Back to planning and input welcome.


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Oct 21, 2017
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Hello everyone

So I been away for few years as life plans changed and now I'm back. I don't have land to build a house which was the OG plan but instead I am currently renovating a town house. One day I will find that land haha

I have a load of cells that I've collected from many dell laptops, mix manly of Samsung and LG with the odd Panasonics thrown in ready to make my very own DIY Power wall. I like to do things so they look factory made, I wish I didn't but I do haha so looking for advice and direction to making my packs.

So first any advice on the battery pack layout i.e. 1S60P vs 4S40P (remember this is for example) is there a advantage / disadvantage to a particular layout when using solar and wind turbine? or is it the charge controller that plays a key part to battery layout or is it down to personal preference haha?

I am honestly so rusty on this as I think it was around 2017 to 2018 I was last looking to start this!

Thanks for your patience haha!

James
 

Oberfail

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Jun 22, 2021
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The lower the voltage, the higher the amperes have to be, for the same wattage.
You also need way thicker cables for higer amperages which adds cost quickly. Most stuff is made for 12v or higher anyway, so a 1s pack would be harder to make.
 
Joined
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Messages
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The lower the voltage, the higher the amperes have to be, for the same wattage.
You also need way thicker cables for higer amperages which adds cost quickly. Most stuff is made for 12v or higher anyway, so a 1s pack would be harder to make.
Hey Dude, thanks for the reply completely get this and understand from my camper conversion days about the battle volts vs amps with cable thickness just wondered if there was actually a preferred or recommended layout.

Currently my mind is thinking from past experiences of off grid on boats and campers etc using lead acid 24v or 48v so im guessing that would be 7S or 8S to achieve around 24v or double that for something close to 48v then comes the hard part how many in parallel! Any recomendations??

My thinking would be maybe 16S24P with minimum of 5 packs. I have around 2000 good cells ranging from 2200mAh to 2800mAh and I think the numbers work out however does someone else see a better plan?
 

Oberfail

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Jun 22, 2021
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7s for 24v, 14s for 48v
Lower voltages are safer to handle, higher ones are able to deliver more watts with the same size of cable.
How many you want to put in parallel, depends on how much capacity / output you need.

And another suggestion. If you want your cells to last many more cycles, build a pack with a bigger capacity then needed and reduce the voltage limits for the cells. For example 3.4v-3.9v instead of 3.0v-4.2v.
 

italianuser

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Feb 25, 2020
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503
Welcome back James!

About your question(s): the voltage choice depends on what voltage your load uses. If it's a DC load then that voltage wins and your system will be built using that voltage for each piece. If you load works with AC then you can choose the best voltage for you. Devices working at higher voltage cost more.

Often, if you decide for a 24V system your choice for 18650 will be a 7S. For a 48V system you could go for a 14S. Higher that 48V I have no experience at all!

1st Scenario, my first small solar system, all nominal 12V: AC Load, "12V" panels, 12V AGM batteries, 12V regulator/charger, 12V inverter.
2nd Scenario, my new solar system, all nominal 48V: AC Load, "24V" panels in 2S configuration, 14S 18650 battery, programmable inverter (+charger).

For choosing how many cells in parallel you could also consider the battery design: it could be limiting to choose a 24P for example, if your cell holders are 3x5. I bought 4x5 cell holders so a 20P or 40P is perfect and makes my life easier for all the soldering/welding part.


1633283772863.png

[ 3x5 Cell Holder ]

I'm curious about wind systems... when you're ready please do share photos / configurations / etc!
 
Joined
Oct 21, 2017
Messages
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Welcome back James!

About your question(s): the voltage choice depends on what voltage your load uses. If it's a DC load then that voltage wins and your system will be built using that voltage for each piece. If you load works with AC then you can choose the best voltage for you. Devices working at higher voltage cost more.

Often, if you decide for a 24V system your choice for 18650 will be a 7S. For a 48V system you could go for a 14S. Higher that 48V I have no experience at all!

1st Scenario, my first small solar system, all nominal 12V: AC Load, "12V" panels, 12V AGM batteries, 12V regulator/charger, 12V inverter.
2nd Scenario, my new solar system, all nominal 48V: AC Load, "24V" panels in 2S configuration, 14S 18650 battery, programmable inverter (+charger).

For choosing how many cells in parallel you could also consider the battery design: it could be limiting to choose a 24P for example, if your cell holders are 3x5. I bought 4x5 cell holders so a 20P or 40P is perfect and makes my life easier for all the soldering/welding part.


View attachment 26177

[ 3x5 Cell Holder ]

I'm curious about wind systems... when you're ready please do share photos / configurations / etc!
Thanks dude for the reply and once I get to doing wind power I will most certainly be sharing. For the UK and where I live it actually seems a good solution for harnessing power through the night too. Biggest downside is most home turbines I've come across are not high wind safe and require covering haha cant win them all!

What you are saying makes perfect sense. I also found some of my plans from 5 years ago in which I had settled on 14S due to everything in the house being on AC. I was also looking to use a Schneider Conext inverter. From that it will go to my consumer board.

100% using 4x5 Cells, I brought a load ages ago and then not that I remember doing it I made a load of bus bars using the copper electrical wire in a drill method however I may not use and go for a more professional look any suggestions for for what to use?

Taking your advice @italianuser and @Oberfail if I go 14s40p I'm using 560 18650 cells a pack, I probably actually have enough for 4 packs, changing high and low voltages should to 3.4v - 3.9v for more cycles I should see 48v to 55v available to use, the cells average is 2300mAh after testing capacity so if my maths right around 5kWh each.

Everyone still using Batrium?

Ok guess I might be busy making some schematics tonight and tomorrow for you all to laugh at and correct :)
 

Wolf

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2nd Scenario, my new solar system, all nominal 48V: AC Load, "24V" panels in 2S configuration, 14S 18650 battery, programmable inverter (+charger).
I would be more inclined to go with 3s on the panels. 2s is pretty close to nominal V of the 48V battery and you want a bit of leeway to be able to charge the battery to at least ≈ 4.1V per pack or ≈ 57.4V for the Battery. A good Charge controller will handle the extra voltage of 3s just fine.

Everyone still using Batrium?
I am.
I have played around with several others but I keep coming back to the Batrium. The data collection especially with either Watchmonudplistener by @daromer or Node Red, both able to write to an influx db rather easily and visualize the data with grafana. There is the DIY BMS by Stuart Pittaway https://github.com/stuartpittaway/diyBMS which is also a nice project.

Wolf
 
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Oct 21, 2017
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@Wolf well looking around its still very much a minefield of potential BMS options! Like you said I was draw to Batrium due to the ease of data. With 14s40p for example was that 14 Longmons required? Ill admit I cant for the life of me remember. I did notice they do something called CellMate-K9, Expensive but range says 3-16s anyone used this?

@Oberfail I didn't realise but I have looked at Lithiumbatterypcb.com for a skateboard Idea! Only just remember looking at the site! ;)

Also anyone know any software that helps create wiring diagrams? :unsure:
 

italianuser

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Feb 25, 2020
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I would be more inclined to go with 3s on the panels. 2s is pretty close to nominal V of the 48V battery and you want a bit of leeway to be able to charge the battery to at least ≈ 4.1V per pack or ≈ 57.4V for the Battery. A good Charge controller will handle the extra voltage of 3s just fine.
panel specs.jpeg
I call them "24V" with quotes... but ehm 😄
 

Wolf

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With 14s40p for example was that 14 Longmons required?
Yep. I prefer to have a physical piece of equipment at or near each pack for temp sensing of the individual pack and if anything goes wrong with a single longmon easy to replace. With an all in one BMS package if 1 channel goes bad you got to replace the whole thing. As an end result with my 14s80p X 4 I will have a total of 56 longmons and of course I have 4 spares in case I have one or more go south.
I call them "24V" with quotes... but ehm 😄
Yep I get it. I still would go 3s. 120V Voc is perfect for a decent charge controller. and ≈9 amps is good for a reasonable wire size solution from the panels to the combiner box then charge controller. Let the Charge controller make the amps from the voltage then use the fat wire from there.

Wolf
 
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Joined
Oct 21, 2017
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Hey!

Sorry for the silence! I've been busy with work and family and to top it off I must have changed my mind way to many times about my plans, where to have the power wall, etc, etc! haha sorry!

Ill start by saying I mocked a 14s80p battery in cell holders etc and wow they weight in god dam it! hahha So I then thought that's fine ill server cab them on shelves but soon realised my plan of continually adding over the next couple of years turns complicated once chest height with the weight haha so scrapped the original 14s80p idea.

Im now going with the 1s80p design which most seem to build! also means I can use the fused nickel strips easily as to cutting 1 x 80 lines hoping that the cut stays straight which should keep it nice and pro looking. Anyone recommend using insulating paper to finish like this?https://www.ebay.co.uk/itm/224448272645
 
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Oct 21, 2017
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I have a 14s32p pack, i can lift it but barely move it around. For packs you're going to have to move, stay under 200 cells.
Hahaha Learnt this the hard way hahaha

Also have another quick question! Busbars.... to equally charge / discharge the batteries with the fused nickel strips is it good practice to run a busbar around the positive and negative on top? Would you recommend copper, brass or Aluminium? And is solder still the best method of attaching the busbar to the nickel strip?

Almost finished a couple of plans! will be sharing soon! :cool:
 

Wolf

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Would you recommend copper, brass or Aluminium? And is solder still the best method of attaching the busbar to the nickel strip?
Copper! Alu doesn't solder very well at all and brass resistance is a bit high.
Here is how I designed my Bus bars.

1634957310705.png1634957074471.png
Read all about it here.

Wolf
 
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