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diy solar

EG4 6500EX 120/240 Setup, 48V 105kWh Battery & Overkill 100A BMS Install


Solar Wizard
Oct 10, 2022

I've made this my build thread, so while there is an OP question below if you keep reading I'm slowly posting updates of my entire system. Mods please feel free to move if desired.

System summary:
(2) EG4 6500s for 120/240V config.
(40) Hyundai 390W panels in 10s4p to stay under 500VDC EG4 limit but attempt to max out amps, roughly 15kW.

EDIT NOTE: Due to discussion in another thread, specifying my strings are in fact 10 panels, and my VOC was tested and verified to be be roughly 440V BEFORE I wired my system. My panels are not hitting the ideal voltage values labeled on them. When building your system it is critical you ensure your VOC does not exceed the 500V limit of a 6500EX inverter or you will let out the magic smoke!

(8) banks of 16s LiFePO4 BYD 260ah cells run on (8) Overkill 16s 100A BMS
Separate load center for this setup isolated from my grid panel.

I'm basically following Will's EG4 setup, only with my own batteries. My intent is to charge the 8 banks using the system to "100%" then pull them one bank at a time from system to top balance with a separate DC charger and then reinstall. I know I need to setup the EG4s Setting 05 to USE. And then pick settings 26, 27 and 29. I'll also need to program the Overkills. Once everything is top balanced my intent is to cycle with 5% to 95% limits. I will not be moving any loads from my grid panel to offgrid panel other than a quad outlet for load/sanity check testing each leg until after I top balance all banks.

So my question is what does everyone think I should use for setting up the charging limits for the initial full charging (pre-balance) to get them as close to max as safely possible, and then later for use on both the EG4 and the overkills once all 8 are top balnced and I move into regular use? I'm probably 2-3 weeks from turning the system on. Really appreciate input here.

Dec 2022 - 127kWh (system offline for work 9 days)
Jan 2023 - 141.2kWh
Feb 2023 - 449.7kWh (Eastern trees removed)
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Set your EG4 charge/discharge voltages a comfortable margin between what the BMS is programmed. Ask 10 people what those voltages are and you will get 11 different answers. Obviously you need to stay between recommended values for LFP and program your BMS to protect the cells. Then search the forum for the many discussions on how people cycle their cells. Some want max capacity, some longest cell life and everything in between.
My first guess plan is to set the EG4 at 2% and 100% voltages and then the Overkills at 5% and 100%. Get the banks charged once to cutoff, then remove & top balance, and then set Overkills to 5% and 95%. I'm just not sure how close I can work the values between the Overkill and EG4 without creating issues.

Or should I make the EG4 be the middle zone and the overkill be the outer?
I spoke with Signature Solar and Overkill. They both recommended I use the 6500EX to control the normal cycling and use the BMS as a more extreme cutout.

General (fake) example. If I wanted to cycle 46V to 54V I set the 6500 to that and then set the BMS to 45.5V and 54.5V.
I spoke with Signature Solar and Overkill. They both recommended I use the 6500EX to control the normal cycling and use the BMS as a more extreme cutout.

General (fake) example. If I wanted to cycle 46V to 54V I set the 6500 to that and then set the BMS to 45.5V and 54.5V.
Yes, the BMS is NOT intended to be a controller. Its a safety device like a fuse or breaker, it should only trip and disconnect the battery if there is some kind of Voltage, Amperage or Temperature condition that would cause damage to the battery. Its always the Inverter (and/or charge controller) that is supposed to be set up as the controlling piece of equipment.
Your example is accurate but I would recommend at least 1V difference between the inverter limits and the BMS cut out limits.
Started top balancing the first of 8 banks last night after I hit 53.6V on the whole array. The remaining 7 banks are just above 54.0V after today's input. I'm going to start moving stuff from on grid to the off grid panel tomorrow. Should have all 8 banks top balanced in two weeks, then I can move the majority of house permanently off grid.

Coming back to this thread, here are my current Overkill BMS settings below. I will post my 6500EX settings once I have some time to type it up.

Screenshot_20221205-193432_Overkill Solar.jpg
I pulled that first bank too early. I should have let it top off another 1-2 days on the system. It just finished top leveling today. 6 days.

I bought two more 10A power supplies to help speed up the next pack. The good news is so far the cells delivered and labelled with the lowest capacities are the ones hitting 3.65V first, so I feel confident they were properly tested before shipment.
I have bank 2 charging and bank 1 will go back in service tomorrow morning.

Bank 2 is going to charge way faster. After setting it back up in parallel it was at 3.367V. My first bank I pulled and it was at 3.348V. I also now have 4 small chargers. Based on my data from bank 1, bank 2 should be done top balancing in <12hrs.



Detail on my first LiFePO4 bank top balance. Hopefully this helps someone else in the future. Now that I know what to expect, I should be able to bang through top balancing the remaining 7 packs in the next 2 weeks if not less.

(16) 3.2V 260ah LiFePO4 BYD cells in parallel. Setting (1) 5A and (1) 10A charger to 3.65V with pack starting at 3.348V.

End of each day
12/5 3.352V
12/6 3.355V
12/7 3.359V
12/8 3.360V
12/9 3.366V
12/10 3.376V
12/11 3.447V 1:00am
12/11 3.589V 8:00am
12/11 3.615V 11:00am
12/11 3.631V 5:00pm
12/12 3.651V 9:00am -> disconnect

After letting the pack sit for 2 days, I broke it down. Each cell is now at 3.543V +/-.002V. I'm very happy with this result and quite surprised based on the price I paid for these cells.

The batteries will be cycled between 48V and 57V with charging at 58.4V and a 30min float set on Inverters, with BMSs set to 3.65V for 2 second cell cutoff and 58.4V for 10 second pack cutoff as a secondary safety.
Well we lost power today due to snow storm dropping a tree. I've been moving some stuff from grid to solar since it's down. Did some good result tests.

My garage has a 100A sub panel which I moved to solar.

My air compressor has a 48A in rush and 15A run load, no issues.

I have an Enco knee mill with a 2hp spindle motor. 68A in rush and 8A no load run draw. Nit a hiccup or a light flicker when turning it on. I am extremely impressed. I might still buy a soft starter for the mill just to ease the spike, but holy cow these inverters are impressive.

I have load panel ground tied to my main panel ground. The neutral and ground are not bonded in the load panel.

I have both bonding screws still installed on 2P1 and 2P2.

When I test the loads above, ZERO current on the ground in load panel when on solar or battery supply. When my grid comes back on I will test while grid charging the pack.
Put bank 1 back in service. Pulled bank 3 and it's top balancing now. Gonna put bank 2 back in tomorrow.

Have 2/3 of the house moved to the offgrid panel.
Very nice PW, Brings back memories of starting up my own system. Such exciting times when you can start moving real loads over to your own system.
Very cool to be able to start that 68A load, pretty high in-rush! is your motor 240V?
{I bit surprising for a 2Hp motor? if I read that correctly. Higher in-rush than my 6Hp air compressor}
I don't see where anyone asked, so I gotta know: where are these cells from? were they expensive? Can I buy 48 of them! LOL
Keep posting pics, looking good.
Then later we will start picking at what you are doing with G-N bonds and how close to the Voc your array is set, and what minimum temps you may see someday...but for now, great job!
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System really looks like it’s coming along from where you started! One of these days I hope to get to the point where I can have a system as large as yours (gonna need it living in MI).

Hoping my replacement inverters show up on time this weekend so I can get everything fired back up.

Keep up the great work!
The Enco motor has wiring for 120 or 240V. I have it wired 120V because when we bought the house I didn't have 240V in the garage yet. Just never wired it back as I don't heavy hog on it. Just onsoe twosie jobber work.

On the batteries they are BYD cells used in Asian heavy truck and equipment markets like big forklifts and electric dump trucks. Still 3.2V LiFePO4. Just a different form factor. They are safer than equivalent EVE cells in puncture resistance and venting temps during failure due to the form factor. These cells are basically factory seconds that didn't make the cut to go into a vehicle. But they were $61 each, so the cost savings is very high. They are sold as 260Ah cells, but every cell I have is more than that. They range from 261 up to 283. Each came with a test sticker which matched my top balancing numbers pretty closely. They had all been produced 5 months before I received them. I bought them off Alibaba. Link to the seller below. They were very easy to deal with and communicated in less than 12hr from purchase through delivery. I have no association with this seller, but I would buy again from them in a heartbeat. 60 days from purchase to arrival at my house. I delt with Joyce Lee. The biggest pain was clearing/authorizing the payment with my credit card. US companies hate Alibaba.

The Enco motor has wiring for 120 or 240V. I have it wired 120V because when we bought the house I didn't have 240V in the garage yet. Just never wired it back as I don't heavy hog on it. Just onsoe twosie jobber work.
okay that makes some sense now.
you can redo the motor winding set up for 240 and this will cut the in-rush in half to 34A. AND it will balance the load on your inverters since exactly the same amperage will be on each of L1 and L2 on start up. I did this with my set up and am very happy with the results. no difference to the motor output, no free lunch there.

Interesting about the batteries, and those bullet-proof looking cases (I am thinking about a mobile 'solar generator' or even my RV since some trips are on pretty rough logging roads). That price point for 260Ahr is very attractive. Thanks for sharing the source, I set up an Alibaba account for my business and it streamlined the transactions with the financial institutions it seems, and a bit better shipping rates. Thanks PW.
I bought a 120V plug in soft start for it instead. I just got it this week. I'll post some pics of it this weekend.
Makes sense.
I got a quote from the battery supplier, for 8 cells to do a mobile unit that I can also use in my RV too, using a MPP 2724 (24vDC) system. Appreciated the contact info for the supplier, thanks!
I'm going to build a little shed around the combiner box and underground power. It will have to wait until the ground thaws late spring. I just didn't have the time to do it before the frost set in with everything else that had to get done. I also commissioned my system sooner than I wanted due to a multi-day power outage after an ice storm. So now its a bit harder to modify because I have to plan 2/3 of the house down to power down the system to add items.
Yeah, it’s a whole lot more work when you have to rush to get things done.
I hear ya,
I put my array up on the shop south roof, built to be tiltable between 30 and 60 degrees, but like you, I got the system up and running at the lower angle (summer) and then life happened, and snow came. I have two tilting arrays and I only got the second array lifts completed and tilted up after christmas (ops).
To me, you shouldn't worry about the time-lines too much, you are doing it yourself, and if it takes longer so be it. 99% of the world are still behind where you are on the jouney to site produced electricity, and everything you do has learning potential.
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Adding a note the solar panel frames are made from ground contact pressure treated lumber. My intent is to move the system from NH to KY once we buy a farm. The frames fold up so I can transport them all in a box truck.
Thanks for sharing. I was wondering what the additional hinges were for.
Here is my panel setup. The center panel is grid. The left panel is offgrid loads. I have not finished moving everything yet. Some non-essential items will stay on the grid like our electric dryer and electric stove.

I had to shrink the resolution of the panoram pic for it to post.



What are the 2 black boxes between the busbars and the inverters? T class fuse?

Yes T Class. I'm adding a switch below each soon to ease maintenance. I currently just toggle each BMS forcing the inverters to AC bypass. Then disconnect. Not ideal but I didn't have everything when I commissioned during the power outage.

If you zoom in you can see I even had their outline penciled on the concrete board before I started installing everything.