A friend of mine recently bought an e-bike. Having been involved with golf carts for the last several years, I couldn’t help but be curious about the latest technology used in the e-bike industry, and to see how it compares to the golf cart industry. Even though an e-bike has only two wheels (some have three), where a golf cart has four (some of the older ones had three) they still have a strong “parallelism” in terms of running gear.
With my studies, I soon learned that one of the biggest concerns that bikers have is that of the “range” of the battery-operated motor’s assistance. I also learned quickly that there are several ways to “look” at that.
The first e-bikes were intended to only offer assistance to the rider while the rider was pedaling the bike. The controller of the system would monitor for pedal “activity” and would not offer any assistance if the rider stopped pedaling. That is what a “Class 1” e-bike is still required to meet the standard of. There is no throttle, and the controller is also programmed to shut off the assistance once a speed of 20 mph is reached. The biker (if he chooses to and is able) can exceed 20 mph with his pedaling, but with no assistance from the motor. This set-up allowed the rider to use the e-bike (in most jurisdictions) pretty much anywhere it was legal to ride a regular (non-motorized) bike.
Next came the “Class 2” e-bike. It allowed the rider to control the speed of the e-bike with a throttle (usually mounted on the handlebars or as a “twist” type handle grip) without pedaling at all, if they chose to. The controller still had to shut down any assistance at 20 mph, but just like the Class 1 e-bike, the rider could pedal the e-bike faster than that, but he was on his own. Most jurisdictions still consider the Class 2 “ridable” in most conventional bike riding situations, but not all. Local rules and regulations must be observed.
Next up is the “Class 3” e-bike. This type is NOT allowed to be ridden in a bunch of places that regular bikes can be ridden. That is because they can usually operate with assistance to the rider at speeds up to 28 mph (if the rider is also pedaling) or up to 20 mph hour without pedaling. The Class 3 machine may or may not have a throttle, once again, depending on local jurisdictions.
E-bikes have ratings that indicate the power that the motor can provide. Some common ratings are: 250 watts, 350 watts, 500 watts, and 750 watts. They also have ratings for the battery pack that give you some idea as to what kind of range to expect (if you understand how it works).
So, for the purposes of this article, I will choose an e-bike rather at random, give it some ratings, and go into the math a little bit to try to clear things up (at least a little) about what the range is based on.
For our example, I will use the e-bike that my friend bought. Its ratings are as follows:
350 watts for the motor, rated at 36 volts
10.0 amp hour (Ah) for the battery pack at 36 volts
It has 26 inch wheels
Whenever we talk about batteries, it’s important to understand how they are rated. There are more ways to rate a battery than just one. We often refer to a battery’s ampere-hour (Ah) rating. The Ah rating, in theory, says that that a battery such as a T-105 trojan (a lead-acid golf cart battery that weighs in at 62 pounds), which is rated at 225 Ah, could provide 1 amp into a load for 225 hours or could provide a 225 amp load for 1 hour (neither of which is probably true). As the amount of load placed on the battery is varied, the battery’s Ah performance varies quite a bit. The rating would be much closer to accurate toward the middle of its range, perhaps with a 60 amp load being sustained for around 4 hours, but at least the Ah rating gives us a “relative” number that can be used to compare it to other batteries. As a matter of fact, the T-105’s Ah rating of 225 is derived from testing it with a load that it can sustain for 20 hours. It is called the battery’s 20 hour Ah rating.
Another way that a battery is often rated is called its cold cranking amps (CCA). That rating system is more often referred to in the automotive industry, where we don’t care about the Ah rating at all. Once we get the car started, the alternator takes over to supply the car’s electrical needs as well as re-charge the battery. We only load the battery for a few seconds while the engine is starting. The CCA needs to be quite high, in order to do the work of starting the engine. For an automotive battery, a CCA rating of 350 to 600 is quite common, however it could only be sustained for a few seconds (that’s all that is needed).
So, let’s take a look at the e-bike situation. In our example, the motor says 350 watts. Watts is a rating of power that is derived when we multiply the voltage supplied by the current that is flowing in a circuit. In our case that means that if we multiplied the e-bike’s 36 volt source (battery) by whatever current it needed to supply to run the motor under a load, would come out to 350 watts.
We could express that as W (watts) = I (current in amps) X E (voltage in volts)
So, if we know the W and the E, we can calculate the I
I = W/E = 350 W/36 volts = 9.72 amps
That means that if you were to just forget all about the controller and the throttle and connect the motor directly to the battery pack, under the maximum load that it was rated for, it would draw 9.72 amps of current. Let’s call that 10 amps (close enough) and the math will be much simpler. So, we would expect to see our battery pack spin the motor with a reasonable load. But for how long? That’s where the Ah rating of the battery pack comes into play. The fact that it is amp HOURS (Ah) puts time in the equation. If it has an Ah rating of 10, and we have a load of 10 amps, then we should see the motor spin for about 1 hour.
Of course, that would not be an acceptable way use the motor on an e-bike. We don’t want to just go as fast as the e-bike can go for 1 hour, we want to control the speed to match the riding situation that we are in, and we want our battery pack to last a whole lot longer that just 1 hour. That is what the controller does for us. It “rations out” the energy that is available from the battery pack to assist the rider’s pedaling or even do all of the “pedaling” itself (through the motor). Once again, if the rider of a class 2 or some class 3 e-bikes doesn’t want to pedal at all, he can simply use the throttle to set the speed of the e-bike (up to a limit of 20 mph) and let the e-bike do all of the work. That, of course, makes the job of trying to assign a “range” to the e-bike all but impossible. The weight of the rider, the terrain, the speed to be sustained, the amount of time that the e-bike is told to assist and the amount of assistance that is selected all make a difference in when the battery pack just can’t help anymore.
In order to keep track of things, the controller has a lot of work to do. There is usually a “display” attached to the handlebars of the e-bike that shows the rider lots of information. It shows how much energy is available, how much is being used currently, the current speed, length of the ride so far in both time and miles. It also lets the rider tell the controller what level of assistance the rider desires. On my friend’s bike, he can pick any of 5 different levels of assistance. The controller then “rations out” the energy to the motor as a product of all of these things. So, it’s a constantly changing scenario for the e-bike’s system and for the rider.
Probably the best way to estimate the range of the e-bike is to use the SWAG system (we take a Scientific Wild A@@ Guess) at it. It’s always been my “go to” method when nothing else seemed to make sense.
Let’s start by redefining the amount of energy that the battery pack has in slightly different terms. We’ll use a term called Watt hours (Wh). It’s very easy to come up with. You simply multiply the voltage that the battery pack has in volts times the number of Ah that it is rated for. In our example we have a 36 volt battery pack rated at 10 Ah so, we have 360 Wh available from the pack.
Next is the more complex job of trying to put a number on the amount of energy that is being consumed under different sets of circumstances.
By far and away, the least demanding situation for the battery pack is when the rider is using the e-bike’s system purely to assist his peddling the of the e-bike. Here is where the “level of assistance” that I mentioned earlier gets important. As I said before, my friend’s bike has 5 different levels that it can be set at. So that becomes a variable as well as the terrain, the weight of the rider, etc.
I have studied bunches of documentation about the affect that things like the rider’s weight, terrain variables, speed, and the rider’s demand for assistance, and would like to offer just a few of my conclusions about the subject.
The best way to understand what is happening with the “supply and demand” game that is being played between the rider and his battery pack seems to me to be to take some typical circumstances and see how many Wh the e-bike is consuming each in one. In the following discussion of demand and range, I will be using “average” figures that I have compiled from reading “experts” opinions from literature that I could find and the information supplied by many internet bloggers in their write-ups. Since I don’t have an e-bike to test for myself, for now, I will just trust the opinions formed from their experiences. Perhaps I will be able to update and refine these findings a little later.
In the following examples, I have used data to calculate the range of an e-bike in various circumstances, but it is important to remember that I have used data that I found documented in various articles that were written by actual riders and testers. I DID NOT use the “estimated” range figures from e-bike SALES and MANUFACTURER documentation. We’ll do some comparisons with them later, but these, I believe are more reliable data to go by.
For now, let’s say we have a real light rider weighing in at only 125 lbs. riding on a trail with very few hills and only using the e-bike in the pedal assistance mode. Either the rider has a Class 1 bike that will only operate that way or he has a Class 2 but isn’t using the throttle (only being assisted while pedaling). This scenario would represent the minimum demand to the e-bike’s assistance system and it is estimated that the e-bike would be consuming only about 14.75 watt hours (Wh) per mile. So, if the e-bike had a battery pack rated at 36 volts (rather typical) and with 10 Ah capacity, to convert the supply to watt-hours (Wh), we would simply multiply the 36 volts by the 10 Ah and we would come up with 360 Wh. If our rider is using 14.75 Wh per mile, his range would be about 24.5 miles (360 / 14.75 = 24.407).
125 lb. rider, very flat surface, pedal assist only = 14.7 Wh/mile = range of about 24.5 miles We’ll call this “Circumstance A”
But now let’s say the rider gets a little more aggressive in his demands and actually rides the e-bike without pedaling using only the throttle for at least some short bursts. This is a more “typical” situation and is estimated to demand around 17.7 Wh/mile. Now the range drops down to 20.3 miles.
125 lb. rider, very flat surface, mixture of pedal assist and throttle operation = 17.7 Wh/mile = range of about 20.3 miles We’ll call this “Circumstance B”
But now let’s say that the rider is getting really tired and lets the throttle take over and stops pedaling all together. It is now estimated that demand goes up to around 19.7 Wh/mile, so the range drops down to 18.3 miles.
125 rider, very flat surface, all throttle operation = 19.7 Wh/mile = range of about 18.3 miles We’ll call this “Circumstance C”
Now remember, all three of these circumstances (A,B and C) are on flat land. We’ll get to the hills in just a little bit. And as you can see, the demand put on the battery pack by the level of assistance to the operator seriously affects the range.
Now let’s say our rider went totally off of his diet and jumped up to 250 lbs. It is speculated that his riding the e-bike under the same circumstances would result as follows:
Circumstance A Demand goes up from 14.7 Wh/mile to 23.5 so the range would go from 24.5 miles to 15.3 miles
Circumstance B Demand goes up from 17.7 Wh/mile to 26.5 so the range would go from 20.3 miles to 13.6 miles
Circumstance C Demand goes up from 19.7 Wh/mile to 28.5 so the range would go from 18.3 miles to 12.6 miles
So not only does the amount of assistance demanded make a big difference to the range of the ride (in terms of how much the e-bike’s system will help or take over), but the rider’s weight has a bunch to do with it also.
I won’t bore you will all of the data and the math, but if our rider selected a “hilly” terrain, the range for the assistance from the battery pack could fall to the following:
Circumstance A range of 18.1 for 125 lb. rider and range of 11.4 for 250 lb. rider
Circumstance B range of 15.1 for 125 lb. rider and range of 10.1 for 250 lb. rider
Circumstance C range of 11.4 for 125 lb. rider and range of 9.4 for 250 lb. rider
So, some of my conclusions would be as follows:
On flat land with pedal assistance only, for every increase of 25 lbs. of the rider, there seems to be about a 10% increase in the demand from the battery pack and, therefore about a 10% decrease in range.
In a more typical situation on flat land where the rider is using a mix of pedal only assistance and throttle operation, the range seems to go down closer to about 8% for each additional 25 lbs.
In a throttle only mode on flat land, with no pedaling, the range continues to drop about 7% for each additional 25 lbs.
In a hilly situation, the range falls off very quickly. It can go from around 18 miles with pedal assist only and a light rider (125lbs.) to as low as around 9 miles with a heavy rider using mostly throttle assistance (not much pedaling).
One thing that I was looking closely for, was any apparent significant increase in range with the 48 volt systems that could be attributable just to the fact that there was a 48 volt motor instead of the 36 volt motor. In theory, the 48 volt motor should be a bit more efficient. The motor of an e-bike uses wattage to supply its force. Since wattage is a product of voltage multiplied by current, a 48 volt motor can supply the same wattage as a 36 volt motor with less current flow. That reduces losses due to the resistance of the wiring, windings in the motor, etc. However, it seems that the major difference in range is mostly attributable to the fact that there is a higher capacity battery pack. The more powerful motors in the 48 volt systems provide much better performance, but the major change in range (according to my calculations) comes from the increased Wh available from the battery pack. Remember, the e-bike I used in the above examples was a 36 volt motor rated at 350 watts. Some of the 48 volt systems have motors as large as 750 watts. However, the more “power” you have available, the more you will use, so there goes any huge range increases.
So, I “ran the numbers” for several e-bikes that came with the 48 volt systems and it came out that the ranges increased a lot, but only due to the increased Wh available. If the Wh of the pack went up by 50%, the ranges under all of the circumstances we used in our examples seemed to go up at about the same rate. So, if you go for a 48 volt system that has about 50% more Wh’s, the range will go up about 50% also.
So, our example e-bike only had 360 Wh available (36volts X 10 Ah). If you compare that to the Wh available from a 48 system that has a 14 Ah battery pack, that’s 672 Wh available. That’s getting close to twice as much as in our example, so, of course, the range would be almost twice as far. Almost all of the e-bikes now have the multiple levels of pedal assist which help the rider conserve battery energy when it isn’t necessary also. The following are some randomly selected models that I looked up on the internet and some of their specifications and estimated ranges (I’ll avoid brand names and models). We’ll just call them “Sample A, Sample B, etc.
Sample A
This one has a 48 volt source and the battery pack was rated at 10 Ah (480 Wh). It didn’t get into “flat vs hilly” but did break things down based on the level of pedal assist that was selected:
Pedal Assist Range in miles
1 45
2 35
3 25
4 21
5 17
It also said that with throttle only, its range went down to 20 miles.
Sample B
This one listed a 48 volt source with a 14 Ah battery pack (672 Wh). It has 5 levels of assistance, but only makes a general statement of “estimated range of 28 to 50 miles”.
Sample C
This one boasted of a 48 volt source with a 17.5 Ah battery pack. Wow, that’s 840 Wh. I didn’t know they made them that big, but they sure do. They say that with pedal assist, the range should be around 60 miles and even with throttle only (no pedaling) a range of 35. That’s pretty amazing. Of course, it is a $1700 e-bike, so there ought to be something special about it.
Sample D
Just when I thought I’d seen it all, this one appeared with a 20 Ah battery pack for a total of 960 Wh, with an estimated range of 40 to 65 miles. They didn’t give any breakdown in terms of levels of assistance control and how that affected the range or any of that.
Anyway, I learned that e-bikes are REALLY getting popular and there are an amazing variety of them to choose from. Here in the little town of Okeechobee, Florida, where I am writing this from, we are starting to see e-bikes all over the place. Coming from a background in golf carts, it has been very interesting doing a little research about e-bikes. There are lots of parallelisms between the e-bikes and the electric golf carts. They both have battery packs, controllers and sensors that “tell” the controller what is going on and what is expected of it. They both have a range that they can travel before the Wh’s need to go back into the battery pack (re-charging). In doing this study, I learned a little about the range of the e-bikes and what affects them. I hope maybe you’ve learned a little with me, Ron.
For information about books written by Ron Staley about both electric and gas driven golf carts and their repair, visit the following links.
Electric Golf Cart Repair, both as an eBook and in Hardcopy:
Book: Ronald L Staley: 9780578560557: Amazon.com: Books
Gas Golf Cart Repair, both as an eBook and in Hardcopy:
Gas Golf Cart Repair Book: Ron Staley: 9798987911303: Amazon.com: Books