Bigbattery.com coupon code: "diysolar" for 10% off BYD 3kWh LiFePO4 Packs

GVSolar

Solar Addict
As you know, there’s been a great deal of discussion about the actual useful capacity of these used BYD 24v batteries. Perhaps this post will be informative. Please forgive the lousy formatting - I took my notes in a word processor, not a spreadsheet.

Here are the basic breakdowns of the charge/recharge cycles that I used to “wake up” my Tech Direct/BYD units. I repeated the same charge/discharge cycle three times with varying depths of discharge.

First I charged each unit separately to an equal voltage of 26.3. Then I individually charged all three units with an 800w LFP Charger (23 amp average charge) - to an equal voltage of 28v (that’s the BMS cutoff). I then connected all three units in parallel - and discharged them all to 24 volts using a 500 watt heater. I then recharged them again to 28volts.

Round ONE Charge to 28v
(A/B/C Combo) Lifepo4 Charger Profile
800w LFP Charger17.2 hoursR1
(Battery B’s meter shows .1 less voltage than reading taken at terminals)
TIME CHARGE Current CHmeter BATT A BATT B+.1 BATT C
1/24/20 DC bulk 23a/b/c 26.7 28.0 27.9 28.0

First Discharge to 24v:
Round One Discharge (A/B/C Combo) to 24v
TIME DISCHARGE Current METER BATT A BATT B+.1 BATT

1/29/20 END 18.1 amps 24.0 24.0 23.8 23.9
TIME Capacity Energy METER Time Int R Ext R
2:09 END 315 AH 8.14 kwh 24.0 17:12 hrs 216 mOhms 1.4 Ohms

Recharge again to 28V (BMS cutoff):
Round TWO Re-Charge to 28V
(A/B/C Combo) Lifepo4 Re-CHARGE Profile
800w LFP Charger14:35 hours R2
TIME CHARGE Current CHmeter BATT A BATT B+.1 BATT C

1:35 pm DC 621w 23a/b/c 27.2 27.5 28*cutoff 27.5
(A/B/C Combo) Lifepo4 METER PROFILEwith LFP Charger ReCharge #2 to 28v
TIME Capacity Energy Meter Time Int R Ext R
1/31/20 @ rest for .5 hour
2:30pm start 0 wh 23.8 0 min 155mOhms 1.1Ohms
1:35pm 326 AH 8.68 Kwh 27.5 14:35 hr 0 mOhms 1.2 Ohm*

My second discharge was to 23.5 volts:
Round Two DISCHARGE TEST to 23.5v – three hours rest
(A/B/C Combo) Lifepo4 METER PROFILE500w approximate discharge
TIME Capacity Energy METER Time Int R Ext R
2/3/20 reset AH reset wh 2.2 0 min
4:30pm 0 AH 0 wh 26.7 start 68 mOhms 1.4 Ohms
1:54 END 319 AH 8.23 kwh 23.5 17:14 hrs 246 mOhms 1.3 Ohms
(A/B/C Combo) Lifepo4 DISCHARGE Profile#2with Inverter & Heater (Bmeter)
TIME DISCHARGE Current METER BATT A BATT B+.1 BATTC
2/3/20 @ rest - 3 hrs (small) 26.7 26.6 (7) 26.7
1:54 END 17:14 hrs 18.1 amps 23.5 23.4 23.4-3 23.4

Recharge again to 28V (BMS cutoff):
Round THREE Re-Charge to 28V
(A/B/C Combo) Lifepo4 ReCharge Profile
800w LFP ChargerR3
TIME CHARGE Current CHmeter% BATT A BATT B+.1 BATT C

2/5/20 @ rest for .5 hr 23.6 23.6 (7) 26.7
14.52 min 622 watts 27.8 28* 28*cutoff 28*OVER
TIME Capacity Energy Meter Time Int R Ext R
2/5/20 @ rest 1/2 hr (meter on) 178 mOhms 1.1 Ohms
1:52pm 333 AH 8.85 Kwh 27.8 14:52 hr 0 mOhms 1.2 Ohm*

My third Discharge was to 23 volts:
(A/B/C Combo) Lifepo4 DISCHARGE Profile#3with Inverter & Heater (Bmeter)
TIME DISCHARGE Current METER BATT A BATT B+.1 BATTC
2/8/20 @ rest 3 hrs (small) 26.7 26.6 (7) 26.7
6:00pm start 500w nom 26.7 26.6 26.5 26.6
11:55 END 17:55 hrs 420 watts 23.2 23.2/1 23.0 23.1
DISCHARGE TEST – Round THREE 3 hours rest
(A/B/C Combo) Lifepo4 METER PROFILE500w discharge
TIME Capacity Energy METER Time Int R Ext R
2/8/20
reset AH reset wh 26.8 0 min
6:00pm 0 AH 0 wh 26.8 start 71 mOhms 1.4 Ohms
11:55 END 322 AH 8.32 kwh 23.2 17:55 hrs 263 mOhms 1.3 Ohms

After the next 28v recharge I’ll prepare the batteries for service in my main system. My home is completely off-grid (30+ years) - looking forward to finding out how these batteries perform in a real world situation.

Some very general observations:
As you can see, the recorded battery capacity rose in each charge/discharge cycle – obviously because of the constantly increasing depth of discharge/recharge. Whether that will represent a general increase in capacity over time remains to be seen.
As an approximate average, I would rate the usable capacity of these three TD/BYDs at 110AH/2.95kwh each, or 330AH/8.85kwh total.

Not bad for a 4-6 year old battery of unknown heritage... and for the money, an excellent bargain (assuming at least another 5 years of good service). A comparable Battleborn battery bank would have been triple the cost. For the AES/Discover Batteries – five times the cost. Of course, then I would have the peace of mind given by a 10 year warranty (but not nearly the same learning curve/fun). And I genuinely prefer the form factor of these refurbished units – especially their well-built roll-a-round cases.

How the TD built-in BMS will perform over time remains to be seen. Because the TechDirect BMS has no cell level monitoring I elected not to push my discharge tests any lower than 23.0v. Only time will tell how the batteries respond to the constant usage (and varying charge/discharge rates) of off-grid living, but overall I am satisfied with the current usable capacity of these TechDirect units.

Some people have reported higher total AH/Kwh; I suspect that is the result of active balancing at cell level with an outboard BMS - and possibly an earlier generation of BYDs that were capacity tested before sale.

One other note: As expected, a charge from 27 to 28 volts took less than 30 minutes – and the last half-volt happened in less than 5 minutes. That sudden uptick/dropoff would occur in discharge as well – something to be keenly aware of when I program my final solar charging parameters.

If you have a meter setup that allows for it, the battery’s internal resistance seems to be an excellent indicator of actual SOC. During my charge cycle IR would end at damn near zero and begin at something close to 180 mOhms. The reverse is true for the discharge cycle – ending IR was at about 263 mOhms at 23v. In the midzone (where there is very little voltage shift) keeping an eye on that internal resistance reading could be very helpful in determining true SOC.

As always, your mileage may vary downhill in a tailwind. Hope some of this was helpful, and best to all.
 

madsci1016

Solar Enthusiast
Hi there.

I have a "4" in front of my results. I'm sitting slightly above 4kWhr per pack right now. Bought in december from batteryhookup but sent from California so it was probably drop shipped from big battery.

There was variation. I had two packs at 4.2 and some packs at 3.5. I didn't do extensive tests before I put them all together, 2s3p (6 packs) for 48V solar wall and commissioned it fully. After my last baseline cycle of the whole array (3.6 to 3.0V) I clocked in 465AH. At nominal 51.2V, thats 4kWhr per pack average. Batrium BMS btw. Average 2kw discharge and 3kw charge. Divided across 3 strings though so like 0.16C rate?

I have actually not balanced them yet, as I don't believe it will help at all. The packs where pretty well "middle balanced" from the start, meaning the same cells that went low first also went high first. It's clearly an uneven wear issue. I purposefully paralleled all my cells months before DavidPoz, because of this. I do believe it helped.

I am going to top balance them soon an experiment with adding headway cells in parallel with the weak cells to "unlock" the extra capacity in the strong cells. That will be in 2 weeks.

I am happy with my buy, as that was the minimum promised. But i totally get the beef everyone else has. Don't say "guaranteed 4kwhr minimum" and not stand behind it.

But anyway, throwing my results into the ring for discussion.
MVIMG_20200129_165143.jpg
 
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Nick

New Member
"Big battery" is the same business as "tech direct" (popular ebay battery store). I just signed up for their affiliate program, and they have BYD packs.

Most of their batteries are super cheap, but they are cobalt based packs. NMC and Lipoly. I am going to make a very long video about the dangers of using a used cell NMC pack (nissan leaf cells) in about a day or two. I do not recommend anyone using these batteries unless they know what they are doing. Video to come.

Our coupon code for 10% off is: "diysolar"

Big Battery LiFePO4 Packs
Ready built BYD packs that come assembled with enclosure, BMS and circuit breaker for $799: https://bigbattery.com/product/powerwall/
View attachment 6975View attachment 6983

You just need to connect your system to a 175A anderson powerpole connector, and you are done.

Downsides to these batteries:
  • Shipping cost is huge! But its flat rate after you buy one pack, so pretty cheap if you want to buy multiple packs
  • No low temp charging protection from what I can tell

I have the battery ready to hook up to my solar shed, but I am waiting for the anderson connector to come in the mail today, then I will do a capacity test:

View attachment 6982

They also sell BYD packs that you can add your own BMS for $450: https://bigbattery.com/product/24v-lifepo4-4-4-5-kwh-battery-modules/

View attachment 6984

Attached are more photos if you are interested.
Can you provide a close up of the bms or the model number
 

ghostwriter66

"Here - Hold my Beer"
Anyone have any idea how long they will last? I am thinking of getting some of them but I don't know how long they will be good for.

I'm referencing Wills video that he made today (battery in #43 post) ...

So A few concerns …. FIRST … the battery percentage between new and now is pretty high showing that they are pretty degraded … And we all know that once a battery starts showing that level of degradation then it’s a downhill slide relatively quick to the bottom …

SECOND … so these look like you can get 3.76 kWh for $850 with a used battery …. BUT on Alibaba you COULD get 5.12 kWhH for $844 for (8) 3.2V 200aH BRAND NEW batteries …(ours just came in today) ...

So not sure why to by used and take a risk that you are getting END OF LIFE batteries when you could get new ones CHEAPER and more aH's ??
 

nebster

battery dude
And we all know that once a battery starts showing that level of degradation then it’s a downhill slide relatively quick to the bottom …

Do we? Can you share some sources for data on this?

I can't find very much about heavily-degraded cells. Even less so, cells first used a lot in hot and challenging environments and then removed to cool and relaxed environments like DIY ESS.
 

GVSolar

Solar Addict
Will.. I'm hoping you'll still do a capacity test on your pre-built BYD unit. Curious to see your review and how it compares. Thx.
 

Chefwhowa

Solar Enthusiast
I'm referencing Wills video that he made today (battery in #43 post) ...

So A few concerns …. FIRST … the battery percentage between new and now is pretty high showing that they are pretty degraded … And we all know that once a battery starts showing that level of degradation then it’s a downhill slide relatively quick to the bottom …

SECOND … so these look like you can get 3.76 kWh for $850 with a used battery …. BUT on Alibaba you COULD get 5.12 kWhH for $844 for (8) 3.2V 200aH BRAND NEW batteries …(ours just came in today) ...

So not sure why to by used and take a risk that you are getting END OF LIFE batteries when you could get new ones CHEAPER and more aH's ??
@Will Prowse
So you can say I'm a beginner in this solar world but I did hook up my system myself by watching Will videos, so I never built a battery and just worried that I would burn something up. I was wondering if its better to buy that battery system all set up or maybe if you could build a new battery for me and I would pay for you to do it?
 

nwillitts

Solar Addict
I'm referencing Wills video that he made today (battery in #43 post) ...

So A few concerns …. FIRST … the battery percentage between new and now is pretty high showing that they are pretty degraded … And we all know that once a battery starts showing that level of degradation then it’s a downhill slide relatively quick to the bottom …

SECOND … so these look like you can get 3.76 kWh for $850 with a used battery …. BUT on Alibaba you COULD get 5.12 kWhH for $844 for (8) 3.2V 200aH BRAND NEW batteries …(ours just came in today) ...

So not sure why to by used and take a risk that you are getting END OF LIFE batteries when you could get new ones CHEAPER and more aH's ??
well,china aint shipping anything right now so that's a problem.
do you have a link to your seller at alibaba?
 

jasonhc73

Cat herder, and dog toy tosser.
I'm referencing Wills video that he made today (battery in #43 post) ...

So A few concerns …. FIRST … the battery percentage between new and now is pretty high showing that they are pretty degraded … And we all know that once a battery starts showing that level of degradation then it’s a downhill slide relatively quick to the bottom …

SECOND … so these look like you can get 3.76 kWh for $850 with a used battery …. BUT on Alibaba you COULD get 5.12 kWhH for $844 for (8) 3.2V 200aH BRAND NEW batteries …(ours just came in today) ...

So not sure why to by used and take a risk that you are getting END OF LIFE batteries when you could get new ones CHEAPER and more aH's ??
Pictures and link... (or it didn't happen.🤣)

How about the link to the battery you bought, not the store.
 

ghostwriter66

"Here - Hold my Beer"
Pictures and link... (or it didn't happen.🤣)

How about the link to the battery you bought, not the store.


Our total came to $426.20 .. all inclusive .. four 3.2V 200aH .. busbars ... shipping ...

Dongguan Lightning Energy Technology Co.,Ltd

Email: Nikkie@lightning-power.cn

Wechat: lightning-power

Web: https://shandian.en.alibaba.com

Make sure you mention to Nikki that you saw this at www.diysolarforum.com ...
 

ghostwriter66

"Here - Hold my Beer"
@Will Prowse
So you can say I'm a beginner in this solar world but I did hook up my system myself by watching Will videos, so I never built a battery and just worried that I would burn something up. I was wondering if its better to buy that battery system all set up or maybe if you could build a new battery for me and I would pay for you to do it?

Honestly you can build your own battery yourself -- its so easy .. and all of us are here to help you ... you are truly just putting together 4 batteries in series using the busbars that come with the battery -- and attaching a BMS ... and DONE ...

If all four batteries are from the same manufacturing cycle (which is highly likely) you probably won't even need to Top balance -- and anyway your BMS will do that for you ...

And if all of this takes you more then 15 minutes then you must have stopped to have a beer in the middle .. LOL
 

maxx123

Solar Enthusiast
Honestly you can build your own battery yourself -- its so easy .. and all of us are here to help you ... you are truly just putting together 4 batteries in series using the busbars that come with the battery -- and attaching a BMS ... and DONE ...

If all four batteries are from the same manufacturing cycle (which is highly likely) you probably won't even need to Top balance -- and anyway your BMS will do that for you ...

And if all of this takes you more then 15 minutes then you must have stopped to have a beer in the middle .. LOL
You had doubt about the BYD 24v batteries from the beginning
if the batteries are at 60% then going out buying big bms is not needed so instead of it being 220ah would it be more like 140ah
 

Will Prowse

Admin
Staff member
Moderator
@Will Prowse
So you can say I'm a beginner in this solar world but I did hook up my system myself by watching Will videos, so I never built a battery and just worried that I would burn something up. I was wondering if its better to buy that battery system all set up or maybe if you could build a new battery for me and I would pay for you to do it?
If you watch enough battery build videos, you can make your own battery. But if you want something that you can throw into your system and forget about it, a battleborn is nice. That is a really tough decision. If I was completely new and buying 1000's of dollars of batteries, I would go with a ready built system for peace of mind. But if you watch enough videos and hang around this forum, you can build whatever battery you wish.
 
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