SOK vs. Big Battery (Charge & Discharge Rates)

myrkr

New Member
So I've read pretty much every thread I can find here about the SOK and Big Battery Powerblock options, along with watching Will's recent video on them and reading through this long thread on Big Battery getting caught making false charging claims (located here for anyone who hasn't seen it https://diysolarforum.com/threads/is-big-battery-full-of-crap.14319/).

I'm in the market for a prebuilt lifepo4 pack, and for a while was considering the Battleborn, but then became interested in the SOK and Big Battery offerings seeing how they seemed more closely aligned with something I could build myself (and possibly service in the future), plus much lower cost. I do plan at some point in the future when I have time to build my own pack, but for right now I'm working backwards from a deadline and I need a working battery I can just install and use as my time is allocated to other projects.

With that said I'm still interested in the Big Battery offering, since it looks like it's a decent build once you account for them owning up to their mistake and fixing the BMS issues so all units will have the proper temperature charging profile. Here are the two options I'm considering

Big Battery 24V 170ah Pack (x2) (8160Wh)
$1350 (x2) = $.33 cents per Wh
Max Discharge Current: 175A
Max Charge Current: 100A

or

SOK 12V 200ah (x2) (4800Wh)
$1030 (x2) = $.43 cents per Wh
Max Discharge Current: 100A
Max Charge Current: 50A

My plan is to use a Victon 24/3000/70 which on the inverter side can output 2400 continuous watts with surges as high as 6000 watts. I think for my use I'll probably end up near the 2400 watt mark sometimes with surges into the 3000-4000 watt area briefly.

From looking at the SOK Max Discharge Current it appears than I'd be right at the 100A discharge limit to pull 2400 watts with my inverter, but anything beyond 2400 watts will be beyond the capacity of the SOK battery. Is my math right here? And as for charge current with the SOK I'll be limited to a max of 1200 watts, which will be fine for my solar charge capacity, but my alternator charge capacity will be around 1440 watts, and my shore charge capacity around 1680 watts. So it looks like the SOK would require me to scale back my charging plans for DC-DC as well as shore.

Based on all of this my questions are...

1) Is my math on the SOK charge/discharge limitations correct? Will I be limited to a max of 2400 watts from my inverter for discharge and a max of 1200 watts for the charge from DC-DC and shore?

2) Given the low cost of the Big Battery pack, plus the decent build quality and cells (with BB fixing the low charge temp error they made) is it really the best option given my charge/discharge needs all things considered?

3) Are there any other prebuilts on the market you'd recommend that are at least as good as the SOK/Big Battery in terms of cost and quality?

Thanks!
 

snoobler

Solar Honey Badger
Moderator
1) Yes.

2) IMHO, besides building your own, AND provided you test your battery and identify any issues within the first 30 days, yes.

3) No.

I won't consider any LFP battery that doesn't have at least 1C discharge and 0.5C charge rates. They have lower ratings because they are lower quality cells. That means the SOK is off my list.
 

myrkr

New Member
1) Yes.

2) IMHO, besides building your own, AND provided you test your battery and identify any issues within the first 30 days, yes.

3) No.

I won't consider any LFP battery that doesn't have at least 1C discharge and 0.5C charge rates. They have lower ratings because they are lower quality cells. That means the SOK is off my list.

Thank you!
 

myrkr

New Member
The cells might be high quality and the BMS be the limiting factor. Don't know if either is the case here, just shouting another option is possible ;)

On the SOK battery "Questions" page someone asked about getting a different higher output BMS and the response from SOK battery was...

"The BMS rated at 100A, 2pcs batteries can not run the 4,000W inverter."

Which makes it seem like the BMS is limiting to 100A, whether or not that is to protect the cells since they can't handle anything more than that is not known though. So it could be a BMS limitation, or a combination of a BMS limitation + cell limitation. For my use though 100A won't work, so the only pre-built budget option that is decent is the Big Battery offering. At some point in the future when I have more time to work with I look forward to building my own pack, but for now since I need something drop-in ready it seems like the Big Battery is the direction I'll be going.
 

SOK-MIN

New Member
On the SOK battery "Questions" page someone asked about getting a different higher output BMS and the response from SOK battery was...

"The BMS rated at 100A, 2pcs batteries can not run the 4,000W inverter."

Which makes it seem like the BMS is limiting to 100A, whether or not that is to protect the cells since they can't handle anything more than that is not known though. So it could be a BMS limitation, or a combination of a BMS limitation + cell limitation. For my use though 100A won't work, so the only pre-built budget option that is decent is the Big Battery offering. At some point in the future when I have more time to work with I look forward to building my own pack, but for now since I need something drop-in ready it seems like the Big Battery is the direction I'll be going.
Hi, This is Min from SOK, this is the first time i reply questions about SOK battery.
The battery cells could be discharge at 200Amps, but we limit the current on BMS. we rated it maximum discharge current is 100Amps, but just in case some customers would use the load over 100Amps, so we set the cut off current at 130Amps. If running the loads over 130Amps, the BMS would cut off. when we design this BMS, what we think about is: how to make sure the battery would work for long long time ? High current charge or discharge would short the cycles life. That's why we rated the current is lower than other Lifepo4 battery.
Hope this would help you.
We have customer use the 200ah on 2200/4400 WATT GIANDEL inverter, and it's working great.(review on amazon from customer)
Hope this is not advertising, and this reply just for your questions.
Thank you.
Min
 

jmcgurk

New Member
super dumb question.. as an example, If I'm drawing 3000watts 250amps... ish. This would be too much for 1 battery, but could 2 batteries manage it for a short time? splitting the load across both? Max charge/discharge is still a bit fuzzy to me when looking at battery banks. Pretty clear on individual batteries..

I have 2 200ah SOK batteries in my shopping basket.. this is the only thing stopping me... :)
 

BiduleOhm

Electronics Sorcerer
Yes ;)

NB: the batteries need to be properly wired (same size and length of wires for both of them so they share the current equally).
 
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Pappion

Retired Engineer Tech
Have you heard of the 100 amp rule? Don't get larger wires, move to a 24v system.

I really don't need that power for boon docking. No microwave, hairdryer, coffee machine. TV and DVD are OK on 100w inverter. Laptop has 12v power brick. Propane is good for Frig, hot water, and heat.
 

jmcgurk

New Member
I've considered going to 24v, but also trying to re-use some of what I have and.. of course the physical footprint has to be super small for the van. In my case, we are 100% electric.. with an induction cooktop, heater, hot water, microwave..
 

Pappion

Retired Engineer Tech
Damn memory, it's the150 amp rule. Not much of an error if 100 amps is going to the inverter.
 

jmcgurk

New Member
well.. I love a good rule of thumb.. but doesn't nearly everyone make a 3000w 12v inverter? would that not need 250amps from that batteries? What's the logic behind the rule?
 
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Pappion

Retired Engineer Tech
If you will buy it, some one will make it. Good or not. So what gauge wire do they take? Whats the wire voltage drop? There are calculators out there. figure 238A + 0.1% inefficency, more for wire voltage drop.
Anyway SOK BMS is 100A output, 100AH or 206AH models. I would not want to push it due to heating BMS FETS.
I read that 1800W inverter is good rule of thumb. About 16.7A 110VAC, 143A 12.6VDC. Maybe not enough for MW, or Hair dryer. There are stove top coffee makers.
 

jmcgurk

New Member
ok... like I said.. I'm good with rules of thumb.. and we do use a stove top coffee maker.. but my stove is an induction cooktop.. at 1800w.. so.. having to rethink my solution. especially the given space under the 2nd row seats in my sprinter. :)
 

Pappion

Retired Engineer Tech
I reread the part about you being 100% electric. I doubt you have enough roof area for the solar too.
If you must boondock bring a propane stove, a heater buddy, and 20lb propane tank.
 

jmcgurk

New Member
We carry small backpack type propane setups. But would like to be able to go off grid for 3-4 days w/o all the extra stuff, and not overly worried about solar if I can charge up before the weekend... . I have a feeling I'm fighting physics here.. space vs capacity vs design.. bah.. Space in a Sprinter for 4 people is very limited..
 

Pappion

Retired Engineer Tech
A generator would help. Some campgrounds have quiet hours and only allow it twice a day.
 

Steve21

New Member
So I've read pretty much every thread I can find here about the SOK and Big Battery Powerblock options, along with watching Will's recent video on them and reading through this long thread on Big Battery getting caught making false charging claims (located here for anyone who hasn't seen it https://diysolarforum.com/threads/is-big-battery-full-of-crap.14319/).

I'm in the market for a prebuilt lifepo4 pack, and for a while was considering the Battleborn, but then became interested in the SOK and Big Battery offerings seeing how they seemed more closely aligned with something I could build myself (and possibly service in the future), plus much lower cost. I do plan at some point in the future when I have time to build my own pack, but for right now I'm working backwards from a deadline and I need a working battery I can just install and use as my time is allocated to other projects.

With that said I'm still interested in the Big Battery offering, since it looks like it's a decent build once you account for them owning up to their mistake and fixing the BMS issues so all units will have the proper temperature charging profile. Here are the two options I'm considering

Big Battery 24V 170ah Pack (x2) (8160Wh)
$1350 (x2) = $.33 cents per Wh
Max Discharge Current: 175A
Max Charge Current: 100A

or

SOK 12V 200ah (x2) (4800Wh)
$1030 (x2) = $.43 cents per Wh
Max Discharge Current: 100A
Max Charge Current: 50A

My plan is to use a Victon 24/3000/70 which on the inverter side can output 2400 continuous watts with surges as high as 6000 watts. I think for my use I'll probably end up near the 2400 watt mark sometimes with surges into the 3000-4000 watt area briefly.

From looking at the SOK Max Discharge Current it appears than I'd be right at the 100A discharge limit to pull 2400 watts with my inverter, but anything beyond 2400 watts will be beyond the capacity of the SOK battery. Is my math right here? And as for charge current with the SOK I'll be limited to a max of 1200 watts, which will be fine for my solar charge capacity, but my alternator charge capacity will be around 1440 watts, and my shore charge capacity around 1680 watts. So it looks like the SOK would require me to scale back my charging plans for DC-DC as well as shore.

Based on all of this my questions are...

1) Is my math on the SOK charge/discharge limitations correct? Will I be limited to a max of 2400 watts from my inverter for discharge and a max of 1200 watts for the charge from DC-DC and shore?

2) Given the low cost of the Big Battery pack, plus the decent build quality and cells (with BB fixing the low charge temp error they made) is it really the best option given my charge/discharge needs all things considered?

3) Are there any other prebuilts on the market you'd recommend that are at least as good as the SOK/Big Battery in terms of cost and quality?

Thanks!
Be careful, I ordered my SOK over two months ago, still no sign. They keep delaying and giving me excuses, be careful with these guys.
 

Pappion

Retired Engineer Tech
SOK 100AH battery has same 100A output limit as the 206AH battery. IMHO: They use the same BMS.
 
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