This is the second in a series of technical articles covering some of e-bikes complexities in quite full detail so that all aspects of the subject can be appreciated.
It's impossible to accurately measure what electric current there is stored in a battery since they are chemical devices, the electricity existing in a different form as a change of chemical state.
Therefore, what these battery meters on our bikes do is use the fact that a battery voltage declines very slightly as it discharges. They check the voltage coming from the battery and register it's level on the LED lights. This isn't very accurate but gives a rough idea of the state of charge when a bike is standing still.
The problem comes when riding though. If the throttle is opened and the motor runs, it draws current and the voltage coming from the battery drops due to the increased load drain, and the LED lights reflect this drop in voltage. On a steep hill when the motor is working very hard, the drain of current is greatest, the voltage drop is also greatest, so the red or lowest light can come on.
The only way to measure the battery content on these meters when riding is if you shut the throttle and stop pedalling for a moment and then look at the meter, though it's still not precise then.
Some owners use the battery meter as an economy meter while riding, trying with careful throttle use to avoid the lights dropping and so get better range, but it's fiddly doing this. If this type of usage is intended, it's better to buy one of the rather expensive (£50 to £100) consumption meters like the "DrainBrain" (now known as the CycleAnalyst) or "WattsUp". These measure the current being used while riding and can assess what the battery had in it once all the current is used. It's then possible to predict with some accuracy in future the remaining content in a battery, and this type of meter is also very easy to use to monitor consumption as you ride, and thus keep it low to get the best range.
There's no economic case for using these though, since the minute saving in charge current which could be achieved by careful riding with one could mean it would take around 10 to 24 years to recover the cost of the consumption meter, so they have the status of executive toy for most users, good fun but of limited practical use. Bicycle testers and reviewers find them invaluable of course.
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It's impossible to accurately measure what electric current there is stored in a battery since they are chemical devices, the electricity existing in a different form as a change of chemical state.
Therefore, what these battery meters on our bikes do is use the fact that a battery voltage declines very slightly as it discharges. They check the voltage coming from the battery and register it's level on the LED lights. This isn't very accurate but gives a rough idea of the state of charge when a bike is standing still.
The problem comes when riding though. If the throttle is opened and the motor runs, it draws current and the voltage coming from the battery drops due to the increased load drain, and the LED lights reflect this drop in voltage. On a steep hill when the motor is working very hard, the drain of current is greatest, the voltage drop is also greatest, so the red or lowest light can come on.
The only way to measure the battery content on these meters when riding is if you shut the throttle and stop pedalling for a moment and then look at the meter, though it's still not precise then.
Some owners use the battery meter as an economy meter while riding, trying with careful throttle use to avoid the lights dropping and so get better range, but it's fiddly doing this. If this type of usage is intended, it's better to buy one of the rather expensive (£50 to £100) consumption meters like the "DrainBrain" (now known as the CycleAnalyst) or "WattsUp". These measure the current being used while riding and can assess what the battery had in it once all the current is used. It's then possible to predict with some accuracy in future the remaining content in a battery, and this type of meter is also very easy to use to monitor consumption as you ride, and thus keep it low to get the best range.
There's no economic case for using these though, since the minute saving in charge current which could be achieved by careful riding with one could mean it would take around 10 to 24 years to recover the cost of the consumption meter, so they have the status of executive toy for most users, good fun but of limited practical use. Bicycle testers and reviewers find them invaluable of course.
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