Best Li-ion cell model for ebike pack?

Batteries, Chargers, and Battery Management Systems.
Post Reply
cg_ebiker   10 mW

10 mW
Posts: 22
Joined: Mar 28 2020 11:58am

Best Li-ion cell model for ebike pack?

Post by cg_ebiker » May 12 2020 11:14am

Hi guys,

I am at the point in my 7kW ( :) ebike project where I'm starting to work on the battery. I have just bought a Malectrics spot welder. Originally I was going to buy LG HG2 cells for their capacity, dischard and price but I have look through a large range of options and also identified the Samsung 30Q and Molicell P42A as potential candidates. The Samsung 30Q cells are 18650 and the molidcells are 21700. It really comes down to whether it's better to have more 18650 cells to spread the load or fewer 21700 cells with lower risk of a cell being damaged? Any thoughts or suggestions for good cells. For reference I am NOT going down the lipo route.

999zip999   100 GW

100 GW
Posts: 9698
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Best Li-ion cell model for ebike pack?

Post by 999zip999 » May 12 2020 11:50am

All the info please . Bike or electric motorcycle ? Controller and motor ? This will help in giving good advice.

User avatar
amberwolf   100 GW

100 GW
Posts: 30787
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Best Li-ion cell model for ebike pack?

Post by amberwolf » May 12 2020 12:07pm

How big is your pack space?

What voltage will it be?

What is your peak current requirement? And how long does the peak have to last?

What is your sustained current requirement?



If you have the space, you might look into used large-format EV cells instead--they are much easier to assemble, with less interconnects (so potentially more reliable), and are designed for the loads you're likely to see, and are unlikely to cost any more.

Nisssan Leaf cells are easy enough to get, and if you are in the UK / Europe, you might check out jimbob01's new EIG cells in the for sale section. (I'm using the same type, but from another source, and old/used, and they work well for my heavy SB Cruiser trike).

bww129   100 mW

100 mW
Posts: 35
Joined: Apr 14 2020 7:44am
Location: Lancaster PA, USA

Re: Best Li-ion cell model for ebike pack?

Post by bww129 » May 12 2020 10:13pm

A guess would be that for 7kW you're probably looking at a 20S 74V 100A pack.

For the 30Q cells you'd want a 20S10P pack (conservative 10A per cell) or 20S7P minimum (maximum 14.3A per cell). 20S10P gets you 30Ah at 200*48g=9600g. 20S7P gets you 21Ah at 140*48g=6720g. That's 3.125Ah/kg for those 18650 cells.

For the P42A cells you'd want a 20S4P pack (very conservative 25A per cell) or 20S3P pack minimum (conservative 33.3A per cell). 20S4P gets you 16.8Ah at 80*67.8g=5424g. 20S3P gets you 12.6Ah at 60*67.8g=4068g. That's 3.097Ah/kg for those 21700 cells.

To get the same capacity as the 30Qs with the P42As you'd need 20S5P for 21Ah at 6780g which is just slightly heavier than the 20S7P 18650 pack.

As the other guys said, it really comes down to what's more important to you: current, capacity, volume, weight, price (you can figure that one out!), build complexity, etc. Note that the cell capacities are when discharged to 2.5V. Since almost nobody discharges the cells below 3.0V the actual capacity will be less than the manufacturer specified capacity.

cg_ebiker   10 mW

10 mW
Posts: 22
Joined: Mar 28 2020 11:58am

Re: Best Li-ion cell model for ebike pack?

Post by cg_ebiker » May 13 2020 5:32am

Thanks for the quick replies!

1. This is an electric moped using an 'enduro' frame (the common ones)

2. Sabvoton 72150 controller

3. Motor is the handicap here - rated at 4-5kW at 48V but manufacturer says it can handle 60V max with peaks up to 12kW.

4. This means at the moment my limit is 14s (51.2V) If I upgraded the motor down the line I could adjust the pack to suit.

5. The container designed to hold batteries is 32x19x12 cm but could potentially use most of the inner space of the frame which is about 40x20x10. I was thinking of putting the cells in the metal container for safety rather than having them in just the frame but that's not absolutely necessary.

5. I am rebuilding the bike on a new frame so have an idea of what the motor can do. I will probably be running it normally around 4kw continuous (80A ish) with a 'sport' mode which will give it the full 7-8kW (Full 150A). Hard to say for how long as I don't really know how much power will be required to reach a certain speed with the new controller but max 10s?

6.I've had a quick look at used EV cells but they seem to be over £500 for the voltage and capacity I would need as well as being used so would have more wear and less life. They also look very heavy for what they are. All together I think i might give this one a miss unless someone can persuade me otherwise!

7.For the 30Q cells i worked out I would build a 14s12p pack to give around 1.4kWh and 180A discharge. For the P42A I worked out a 14s7p pack for 1.5kWh and 210A discharge.

8.I am looking for a way under £400 that can give me the most capacity and discharge rate for future upgrades. Weight isn't too much of an issue as extra kg or two isn't going to massively affect the performance.

9. Wow this is getting long! My calculations are comparing it to my old bike which as bww129 pointed out never ran the cells to 2.5V.

Thanks for helping me out!

goatman   10 MW

10 MW
Posts: 2144
Joined: Jun 23 2019 6:50pm
Location: Surrey, B.C.

Re: Best Li-ion cell model for ebike pack?

Post by goatman » May 13 2020 6:52am

molicel seems to be a copy cat of Samsung. the P42a is like a 40t, the m50a is like a 50e. im waiting for molicel to return an email. if you go to ebike build thread. look for sinister r9 build. he has a build with molicel. I don't know the 30q equivalent off the top of my head
viewtopic.php?f=6&t=104047

80 amps continuous from 7p of 21700 is 11+amps/cell
heres the temp of a 40T continuous at 10 amps continuous
viewtopic.php?f=14&t=102682&hilit=40t+t ... 5#p1503088

cg_ebiker   10 mW

10 mW
Posts: 22
Joined: Mar 28 2020 11:58am

Re: Best Li-ion cell model for ebike pack?

Post by cg_ebiker » May 13 2020 7:52am

Thanks for pointing out the Samsung 40!. As you say it is basically identical apart from being 4000mAh instead of 4200. I'd probably trust it more than the molicel if they are a clone anyway. Same price as well. I'll look in to them a bit more

999zip999   100 GW

100 GW
Posts: 9698
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Best Li-ion cell model for ebike pack?

Post by 999zip999 » May 13 2020 8:52am

For the price and quality and U.K. I would go with these bolt together. I wanted to buy them but the shipping cost to us is more than the cells themselves. But you live in the UK I think he's in London.
viewtopic.php?f=31&t=102908

User avatar
amberwolf   100 GW

100 GW
Posts: 30787
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Best Li-ion cell model for ebike pack?

Post by amberwolf » May 13 2020 1:23pm

cg_ebiker wrote:
May 13 2020 5:32am
3. Motor is the handicap here - rated at 4-5kW at 48V but manufacturer says it can handle 60V max with peaks up to 12kW.
The motor can handle probably 200v or more. But it spins faster the more voltage it gets, so with a non-current/torque throttle controller, you get more speed with more throttle (approximately). So the thing is what speed you want out of it, vs the kV (RPM per volt) the motor has, vs the wheel size, and any gearing between the motor and the wheel, determines the voltage you would want to use.

The practical limit for motors is actually phase amps, not volts, (and not battery amps) as there is a point at which it causes more heating than torque.

6.I've had a quick look at used EV cells but they seem to be over £500 for the voltage and capacity I would need as well as being used so would have more wear and less life. They also look very heavy for what they are. All together I think i might give this one a miss unless someone can persuade me otherwise!
Cost: I don't know what used cells run these days. New EIG cells are £10 each (in groups of 50) from Jimbob01 over in the for sale section; mine are used from someone that changed to different cells, testing out different stuff, IIRC. So a 14s1p pack, 52v 20Ah, 1kwh, 100A capable *continuous* and 200A burst for 10 seconds, would cost only £140 for the cells (if bought in lots of 50--I'm sure he'd sell them in lower quantities but the cost might be higher--even so it's still cheap), and he has busbars to connect them that would be something like another £20ish. Double that cost for 2kWh and 200A continuous and 400A burst. The only catch would be shipping if you're not in the UK, it might double the cost of the battery. :(

Lifespan: EV cells may have a thousand or more cycles capability before significant degradation. 18650 may have a few hundred. Depends on the specific cell. The EIG cells I have on my trike were used when I got them years ago, how used I don't know, but they're still doing well--not new-well, but just fine for my purposes (about 4kw max right now). I'll find out soon if they perform as well at double the power level. The ones I used on CrazyBike2 were used twice as hard (at 1p vs 2p, same power levels), and still performing well by the time I started using them on SB Cruiser, years later (before I changed to the new set of used cells in 2p).

I haven't used the Leaf cells myself but reports seem to be similar.

Weight: IIRC my 14s2p "52v" 40Ah EIG pack weighs 35lbs; it's not in a container, just the cells and heavy brass busbars (which probably are a couple pounds or more; you could use regular wire and ring terminals instead but busbars make it easy). My 14s1p in a heavy steel ammocan is about 20lbs. IIRC the A123 20Ah pach I have, in an identical ammocan, weighs about 30lbs.

Generally EV cells will be lower internal resistance, meaning less voltage sag and less power wasted as heat inside the cells. I don't recall ever noticing a temperature difference in the cells between sitting at ambient for hours, and using them hard for a while, though I don't have a temperature sensor in there so it's all hand-tested.

Where the 18650 stuff generally has noticeable temperature changes. The one old Luna pack I have here is only 4p, and not very good cells, so it can't even run the trike, it would probably get hot enough to damage it, if not actually fail dramatically. The one time I did test it out on the trike on a much less powerful early version, it got very hot, almost 25F hotter than ambient, in a very short ride. So it's probably not the best example. I'd love to long-term test a better pack, that's big enough to handle the trike's demands, technically equal to the EIG 2p pack (200A/400A@10sec), and see the differences, but it's too much work to build one (welding it all up, etc) even if I had the cells here. ;)

I don't use a BMS, and the cells remain balanced throughout the discharge range, full to empty, any time I have manually checked them. Can't say that about the 18650 pack even when used at low loads--it requires the BMS to keep it balanced. :/

However, the main thing is that they are compact, low-resistance (and consistent properties between cells!), easy-to-connect (bolt together, for Leaf and EIG) cells. The last part is my favorite bit because everything else I have to do to build my stuff is hard enough, but I appreciate the rest of them too. ;)


Which type is a better fit for you depends on your needs, desires, budget, and DIY ability.

7.For the 30Q cells i worked out I would build a 14s12p pack to give around 1.4kWh and 180A discharge. For the P42A I worked out a 14s7p pack for 1.5kWh and 210A discharge.
Keep in mind that the harder you use the cells, the less capacity you will actually get out of them. While a cell may be rated for say, 10A and 3Ah, you wont' really get both of those at the same time. How much different it is depends on the cells' internal resistance, and thus how much of the power it puts out is wasted as heat. The discharge curve charts on various battery test threads and sites will help you figure that out--it's not just about the specification numbers. ;)


Note that most of this stuff doesn't matter for most bikes--it's the ones that need the high currents that make it harder to build a good battery for that is still small and affordable.

999zip999   100 GW

100 GW
Posts: 9698
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Best Li-ion cell model for ebike pack?

Post by 999zip999 » May 14 2020 4:06pm

A.W. Liked thoughts EIG cells bolt together 14s 10p of Samsung,30q cell is 700.00 usd plus parts 100.00 more for one battery. The 50 box gives you 3 -14s packs for cheaper.

Cephalotus   10 kW

10 kW
Posts: 729
Joined: Jun 18 2012 12:27pm

Re: Best Li-ion cell model for ebike pack?

Post by Cephalotus » May 15 2020 6:15am

Almost all lage battery packs built with those cells (edit: 30Q) have failed in the pedelecforum.de, as users have reported over here. There is no possibility to repair those packs, the cells fail one after one. Only very few people report no issues. Maybe this 30Q cell was never intended to be used in large cell packs, but only in small power tool battery packs.

Some say, that the 30Q is based on a very unusual chemistry.

It is said that also from LG HG2 there can be the occasional bad cell (1 out of 200? wild guess), but you can detect them from self discharging when storing them for a few weeks. The good cells stay good. LG HG2 is a Li-C/Si + NMC 811 cell.

Maybe the quality of the 30Q cells differs from different sources.

Your bet.
Last edited by Cephalotus on May 15 2020 8:27am, edited 1 time in total.

cg_ebiker   10 mW

10 mW
Posts: 22
Joined: Mar 28 2020 11:58am

Re: Best Li-ion cell model for ebike pack?

Post by cg_ebiker » May 15 2020 6:18am

The more I think about it, the more I'm leaning towards the c020 cells. They offer great energy density for the price and can easily be bolted together for easy maintenance or upgrades.If I was going to use li-ion, it would probably be the 40T but interesting to hear that some cells often fail in a large pack...

goatman   10 MW

10 MW
Posts: 2144
Joined: Jun 23 2019 6:50pm
Location: Surrey, B.C.

Re: Best Li-ion cell model for ebike pack?

Post by goatman » May 15 2020 8:38am

cg_ebiker wrote:
May 15 2020 6:18am
The more I think about it, the more I'm leaning towards the c020 cells. They offer great energy density for the price and can easily be bolted together for easy maintenance or upgrades.If I was going to use li-ion, it would probably be the 40T but interesting to hear that some cells often fail in a large pack...
my battery guy builds high discharge packs for a customer. the 30q would fail and they switched to 40t, no more problems for that customer, I did see the packs were 17s4p wich is what I run. his next shipment of 40T is already sold out before its even arrived. I like to buy local and Molicel has a wharehouse in Maple Ridge BC so that's why I was looking at the P42a

bww129   100 mW

100 mW
Posts: 35
Joined: Apr 14 2020 7:44am
Location: Lancaster PA, USA

Re: Best Li-ion cell model for ebike pack?

Post by bww129 » May 15 2020 3:36pm

Cephalotus wrote:
May 15 2020 6:15am
Some say, that the 30Q is based on a very unusual chemistry.

Maybe the quality of the 30Q cells differs from different sources.
The INR in INR18650-30Q means they're a Lithium Manganese Nickel chemistry. Is there any evidence that Samsung added something proprietary to make the chemistry "very unusual"? I'd be interesting in knowing this because I have a pack that uses 30Q cells.

Samsung is one of the better quality cell suppliers with facilities in different countries. Quality issues can happen but the better suppliers do testing and have quality checks in place to reduce the chance of bad cells leaving the factory.

john61ct   100 GW

100 GW
Posts: 6288
Joined: Dec 18 2018 2:06pm

Re: Best Li-ion cell model for ebike pack?

Post by john61ct » May 15 2020 3:52pm


bww129 wrote:The INR in INR18650-30Q means they're a Lithium Manganese Nickel chemistry.
Absolutely untrue, at least wrt to across all the major makers.

IMR, INR, and ICR are just part of manufacturer's model number prefixes, not actually designating chemistries. Yes they are **supposed** to designate particular chemistries for the manufacturers, but that turms out to mostly be marketing spin.

Are you saying you **know** that assertion is true within Samsung's lines?

Or is it just something you read from a source you trusted?

_____
And yes all the leading vendors are constantly doing R&D on both the chemical mixtures and the physical design / build specs.

That is how constant incremental improvements have taken place with such dramatic cumulative results over the past decade.

The reason 30Q cells now have such a bad rep is inconsistent QA, high failure rates of a certain percentage of cells even all within the same batch, apparently unpredictable.

Much better choices out there, including from Samsung, indeed a top maker in general.

bww129   100 mW

100 mW
Posts: 35
Joined: Apr 14 2020 7:44am
Location: Lancaster PA, USA

Re: Best Li-ion cell model for ebike pack?

Post by bww129 » May 15 2020 4:38pm

I had previously only seen the Samsung 30Q chemistry described as INR/NMC, which is typically Lithium Nickel Manganese Cobalt Oxide LiNiMnCoO2, according to various sources across the internet. I had not seen anyone disagreeing or saying otherwise, so you take what little info you can get, right?

After a fair amount of digging I found one document I hadn't seen before (which appears to be from Samsung SDI) that says the 30Q chemistry is NCA or Lithium Nickel Cobalt Aluminum Oxide LiNiCoAlO2 - https://eu.nkon.nl/sk/k/30q.pdf

It also has a whole bunch of other good information about the performance of the cell under various conditions.

john61ct   100 GW

100 GW
Posts: 6288
Joined: Dec 18 2018 2:06pm

Re: Best Li-ion cell model for ebike pack?

Post by john61ct » May 15 2020 7:06pm

Yes it seems NCA rather than NMC.

INR just being part of the full model number, not necessarily designating a specific chemistry.

Post Reply