battery questions with Skybox.

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battery questions with Skybox.

Post by Dforster »

Also posted a version of this under storage, but these are skybox specific so I moved it here..

I have a bank of 100ah ready to go, other than the BMS. have just a few questions. Not much experience using these batteries so I'm asking here first.

I got my bank from a local guy. He resells from his Chinese supplier. Tests and balances them before sending me the complete pack ready to use (minus bms)

1. is it safe to use without a bms until i get one? someone told me it was ok with lifepo4 with the skybox, but I kind of have some doubts. They won't get heavy use, mainly just in case backup is needed until I get my BMS installed. Then I may use to offset evening grid use.
2. what specific settings do I use on the skybox? it is not straight forward to me yet.. I guess I know I will choose "custom lithium" since they only have a few commercial versions in the menu.. I've pasted some of the other settings below in case anybody has experience with these.
3. is it ok to have a bank of 100ah and add another bank of 280's later on? If I parallel the two 48v banks will skybox just need to know it is a 380ah single bank?
4. I'm planning to use 2awg cables about 5' long or less. I think this is ok for either the 100ah or 280ah pack.
5. i plan to order an 80 amp and a 200 amp bms for the 100ah and 280ah. are these about right? (assuming I can mix the banks)

Charge Efficiency Factor Default: 98 %
Battery Installation Cost Default: 0
Absorb end amps per string Default: 10 A
Charge amps per string Default: 30 A
Discharge amps per string Default: 30 A
Number of strings Default: 1
Minimum SOC Default: 20 %
Maximum SOC Default: 100 %
Absorb Charge Default: Timed
Absorb Voltage Default: 55 V
Rebulk Voltage Default: 48 V
Max Absorb Time Default: 00:30 HRS:MIN
Low Battery Cut-Out Voltage LBCO Default: 50 V
High Battery Cut-Out Voltage HBCO Default: 58 V
LBCO Time Delay Default: 00:10 MIN:SEC
HBCO Time Delay Default: 00:10 MIN:SEC
Low Battery Restart Default: 51 V
High Battery Restart Default: 56 V
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Re: battery questions with Skybox.

Post by raysun »

Forgive the snarky parts of the comments below, however, they are apropos.

"One will destroy one's first battery" is a somewhat acerbic truism from the lead-acid days. Its true with lithium too, it just happens faster.

TBH, the LiFePo4 battery pack can be used without a BMS, but it removes important safety factors. IMO a BMS-less battery is not for experimenting with integrating a lithium battery into a inverter power system. Excursions outside the specified cell parameters, unintended or not, will result in damage and possibly cell death. At least with LiFePo4, the chance of burning down ones house is greatly diminished by the chemistry.

The Flying Wallendas did their high wire acts without safety nets, it was a big part of their draw, its also a big part about why there are less Flying Wallendas these days.

The setup parameters will depend on the physical layout of the cells. The charge/discharge parameters will have to exhibit a good degree of "self-control" to assure excursions outside the cell parameters never happen. I'm guessing these are 100AH prismatic cells @ 3.2V nominal? Are they wired 16 cells in series?

The 100AH battery pack cannot have a 280AH battery battery pack added to it. The different native capacities will all but guarantee uneven charging and early failure of one pack or the other. It will be better to make sure the eventual BMS is capable of operating in parallel with like battery packs/BMS. Three 100AH packs of the same cells as now will give the best chance for a stable 400AH battery.

IME, get a BMS that matches the capabilities of the cells in the battery pack. Your supplier should be able to provide some guidance. Also, get the BMS installed and the battery fully tested before hooking it up to the Skybox. It will lessen the likelihood that the pack comes to grief during the learning phase of the implementation.

2 AWG Copper is rated at 115A. Probably OK for a 5kW load, but it doesn't leave a lot of margin. Since the cables are so short, why not step up to 2/0 AWG and never have to be concerned about the wire overheating.
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Re: battery questions with Skybox.

Post by SHunsader »


I mostly agree with everything raysun says in his reply. I have 2 Skyboxes with different sized battery arrays on each Skybox, growing monthly.

Do a little homework online and you'll see that you're really asking for trouble if you don't use a BMS. It provides a LOT of benefit, including safety.

Skybox needs to LEARN the capacity of the battery bank. Even though you tell it what the bank is rated for, it still needs to learn. At least the way I've been provisioning my banks, the first discharge only discharges 1/2, then improves a little more on night 2, and by the end of night 4, pretty close to capacity. BUT, Skybox always oversteps....learning the top end, and in doing so, it's going to hit the Low Battery Cut Out voltage, and send your Bank to 1% (that's a place holder, per Senior Support person Chuck). FYI, if you want true capacity from your battery bank, you're going to need to charge/discharge for at least a week to assure yourself (and Skybox) that the capacity is there when you need it.

I've lived and breathed this Skybox 'stuff' since my power up date, Feb 12, 21 and am still cutting in new features. Because of my distain for my grid provider, my initial plan of just covering loads over peak periods has changed. I'm now working on being free from the grid. I'm still provisioning batteries (just got 2 banks of 14 kWh more yesterday), for my 2nd Skybox. Each bank needs to be confirmed and charged before tying them together, so it's been a long haul getting to this point.

The guy I've purchased the Lishen 272 aH banks from sold me Daly 150A BMS's with Blue Tooth dongles. It makes it quite easy to see exactly what's happening with each cell, and tells me pretty quickly whether the Skybox has it right, or not.

I'm pretty analytical and happy to help.

Let me know if/how I can help. - Steve
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Re: battery questions with Skybox.

Post by Dforster »

Thanks to both of you for the replies.

I suspected bms-less operation was not good. So that's why I was inquiring from the experts here..

I actually got my BMS and started connecting it. Working through some bad instructions but I think I've got it pretty much figured out. It's my first time connecting a BMS so I'm checking all my steps to get it right the first time. Good English instructions are hard to come by, as is expected I suppose.

Little disappointed I can't use my 100ah with my 280ah that is on the way. My battery supplier thought I could but he wasn't sure. I don't think he has ever tried it. But I won't have trouble getting my money back out of it I think, or possibly find another use for it. my boat trolling motor, etc. its a 12 volt but I could redo this pack and have quite a trolling motor setup!

I'm sure I will have other questions. Thanks for the offer!
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