diy solar

diy solar

NMC Bank, Bus Bars and Batrium Love

Definitely check the calibration of your cellmons. I bought my Batrium “battery angel” in 2012, and a couple of the cellmons were out of whack - i got them replaced. Over the years a few if them have failed also - might pay to keep a spare. I still use my original batrium, although it has been demoted to a 12V cabin system on my property.
 
Been a couple days. The deep discharge to low SoC resulted in a 0.07-0.08V cell deviation, but I was well into the lower leg. I'm not concerned about that. During the initial charge from low SoC, by the time the cells hit 3.5V, the gap had narrowed to .03V.

I enabled auto-level at 0.00V during this portion:

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By the time it leveled off, they were .00-.01V apart. I disabled balancing and let it run. Here's were I am:

1657823201147.png

#3 is no longer a concern as I've seen it flagged as the high cell from time to time.

The only remaining concern is that a ~2500W input results in an immediate widening to 0.03V, and the max is usually on #11. I'm going to triple check that module to see if I missed torquing any nuts. A .03V increase @ 50A means the cell has 0.6mΩ higher resistance than the low... I'm not really worried about it, but having such fine granular data means I have to check it out (/plenty to obsess about).

I'm only charging to 3.75-3.76v/cell, and I have balancing set for 3.92V. I plan to allow cycling between 3.50-3.75 while I'm offsite. I'll bump that up to 3.92 when we are on-site. Successfully ran the absorption fridge on AC for 24 hours. VRM reporting 9.3kWh of consumption from 3.76V down to 3.63V just before the solar started; about 71% down to 46%, respectively.

Gonna leave balancing off and just check things periodically (obsessively, since I can do remote desktop and VRM from my phone - it's literally the first thing I do when I grab my phone in the morning).

Still some stuff to do with additional safeties (MPPT hard cut-off, inverter hard cut-off and SHTF relay).

I'm almost ready to feel like this is headed for the win column. If no fire for six months, I'll lean further in that direction...

Oh... and about not having remote projects... The second set of bus bars for the second battery is complete, and the same fabricator is going to look at modifying my assembly fixture to see if I can get some additional clearance to build the modules easier:


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If they're taken out and reassembled immediately, the fixture works great. Unfortunately, due to the start/stop nature of the work, I
disassembled everything and they sat on a shelf at about 80% SoC for a couple years with a 5-105°F temperature range. They swelled a bit, and I come up 2-3 short when I go to get 21 in the module.

I currently have 18-19 cells in each of the modules with around 17 loose cells remaining. I'm hoping that being under compression for a couple months have shrunk them a bit.

The fabricator is going to move the flange back as far as he can and then add a plate to support it. This should greatly expedite the assembly of the new modules.

My goal is to have battery #2 deployed before winter. :)
 
Gonna leave balancing off and just check things periodically (obsessively, since I can do remote desktop and VRM from my phone - it's literally the first thing I do when I grab my phone in the morning).

Welcome to the club!
But the first rule of the club is don't talk about the club.
 
More cell wonkiness:

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Again on #14, which is where the jumper is placed between positions 14 and 15 when using only a 14S battery. Probably a connection issue. Won't know until I get up there again. Saw 3.89 on the toolkit, and it logged 3.88V on #14. It's doing a small 7KB dump every 15 minutes.

Auto-level enabled, and it immediately dropped back to 3.75V, and I didn't even see it balance. Part of me wants to leave auto-level on to catch it and bring it back down, but I'd really rather KNOW about it. We'll see how it goes. As it stands, it's set to start balancing at >=3.92V, and I'm only charging to 3.75V.
 
More cell wonkiness:

View attachment 102690

Again on #14, which is where the jumper is placed between positions 14 and 15 when using only a 14S battery. Probably a connection issue. Won't know until I get up there again. Saw 3.89 on the toolkit, and it logged 3.88V on #14. It's doing a small 7KB dump every 15 minutes.

Auto-level enabled, and it immediately dropped back to 3.75V, and I didn't even see it balance. Part of me wants to leave auto-level on to catch it and bring it back down, but I'd really rather KNOW about it. We'll see how it goes. As it stands, it's set to start balancing at >=3.92V, and I'm only charging to 3.75V.
Yeah, that's an odd one for sure.
If you think the issue is the jumper, there are solder points on the boards to achieve the same thing as the jumper.
 
As luck would have it my DSL connection is on the fritz. I've been blind since Saturday 9pm MST.

Lots of rain and lightning may have taken out the connection. My neighbor stopped by and did three things for me:

1) Checked that power was still active and confirmed SoC was around 57% this morning.
2) Conducted troubleshooting of the DSL connection
3) turned off the Wifi plug providing AC power to the fridge. No need to taunt fate with excessive loads.

Frontier tech is schedule, and my neighbor will be helping out. Thank goodness for good neighbors and doubly so for those that are retired and a little bored... :)
 
Thanks Neighbor!

DSL modem on the fritz. Tech replaced:

OH NOEZ! Data loss:

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CCGX has very limited storage, and I'm logging every 60 seconds. 32GB MicroSD ordered... :)

No fire and battery happy!

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.01 dV after 4 days unsupervised. Turns out the AC power stayed on to the fridge as it turned itself back on at a scheduled time. Forgot about that. New router means new wifi and password, so my wifi plug is on, but I can't control it yet.

Still... pretty happy!
 
So cool to see you're system up/running!

I've been running Batrium w/longmons for a few years now - on 18650 (lithium-ion) packs. I find that once 'balanced', healthy packs don't need active balancing. After 9 months the max difference will increase by 20-30mv - at which point I use Auto-Level for a week to bring it back down.
View attachment 102325

Since I rarely reach 4.0v (max charge) but often cut-off at 3.54v (min) and because Auto-Level is more effective when the packs aren't charging/discharging - I tend to bottom-balance.

I also don't even try for 'exact balance'. The pack max difference will vary from 40mv to 70mv thru the full range (3.54v -> 4.0v) but stay the same every cycle. So I go with that as it doesn't make any operational difference. Here's this morning's snap of the state.
View attachment 102324

Ran across this recently - the limits of longmons voltage measurements.... and I wonder what the MM8 limits are. It's a bit eye opening as to the accuracy of what you see on the screen for balancing.... https://s3.amazonaws.com/helpscout..../BMon-and-LMon-LeafMon-Data-Sheet-Ver-2.0.pdf
View attachment 102328

In my trailer, I have a 14s88p bank w/Batrium. It's been over a year with modest active use (20days) and the rest just sitting. The initial balance of 10mv max difference hasn't changed at all with no balance:
View attachment 102329

I did check the individual voltage against my fluke, and all were within ±.005V. Still having the occasional +0.12V jump on cell 14.
 
On a whim, did a discharge test from 4.15V/cell with SoC set to 100%:

1662162943732.png

Load was my 120W background load and the fridge cycling on and off with another 425W or so. Fridge ran more than 2/3 the time. 20kWh consumed.

Battery had been set to 420Ah based on my last partial discharge, and I'd say -417.56Ah is close enough. Further confirmed the 80/20% SoC correlation to 3.92/3.50V per cell, respectively.

Discharge protections triggered the inverter off. I had trouble getting it back on. About 15 minutes after I gave up, it turned itself back on.

MPPT turned back on. 5 hours later with PV waning, I nabbed about 4.8kWh and got back to 21.5%:

1662163360449.png

Happy to see the voltage range is only 0.02V (Batrium balancing disabled).

Will be leaving the fridge on propane tonight and forecast says I should nab enough kWh to get back to 80% tomorrow.

Confidence is up as I was able to do this all remotely and expected it to go well. Still not sure why the inverter didn't turn back on when the recovery voltage was achieved, but patience prevailed.
 
Poor planning on my part as I did this right before we planned to go for the 3 day weekend; however, there was an interesting side effect...

First time ever I've ever seen a full day max power PV graph:

1662431809994.png

It was pretty much clear skies all day. I think the dips were either MPPT temperature related or MPPT sweeps or both. It was pretty hot in the container... 95°F+ with the door open.

Harvested 20kWh (from 3kW PV) and consumed 15kWh according to VRM. We were running the A/C hard most of the day. One just barely cuts it in the big trailer.

Hammered the battery pretty hard dipping down to 10% and not getting back up to 50% in our two full days:

1662432185982.png

We left earlier than usual, and we didn't need A/C, so the system got "fully" charged to 3.92V/cell today.

FWIW, I'm pretty sure we have the rodents on the run. We found a few dead ones in the storage area in new traps, and none in the interior traps... AND we didn't hear any in the ceilings or walls. Exterior Rat-X bait stations were depleted, and I only picked up one rat on an external camera (usually 1-2/day). We also installed these audible emitters that blare predator sounds and flash LEDs in each trailer. While we're there, we can switch to ultrasonic mode, but they are freaking LOUD in audible mode! Fortunately, our neighbors can't hear them 1/4 mile away. :)
 
Aaaaand. ONE more...

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Cells charged to 4.16-4.18V and discharged to inverter cut-off + overnight wait until charge.

450Ah extracted.

In my infinite stupidity, I timed this to coincide with a surgical procedure. Forgot all about it until after the sun was down (yet another example of how shitty the Human BMS is). Inverter shut down at 3.00V, but the BMS, MiniPC running the Toolkit, and the access point in the container are all powered by 12V from a 48-12V converter. Fortunately, there was enough juice to power the ~20W of loads through the night with one cell getting down to 2.98. Spec on these Panasonic cells says 2.5V, but I never want to explore that.

450Ah extracted means these cells are yielding about 89% of rated capacity. That tickles me to no end.

I have one more module (one of the 21P "clamps" that forms a cell) en route from the source (gotta have SOME spares!). I'm going to interleave those in with the remaining cells from the 7 other packs to try and equalize "cell" capacity. The ugly orange tool has been modified and can accept TWO more cells than before. This is still not enough for 21 swollen cells, BUT only 38% of each module will be from swollen cells, so I'm pretty confident that I can get them all assembled with the fixture.

Temps have taken a nosedive... ambient was 26°F this morning. Got to test the Batrium charge temperature cut-off, (I'd simulated it at higher temps before with success), and so-far, so-good. If I'm reading things correctly, it's still allowing the MPPT to contribute to loads, but it keeps the charge current slightly negative.

Still more to do (insulated box, expansion board to inverter/charger relay-based cut offs and fully external relay cut-off), but I'm putting this in the win column.
 
One more blathering into the ether (who am I kidding... there will be more)....

I've been having issues with the system allowing VERY LOW current, 0.2-0.7A of current "leaking" into the battery when charging is disabled (low temp charging protection).

This is "software" control. Batrium is telling the GX how to behave based on my safety parameters. In this case, the charging is disabled at 5°C by default. At that time, the Batrium says to limit charging to 0.0A. The GX allows the system to continue to use PV for loads.

I have confirmed:
  • Current is physically flowing to the battery. Clamp meter isn't particularly accurate at that level, but I see (+) amps in one direction and (-) when I flip the clamp around. The values are similar to what the shunts report.
  • The Batrium is indicating 0.0A to the GX
I have also set the GX is set to restrict charging to 0A.

In all cases, a little current is allowed to flow to the battery. The BMS is pulling power from the load side of the BMV, and the Batrium shunt is between the BMV and the battery, so all loads are accounted for. The Batrium shunt itself pulls power, but that's definitely not a big value - definitely nowhere near the 10-35W the current flow suggests.

Here's a test run where I set the temp cut-off higher:

1667848556023.png

The box indicates data at the end of the charge restriction section showing 0.5-0.7A between the Batrium and BMV (usually on top of each other). Temp has increased to 45°F. The MPPT is producing 160W to power loads.

I replicated the same behavior by having DVCC restrict charge current to 0A - this will override the BMS limits, so it looks like the issue is what the GX considers to be 0A of charge current. I had my lead-acid batteries restricted to 30A, and I recall seeing them hovering at 29.7A regularly, so I know it can work right. There might be a program logic issue with 0A.

We all know that charging below freezing isn't some binary switch. There's a rate at which Lithium can be charged as temperatures progress lower, but without cell manufacturer data, it's all based on hope. 0.7A is the worst that I've seen and 0.7A/450Ah = 0.0016C, so I'm reasonably confident (hopeful) that no damage is being done. It also helps that temps have barely dipped below freezing, and most of this is happening at the 3-10°C safety level.

As easy as it was to do, that prompted me to accelerate the implementation of the secondary safety on the MPPT - The Batrium Expansion Board Relay 1 is now connected to the MPPT control relay. If closed, MPPT function. If open, MPPT turned off.

New control logic as follows:
Below 8°C, Batrium charging disabled. Sends "0.0A" charge limit to GX. GX uses PV to power loads and leaks 0.2-0.7A to battery.
Below 3°C, Batrium critical condition triggered. Relay 1 opens disabling MPPT completely.

Based on my cheap IR thermometer, the Batrium sensors read about 3°C high.

Note that Critical conditions span multiple criteria. In this case, cell voltage over 4.20V, pack voltage over 58.8V, temp value below 3°C and temp value above 45°C will all disable the MPPT.

I've been threatening to do it, and I had most of the wiring done, but I have had the second Quattro hung on the panel for months - doing nothing. When I looked things over, I realized I was about 20 minutes from being done with installation... I was wrong... it was 15 minutes as the VE.Bus Quick Configure tool is WAY easier than the manual configuration.

So, yep... I now have 120/240VAC split phase. Now each of the 5th wheels get their own inverter to themselves as the 50A to dual 30A splitter each takes one leg.

Sight to behold...

1667851062686.png

Downright luscious.

'Twas a beautiful weekend for November. Nights were around freezing, but daytime winds and temps were very comfortable with lots of sun. It was quite comforting to look at the big battery's SoC and have no qualms running the 1500W "fireplace" for a couple hours to keep the temps comfortable during a movie.

Spent some time under the 5th wheel to try and find additional points of ingress for the rodents. I sealed off another 5 spots that might allow access. We've all but eliminated them from the living area, but they are making it into the ceiling. To that end, we opened some foamed holes that they had been previously entering and created a "kill zone". It's an isolated cabinet that only allows entry/ext from the ceiling area. Snap traps, sticky traps and poison bait await. It's probably going to be horrifying, but I can't stand hearing them scurrying around up there. This is the nuclear option.

Also helped the neighbor get suitable gauge wire on his FM80 x2 outputs to battery. His two arrays are capable of nearly maxing out the FM80s, so we installed 2awg (biggest the FM80 could manage) welding cable with 100A breakers (midnite solar) on the output. Also implemented a (-) bus bar to better manage cables between his two inverters and the charge controller. Following day, he saw a total of 130A MPPT out at peak solar and was tickled sh!tless.

Off-grid wins all around!
 
AND... one more.

Basically a repeat of the 10/24/22 test. Low temp charging protection was needed a lot this winter, so I was concerned that some potential damage might have occured. It's not a hard cut-off. It's the Batrium telling the GX to not charge more than 0A. In this case, the GX tends to maintain a very small 0.3A draw on the battery while PV powers loads; however, when the load turns off, the PV sends a "pulse" of current that tapers as the GX backs the MPPT to near 0A. My batteries will get hit with a few seconds of very low C rate charge. Each "cell" is 450Ah (21 parallel cells each rated for 150A - about 6C), so the C rate with a 10A current is about 0.003C on a per cell basis.

Used a 1500W heater periodically and the normal ~180W background load to conduct the discharge test... from 3.5 hours away :p

Whelp, hit right around 450Ah (451.7) again:

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Cells stayed nice and tight until they dipped below 3.50V (about 10% SoC):

1681586194225.png

Batrium automatically cut the inverters off, and the voltage rebounded. Enabled the MPPT, and it's a good day for charging!

1681588842683.png

2919W out of 2970W rated. Happy. Love thin clear air and low temps. :)

Conclusion:

Nothing bad happened over the winter and existing low-temp charging protections were adequate. No loss of capacity in 5.5 months of operation.

Still need to get the second half of the battery built. I've had some issues with a spare 21P module I ordered - four dead cells and excessive self-discharge on most (not bad per se, but notably worse than what I already have). It kinda threw a wrench into my plans for spares and the initial configuration.
 
>.... 10A current is about 0.003C on a per cell basis. .....
I've read that low temperature charge damage on the cell chemistry can be negligible at very small currents. 0.003C might qualify as low current levels / no damage. Have you seen any specific curves / data on this?
 
>.... 10A current is about 0.003C on a per cell basis. .....
I've read that low temperature charge damage on the cell chemistry can be negligible at very small currents. 0.003C might qualify as low current levels / no damage. Have you seen any specific curves / data on this?

Heard the same. Have no idea. These are PHEV cells that I believe are Yttrium doped and good down to -20°C, but I don't have any hard data. I'm assuming they're only 0°C tolerant as is typical. I have the MPPT completely shut off at 1°C with 0A charge allowed between 1 and 7°C. Unrestricted above that.

I have a few marginal cells. I might do some cycling in a freezer... :p
 
Most Li NMC cells should be fine to at least -5C. But the charge rate should be less than 0.5C. Many EV grade cells are using a different electrolyte specifically to help in low temperatures. But it may be difficult to know if your cells have this. With this MP based ester electrolyte, Li NMC cells can charge at 0.5C down to -20C and still function at lower current down to -40C. The Chevy Bolt that my cells come from had no charging restriction to -10C, but would run a heater below that while charging. So they are probably an in between cell type. And of course, Chevy has a 10 year warranty to deal with. Where I am in So Cal, the outside temp rarely dips below 0C freezing, and even when it did, the inside of my garage stayed over 5C. But I still set my BMS to stop charge at 2C to be completely safe. my charge rate never exceeds 0.15C even in the best conditions. In the car, these cells are rated for 1.0C charge rate. But that is also with an active liquid cooling system.

As for the cell balancing talk, even with NMC cells in our use, it is best to only run the balancer at your top 1/4 of your state of charge range. when the cells are full, pull them as close as you can. But while discharging, let them spread. In a perfect world, each cell group will have put out the same amp hours. A weak cell group may lose 30% of it's charge, while a strong cell group may only lose 20% of it's charge. If you keep trying to balance, it might give you a tiny bit more run time with an active balancer, but not with a pas.ve type. it will waste energy pulling down the strong cell to have it keep up as the voltage falls. Don't worry about it, let the weak cell fall faster. It will determine your usable energy when it hits low cell cut off.

When you go to charge up again, the lowest weak cell is also going to rise faster as it has less capacity. All of the cells get the same amount of current. They should all reach full at the same time again. So only have the balancer trying to balance as it reaches the top of your charge range.
 
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