How to calculate pack and charger?

rememberthemagic

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I am looking to build a pack for a 48v cart, it has a 3.3hp 48v electric motor on it (3kw/9kwpeak), I have access to a few hundred Li-ion Samsung 18650 2200mah cells. Knowing that I want to be able to run this around lets say 2 hours max per day what would one suggest for a pack size and charger?

I have yet to purchase anything so now is a good time to get ideas / opinions from the group to point me in the right direction. Why re-invent the wheel when we have access to so many experts =o)
 
3kW@48V would mean 67Amps flowing, 9kW means 187,5A. Check the data sheet of your cells for rated discharge current. This is sometimes measured in C, which means a multiple of capacity. Example: If the cell's discharge rate is 2C and the cell has 2200mAh, the cell can max. deliver 4.4Amps.

Then devide the amps you think you'll need (anything between 67 and 187,5A) by this value and you'll know the minimum of parallel cells. For 48V, 14s is quite common, so then take the number of cells you calculated and multiply it with 14 for the cell count overall.

The charger also depends on the specs of your cells, resp. max. charge current - and how fast you want to charge. Also keep in mind that you might need balancing, overcharge and overdischarge protection, commonly knows as BMS...
 
I did write an answer here long as an a4 page... But i fucked it up. I dont want to rewrite how to do this today so I leave it for tomorrow or if someone else want to answer.
 
you would need a min of 14s 160p to equal the standard 8 golf cart batteries.

if you go with high amp drain bats like in a cordless drill you could get away with half as many.
 
owitte said:
3kW@48V would mean 67Amps flowing, 9kW means 187,5A. Check the data sheet of your cells for rated discharge current. This is sometimes measured in C, which means a multiple of capacity. Example: If the cell's discharge rate is 2C and the cell has 2200mAh, the cell can max. deliver 4.4Amps.

Then devide the amps you think you'll need (anything between 67 and 187,5A) by this value and you'll know the minimum of parallel cells. For 48V, 14s is quite common, so then take the number of cells you calculated and multiply it with 14 for the cell count overall.

The charger also depends on the specs of your cells, resp. max. charge current - and how fast you want to charge. Also keep in mind that you might need balancing, overcharge and overdischarge protection, commonly knows as BMS...

Excellent, so from what I can determinethe max these cells can produce is 10A (continuous discharge) they are -ICR18650-22P (Honestly not sure how to read this chart -http://www.tme.eu/en/Document/cf2b91a94627173083963b831db6ea62/ACCU-18650-2.2P-HV.pdf )

When I measure the cart in motion its drawing 12 amps (I agree the match doesn't add up, so lets assume 67amps so 67/10c so apx 6.7 rounded down to 6 cells in parallel. This gives us a total of 14 cells in series 6 in parallel or 84 cells per pack?

My goal is safety first (so yes to BMS) followed by cell life second and capacity third. I see a ton of BMS boards on ebay but not sure if I need balancing, etc.. for this project so it makes picking one a chore. Any feedback would be appreciated and a I have no reservations to making a donation via paypal for your help =o)


daromer said:
I did write an answer here long as an a4 page... But i fucked it up. I dont want to rewrite how to do this today so I leave it for tomorrow or if someone else want to answer.

Oh noooooooooo, what happened to your post? I feel your pain I lost a post to a guy on a Freenas project that I spend the better part of an afternoon typing up and wanted to pound my head against the wall for not copying it before I sent it out (just in case).

I hope you day goes better tomorrow and you are willing to share some insight.


1958greyhound said:
you would need a min of 14s 160p to equal the standard 8 golf cart batteries.

if you go with high amp drain bats like in a cordless drill you could get away with half as many.

Currently the way this cart is setup (right or wrong) as I received it is with 4 12v 150ah batteries. The batteries I have access to are:http://www.tme.eu/en/Document/cf2b91a94627173083963b831db6ea62/ACCU-18650-2.2P-HV.pdf
 
1958greyhound said:
to equal USABLE CAPACITY ofthe 4x 12v 150ah lead acid.

14s 35p
490 cells total.

Okay yeah I think with that many cells I'll build two separate packs and put them in parallel 2 of 14s18p
 
Just beware of how you interconnect the paralelled packs. Perhaps easier to build 7s35p and then hook 2 of those together to 14s instead?
 
daromer said:
Just beware of how you interconnect the paralelled packs. Perhaps easier to build 7s35p and then hook 2 of those together to 14s instead?

Good to know, I figured it was easier to parallel to packs (like you parallel 2 car batteries) than to put 2 in series, that not the case?

I did actually get some accurate current measurements today, the cart draws close to 200amps at 48v when you first floor it, then maintains about 100amps, Most of the time I am at about 75% throttle and see 60amps as average.
 
daromer said:
Just beware of how you interconnect the paralelled packs. Perhaps easier to build 7s35p and then hook 2 of those together to 14s instead?


Why do you say that Daromer? "Beware of how you interconnect the parallel packs." I'm curious as I was planning a future parallel interconnected system. I'm not challenging I'm honestly trying to learn. Thanks, Alec
 
Im talking about the balance part. Connect 2 14s packs in paralell 100% requires 15 wires!
But to hook up 2x 7s packs in series requires 2 wires ;)

Its just a matter of make sure that you always maintain them in balance in the cart and in that sense its best to make sure they all are "paralell".

If the cart draws 2000A at the start you should consider to have a capacitor bank hooked up to it as well. That will cope with the initial pull pretty well and you dont need several 1000 cells.
 
daromer said:
Im talking about the balance part. Connect 2 14s packs in paralell 100% requires 15 wires!
But to hook up 2x 7s packs in series requires 2 wires ;)

Its just a matter of make sure that you always maintain them in balance in the cart and in that sense its best to make sure they all are "paralell".

If the cart draws 2000A at the start you should consider to have a capacitor bank hooked up to it as well. That will cope with the initial pull pretty well and you dont need several 1000 cells.

Yeah, so the idea would be the "permanently" mount these in the cart, the motor draws 200 amp on start and then 100 at full throttle, most of the time I run 75% throttle and it averages about 60amps.

What would recommend for a BMS ?


So the next challenge is BMS and balancing / charging and is that easier to do in 2 packs wired in series, or 2 packs wired in parallel?
 
It depends on how you going to charge? If you charge with a proper RC charger then no need to add any BMS stuff to it. Then its just enough to have under voltage protection.

Just as I said before hook the 2 7s packs up to an iCharger DUO 308 or 4010 and you can charge them with either 30 or 40A :)
 
so 2 of these, (iCharger DUO 308) one to each pack and separate the packs electrically before I charge them? Looks like about 300USD for each unit, With this do you still suggest that I fuse each cell to the bus bar as I build it?


daromer said:
It depends on how you going to charge? If you charge with a proper RC charger then no need to add any BMS stuff to it. Then its just enough to have under voltage protection.

Just as I said before hook the 2 7s packs up to an iCharger DUO 308 or 4010 and you can charge them with either 30 or 40A :)

so 2 of these, (iCharger DUO 308) one to each pack and separate the packs electrically before I charge them? Looks like about 300USD for each unit, With this do you still suggest that I fuse each cell to the bus bar as I build it?


daromer said:
Im talking about the balance part. Connect 2 14s packs in paralell 100% requires 15 wires!
But to hook up 2x 7s packs in series requires 2 wires ;)

Its just a matter of make sure that you always maintain them in balance in the cart and in that sense its best to make sure they all are "paralell".

If the cart draws 2000A at the start you should consider to have a capacitor bank hooked up to it as well. That will cope with the initial pull pretty well and you dont need several 1000 cells.

so 2 of these, (iCharger DUO 308) one to each pack and separate the packs electrically before I charge them? Looks like about 300USD for each unit, With this do you still suggest that I fuse each cell to the bus bar as I build it?


1958greyhound said:
you would need a min of 14s 160p to equal the standard 8 golf cart batteries.

if you go with high amp drain bats like in a cordless drill you could get away with half as many.

So what battery cap are you suggesting? IT may be cheaper to do it that way than to purchase the extra smaller cap batteries?
 
higher amp drain.
standard laptop cells have .2c - 1c drain

the 10 amp you have should work, so if max draw is 200 amps you need 100p min



why do you want 2 dif packs?
 
1958greyhound said:
higher amp drain.
standard laptop cells have .2c - 1c drain

the 10 amp you have should work, so if max draw is 200 amps you need 100p min



why do you want 2 dif packs?

Yeah the spec is confusing to me:
http://www.tme.eu/en/Document/cf2b91a94627173083963b831db6ea62/ACCU-18650-2.2P-HV.pdf
Shows .2C but below that a few lines it shows 10A (Cont Discharge).

Just figured 2 packs would most likely be easier to fit in the space below the seat in the cart, otherwise no real technical reason.

The cart does draw 200 amps when you torque it up (stomp the pedal from a dead start) and so I need to account for that. Wow 100P is going to be a HUGE $$$ pack!
 
0.2C is the typical discharge for full capacity.

Nominal discharge is 1C and mach discharge continous is 5C.
Lets say your nominal should be 1C. then you need 30p roughly. For the maximum rate that you have ie 200A you need 20P to accomodate and have some safety.

I would rather go for 30p to save on the pack than 20p. 100p if you want to utilize the full pack capacity under 200A load :) I guess that is overkill than having alot of juice over a long time.
 
daromer said:
0.2C is the typical discharge for full capacity.

Nominal discharge is 1C and mach discharge continous is 5C.
Lets say your nominal should be 1C. then you need 30p roughly. For the maximum rate that you have ie 200A you need 20P to accomodate and have some safety.

I would rather go for 30p to save on the pack than 20p. 100p if you want to utilize the full pack capacity under 200A load :) I guess that is overkill than having alot of juice over a long time.

Then I start to wonder if the math works out better to just do something like thishttps://www.imrbatteries.com/sanyo-ncr20700b-4000mah-15a-flat-top-battery/

BTW, I did a paypal donation today under my work email, thanks for your help!
 
you can charge them at 1c
10amps discharge

capacity was checked at .2c
you will end up getting 1000-1500 mah out of them
 
20700 is a different size of cell :)
 
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