diy solar

diy solar

Big Battery 24v A123

Cut off at 3.0 volts - isn't that about 10% SOC? What voltage did you charge them up to?

Assuming that is 10% SOC the Wh is about 2693 with a fairly mild discharge rate of 20A.

What they said:

Nominal Capacity: 2.45kWh (92.8Ah)

Energy – 100% DOD, Nominal: 2.6 kWh

EV Energy – 80% DOD, Nominal: 2.1 kWh
I think my charge voltage is 28.7
 
Both of those are good choices. I needed a little more portability and I like how easy it is to customise the victron. I sacrifice some charging power for those features but it works with my plan :)

@No.15 Does that victron taper off well when battery is full in go into a float mode where you’ve set the parameters for charging. Can’t find much info or video on that model. I’m looking at the 24v 12a model.
Looks to have a bulk charge of a tiny bit less than the recommended 28.8v for the A123 battery but that isn’t enough to worry about.
I’m using a 30v 10 a bench PS currently but looking for a better setup.
 
@No.15 Does that victron taper off well when battery is full in go into a float mode where you’ve set the parameters for charging. Can’t find much info or video on that model. I’m looking at the 24v 12a model.
Looks to have a bulk charge of a tiny bit less than the recommended 28.8v for the A123 battery but that isn’t enough to worry about.
I’m using a 30v 10 a bench PS currently but looking for a better setup.
This thing is really customizable. You go in advance mode and set any kind of voltage profile that you like. its pretty slick and easy to use and all the settings are customizable (well most)

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I finally got my Overkill Solar BMS and battery wired up. I ended up using a small PCB board to connect the balance cables to the existing connector that came with the battery.

Here's the pinout I used if you are looking at the holes of the connector. The 2nd column is the voltage I measured when I traced the wire.

Top Row Right to left
S8 26.6 VDC
S8 26.6
S7 23.3
S6 19.9
S0 GND

Bottom Row Right to left
S5 16.5
-- UNUSED --
S4 13.3
S3 9.9
S2 6.6
S1 3.3

PXL_20200915_225750166.MP.jpgPXL_20200915_225800354.MP.jpg
 
I finally got my Overkill Solar BMS and battery wired up. I ended up using a small PCB board to connect the balance cables to the existing connector that came with the battery.

Here's the pinout I used if you are looking at the holes of the connector. The 2nd column is the voltage I measured when I traced the wire.

Top Row Right to left
S8 26.6 VDC
S8 26.6
S7 23.3
S6 19.9
S0 GND

Bottom Row Right to left
S5 16.5
-- UNUSED --
S4 13.3
S3 9.9
S2 6.6
S1 3.3

View attachment 22867View attachment 22868
What’s your plan for the two overkill BMS temp sensors?
 
I removed the original sensors (3 one in the center) and wires to put the sensors in the place of the originals on the buss bar ends. I did have to extend one of the sensor wires to reach the farthest from the BMS but it was very simple. I am impressed with the range of the Bluetooth. It has no trouble even 50-100’ away out in the garage. ?
B6EB292A-F8F2-436D-A25F-9E16B384D2F0.jpegCB909F2F-BD6E-4BD6-98B7-3CAF55AD30E0.jpeg
 
I removed the original sensors (3 one in the center) and wires to put the sensors in the place of the originals on the buss bar ends. I did have to extend one of the sensor wires to reach the farthest from the BMS but it was very simple. I am impressed with the range of the Bluetooth. It has no trouble even 50-100’ away out in the garage. ?
View attachment 22929View attachment 22930
Nice! I agree the range is pretty good with the bluetooth dongle. Btw, how did you mount your BMS without electrical tape lol.
 
One of the cells went under voltage last night. Have you guys seen this with your battery? Were you able to just use it out-of-the-box?
Screenshot_20200917-090058.png
 
Yeah I have one cell that drops lower than the pack in the lower knee. Hasn't been a problem as they all stay close through the flat part of the discharge. I also have one that is higher as the pack nears full charge. Also not a problem. I started charging on a PSU at 28.2v 10a and now the BMS doesn't reach cell over voltage (3.65) and disconnect. The battery reaches 95% SOC which i prefer.
 
Yeah I have one cell that drops lower than the pack in the lower knee. Hasn't been a problem as they all stay close through the flat part of the discharge. I also have one that is higher as the pack nears full charge. Also not a problem. I started charging on a PSU at 28.2v 10a and now the BMS doesn't reach cell over voltage (3.65) and disconnect. The battery reaches 95% SOC which i prefer.

What is your LVD setting? I set mine to 3.05V and this trips so the BMS shuts down at about 25.2VDC pack voltage.
 
What is your LVD setting? I set mine to 3.05V and this trips so the BMS shuts down at about 25.2VDC pack voltage.

I have mine set to 2800mv. I usually start charging at 3000-3100mv though, I don’t let it get to the lvd. . I’m charging solely by shore power currently. Connecting to solar is in the works. ?
 
This one cell dipping faster than the rest is affecting my usable capacity range. Sad. It started with only 0.02 V difference.

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Don't go by the voltage readings alone. set your lvd to 2.5 and charge to full 3.65 also set to balance during charge only.
If your disconnecting at 3.05 you won't find the full capacity.
Do a capacity test. down to 2.5mv lvd. You can set it higher later.
Have you run a capacity test yet? That will show your usable capacity.
You may have to cycle the battery a few times. Mine showed greatly improved capacity after i ran 5 full cycles.
If you go back and read thru this thread from the beginning there is alot of good advise from others on this sobject.
 
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Seems like the OverKill is about the only BMS folks are posting about. I still say we only need a cell balancer when used indoors for off grid solar. But a decent cell balancer curiously costs a similar amount to a BMS.
 
I still say we only need a cell balancer when used indoors for off grid solar.
That may be the perfect solution for your risk return curve. Others like myself may prefer something with a LVC because that is where i have had the biggest issues in the past five years. I think with used cells the risk of a cell(s) imbalance is more likely.
 
Don't go by the voltage readings alone. set your lvd to 2.5 and charge to full 3.65 also set to balance during charge only.
If your disconnecting at 3.05 you won't find the full capacity.
Do a capacity test. down to 2.5mv lvd. You can set it higher later.
Have you run a capacity test yet? That will show your usable capacity.
You may have to cycle the battery a few times. Mine showed greatly improved capacity after i ran 5 full cycles.
If you go back and read thru this thread from the beginning there is alot of good advise from others on this sobject.
I'm torn. Previous posts suggest to avoid going below 3.0v. I'll try a few more cycles and hopefully it improves.
 
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