Why are most kit batteries small?

[Dumsterdave]

What's the point of having a 48v 12 ah battery if you have a 1000w motor. Maybe im wrong, but dont you just multiply the two numbers (48*12=576) to get how much power you are putting out?. Does this mean that the 1000w motor is only operating at 576 watts instead of the 1000 watts? how does this affect the power? is it less or does it just have less range or both?

 

[docw009]

Watts is indeed volts x amps. Your error here is using 12 AH (amp-hours), which is the power capacity of the battery, not how many amps it can give you under load. That kit battery could probably deliver 20-30 amperes. It depends on the ability of your controller. So 20 amps delivered is around 1000 watts. A fully charged 48V li-ion 18650 type battery is more like 54 volts too.

I've always taken !2 AH to mean the battery capacity is around 20 amps for .6 hours, or 10 amps for 1.2 hours.

 

[Chalo]

You've got a stack of mistaken assumptions here. A 1000W kit is designed for a maximum continuous output of 1000W mechanical power. On one hand, that means your battery has to supply 1200 to 1500 watts of electrical power to accomplish that output; on the other hand, you won't run at full load plus full throttle very much of the time.

Having half an hour or so of full-power energy in your battery means you can ride for an hour to several hours, depending on how you spend it. It does not mean you only get to ride for half an hour.

The amp-hour capacity of a battery has little relation to its maximum power, except that like for like, bigger (more amp-hours) batteries generally offer more power. Switch to a different kind of battery, and the smaller battery could be a lot more powerful. And of course the controller or the motor could be the upper constraint on how much power your system can consume and produce.

 

[docw009]

True. Chalo. I've put this clamp-on ammeter onto my ebikes. I'm aware that Ebikes don't draw max current unless maybe one were to flog a motor up a hill or run at full throttle into a headwind.

In PAS mode, my BBS02 might draw 1-3 amps while pedaling along, and then only if the bike speed is below the limit programmed by the controller. That's 50-150 watts, about what a bike needs at low speed. Usually in PAS1 or PAS2, I am turning the crank faster than needed and the motor is just loafing and drawing little current. I haven't checked current draw at higher PAS speeds. Too hard to watch the meter. Maybe it takes a sustained 2-4 amps at 20 mph.

The current does spike toward 16 amps on my BBS02 if I use the throttle, but it drops quickly as the bike gains speed.
[attachment] attachment=0]ammeter.jpg[/attachment]

 

[spinningmagnets]

The battery packs are small to keep the price low, because so many customers are very price-sensitive.

The Amp-hours (Ah) are explained in the posts above. To achieve 1000W, a 48V battery would need to provide the current of roughly 21A (48 X 21 = 1008). A 10-Ah battery pack is likely using 2.5-Ah cells in a "four cells in parallel" (4P) configuration (4 X 2.5 = 10). If that is true, then you are trying to draw 20A from a 4P configuration, meaning 5A per cell in the parallel strings.

5A from a 2.5-mAh cell. Since many new customers are not aware of these things, or their importance, they shop by lowest price. They are then are disappointed when the lowest price battery (using cheap generic cells) does not provide the "awesome performance" they were promised.

A tiny battery pack made from high-quality and high-current cells can still have great performance, but...its small size still means short range.

 

[LewTwo]

... not mention that not everyone needs all that much power. I seem to be getting along fine with 36V and 6 Ahr (and of course it has the advantage of being a heck of lot lighter). Remember that old bit "different strokes for different folks."

 

[Chalo]

Not so long ago, many of us were using lead acid packs with less than 400 Wh hypothetical capacity and no more than 200Wh practical capacity. We may have longed for more, but we made do with what we had. To us, having more than 500 Wh of usable energy available in a small lightweight package represents the answer to our wishes-- less than half the weight we used to carry as batteries with well more than twice the range.

 

[Eskimo]

With a small pack seller can also make the best profit out of it.
To sell 12Ah/36V-pack with 600 euros is half crazy, but to sell 24Ah/36V-pack with 1200 euros would just make customers say no.
if you scale up those prices they are asking you end with totally mad figures with something like 30Ah/48V-pack when compared to lipo/DIY-solutions.
My (max) 40Ah/54V-lipopack would cost around 2500 euros using those branded factory bricks. It"s just nuts.

 

[amberwolf]

Besides cost, weight and size are also factors.

Efficiency of a system in stop-and-go city riding is affected by that. As one example, my (very heavy) SB Cruiser takes about 1-2wh/mile less with only one of my two ~25lb battery packs on it. I'd venture to guess that one pack is around a bit less than a tenth of the total weight.

 

[cycleops612]

Whatever. The point folks is, dont.

Treat the kit & battery as separate purchases.

They are not related, other than right voltage.

no need for same vendor.

Get pouch cell lifepo4

figure the max power output u would want

figure roughly how many hours at an averaged suitable power level would get you thru u day w/o pedaling, just in case. e.g. averaged out, if i can have a mean of 350w for an hour. That will get me thru that 500w hill for 10 mins + that 20 mins of 200w easy stuff + ... etc.

get 2 chargers?, pretty cheap? - maybe leave 1 at work, or a lighter weaker onboard travel job - dunno - i like having a spare

almost ignored it seems is that lifepo4 is indestructible~. expensive items and the others are fragile and tedious to store. lifepo4 is ok for 2k charges - forever, and u can store it any which way as long as u like i think. its a risk which should be factored in.

 

[dogman dan]

Plenty of flavors to choose from nowdays.

Now that I have been involved with selling this stuff for two years, I can say that very few of the people I talk to need more than 500 watt hours. Most only need about 350wh.

They aren't riding the speeds that the typical ES guy does, or using much more than 300w to cruise. 20 mph on a bike flat out scares them, and unlike me, they don't enjoy a good thrill on their ride. A 500 watt rated motor is all they need, but a controller rated to 750 -1000w is often appreciated because they are fat, and hills a steep. I consider myself overweight, with my homer simpson looking body. But at 180-190, apparently I'm way below the norm these days, which seems to be 240-280 for men.

People do ask a lot about the weight of it all, and can hardly believe the whole system is often 20-25 pounds, with a 10 ah lifepo4. So they do like a 30% lighter and smaller battery for sure.

 

[imagesinthewind]

So, is having a bigger motor and corresponding battery than you might need a bad thing other than the extra weight?

I went with 48v 1000w front hub with thick stainless torque arms and a 48v 20aH battery. Together about 25 extra pounds on my LWB recumbent. I could have gone smaller and lighter, but my research said that longer steeper hills would overheat a smaller motor quickly. I live in SW Denver. We dont have hills, we have foothills which are small mountains.

Even though I stay mostly to flatter areas, our 'hills' can be 6-7% grades and as you said, we are fat and hills are steep. I'm actually coming off a couple knee surgeries and cannot push as hard as I'd like on those hills. And recumbents aren't known for their climbing abilities. I will use both pedal assist and throttle when needed, saving throttle for those short steeps.

Did I get to too much? Will i regret it?

Ginny

 

[dogman dan]

I can't see having the range for a long ride when you live in Denver, as anything but plus plus plus.

In fact, you still don't have enough for a really nice ride, up those mountains.

Motor just right, battery can always get bigger on the weekend. You should be able to do 10 miles of 7 to 8% grade on that motor, with no damage to it, as long as you can pedal enough to keep your speed in the 14-15 mph ballpark for most of it. Shorter of course, if you can't. Slower is ok for short bits, like a switchback turn that's actually 15% for a hundred feet.

Budget for another 10 ah or more next year, then you will have 20 ah a year old, and 10 new, and at least 25 ah of actually usable power. Add another 10 in year three, figuring to replace the original one in 4 years.

This is what I do, trying to maintain at least 80 mile range potential each year, Just buy 10-15 ah each year.

Likely you have the right size for your knee this year, but next year, bet you want more.

 

[cycleops612]

I can't see having the range for a long ride when you live in Denver, as anything but plus plus plus.

In fact, you still don't have enough for a really nice ride, up those mountains.

Motor just right, battery can always get bigger on the weekend. You should be able to do 10 miles of 7 to 8% grade on that motor, with no damage to it, as long as you can pedal enough to keep your speed in the 14-15 mph ballpark for most of it. Shorter of course, if you can't. Slower is ok for short bits, like a switchback turn that's actually 15% for a hundred feet.

Budget for another 10 ah or more next year, then you will have 20 ah a year old, and 10 new, and at least 25 ah of actually usable power. Add another 10 in year three, figuring to replace the original one in 4 years.

This is what I do, trying to maintain at least 80 mile range potential each year, Just buy 10-15 ah each year.

Likely you have the right size for your knee this year, but next year, bet you want more.

I like your work dogman, but not so with the bike i have been trying to alert folk to.

its the frame integrated bofeili motor bike from longyeah. 24 gears says it all. Mone with 350w, will climb anything shy of a cliff in low low, and with a crap battery.

I started a thread on it - "~the worlds best unheard of ebike"

25/26 miles is 40km~

if he is content with a target normal of 25-30kph (as u suggest), allow 2-250watts for that normal & if achieved, its 75-90 minute trip, or ~320 watts used for the trip.

It bears remembering there are hills & there are hills. Climbs with a long steady descent after, are not entirely lost power. On the brakes during descent, is.

a 15ah lifepo4 5.5kg 36v is of course, 540 wh, or 20ah/720wh is about 7kg.

factory made ebike is, ex battery, 23kg & has a max load of 120kg

I am about to buy a 15ah for mine btw. part of my reasoning is you get a lot for little more than a 10ah.

I will simply find a way to strap it behind the seat post, as low and central as i can, & live with the wobble if any.

I would be very confident a sparingly used 48v 720w version of mine with 700wh of lifepo4 would do a great job of it.

&BTW, the integrated motor has excellent heat dissipation (48v is a plus for this also) in the form of the frame as a heatsink. Perfect for denver.

cold is an issue in denver. I wonder which chemistry is preferred?

It occurs to me, that given its importance, we should be prepared to live with the battery being 10% of GVM. What do you think dogmanDan? Some of your famed sagacious synthesis please.

what we do know, is he is asking a lot of an ebike, denver & 26m etc.

The single best thing he can do to stretch his limited power reserve, is to operate the motor in its preferred rev range, and thats precisely what this bike precisely does.