gameofbikes
1 W
I am looking for a battery to pair with the BBS02 750W I'm about to order. I'm located in the US and my state allows this motor.
Use cases
Daily commute (~5mi each way). I live in a hilly area, with some of the hills being very steep. I also want to lug 2-3 bags of groceries home up a big hill. For the steepest hill, which my home happens to be on top of, I cannot pedal up the hill myself, I always have to walk the bike up. I'm moderately fit, and weigh 165lbs. Living on this hill is a big negative incentive for me getting out and about, because I always think about how grueling the trip home will be.
About 75% of my commute to school will be mostly flat, or mild 2% slopes. For those flatter portions I will probably use just enough assist to offset the extra weight of the ebike kit/battery/cargo, plus maybe a little extra oomph. So probably pedal assist setting in the 3-4 range (out of 9). I will always pedal at least at a moderate effort level.
Form Factor / Packaging:
I prefer something that mounts to the frame, like one of the bottle bracket mounted ones. I don't like the big triangle packs, I find they look ugly on the bike and they would be too awkward to carry around when I lock my bike up. Small rear saddle bags (the kind that hang off the back, just under the seat) would be good but I don't think they could carry enough battery, though I could be wrong about that.
Battery Tech / Safety
I'm new to the ebike world, but from what I see, people are buying lithium polymer cells from hobbyking and putting them in bags. I don't want to deal with anything that has a risk of burning down my home if I make a simple mistake, so I don't think those lippo's are for me. I store the bike in my living room, and I don't want something with exposed wires and stuff there. I also am on a limited budget (~$500, though even that much is more than I thought I would spend, but I think my previous budget was unrealistic). I will be in school for the next 3 years and would like the battery to last that entire time. So based on my desire for safety and long life, I think LiFePO4 would be suitable. Are there other suitable chemistries based on my needs?
I wouldn't mind something DIY, as long as the end result is safe, wires are hidden from sight, reliable, and lasts 2-3 years (~2,800 miles / year). Is there some DIY option that would be suitable for me with minimal risk of fire/explosion?
Battery Specs
Because I need the bike to be able to carry loads, and to carry those loads up hills, I want to be able to max out the motor, which means 48V, and at least 25A continuous discharge. High speeds aren't that important to me. My commute is about 4.7 miles each way, so I think a 9Ah might do the trick, but a little extra for longer trips would be welcome, so i'm looking for the range of 9-15Ah. I don't know how fast I go currently, but probably average, so I'm guessing 18-22mph would be a good target speed. What batteries would you suggest that fit all the above criteria?
I have done quite a bit of research already, so I'm not coming here empty handed:
I'm finding it quite hard to locate a downtube mounted battery that meets these specs. I've found some on aliexpress, but I don't know if the vendors are reliable. The thing that's extra infuriating about them is even if they have good vendor ratings, they often do things like have two different sets of specs on the same page that contradict each other, and sometimes both of those contradict info in the product listing title. That doesn't instill confidence, as I have no way of knowing what to expect.
I looked at e3mv's batteries based on Paul's reputation for high quality. I think the product info on his downtube batteries is outdated since it doesn't have any info about the 25R based batteries, and there is one part i find confusing. Does anyone know the rated discharge, and max continuous discharge of the various batteries on this page: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161 ?
And the part that confuses me is this:
Does this mean all the batteries have a discharge rate that is limited? Does he configure the BMS limited discharge rates different based on the cells? I emailed him about these two things using the "Contact Us" link on his site, but haven't gotten a response yet. Is there a better way to contact Paul?
Em3ev seems like the best option, but they are by far the most expensive. When you include shipping, em3ev batteries $/Ah cost is easily cost 2-3x more than most of what I find on aliexpress. I created an excel sheet with batteries, specs, urls, vendor reputation, Ah. $/Ah, Ah/kg, etc for tons of different places including conhismotors, em3ev, lots of different aliexpress vendors, and a few other retailers who are based in or ship to the USA. If anyone is interested in that sheet let me know and I'll send it over. Side note: I think it would be cool to see a public battery buying guide with that type of info, that ES members could update on a regular basis.
Update 2015-01-05:
Got a reply from Paul @em3ev:
Still seems like this battery shouldn't run up a steep hill for more than a few seconds, as the BMS is apparently rated for 20A.
Use cases
Daily commute (~5mi each way). I live in a hilly area, with some of the hills being very steep. I also want to lug 2-3 bags of groceries home up a big hill. For the steepest hill, which my home happens to be on top of, I cannot pedal up the hill myself, I always have to walk the bike up. I'm moderately fit, and weigh 165lbs. Living on this hill is a big negative incentive for me getting out and about, because I always think about how grueling the trip home will be.
About 75% of my commute to school will be mostly flat, or mild 2% slopes. For those flatter portions I will probably use just enough assist to offset the extra weight of the ebike kit/battery/cargo, plus maybe a little extra oomph. So probably pedal assist setting in the 3-4 range (out of 9). I will always pedal at least at a moderate effort level.
Form Factor / Packaging:
I prefer something that mounts to the frame, like one of the bottle bracket mounted ones. I don't like the big triangle packs, I find they look ugly on the bike and they would be too awkward to carry around when I lock my bike up. Small rear saddle bags (the kind that hang off the back, just under the seat) would be good but I don't think they could carry enough battery, though I could be wrong about that.
Battery Tech / Safety
I'm new to the ebike world, but from what I see, people are buying lithium polymer cells from hobbyking and putting them in bags. I don't want to deal with anything that has a risk of burning down my home if I make a simple mistake, so I don't think those lippo's are for me. I store the bike in my living room, and I don't want something with exposed wires and stuff there. I also am on a limited budget (~$500, though even that much is more than I thought I would spend, but I think my previous budget was unrealistic). I will be in school for the next 3 years and would like the battery to last that entire time. So based on my desire for safety and long life, I think LiFePO4 would be suitable. Are there other suitable chemistries based on my needs?
I wouldn't mind something DIY, as long as the end result is safe, wires are hidden from sight, reliable, and lasts 2-3 years (~2,800 miles / year). Is there some DIY option that would be suitable for me with minimal risk of fire/explosion?
Battery Specs
Because I need the bike to be able to carry loads, and to carry those loads up hills, I want to be able to max out the motor, which means 48V, and at least 25A continuous discharge. High speeds aren't that important to me. My commute is about 4.7 miles each way, so I think a 9Ah might do the trick, but a little extra for longer trips would be welcome, so i'm looking for the range of 9-15Ah. I don't know how fast I go currently, but probably average, so I'm guessing 18-22mph would be a good target speed. What batteries would you suggest that fit all the above criteria?
I have done quite a bit of research already, so I'm not coming here empty handed:
I'm finding it quite hard to locate a downtube mounted battery that meets these specs. I've found some on aliexpress, but I don't know if the vendors are reliable. The thing that's extra infuriating about them is even if they have good vendor ratings, they often do things like have two different sets of specs on the same page that contradict each other, and sometimes both of those contradict info in the product listing title. That doesn't instill confidence, as I have no way of knowing what to expect.
I looked at e3mv's batteries based on Paul's reputation for high quality. I think the product info on his downtube batteries is outdated since it doesn't have any info about the 25R based batteries, and there is one part i find confusing. Does anyone know the rated discharge, and max continuous discharge of the various batteries on this page: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161 ?
And the part that confuses me is this:
Discharge Current, recommended 20A continuous (BMS Limited, see following suggestions regardfing specific cell types).
Does this mean all the batteries have a discharge rate that is limited? Does he configure the BMS limited discharge rates different based on the cells? I emailed him about these two things using the "Contact Us" link on his site, but haven't gotten a response yet. Is there a better way to contact Paul?
Em3ev seems like the best option, but they are by far the most expensive. When you include shipping, em3ev batteries $/Ah cost is easily cost 2-3x more than most of what I find on aliexpress. I created an excel sheet with batteries, specs, urls, vendor reputation, Ah. $/Ah, Ah/kg, etc for tons of different places including conhismotors, em3ev, lots of different aliexpress vendors, and a few other retailers who are based in or ship to the USA. If anyone is interested in that sheet let me know and I'll send it over. Side note: I think it would be cool to see a public battery buying guide with that type of info, that ES members could update on a regular basis.
Update 2015-01-05:
Got a reply from Paul @em3ev:
The 25R cells are simply a high capacity and high power cell. It performs like the 20R, but has significantly greater capacity.
I have now added some additional info to the listing which mentions the 25R cells. I’ve copied this below. The BMS is the limiting factor in these packs when using the higher power 20 and 25R cells. The 20R or 25R cells are able to deliver 80A in a 4 parallel configuration, but the BMS is rated to just 20A continuous.
<snip>...
The high Power 20R and 25R packs can deliver 30A or more, but we recomemnd the continuous discharge rate is kept to 25A to avoid stressing the BMS.
Still seems like this battery shouldn't run up a steep hill for more than a few seconds, as the BMS is apparently rated for 20A.