15s (48v) and a 16s (51.2v) battery in parallel!!???!?!?!

[JohnZEBSolar]

I am currently running several Lux Power 12ks in parallel. I am currently using 15s batteries (48 nominal voltage). I am wondering what the negative impact would be if I were to add 16s batteries (51.2 nominal voltage) to this setup. I don't believe these batteries would communicate with each other since they are different brands, although they both run off of the pylon protocol. So, my idea was to parallel all of them together, use communication for only the 16s's and operate the 15s's without communications. I believe I would want to change my top and bottom voltage cutoffs appropriately as to not damage the batteries from overcharge or over-discharge.

Any info, or insight would be greatly appreciated. Anyone with experience on 15s and 16s battery parallel systems would also be greatly appreciated.

Thanks to all!!!

Have a sunny day!!!

 

[sunshine_eggo]

You've found the other thread and discovered that there are well articulated downsides. I'm guessing you just want to do what you want to do and don't really care to hear anything that contradicts your idea. In case you're actually receptive:

15S full at 3.65 * 15 = 54.75V or 3.42V *16.
16S empty at 2.5 * 16 = 40V or 2.67V * 15.

You'll lose capacity at both top and bottom, and you'll have to rag the 15S out at the top shortening its life and the 16S out at the bottom.

The 15S battery is going to want to rest at about 51.45V, but the 16S will continually discharge into it holding it at elevated voltage, which is harmful to it.

Additionally, the 15S battery is likely dictating what the charge voltage is to the inverter, so you would have to change it in the 15S BMS.

Stick with one or the other. In the end, the economics will work out in your favor.

 

[42OhmsPA]

It's a bad idea, don't do it.
See explanation from @sunshine_eggo above.

END THREAD.

 

[SparkyJJO]

It is a good way to waste money at best, or break stuff at worst.

Stick with 15s or replace all with 16s.

You don't wanna look like my avatar.

 

[LakeHouse]

I am currently running several Lux Power 12ks in parallel. I am currently using 15s batteries (48 nominal voltage). I am wondering what the negative impact would be if I were to add 16s batteries (51.2 nominal voltage) to this setup. I don't believe these batteries would communicate with each other since they are different brands, although they both run off of the pylon protocol. So, my idea was to parallel all of them together, use communication for only the 16s's and operate the 15s's without communications. I believe I would want to change my top and bottom voltage cutoffs appropriately as to not damage the batteries from overcharge or over-discharge.

Any info, or insight would be greatly appreciated. Anyone with experience on 15s and 16s battery parallel systems would also be greatly appreciated.

Thanks to all!!!

Have a sunny day!!!

Maybe this would be possible with some programmed logic and heavy-duty switches. Something like run off the 15's only below 48V (3V/cell on the 16s), run off both between 48V and 51.75V (3.45V/cell on the 15s), and the 16's only above 51.75, with the switch to 'both' only occurring when voltages match within a small margin. There would probably need to be quite a bit more logic involved than just that, and each set of batteries would obviously need to be capable of running the entire system. Plus the 15s might have trouble staying in balance and would be unhappy being forced to rest above 3.4V/cell. Probably there are a multitude of other issues I'm not currently thinking of.

The most likely result would be something that ends up being at best a huge pain to operate, and at worst dangerous. I'll add a fourth voice to the chorus of: Don't do it.

 

[JohnZEBSolar]

You've found the other thread and discovered that there are well articulated downsides. I'm guessing you just want to do what you want to do and don't really care to hear anything that contradicts your idea. In case you're actually receptive:

15S full at 3.65 * 15 = 54.75V or 3.42V *16.
16S empty at 2.5 * 16 = 40V or 2.67V * 15.

You'll lose capacity at both top and bottom, and you'll have to rag the 15S out at the top shortening its life and the 16S out at the bottom.

The 15S battery is going to want to rest at about 51.45V, but the 16S will continually discharge into it holding it at elevated voltage, which is harmful to it.

Additionally, the 15S battery is likely dictating what the charge voltage is to the inverter, so you would have to change it in the 15S BMS.

Stick with one or the other. In the end, the economics will work out in your favor.

Thanks for your info. I am actually looking for info that contradicts my idea and also trying to learn more from this.
I appreciate your thoughts, very informative.

 

[JohnZEBSolar]

It is a good way to waste money at best, or break stuff at worst.

Stick with 15s or replace all with 16s.

You don't wanna look like my avatar.

Thanks, I think I will probably do one or the other... but if I do it, I will set my camera up, and maybe I can get you a real life picture to use in place of your avatar. Lol

 

[JohnZEBSolar]

Maybe this would be possible with some programmed logic and heavy-duty switches. Something like run off the 15's only below 48V (3V/cell on the 16s), run off both between 48V and 51.75V (3.45V/cell on the 15s), and the 16's only above 51.75, with the switch to 'both' only occurring when voltages match within a small margin. There would probably need to be quite a bit more logic involved than just that, and each set of batteries would obviously need to be capable of running the entire system. Plus the 15s might have trouble staying in balance and would be unhappy being forced to rest above 3.4V/cell. Probably there are a multitude of other issues I'm not currently thinking of.

The most likely result would be something that ends up being at best a huge pain to operate, and at worst dangerous. I'll add a fourth voice to the chorus of: Don't do it.

Very good info! Thank you.

 

[sunshine_eggo]

Maybe this would be possible with some programmed logic and heavy-duty switches. Something like run off the 15's only below 48V (3V/cell on the 16s), run off both between 48V and 51.75V (3.45V/cell on the 15s), and the 16's only above 51.75, with the switch to 'both' only occurring when voltages match within a small margin. There would probably need to be quite a bit more logic involved than just that, and each set of batteries would obviously need to be capable of running the entire system. Plus the 15s might have trouble staying in balance and would be unhappy being forced to rest above 3.4V/cell. Probably there are a multitude of other issues I'm not currently thinking of.

The most likely result would be something that ends up being at best a huge pain to operate, and at worst dangerous. I'll add a fourth voice to the chorus of: Don't do it.

A switching solution could also trigger short circuit protection, so the point at which they're joined must be very precise with negligible voltage difference between them.