large battery pack for track bike

[laapmetot]

hi guys, new member, I'm doing research for a >200Hp electrical track bike and am reading here for a while. My plan is to use a 96S20P pack that is able to utilize the potental of 35 amps batteries like the Sony US18650VTC5A for short peak bursts. Things I'm struggling with at the moment:

- battery type. I like the aforementioned one as it can draw 20 amps until empty without overheating, and allows for 35A peaks. capacity is not up to some others like the panasonic ncr19650b found in tesla's but it seems that capacity and amps dont combine too good.
- serial connections. the nickel strips dont seem to cut it on much more then 10-15 amps although some claim it can be done when using more strips on top of eachother. Copper seems much better, but a pain to weld as I read it. I see some weldless packs that got me thinking: looking into that. Would also allow for safe and easy (dis)assembly
- As I would do 4x 15 min sessions at the track, I need to charge in between. Ideally <1 hour to be back at >80%. Probably gonna need a 400V DC fastcharger
- safety. I could make low voltage subassemblies and disconnect them to work on safely.
- heat buildup. Its a large pack, and if its continuously discharged/charged I probably overheat it halfway of the day. Thinking to add aluminium strips between batteries and leading that outside of the pack with heat sinks. That would interfere with connection strips though
- BMS: 96S BMS dont seem to be readily available. Maybe I can use several, but how to link up? Still looking for that, orionBMS seems a valid option

gonna post some first designs soon, feel free to already comment/criticize

 

[SlowCo]

Look at jonescg's threads, lots of info there:

https://endless-sphere.com/forums/viewtopic.php?f=31&t=38252

https://endless-sphere.com/forums/viewtopic.php?f=10&t=29916

And search Endless-Sphere for other battery builds.

 

[SlowCo]

Also a thread worth reading:

https://endless-sphere.com/forums/viewtopic.php?f=30&t=81074

 

[kdog]

hi
a few things..
are you going to be building this?
if so a 96s20p pack is going to be very complex and i would want quite a bit of experience building batteries before tackling something this big- esp for high drain situations.
The C rating of most batteries is ovverrated except maybe in perfect conditions( being in a vehicle isnt one of them)
At 20amp continuous discharge that sony cell will get really hot and die a premature death. Your expensive++ pack will be shot waaay to short a time, there are so many critical factors to consider, gettting one wrong could be expensive at best
not saying it cant be done (or that you cant do it), just dont underestimate the complexity/expense/ danger of this undertaking.
youll find lots of good info here on ES.

 

[laapmetot]

hi slowco, thanks for the links and kdog for you concern. Yes, its a massive pack at 400V unloaded and 700amps peak. One mistake and only a dentist will be able to identify the remains.
Indeed a lot of information here, and I'm also working together with the guys from Eindhoven university who recently completed a tour around the world in 80 days on their custom build electric motorcycle called "storm".https://www.storm-eindhoven.com/

For sure I will make smaller packs first to do tests, learn/try firsthand the do's and don'ts and make mistakes without (too much) damage. WHen building the bike I'll start with a (much) smaller pack just to figure stuff out before paying top dollar for a full pack which is not required to get started anyway. I'll just post as I go along and I'm happy to take advice from people who been there done that.

 

[SlowCo]

Ah, now I understand your username: laapmetot reversed = totempaal (Dutch for totem pole..)

In case you you didn't hear from Nkon yet:
https://www.nkon.nl/
A well known battery cell supplier from the Netherlands.

 

[SlowCo]

And read this thread about pack building:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=84412

Good luck and keep us updated on your progress.

 

[laapmetot]

Seems that for high current packs copper tabs are the way to go, apart from being a b*tch to weld except possibly that sunstone welder at high $$$$. Maybe this is an option for high current tabs? 0,3mm nickel soldered to 1mm copper and then spotweld the open area on to the cell.

 

[Ohbse]

Complex multi layer multi metal inter cell connections are not necessary. Simply using correct geometry with even and maximised inter-group surface area and multiple layers of pure nickel sheet reduces termination resistance to negligible levels compared with cell IR. 0.2mm large format sheet cut to the dimensions of your serial connections is easy to weld with very cost effective and reliable methods and can be stacked as much as required, even beyond 30a per cell if required. At your desired power level, there aren't many tracks that will allow you to run a >50% duty cycle at your power peak due to the speeds involved, as such you do not need to build your pack to 100% load levels of conductor area.

While there is considerable noise around the forums regarding exotic material spot welding, this is just not required to build a pack that can utilise the full power available from the latest generation 18650's. Pure nickel may become more expensive, however more complex and risky weldments significantly increase the chance of damaging an individual cell due to the energy levels required. Only a handful of damaged cells will easily eclipse the total cost of nickel termination.

Something like a Sony VTC or a Samsung 30q cell will easily be able to deliver the power peaks you require, potentially higher in the quantity you're describing. Note that there's no inherent reason to go to such a high voltage, you can achieve the same power output with a lower pack voltage and more current with a suitable motor winding. Controller choice can be a challenge, but worth considering avoiding the mega lethal voltage range if it's possible.

 

[Matador]

While there is considerable noise around the forums regarding exotic material spot welding, this is just not required to build a pack that can utilise the full power available from the latest generation 18650's. Pure nickel may become more expensive, however more complex and risky weldments significantly increase the chance of damaging an individual cell due to the energy levels required. Only a handful of damaged cells will easily eclipse the total cost of nickel termination.

Any good source for real pure nickel strips ???
All I can find is retailer/suppliers selling nickel-plated steel strips (very poor conductivity)... Some seller don't even know that they are not selling the real deal .

 

[hedsik]

You don't want to use 18650's for your project.
Use high discharge (60C) 5ah/6.5ah LiPo pouches put together with copper busbar by Chris Jones
He currently runs a 600volt race bike battery using this method and makes custom batteries for happy customers (myself included).

 

[liveforphysics]

Sadly, Sony stopped making the VTC-5's almost a year ago now, so what you find is likely counterfeit or old stock.

 

[jonescg]

Hi guys,

Yes it does sound to me like you will need pouch cells over 18650s. The pouch cell is the best compromise on power and energy density.

96s is 355 volts nominal, and 403 volts fully charged. These voltages are fine and safe if the battery has been built with physical and electrical isolation in mind. I have a 700 V battery on Voltron and it has never ever let me down (or touched me up!).

What kind of bike mass will you be shooting for? In all reality 6-12 kWh is about as big as you can get on a race bike, and by then you are very close to 240 kg total mass. If you went for 5 Ah pouch cells you could go for a 5p pack (8.8 kWh) or even 6p (10.6 kWh). This would have no difficulty delivering the crazy amps you seek.

Since you are in the Netherlands (I assume) I can't send cells or built packs to you, but I can provide kits so you can assemble it yourself. Happy to guide you on safe pack design and layout too.

Cheers,
Chris

 

[laapmetot]

very very interesting concept with the pouches, I kinda discarded that option as I didnt encounter any so far, but I'm very impressed by the Voltron bike! I see 600V-250amps sprints which equal to 200hp (at the controller?) so how does that thing not wheely?

I chose for relatively high voltages, as the P=I^2*R means that heat buildup in connectors/leads etc. goes up kwadratic, or the size does with raising amps and lowering voltage to get the same power. Just seems more efficient. If you want to play it really safe you would need to stay below 48 volts but the amps on that would be crazy, and leads the size of your arm.

I was aiming for a 14kWh pack that would equal 92 kg (96Sp20 = 1886 cells x 49 grams= 92kg and 1886cells x 3,3V x 2.250 = 14kWh) Including housing and stuff probably 100 kgs. If that keeps the whole bike at 220kgs I'm happy.

On my 180HP trackbike, I'm at 45% of the time full throttle on a lap on the track in Belgium I go to regularly.

For the controller I think this would be a nice option http://www.instructables.com/id/200kW-AC-Motor-Controller-for-Electric-Car/?ALLSTEPS#intro
For the motor I'm considering the 100kW continous/200kW max emrax engine

 

[jonescg]

About 175 kW to the rear wheel (230 hp). The motor and inverter is very efficient. High voltages are the easiest way to overcome I2R losses. Provided the motor is wound to take advantage of these voltages of course.

The manufacturer I use can produce a 6.5 Ah pouch cell which would work with the screw terminals. The cell is good for 10C continuous and 20 C bursts, but still has at least 180 Wh/kg. I think it's the best option for racing as it still has enough power while giving you enough energy to go the full race distance.

You will be doing very well to get a 14 kWh battery into a competitive race bike and have it weigh under 220 kg. We have a 6 kWh battery in Voltron and it tips the scales at 212 kg. You would need to go full carbon fibre to achieve these numbers I think. With these new 6.5 Ah pouches I think 12 kWh would weigh about 85 kg including enclosure.

 

[laapmetot]

just finished reading the whole post of the voltron, nice nice nice! What a roller coaster in more then one way.

Really appreciate your offer to help out Chris! To be honest I underestimated the stuff around the batteries like BMS, charging, switching, fuses and the likes. Conclusions for me so far:
- high voltage makes sense. 200V might sound safer but what's the difference between dead or really dead. Anyway will read up on safety and working requirements like materials, tools and procedures.
- engine: AFM140-4 is really large and heavy. emrax 268 comes in at half the weight/size which I really like. 200kW max: enough I think. They also used an emrax engine in the around the world tour of storm. Granted: no race application but still impressive.
- I found a charger that can charge to high voltages, that would eliminate some of the switches and controls to deal with 2 chargers. I believe its based on an open source design. https://emotorwerks.com/store-juice...-higher-voltage-batteries/category_pathway-17
- More voltage considerations:When I can use the 400VDC public chargers or 400V 3phase when DC is not available, that could charge a pack at 560 volts end of charge which also nicely matches the emrax medium voltage engine. It would also stay within the range of common available 600V parts making it a bit easier/cheaper, and within the IGBT range of the controller I'm looking at. So a 130S pack. Does that make sense?
- pouches over 18650: much higher amps, less coolings issues and definately easier to make a stack of them/swap them. I like it!
- BMS still an unknown, unfortunately in the voltron thread that remained largely unclear (chris, they seem of the shelf? Would you mind sharing more details?)
- cog: I will try to get the pack less high, probably more in the length direction of the bike. Will do some preliminary CAD
- power over agility. Maybe not the fastest in the end but definately my kind of fun! (Í'm 6.4 and 210 pounds so a low powered bike doesnt work on me anyway)

 

[laapmetot]

did order `10x 5000mAh 20C cells, they are in already. See pictures for test solution with screw-on tabs in 10S1P pack for 30-42V and 100amps. Building that now and then do some testing!

 

[laapmetot]

did some tests with charger and just 1 pack, basically a 1C charge and 1C discharge. what I noticed:
- battery is indeed exactly 5000mAh at 1C discharge
- pack gets hotter during discharge then charging, while amps are the same. I didnt expect that.

see pics for charger and graphs charging and discharging

 

[okashira]

did some tests with charger and just 1 pack, basically a 1C charge and 1C discharge. what I noticed:
- battery is indeed exactly 5000mAh at 1C discharge
- pack gets hotter during discharge then charging, while amps are the same. I didnt expect that.

see pics for charger and graphs charging and discharging

If you're extremely competent/careful or lucky the HK Lipo's can work great.
Otherwise id still run 18650's. 25r's 30q's, hg2's, he2's, etc.. can all meet your needs and offer much higher quality. (And safety!!)

It's totally possible to weld nickel and stack / reinforce with soldered copper to achieve 40A per cell burst capability.

 

[spinningmagnets]

The bonding of thick copper busses onto a nickel sub-plate is brilliant (IMHO). I believe that holds a lot of promise. We won't know until there are more experiments (I am no expert). I am in the middle of assembling one of the pocket spot-welders, so I can't try that out yet. If you are in a hurry, I'd recommend going that route, or...at least weld up a few cells to try out before committing the entire pack planning to that direction.

If I am reading that graphic correctly, the 1mm thick copper bus is about 60mm wide, so 60mm squared area of cross section, equal to 7.7mm squared, so equal to 8.5-ga round wire for the series connection?

700A peak across 20P is...35A per cell and each 8.5-ga bus? (of course normal running might be half of that, or less...)

 

[laapmetot]

what I found is that the 18650 cells that offer high capacity, dont actually deliver that on high currents. A 3000mAh cell that could do 10C, has only that 3000mAh at 0,2C-1C and at higher currents they suffer and end up with around 2500 mAh which equals the energy density of the pouches but without the advantage of much higher drain. And when using them all the time at 10C their lifetime/safety is also not that great. I'm thinking now to use 40C pouches and limit powerdrain at 20C peak to have a safety margin.

 

[laapmetot]

Been silent for a long time due to my company being extremely busy, but in the idle hours work has been done. I did make a 10S1P pack from 5000mAh cells/20C to play around. Also did make a 4kW resistor to test real life capacity, 1C charging and temperatures. That all looks quite wel actually and capacity is as expected a bit less then 5000mAh if you drain them fast but not too bad, around 4600mAh. temperature of the batteries remain below 50'C when discharging them at maximum and charge them at maximum repeatedly. Probably worse in a large pack though.

Also fun: you can actually weld with this pack
[youtube]j-TYV0pxH60[/youtube]

 

[Mugenski]

I really like that screw mount design for pouch tabs. I've never had much luck soldering them so something like this would be great it its reliable. Keep us updated!

 

[jonescg]

Great progress!

Looks like a solid termination system. Having metal on either side of the tab makes for a solid connection, but it does add weight and complexity.

I've since developed a quicker way to populate my PCBs with nuts on the underside of the PCBs, so I'll post that in the Sale thread soon.

Chris