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sanity check, before power loading
#1
Hello,

 Thanks for the group to help getting me to this level.

text side first and picture after this.

2x 340w 42v panels in parallel connect to a mpt 7210A feeding pos/neg bus, connected to (will increase after getting basic down first) 7S4P (about 4.8 ah at 24v) through a battery protect to a 1kw GTI to feed back into the house.  



I need to make the positive and negative buss bars but almost everything else is on hand.  



second part of the question, one that i am unsure and safety says I am need to ask.



If i tie in a line from positive buss and load of battery protector, will this let me still use the grid tie invertor while the charge controller is charging the batteries.  

I understand that the battery protect will turn back on when it is charge back to a level that it is programmed to do.

I just want to make sure that it does so safely.



Future projects and upgrades.

I have enough for 7S28P to finish building but wanted to get something for testing so i can build up on my learning with lower power load first.  Additional 7S4 or 3P packs will be adding on as they are tested and good.

Thank you for taking time read this.

CB
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#2
1. Your second image wont work. Look at it and you will see whats wrong. You basically just bypassed the protector
2. You need a BMS to protect the unit
3. The MPT7210 is boost controller so input voltage need to be lower than output. Yours is other way around so it wont work
4. The Grid-tie inverter is made to deliver up to 1kw of power. that at 24V is 41A. That per cell is 10A. Thats not doable and you will kill the cells unless you have high current cells
5. You basically have 700W of solar. That is also way to much for that small pack as starter unless you limit charging current.


So correct above first and look into your design. You have several flaws.

A good rule of thumb is 0.5-1A as max current per cell on laptop cells as example. NOT higher than your tested max current. So if you test at 0.5A you should never go above that in your real application.
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#3
(06-24-2019, 02:59 PM)daromer Wrote: 1. Your second image wont work. Look at it and you will see whats wrong. You basically just bypassed the protector
2. You need a BMS to protect the unit
3. The MPT7210 is boost controller so input voltage need to be lower than output. Yours is other way around so it wont work
4. The Grid-tie inverter is made to deliver up to 1kw of power. that at 24V is 41A. That per cell is 10A. Thats not doable and you will kill the cells unless you have high current cells
5. You basically have 700W of solar. That is also way to much for that small pack as starter unless you limit charging current.  


So correct above first and look into your design. You have several flaws.

A good rule of thumb is 0.5-1A as max current per cell on laptop cells as example. NOT higher than your tested max current. So if you test at 0.5A you should never go above that in your real application.

First thanks for feedback.

1.  I see it again, in my head it would not work but it looked crazy like it could work after I put it on digital, I see the bypass again that I could see in my head but lost it.


2. I dont have one right now, but working on getting one, setting this up to get a buffer battery so i can see if it will run.  

3. According to the manual, it works in two different modes. MPPT and DC/DC, I have it set to limit battery to 24v and it was doing this, i am pretty sure I tested to make sure, I am questioning myself right now...

4. I was doing my math on the wrong side, I was doing the outbound of 1k/120v with 8 amps.  This was the second main thing my head was screaming, this is not right... THANK YOU!!!!!!!!

5. The max output of the 7210 is 10 amps but I set max to 9.1 amps. This is not fully running and testing. I still have work to do and I have a makeskyblue MPPT Solar Charge controller on way.. non-aff amazon link, 

I test all at 1 amp to push them hard in testing to help weed out bad one early, or that is my though process.

Thank you very much, I will go back and work on my wiring to make sure it is rating for 60 amps or more.


For the BMS, if am understanding it correctly, I will make a new pic to ensure my typing/thoughts are clear. 

I would like to be able to still feed the GTI when the battery is to low, but that might not be possible, with out a lot more money/configuring. 



I tried to color it a little bit more to make sure lines are clean.  I dont have a lot of software on this one to make fancy diagrams, miss my days of visio access for this. 

I have been told that I come across as arguing so if something looks like I am, i am not. I am trying to learn, save money and be safe.  I did put a fuse on each cell and setting this up so i can chunk it out of the area if something go wrong at this point.  

Again, than you very much for the feedback.  I know AC but dc, i am all right hands.  I am left handed....

CB
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#4
3. Yes in Boost mode only. What you potentially do is drag down the input to a very low voltage loosing alot of potential energy. Its the wrong device for your application.

5. And once again wrong device because you can only use a fraction of what your panels can deliver. Think long-term and not just for the "test"

Feed the GTI from what? If the battery is low then you dont have anything to feed it from. If there is enough sun the batteries will also have enough jouce. Once again the 1kw inverter is to large for this setup if you plan to hook it up to the battery. It will work if its running on the panels only. But neither less if the battey is there it will drag it down untill empty and the solar panels will never catch up

700w is less than 1kW.

A BMS is to protect. For instance if cells have low voltage it disconnects the pack in case of emergency. Its not made to be an "on-off" switch.
CBlack likes this post
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#5
Daromer,

For the time being, I did feed the solar panels into the 1k grid and it is pushing power in. So for the gti, it is not doing a constant 1k push but want it can, it is pushing. That is the reason I got it but had to be on and running to make sure it was doing it. Still have a lot to do but getting the panel and gti working help with the feeling of making positive gains. I shelved the 7210 and I guess it is wrote off as a learning lesson.

Thank for the help.
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#6
It works in solar yes.... Because it do mppt but the battery Will be drained max. Ur trying to use it wrongly.

IF you hook it to such a small battery it Will max the battery untill it dies
CBlack likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#7
(06-26-2019, 04:19 AM)daromer Wrote: It works in solar yes.... Because it do mppt but the battery Will be drained max. Ur trying to use it wrongly.

IF you hook it to such a small battery it Will max the battery untill it dies
Understand, i finally got it straightened out making real progress. I have amp meter to measure on the way for testing to check for efficiency.
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