Going all in - 600ah @ 48v of battery + 4,000 watts of solar

[kcmusa]

Just need solar to finish the job, check out this setup.
https://youtu.be/Wy-EHwXGRXo

[18LT]

Originally Posted by ependydad

@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'd like to build a couple of lifepo4 batteries but the DIY forum I read has so many different thoughts about compressing the cells, especially high amp-hour cells, that I think I'll stay with factory-built batteries. I'm pretty sure I'd find a way to completely destroy the cells and/or bms. Maybe more than once.

[18LT]

Originally Posted by kcmusa

Just need solar to finish the job, check out this setup.
https://youtu.be/Wy-EHwXGRXo

I can't even imagine how much the owner has invested in the solar charge system, much less the rest of the system. Impressive.

[Ballistic]

Originally Posted by 18LT

I'd like to build a couple of lifepo4 batteries but the DIY forum I read has so many different thoughts about compressing the cells, especially high amp-hour cells, that I think I'll stay with factory-built batteries. I'm pretty sure I'd find a way to completely destroy the cells and/or bms. Maybe more than once.

I say build it. If you recall NiMH had its own issues when they were released. Getting too hot, oozing and popping like a firecracker.

[Richard Dietzen]

Originally Posted by Larry-NC

Doug's a smart guy, but I don't understand anyone who runs the A/C all year, especially when the furnace is running.

Ask any woman with a bad case of hot flashes. He might need an electronic blanket on his side. [emoji23]

[TitanMike]

Originally Posted by 18LT

I'd like to build a couple of lifepo4 batteries but the DIY forum I read has so many different thoughts about compressing the cells, especially high amp-hour cells, that I think I'll stay with factory-built batteries. I'm pretty sure I'd find a way to completely destroy the cells and/or bms. Maybe more than once.

You really aren't compressing the cells as much as you are preventing them from swelling.

Here's a cutaway of a prismatic cell:



The internal cells are merely wrapped without any individual containment support under than each other and the outer case.

Cylindrical cells like used in Battleborn batteries are each contained by their own case and swelling isn't an issue.

Regardless of what the opinions are on the internet, reputable cell manufacturers all recommend "compression". Not to the point of crushing but merely a "firm squeeze" to keep the internal cell material from separating which is indicated by a bulging case.

[Hclarkx]

Originally Posted by ependydad

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.

Being spreadsheet-knowledgeable, this might be useful to you. It focuses on minimizing generator operation through periods of inclement weather when boondocking or dry camping. It assumes mini-split A/C but you can fudge the numbers to represent a conventional roof unit.

https://diysolarforum.com/resources/...ther-data.154/

[Hclarkx]

Originally Posted by TitanMike

You really aren't compressing the cells as much as you are preventing them from swelling.

Here's a cutaway of a prismatic cell:



The internal cells are merely wrapped without any individual containment support under than each other and the outer case.

Cylindrical cells like used in Battleborn batteries are each contained by their own case and swelling isn't an issue.

Regardless of what the opinions are on the internet, reputable cell manufacturers all recommend "compression". Not to the point of crushing but merely a "firm squeeze" to keep the internal cell material from separating which is indicated by a bulging case.

Interesting post! An observation ... the particular cell in the image does not need compression. It has compression built-in. It's probably a Calb cell. Others may have the thick plastic case, but most Calb if not all Calb cells do. They cost a bit more, but save a lot of work in the bank construction. And probably make smaller and lighter banks than most compression set-ups. And there are other advantages of this type of cell.

[Hclarkx]

Originally Posted by 18LT

I'd like to build a couple of lifepo4 batteries but the DIY forum I read has so many different thoughts about compressing the cells, especially high amp-hour cells, that I think I'll stay with factory-built batteries. I'm pretty sure I'd find a way to completely destroy the cells and/or bms. Maybe more than once.

Compression is optional. Most factory-built LiFePO4 batteries have little or no compression. You will likely get 10-15 years life without compression and a few more with compression. Given those additional years are way out in the future, their present worth is small. Also, advancing technology may obsolete our current LiFePO4 batteries by then making compression a waste. Though any kind of home made cell holder that will make a 12V battery movable and deal with terminal stress will probably provide some compression.

Or, there are cells with built-in compression as I noted above. I used those on my last build and really like them. They make for a much easier installation.

HOWEVER, if you aren't super comfortable with the idea and your skills and would greatly enjoy the experience, I strongly recommend going the factory-made option. The higher cost is now modest and when you get all the pieces for a self-build, you may save very little. And, you will be much more likely to get grade A cells in a factory build than a home build.

So, I've been there, done that, and don't recommend it unless you look at it as a hobby.

[CHICKDOE]

I read this post this morning and have been thinking about it for a few hours. Do I read it that you are going to build two identical 304 amp-hr battery packs? Each will have its own charger, inverter, and power one of the 50 amp legs?

Is this is the case the only issue I can see is the two legs sharing a common neutral. In normal 50 amp service the neutral only Carrie’s the imbalance between the two hots. This is because the two hots are 180 degrees out of sync. With two independent inverters you cannot guarantee that they will be 180 degrees out of sync. In fact, if they were in sync the neutral would have to carry the combined current from each leg.

Now I am not an expert so I may be wrong. It wouldn’t be the first time! But keep us informed. What I think you are building is something very similar to the Tesla Power Wall. Depending on how it turns out your experience might be directly transferable to a home built home battery backup. Running at 48 vdc allows smaller 12 volt cabling than 12 vdc would require.

[doanshop]

Ok I have to ask why you are running the furnace if you like it cool who is in the other part of camper that they need heat

[ependydad]

Originally Posted by doanshop

Ok I have to ask why you are running the furnace if you like it cool who is in the other part of camper that they need heat

Kids. Family of 4 here. Well, it'll be 3 in the motorhome- daughter is moving out. Going to miss her but didn't keep a camper bed dedicated to her.

[ependydad]

Originally Posted by CHICKDOE

I read this post this morning and have been thinking about it for a few hours. Do I read it that you are going to build two identical 304 amp-hr battery packs? Each will have its own charger, inverter, and power one of the 50 amp legs?.

I'm building 2 identical 304 amp-hr battery packs, yes. But I'm going to then wire them in parallel so that they appear to the RV as a single 608 amp-hr pack @ 48v.

They'll share the 2 inverter chargers (Victron MultiPlus II, as of now).

Originally Posted by CHICKDOE

Is this is the case the only issue I can see is the two legs sharing a common neutral. In normal 50 amp service the neutral only Carrie’s the imbalance between the two hots. This is because the two hots are 180 degrees out of sync. With two independent inverters you cannot guarantee that they will be 180 degrees out of sync. In fact, if they were in sync the neutral would have to carry the combined current from each leg.

I'm speaking a bit out of turn here and have people smarter than me guiding me. But, the 2 inverters do actually sync up with each other via a communication bus and can put out proper out of sync 120/240v power as the RV expects.

Originally Posted by CHICKDOE

Now I am not an expert so I may be wrong. It wouldn’t be the first time! But keep us informed. What I think you are building is something very similar to the Tesla Power Wall. Depending on how it turns out your experience might be directly transferable to a home built home battery backup. Running at 48 vdc allows smaller 12 volt cabling than 12 vdc would require.

I actually wouldn't mind building something like this for the house backup. We seem to lose power here frequently but, so far, not for long. Each summer there's a threat of a hurricane rolling through, but so far so good- we've been lucky with not getting hit.

And yes, the smaller wiring size with 48v is definitely something I'm looking forward to! I'll still have some larger wires feeding the 12v system (using 48v-to-12v converters) but they shouldn't be high enough amp draws to really worry about mega-sized wires.

[jbflag21ds]

Originally Posted by ependydad

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.

My 13.5k A/C with easy start runs via my inverter (claimed 85%+ efficiency but take that for its worth) pulls average 108A as read by my built-in BMS while the compressor is going.

I bet that 15k unit could be 110-120A after inverter losses, but hopefully the OP's unit won't be cycling much over night as heat build up should be much less than during the day.

[NJKris]

Believe it or not, that 85% inverter efficiency is when inverter is at/near max load. Smaller loads cause a greater efficiency loss.

[doanshop]

Originally Posted by ependydad

Kids. Family of 4 here. Well, it'll be 3 in the motorhome- daughter is moving out. Going to miss her but didn't keep a camper bed dedicated to her.

Ok I just had to ask now I understand. Thanks

[ependydad]

Originally Posted by jbflag21ds

My 13.5k A/C with easy start runs via my inverter (claimed 85%+ efficiency but take that for its worth) pulls average 108A as read by my built-in BMS while the compressor is going.

I bet that 15k unit could be 110-120A after inverter losses, but hopefully the OP's unit won't be cycling much over night as heat build up should be much less than during the day.

Nice to see some real numbers to it. I'm not too stressed with them. Even if I run 120A 100% of the time over night, that'll barely stress my bank at all. Just gets back to the recharging funtime that TitanMike raised for the next day. But that's a future ependydad problem.

[TitanMike]

Originally Posted by ependydad

Just gets back to the recharging funtime that TitanMike raised for the next day. But that's a future ependydad problem.

You might have one of these in your future for the rechrging funtime

https://dcautogen.com/product/v4-48v...-dc-generator/

A dedicated 48 volt DC generator that doesn't need to feed a converter in order to charge the battery. Uses a permanent magnet generator which is more efficient than the old designs and is also a "smart generator."




Just to put a smile in your day:

[aeblank]

Aren't you the ependydad with the big 5er and Dodge dually that used to full-time? Or am I confused?

[ependydad]

Originally Posted by aeblank

Aren't you the ependydad with the big 5er and Dodge dually that used to full-time? Or am I confused?

One and the same. Sold them both and was supposed to take 3-4 years off from RVing. Wife told me she had other plans and my Jayco motorhome should becoming in the next couple of weeks.