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My 64kwh BYD battery bank

jasonhc73 said:
Your turd turned out really nice. I'm moving 4 of my little turds into my cargo trailer real soon. I've gone to the shiny and new side with 280ah cells.

I really do recommend the balancer, it has made these BYD's super stable.
I can and regularly draw them down to 44.0V. But I still can't get them to charge much over 53.1.
I bulk at 58.4V, float at 53.1V, and cut off at 44.0V. On bright sunny days, the charge gets up to 54.1V or 54.2V, but discharges to 52.8V~53.1V pretty much instantly. I don't recommend the cut-off being lower than 47.0V without an active balancer.

Since you don't use the high-resistant tracing as I did, you will be able to get a lot more balancing current. These cells stay balanced with the active balancer a lot better than expected.

I use this one:
www.ebay.com

2S ~ 16S 2A Active Balancer Li-ion Lipo Lifepo4 LTO Battery Equalizer BMS APP JK | eBay

â Support all pool types such as : Li-ion, Lipo, Lifepo4, LTO, super capacitors and other batteries. It is only balancer, it is not protection board.
www.ebay.com
I am limited to 1 amp, and sometimes less because there is so much measured resistance from the line tracing being so small.

"Meta Grid" uses the 5 amp version on his entire "battery".
@solardad The 5 amp version in use:


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Another Cargo Trailer setup.

This is now officially a legitimate sickness. My 4th off-grid system: The players: This setup is actually cheaper than going with a PWM Hybrid all in one unit 48V unit. I have AC input to charge the 48V batteries with shore power. (The 21.99 charger) A way more than I will use MPPT battery...
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ps - 18 BYD packs is about 36 kWh.
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He's actually the reason I purchased the 10a ver.
 
jasonhc73 said:
Your turd turned out really nice. I'm moving 4 of my little turds into my cargo trailer real soon. I've gone to the shiny and new side with 280ah cells.

ps - 18 BYD packs is about 36 kWh.
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You must have got some really turdy turds. Even before correcting the modules I got an average of 3.1 kwh per module with a total of 55kwh. Correcting the three crappiest cells on each one makes a HUGE difference and I easily get 3.6kwh per module average when bench testing. I expect I'll do even better now its assembled and do a pack discharge test with the active balancer going. I've done one test with alligator test leads paralleling the modules and I got 67kwh.
 
Maast said:
You must have got some really turdy turds. Even before correcting the modules I got an average of 3.1 kwh per module with a total of 55kwh. Correcting the three crappiest cells on each one makes a HUGE difference and I easily get 3.6kwh per module average when bench testing. I expect I'll do even better now its assembled and do a pack discharge test with the active balancer going. I've done one test with alligator test leads paralleling the modules and I got 67kwh.
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What are you doing exactly to correct your cells? .... "Correcting the three crappiest cells on each one makes a HUGE difference..."

Are you just top balancing them and then adding the active balancer or..???

My add on's just showed up this evening, I'm stoked!
 

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Huck said:
What are you doing exactly to correct your cells? .... "Correcting the three crappiest cells on each one makes a HUGE difference..."

Are you just top balancing them and then adding the active balancer or..???

My add on's just showed up this evening, I'm stoked!
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diysolarforum.com

BYD packs — one year on — survey

HI, Im calling out to anyone that purchased the original 24v BYD packs. I bought 4 early this year (2020) and they seem to be holding up ok. They are definitely not the bargain they were when they first came out, as I can now buy way more new IifePo4 storage in 280ah cells from China, including...
diysolarforum.com diysolarforum.com
 
Huck said:
What are you doing exactly to correct your cells? .... "Correcting the three crappiest cells on each one makes a HUGE difference..."

Are you just top balancing them and then adding the active balancer or..???

My add on's just showed up this evening, I'm stoked!
Click to expand...
With the first couple packs I stripped I cycled them a few times and established a rough correlation between amp hours per cell and voltage. Then I took them up to a balanced 3.5v for each cell and discharged them until the first one hit 2.9v and ended the test.

2.8 to 2.9 is about 20ah undercapacity and 2.9-3.0 is 15ah undercapacity, 3.0-3.15 is about 8ah undercapacity.

Then I added Liitokala 15AH cells and Headway 8AH cells in groups of two or one to the weak cells by attaching them directly to the module aluminum connection bars with 12 gauge leads. If you look at one of the photos you can see the sides of the blue cells laying on top of the module cells and if you look at another you can see the green wires I used to attach them with.

I deliberately overprovisioned the worst cells with 30ah as I want the new cells to do most of the work as they have significantly lower internal resistance than the BYD cells so they'll give up their charge more readily. It should slow down the degradation of the worst cells a lot.

After I corrected the module I'd do another cycle and observe how the bottom end behaved and how far out my corrections were and adjust them. After I was happy with it I'd write down the corrected capacity, put it on the rack and move on to the next one.

There's a reason it took 6+ months.
 
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I'm seeing 2.7kwh per pack usable..cycling 3.06v-3.4v..these days I a pulling over 50kwh nightly on sunny day running a couple heat pumps...the byd's have been very stable and I have seen no degradation on the trimeric meter over the past year of daily cycling.
 
Maast said:
With the first couple packs I stripped I cycled them a few times and established a rough correlation between amp hours per cell and voltage. Then I took them up to a balanced 3.5v for each cell and discharged them until the first one hit 2.9v and ended the test.

2.8 to 2.9 is about 20ah undercapacity and 2.9-3.0 is 15ah undercapacity, 3.0-3.15 is about 8ah undercapacity.

Then I added Liitokala 15AH cells and Headway 8AH cells in groups of two or one to the weak cells by attaching them directly to the module aluminum connection bars with 12 gauge leads. If you look at one of the photos you can see the sides of the blue cells laying on top of the module cells and if you look at another you can see the green wires I used to attach them with.

I deliberately overprovisioned the worst cells with 30ah as I want the new cells to do most of the work as they have significantly lower internal resistance than the BYD cells so they'll give up their charge more readily. It should slow down the degradation of the worst cells a lot.

After I corrected the module I'd do another cycle and observe how the bottom end behaved and how far out my corrections were and adjust them. After I was happy with it I'd write down the corrected capacity, put it on the rack and move on to the next one.

There's a reason it took 6+ months.
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Incredible. ("tested aviation tech. tough").
 
In the past I would have said WOW that's allot but today considering Im not far behind you, Ill catch up soon hehe.
 
iamrich said:
Not as impressive as my 2 BYD setup, but... Oh wait.... :p

I am not going to lie, I have already saved all the pictures to my folder for review. Very impressive!!!!
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BTW, if you strip them down this is what you get, by FAR the best way to cut the aluminum connection bars is a set of sheet metal snips. You end up with lots of copper bits that could be useful.

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Maast said:
BTW, if you strip them down this is what you get, by FAR the best way to cut the aluminum connection bars is a set of sheet metal snips. You end up with lots of copper bits that could be useful.

View attachment 39846
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I think you need 4 more packs to add to your collection...

I have half of my "shiny and new" mostly installed. I still need to put the balancers on.
 

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Maast said:
BTW, if you strip them down this is what you get, by FAR the best way to cut the aluminum connection bars is a set of sheet metal snips. You end up with lots of copper bits that could be useful.
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LOL! I just started that on my second pack today.

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At least I finally got my panels installed today.

IMG_8855.jpg
 
jasonhc73 said:
FIY the balancer on the new pack.
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Nice! Yeah - If I knew then what I know now I would have stuck with the 280ah cells I was testing. When I saw the David Poz video I jumped on them with both feet. In the end it wasnt a waste of money, but it was a stupid amount of work to get them usable.

NEVER going to buy used cells ever again.
 
jasonhc73 said:
FIY the balancer on the new pack.
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I just noticed, your cells wire resistance is really high compared to mine. Mine range from .061 to .078. Not sure if thats cell resistance or wire resistance, but if its wire resistance I'm connecting to the busbars with 5 feet of 12 gauge wire.

What does that mean anyway "cells wire resistance"?
 
Thats one HUGE shiny turd. Are those ground rods as buss bars? How many amps is that good for?
I had considered doing something like this but a steady supply of affordable and consistent cells is hard to find.
 
Maast said:
I just noticed, your cells wire resistance is really high compared to mine. Mine range from .061 to .078. Not sure if thats cell resistance or wire resistance, but if its wire resistance I'm connecting to the busbars with 5 feet of 12 gauge wire.

What does that mean anyway "cells wire resistance"?
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It's the wire resistance. All be because of using plug and play plug. 24 awg wires and pcb wire traces.
 
Deveak said:
Thats one HUGE shiny turd. Are those ground rods as buss bars? How many amps is that good for?
I had considered doing something like this but a steady supply of affordable and consistent cells is hard to find.
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They're just 6 gauge bare copper wire I picked up from lowes and straightened out by twisting it with a drill. I didnt use large wire because of its ampacity but for its low resistance.

Because the cells are paralleled in a vertical stack vs all going to a central connection point resistance is a concern if charge needs to transfer from one end of the stack of paralled cells to the other end so using a large gauge wire solves that. There will still be some voltage differences but very little.

The biggest point of resistance is where the busbars connect to the aluminum of the cell connection bars - which is also why I soldered the tin-coated copper strips to the bar to get the lowest possible resistance connection and used two screws to connect to the aluminum with.

All in all I used just under 100 feet of 6 AWG.
 
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