30Ah 28s LiPo from 7s bricks

Batteries, Chargers, and Battery Management Systems.
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Re: 30Ah 28s LiPo from 7s bricks

Post by john61ct » May 28 2020 7:48am

So there aren't any ready to go master CAN controllers people sell to work with their modules?

Would seem pretty easy to get an MCU programmed to handle that. . .

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Re: 30Ah 28s LiPo from 7s bricks

Post by hallkbrdz » May 28 2020 8:23am

Thanks for asking, I've been looking at the Zeva BMS as well so had similar thoughts...

As I understand it... I'll need a master BMS and a couple slaves to monitor the pack (once I decide what cells / bricks to use) when running. Those will need to talk to the motor controller and something overall to let me see the health (temperature, total voltage) of the pack, and the temperature of the motor and possibly controller with attention getting lights / buzzer to warn me when getting critical and/or to just shut it down. The BMS will also need to talk to the charger (when hooked up) to stop it from over-charging and to slowly balance the pack differences when I have time at home. Plus something to record all the data that will put up with the extreme kart vibrations. And of course it all needs to be waterproof (non immersible of course).

Oh and either a large charge battery pack or a gas generator to power the charger at the track (AC plugs are basically non-existent).

That complete engine / dash / harness swap from a MK4 VW I did into my Corrado was a cakewalk to everything I'm having to learn to do this. I've been looking into this seriously for a little more than a year and still feel ignorant since most how-to-build an EV topics are geared towards cruising and not pushing components in racing.

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » May 28 2020 8:43am

Zeva by themself are selling also master unit.
https://zeva.com.au/index.php?product=132
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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hallkbrdz   100 W

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Re: 30Ah 28s LiPo from 7s bricks

Post by hallkbrdz » May 28 2020 10:25am

Yes, I saw that. No mention if it is water resistant (IP65) or can be read in direct sunlight though. It would be the best for what I really need, and is inexpensive, but I may have to coat the circuit board for water protection and shield it somehow so it can be read.

I've also looked that the AEM Carbon displays. Their loggers are separate: https://www.aemelectronics.com/products ... h-Displays

And of course AIM has a very nice dash and logger: https://www.aim-sportline.com/en/produc ... /index.htm

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » May 29 2020 12:42am

Actually when racing I do not have time to look at my tablet at all. I have cycle analyst in my wheel and in straights i can see how many Ah I have used, but thats also not important anymore, because I know how many Ah i'm using per lap.
I have low voltage cutoff configured in sevcon and that is enough because i will never run my batterys empty. So there is very little possiblility that one cell will go very low.
Inside each battery I have dc/dc for 12V and 3pcs of zevas and olimex with 4 line lcd where i can see lowest/highest volt and temperature.
Olimex is also recording canbus data (battery voltages, and sevcon data) but i'm not using these because using my windows program log i multiple times easier :) Olimex is also capable of controling my elcon canbus charger and as i have in each battery charge port i can let one pack for charging when racing with another one.
In allmoust all Estonian kart tracks have 32A three phase power outlet that is ususally always not used. There is also regular 220V ones that gas karts are using with long extension cords. But i have made a three phase to 3x 220V extension cord for myself that i can use for charging my battery on site.

Usually i do not want to race with rain, but have raced with very light rain or wet tracks. My batterys are sealed for splashes but for heavy rain i do not want to use them. Also i have my motor air cooled (forced centrifugal fans) so that also do not like rain :)

As for vibration, right now all components are still working ok.
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 24 2020 11:26am

Tested lipo pack in kart track. Was not regular race but special event, only 3 laps + tire warmer lap.
But it seems that voltage drop was very minimal. 558A was max i got on that track (because of the obstacles) and with that voltage was 103,43V. At beginning of the race voltage was 114,51v but max amps was already at third lap so voltage drop was less than 10v.
And it seems that it accelerated also better with lipo than my small lifepo4 because of that little voltage drop.

Lipo battery practice.
https://youtu.be/-JImaewEbJo
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 24 2020 12:57pm

I used in practice 5,37Ah and in 1st race 6,44Ah, so together 11,81Ah. Battery should be 35Ah but when I tested one brick with 70A then usable was around 3,6Ah, that makes usable in whole battery 25,2Ah :)
And as cell voltage after 1st race were around 3,81v i tought that i let lipo be in storage voltage and use my lifepo4 packs in 2nd and 3rd race.
After 1st race whole pack voltage was 106,75v and before practice it was 115,19v. So 8,44v drop in 11,81 used Ah, that makes 0,715v drop with each Ah. And if we go from here then 25,2Ah usable is around 18v drop. So if I would used only my lipo in all races it would had 97V in resting, that makes 3,47v in cell level and considered 0% and empty. So voltage drop is not linear it seems.

I have to test it in kart track and make 10+2 laps in first try and see can i use it more that 10 laps race.
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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hallkbrdz   100 W

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Re: 30Ah 28s LiPo from 7s bricks

Post by hallkbrdz » Jun 24 2020 3:10pm

Ouch.

I had estimated (based on other tests of similar Lipo packs of that brand I found online) that the real capacity of those "5000mAh" bricks would be roughly 4500mAh under load. But 3600mAh, that really hurts at only 72% of advertised rating. At least now I've been able to update the spreadsheet and adjust the calculations some to be more accurate. :bigthumb:

So now it shows for my wimpy 100cc TAG final I'd need 4S8P (29.1kg) of those bricks. :confused:

I'm just jumping to test out the Zero NMC cells (Farasis / A123) to see how they handle the load. I'll try it with the full 7.2kWh pack first (heavy but easy), although I'll need to get something like you have on order to record the internal pack BMS outputs.

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Re: 30Ah 28s LiPo from 7s bricks

Post by john61ct » Jun 24 2020 11:11pm

Note that just because capacity at crazy high C-rates is much lower than rating, does not imply dishonest labeling, that might just be Peukert's Law in action.

Take a brand new pack, and do a precisely controlled timed CC load test at say 0.05C, if you get within 90-95% of rating, that's just how the industry rolls. . .

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Re: 30Ah 28s LiPo from 7s bricks

Post by hallkbrdz » Jun 25 2020 4:22am

For non hobby cells the capacity rating discharge usually seems to be 0.5C, and that's slightly conservative. Plus the large manufactures publish their own discharge charts showing various loads, something that LiPo pack companies don't seem to do. So I based what before I had on 3rd party tests.

A 0.5C discharge is not how we use these cells of course, so without testing data that matches our use case the best available test data is from those constant load charts. From that we can see the true starting voltage and capacity down to the voltage we want to stop at. Unfortunately the straight load discharge graphs don't seem to provide similar overall results from stretched out pulsed discharge loads. This seems to be a characteristic of at least this battery's LiPo chemistry. So with this information I think it is reasonable to make adjustments to set the expectations for similar products based on this type of cell. As more information becomes available this can of course be refined upward, or downward to closer match real results.

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 26 2020 3:49am

January 2019 I tested one of my 7s 5Ah brick with 70A
As you can see that after 3 minutes my duo 4010 stopped discharge because of cell voltage went under 3,5v under load.
I must admit that it was not charged to 4,2v but to 4,1v so there can be a little bit more inside :)
And as I said earlier I got 3600mAh out from the 5000mAh brick :(
DisCharging TURNIGY HEAVY DUTY 5000MAH 7S 60C.jpg
DisCharging TURNIGY HEAVY DUTY 5000MAH 7S 60C.jpg (138.16 KiB) Viewed 372 times
So one thing for sure is that I need to just run laps in the kart track to see how many i can get.
As i have remote live information available then it can be done with two people (one racing and another monitoring and speaking to the driver what parameters are).
Just have to find time to actually do it :)
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 13 2021 1:46pm

Even my lipos that should be very high C rated warmed up a lot after 14 laps of racing.
I have 7 of 5Ah packs in parallel so 35Ah in total and used ~32Ah from them during the race.
Temp sensors are between bricks so measuring outside temperature of 5Ah turningy heavy 7s brick.
2021_Temps_14Laps.jpg
2021_Temps_14Laps.jpg (130.98 KiB) Viewed 201 times
So I could imagine how 14x 21700 molicell in parallel (10C each = ~600A) will be event more hot after that race.
And this is the reason I did not went to 21700 (event I could get 56Ah bruto and around 45Ah usable)
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 27 2021 1:59pm

Concluded that 7pcs in paraleel (35Ah) is not enough for 14 laps, so will add one more in parallel.
But there is a problem, hobbyking does not have my 7s 5Ah Turningy heavy or in warehouse and ETA is september :(
So instead bought 56 pcs of 4Ah samsung 21700 and will build 4 pcs of 7s2p units instead.
I do not have monitoring during racing in these new addons (neither will they connected to lipo pack bms), they will be 8Ah and are in parallel with 5Ah lipo units. So they can't be run empty, only consern is that they will be to hot and not from the acceleration but between acceleration they will give energy back to lipo because they did not contribute to acceleration that much (have higher internal resistance). But I'm not very conserned as 2p will result in 70A so called continious and with ~35-40kw at 100v its ~400A devided by 8 will do 50A and even less because of higher resistance.
They should work and give me 2 more laps (actually lipos will not be so empty after 14 laps as without them)

But lets see, 21700 will arrive soon, and I can do a test.

BTW. I will charge these 21700 7s2p units separately from the lipo pack. Using my 4010duo icharger (2pcs of 7s units in one output and 2pcs of 7s units in second output) charging with 6A (can do faster if needed) should be at the same speed as charging my lipo 28s with 23A.
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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nuxland   100 W

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jun 28 2021 12:04pm

nuxland wrote:
Jun 26 2020 3:49am
January 2019 I tested one of my 7s 5Ah brick with 70A
As you can see that after 3 minutes my duo 4010 stopped discharge because of cell voltage went under 3,5v under load.
I must admit that it was not charged to 4,2v but to 4,1v so there can be a little bit more inside :)
And as I said earlier I got 3600mAh out from the 5000mAh brick :(
And real word test confirms that 3600mAh per brick is optimal usage if you want that your lipos last also.
In this graph I actually used 4400mAh per brick in race and it was too much. in cooldown lap voltages went below normal.
Attachments
Over_4428mAh.jpg
Over_4428mAh.jpg (146.06 KiB) Viewed 160 times
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by john61ct » Jun 29 2021 8:13am

aka "avoid the shoulders"

goes for the top one as well

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jul 02 2021 8:36am

1st 7s2p brick is done (heatwraping remaining). 3 more to go.
Regular nikkel and 0,2mm copper on top. Should be enough for 70A cells are capable of.
Attachments
7s2p_Copper.jpg
7s2p_Copper.jpg (243.28 KiB) Viewed 129 times
7s2p_21700.jpg
7s2p_21700.jpg (332.48 KiB) Viewed 129 times
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jul 05 2021 1:44pm

Zipped and weighted how much extra weight I have to carry.
7s2p_Weight.jpg
7s2p_Weight.jpg (194.05 KiB) Viewed 110 times
Also made myself 4 pcs of XT90 male<->male extensions to connect these to my lipo pack.
7s2p_Charging.jpg
7s2p_Charging.jpg (271.68 KiB) Viewed 110 times
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Jul 12 2021 10:43am

Installed 4pcs of extra 7s2p 21700-s and will test on wednesday at the track.
Will charge these to 4,2v each separately and also lipo back to 4,2v.
So connecting these xt90 connections is safe :)
Attachments
Installed_Extra_7s2p.jpg
Installed_Extra_7s2p.jpg (308.2 KiB) Viewed 89 times
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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Re: 30Ah 28s LiPo from 7s bricks

Post by nuxland » Aug 05 2021 12:47pm

Test went great and everything works as I thought it will work.
This extension gave me 2 more laps.


So charged lipos to ful 4,2v and 32,317Ah went in with 15A charging. That is around 4,616Ah per one brick (5Ah should be bruto).
Also charged 21700 to 4,2v and result was A=6,104Ah ja B=6,368Ah ja C=5,961Ah ja D=6,261Ah. So average 1500mAh was taken more from 21700 than from lipo bricks. And actually 21700 is bigger capacity (8Ah) and therefore gave energy back to lipos.

After charging to full I connected 21700 addon's to main pack and discharged with my 3kw resistor bank back to 3,850v.
Lipo discharge curve is a little bit different than liion's. I'm discharging with 25A so devide by 8 should be 3,125A per lipo brick and from 21700 addon.
But at first only 1,85A was taken from 21700, then after discharging 2,6Ah around 2,66A was taken from 21700. At 6,6Ah 5,82A then at 7,6Ah 6,46A.
At 8,9Ah 5,86A and at 14,88Ah it stabilised to 3,21A so evenly distributed among lipo bricks and 21700 addon.
Then I disconnected the load but still around 1,82A went from 21700 to lipos. It's simple there was voltage rise in 21700 but allmost none in lipos do the load going away.
Electric kart 60kw: viewtopic.php?f=34&t=68543
100v 35Ah LiPo battery: viewtopic.php?f=14&t=97763
100v 25Ah LiFePo4 battery: viewtopic.php?f=14&t=85912
Scooter battery: viewtopic.php?f=14&t=108227#p1582703

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