DIY HI POWERED PACK: First time, General questions

Jonathan1981

100 W
Joined
Mar 29, 2011
Messages
180
Tried to search the forum for something similar to what I'm doing but couldn't find anything that relevant.

Just starting to research, learn and get into DIY pack building. My first DIY pack will definitely not be this big but I think it's something I'd like to do eventually, to have for vehicle applications AND as a spare energy backup for household use.

Right now, I'm mostly trying to figure out the basic principles to battery pack building and energy system setups...bare with me as some of my questions will probably be noobish for experienced builders.

I've attached some images of a proposed 18S42P pack.... Samsung 30Q 3ah 15A cells.....so 72V system...Peaks of 300A. Noticing that for that high draw most BMS's come with a huge @ss relay...

1. Why is a relay required for 300A draw and not 200A? how exactly are they connected? does the BMS provide the 12V power to power them?

2. On my cad mock-ups, I've used a laser cut nickel plate(to be spot welded).....from further research, it seems like I will need to add buss bars to these connections I assume? Are there any preferred methods for connecting up such a high draw capable batt pack? What sort of thicknesses are generally required? I notice Tesla uses thicker bus plate and small "fuse" type wire......does the fuse wire need to be specked to the max output of each individual cell (for 30Q, is it 3ah or 15A discharge capable?) or the overall output of the grouping of parallel cells?

3. From the images, is my general connection logic sound?

Many other questions but I guess that gets the ball rolling...
 

Attachments

  • 18S42P_Batt-pack_BACK.jpg
    18S42P_Batt-pack_BACK.jpg
    117.4 KB · Views: 2,096
  • 18S42P_SUBPACK_2_back.jpg
    18S42P_SUBPACK_2_back.jpg
    115.7 KB · Views: 2,096
  • 18S42P_SUBPACK_3_FRONT.jpg
    18S42P_SUBPACK_3_FRONT.jpg
    122.6 KB · Views: 2,096
  • 18S42P_Battery_pack.jpg
    18S42P_Battery_pack.jpg
    102.7 KB · Views: 2,096
After some research, slight revision on that initial concept...not sure if fuses are required on both sides, anode and cathode...
 

Attachments

  • 2019-03-08 (3).jpg
    2019-03-08 (3).jpg
    208.3 KB · Views: 2,060
  • 2019-03-08 (4).jpg
    2019-03-08 (4).jpg
    198.6 KB · Views: 2,060
wow, you are making stuff a lot more complicated than it needs to be. also a lot more expensive.

first: switch out the cells for 29E and save some money. dump the busbars and just use straight nickel strips/plates. forget busbars and fuse wires. they are not needed.
 
Hello,

I prefer fuse wired battery instead spot welding rigidly the cells. If it is made carefully, no evidence, spot welding would be less harmful solution on the cells, but results a less safe pack.
Here is my 2nd build:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92645
More info you can find on the forum if you search for "fuse wire".
It is enough to have only 1 wire/cell, preferably on negative terminal (can). However, it is important to use low temp. solder (leaded) and solder right at circumfence, not at the center of the bottom. Your intended 7A/cell load is perfect fit.
Edit:
My current favorite solution is to have both +-busbar on the positive side and fuse wire soldered to the circumfence on top of the cell.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88039&start=75#p1435658
Like this, but fuse wire only on negative side.
 
flippy said:
wow, you are making stuff a lot more complicated than it needs to be. also a lot more expensive.

first: switch out the cells for 29E and save some money. dump the busbars and just use straight nickel strips/plates. forget busbars and fuse wires. they are not needed.

This is not for an ebike pack, but an e motorcycle with potential amp draw ~ 300amps. That's a lot! and requires more than just nickel strips. Also the 29E is 2C rating, not good. 30Q's are 15A continuous.

As I research into high powered ev's, seems like everyone is doing fuses and bus bars... I've been playing around with different bus bar designs, I've changed it again. I'll post up what I have soon.

thanks for your feedback
 
takyka said:
Hello,

I prefer fuse wired battery instead spot welding rigidly the cells. If it is made carefully, no evidence, spot welding would be less harmful solution on the cells, but results a less safe pack.
Here is my 2nd build:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92645
More info you can find on the forum if you search for "fuse wire".
It is enough to have only 1 wire/cell, preferably on negative terminal (can). However, it is important to use low temp. solder (leaded) and solder right at circumfence, not at the center of the bottom. Your intended 7A/cell load is perfect fit.
Edit:
My current favorite solution is to have both +-busbar on the positive side and fuse wire soldered to the circumfence on top of the cell.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88039&start=75#p1435658
Like this, but fuse wire only on negative side.

Takyka, nice pack design in first link. Thanks for the feedback also!
 
Jonathan1981 said:
Also the 29E is 2C rating, not good. 30Q's are 15A continuous.
pulling 15A from 30Q's will kill them faster then you will care for. anything more then 5A will cook the pack. you must have active cooling for the cells just to keep them from going thermal. i measured temperatures beyond 60C during 10A discharges in open air.

motorbike does around 5kW on the highway. because of the low voltage you will see 80~100A easy just to sustain speed. i would put in a lot of temp sensors in the pack and keep it well under 50c in the center. i doubt you will be able to hold 5kW sustained without heating the pack considerably.

you can pull 300A with just nickel strip without any issues. i built pently of packs already well into the 500A range.
 
flippy said:
Jonathan1981 said:
Also the 29E is 2C rating, not good. 30Q's are 15A continuous.
pulling 15A from 30Q's will kill them faster then you will care for. anything more then 5A will cook the pack. you must have active cooling for the cells just to keep them from going thermal. i measured temperatures beyond 60C during 10A discharges in open air.

motorbike does around 5kW on the highway. because of the low voltage you will see 80~100A easy just to sustain speed. i would put in a lot of temp sensors in the pack and keep it well under 50c in the center. i doubt you will be able to hold 5kW sustained without heating the pack considerably.

you can pull 300A with just nickel strip without any issues. i built pently of packs already well into the 500A range.


pulling 15A from 30Q's will kill them faster then you will care for. anything more then 5A will cook the pack. you must have active cooling for the cells just to keep them from going thermal. i measured temperatures beyond 60C during 10A discharges in open air.

Interesting, so that's way off manufacturing continuous amp spec... :(. I should probably know this but what is considered a harmful temp for battery? +40C?

So if you're saying the 30Q's can only reasonably sustain 5A without going crazy thermally, that would be 5x30 = 150amp max draw then?? for a 18S30P pack... if that's correct I'll need to reconsider the BMS I was going to get.

you can pull 300A with just nickel strip without any issues. i built pently of packs already well into the 500A range.

you're kidding... so then why is everyone on youtube doing the fused cell, bus bar thing for their large, high draw packs? It's everywhere.

So you're saying I could build a 18S30P pack of 30Q's just like any other normal ebike pack without bus bars etc.?
 
Hello friend, this website is a jewel!
https://lygte-info.dk/review/batteries2012/Common18650IndividualTest%20UK.html
Though it took some time to find the correct page.
This page, my friend, is the 30Q
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-30Q%203000mAh%20%28Pink%29%20UK.html
It states the max continuous discharge is 15A, and can go a tad higher for short bursts.
Very good discharge curves, capacity is nearly constant and they track perfectly. Even the 20A curve maintains a decent voltage, but as can be seen below the cell gets warm.
The tail on some curves is because I continue to record after stopping the discharge (If the cell is hot), i.e. it shows how much the voltage recovers.
The cell will heat up at a 10A load, but it is rated for it.
The cell can also handle 20A for some time, but you are supposed to stop when it gets hot (As I do here).
Remember the chart shows above ambient temperature, the actual cell temperature goes above 75°C.

Conclusion

This cell is very good, it can handle about 15A continuous discharge and has no problems with 20A pulses.
 
markz said:
Hello friend, this website is a jewel!
https://lygte-info.dk/review/batteries2012/Common18650IndividualTest%20UK.html
Though it took some time to find the correct page.
This page, my friend, is the 30Q
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-30Q%203000mAh%20%28Pink%29%20UK.html
It states the max continuous discharge is 15A, and can go a tad higher for short bursts.
Very good discharge curves, capacity is nearly constant and they track perfectly. Even the 20A curve maintains a decent voltage, but as can be seen below the cell gets warm.
The tail on some curves is because I continue to record after stopping the discharge (If the cell is hot), i.e. it shows how much the voltage recovers.
The cell will heat up at a 10A load, but it is rated for it.
The cell can also handle 20A for some time, but you are supposed to stop when it gets hot (As I do here).
Remember the chart shows above ambient temperature, the actual cell temperature goes above 75°C.

Conclusion

This cell is very good, it can handle about 15A continuous discharge and has no problems with 20A pulses.

half of those are fake chinese cells lol...
 
Jonathan1981 said:
Interesting, so that's way off manufacturing continuous amp spec... :(. I should probably know this but what is considered a harmful temp for battery? +40C?
So if you're saying the 30Q's can only reasonably sustain 5A without going crazy thermally, that would be 5x30 = 150amp max draw then?? for a 18S30P pack... if that's correct I'll need to reconsider the BMS I was going to get.
you're kidding... so then why is everyone on youtube doing the fused cell, bus bar thing for their large, high draw packs? It's everywhere.
So you're saying I could build a 18S30P pack of 30Q's just like any other normal ebike pack without bus bars etc.?

in the same order:
45C core temp in your pack should be the upper limit.
yes.
how high can you go with voltage with the controller you selected?
everyone does it on the youtubes because everyone is using shit secondhand used cells, they have seen tesla do it, they are copycatting each other.

i would make the pack in such a way that you dont need bus bars.
 
Yeah, that's super helpful. Thanks. I'm reworking the design, I'll post up some images for your feedback, you can let me know what you think.
 
Just so you know it.

30Q is a bad cell with terrible aging properties.
It does have nice low esr but its quickly killed, no matter how gentle you threat it.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=97844&p=1435146#p1433642

Neither can Sanyo GA be recommended for high drain packs as it practically dies after first 50 cycles.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96360#p1447298

And finally stay away from LG MG1 2900mAh that has the far worst cycle life in its class.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=97844&p=1436393#p1434112
 
Honk said:
Just so you know it.

30Q is a bad cell with terrible aging properties.
It does have nice low esr but its quickly killed, no matter how gentle you threat it.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=97844&p=1435146#p1433642

Neither can Sanyo GA be recommended for high drain packs as it practically dies after first 50 cycles.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96360#p1447298

And finally stay away from LG MG1 2900mAh that has the far worst cycle life in its class.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=97844&p=1436393#p1434112

hey, thanks for the links! super helpful, what would you recommend then? best cell/$ for high power EV?
 
Samsung 29E without any doubts.
Best bang for the buck and proven sturdy and longlife when cycled between 4.1V to 3V.
Keep away from prolonged hot storage.
Keep charge current at 0.5C max and discharge at 1C max and the cells might outlive your bike, boat or where ever they will be used.
 
Jonathan1981 said:
hey, thanks for the links! super helpful, what would you recommend then? best cell/$ for high power EV?

25R seems to be the best bang for the buck, I did a spread sheet on nkon cells. Others have stated PF or 29E but those are low discharge cells. 25R is 20A 18650 at 2.5Ah which is what you require friend.

29E is nothing you want to look at
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-29E%202900mAh%20%28Blue%29%20UK.html
Max. Discharge Current: 2,750mAh (continuous discharge), 8250mAh (not for continuous discharge)
 
29E is really what should be looked at.
Build enough big pack to keep it within the suggested limits and it will last for very very long time at many cycles.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96079&p=1450089#p1450053
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96079&start=25#p1411883
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88130&p=1424249#p1424249
https://endless-sphere.com/forums/viewtopic.php?f=14&t=98885&p=1447987#p1447862
 
i would agree with markz, the 25E has lower IR so heats up less, something that is very imporant in a pack that gets drained in an hour.
the 29E is cheaper and higher capacity but with 8A loads it does get warm. not as warm as the 30Q ofcourse but still something to keep in mind when putting a few hundred together with no cooling.
 
If a high drain cell is an absolute must there is 25S.
It handles 30A nicely besides some heating up.

https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-25S%202500mAh%20%28Purple%29%20UK.html
 
29e vs 30q is hardly a competition, the 30q is the correct cell for your defined requirements. I have built many packs with 30q - the one on my daily bike is 20s12p, I hit discharges of 160 amps every day. Peak pack temperature is <30c at conclusion of my journey of ~17km. This pack has done >18,000km, over 500 cycles - when I last discharge tested it not that long ago it still had 93% of its original capacity. Measured DC IR has increased by about 15% over 2+ years. I charge to 4.1v and discharge to ~3.7v on most of my cycles. If you size your pack correctly so you're not doing 100% DOD cycles and not pushing 2c+ continuous discharge rates (which you have!) then this will last a very long time. Theoretical degradation after 1000 cycles are irrelevant to an enthusiast motorcycle where that will translate to 50,000 km+

I did extensive discharge testing at the time I built this pack, Samsung 25R, 29E, LG MG1, HG2, HE2, HE4 - The 30Q was the best compromise of pulse discharge, overall capacity, cycle life, cost etc I could find. Don't do deep cycles on a constant basis and it will last more than long enough.
 
Ohbse said:
29e vs 30q is hardly a competition, the 30q is the correct cell for your defined requirements. I have built many packs with 30q - the one on my daily bike is 20s12p, I hit discharges of 160 amps every day. Peak pack temperature is <30c at conclusion of my journey of ~17km. This pack has done >18,000km, over 500 cycles - when I last discharge tested it not that long ago it still had 93% of its original capacity. Measured DC IR has increased by about 15% over 2+ years. I charge to 4.1v and discharge to ~3.7v on most of my cycles. If you size your pack correctly so you're not doing 100% DOD cycles and not pushing 2c+ continuous discharge rates (which you have!) then this will last a very long time. Theoretical degradation after 1000 cycles are irrelevant to an enthusiast motorcycle where that will translate to 50,000 km+

I did extensive discharge testing at the time I built this pack, Samsung 25R, 29E, LG MG1, HG2, HE2, HE4 - The 30Q was the best compromise of pulse discharge, overall capacity, cycle life, cost etc I could find. Don't do deep cycles on a constant basis and it will last more than long enough.

your personal experience is not valid for this use case. this is a motorbike, not a scooter or ebike. 17km is done in less then 9 minutes with a motorbike on a highway.

the >average< load for a motorbike is around 5kW. with your battery that would mean 70A continous (5.8A per cell). well into the range of self heating. this pack is also considerably bigger and the center of the pack would get WAY too hot with such currents and a high IR cell like the 30Q. you are hardly using those cells over their full range. a motorbike usually runs its pack almost empty.
500 cycles on a pack that will cost 2300USD in cells alone is economically "unviable" as you would wear out the pack in just tens of thousands of miles, for a daily driver that would mean 3 years at best so you would write off 1000+ bucks a year just in pack wear and that ignores the case the cells will get incredibly hot also reduding lifespan and possibly start a "pack ending event" due to overheating. especially during the summer on a highway.

no, in order to be economically viable you need longer lasting cells that are higher current, preferably cheaper and more of them. how much more depends on the physical space that is available. in order to increase efficencly and reducing currents i would crank up the voltage as high as possible. 144V or so if the controller can take that.

just for your amusement i have a link to my just completed lifecycle testing of a 29E at 8.25A. despite if being in free air it got "warm" to the touch. on itself not that amazing but cram 700+ of them in a closed space and you got yourself a nice nuclear reactor going 2 inches from your manhood.

https://drive.google.com/file/d/1AWTQlij0X1qYCiamB4hx25xNOyC0tWGd/view?usp=sharing
 
flippy said:
Ohbse said:
29e vs 30q is hardly a competition, the 30q is the correct cell for your defined requirements. I have built many packs with 30q - the one on my daily bike is 20s12p, I hit discharges of 160 amps every day. Peak pack temperature is <30c at conclusion of my journey of ~17km. This pack has done >18,000km, over 500 cycles - when I last discharge tested it not that long ago it still had 93% of its original capacity. Measured DC IR has increased by about 15% over 2+ years. I charge to 4.1v and discharge to ~3.7v on most of my cycles. If you size your pack correctly so you're not doing 100% DOD cycles and not pushing 2c+ continuous discharge rates (which you have!) then this will last a very long time. Theoretical degradation after 1000 cycles are irrelevant to an enthusiast motorcycle where that will translate to 50,000 km+

I did extensive discharge testing at the time I built this pack, Samsung 25R, 29E, LG MG1, HG2, HE2, HE4 - The 30Q was the best compromise of pulse discharge, overall capacity, cycle life, cost etc I could find. Don't do deep cycles on a constant basis and it will last more than long enough.

your personal experience is not valid for this use case. this is a motorbike, not a scooter or ebike. 17km is done in less then 9 minutes with a motorbike on a highway.

the >average< load for a motorbike is around 5kW. with your battery that would mean 70A continous (5.8A per cell). well into the range of self heating. this pack is also considerably bigger and the center of the pack would get WAY too hot with such currents and a high IR cell like the 30Q. you are hardly using those cells over their full range. a motorbike usually runs its pack almost empty.
500 cycles on a pack that will cost 2300USD in cells alone is economically "unviable" as you would wear out the pack in just tens of thousands of miles, for a daily driver that would mean 3 years at best so you would write off 1000+ bucks a year just in pack wear and that ignores the case the cells will get incredibly hot also reduding lifespan and possibly start a "pack ending event" due to overheating. especially during the summer on a highway.

no, in order to be economically viable you need longer lasting cells that are higher current, preferably cheaper and more of them. how much more depends on the physical space that is available. in order to increase efficencly and reducing currents i would crank up the voltage as high as possible. 144V or so if the controller can take that.

just for your amusement i have a link to my just completed lifecycle testing of a 29E at 8.25A. despite if being in free air it got "warm" to the touch. on itself not that amazing but cram 700+ of them in a closed space and you got yourself a nice nuclear reactor going 2 inches from your manhood.

https://drive.google.com/file/d/1AWTQlij0X1qYCiamB4hx25xNOyC0tWGd/view?usp=sharing

So I've looked at everyone's links and did the research...

So Flippy, I see what you're saying, the 29E's technically would be better for my pack except for one big problem, the C rating is not enough. @ 30P, it only gives me 85A draw, which is not going to cut it. And 30P is a HUGE pack already that barely fits my constraints as it is, so no options on sizing up with more cells...

The amount of use this pack would get, I wouldn't even reach 500 cycles in 5 years lol

so for those reasons among others, I think 30Q's would do the trick....

BUUUUUUUUUUUUUT....

you guys never mentioned the magical 21700 form factor!

I've looked @ the new LG M50's, so 5000mah Cap, 1.5C (have been tested reliably to 2C continuous)..... and I think that's the route I'll go if I do build this thing. This will allow for a thinner 18S20P pack, less cells, less connections, fits my size requirements with room to spare, gives me MORE overall Cap of 100ah! weirghs less.....current draw is not quite as good but I can live with that, I'll set the controller to 185A... that should be more than enough, my Surron pulls ~ 80A and that thing hauls...

only downside is price :(
 
Cant you increase the voltage any higher?
 
Back
Top