2kW battery suggestion

[harrisonh]

I'm looking for suggestions on batteries.
I currently have a 10s7p Panasonic NCR18650GA, 40A rated, downtube battery (from ebikes.ca)

My commute is 10 to 14 miles one-way. (25min - 40min) Elevation: Flat (less than 100m = 300ft of climbing either way)

Wants and current limitations:
1) 2kW-2.5kW continuous power ~= 40mph cruising
With 40A*36V, I get just under 1.5kW. I'd like to be able to keep up with cars (or keep cars from catching up from a previous intersection and having to pass me). Currently I get to about 30mph, but the speed limits around here are 40-45mph, so it's always a game of constantly looking back and moving over on the sidewalk as cars approach, or pissing off a few cars and feeling unsafe as they pass too close sometimes.
Sidewalks limit me to <15mph (few cars take notice of bikes since there are so few bicycle commuters, and it's also super bumpy and often frozen over with snow that people walked in). This makes my commute take up too much time and not enjoyable.

optional 2) Capacity to not need to charge at work. (1.5kWh to 2kWh?) I use about 500-650kWh currently one-way.
I currently charge at work and home, but taking the battery into work is not the most convenient.
This criteria seems a bit difficult, so could compromise.

To try to address (1), I upped my CA3 and Lebowski controller to 50A, hoping that 7A/cell would be manageable. But that only gets me to ~35mph. The battery also gets way too hot after 30 minutes. (goes up about 35C from starting temp)

Controller and motor seem to have no problems. I get about max 70C stator.

I thought about a few ways, and think options 1, 5, 6, or 7, might be the best. Would appreciate other suggestions and thoughts.

Option 1) Buy a small 72V high power pack.
https://ebikes.ca/shop/electric-bicycle-parts/batteries/b7208li-dt.html
Pros: Gets me requirement (1) easily. Bike will be light and fun to ride.
Cons: Give up on requirement (2). Won't work with my standard voltage (60V) Cycle Satiator, so will cost more. Present battery can't be used in conjunction.

Option 2) Series connect a similar capacity downtube battery.
https://ebikes.ca/shop/electric-bicycle-parts/batteries/b3620li-dt.html
Pros: Fulfills both requirements.
Cons: Would need to figure out where to store battery (pannier? backpack? under downtube?)
Since fulfills requirement 2, would be heavy and uncomfortable if have to put in pannier or backpack.

Option 3) Use Ligos
https://ebikes.ca/shop/electric-bicycle-parts/batteries/36v-ligo-battery.html
Use 7 Ligos in series to get similar result to option 2.
Pros: When my downtube battery reaches end of life, I can buy more Ligos and just use those for whatever power/capacity I need.
Can potentially change form factor to mount to bike more easily than option 2.
Very nifty. (can use as 3 in series as a travel-friendly 110V power source ?!)
Cons: Super expensive relative to other options.
Since fulfills requirement 2, would be heavy and uncomfortable if have to put in pannier or backpack. Easier

Option 4) Get Large-ish 14s battery
https://em3ev.com/shop/50v-14s6p-small-triangle-pack/
Pros: Would still require charging at work. Tidy.
Works with my standard voltage Cycle Satiator.
Cons: Present battery can't be used in conjunction.
Barely increases power capability, up by about 20%+ (20% more cells, but can also choose higher power cells)

Option 5) Make custom 10s7p series booster pack to fit in my triangle.
Pros: Gets me all my requirements. Neat.
Get a new project to play with. (had fun building the Lebowski Controller)
Cons: Heavy. Won't be able to complete for a while since I'm busy with school and work.

Option 6) Parallel packs instead of upping voltage. Change my 1mOhm (50A continuous rated) CA shunt.
Option 6a) Use a few Ligos in parallel
Option 6b) Make custom parallel booster pack to fit in my triangle.

Option 7) Do nothing. I've only used the pack 80 times (one-way trips). So it still has lots of life in it. Wait for a few years/decade for new tech.
Pros: cheap
Cons: I don't ride to work much due to my two criterias.

 

[amberwolf]

Some random thoughts below, that might be things you've already worked out or thought of, but just in case:

I currently have a 10s7p Panasonic NCR18650GA, 40A rated, downtube battery (from ebikes.ca)

I looked up the cells listed above, and they come up as 3.5Ah rating per cell, at complete dead to complete full. BMS limiting them means you probably only get about 3Ah per cell, at a guess. So that's 3 * 7 = 21Ah, or around 777wh total available in the pack.

I use about 500-650kWh currently one-way.
<snip>
My commute is 10 to 14 miles one-way. (25min - 40min) Elevation: Flat (less than 100m = 300ft of climbing either way)
<snip>
Currently I get to about 30mph,
<snip>
Sidewalks limit me to <15mph

With those present usages (assuming you mean Wh, not kWh), then you're probably seeing around 35-65wh/mile, depending on which combination of conditions you're getting what usage under.

That's fairly high, and it's going to get a lot worse at 40mph, so you won't need a battery that is just say, twice as big, but probably one that is up to four times as large as what you have now, just to have enough capacity for both ways, not counting what you need to handle the power needs. So at a guess, you could need about a 3kWh pack, worst case.

It could be worse or better, depending on how much of your present route is high speed vs low speed, and how much of your route will be at the 40mph vs the slower speeds. And how much stop-and-go you have, since accelerating a greater mass will take more power, too. Since you can monitor your wh/mile usage on various different-speed segments of your commute separately yourself, and take notes of them, then reset that CA stat for the next segment, and so on, you can get a clearer idea of how much really slow vs how much fast riding you get, and the actual wh/mile usage for each, to compare with what you'd use if you could do 40mph the whole way (or whatever).



Something else that may not bother you, but I'll point it out anyway, because some poeple don't think about this part. If you have, then just ignore this part and skip to the next stuff. It takes quite a bit more distance and/or more braking power and traction to stop from 40 than 30mph, and more mass means worse yet, and in winter conditions including snow it can be much worse. Your brakes might be good enough to lock up the wheel, but your tires might not be able to grip well enough to slow you quickly enough at the higher speeds. Non-smooth-roads at 40 vs 30 make a much worse ride on something not setup to take it, too, and a bump that's just bad at 30 can send you flying thru the air and/or break wheels/etc at 40.

1) 2kW-2.5kW continuous power ~= 40mph cruising

I haven't looked up the power usage for 40mph, so I'll use your 2.5kw number since that would probably work. For that, we'll assume you need higher voltage for the higher speed, too. If 36v gets you to 35mph already, then a 48v (13s) or 52v (14s) pack should get you to 40, motor-RPM-wise. So if you assume 52v, then 2500 / 52 is 48A. So whatever pack you use at 52v would need to be able to sustain 48A minimum.

Since the pack capacity might have to be around 3kWh, then 3000 / 52 = 58Ah. So you'd only be using the pack at less than 1C, and even an average-quality pack could handle that. (depending on the *peak* power needs)

The bad part is that a 3kWh pack (of any voltage) is probably going to weigh around 50lbs-ish. My EIG 2kWh pack (pouch cells) on SB Cruiser is around 38lbs, IIRC, and the size of a decent stack of trade paperback books. (52v 40Ah, 14s2p)

Option 1) Buy a small 72V high power pack.

If you don't mind the expense of a new charger, and inconvenience of having to charge at both ends of the trip, this is likely to be your "simplest" and "lightest" option, depending on how many Wh it will really take to do 40MPH for the worst-case distance of your trip (under the worst conditions you know you'll encounter, since a simple small headwind that wouldn't affect your usage much at lower speeds will make a much grearter difference at this speed).

Option 2) Series connect a similar capacity downtube battery.

Keep in mind if you series packs, the BMS FETs of each one have to be able to handle the *full series voltage* of *both packs*, because if one shuts off for any reason, that's the voltage that will be present across it's output FETs. If it cna't handle it, it's possible it will simply not turn back on the output again after recharge (or clearing whatever condition caused the shutoff), *or* that it will "silently fail", so that it leaves the FETs danaged in a way that is stuck *on*, and it won't be able to shut off the output at all, but you won't know that, and can then damage the cells themselves (running them down too low or too hot, etc). HOw likely either failure is, I couldn't say, but they are both possible in this case. (like if the Fets are only capable of 80v, but the full seriesed packs voltage or any potential regen voltage is up to 84v, etc).

Option 3) Use Ligos
https://ebikes.ca/shop/electric-bicycle-parts/batteries/36v-ligo-battery.html
Use 7 Ligos in series to get similar result to option 2.

I'm assuming you mean in parallel, since 7 in series would be around 250v. :lol:

While this is probalby the most expensive option, it's the most flexible...with the same caveat as option 2: all your packs' BMSs have to handle the full pack voltage if they switch off during use. You can add or subtract range / power / weight / size simply by adding or removing pairs of seriesed packs.

Option 4) Get Large-ish 14s battery
Barely increases power capability, up by about 20%+ (20% more cells, but can also choose higher power cells)

Keep in mind that generally, the higher power delivery a cell has, the lower it's capacity is. I don't know for the specific cells they use, so you'd have to ask them about that.

Option 5) Make custom 10s7p series booster pack to fit in my triangle.

Same requirement as option 2 about the BMSs.

Option 6) Parallel packs instead of upping voltage. Change my 1mOhm (50A continuous rated) CA shunt.

You can just parallel a second identical shunt, set the CA to 0.5mOhm, and change the CA to high range mode (youd' have to do the latter anyway, if the new shunt's resistance is low enough).

 

[harrisonh]

I apologize for all the typos, but you understood my intention for each of them

With those present usages (assuming you mean Wh, not kWh), then you're probably seeing around 35-65wh/mile, depending on which combination of conditions you're getting what usage under.

That's fairly high, and it's going to get a lot worse at 40mph, so you won't need a battery that is just say, twice as big, but probably one that is up to four times as large as what you have now, just to have enough capacity for both ways, not counting what you need to handle the power needs. So at a guess, you could need about a 3kWh pack, worst case.

It could be worse or better, depending on how much of your present route is high speed vs low speed, and how much of your route will be at the 40mph vs the slower speeds. And how much stop-and-go you have, since accelerating a greater mass will take more power, too. Since you can monitor your wh/mile usage on various different-speed segments of your commute separately yourself, and take notes of them, then reset that CA stat for the next segment, and so on, you can get a clearer idea of how much really slow vs how much fast riding you get, and the actual wh/mile usage for each, to compare with what you'd use if you could do 40mph the whole way (or whatever).

Thanks for all the tips.

For concrete power/capacity numbers:
I used 650Wh for 14 miles one-way at 30-35mph cruising at ~50A. 25mph average moving speed. Slight headwind.
Started at 42V, and hit 30V with voltage sag for the last minute or two.
So yes, at 40mph cruising, I'd likely need (40/35)^2 more capacity = 750Wh used. So I think I would need >1.1kWh battery capacity for just one-way.
https://www.strava.com/activities/4729787079

I never thought frame flex would be a problem. "It's just a hunk of metal, must be stiff and strong enough?" With 20lb in my panniers, and 8lb battery, I feel it squiggle . So a 30lb battery is definitely not gonna work unless I get a new bike :? But carrying this up my stairs is already a pita so....
I've decided keeping my battery capacity for 1-way trip is how I would go.

New criteria:
1.2kWh, 2.5kW battery

Also, I realized if I build my own small pack, besides paralleling, I can also make it a series pack, but lower voltage, like 6s7p.