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Old 04-18-2021, 04:24 PM   #1
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Battery bank question for the Wizards

Hey gang,
I think I've got this electric figured out. Looking to hook up 8, 6v 235AH golf batteries.
If I've done my math, and hook everything up right, I'm looking for a 12v system, with 940AH total (470ah usable, because I can only deplete batteries to 50%, right?)
I'm looking at these batteries - https://www.batteriesplus.com/productdetails/sligc125

And using this guide as a reference:
https://www.explorist.life/3000w-inv...per-solar-kit/

I've included a photo of what I think my battery bank should look like? I know all of the wires need to be the same length, and 4/0 gauge - wires in sketchup photo are just for connection reference.

Calling any and all who can share a moment and drop some knowledge nuggets, I would be VERY grateful. This is the most expensive part of our build so I want to be sure I've got it figured out.

You all are the best - thank you!
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Old 04-18-2021, 04:34 PM   #2
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Check your local sams club for prices too. The diagram you show is for 12 volt batteries. Golf cart batteries are 6 volt. That won't work the same.
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Old 04-18-2021, 07:08 PM   #3
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Could I substitute the 6v batteries in the guide? Some we may upgrade to Lithium in the future (few years) so I'd like to have some of the components wired up already if possible?

Also - realized my photo didn't upload, trying to attach here.
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Old 04-18-2021, 07:33 PM   #4
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6V GCs if "Duracell" branded FLAs - actually Deka / EPM - are by far best value on the planet!

Sold at Sam's as well as Lowe's too.

Forget about warranty if one seller is cheaper.

Do **not** pay for shipping!
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Old 04-18-2021, 07:37 PM   #5
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https://thecampingnerd.com/how-to-wi...v-batteries-rv

but this is canon: http://www.smartgauge.co.uk/batt_con.html
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Old 04-18-2021, 07:42 PM   #6
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Some may or may not require a core, or charge you for the core. On 6 batteries it could be over $100.
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Old 04-18-2021, 11:54 PM   #7
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Just a FYI, when we made electric cars with flooded lead acid, the acidic fumes corrodes everything around them, and is actually explosive when charging them. So you really need to isolate and vent them to the outside. So dramatically better with Lithium.
I frankly would not waste my time and money on lead acid at this point.
If you don't have the budget for them, I'd get them anyway, but go with a smaller pack instead..for now.
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Old 04-19-2021, 03:50 AM   #8
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nobody's talking for EV usage

completely different use case.

A quality LFP bank will yes be far superior

but cost in the US at least 8x the FLA cost plus extra infrastructure, different design issues

even accounting for usable amps
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Old 04-19-2021, 08:28 AM   #9
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Your battery pack will not charge or discharge evenly if arranged that way due to different amperages through the individual serialized batteries. This is best, feel free to move them around anyway you need to make them fit, but ALL cables labeled "A" should be the same length, as well as "B", and "C". The final positive and negative leads out of the battery bank do not need to be the same length.

Think about it this way, if you want to pull electricity from any battery in the bank, the length of leads to the final terminal needs to be the same, it doesn't matter if the lead is positive or negative, but the total length needs to be the same.
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Old 04-19-2021, 08:58 AM   #10
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There are some LFP options out there that will be close in price for almost double the usable capacity (same-ish rated capacity). For same ish actual capacity I think you can do even better cost per watt hour.

Do you know what your typical maximum draws might look like?
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Old 04-19-2021, 01:04 PM   #11
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Quote:
Originally Posted by Bear Gerschafer View Post
Hey gang,
I think I've got this electric figured out. Looking to hook up 8, 6v 235AH golf batteries.
If I've done my math, and hook everything up right, I'm looking for a 12v system, with 940AH total (470ah usable, because I can only deplete batteries to 50%, right?)
I'm looking at these batteries - https://www.batteriesplus.com/productdetails/sligc125

And using this guide as a reference:
https://www.explorist.life/3000w-inv...per-solar-kit/

I've included a photo of what I think my battery bank should look like? I know all of the wires need to be the same length, and 4/0 gauge - wires in sketchup photo are just for connection reference.

Calling any and all who can share a moment and drop some knowledge nuggets, I would be VERY grateful. This is the most expensive part of our build so I want to be sure I've got it figured out.

You all are the best - thank you!
I think K's advice is wise-go with a smaller capacity LiFePo solution, and your money will not go to waste.

What is driving the need for so much juice? Maybe there are ways to get along with less, at first, to step into Lifepo.

It's worth the thought experiment at least.
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Old 04-19-2021, 02:22 PM   #12
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Quote:
Originally Posted by Rucker View Post
I think K's advice is wise-go with a smaller capacity LiFePo solution, and your money will not go to waste.
I was on mobile when I posted. To put some numbers out there, OP is looking at:

Quote:
Originally Posted by Bear Gerschafer View Post
Looking to hook up 8, 6v 235AH golf batteries.

If I've done my math, and hook everything up right, I'm looking for a 12v system, with 940AH total (470ah usable, because I can only deplete batteries to 50%, right?)
Doing the math:
8 * 6V * 235Ah = 11280Wh
8 * $144.99 = $1159.92
$1159.92 / 11280Wh = $0.10 per Wh or $102.82 per kWh

Double the cost for usable, I didn't factor in shipping cost of those golf cart batteries either, no idea what that is.

Using LFP 280Ah EVE Cells (3.2V * 280Ah = 896Wh per cell), you'd need (11280Wh / 896Wh) "12.59" cells for the same rated (not usable) capacity. Since this doesn't divide well by 4 (for 12V system) we'll go with 12 cells for a rated capacity of 10752Wh.

12 cells shipped to US is estimated at $1389.60. Add $100 or so for the BMS, $200 if you need really high discharges, so $1589.60.

Math again:
12 * 3.2V * 280Ah = 10752Wh
12 cells shipped ($1389.60) and BMS ($200) = $1589.60
$1589.60 / 10752Wh = $0.14 per Wh or $147.86 per kWh

For eight cells (a bit above usable capacity of the OP's batteries):
8 * 3.2V * 280Ah = 7168Wh
8 cells shipped ($944.10) and BMS ($200) = $1144.10
$1144.10 / 7168Wh = $0.15 per Wh or $159.61 per kWh

For the same rated capacity you pay more out of pocket, for a bit above same usable capacity you pay less out of pocket. Either way you blow cost per Watt-hour out of the water comparing usable capacity to usable capacity.

Key downsides:
  • While solar forums users and YouTubers like the EVE cells I linked, and the supplier has established a "niche reputation", both Basen (the supplier) and Alibaba's reputations are not yet "mainstream". Make of that what you will...
  • It will take at least a month for the cells I linked to arrive. It ships via ocean and then via courier. I've been waiting a month.
  • As with any lithium system, you need to know what you are doing, understand the role and function of the BMS. And wiring in the BMS can be confusing for someone without experience.
  • LFP cannot be charged in freezing temperatures which creates limitations as to where they can be installed. Additionally you need to pick a BMS with a temp sensor as to guarantee shut off charging below freezing.
Key upsides:
  • Performance
  • Lifespan
  • Value
As for whether the cells perform to specification, Will Prowse and Off Grid Garage did tests of cells from this supplier, search YouTube for "EVE 280Ah LiFePO4" to get some results there.

I ordered 52 cells for a 16S3P (48V) pack in two batches, batch one arrives for me Thursday and I'll be detailing everything in my build thread.
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Old 04-22-2021, 10:38 PM   #13
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Big thanks to all the replies! Sorry I dropped out for a few days.

A fellow skoolie fam member mentioned this guide for battery reference - this was what i used to build the model above. Definitely noted that all wire lengths need to be the same.

Definitely trying to help the budget with the 6v golf batteries - I've been going back and forth between the LiFePo batteries, but based on my energy budget (I think I did it right?) I'd need 400Ah /day (389.18Ah used in budget, + buffer).

I used Explorist.Life's energy budget - and have used their guide along with FarOutRide + EVERYTHING I've seen on this forum for knowledge.

If I've understood correctly, I can only use 50% of the 6v battery capacity or risk damage - whereas if I go LiFePo i can use all 100%.
That is still 4x 100Ah LiFePo batteries - coming in way too close to $4k for my comfort right now (first timer)

I've seen some pretty advanced "cell-built" batteries out there, but that honestly just seems way too over my head for right now. All of the components I'm using will be able to handle the LiFePo battery update if we go that route down the road.

Thank you again for all of the input - this is a huge help.
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Old 04-23-2021, 12:50 PM   #14
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LFP cells should not use more than 80% of their theoretical capacity if you want them to last

do not rely on the BMS for your normal cycling LVC, that is there to act as a backup failsafe when the "userspace" controls fail

For really good longevity the voltage shoulders at both ends are best avoided

even a 10% higher average DoD% can triple lifespan cycles.

Note that nameplate Ah ratings cannot be trusted, you need to benchmark **actual** capacity during the initial commissioning / breaking in period.

Plus as the battery wears, remaining capacity gets reduced.

So for usable Ah with LFP, best to figure 70-75% rather than the 50% with lead.

The main advantages for LFP besides longer replacement cycles, is the much higher CAR, faster recharging, and no need to get back to high SoC for cell health.
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Old 04-24-2021, 05:19 PM   #15
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I went from 8 x 12v batteries all in parallel like this.
I have 1140 watts of solar and I was having issues with going below that 50% threshold over night..
I changed to a 24v system and I barely depleted my batteries about 5% of full charge.
I’ve been EXTREMELY HAPPY since I went to the 24v system.
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Old 04-24-2021, 07:31 PM   #16
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If going with that many batteries I would recommend 24v system it will save you money, same watts,

Just putting this out there Iím still building and itís on the back burner right now due to family stuff (new member on the way)

I will be going with a 24v system with eve 280ah cells or similar, I will bring installing at least 1000 watts of solar, and a growatt 24v 3000w all in one, this thing has 3000w inverter, a transfer switch AC charger, and mppt solar charge controller all in one unit, for my 12v lighting and water pump and any fans I will run a 24v to 12v step down converter

24v uses small cables and cheaper charge controllers
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Old 04-24-2021, 08:24 PM   #17
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I had been debating between the 24v and 12v system for a while - I honestly cant remember what made the final call for 12v.
As a novice I'm relying on everything I can source on the internet and there is just so much more info on the 12v setup for skoolie / van conversion - I think that is why I made the final call to 12v for our first build.
I know there are converters / step-down units for 24v to 12v, but it just seemed more intuitive to "follow the lesson plan" with 12v and learn that way, rather than using the info I've found and translating it into 24v - once I have a better understanding of solar & battery bank setups I think I'll be more confident to upgrade / adjust my setup.

Definitely some interesting advice on 12v batteries vs 6v - and FLD vs AGM.
I think I'm still leaning into the FLD 6v golf batteries, the Trojan T105-RE mentioned in this another post here have free shipping

I'm not opposed to maintaining & filling batteries - I've taken care of forklift batteries in the past so it's nothing new. Honestly I kind of get off on taking care of systems like that (I'm literally chomping at the bit to get into the dash board and clean up my rat's nest)

I really appreciate all of the input so far - I've said it before, and I'll say it again; I wouldn't have made it this far, this fast, without y'all!
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Old 04-24-2021, 08:49 PM   #18
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i have always used 12 volt batters as i used 6 volts golf cart batteries and had lots of problems there a good system out there from https://www.renogy.com/deep-cycle-ag...-12-volt-200ah i bought 4 and 300 watts of solar and i am doing great
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Old 04-24-2021, 09:33 PM   #19
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24V (and 48V) can be useful for a variety of reasons...


My rule of thumb is the 100A threshold- If you are regularly charging at around 1200W or more, or drawing 1200W or more, I suggest considering 24V. 2400W, consider 48V. Components work less hard and some things are much cheaper.



If you're always well under those numbers there is little benefit to going above 12V.
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Old 04-24-2021, 10:38 PM   #20
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Quote:
Originally Posted by kazetsukai View Post
[*]It will take at least a month for the cells I linked to arrive. It ships via ocean and then via courier. I've been waiting a month.
And maybe you'll be waiting a lot longer than that! I was on the beach at Seal Beach CA yesterday, and I counted at least two dozen container ships at anchor outside the ports of Long Beach and Los Angeles waiting for a berth to unload. If you've noticed that retailers have less stock of Chinese-made items these days, that's why. These container ships are huge, as large as the ill-fated Ever Given, so there are maybe half a million TEUs now waiting to be unloaded. And then they all have to be put on rail cars to be transported across country: BNSF and UP are running 16,000 ft double-stack trains just to clear the logjam at the ports.

John
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