Paralleling 2 48v 3.8kw bigbattery powerwalls

I bought two powerwalls from bigbattery because they said that they can be paralleled. i have not been able to find anyone who has done so but want to hear from you guys on how i should go about this. I also am trying to find how i should program my tristar mppt 45amp controller for these batteries. I tried contacting big battery but got no answer the past few times. i talked with techdirect because i saw they had a very similar battery pack, if not identical and they told me to set eq to 58.5v absorb to 58.4v and float to 58.0v.

I was thinking in order to parallel them i was going to plug an anderson sb 50 into each battery and run the positive and negative wires from both into another sb50, then have another sb50 connector plug into that with two positive and two negative wires coming out that can go to my inverter and cc. would this work?

Welcome to the Forum. I think you will find this a more helpful site for users of Lithium batteries. The atmosphere can get pretty toxic over on solarpaneltalk.com especially for advocates of Lithium batteries.
As I mentioned on the thread on that forum, there are several approaches but SB50s are fine for the initial connection and I think that is what comes with the batteries. I will post the battery specs and the settings in a later post. In the meantime what is your charge controller or inverter and does it allow you to disable EQ or set an EQ time?
Here is one discussion
I will post more.

Here is probably the best thread about these batteries.

It was started by this forum's founder Will Prowse and has some good pictures of how people have paralleled them. I saw one post with eight in parallel. After reading this you should feel a lot better about your purchase.
Rick

thank you very much i will take a good look at those right now! and currently i have a tristar mppt 45 amp for my cc and an aims 1500w 48v pure sine wave inverter which i will soon upgrade to a bigger one most likely from aims as well.

I don't know the details on how to program them to disable EQ. You got my earlier Absorb setting of 56.5 volts which is conservative 4.05 volts per cell. You won't lose much capacity at that setting and you can see if any cells try to go higher which would indicate a weak cell with less capacity. After you get the BMSs installed and have a few charging cycles then if the voltage differences at the top are pretty close then you can try a little more.
As far as Float is concerned there is debate. The concept is that you do not need to Float Lithium because they do not self discharge as fast as Lead Acid. If you are going to be exercising your pack every day then there is some logic to having a float setting half a volt below the Absorb setting so later in the day after the Absorb charging is finished, the cells can be given a little more energy from the sun so you go into the evening with more in the battery. My inverter/charger has a lot of other settings that I won't bother you with. Feel free to ask if you do have a question. There maybe a lot of users with your charge controller and they may be able to give you specifics for your CC, beyond my general concepts.

When it comes time to get a couple of BMSs check out the other threads for members that have ones that work well for these 14S packs. They probably have recomendations on Amp capacity, communication capabilities, separate charging and discharge ports versus single port. That may affect your wiring strategy and you will have to decide on fuses and/or breakers,

Ampster said:

Here is probably the best thread about these batteries.

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

"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...

diysolarforum.com

It was started by this forum's founder Will Prowse and has some good pictures of how people have paralleled them. I saw one post with eight in parallel. After reading this you should feel a lot better about your purchase.
Rick

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CAUTION: I saw this thread and was curious about the 48v spec ( while still using the same form factor enclosure as the original 24v model). I did a little digging and I don't think that our original discussion threads apply here - as it appears these are NMC batteries - NOT Lifepo4/BYDs. TechDirect has these same units - the ones listed as BigBattery on their website - but with a lot more technical detail. These units are recycled BMW 48v Lithium Nickel Manganese Cobalt Oxide from Samsung/Bosch. Same enclosure, but different guts inside. Consequently many of the details in those earlier discussion threads would not be relevant or wise. Just a heads up...

Take a look:

Those links I posted my be for a different battery. I think those are the BYD 24 volt pack that are LFP. I know the box in some of the pictures looks the same and the spec sheet you posted from Techdirect.

GVSolar said:

Consequently many of the details in those earlier discussion threads would not be relevant or wise. Just a heads up...

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Thanks, I discovered that and alerted @mcmullen7242 via PM and a post on another thread. It was too late to modify my original links. Is there a discussion link for those?

Ampster said:

Those links I posted my be for a different battery. I think those are the BYD 24 volt pack that are LFP. I know the box in some of the pictures looks the same and the spec sheet you posted from Techdirect.

Thanks, I discovered that and alerted @mcmullen7242 via PM and a post on another thread. It was too late to modify my original links. Thanks for the correct link.

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Glad to be of service. I found it wise to pay careful attention to their specs - and ask questions - some of their details can be kinda fuzzy at BigBattery/TechDirect.

As to discussion links - maybe this would be it. I really don't know much if anything about that chemistry - or the original BMW battery. The BB/TD guys are very much into repurpose/added value construction of existing recycle battery supply chains. So I guess this is another example of that methodology.

I introduced @mcmullen7242 to this forum because he was getting no information on another forum and I feel responsible for telling there was lots of info on those BigBattery packs. I still hope to find some. But at least this is a friendlier place to talk about Lithium batteries.

so my plan is to get an anderson 175 connector and make a y adapter between the batteries with two other sb50s going to the battery. i am also thinking of installing this bms but going to look more into it (https://www.ebay.com/itm/Balance-1-...o4-LTO-Li-ion-Battery-BMS-Smart-/192838533652). i was going to set the following into my tristar mppt 45amp controller, 56.5v for absorb 58 HVD 49 for discharge. if anyone has any recommendations for setting for my controller or anything else that would be appreciated

TechDirect has those #6 Anderson SB175 serial connectors (and others) pre-made if you are interested:

Your BMS choice looks good. I am a big fan of being able to access from my smart phone so that is an option I would pick. YMMV

GVSolar said:

TechDirect has those #6 Anderson SB175 serial connectors (and others) pre-made if you are interested:

Anderson SB175 to SB175 Y Series cable 36" 6 AWG

info@techdirectclub.com

www.techdirectclub.com

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Thank you but the two batteries need sb50 connectors going to one sb175. I ordered them on amazon and getting the cables from a local store. Once I make the connector I’ll post some photos in case someone else wants to see

Ampster said:

Your BMS choice looks good. I am a big fan of being able to access from my smart phone so that is an option I would pick. YMMV

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Perfect thanks!,I don’t plan on draining these two batteriesmuch during the day and gonna hook it up just with the stock bms at first to see how it goes on Monday or Tuesday. Then whenever that bms arrives I’ll look hook it up. Gotta watch some videos and learn more before hooking it up as well.

@mcmullen7242 Were you able to make the connector? I'd love to see some pictures of how you did that. I'm trying to figure it out as I've got the two powerwalls from big battery as well.

Sorry have been really busy as of late and tight on funds but I should be getting to it soon. I’ll draw up a diagram later on today when I have time on how I plan on doing it. Haven’t been on the forums lately either so will have to catch up and see if more info has been posted about these batteries