30Ah 28s LiPo from 7s bricks

[nuxland]

Everybody have suggested that I should use lipo-s in my kart. So now I have made a plan to build this battery.
And actually there is multiple goals to achieve when building this.
1. It should be lighter than my current ones.
2. I want to use this for my two controller+motor 1/4 mile test insted of two lifepo4 packs.
3. Not needing to cool pack between races

Right now plan is to get 24pcs of Turnigy Heavy Duty 5Ah 7s 60C bricks. And use them in configuration 4s6p, so total of 30Ah and 28s. I think these will provide me average 200A in 8 minutes with max 640A easy. And also like 1300A for 10 seconds when using two motors.
Bought one for testing and measurements, its 50mm x 60mm wide and 160mm height with wires. I would prefer that it had 8AWG wires instead of 10AWG ones. Case would be made of 3mm hobby plane plywood so that it has 24 slots for bricks 4 in width and 6 in length. And there will be additional 50mm in the side for wires and bms and fuse and dc/dc and olimex with lcd.
So total size will be like 268mm width and 381mm length and 180mm in height.
Weight will be like this, this is my estimate.
1. 24 bricks 0,91kg a pcs will be 21,84kg
2. harnesses with 20cm 8AWG cable to each brick and xt90 and crimps and lugs will be around 2,37kg
3. two anderson 350 (one for each controller) will be 0,5kg
4. 3pcs of zeva bms + olimex + fuse + lcd + dc/dc is aprox 0,7kg
5. balance cable harnesses around 0,5kg
6. plywood will be around 3kg
so together around 28,91kg, lets round it to 30kg YES it will be lighter than my 25Ah lifepo4 pack that is 37kg.

will add more info and drawings when they are ready.

 

[Upperfoot]

I definitely think LiPO is the best route for you for Power / Weight ratio

I know 10AWG can handle 100 amps continuously at 1 foot in length (Courtesy of Doctorbass)

[youtube]Y_z9eaq6Daw[/youtube]

And 150 amps for the XT90's !

[youtube]4rcCdCVBXAI[/youtube]

What setup are you going for? Two Gen 4 Size 6's in Master/Slave and two Zero 75-7 motors? Your becoming a speed fiend!

 

[jonescg]

Happy to help if you want some screw terminations and busbars etc
Too many XT90s makes me shudder.

 

[nuxland]

Made a mock-up from cardboard to see how all the stuff will fit
There will be two 350A anderson just for two motor setup
In regular races I will use only the back one (the one where there is also charger port).
Idea is that if I need to change one brick, then this can be done easily, just disconnect it and slide out
Top and side will be covered with plexiglass.

 

[nuxland]

Increased from 30Ah to 35Ah. So 28 Bricks together. Got aluminium and plywood water and laser cut.
In the process of threading aluminium and then starting to add bms and fuse and other stuff.
One brick is about 890g so 28pcs will be 27,44kg. I think it will be about the same weight as my A123 25Ah pack ~37kg.

 

[Upperfoot]

Nice one Nux! Can't wait to see your results, I bet you won't even notice the voltage drop when you put your foot down with this new pack!

 

[Bmr4life]

Any more pics of progress?

 

[nuxland]

Have not done anything from june, because have had zero time
But made balance wires for all the packs and started to do main outputs in may.

 

[nuxland]

Now two output 350A andersons are done.
Also zeva bms is in place and wired also dc/dc.
Olimex and LCD is still to be added.
And then I need to do all XT90 wires from bricks.

 

[nuxland]

Some progress

Making of harness:


Harness done and final weight:

 

[nuxland]

Weighted how heavy is battery box without batteries


Also did first voltage test with 4pcs of 7s bricks in series.
https://www.youtube.com/watch?v=rNIpTjdEGmw

 

[nuxland]

Did a first charge and discharge test yesterday.
[youtube]H8lBknp5E84[/youtube]
It seems i need to charge them again to 4,15V and then use my iCharger 4010 Duo to top balance each parallel 7s group to 4,2v.
When I thought it in my mind it did not looked so messy with the balance leads
Only reason I have built it with lipo bricks is so I could use these bricks somewhere else also.
But if it is good and working well I'm thinking of breaking up these 7s and configure them as 7p instead. And then use copper plates to put them in serial. I have 28 slots in my battery unit so it is doable

 

[hallkbrdz]

Following closely, as I've bit the bullet and are working out the details of a build. Your array looks pretty close to mine (I just have a little more capacity calculated in).

What do you think of the LiPo bricks so far? I read lots of good and bad about them, but have no experience with that formula. Weight wise they are about the same as 18650 Sony VTC5A cells, especially once I add in the buss bar weight. Space wise they are about twice as compact as cylindrical cells with spacing for cooling - which is a really good thing!

 

[john61ct]

I'm thinking of breaking up these 7s and configure them as 7p instead.

Wow I'd **really** like to learn how to do that properly. Links to any threads or videos?

 

[hallkbrdz]

Charging a large number of LiPo bricks seems to be a real ordeal compared to Li-ion. I'm looking at the 5200mAh 22v ones as the best match. Apparently they should not hold a full charge for long before use. Yet I have to charge 2 sets of 35 or so bricks before a race day at what, a half hour each (from storage voltage). With a quad charger like the Dynamite Prophet Sport Quad 100W, 70 charges will still take about 18 hours. So I'll need four of those running in parallel to get it down to a more reasonable 4 hours the evening before.

Hopefully I'm missing something here - or not?

 

[john61ct]

Parallel charging.

But better to just buy more chargers.

Do your balancing another time.

 

[nuxland]

I do plan to charge when arriving on track.
As i also have lifepo4 packs then i can charge them previous evening. And then use my 3kw elcon charger to charge lipo on racing track. As i have already balnced them and have zeva bms units inside pack i can easyli charge them all to 4,15v (this is my balance voltage in zeva) or when one cell goes to 4,2v.
And this is automatically done and i do not have to manually supervise them.

 

[nuxland]

Pack has now sat on balance voltages for a month.
in 23th of april voltages were min: 3,830 and max: 3,836 so difference 6mV
now today 24th of may there was min: 3,820 and max 3,826 difference still 6mV
But discharge was 0,01V or 10mV in 30 days. And this was bms that was taking this
So we can say that in 1 year it will go down 120mV or 0,12V and i have to balance it twice a year to maintain 3,8V

Will try to make a testrun next week to record some load data also.

 

[nuxland]

Made a quick test today, just one stright road and two accelerations.
But it behaved ok (just need to add 3 extra wires for measuring 2,3,4 bricks first cells, right now these showed lower than the rest).
So 102,25 Voltage with 615,38 Ampers will do 62922,605 Watts from the battery, biggest amount I have seen

 

[Upperfoot]

Very nice Nuxland! Looks like those LiPO's are doing the job nicely, 8kg lighter, 5AH more, while pushing out more amps.

Did you measure any temperatures?

 

[nuxland]

It is actually the same weight as my 2,5kw lifepo4 pack. My small lifepo4 pack has also had over 600A output. The voltage drop were yes a little bit higher in lifepo4 but then lifepo4 does not have voltage drop when it gets empty as does lipo.
Yes I measured tempereture in outside of the lipo but there was no rise in that short run. Attached picture showing their locations.
Four are measuring lipo packs and two are measuring output + and - connections.

I need to rewire some wires to zeva, because right now i got voltage drop on lipo brick first cells, that was not right.
And then program olimex and my windows program to show them correctly.

So i have to make these changes and then go to track to see real results. Right now I got reassurance that my design worked

 

[hallkbrdz]

Looking good!

 

[nuxland]

Changed my zeva measurements wires to eliminate false reading due voltage drop between pack interconnections.
And now I can measure what is voltage drop between my packs that are connected to 7x8AWG wires.
Actually lipo bricks have 10AWG wires itself

 

[john61ct]

Have you been happy with Zeva?

reliability, design for failure modes?

 

[nuxland]

Yes I'm. But zeva bms is not stand alone product. And for me it is just perfect because of that.
You need some kind of master communication unit, zeva bms just listens commands and outputs information through canbus.
Also it's balance current is very small, but it's not revelant for me.
I have 9 pcs of zeva modules. 3 are the first onese, 3 another ones are with improved wire connections. and 3 last ones have also new protocol that it measures by 1mV. Old models were measuring by 10mV
All my modules are working perfectly but i'm not using them that often either
First ones are 5 years old already.