Creating My First Battery Pack

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Oct 21, 2017
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Hello

So thought I would concentrate on one thing this evening. Figuring out how I should connect my cells together.

Without getting in to deep I've watch a lot of video's and left undecided on how I should do my series and parallel configuration.

So keeping this simple my powerwall will be an ever increasing design in capacity. Picture 4 server cabs if you will and Im starting on the first 3u tray.

I am to achieve 48-60v for my inverter. Now for simplicity should I say go 15s16p per pack to utilise the easily available 4x5 cell holders out on the market and should see around 63v-45v as the pack is used. For me I can see a plus side that I could remove a pack from wall to periodically check and all I would do is alter the capacity.

Or is this a bad idea. is there a con with this and something like asmaller series a better idea say 7s74p and except that everything is done in pairs because of some pro's that I haven't considered?

Would you recommend lower voltages for safety? Also thinking about the potential of a completely off grid house would it be in my interest to increase safety measure when handling and increase the voltage for potential kw output.

I have realised that Batrium is looking a must so not really understanding how all their products work would I be ruling say longmons out with a 15s16p as if I read right the range is up to 5.4v? Which means maybe I go 1s80p like I've seen done and except I work in groups of 15 to achieve my desired voltage?

As always any input is honestly well recieved as just trying to get my design right with minimum mess up's.

thanks
 

DarkRaven

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You said you will start with a 3U tray in your 19" server racks. Is this the size you will continue to use when expanding the system? With something this size you should settle for a standard to make your life easier. If so, what is the usable size within such a module for cells?

Higher voltage is usually better the bigger the system is to keep the current as low as possible. 14S lithium matches 48V systems. 58.8V fully charged, 51.8V nominal, 42.0V empty.

As you said, two approaches:

1. Build 3U modules as single cells and arrange them in series. Like this you can't start with a single module.
2. Build 3U modules with the desired system voltage, 14sXXp, XX whatever fits into the modules.

2. has the advantage that you can start with one module and you can remove a module from the system at any time without affection operation. But you need monitoring and balancing for each module. At the end this is basically a financial question. You're buying yourself some advantages and mitigate the disadvantages with money.
 
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DarkRaven said:
You said you will start with a 3U tray in your 19" server racks. Is this the size you will continue to use when expanding the system? With something this size you should settle for a standard to make your life easier. If so, what is the usable size within such a module for cells?

Higher voltage is usually better the bigger the system is to keep the current as low as possible. 14S lithium matches 48V systems. 58.8V fully charged, 51.8V nominal, 42.0V empty.

As you said, two approaches:

1. Build 3U modules as single cells and arrange them in series. Like this you can't start with a single module.
2. Build 3U modules with the desired system voltage, 14sXXp, XX whatever fits into the modules.

2. has the advantage that you can start with one module and you can remove a module from the system at any time without affection operation. But you need monitoring and balancing for each module. At the end this is basically a financial question. You're buying yourself some advantages and mitigate the disadvantages with money.

DarkRaven, Thanks for the reply. The server rack and 3u was an example, reality is no doubt I will be seeing at least 6u spaces to allow effective cooling. The Cab layout will be governed by the size of the battery packs essentially.

Love the phrase mitigate the disadvantages with money! Made me chuckle but no doubt is very true.

Was I right when reading the longmon's that they can handle up to 5.4v? Is there an alternative out there for me to use on a 15sXXp layout that batrium or whoever do? I do feel like monitoring is important when trying to run an offgrid home :)
 
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Hi all

So battery pack design is this 15s24p. Included in this pack if I am right in thinking 15 Longmons to read each serial line. So hopefully if I have read this correctly too I could over time wire in 16x 15s24p packs in a 16s1p configuration to utilize 240 Longmons attached to one Watchmon and give me a grand total of around 50kwh to my home.

So do these calculations sound roughly correct? 15s24p, 360 18650 LG cells around 2600 mah per cell tested and confirmed 2A rating giving the pack around 55v, 3.1Kwh, 48A rating?
 

DarkRaven

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Is there a reason for 15s? 14s would be the default as this is 48V. 15s will give you between 45.0V and 63.0V exactly, nominal voltage will be 55.5V. Capacity is 62.4Ah, that gives you 3.46kWh and with a maximum current of 48A you can draw ~2600W from the battery when it has a decent charge and more like ~2100W if it becomes empty.
If you build more of these modules you have to put them in parallel, not in series. So with 16 of these you have to build a (1s)16p configuration, ohterweise you will increase the voltage to 16x55.5V = 888V. I said higher voltage it good, but that is probably a bit TOO high :D
I think you could use a single WatchMon for this, but you should confirm that with Batrium or users more familiar with the system.
 

daromer

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1 Watchmon can have up to 250 *mons attached on 1 type of chemistry. That should be more than enough for 300kWh of storage or more :)

15s is generally to high for some devices. Just make sure your device can go to 65V or so without issues and your good. (Some headroom is generally wanted and you never know when you actually need to fully charge it)
 
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f@*k me Im so pants at proof reading I meant 1s16p dude not 16s ahhahaha!! @darkraven!! its even on my spreadsheet I have so how I typed that wrong is beyond me!!!!

Just to clarify I do not intent on reaching a voltage of 888 only around 48v hahahah

Someone ban quick reply for me please!!

@daromer, 100% right the inverter can only go to 60v (Schneider Conext XW+) just read the spec again its 42v-60v and lets face it Ive been so busy trying to use the cell holders so I dont cut them and completely over looked the potential max voltage. think 15s has the potential fully charged to deliver 63v which if I guess doesnt damage the inverter would error it! Thanks that could have been a costly mistake! Plan plan plan hey! Well for me anyway!!!

so Im now going 14s40p in my design, 560 cells @2600mah, around 51v, 104ah, 4.8kwh, with 80Amps, 14 Longmon's. Does this sound about right and a better plan? Thanks for your patients!
 

daromer

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Sounds like a good start!
 
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:)

So whilst we are talking battery packs I plan on initially building 4 packs. This is to give me around 19-20kwh to utilise as I build my off grid home. Hopefully this is enough for power tool battery charging hhaha Any advice on BMS's?
 

daromer

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Batrium? :)
 

skyfridge

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IAMJAMESMANNION said:
:)

So whilst we are talking battery packs I plan on initially building 4 packs. This is to give me around 19-20kwh to utilise as I build my off grid home. Hopefully this is enough for power tool battery charging hhaha Any advice on BMS's?

20kwh? That's not an offgrid home. It's a palace. Can I marry you for the money?
 
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daromer said:

Daromer sorry I was having a funny five minutes last night! I my mind I was actually thinking about how to do balance charging and wrote BMS..

skyfridge said:
IAMJAMESMANNION said:
:)

So whilst we are talking battery packs I plan on initially building 4 packs. This is to give me around 19-20kwh to utilise as I build my off grid home. Hopefully this is enough for power tool battery charging hhaha Any advice on BMS's?

20kwh? That's not an offgrid home. It's a palace. Can I marry you for the money?

skyfridge, I should introduce you to my fiancee, she is the biggest power waster I have ever meet! Lights on, tumble dry everything, tv's left on, chargers left in the walls powered, ovens preheated ages before use, kettles boiled full for one cup!! hahhaha off grid home and I have to go big!!
 

skyfridge

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IAMJAMESMANNION said:
skyfridge, I should introduce you to my fiancee, she is the biggest power waster I have ever meet! Lights on, tumble dry everything, tv's left on, chargers left in the walls powered, ovens preheated ages before use, kettles boiled full for one cup!! hahhaha off grid home and I have to go big!!

She and I probably wouldn't get along.

I've been off grid for over five years and survived on a 12V 230Ah lead acid battery bank. I couldn't get the gf to understand that you just don't watch movies after dark in the winter or vacuum on a cloudy day. I've been single for almost three years. :rolleyes:
 
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Throwing money at 18650's is my compromise to keep the fiancee!

Just trying to work out the best way to take each 14s40p battery pack to the inverter now. So for my initial plan I will be taking 4 packs in Parallel (Not Series like I keep typing!) to hopefully get me this desired 19Kwh powerwall. Now my thinking is each cell is to be fused for individually. They are LG-ICR18650D or Samsung ICR18650-30B cells with a max rating of 2A.

Im using twisted 2+e uk power cable twisted strips to fuse to. I cant decide if fuse rating for each Parallel line. Maybe 4a? at the 15s end I was going to glue two cooper bars, positive and negative, then simply tap the bars, use some correct awg cable, I thnk 9 AWG 16mm2, to a Anderson 120a SB Connector. This is the pack then ready to install into the wall but what is best practice from this point to the inverter? Should I then go to a rotary isolator due to the total current further up the chain? Could I Used consumer unit fuses on a rail before it passes on to the Inverter?
 

DarkRaven

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You have to figure out what your load is going to be before making decisions here. Otherwise it is just guessing and guessing isn't good.

Oh, also, are you using new cells? If so then they are rated for much more than 2A and their short circuit current can be something like 40A or even more.
 
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DarkRaven said:
You have to figure out what your load is going to be before making decisions here. Otherwise it is just guessing and guessing isn't good.

Oh, also, are you using new cells? If so then they are rated for much more than 2A and their short circuit current can be something like 40A or even more.

Unfortunately I have no way of working out my load. I cant guarantee what I spec now will be available over the next 2 years of my offgrid build so I have no choice but to guess. Not the best practise I know so looking to over estimate and hopefully its a lot less. I was thinking maybe I should design it for two house load charging 4 cars.

I will make a rough guide but there will be so many things I over look no doubt!

Batteries will all be used LG or Samsung cells recovered from Dell 97WH battery packs. I have toyed with the idea of new but current prices vs used make me think used is the way forward. Especially asso far I have only had 2 dead cells out of 600 and i've not seen a battery under 2600mah. These have come from my place of work so I know future packs could be some what different. I was aware of the short circuit but Im not sure how to had that in as a factor when spec'in the cable from the battery pack, to its next route, to the inverter. From the inverter is easy, 240v AC here in the UK and building control determine how the interior gets wired.
 

DarkRaven

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Start with what you need to power now. No need to plan for years in advance. Maybe you have to rebuild parts of your system for whatever reason in the future anyway but you have to start somewhere. And only by knowing the requirements you are able to properly size everything. Cables, fuse wires, fuses/circuit breakers, connectors and so on.
 
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DarkRaven said:
Start with what you need to power now. No need to plan for years in advance. Maybe you have to rebuild parts of your system for whatever reason in the future anyway but you have to start somewhere. And only by knowing the requirements you are able to properly size everything. Cables, fuse wires, fuses/circuit breakers, connectors and so on.

OK

I've spent some time putting a list together of appliances but I used watts, well actually max watts of all appliances. Should I convert this?
 
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