Battery Size Advice for new e-bike

[dicas]

I'm looking at building a e-bike for my commute (5 miles each way = 10miles / day) and the goal is to cut down cost to the essencial so that its cheaper to use the bike than paying for Bus and Tube here in London. (Please excuse me, but I'm not a Bike fanatic, just rather have the freedom to ride to the office and not spending the insane amount per month in crowded public transportation).

For the motor I was looking at a front wheel hub (to save on changes to the bike) - MagicPie II 26' already comes with controller and all gears so no big work or mods needed to end up with more expensive stuff.

For the Battery I was looking at getting Lipos from HK but I'm not sure on what to get. So I'm not a freak speed and in the middle of London trafic I don't think speed is a must. The course from Home to the office and back has no big climbs so I was looking at putting 6s x 2 to get 44.4V and my main problem is the capacity. My options are:

2x 6s with 5000mAh for 44.4 V with 5Ah (I don't think this would let me get much more than one way trip
2 x6s with 8000mAh for 44.4 V with 8Ah (could give me a litle more but not sure I would be able to come back home)

If this would be enough for now fine, if not I could consider 2x 6S series x2 parallel for 10Ah or 16Ah.

Any advices?

[Ykick]

When you wire 2qty 5Ah 6S bricks in series that's considered 12S1P for about 5Ah. You should at least go 12S2P for 10Ah to do your 10 miles. RC Lipo can deliver high C rates but that will change over time/use so 1P is not recommended except for very low power (true 200W) applications.

5Ah or 8Ah bricks, I'd say 12S2P minimum and 12S3P if you can afford 6qty RC Lipo bricks.

[SamTexas]

Any advices?

Not until you provide some additional info on how you intend to use your ebike.
1) Are you planning to be UK legal (250W and 25kph max)? Or are you going to ignore it? If so, what's your desired speed?
2) Are you planning to do some real pedaling? At least 30% from you, the rest from the motor. Or are you going to let the motor do all the work?

How much battery capacity you need depends on how you intend to use your ebike. 44.4V, 5Ah is more, much more than sufficient for your 10 miles range if you are UK legal and doing pedal assist.

[dicas]

Well, I know theres the 250w limit, not quite sure how its enforced, but if it is, not a big issue, as I said I'm not expecting to cycle at the speed of light.

I'm not too fond of pedalling, so what I had in mind was to see how I would do, if I find that pedeling as you say 30% is not a big effort in the morning when I'm not too fond of doing putting my legs to work.

So lets assume I don't want to go more than 25kph and that I would probably pedal like 10%

[SamTexas]

I'm not too fond of pedalling, so what I had in mind was to see how I would do, if I find that pedeling as you say 30% is not a big effort in the morning when I'm not too fond of doing putting my legs to work.

Trust me, the amount of work for 30% assist at 25kph is less than walking at 2mph.

So lets assume I don't want to go more than 25kph and that I would probably pedal like 10%

Good enough info for me.

For 10 miles range:
As I pointed out in earlier, 44.4V, 5Ah is more, much more than sufficient if you're UK legal and doing 30% assist.
44.4V, 5Ah is still more than sufficient for you at 25kph max at 10% assist. Heck, it's still sufficient for you at 25kph and no pedalling at all (0% assist).
The key here is speed. At max speed of 25kph, you don't need a lot power at all. And 222Wh (44.4 x 5) is more energy than you need to cover your 10 miles. I can give you numbers and calculation to backup my recommendation but I don't think you'd interested.

[jonescg]

If you are of reasonable health and aren't afraid of the rain, I would recommend you just ride a regular old pushbike. 5 miles is what, 8 km? Seriously, you could ride that in under 30 minutes. And even if you can't first up, you will be doing it in under 25 mins within a week.

Save your money and pedal man!

[dicas]

jonescg, thanks for the advise, I'm just to lazy... and from the cost I'm estimating its just ok to get the electric kit. But my plan is first get the bike and see how tired I get of riding one day. But even if its not to hard, I don't think that it would be too bad to have the motor for those days where I'm too lazy.

As for the rain, I don't mind it I used to drive my motorcycle all year so its ok.

So going from the feedback, I will try with the 12S on 5h or maybe 8h and if I see I need more I just need to get more pairs. So that was my initial assumption that maybe I could get away by not spending to much on the initial setup but have the ability to grow to more capacity say 10h or 16h with 12S2P.

Thank you all for the advises.

[dicas]

Just one thing I was looking is the C rate on the batterys as from what I've been reading and some calculations I wouldn't need more than 20C correct? But the 8000mAh batteries from Turnigy are nano with a rate of 25C to 50C not sure if its worth the diference in price.

[BikeFanatic]

I have a similar ten mile commute , I go about 25-30 KPH on my setup, I rarely pedal, and I get 4 AMP hour for the ten mile course. I do recommend you get the higher amp hour batteries however. I found the cheapest ones 12 series 5 amphrs
just run out of juice at the end, they get really stressed the last mile, and will eventually give you less and less range.

I recommend if you are going with just two bricks that you get the 5.8 amp hour size turnigy, or the 8 amphour size if you can afford it. then a 150 watt charger or two and you will be set. Charge every day and you batteries will last a while.

And it will be fun to go to work on the electric.

good luck

[dicas]

Thanks on the info. The Charger I already have from the RC and its able to charge 6S to a max of 6A, so considering I'm not in a hurry if I just charge the batterys at home, I believe it could do with a slow charge everyday.

The 8000ah are a litle to steep on price:

Turnigy 5000mAh 6S 20C Lipo Pack (DE Warehouse) - $66
Turnigy 5800mAh 6S 25C Lipo Pack (DE Warehouse) - $87
Turnigy nano-tech 6000mah 6S 25~50C Lipo Pack - $74.41 (I guess these would get custom taxes there not in Europe)
Turnigy nano-tech 8000mAh 6S 25~50C Lipo Pack -$108 (I guess these would get custom taxes there not in Europe)

The 8000ah are a litle high in price, considering that I could get taxes on top of that I believe that it would be cheaper to get 10ah with 2P of the 5A than just the 8A or get something in between with the 6A... not really sure what to get

[cwah]

What about buying with me an A123 pack from Victpower? I'm from london too the shipping cost could be greatly reduced.

[dicas]

I don't have a big knowledge about A123 cells, but since I already have the Lipo charger and used to the RC Lipo was my first choice. I believe that using A123 cells I need a new charger so the savings I may have on shipping would go to a new charger...

[Ykick]

I tend to lean towards 5Ah bricks because it's what I'm used to fitting inside bags and stuff but I suspect it's also produced in much higher numbers than 8Ah or those 5.8Ah bricks. No guarantee of better quality but I'll take high volume factory runs over low volume any day.

Another thing to consider is that we see 5Ah and throw that around like it's always gonna deliver that amount. In many cases they'll come really close to that at extreme LVC/HVC but with RC Lipo you really only count on 80% of label capacity. For added safety and longevity plan to use only about 60% on a regular daily basis. If you ride in cold weather then you need even more capacity to offset the losses that occur around freezing.

And finally, no battery has been invented yet that increases capacity as it's cycles and ages. Nope, my 2 year daily 5Ah RC Lipo bricks are now only good for about 3-3.5Ah as opposed to 4-4.5Ah when new. My personal choice for 12S2P 30A bike would be 6S 20C 5Ah Turnigy's.

[cwah]

A123 pack are cheaper than lipo now. They also can be discharged at full capacity and are hassle free for daily usage.

Furthermore, it has more than 1500 cycles and that's perfect for daily commute.

Your lipo is going to be expired in 2 years and you'll have to throw it away. It's a direct loss and you won't be able to sell it.
2 years later, your A123 pack will still be working and you can even sell it back at half price.

I also have the lipo charger (dual hyperion) + power supply. But as I'm cycling my pack every day I'm thinking about something more "long term" that has high life cycle and calendar life.

[dicas]

Well I believe that the best way to go would be to get 12S1P for starters and then get an aditional pair to get 12S2P. So from what you say 20C would be ok and at the cost of these 5A 20C I could always manage to get more pairs without a big investment.

[dicas]

cwah, so if I wanted to get a similar pack to the Lipos 12S1P and later on get an aditiona 12S1P to make 12S2P what would be the cost? Also what would be the estimate cost on a charger for them?

[Ykick]

Well I believe that the best way to go would be to get 12S1P for starters and then get an aditional pair to get 12S2P. So from what you say 20C would be ok and at the cost of these 5A 20C I could always manage to get more pairs without a big investment.

It can work building up a pack like that but just be very, very careful pushing RC Lipo to extreme capacity. In most examples, it doesn't turn out well. 2P would give you much more breathing room from "ifs" and errors.

[TylerDurden]

To calculate the required battery capacity (Watt hours (Wh)):

Determine how many watts you will draw for 25kph. (Use a calculator like this: http://www.kreuzotter.de/english/espeed.htm )

Multiply that number by how many hours you will travel (Wh).

The drive system will only be about 75% efficient so multiply the Wh by 1.25 ... That product is the battery capacity needed if you drain the battery 100%.

Multiply the result by 1.25 again to factor using only 75% battery capacity to avoid full discharge and prolong battery cycle-life.

25kph might use 150W-200W by my estimate. Hills/wind/cargo may require more power.

[dicas]

So the 150w to 200w fits in the availability of the 12S1P but I do think that that I will end up later on getting the second pack for 12S2P.

Well I believe that my option will be to go for 12S1P to start next month and then get the second pack . Also as stated previously by another member these Lipos allow me tho put them in a bag and take them to charge with a simple solution that costs around 15£ (already got a bag from amazon with a lovefilm voucher for free:) )

Besides if I do feel that the 12S1P is too small its not a big investment to go for another pair and I haven't thrown money. Also if I save in public transport what I'm spending each month its nothing to just get a new pack of batteries when these die up.

[cwah]

I'm at work now so I can't explain very much.

But I think that under 500W motor or 40 kph it's not really fun to commute.

For me I use 20wh/km, have peak at 2000W and 1000W continuous. Daily. That's a nice way to commute. I only have 10 km each way but I'm using around 350-400wh / day to commute. And I love commuting

ps: sometime I travel at 25 kph to save the battery, but that's plain boring and really not nice way to travel I think.

[dicas]

I get it, since I remenber on the days I was driving my motorcycle doing 60 or more km/h but honestly, at the moment the hub motor is not even more than 1000w so thats a limit. Also I honestly think that even at a slower speed is less borring than the bus:) I'm just looking at it as a step up so I don't need to peddle all the way to the office.

[cwah]

Ok, I understand. I tried many time the 25kph but it's really not for me. 40 kph is the right speed for me, especially when I'm commuting and that I just want to arrive work as fast as possible. I have a little 250W Direct drive motor I peak at 2000W lol.

So, just to answer your question if you ride conservatively, so around 25-30kph. You should use around 10-12wh/km. For a 10 miles commute, that's around 16km. So you need around 150-200wh/day to commute. Your lipo has to have at least 50% more capacity for maximum longevity, so a 300wh lipo would work fine for your commute.

Just remember that this setting wouldn't allow you to go out anywhere in london then go back home as you have just enough battery for a work-home journey.

I need to increase my battery capacity because I don't have enough battery to go out to meet my friends after work... without being out of battery. So even if I only use around 350-400Wh daily, I need the double for cases where I go out with my friends or any other occasion.



Now, let say you want to stick with your 300wh lipo. In HK europe, the lipo cost around 0.5-0.6$/wh. So a 300wh lipo would cost 200-250$ shipping cost included.

Now, let say you want a bigger pack, something like an A123 36V20AH (720wh). It would probably be around 450$. But you'll have 2.5 times the lipo capacity, you won't have any charge hassle with the balancing to care about, and you'll be able to sell it at half price in 2 years when we'll have better battery. So in total the battery would be half price.

And of course, you can push the motor to 1000W continuous without having to worry about the range or diminishing the cycle life of the battery.


That's my little crazy calculation. The price is so low for A123 that I'd like to try them

[999zip999]

Cwah why don't you let him try your bike ? The motor and controller is a big part in this match for range. Plus how about if buying from H.K. buy an extra brick rule. Have yoy tried a ebike. Go to a local store.

[lcyn]

I have the same distance commute, on mostly flat ground. I use a 350 geared hub, (E-Bikekit), and Turnigy Nano 8000Mah, 6s. (44v). I use 2-2.5 AH for the round trip, travelling at 19-20MPH. So the Nano 8000MAH should work well for you, with power to spare.

[cwah]

Yes of course, I can meet him so he can try my bike. It's my crazy little "power eater" (it's his nickname as he uses a lot of watts)


It benefits the compactness of a Brompton (really useful when it's raining so I can take the tube/bus with my bike to go back home) and can go almost as fast as a moped (50kph), althought I don't need more than 40kph on daily basis.

Dicas, just tell me if you want a trial of this bike. I'm close to central london