This is a report on the range achieved for the first 9 charges of the 18Ah battery on my 3 speed Kalkhoff Agattu over my first 10 weeks of ownership. To save you reading all the details below, I get 40 miles on hills with max assist, and 80 miles on flattish terrain around 10-12 mph.
Because I had been concerned about reliably getting 30 miles range when the battery was a year or two old, and also when used on cold but not freezing winter mornings, I arranged for the bike to be supplied with the new 18Ah 25.2v Li-ion battery. I understand this battery is made for Derby Cycles by BMZ in Germany. I had quite a long wait for the new battery to become available. Eventually at the beginning of April, when I could wait no more, Tim of 50Cycles arranged for an 18Ah battery which had come in on one of the more upmarket Kalkhoff bikes to be put on my bottom of the range 3-speed Agattu, replacing the standard 8Ah one.
I have recorded each of the 9 charges so far, noting the time the battery went on charge and the time at which each of the 5 LEDs on the battery stopped flashing and became continuously illuminated. I have a mains power meter measuring the input to the battery charger. This showed that for the last 40 minutes or so before the charger cuts off and the battery is fully charged, the mains power ramps down from around 70-71 watts to 29 watts. I understand that the purpose of this final period of reduced charge rate at the end of a charge cycle is to achieve the maximum possible charge without reduction of the life of the battery.
The charge ups are shown in the following diagram.
The first charge from what I think must have been a deeply discharged state took just over 12 hours. Before charges no.3 and no.5 the bike was run until the low voltage cut-off operated. This means that in the preceding riding the total battery energy of 453.6 Wh had been used. (Note: the label on the battery says, "25.2V 453.6Wh," and this must have been calculated as follows 18 x 25.2 = 453.6 ).
I recorded the miles covered between each charge using a Garmin Etrex H. I also have also noted the assistance level setting and the type of terrain. Between charge nos 1 and 2, and between 8 and 9, I kept on maximum assist and rode rather hilly routes with gradients up to 5% in top gear and about 13% in bottom gear. The 84 miles before charge no.3 was all pretty flat typically 10-12 mph with occasional slopes up to about 2%. Most of 73 miles before charge no. 5 was similar with the exception of 10 miles on a sandy and hilly forest trail where I often had to switch to max assist, and sometimes had to push the bike when the bike sank into the sand.
Before charges nos. 2,4,6,7,8,9 the battery was not completely run down. One can judge roughly how far the battery had been discharged by working out the ratio of the charge up time to the 10.7 hours taken for charges no 3 and 5. For example charges no. 8 and 9 which took about 7.2 hours, are about 0.67 of the time for a full charge, so one can estimate roughly how far I could have ridden before reaching cut off by multiplying the actual distance by 1.5. Thus if I had continued to cut-off as I was riding before charge no. 8, I would have reached 54 x1.5 = 81 miles, and before charge no. 9, 27 x 1.5 = 40 miles.
So calculating the range to cut-off in the above manner, I get the following for my 8 periods of riding
43 miles - All in max assist. Repeated hills up to 13%
84 miles - All in min assist. Flattish gentle riding 10-12 mph.
73 miles - Mostly medium assist. Flattish but lots of stops and hard acceleration. Some fast ridng above power cutout
73 miles - About 10 miles on sandy , hilly trails with some use of max. Rest in min assist. Flattish gentle riding 10-12 mph.
72 miles - All in min assist. Flattish gentle riding 10-12 mph.
76 miles - All in min assist. Flattish gentle riding 10-12 mph.
80 miles - All in min assist. Flattish gentle riding 10-12 mph.
40 miles - All in max assist. Hills 5 to 13%, mostly very close to 14 mph, except for the hills steeper than 5%.
In summary, I do seem to get consistently around 80 miles when riding on flattish terrain at 10-12 mph and minimum assist. In maximum assist with steep hills and also sustained riding at 14 mph which is the point where the motor controller starts reducing power, I consistently get very slightly over 40 miles.
From these ranges we can calculate energy per mile from the battery:
80 miles for min assist converts to 5.6 Wh/mile, and
40 miles for max assist converts to 11.3 Wh/mile.
These are probably quite low figures for a "frail, elderly" 92 kg rider, but it is obviously an efficient bike, and I have been getting fitter over the 2 month period, since I am less tired now, even after last set of rides at around 14 mph. I note that 14 mph @11.3W/mile is an average power from the battery of 158 watts. Taking an overall efficiency of say 75%, that is 118 watts supplied to the tyre from the motor. Since I was in max assist there would have been an additional 59 watts from me. Making a total of 177 watts.
According to this Bicycle Speed (Velocity) And Power Calculator, I would expect that 177 watts into the tyre would drive me at 15 mph on a 0% gradient with no wind, or on a 1% gradient, often encountered even in flattish terrain round here, it would drive me at 12.5 mph. So the numbers do roughly make sense, but I wish we had access to a well calibrated dynamometer, as well as something to accurately measure my own power output. Then we could really evaluate and compare bikes' ranges under controlled conditions.
It will be interesting to take similar data in a year or two's time. This battery is supposed to have a life of 1100 charging cycles. At a rate of one charge per week that will take 21 years, however I am expecting the battery chemistry to go off long before then, and even if it does not, I doubt that I will be able to keep up such riding into my 90s!
Because I had been concerned about reliably getting 30 miles range when the battery was a year or two old, and also when used on cold but not freezing winter mornings, I arranged for the bike to be supplied with the new 18Ah 25.2v Li-ion battery. I understand this battery is made for Derby Cycles by BMZ in Germany. I had quite a long wait for the new battery to become available. Eventually at the beginning of April, when I could wait no more, Tim of 50Cycles arranged for an 18Ah battery which had come in on one of the more upmarket Kalkhoff bikes to be put on my bottom of the range 3-speed Agattu, replacing the standard 8Ah one.
I have recorded each of the 9 charges so far, noting the time the battery went on charge and the time at which each of the 5 LEDs on the battery stopped flashing and became continuously illuminated. I have a mains power meter measuring the input to the battery charger. This showed that for the last 40 minutes or so before the charger cuts off and the battery is fully charged, the mains power ramps down from around 70-71 watts to 29 watts. I understand that the purpose of this final period of reduced charge rate at the end of a charge cycle is to achieve the maximum possible charge without reduction of the life of the battery.
The charge ups are shown in the following diagram.
The first charge from what I think must have been a deeply discharged state took just over 12 hours. Before charges no.3 and no.5 the bike was run until the low voltage cut-off operated. This means that in the preceding riding the total battery energy of 453.6 Wh had been used. (Note: the label on the battery says, "25.2V 453.6Wh," and this must have been calculated as follows 18 x 25.2 = 453.6 ).
I recorded the miles covered between each charge using a Garmin Etrex H. I also have also noted the assistance level setting and the type of terrain. Between charge nos 1 and 2, and between 8 and 9, I kept on maximum assist and rode rather hilly routes with gradients up to 5% in top gear and about 13% in bottom gear. The 84 miles before charge no.3 was all pretty flat typically 10-12 mph with occasional slopes up to about 2%. Most of 73 miles before charge no. 5 was similar with the exception of 10 miles on a sandy and hilly forest trail where I often had to switch to max assist, and sometimes had to push the bike when the bike sank into the sand.
Before charges nos. 2,4,6,7,8,9 the battery was not completely run down. One can judge roughly how far the battery had been discharged by working out the ratio of the charge up time to the 10.7 hours taken for charges no 3 and 5. For example charges no. 8 and 9 which took about 7.2 hours, are about 0.67 of the time for a full charge, so one can estimate roughly how far I could have ridden before reaching cut off by multiplying the actual distance by 1.5. Thus if I had continued to cut-off as I was riding before charge no. 8, I would have reached 54 x1.5 = 81 miles, and before charge no. 9, 27 x 1.5 = 40 miles.
So calculating the range to cut-off in the above manner, I get the following for my 8 periods of riding
43 miles - All in max assist. Repeated hills up to 13%
84 miles - All in min assist. Flattish gentle riding 10-12 mph.
73 miles - Mostly medium assist. Flattish but lots of stops and hard acceleration. Some fast ridng above power cutout
73 miles - About 10 miles on sandy , hilly trails with some use of max. Rest in min assist. Flattish gentle riding 10-12 mph.
72 miles - All in min assist. Flattish gentle riding 10-12 mph.
76 miles - All in min assist. Flattish gentle riding 10-12 mph.
80 miles - All in min assist. Flattish gentle riding 10-12 mph.
40 miles - All in max assist. Hills 5 to 13%, mostly very close to 14 mph, except for the hills steeper than 5%.
In summary, I do seem to get consistently around 80 miles when riding on flattish terrain at 10-12 mph and minimum assist. In maximum assist with steep hills and also sustained riding at 14 mph which is the point where the motor controller starts reducing power, I consistently get very slightly over 40 miles.
From these ranges we can calculate energy per mile from the battery:
80 miles for min assist converts to 5.6 Wh/mile, and
40 miles for max assist converts to 11.3 Wh/mile.
These are probably quite low figures for a "frail, elderly" 92 kg rider, but it is obviously an efficient bike, and I have been getting fitter over the 2 month period, since I am less tired now, even after last set of rides at around 14 mph. I note that 14 mph @11.3W/mile is an average power from the battery of 158 watts. Taking an overall efficiency of say 75%, that is 118 watts supplied to the tyre from the motor. Since I was in max assist there would have been an additional 59 watts from me. Making a total of 177 watts.
According to this Bicycle Speed (Velocity) And Power Calculator, I would expect that 177 watts into the tyre would drive me at 15 mph on a 0% gradient with no wind, or on a 1% gradient, often encountered even in flattish terrain round here, it would drive me at 12.5 mph. So the numbers do roughly make sense, but I wish we had access to a well calibrated dynamometer, as well as something to accurately measure my own power output. Then we could really evaluate and compare bikes' ranges under controlled conditions.
It will be interesting to take similar data in a year or two's time. This battery is supposed to have a life of 1100 charging cycles. At a rate of one charge per week that will take 21 years, however I am expecting the battery chemistry to go off long before then, and even if it does not, I doubt that I will be able to keep up such riding into my 90s!
