Affording a powerful battery

[sebastianzkerr]

Currently I am making a small, lightweight, sporty electric motorcycle, and am planning on using the 20kW cyclone hub motor. I'm aware that the 20kW is the peak power, but I still think it's a good choice for it's price. The only problem is the batteries; I'd like to make my own custom battery pack from 21700 Lithium-ion cells, but it seems to be pretty costly. Doing the math, for a 33S-5P pack, using the Samsung 30T cells (https://www.imrbatteries.com/samsung-30t-21700-3000mah-35a-battery/), the cost would be around $900 USD, which is kind of a lot... And even then, I only get 1.8kWh from it. For a 6kWh battery pack, which was sort of my goal, it would be damn near $3,000. Li-ion is my chemistry of choice due to the energy density, especially since I'm trying to keep this bike under 100kg if I can. Fitment isn't a big issue since I'm planning to create a custom carbon frame to keep the battery and controller tucked away and help weight balance. Inspiration comes from this: (http://novusbike.com/en/bike) but with a bit less radical of a design. So is there a better way to do this? A cheaper cell for my requirements (120V@170A)? Maybe a cheap pre-made battery that will work fine?

 

[flippy]

redo your calculations with the samsung 29E or the panasonic PF depending on what you can buy cheaper.
please forget any other size then 18650 if you care for your wallet.
a 6kWh battery with 18650 would set you back 1200~1500 euro just for the cells. add another 500~750 to that for nickel, cell holders, a spot welder and cables and a bms that would still net you under the 2000 in pure cost if you are going to do it all yourself.
the battery would weigh about 25ish KG depending on how much the casing is going to weigh.

 

[sebastianzkerr]

redo your calculations with the samsung 29E or the panasonic PF depending on what you can buy cheaper.
please forget any other size then 18650 if you care for your wallet.
a 6kWh battery with 18650 would set you back 1200~1500 euro just for the cells. add another 500~750 to that for nickel, cell holders, a spot welder and cables and a bms that would still net you under the 2000 in pure cost if you are going to do it all yourself.
the battery would weigh about 25ish KG depending on how much the casing is going to weigh.

With the Samsung 20S, I would need 198 cells (33S 6P) which I'm finding for just beneath $850. Only 1.4kWh for the pack, but I can probably accept that for the price. I'll keep looking though. Thanks for the advice about 18650s, I wanted to use them at first but for some reason determined the 21700 to have a better $/wH ratio.

 

[spinningmagnets]

You might consider Chevy Volt cells as an option, although there might be difficulties in finding them to buy, and then finding an acceptable way to assemble them.

 

[flat tire]

"Hey guys I'm on a budget so I'm going to build a battery in a way I've never done before that requires additional hardware I don't have and non-trivial setup cost. Oh and by the way, I'm going to choose a really stupid cell seemingly at random. But it costs too much! Help me afford a battery!"

Get more money, steal a battery, buy salvage EV cells, buy used battery from a member on here, or at least spend a little time finding canned cells that have decent $/KWH.

 

[flippy]

I'll keep looking though. Thanks for the advice about 18650s, I wanted to use them at first but for some reason determined the 21700 to have a better $/wH ratio.

the bigger cells actually have pretty poor $/Wh ratio once you get into the bigger batteries. and for a 6.5kWh battery you need 550~600ish cells, they are about 2 euro in bulk. it litteraly does not get cheaper then that.

 

[Dui ni shuo de dui]

If you want to use a 1.7KWh battery with a 20KW motor, you will have to take into account discharge rates.
I havent' looked at the specs of the cells you mentionned, but I'd be surprised if they can handle that much for long.
You have to take that into account in your decision, it's possible to do a short term money saving on your pack by downsizing it, but if you have to change it every six month because you roast the cells at gigantic C ratings it might add up pretty quick.

 

[flippy]

added issue is that a 1.7kWh battery means you will drain it in under 15 minutes on the highway. that is basically a 3~4C constent draw. shit will get hot yo.

i dont see how a pack like that does not kill itself in more then 6~8 monts at best.
you need at LEAST a 6~8kWh battery in order to get any decent lifespan out of it.

 

[sebastianzkerr]

"Hey guys I'm on a budget so I'm going to build a battery in a way I've never done before that requires additional hardware I don't have and non-trivial setup cost. Oh and by the way, I'm going to choose a really stupid cell seemingly at random. But it costs too much! Help me afford a battery!"

Get more money, steal a battery, buy salvage EV cells, buy used battery from a member on here, or at least spend a little time finding canned cells that have decent $/KWH.

The reason I chose the cell in the example is because of it's claimed ability to support a 35A continuous draw, meaning I'd need less of them in parallel to support my system (or more in parallel for a safer battery). As for additional hardware, cost isn't a big problem, it's just the fact that I'd rather not spend as much building a battery pack as I did building the rest of the bike.

 

[sebastianzkerr]

added issue is that a 1.7kWh battery means you will drain it in under 15 minutes on the highway. that is basically a 3~4C constent draw. shit will get hot yo.

i dont see how a pack like that does not kill itself in more then 6~8 monts at best.
you need at LEAST a 6~8kWh battery in order to get any decent lifespan out of it.

Good point, although for more range I'd like to have an "eco" setting that limits it to something like 72V and 50A or something, which would be a big improvement. Still not much though.

 

[flippy]

you cant "limit" the voltage. it does not work that way.
a battery cannot limit itself, you can only reduce the demand. that means capping the amps and limiting your top speed.

 

[billvon]

The reason I chose the cell in the example is because of it's claimed ability to support a 35A continuous draw, meaning I'd need less of them in parallel to support my system (or more in parallel for a safer battery). As for additional hardware, cost isn't a big problem, it's just the fact that I'd rather not spend as much building a battery pack as I did building the rest of the bike.

?? Often the battery is the most expensive part of ANY ebike project.

Fortunately you can spend whatever you like to get whatever performance you like.

 

[sebastianzkerr]

you cant "limit" the voltage. it does not work that way.
a battery cannot limit itself, you can only reduce the demand. that means capping the amps and limiting your top speed.

Sorry, I'm not very experienced.

 

[leffex]

Currently I am making a small, lightweight, sporty electric motorcycle, and am planning on using the 20kW cyclone hub motor. I'm aware that the 20kW is the peak power, but I still think it's a good choice for it's price. The only problem is the batteries; I'd like to make my own custom battery pack from 21700 Lithium-ion cells, but it seems to be pretty costly. Doing the math, for a 33S-5P pack, using the Samsung 30T cells (https://www.imrbatteries.com/samsung-30t-21700-3000mah-35a-battery/), the cost would be around $900 USD, which is kind of a lot... And even then, I only get 1.8kWh from it. For a 6kWh battery pack, which was sort of my goal, it would be damn near $3,000. Li-ion is my chemistry of choice due to the energy density, especially since I'm trying to keep this bike under 100kg if I can. Fitment isn't a big issue since I'm planning to create a custom carbon frame to keep the battery and controller tucked away and help weight balance. Inspiration comes from this: (http://novusbike.com/en/bike) but with a bit less radical of a design. So is there a better way to do this? A cheaper cell for my requirements (120V@170A)? Maybe a cheap pre-made battery that will work fine?

If you haven't done this before it will be hard for you to make something exactly as you describe. Have you build any ebike before this day?

I believe you can make the frame.
I believe you can connect motor and all the cables and connectors.
The hard part is the battery for you because there's no easy way to build a big battery, reliable and able to do what you want it to do easily. After that is making connections and deciding if it should have a bms and a battery that is capable and will work directly with your battery charger if you haven't thought about it yet.

You can make a battery almost for nothing but it may have some disadvantages like "more weight" being made from lower quality cells(cells who can't supply a lot of current, A) and so have to use more in parallel to make it viable.

Example battery: 90v, 58ah, 165a max load continuous. Samsung 29E's e6 about 1000$ and 5kw battery.

I have found and measured a few hundred used cells the last couple of months but they are not so good as I thought. When I tested the used cells they gave very little energy when used to maximum power capacity. It's like if I fueled my car and I could only go 50km/h with it and if I went higher than that my car would start to use 2 and 3x the amount of fuel. That happens if you use low quality cells in a battery. The lowest A rate for a 18650 I will use is a 10A capable cell. Like the one you found or Samsung 25R, 29E, 30Q or 35E, Panasonic 2900PF or LG MJ1. A Sony v5 cell or higher. Sanyo GA.

I am building a few battery and I will start making modules instead of a big piece, 5S 20P or 25p Panasonic PF bank. Size is about 30x17x7cm containing 100-125 cells. That is about 1kw battery block capable of 200-250 amps.

 

[inedible]

Nissan Leaf cells are great. They're the size of a stack of printer paper, so they don't fit well on ebikes, but for motorcycles and scooters they're great. You can often find people selling them for $100 each for ~64AH 7.4V modules. Ten of these gives you ~4800WH for a thousand bucks. They can provide 600A peak and 250A continuous, and they last 5000 cycles at 80% DoD. They're also a very forgiving chemistry, LiMn2O4, which stays in balance really well, and is quite safe. I used a pack for 3+ years without a BMS, and only balanced it a couple times, like once a year at most.

Best part about them is they're big self-contained units that can be bolted together with bus-bars. No soldering or spot welding or fiddling around with hundreds of cells. The most you'll need to do is cut some copper sheet into strips and drill two holes in them.

 

[flippy]

Yeah, until you dont put in the compression bars and plates and you burn your scooter down.
There have been several of these events in europe alone with cells from all kinds of sources