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Old 03-12-2022, 04:30 PM   #1
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Going all in- building a battery pack: 608ah @ 48v

Our biggest blocker to boondocking is that we run the bedroom air conditioner every night. We may have the furnace on in the rest of the RV, but we’re still going to have the bedroom A/C on.

I made our first purchase last night to support that plan- I bought 32 lithium cells that are 304 amp hours. I’m going to build 2 x 48v battery packs (which is the equivalent to 24 of the Battleborn batteries at a fraction of the cost).

This will give me PLENTY of power to run overnight and still have lots of reserve battery in the morning.
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Old 03-12-2022, 06:18 PM   #2
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But how is that going to affect your A/C usage? Certainly you don't plan on running an A/C on battery all night. If that is even possible.
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Old 03-12-2022, 07:00 PM   #3
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Nice! Take plenty of pic’s and share your progress with us.
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Old 03-12-2022, 07:17 PM   #4
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It is possible Kris!

One lithium battery would run the ac likely an hour. 8-10 gets you all night maybe.

Busses are big enough.

Going to need a lot of big wire.
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Old 03-12-2022, 07:58 PM   #5
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He said he'd have enough for 304 amp hours, which is great, but I know he's getting a giant RV which probably has 15k btu AC units. Running one in bedroom, I have no idea how many amp hours that would consume all night. At night it's generally cooler, so will cycle less frequently. Maybe I read it wrong and he has 32 cells at 304 amp hours EACH, that would be insane, lol.
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Old 03-12-2022, 09:09 PM   #6
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Doug's a smart guy, but I don't understand anyone who runs the A/C all year, especially when the furnace is running.
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Old 03-12-2022, 09:19 PM   #7
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But how is that going to affect your A/C usage? Certainly you don't plan on running an A/C on battery all night. If that is even possible.
100% going to run the bedroom A/C overnight on battery power. It's 608 amp hours at 48v which is the same as 2432 amp hours at 12v.

A 15k RV A/C takes about 100 amp hours per hour of running. I would literally be able to run it for 24 hours straight before I start to worry about how to recharge. Running it overnight for 8-10 hours won't be much to write home about.

Heck, I could likely even run both air conditioners if I really needed to. But I won't plan on that for any significant amount of time.

It'll be carried by a pair of inverters- one per 50amp leg. It'll essentially allow me to run anything I want off of battery power.
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Old 03-12-2022, 09:22 PM   #8
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Doug's a smart guy, but I don't understand anyone who runs the A/C all year, especially when the furnace is running.
(lol, keep your mind out of the gutter as you read this...)

Both wife and I sleep hot. With the door closed to the bedroom, the room heats up just from the body heat and it makes us sleep uncomfortably. So, we run the A/C to cool us and down.
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Old 03-12-2022, 09:24 PM   #9
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Nice! Take plenty of pic’s and share your progress with us.
Can't wait to get started! I just ordered the two Overkill Solar BMSs tonight. And, of course, I've been keeping a spreadsheet of parts.
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Old 03-12-2022, 09:28 PM   #10
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Just remember, huge battery packs require similar chargers.

I deal with charging a 17Kwh battery on a regular basis in my car.

By my calcs the fully developed battery "bank" will be around 29Kwh+ . Impressive but how fast will it charge?

Charging from fully depleted will take the full output of a 4kw generator for 8 hours.

Weight is going to be impressive. Best educated guess will be around 700+: pounds.

Will be interesting to see how it turns out.
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Old 03-12-2022, 09:32 PM   #11
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Nice! Take plenty of pic’s and share your progress with us.

This! Post your progress as you go please. Don’t listen to the negative Nancy’s. Just because they don’t agree doesn’t mean others shouldn’t proceed.

We’re planning on doing about 1/3 of your system (800ah@12v) as 100% of our RV time will be boondocking for weeks. Liberty is a great thing.
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Old 03-12-2022, 10:14 PM   #12
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I may have to come to FL just to see this thing once it's done. And like TitanMike said, I'm curious about how charging system will look.
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Old 03-12-2022, 10:26 PM   #13
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Just remember, huge battery packs require similar chargers.

I deal with charging a 17Kwh battery on a regular basis in my car.

By my calcs the fully developed battery "bank" will be around 29Kwh+ . Impressive but how fast will it charge?

Charging from fully depleted will take the full output of a 4kw generator for 8 hours.

Weight is going to be impressive. Best educated guess will be around 700+: pounds.

Will be interesting to see how it turns out.
Good call on both accounts. The 29Kwh is right about right, give or take.

Yep, recharging from empty will be a challenge no matter what I do. I used the air conditioner for 24 hours for example purposes.

And the cells alone should be about 400 pounds, but once I add a containment box, BMS, wiring and whatnot- I think 700 pounds might be high but not out of bounds. The motorhome should be coming in around 4,600 pounds of CCC. Even knocking off people + pet weight, we should be in pretty good shape.
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Old 03-12-2022, 10:28 PM   #14
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This! Post your progress as you go please. Don’t listen to the negative Nancy’s. Just because they don’t agree doesn’t mean others shouldn’t proceed.

We’re planning on doing about 1/3 of your system (800ah@12v) as 100% of our RV time will be boondocking for weeks. Liberty is a great thing.
We are heavy electric users. Mostly because I've made the outlets in the house hot. Given the inverter plans, I'm expecting my past history to be a mere blip (which was 300+ ah per day with only a 1000W inverter).

I haven't seen any negative Nancy's so far. Some real questions, some real input.

And definitely- going to be capturing as I go. It's going to be fun, no matter what!
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Old 03-12-2022, 10:29 PM   #15
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I may have to come to FL just to see this thing once it's done. And like TitanMike said, I'm curious about how charging system will look.
I'm actually coming up your way-ish. Our plans are to head to the southern Jersey shore and then over to York, PA so I might save you some miles.
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Old 03-12-2022, 10:51 PM   #16
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Good call on both accounts. The 29Kwh is right about right, give or take.

Yep, recharging from empty will be a challenge no matter what I do. I used the air conditioner for 24 hours for example purposes.

And the cells alone should be about 400 pounds, but once I add a containment box, BMS, wiring and whatnot- I think 700 pounds might be high but not out of bounds. The motorhome should be coming in around 4,600 pounds of CCC. Even knocking off people + pet weight, we should be in pretty good shape.
What are you planning for a BMS? The cells and connectors are the easy part. The BMS is essential on so many fronts. Current carrying capacity in and out, cell balance (which will be paramount which will be a MAJOR job with all those cells), overtemp limit, over discharge limit, temp, and so on and so forth.

Another thing that is often overlooked is how to secure the cells together to prevent swelling. I assume the cells are prismatic type. Ideally they will be placed side by side and then clamped in place by any one of a variety of methods. A couple pieces of plywood at each end secured with steel banding like that used to secure materials and packing for transport is one. Another is either plywood or metal plates that overlap the ends of the cell "pack" and using pieces of all thread clamp the cells tightly together. Just wrapping them with tape and putting them in a box will probably not yield desired results.

When it comes to cell connectors be sure to take into consideration how much current each will be carrying. Many like to double up the connections to make sure there is no heating issue with high current.

Needless to say you will have a lot of stored energy and be sure to protect the battery terminals from any possible shorting. If that energy is suddenly released by an accidental short within the battery enclosure, lets just say you really don't want that to happen. A good non conductive enclosure would be a must in my book. Any short proofing provided by a BMS is really only effective for current passing OUT of the battery and BMS with any short in the enclosure releasing a lot of energy in a real hurry.




Like I said, I'm interested in how it all turns out. Sounds like you might be able to plug the stick and brick home in when the power company turns out the lights.
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Old 03-12-2022, 11:08 PM   #17
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@TitanMike, the BMS came highly recommended to me from a buddy who has built 24v packs. It's the Overkill Solar 48v BMS. I'm doing a pair of them, one for each pack that I'm building (vs. using 1 for both wired in parallel).

https://overkillsolar.com/product/bm...6s-lifepo4-24/

I have to find the space that I'm putting these into first to know how I'm securing them. But longest story shortest- just what you're saying. Plywood on a couple of sides and strapping around them. I hadn't thought about the metal strapping, that's a very good idea.

I've also read debates on a DIY forum as to if I should be putting some kind of foam padding between the cells in the pack.

I also hadn't taken the top of them into account to prevent an accidental short. But I do like the idea of some kind of top. I might just get some thick Lexan/Plexiglass so I can see what's going on without having to crack open a lid.

Funny that you mention about powering the house, my wife actually mentioned about adding a lifted carport so we could park it here.
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Old 03-12-2022, 11:21 PM   #18
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For the charging system I've been having numbers running around in my head that are somewhat formidable.

Charging a 29 kwh batttery bank at it's max C-rate of .5 will take a charge current of 300+ amps. (when fully developed to 29 kwh of course).

300 amps at 48 volts is 14.4 Kw. If charging with a 120 volt input charger that means the charger will draw 120 amp. Reason #1 that chargers this large usually operate on 240 volts with input amperage more like 60 amp.

Realistically that's beyond the capability of most, if not all, RV electrical systems.

A charger able to operate within the 120 volt power limits of an RV would more likely have a rating of 50 amp output with a 20 amp, 120 volt input (2400 watts/48 volts=50 amp). Carrying that forward to replace 600+ amp hours at 50 amp charge rate will take 12 hours, give or take.

Time could be cut in half if true 240 volt service is available and a 240v 50 amp charger is used. Generator would have to be able to supply 240 volt power at a minimum of 5-6kw.

This is going to be a big project, not only the battery, but support equipment as well.

Are you sure you aren't really just building a clandestine EV power plant for your coach in case gasoline becomes even more outrageous in price?
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Old 03-13-2022, 01:28 AM   #19
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I've also read debates on a DIY forum as to if I should be putting some kind of foam padding between the cells in the pack.
I'm surprised this is debated on DIYSolarforum. It's pretty much a no-brainer, at least in the mind of an EE. The blue plastic film around the aluminum cans on the battery style you are probably getting is tough, but you want a second line of defense since a can to can short would be catastrophic. Ideal in my book is fish paper. It's tough electrical insulating paper made for applications just like this. Another option is thin plastic chopping matt (about 1/16" thick). This stuff is tough and being nylon or similar, it is a good insulator. These facilitate compression if you go that route.

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I also hadn't taken the top of them into account to prevent an accidental short. But I do like the idea of some kind of top. I might just get some thick Lexan/Plexiglass so I can see what's going on without having to crack open a lid.
One admonition that you don't hear often is, insulate your tools!!!!! I've used a few layers of PVC electrical tape but prefer 3:1 shrink wrap when it will fit. The only metal showing on my 1/4 drive torque wrench is the scale where you set the torque. Someday I'll get a digital one that can have no metal showing.

I've used 1/4" plexiglass for top covers. It's nice. The Overkill BMS does not have any mounting facility but double-stick foam tape (two strips to not inhibit air flow) holding it on top of the plexiglass panel works though I like a tie wrap as backup. Then maybe a bit of plexiglass above the BMS as well.
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Old 03-13-2022, 02:09 AM   #20
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Don't forget to remove your rings when working with your battery.
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