Low mileage on 48v 13Ah battery

K

kenvelu

New Member
HI everyone!

Just bought 48v 13Ah battery for my 48v 1000w ebike. The battery is of Chinese origin. According to a highly accepted math calculation the range that I am supposed to get, is 48 times 13 devided by 20 gives me 31miles which translates into almost 50km. In fact, I only get 20km,not even a half of an expected range.
Is that because my 13Ah battery is not strong enough for 1000w motor?
Is riding faster rather than slower decreases the range?
I mostly ride on trails,but the surface is very fine and flat ,so I doubt this causes such a drop in mileage.
My weight is 165lb.
Any thoughts?
 
If you have a display, see how much watts its pulling.

Your battery provides about (48*13) 624 watts.

My assumptions: On 48v motor, standard assist on my Radwagon roughly 408 watts.
That means I would drain it in about 624/408 = 1.5 hrs. With a 16 mph average speed, I could go 16*1.5 = 24 miles.
Say a 1000 watt motor provides 33% more assist at 542 watts. That's about 1.15 hours before its drained. That's still 18 miles.

If you had an 8.8 ah battery, then 12 miles would make more sense. (48*8.8/542*16avg) = 12.4 miles (20 km)
 
Your equation works for bike speeds around 16-18 mph. That divider of 20 more than doubles at 25 mph. Just pushing thru the wind costs a lot a of power. If you have to stop a lot, getting back up to speed also costs power.

Still, only 20Km, or 6 miles is very disappointing. How fast were you going?
 
The (48 * 13)/20 is a decent rule of thumb but there are many exceptions to it. That supposes that you are using 20 watts per mile, is what that is. It's easy to exceed that. I was pushing my bike kind of hard the other day and the watt meter said around 965 watts. I wasn't using that much for long, but think of the drain on the battery for that time! The battery was discharged more deeply by the time I got home than it usually would have been when using my normal effort.

Your weight and the riding surface shouldn't make a large difference (as you suspect), based on your description.

The faster you ride, the more current you draw, and that is the most likely culprit. For instance, on my bike, I can get about twice the distance by keeping my speed down around 25kph than if I ride at 40 kph. If you graphed the amount of current needed for the faster speed, it would be a curve that gets steeper as speed increases.

There are a number of factors at play; the most prominent is air resistance. Think of how much harder it is to ride a regular bike into a headwind of 30 kph than 15 kph. You don't pedal twice as hard, it's more like 3 or 4 times as hard.

Another is how we measure battery capacity. You can't use the whole 13 amp hours. You would damage the battery if you tried to. Even if you rode until the battery stopped working, you wouldn't have used 13 amp hours.

Still, there might be something wrong with your battery. Try cutting your speed in half and see how many km you get per charge. If you get much better distance, than you just have to decide whether distance or speed is more important. If not, then I hope whoever sold the battery stands behind it and will take care of you.

@harryS, you meant 20km/12.4 miles. Momentary lapse I reckon.
 
I normally go pretty fast at least 35-40 kph, hopefully going slower will give me much more range. I don't have a display on my bike,so no idea how many watts it draws.
Thanks everybody for reply!!!
 
Not hopefully, riding slower uses a lot less battery. You definitely won't be happy when it gets cold, battery life really drops in the cold! Are you using a phone to judge speed since you don't have a display?
 
harryS said:
Your equation works for bike speeds around 16-18 mph. That divider of 20 more than doubles at 25 mph. Just pushing thru the wind costs a lot a of power. If you have to stop a lot, getting back up to speed also costs power.

Still, only 20Km, or 6 miles is very disappointing. How fast were you going?
Click to expand...
I think 20kms is equal to more like 12 miles, but it's still not far is it?
 
kenvelu said:
I normally go pretty fast at least 35-40 kph, hopefully going slower will give me much more range. I don't have a display on my bike,so no idea how many watts it draws.
Thanks everybody for reply!!!
Click to expand...
Maybe I missed it, but curious to know how much pedaling you're adding?
 
Yes Dave, I did some bad mental math. 20 km is 12 miles, so kenvulu was burning about 40-50 wh/mile on his ride.

This makes sense to me. Those 1000W motor kits can reach 30mph pretty easily. At that speed, unless one has a road bike with high gearing, most riders cannot keep the pedals up with the bike speed, so it's all motor that is fighting the wind.

Here's a fun calculator on watts vs speed. It tells you the power needed depemds on the cube root of velocity,

https://www.gribble.org/cycling/power_v_speed.html

Here's an equally fun image that illustrates air resistance too.

lowraceryx7.jpg
 
harryS said:
Yes Dave, I did some bad mental math. 20 km is 12 miles, so kenvulu was burning about 40-50 wh/mile on his ride.

This makes sense to me. Those 1000W motor kits can reach 30mph pretty easily. At that speed, unless one has a road bike with high gearing, most riders cannot keep the pedals up with the bike speed, so it's all motor that is fighting the wind.

Here's a fun calculator on watts vs speed. It tells you the power needed depemds on the cube root of velocity,

https://www.gribble.org/cycling/power_v_speed.html

Here's an equally fun image that illustrates air resistance too.

View attachment 24918
Click to expand...
Thanks for the clarification Harry!
Interesting site too!
 
I recently purchased 48v 17ah battery from China for $400 including shipping. No custom duty. I did a test run this week, On a full charge, I was able to get only 35kms. I thought it would get me atleast 40 - 45kms. Unfortunately not the case. Yet, I am happy with the battery performance.

Ride weight - 200lbs
Bike weight - 60 lbs
Terrain - Flat road
Speed - 28kms
Assistance - Throttle (no pedal)
 
ramg1967 said:
I recently purchased 48v 17ah battery from China for $400 including shipping. No custom duty. I did a test run this week, On a full charge, I was able to get only 35kms. I thought it would get me atleast 40 - 45kms. Unfortunately not the case. Yet, I am happy with the battery performance.

Ride weight - 200lbs
Bike weight - 60 lbs
Terrain - Flat road
Speed - 28kms
Assistance - Throttle (no pedal)
Click to expand...
Without knowing the maker it’s imposs to judge . China sources can vastly overestimate their pack size and only deity know which cells they used... more info please!
 
The battery is called Silver Fish and nothing more at the site. Battery produced by Jentebattery.com. Nothing more, I can find or share about the battery.
 
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