How to calculate pack and charger?

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rememberthemagic

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1958greyhound said:
you can charge them at 1c
10amps discharge

capacity was checked at .2c
you will end up getting 1000-1500 mah out of them

so lets say 1250 (middle of the road) and I need we think 200amps peak, 100amps avg, so 100amps/1.250=80 cellsin parallel
so 14 rows (series) and this duplicated (parallel) 80 times... Holy Cow,

Then factor in I need 200amps peak, so that pack at least 50% larger now we are talking about 160P I see why someone mentioned looking at larger cells! Perhaps a cart is not a good idea for a Li-ion project?


daromer said:
20700 is a different size of cell :)

Well since I don't have anything at this point I would try anything if it makes sense. So if you had to do this all over again with all you know and have been thru would you build the packs and solder them, or weld them, or just by them pre-assembled? What is a basis must have tool/setup for someone wanting to get into this and grow? Seems to make sense to follow the advice of someone here vs starting from scratch and buying junk that you throw away in 3 months when you learn there are better ways of going things and better tools, etc..
 
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your comparing capacity, how long something lasts
to amp draw, which is how strong it is.


how many of these cells do you already own?
 

rememberthemagic

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1958greyhound said:
your comparing capacity, how long something lasts
to amp draw, which is how strong it is.


how many of these cells do you already own?



None, just in the planning stages. I have the money and ready to purchase just need to know what to purchase, i.e. what makes sense to purchase. Currently the batteries I have are flooded lead acid 150ah 12 volt (4 of these wired in series) and my long term plans are to add 32 more solar panels and build a powerwall. so, before I dive into a MAJOR project like a powerwall I wanted to get my feet wet per say, learn the process, figure out what tools I need, test equipment, chargers, etc.. and there is not better way to do that than to take on a smaller project first. Well since the flooded lead acid cells are 2 years old and weak (previous owner didn't maintain them well) I figured this is a perfect first project to get started in so here I am. I am willing to compensate someone for their time to help me out as I am self employed and understand the value of time=money.

I am an engineer by trade (EE) but mainly do computers now (servers, networking, etc.) so while I'm no idiot this is not my field and I am intelligent enough to know I am not intelligent enough to do this alone, unless I want to piss away a lot of time making the same mistakes most of you have made already. Why re-invent the wheel when you have experts here willing to help? I would gladly trade my 27 years computer experience for someone with battery experience (i.e. powerwalls, e-bikes, etc) that is willing to trade out time, knowledge, etc..

I am not trying to make a living doing this, it just looks fun and I want to learn, etc.. so I posted on this site hoping the forum would offer up some ideas/designs, etc.. that I could learn from. I know its not simple, I respect the time/energy you and others have put into your packs, the knowledge you have acquired purchasing batteries, testing, assembly, bms, charging, etc.. and want to join in on the fun =o)
 
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build the pack 14s80p and use standard cells.
if your going to buy brand new 18650s, dont and just buy winston 100a lipo.
 

daromer

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I would also consider buying premade packs. Especially LiFe packs. Generally not much more epxensive and def not more expensive in terms of total capacity over time.
 

rememberthemagic

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1958greyhound said:
build the pack 14s80p and use standard cells.
if your going to buy brand new 18650s, dont and just buy winston 100a lipo.

Then I guess the question becomes do you pay $483 for a 12v 90/Ah Winston, or $300 for a 150/Ah Lead Acid

Is it true that you don't need as large a capacity battery for LiFePO4 as compared to Flooded lead acid?
 

daromer

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Its def true yes!
The LiFe can often be cycled 50 or hell even 80% DOD easily and still do 2-5000 cycles meanwhile some lead acid only do 200-500 on that depth. Proper solar lead acid can do more but they still cant beat the LiFe what i know about so far.

Edit: The packs I have here is said to do up to 5000 cycles 80% DOD with 60% capacity left after those 5000 cycles. That is alot! :)
 

rememberthemagic

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daromer said:
Its def true yes!
The LiFe can often be cycled 50 or hell even 80% DOD easily and still do 2-5000 cycles meanwhile some lead acid only do 200-500 on that depth. Proper solar lead acid can do more but they still cant beat the LiFe what i know about so far.

Edit: The packs I have here is said to do up to 5000 cycles 80% DOD with 60% capacity left after those 5000 cycles. That is alot! :)

So lets say you run the cart 5-10 mins at the time (with rest between for recovery) its my assumption that you could use a smaller cap battery (like a 90Ah) and be fine?
 

daromer

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Without all variables i would say that the increase of runtime due to resting is minimal and going for smaller battery will only yield in shorter run-time.

As long as the battery will withstand the current without issues.
 
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your not going to get a shorter run time battery because you need thebamp draw.

tesla has a 85kw battery, they advertise it for the miles it will go, but in rrality it has to be that big for when you floor it.
 

rememberthemagic

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1958greyhound said:
your not going to get a shorter run time battery because you need thebamp draw.

tesla has a 85kw battery, they advertise it for the miles it will go, but in rrality it has to be that big for when you floor it.

So what is the magic math for all this?
 
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series for the volts
parallel for the capacity
parallel for the amp draw.

series times what ever larger parallel number you get is the total cell cout you need.
 

rememberthemagic

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1958greyhound said:
series for the volts
parallel for the capacity
parallel for the amp draw.

series times what ever larger parallel number you get is the total cell cout you need.

ok, so 2900mah battery here we come... I have to find some on the east coast of the United States =o)
 
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