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diy solar

Feedback request Xuba battery build (HS senior project)

I agree. I have been very fortunate to have several posters be patient and try to walk me through this process...

And when I get ready to build mine you can walk me through it. :p Don't worry, I won't be starting mine for at least a month...more likely 6 weeks.

Good to see you are coming along with your build and being careful.
 
Do you know which ice chest? Can you provide a link? And are you building a square pack or just going to make it long?

Me too, me too, me too....lol. Although I am a little more north than you.
The cooler I am using is an Igloo 48 Qt. Island Breeze that I bought a couple or three years ago at Wal-Mart. It was cheap and very similar to this one they have now: https://www.walmart.com/ip/Igloo-48-Qt-Laguna-Cooler/169502621 It is pretty close to a plain box which is good - the walls are fairly straight. I drilled holes to install main battery terminals, but the walls of the cooler have an air space so the terminals I bought barely fit. Your 280AH cells are thicker than my 202AH cells, so I don't know whether 8S of the 280AH would fit in there. I have a bit of room to spare in mine.
 
Thanks. I am really liking the cooler idea for a battery box. They are sturdy, can hold the weight, come with handles "and wheels" and cheap.
 
I agree. I have been very fortunate to have several posters be patient and try to walk me through this process...

So was curious on how you are coming along with your build? Any updates or do you need help with anything?
 
Going to have to put it on hold for a few weeks. I was supposed to already be back at school but my Covid test came back Negative-Borderline so I had to restest and am waiting on the results. Should get them tomorrow morning. I go to a residential high school and will be there for six weeks if we get to stay. The way things are going at some of the colleges, I might only be gone for a few days...who knows.

It took me quite a bit of time to recharge the cell I had capacity tested and then when I put all together in parallel, I still had one cell that would not balance. I went to the store and picked up some washers and that did the trick. I must not have been getting a solid connection so they could not balance properly.

I really appreciate you checking in. I should have followed up but was busy packing and all. Thanks again for your help and I will be back in touch soon.
 
Covid has messed up everything. Hoping your retest is negative. Glad to know you got the cells to balance. It seems there is always that one....lol.

I appreciate your reply and look forward to hearing back from you when you have time. Stay safe and keep well.
 
Hi again,

I hope everyone had a great Labor Day weekend! I had some free time and read back through my thread and would like to ask a few more questions so that I have all ready to go when I return home in early October.

To refresh everyone's memory, I am assembling a DIY 24volt solar system. I have 8 of the Xuba 280ah cells and will connect them to a MPP Hybrid Inverter, monitoring the battery with the Overkill BMS. (Further specifics are listed earlier in the thread)

lmwilco1 was gracious enough to give me a recommended guideline but after reading back through it I would like to do the simpler version that he indicated. In this case, I will connect the main positive from my battery bank to my Tocas 120 Amp Circuit Breaker and tehn on directly into the MPP Hybrid Inverter.

I have this shunt but I do not think I need it? NOYITO 300A 75mV Metal Shunt Resistor External Shunt for Current Ammeter Analog Panel Meter as I thought shunts were mainly used to measure but does my BMS/MPP Hybrid Inverter do that already? (Sorry if I am misunderstanding)

I will attach the Overkill C- terminal (i.e., main negative) directly to my MPP Hybrid Inverter.

Finally, a question on the pre-charge resistor. Can someone give me a link to a decent one I can purchase for my 24 volt system? When I googled I mainly found 36v/48v - does it matter if I use those? My understanding is that I will just attach it to both connections on my circuit breaker for about 30 mins before I switch on my MPP Hybrid Inverter, take it off, then turn on the system.

Any downsides to doing the above? My understanding is that all should work safely and effectively by doing it this way?

Thanks again.
 
I hope everyone had a great Labor Day weekend! I

I did and hope you did too. :)

I have this shunt but I do not think I need it? NOYITO 300A 75mV Metal Shunt Resistor External Shunt for Current Ammeter Analog Panel Meter as I thought shunts were mainly used to measure but does my BMS/MPP Hybrid Inverter do that already? (Sorry if I am misunderstanding)

I think the MPP Solar gives readings for watts, current and voltages on both the AC and DC side. It's been awhile since I have looked at them but no you don't really need the shunt. You could install a coulomb meter which would measure Wh's, Ah's and give you capacity measurements. You would need to find a meter that would work with that shunt. Or just buy the whole thing. There are recommendations on the forum. I personally use the Juntek which can be found on aliexpress. I have the 100 amp version but plan to get the 300 amp version for my next build. Before purchasing I recommend looking at the youtube videos of the meter as there are a couple of drawbacks, but this is true of any cheap meter.

There are also meters that use hall sensors. I have one of those too but don't use it. They are ok and very easy to wire up but not as accurate as a shunt based meter.

I will attach the Overkill C- terminal (i.e., main negative) directly to my MPP Hybrid Inverter.

That's a short wire. I am sure you have figured out the size of wire needed to extend that based on length and load? I believe the B- should be connected directly to the battery. Just making sure that's how you have planned it.

Finally, a question on the pre-charge resistor. Can someone give me a link to a decent one I can purchase for my 24 volt system? When I googled I mainly found 36v/48v - does it matter if I use those? My understanding is that I will just attach it to both connections on my circuit breaker for about 30 mins before I switch on my MPP Hybrid Inverter, take it off, then turn on the system.

From what I have read any 5 watt, 50 to 100 ohm resistor will work. The voltage rating of the resistor should meet or exceed the voltage of your pack. And it won't take 30 minutes to precharge....more like 30 seconds at most. Just make sure, of course, the breaker is in the off position, and the inverter is off before you put the resistor across the breaker. I assume you have breakers on the AC side?
 
I have a Victron BMV and think it is the most useful for state of the battery. They now have what they call a "Smart Shunt" that is cheaper.

Heard some shunts only measure in one direction which to me is useless. Victron's measure in both directions. Good Luck
 
I have a Victron BMV and think it is the most useful for state of the battery. They now have what they call a "Smart Shunt" that is cheaper.

Heard some shunts only measure in one direction which to me is useless. Victron's measure in both directions. Good Luck
I have this shunt I plan to use in my build just have not installed it yet.
 
Thanks for the replies but I do not understand what I need to measure that the BMS or the MPP Hybrid Inverter will not measure already?
 
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I have an Overkill 8s BMS, and so far it seems to be tracking the capacity of my battery. I installed a shunt, but I hardly ever look at it. My shunt meter is not that useful since it is only unidirectional. It does give me a second opinion as to how fast the pack is discharging, but that's it as far as I can tell.
 
Just got back home yesterday and connected everything. I downloaded the app for the Overkill BMS and was wondering if anyone has the settings listed for 24v system using the Xuba 280ah batteries?

So far it looks like it is working, I need to look at the settings for the MPP Hybrid Inverter...I also need to make a more permanent cover for the battery plus connect the solar panels, but hopefully I can capacity test the battery bank now.
 
Sounds like you have made good progress. I don't know if you have the latest instructions for the Overkill BMS, but everything you need to know is there. To determine the full capacity you will want to charge fully to 29.2 volts, and then discharge to 20 volts and set your BMS accordingly. There is no way each cell is going to be equal even after top balancing but you will still get a very good idea of the battery capacity and how well your cells are balanced. Remember to write down the voltages for each cell and keep close track initially.

Once that's done you need to figure out the settings for the MPP. I would go with 28 volts fully charged and 24 volts discharged at least to start with and you might like to leave it there. But this is up to the user depending on how conservative one wants to be.

You will want to set your cutoffs on the BMS to be higher than your MPP charge voltage cutoff and lower than your MPP low voltage cutoff. If you use 28 and 24 on your MPP, you would want to set your BMS high voltage disconnect at 29.2 and your low voltage disconnect at 20 volts. That's my understanding and what I plan to do.

I am sure someone else will chime in here with suggestions. I should have my 8 cells soon and am still planning on the same BMS as you have.
 
Gazoo, you raised the issue upthread about having a breaker on the AC side which the MPP manual also mentions. I do not envision plugging into the wall too often to charge but would like the option, so my question is can I go with having a surge protector plugged into the wall and then plug the Hybrid MPP into the surge protector? My house has a fuse box and the surge protector would also have a fuse (I need to figure out what these fuses are rated) so is that not adequate?

I hooked all up and was charging phones and running a light from the batteries, per the BMS all of the cells were discharging pretty evenly. I hooked up a kettle to boil water and the MPP beeped and indicated the voltage was low but all cells are 3.3+ which should be adequate I would think. I plan to go through all settings, then recharge and run a load test again.
 
Gazoo, you raised the issue upthread about having a breaker on the AC side which the MPP manual also mentions. I do not envision plugging into the wall too often to charge but would like the option, so my question is can I go with having a surge protector plugged into the wall and then plug the Hybrid MPP into the surge protector? My house has a fuse box and the surge protector would also have a fuse (I need to figure out what these fuses are rated) so is that not adequate?
I don't see why that would not be ok. Funny you asked, today I was looking at those power strip surge protectors with built in breakers.

I hooked all up and was charging phones and running a light from the batteries, per the BMS all of the cells were discharging pretty evenly. I hooked up a kettle to boil water and the MPP beeped and indicated the voltage was low but all cells are 3.3+ which should be adequate I would think. I plan to go through all settings, then recharge and run a load test again.
Good to know your cells are discharging fairly evenly. As far as the kettle your cell voltage is good. You said you are going to go through the settings and that's a good step. Also do the obvious, double check your connections and so forth. And check the cell voltages at the cell terminals while you are running a load test with your multimeter.
 
Hmmm??? So I bought a highly rated surge protector that arrived today. I went through and updated my settings on the BMS and MPP Hybrid Inverter then plugged all in and it does not seem to be charging? On the MPP screen, the input voltage mirrors the output voltage? So what is coming in is going out simultaneously. It makes no sense as I do not have anything drawing power while I am trying to charge.

One of my cells will spike up to 3.8 per the BMS reading but it only stays there for an instant and then drops back to 3.33ish...any ideas?
 
I decided to turn off the MPP until I could figure out what is going on and when I did I noticed that the output now reads 0 so I will wait for a bit and see if it now charges the battery bank. Not sure why this happened?
 
Someone else will have to chime in here regarding that. Or you could search the threads and post in a thread that is related to your MPP. I would love to help you with that but I don't own the MPP.
 
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