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First build questions
#1
Question 
I am researching my first build.  My first step build goal is something like an Enphase AC battery.  I think I will use a 7sXXp with a 24v inverter, starting with an Enphase M215.  I would like to be able to increase the XXp as large as necessary and increase it in small increments as cells become available.  Every 7s4p would approximately give another hour of nighttime output, I think.

The components I am considering are:

BMS:  electrodacus SBMS40.  I think this is more advanced and more affordable than the Battrium.

Battery holder:  a battery kit system from diybatterystore.  This is a solderless system, with cell level fusing.  I am open to suggestions.

Cells:  I don't have a source for used laptop or ebike batteries.  So I guess I am limited to buying them.  Are there suggestions on where to go to not get junk but yet be economically viable?  ebay?  Alibaba? online?

I may be able to get old packs of NiCd batteries for nearly free.  Is NiCd a viable battery choice or not worth the trouble?

I am looking for constructive criticism and suggestions!

rearden
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#2
Welcome!

This is my "suggestions" towards your setup but of course with some personal opinions.

BMS: Electrodacus is a very nice unit. You cannot really compare this to Batrium. Batrium is ALOT more advanced than Electrodacus view but electrodacus have solar MPPT charger and batrium is just a pure bms. For solar charger + bms its a wise choice for sure!

Battery Holder: Im not sure that kit is the best kit but it is "a" kit. If you want solderless you can always try it out. Its pretty expensive per cell but you save alot of time. I have not actually seen that system in use more than the creator doing it himself. It looks nice on the rendering but i dont know how it looks in real life.

Cells: Skip all those ebay, ali and so forth if you dont want to guess what you get. Where do you live? New or 2nd hand cells? When it comes to cells and other stuff to they saying "you get what you pay" is for sure true. I have yet not seen many chinese cheap cells perform as known brand cells do Big Grin

NiCd: I would not even consider that for a powerwall.



So to Summarize. I would not buy chinese cells nor use NiCd. The other 2 is most likely fine. Perhaps adding 2 cells at a time is not viable with that batterystore kit... ?
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#3
I have some experience with Enphase, I had some M215s as well. They are not ideal for your setup. I believe the Enphase AC battery uses an s270 or an IQ6, but somehow they have additional circuitry to get it to work in reverse (to charge the battery). I tried for months to see if someone was selling a salvage AC battery, but it never came up. And there just isn't any teardowns or anything to give you insight into their internals. I also don't know if you can even tie a battery to its input. I only found one video from India where somebody connected a battery to it, but I never tried it myself. I used 72 cell panels with my m215s and saw that the mppt usually kept the input voltage around 36v. I believe it uses 31v for 60cell panels. So you would need to run 8s, which is the most that the SBMS40 allows for. Good choice, btw. I'm also going to be running Electrodacus' SBMS products.

If you want to limit your system so that you dont export to the grid, you will need the s270 or IQ6 or IQ7, which will let you set a grid profile that restricts export.

You are looking at expandable storage. Search the forum for "cartridge" and you will find some people running that kind of setup. You can add to it all the time.

I'm not going to comment on lithium cells other than to say to do the legwork and you might find some cells for free.

With regard to NiCd, it's not recommended for a lot of reasons. Especially when you mention "old" which is nearly useless, and "nearly free" where you still have to pay for them. I have some brand new NiCd packs and I'm turning them into Emergency Light batteries to replace lead acids. I would not use them in a powerwall, though.
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#4
Thank you for your replies!

Enphase:  It is being considered as the first inverter because it is what I have on hand.  I can get 215w/h out of it or approx. 5kwh/day off my base load per inverter.  Constant ~10A draw at 24v.  I do not live in a Net Metering area.  I am still testing with some lead acid batteries.  I have an EPEVER tracer 40A solar charge controller which I also use for low voltage cut off and load control.  Start up current is a problem.  I assume the enphase MPPT does a sweep and since it is expecting a solar panel to come up gradually it looks like a short to the current source at the beginning.  At the moment I am using a 2.5D-20 NCT as a current inrush limiter.  I want a better solution that would swap to a shorted connection after a period of time.  I am hoping that maybe a sound system inrush limiter may have a drop in circuit I could use but I have not found one yet.  I have found ones for AC, but I don't know if they will work with DC.  Suggestions?

I have 16 Enphase inverters connected to the grid.  What I really want is to divert all exportable power to battery charging for use later.  Next would be to also have it available when disconnected from the grid like a UPS.  And a pony.

BMS:  So one vote for Electrodacus and one vote for Battrium.  I don't need the MPPT solar controller necessarily, I would rather divert exportable  gridtie power to the batteries and keep AC house loads as first priority, but I don't know how to do that yet.  I am looking at a power diverter from one of the guys at Open Energy Monitor but getting that variable source as an input in to a charger is something I don't know how to do and probably needs to be moved to a different part of the forum.
In your view, what useful features does the Battrium offer compared to Electrodacus?

Cells:  So NiCd is out.  I live in the US.  I can look around for more old laptop batteries.  Cost is an important factor.  It would seem to be fairly easy to run up the cost so that the DIY is as expensive as a retail Powerwall.  What should I look for in purchased cells if cheap Chinese are not recommended?

rearden
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#5
Cells if new: nkon.nl or queenbattery (thenderheart does reviews of these cells).
If you can contact any medical center and ask about their battery packs they have to replace is a good source for barely used cells. They have to replace the packs about every 2 years regardless if they were used or not. Ppls lives are on the line with those.
Also check e bike shops. Ignore ecig ships as those cells are heavily abused
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#6
(02-13-2019, 02:15 PM)rearden Wrote: Cells:  So NiCd is out.  I live in the US.  I can look around for more old laptop batteries.  Cost is an important factor.  It would seem to be fairly easy to run up the cost so that the DIY is as expensive as a retail Powerwall.  What should I look for in purchased cells if cheap Chinese are not recommended?

rearden

Try to get an in with an electronic recycler in your area that takes laptop batteries. Might take a little bit of gumshoe work but asking friends who know friends who know.............. I was fortunate to be able to have a friend that deals with this recycler recommended me and we hit it off great. I explained what I was doing, showed then my work so far and he was very accommodating. He was concerned as to what I was doing with these cells and once I showed him my process he was actually excited about it. I lowballed him at 50 cents per pack and he basically said no but $1.50 per lb. is what he gets when he gathers enough to sell to the next recycler. So we struck a deal at $1.50 a pack no matter what size 4, 6 ,9, 12 cell whatever. I get the pick of the litter and you know what I'm going for. Dell, HP, Lenovo, Medical packs etc. No chinese replacement batteries. So on average I get 200 packs at $300  as many 9 cell packs as possible which averages out to about 1500 cells. Thats .20 cents per cell and at about a 40% good rate that's about ~.50 cents a cell. So not to bad. I put it in my budget to go once a month and pick them up. Consistency is the key here so they can see that you are serious and it's not a passing fancy. So now when they get a box of cells they will hold them out for me on purpose as they know I will be there at the end of the month.  Sometimes  but very rare does he not have that number of OE cells that fills my quota.
The rest is just the grunt work of breaking down the packs and testing them according to your preference.
I started in October and initially was going for a 14s100p I have now doubbled that.

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#7
Hi rearden,

About the solderless kit, it looks like the fuses are on the PCB, so if one fuses pops, you can replace the bad cell but I see no easy/safe solution to reset/replace the fuse. It's a 2A rated fuse, but they say the fuse pops a 7-10A which is really high! So If you really want to go solderless, I think this would be a better solution, if you have the money.

Hope this helps...
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#8
(02-13-2019, 02:15 PM)rearden Wrote: Thank you for your replies!

Enphase:  It is being considered as the first inverter because it is what I have on hand.  I can get 215w/h out of it or approx. 5kwh/day off my base load per inverter.  Constant ~10A draw at 24v.  I do not live in a Net Metering area.  I am still testing with some lead acid batteries.  I have an EPEVER tracer 40A solar charge controller which I also use for low voltage cut off and load control.  Start up current is a problem.  I assume the enphase MPPT does a sweep and since it is expecting a solar panel to come up gradually it looks like a short to the current source at the beginning.  At the moment I am using a 2.5D-20 NCT as a current inrush limiter.  I want a better solution that would swap to a shorted connection after a period of time.  I am hoping that maybe a sound system inrush limiter may have a drop in circuit I could use but I have not found one yet.  I have found ones for AC, but I don't know if they will work with DC.  Suggestions?

I have 16 Enphase inverters connected to the grid.  What I really want is to divert all exportable power to battery charging for use later.  Next would be to also have it available when disconnected from the grid like a UPS.  And a pony.

BMS:  So one vote for Electrodacus and one vote for Battrium.  I don't need the MPPT solar controller necessarily, I would rather divert exportable  gridtie power to the batteries and keep AC house loads as first priority, but I don't know how to do that yet.  I am looking at a power diverter from one of the guys at Open Energy Monitor but getting that variable source as an input in to a charger is something I don't know how to do and probably needs to be moved to a different part of the forum.
In your view, what useful features does the Battrium offer compared to Electrodacus?

Cells:  So NiCd is out.  I live in the US.  I can look around for more old laptop batteries.  Cost is an important factor.  It would seem to be fairly easy to run up the cost so that the DIY is as expensive as a retail Powerwall.  What should I look for in purchased cells if cheap Chinese are not recommended?

rearden

Were you successful in getting the m215 to power up with the inrush current limiter? I experienced the same "short" with a battery connected and thought I fried the microinverter. BTW, it's not that the microinverters have a gradual startup, it is just that they are not expecting too much more current than they are rated for. For example, if you have to do maintenance on a solar panel midday, you cover the panel with something opaque, and when you are done, you remove the opaque covering. The microinverter is instantly exposed to the full power of the solar panel and doesn't get damaged. Could even be like 350 watts from a 320 watt panel depending on a lot of factors. But that's still a lot less than what a battery can provide. 

Based on your motivation, it seems like you should look at this post: https://secondlifestorage.com/t-Does-any...r-inverter It talks about using grid tie inverters like your m215s and a second compatible inverter to run backwards to charge batteries when there is excess power. You can then have a contactor to switch from off-grid to on-grid when there is no solar and your batteries run too low. 

Electrodacus is making a SBMS0 which does not do MPPT, it is strictly a BMS. It was going for $130 shipped in his last Kickstarter. Batrium has a lot more customization and functionality and 5x the balancing rate. Each system has its pros and cons. Only you can decide what is right for you and your powerwall.
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#9
(02-13-2019, 03:20 PM)LEDSchlucker Wrote: it looks like the fuses are on the PCB, so if one fuses pops, you can replace the bad cell but I see no easy/safe solution to reset/replace the fuse. It's a 2A rated fuse, but they say the fuse pops a 7-10A which is really high!

Fuses are to protect the cell from the rest of the pack. Not blow when there's a heavy load on the cell.
If 5p, and 1 cell goes short circuit, the other 4 cells will "easily" dump more than 10A into that cell. This will cause the fuse to pop. You don't want the fuse so small you get voltage drop across it.
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#10
I am going to use a timer which I can set different times depending on season so the 215’s mostly get to charge my bank during sun times. So there is no interupting current set up. The inverter just switches to batts as soon as the timer interupts 230v in. And visa versa (Victron charger/inverter) 20ms switch time.
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