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diy solar

Taking the Plunge into DIY Battery

Drunkin Solar

Solar Enthusiast
Joined
Feb 19, 2024
Messages
288
Location
N E Tennessee
Well I gave lots of thought to the pros and cons of a DIY battery bank and decided to dive in.

Went with the Seplos Mason kits purchased directly from Seplos. They went out the door last week and I should see them in about five weeks from across the pond.

My system is a 24V system so I am putting together 3 units 8s for approximately 21kwh of storage using Eve 280k grade A cells.
This should give me about 3-4 days of power as my off grid consumption is generally in the 4-5 kwh a day which should cover most bad weather runs without firing up the generator. The rest of the gear is Victron and 3.1kw of panels backed up with an Onan 7.5 kw generator.

Looking forward to the journey!
 

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Geez.... the three Seplos boxes are here. Was not expecting them for another month. I'm astounded how fast they got here.

Also they have way more factory pre-assembly than what their assembly video shows and the printed out instructions show.
The BMS is mounted to the faceplate along with the screen. Also the balancer boards are mounted. And the handles are pre-installed. Finish looks great. Nice !

Now the work starts
 

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Just finished opening everything up and trying to do an inventory on all the little pieces. As best I can tell without opening up all the little bags of screws and whatnot all looks present and accounted for. The boxes all arrived in pristine condition very well packed. Shipping was lightning speed.

Must say kudos to Seplos....well done!

Can absolutely recommend a direct purchase from them. My sales rep quickly answered every question I had and there were many over a two week period while making my decision to take the dive.

Happy with the purchase
 
You have a link to the seplos 8s cases?

Did you buy your cell from them too or you source them somewhere else?
 
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Hey 740GLE
I can give you a link that connects you directly to my sales guy. PM coming your way...

The cells I'm purchasing locally at Battery Hookup. Eve LF280K v3 and grade A.
Lucky they are about a 25 mi drive for me at the moment.
 
Contemplating the next steps to get these up and running once I get my cells and put it together.

I do not have a charger to top balance the cells and I'd rather not buy a benchtop power supply for a onetime operation and then having it laying around taking up space. Already own more junk than I know what to do with.

A suggestion from another was to just assemble the whole thing and program the BMS and let it charge because the cells are already really close from the factory. I have a spare 370w panel and a little 100/20 Victron SCC and have no time constraints requiring a fast setup and commissioning of the batteries. I know this method will be slow at that rate of charge and would hope that if I leave it setup when it gets to float. My question is will the cells balance out within a week or two? This assumes they are very close out of the box.

All thoughts are appreciated
 
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Contemplating the next steps to get these up and running once I get my cells and put it together.

I do not have a charger to top balance the cells and I'd rather not buy a benchtop power supply for a onetime operation and then having it laying around taking up space. Already own more junk than I know what to do with.

A suggestion from another was to just assemble the whole thing and program the BMS and let it charge because the cells are already really close from the factory. I have a spare 370w panel and a little 100/20 Victron SCC and have no time constraints requiring a fast setup and commissioning of the batteries. I know this method will be slow at that rate of charge and would hope that if I leave it setup when it gets to float. My question is will the cells balance out within a week or two? This assumes they are very close out of the box.

All thoughts are appreciated
This will work perfectly fine. The amount of time it takes to balance depends on your BMS. Does it have an active or passive balance on it? 1A or 2A balancing? Hopefully you didn’t go with a seplos BMS…
 
It is a Seplos BMS. It is passive balance at the moment. Figure if I wind up with balancing issues down the road a Neey could be added later if necessary. Just wondering if I will get some decent balance initially if I let it sit at float.

I've read about the issues with the Seplos BMS v3 and also saw the video you referenced and it seems that they have been taken care of with firmware updates so I'm okay with that. The passive balance issue has been solved.

I almost ruled out the Seplos until I found out things were being taken care of. Seems to me they launched that product prematurely last summer.

Thanks (y)
 
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Also set the SCC to float 8*3.45v and let it bake.

If you’re not in a rush let the BMS do its job.
That was my thinking. If you give it time, which I have plenty of, at some point (hopefully) things are good enough to commission it into the system

Okay then float at 27.6v. That number sounds familiar because I think that is where it's already set at. Won't know till I return to Tenn.

Thanks Again
 
I'm bringing this old thread back up because just this past weekend the first of my three Seplos units was assembled and it all seems good. It fired right up and started charging it the next day. I've included a couple pics for you to see. The assembly was straight forward and took me a little over four hours working at a snails pace and being carefull. Very nice and solid box.

Also a week before the Seplos box I had assembled my first DIY battery from raw cells. It is a small battery I'm using to extend the capacity of my Ecoflow Delta. I purchased all of my cells from Battery Hookup and for the small battery I purchased 8 72ah Calb cells and a JBD BMS to make the assembly. This box is 24v same as the Seplos and it all fit (barely) into a standard group 24 battery box weighing in at about 37 lbs. Pics are below for this setup if anyone is interested in putting together something similar. All of the cells have been banded together with FR4 board in between and a plexiglass surround to provide a little compression on the cells. The BMS was also mounted to plexiglass using nylon hardware. The case was outfitted with a momentary switch and a led light to indicate it's on/off status. Also used the mini Anderson connectors to plug into it. Turned out to be a pretty neat little package. The whole thing is setup to handle a max 60 amp current draw/charge.

Also if any of the Seplos guys on here read this thread I would like to ask if they could send me the .apk file for Android. Can only download it from Seplos with an account setup. Tried to register and it keeps failing. I have given up right now out of frustration.

Thanks to all here for inspiring me to do these builds.
 

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To update this thread the Seplos has finished it's first charge to 100%. It took seven days because I only have a single panel and a 20amp solar controller available to me here and we've had a bunch of cloudy/rainy days back to back to back. The charge used 6kwh to fill it up. I carefully monitored it when it got close to being full and noticed the cells started to diverge their balance once the pack rose above 3.35v. The imbalance by the time the pack went high voltage of 3.65v was around 150mv between the highest and lowest cells. That scared the crap out of me because of the balancing issues these BMS's have had in the past. Then I noticed the passive balancer kicking in and doing it's job which it didn't start doing till the pack went full. I made no changes to the factory settings because I do not have a RS485 to USB adapter yet and haven't been able download the bluetooth app.
The pack ran for two hours more on the absorption voltage of 28.4v and the pack went to about a 75mv imbalance. A couple hours later I rechecked it and the balance had gone all the way down to a <3mv difference. Finally an acceptable number. So the balancing works I just think it should probably start before the pack reaches full charge. I'll mess with the settings coming up and see if that works better. All in all very satisfied with the box.
 
Agreed, I personally don’t like to push my cells past 3.5v as I routinely have long idle times at full SOC.

I have balancing starting at 3.4v I’m fine if I don’t get an extra 2-3% out of the pack.
 
Another update on my Seplos battery build.
Only the first pack out of three has been assembled so far. The next two will be put together by the end of the month.
I have been running the first pack for two months now and the performance is as what should be expected. The pack has good capacity and the cells have remained in balance the whole time. Very happy still with the build.
 

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