Preferred settings for 24 volt Chevy battery bank

Good morning all.
I was referred here by Nobadays on another forum. He very enthusiastically recommended it. I see why, great forums with a nice "tone" as it were.
My existing system consists of 9 x 260 watt Solarworld Sunmodules, a MidNite Solar MS4024 which used to power 8 - 6 volt x 330 amp hour batteries. A weekend cabin located up in the NW Adirondacks, off grid, on water, and had been using the cabin with propane lights, fridge and gravity fed water system. I wanted to go wind or solar for a few years but finding qualified folks up there who are not booked years ahead is hard. I chanced to meet the owner of a solar install company from Rochester, NY while canoeing one morning and he paddled over with me, took a look at what was needed, we discussed my way overblown estimate for usage and he literally installed 7 weeks later, (he had a big job get delayed and I bribed him with having him stay on site to work, eat, paddle, eat...etc) I now have over 30 lights in the cabin, 6 ceiling fans w/DC motors and really enjoying it. Mostly weekends, never had an issue w/capacity.

So after reading up on options I drank the Kool-Aid and purchased 4kwh worth of 24 volt used Chevy Volts, (4) to replace the 1,000 lb battery bank I had to remove from the island every year. I'm heading up this weekend for the first time this season to open up and frankly I am so excited to not have to haul 8 of those monster batteries off the truck, down to the dock, on to a 12' aluminum boat, (4 at a time), over to the other dock, off the boat, and an 83 step, (guess how I know that number) trip...one way... hauling each of those !!! Can't wait to just turn the CC off in the fall and leave all in place! I do have a BMS btw.
MidNite Solar was kind enough to get me the keystrokes needed to adjust my charge settings as the Owners manual was on a flash drive but missing a key chapter...yup...setting charge rates! I, nor MidNite Solar, cannot tell what model Classic the integrated Charge controller is, but he gave me the keystroks as well so that the unit can ID itself to me.
So I'm looking for the generally accepted settings for absorb, float and float time for a 4kw 24 volt bank of Chevy Volt batteries.
As I stated earlier, I had this professionally installed so my knowledge is marginal at best technically so based on the below response from MidNite Solar where should I be? Not looking to push upper limits, prefer to protect against deep discharge...
Also: Why would I not desire a float per below? Does that Absorb time seem reasonable/accurate?
Other Matters:
Cables: I had very thick gauge cables for the lead batteries which won't fit the terminals of the Volts. I can't find the specs on line anywhere for the nut size and I'd hate to walk into a hardware store with a mask on, (NYS COVID-19 law, all must wear masks in public), carrying an unusual large suspicious object .
Recommendation for gauge size to connect the 4?
Positive/Neg line: All from end battery or one on first and one on last in line? My current neg is much longer so if there is an advantage to doing it that way I'll stick with it.
Anything I'm missing?
Apologize for the incredibly long winded first post!
If any of you are ever up in the area....stop on by!
I was referred here by Nobadays on another forum. He very enthusiastically recommended it. I see why, great forums with a nice "tone" as it were.
My existing system consists of 9 x 260 watt Solarworld Sunmodules, a MidNite Solar MS4024 which used to power 8 - 6 volt x 330 amp hour batteries. A weekend cabin located up in the NW Adirondacks, off grid, on water, and had been using the cabin with propane lights, fridge and gravity fed water system. I wanted to go wind or solar for a few years but finding qualified folks up there who are not booked years ahead is hard. I chanced to meet the owner of a solar install company from Rochester, NY while canoeing one morning and he paddled over with me, took a look at what was needed, we discussed my way overblown estimate for usage and he literally installed 7 weeks later, (he had a big job get delayed and I bribed him with having him stay on site to work, eat, paddle, eat...etc) I now have over 30 lights in the cabin, 6 ceiling fans w/DC motors and really enjoying it. Mostly weekends, never had an issue w/capacity.

So after reading up on options I drank the Kool-Aid and purchased 4kwh worth of 24 volt used Chevy Volts, (4) to replace the 1,000 lb battery bank I had to remove from the island every year. I'm heading up this weekend for the first time this season to open up and frankly I am so excited to not have to haul 8 of those monster batteries off the truck, down to the dock, on to a 12' aluminum boat, (4 at a time), over to the other dock, off the boat, and an 83 step, (guess how I know that number) trip...one way... hauling each of those !!! Can't wait to just turn the CC off in the fall and leave all in place! I do have a BMS btw.
MidNite Solar was kind enough to get me the keystrokes needed to adjust my charge settings as the Owners manual was on a flash drive but missing a key chapter...yup...setting charge rates! I, nor MidNite Solar, cannot tell what model Classic the integrated Charge controller is, but he gave me the keystroks as well so that the unit can ID itself to me.
So I'm looking for the generally accepted settings for absorb, float and float time for a 4kw 24 volt bank of Chevy Volt batteries.
As I stated earlier, I had this professionally installed so my knowledge is marginal at best technically so based on the below response from MidNite Solar where should I be? Not looking to push upper limits, prefer to protect against deep discharge...
Also: Why would I not desire a float per below? Does that Absorb time seem reasonable/accurate?
- Set the Absorb charge voltage (Charge/Volts).
- Set the Float charge voltage (Charge/Volts):
- If no Float is desired, then set a low Float value, such as 20V, and the Classic will rest after the Absorb charge cycle ends.
- Set the Absorb charge time, usually very quick, like 4-6 mins (Charge/ChgTime).
- Turn the temperature compensation off by setting the temp coefficient factor from a common -5mV to “Disabled” (Charge/T-Comp).
Other Matters:
Cables: I had very thick gauge cables for the lead batteries which won't fit the terminals of the Volts. I can't find the specs on line anywhere for the nut size and I'd hate to walk into a hardware store with a mask on, (NYS COVID-19 law, all must wear masks in public), carrying an unusual large suspicious object .
Recommendation for gauge size to connect the 4?
Positive/Neg line: All from end battery or one on first and one on last in line? My current neg is much longer so if there is an advantage to doing it that way I'll stick with it.
Anything I'm missing?
Apologize for the incredibly long winded first post!
If any of you are ever up in the area....stop on by!
Comments
I guess if you leave the Chevy batteries fully charged in the fall without any charge or discharge happening they should not self-discharge to any dangerous level.
Sounds like a nice place to chill, except for humping groceries up the 83 steps.
Thanks for the compliment, I'll post some pix in a few. But frankly, I don't mind hauling groceries as much as I did the batteries. it is fun...much more livable too, not as rustic but at least I'm still off grid for a long weekend here and there!
Some things that need to be observed, there should be no temperature compensation or equalization, a float voltage would be approximately 80-% of the fully charged voltage, but not knowing the exact chemistry it's impossible to state a value. This link may provide some information that could be useful https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
One additional point is, when dealing with lithium batteries, one needs to think on a cellular level not overall voltage, this is very important because when approaching the knees cell voltage, or cell block voltage can drift significantly depending on where the cells or blocks were initially ballanced.
Try establishing the exact chemistry along with the charging aand dischargeing curves, this would allow some reasonable predictions on where the settings should be.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
You NEVER want to charge them to 100% and never discharge below 10%
They cannot be recharged below 32F and need cautious charging below 40F
Li batteries burn quite well with lots of toxic (very toxic hydroflouric acid) fumes that you learn about while slowly dying in the hospital
You do not want to get this wrong.
Li batteries require no Float or Absorb cycle. Most adjustable charge controllers can emulate this with a 1 or 2 minute Absorb, and setting Float voltage much lower than normal float would be.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
@solar_dave mentioned cooling, my thought is cooling is required in automotive applications due to extremely high charge and discharge rates, not to mention they are not exposed to free air circulation. In an offgrid application it's generally no an issue as the rates are lower thus not generating heat.
@rachelsdad The BMS linked looks to be a Chargery product which are predominantly designed for automotive applications, usually powering external relays or contactors, not ideal but can be used in off grid, I actually use one for it's graphic display and secondary control but not primary control, primary is done by a BMS ordered to specifications provided to the manufacturer. The reasoning to do it this way was to allow use of the solar without solar disconnect, which the Chargery would do if used as designed to cut charging once the battery is fully charged, this. This can however be overcome with careful programming of the controller by limiting the voltage to stay within the plateau, the downside is the relays or contactors need to be continuously powered to provide a fail safe condition, resulting in wasted energy.
Proceed slowly, gathering information will lead to success, the first step is to establish a maximum/minimum voltage setting, usually around 90% and 20% of maximum/minimum allowable, personally I'm reluctant to offer a value because I'm not using the cells you have, but the rules are generally the same, keep between the knees, the safe zone.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
I did get info from the company I purchased from as well as an installer who uses them frequently.
But yes, I am proceeding slowly.
Thank you
1) the BMS must not disconnect the battery from the CC. It must disconnect the PV from the Controller, or use a logic signal to shut down the controller. If the battery is disconnected in daylight, from the CC, the high voltage PV will likely damage/destroy your controller.
2) capability of BMS. If your solar CC is producing 30A, and your BMS has 2A bypass circuits, you will quickly have a 28A overcharge on one cell. Be sure this is addressed.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,