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Building a pack of Lithium Iron-Phosphate cells. Need help with balance theory/chargi
#1
Hello gents, new to the forum, been searching for a place to find some smarter individuals on this matter. 

I'll start here. I'm building a home PV system. Iv'e made my own solar panels, and since grid tie is very difficult thanks to WE energies, i'm forced to use a battery storage system. Iv'e looked all around at different types of batteries and landed on LifePO4. They are safe, have a high energy density, can discharge pretty deep, i read 80%. Also the cycle life should be a lot better than LA. Specifics on goals below. 


So here it is, i have 160 3.2v 5500mAh lifePO4 cylindrical cells for a grand total of around 2.8kWh of lithium cell. Not bad for $300. My goals are to create a pack, power a 24/7 draw, whilst charging the pack on a 6 hour cycle through the day with the solar. Questions on solar i can pass along to my solar buddies, what i really need help with is the charging system/battery management system, and the overall design of the pack. 

Battery ????'s 
---------------------------

1)With 160 cells... do I want to parallel as many as I can, and series those parallel lines to achieve my desired voltage? 
i.e. Wire 4 rows of 40 parallel cells to achieve 3.2v@ 220 amps, and then series those 4 chains to attain 12.8v @ 220amps? 

2) Choosing a voltage. Since i make my own panels.... voltage is not really any special requirement. I don't need a 12.8v system. It could be a 24v or 48v system. I would assume higher voltages are just better for power transmission... but the transmission distance to my AC inverter is only going to be a few feet anyways. Although using life batteries... I can see finding a charge controller that can balance charge 16 cells might be tricky. More or less i need help verifying my thought process on this. 

3)Balance charging
Is it necessary with LifePO4? I see some say its absolutely critical... and others who say Life can balance itself much like Lead acid due to its larger than Lipo overcharge tolerance. 

4)Balance charging with MPPT. Do MPPT chargers have this ability? Would it be desirable? Otherwise on the charging front i see hobby chargers work very well. Its just a hobby charger wouldn't work with a solar application. I need some form of MPPT that knows how many cells i have much like a hobby charger, and with the abilitiy to balance those cells. 

5)BMS iv'e heard good and bad things about BMS's. Some have fried and destroyed packs. Others have prolonged battery life to 5 years. My question here is; would the answer to my solution be to run a standard 'off the shelf' MPPT to a BMS that manages the cells? I feel that's where i'm headed. 


6)BMS/MPPT charger ratings. 

When i see a battery management system with an amperage rating, is that rating intended to be above the value of the battery? Or is it more or less the max discharge/charge rate? Same question on MPPT's. I assume the latter and more specifically it would pertain to the max charge rate of the battery or the max drain rate, which my load will depend on as well. 



That's all i can think of for now! Any help super appreciated guys!
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#2
You should look at http://electrodacus.com/ which does MPPT charging and is a BMS.
If you look at this Google+ page, you can see the new one he is building.

Most of your questions are general pack design related, which I'm sure others can give answers on too.
series = add voltage
parallel = add current/Ah
What you are talking about is a 40s4p pack
which works out to 12.8V 220Ah

Also power = voltage x amps therefore 2.816kWh

For charge current, look at what the C rate is for the cells you have (or it's listed as current in Amps).
C is ratio of capacity to Amps, so 5.5Ah @ 1C = 5.5A 5.5Ah @ 0.5C = 2.75A
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#3
(12-30-2016, 03:23 AM)station240 Wrote: You should look at http://electrodacus.com/ which does MPPT charging and is a BMS.
If you look at this Google+ page, you can see the new one he is building.

Most of your questions are general pack design related, which I'm sure others can give answers on too.
series = add voltage
parallel = add current/Ah
What you are talking about is a 40s4p pack
which works out to 12.8V 220Ah

Also power = voltage x amps therefore 2.816kWh

For charge current, look at what the C rate is for the cells you have (or it's listed as current in Amps).
C is ratio of capacity to Amps, so 5.5Ah @ 1C = 5.5A  5.5Ah @ 0.5C = 2.75A


Haha thank you! I know quite a bit about cell technology and power already. If someone didn't know the equation for power i think they probably should be no where near lithium technology lmao. 

The size pack i'm actually going for on 12V would be something like a 4S40P or on 24V 8S20P. But theres two different ways to wire that pack, which is kind of what i was directing my questioning to. 

That guys kick-starter looks great! Although it appears he hasn't come through on any of his products. The ship dates on all those pledges were October of 2015 lol. As awesome a concept as it is... I don't think i could trust him to magically start shipping product hes already a year late on.
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#4
The product shipped without issue - you might want to have another read and edit your post.
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#5
Looks like he did start shipping 6 months after his initial expected ship date. I don't see much activity since June. He now has two other kickstarters going but isn't producing the initial kick-starter product? This doesn't do me much good.


Did you have anything to contribute to the original post Sean?
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#6
If you can find someone selling one of his products, buy it - they are superb.

Home made PV is a waste of time, money and your energy (but a fun project) as their lifespan is limited, as is their output - forget 12 and 24 volt systems.

There's little else to add other than opinion, all the answers you seek can be gleaned through a little reading and research.
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#7
Problem is simply he put the later stages of his project on the website rather than kickstarter. Then later removed old information from that website.
Kickstarter is crap at project management, post funding, you pretty much have to communicate via another website.

The SBMS4080 is the original Kickstarter, then he made the SBMS60/SBMS100 versions.
3rd party reviews.
https://www.youtube.com/watch?v=bg1x6X8tZok

https://www.youtube.com/watch?v=MWflnrgVjeE
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#8
(12-30-2016, 09:35 PM)Sean Wrote: If you can find someone selling one of his products, buy it - they are superb.

Home made PV is a waste of time, money and your energy (but a fun project) as their lifespan is limited, as is their output - forget 12 and 24 volt systems.

There's little else to add other than opinion, all the answers you seek can be gleaned through a little reading and research.

I read his bio. Former siemens guy. Like i said his controller is great, its exactly what i need, but my only option is to buy second hand from one of the like 100 people who got units. 

I understand PV is not totally where it needs to be on a sustainability level... but i'm doing more than just powering appliances. I'm doing whats called mining. If anyone here is familiar with bitcoin... its the method of which bitcoin is created. And thus i make money on burning power. So if you can imagine, its more worth while for me to have free power than someone just trying to get off grid Wink

Every 125~ watts can power 1 hashing card for me. A single hashing card produces roughly $40 of revenue per month. Someone saving 15$ a month on 150 watts is less appealing than the fact that i produce money with that power. So yes and no. 


Your last statement says it all. I can read through information all day long and depending on who i ask gives me a different story. If you ask a solar guy if he thinks a powerwall is a good idea, hes going to tell you its a huge hazzard that shouldn't even be attempted. Obviously that is not my perspective or i wouldn't be here right? So a lot of this stuff you call information is actually only regarded as opinion, and i prefer to take opinions from people experienced in this. 


At this time... this forum is the biggest source for custom cell/tesla style battery structure i can find, and a lot of design is very much opinion. Also the answers to a few of those above questions are also a matter of opinion in case. So don't sell yourself short. I'm looking for opinion as much as i'm looking for data.


Also Sean one has to beg the question... why are you here? Especially with such skewed views towards PV lmao.
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#9
arr bitcoin been there.. and never again Smile
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#10
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