, but one will only work with a 14s and the other more expensive one can work at 16s, might as well go with the 14s one. There won't be much of a difference.

The other question to go along with this, is what kind of bms do you plan on using? If it's Batrium or other customizable bms, then you are probably good to go. But otherwise, finding a static 15s or 16s bms is going to be hard, if not expensive
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#9
Another consideration is the solar panels (if any) you intend to use, and in what configuration (series/parallel). They also have a working voltage range that has to be within what the charger expects. I think most chargers work well only when PV voltage is significantly higher than the battery voltage.
But of course you mustn't exceed the voltage limit of the charger.
!!! Big caveat: Voc listed on the spec sheet of solar panels is the maximum voltage it will deliver at 20~25degC. Voltage will go higher at lower temperatures !!!
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#10
I still stand that you really dont have to spend the time
Om battery voltage. Go 14s. Yes fine IF you got a hv version that do higher but dont spend time on it. Waste of time.

Instead you spend time on making sure your panel config matchens the inverter and roof. This is 100* more important because all 48v inverter do 14s... And No..... 15s does not make it more efficient per default Wink
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