Calculate approximate max distance

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Jun 11, 2018
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Is it possible to calculate my approximate max distance on a single charge if given the following.
Battery 48v nominal 54.6v full charge.
Travel 9.5km and battery dropped to 49.9v
So a total of a 4.7v drop for the 9.5km.

Battery is quoted as a 20ah battery. But not confirmed by me.
Thanks
 
chrisdeweyer said:
Battery 48v nominal 54.6v full charge.
Travel 9.5km and battery dropped to 49.9v
...
Battery is quoted as a 20ah battery.
(54.6V) / (4.2V/cell) = 13 cellGroups

Assuming this is a resting voltage:
(49.9V) / (13 cellGroups) = 3.84 V/cellGroup

Using CA3 SOC tables for Li-ion cells, this is about 61% SOC
9.5km/(100%-61%) = 24.4 km

EDIT - Oops - should have used discharge % - fixed above

State of Charge Tables as plotted in CA3 Unofficial Guide:


SOC-Curves.png
 
Given Tekletik's estimate of the state of charge, that means you are using 63.5 Wh/mi. So are you full throttle for this entire distance/time or what?
 
Max distance will depend how slow you go. If you can go 10 mph or less you will get an extremely long range.
 
wturber said:
Given Tekletik's estimate of the state of charge, that means you are using 63.5 Wh/mi. So are you full throttle for this entire distance/time or what?

Haha, yes. Except for when I had to stop 4 times. Then I was on full brakes.
 
Today I will do the same run, except I'll do it on reduced power to see the difference in power consumption
 
chrisdeweyer said:
Today I will do the same run, except I'll do it on reduced power to see the difference in power consumption

The difference should be fairly dramatic.
 
Must be some bike, or rider, to get 65wh/mi full speed. Heavy guy up a mountain?

In general, a rider can expect to use .75 ah per mile running 25-27 mph, full speed for typical 48v hub motor bikes. This estimate includes some reserve. 35 wh/mi is typical at full speed. That would mean 28 miles.

Lets make more assumptions. your battery will put out only 18 ah, so you should expect around 24 miles from that battery.

'If you are getting a lot less, then something is wrong, with your weight, with wind, or the battery is crap. If this is the first ride, the battery might not have gotten fully charged. Charge it, wait half an hour, ride around the block, then charge it. Repeat this about 6 times, and it will help all your cells get full.
 
So today's run had a final voltage of 52.5v
Power was set to a Max of 250watts or a top speed of 25km/h
 
dogman dan said:
Must be some bike, or rider, to get 65wh/mi full speed. Heavy guy up a mountain?

In general, a rider can expect to use .75 ah per mile running 25-27 mph, full speed for typical 48v hub motor bikes. This estimate includes some reserve. 35 wh/mi is typical at full speed. That would mean 28 miles.

Lets make more assumptions. your battery will put out only 18 ah, so you should expect around 24 miles from that battery.

'If you are getting a lot less, then something is wrong, with your weight, with wind, or the battery is crap. If this is the first ride, the battery might not have gotten fully charged. Charge it, wait half an hour, ride around the block, then charge it. Repeat this about 6 times, and it will help all your cells get full.

I was going 48km/h the whole time, except for about 6 stop and starts. I weigh about 85kg with clothes and bag on.
I'll do a longer run and see if the results change
 
chrisdeweyer said:
So today's run had a final voltage of 52.5v
Power was set to a Max of 250watts or a top speed of 25km/h

Can someone help me with the mathematics to calculate the approximate max range at the 250w setting..
It's a little past my comprehension at the moment.

Also, am I assuming correctly that when calculating range that one only goes to 60% SOC. To get maximum life of the battery.
Thanks
 
You can discharge your battery much deeper than 60%. That rule is for lead batteries. It does affect the battery to discharge deep enough for the bms to stop the discharge, but it affects lifespan less than you might think. Do avoid hard riding when the battery is on its last 10-15%, by then ride it home slow. But yes, a milder use patter helps lifespan, ideally you don't let the battery sit fully charged for long periods in summer, and planning to stop at about 20% left is good, simply because it gives you a reserve for bad weather.

What deep discharges do is throw the battery balance off, so that its likely the next charge does not completely fill all the cells. Again, to fix that, charge, wait half an hour, charge again till it holds its full charge after a half hour. Full will be less volts as the battery ages though. Even new, its not going to be what it theoretically would be for long. Repeat the charge to balance your pack if it drops more than a volt after a half hour.


What shortens lifespan on lithium batteries is very high rate discharges, and lots of time in hot enviroment when fully charged. If your battery gets more than just warm on the discharge, back off your throttle and ride with less watts. It will get very noticably warm normally, but if its at all hot, that is very bad. If its hot where you live, nothing you can do about that. I mean if your battery is getting to 150f, that is bad. If possible, charge full and then ride it immediately in summer when its hot. Some charge to 80% in the evening, then finish off the charge in the am when they ride. But all this might be impossible. Don't make your daily routine a huge pain in the ass. Just charge your bike and ride it, and if that means its in the afternoon heat charging outside, it just is what it is. You bought this to use it, and if you try too hard to save it, it just degrades anyway due to the normal enviroment of the world being warm.


When winter comes, do charge it full, and store it where it is cold, but not frozen. Charge it monthly when its cold. Don't charge a frozen battery though. Full and cold, not such a big deal. Full and hot, its slowly degrading.


To guess range, your wattage, say 250w x one hour riding = 250 watt hours. Theoretically you have 1000 wh. 48v x 20 ah is 1000 watt hours. I'm guessing you have 800-900 actual, usable wh. So you should have at least a three hour ride at 250w average.


Get a watt meter. The blue one on ebay is cheap, and it can greatly help you understand what your batteries real full capacity is in wh, and what your actual real world wh/km is at various speeds. Once you know your real capacity, you can calculate the average wh/km you need to make a certain distance. When I did my long distance riding, my magic number was 25 wh/mile. I was packing enough battery to make it across 70 miles of desert with no house with a plug, no water, nothing. So I would keep my average pegged at 25, and know I'd survive the ride. By the last 20 miles, I would know if I could finish the ride faster, or need to pedal harder.
 
Thanks for your input.
I will get a watt meter and use it.
I think the LCD screen that came with the controller is telling a load of bullocks when displaying watts. Eg. Set the controller to 10amp max and the display will say I'm using 360w. But I have a 48v battery.
Regards Chris
 
Depending on the ride, the motor may draw a lot less than that 10 amps at a given moment. It will draw the full power at startup, then pull less hard as the rpm increases.

But once you are cruising, if your display shows watts, it should be close to true for while you are cruising at that speed, at that slope, in that weather. You can then use that number to get a good idea what your wh/km should be, at cruise. Starts and stops, would then increase the wh/km, since each start would use the full 10 amps briefly. That full draw may be so brief that you never see that full wattage on the display. It might be averaging the watts over a few seconds perhaps.

lets say you are cruising at 360w, divide 360 by your battery voltage, which should average around 50v. That would put you at around 7 amps while cruising.
Also if you run one hour at 360w, you'd use 360 watt hours. if your speed was 25kph, then you are using about 14-15 wh/km.

The great thing here is you seem to have a watts display, rather than 5 bars or whatever . this will allow you to do some close enough calculations to figure out how many watts to aim for, to make a certain distance. With a bit of experience, you can then know when to pedal harder, or not, to make it home.
 
Go over to ebike.ca and check out their trip simulator. If you know what motor you will use, and its in the list that is, or you know the exact specs of it you can do it custom. Then at the bottom you can change the Input Type to "Google Maps" and lay out your route, and on the right side it should say "Net Battery Wh", that is how much the trip will use.
 
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