Cycle
Analyst

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The DrainBrain (CycleAnalyst) is a custom handlebar mounted amp-hour meter and wattmeter specifically for ebikes. This unit is a valuable accessory that's long been missing from most electric bike conversions. Not only does it serve as a 'fuel gauge', indicating how much of the battery pack has been used up, it also provides interesting feedback to the rider on their electrical energy consumption and can help diagnose problems that might be occurring with the battery.  Unlike most other amp-hour meters, this one saves the accumulated data when it is powered down. So you can turn off your bike, and turn it on at a later time and the amp-hours, watts hours, peak amps etc. will be unchanged. After the battery is recharged, you reset these statistics by holding the button down for just over a second.

Price:  $150.00
(45A continuous, 100A peak, Speedometer, Bare Wires)

Options:
Trailer Hitch Connectors (40A capable) ... $15.00
Anderson Power Pole Connectors (40A capable) ... $15.00

Description

There are two models available. One unit is designed to plug straight into any ebike that uses trailer-hitch connectors between the battery pack and controller with no additional wiring. Simply insert the moulded plastic shunt in between the battery cable and the controller cable. The second model has plain wire coming out of the shunt for those conversions that don't use the trailer connectors. A thin signal wire then extends to the display box which is clipped to the bike's handlebar.

Once plugged in, the unit powers up whenever the battery is turned on. A push-button on the side lets you toggle between the various display screens. If you press and hold the button for 1 second, then it will reset the amp-hours and watt-hours back to zero.









The main display indicates the instantaneous voltage, current, wattage, and accumulated amp-hours.










The current and wattage are both bidirectional, they go negative when you are regenerating and the amp-hour value can be seen to count down instead of up.











Press the button once and you will see some peak statistics from the trip, including the maximum and minimum amperage, as well as the minimum voltage of the battery. Battery packs that are not designed for high discharge rate will often show a substantial voltage sag at large current draws, and this screen is designed to help capture the extent of it and help you assess if the battery is up to snuff.

Details of the forward and regen current are shown on the next display. This one is pretty self-explanatory, as it simply shows the accumulated forwards and regen amp-hours to the nearest 0.0001 Ah. The Ah reading that you see on the main screen is the difference between the two. Even if your bicycle does not have an explicit regenerating controller, it will still regenerate whenever you are travelling fast enough that the back emf of the hub motor exceeds the battery pack voltage. With a 408 motor at 36V, this will begin to happen around 35 km/hr and a substantial amount of charge can be recovered while going downhill. With a 406 motor, you need to travel around 50 km/hr for noticeable regen.




Press the button once more and you will see even more useful trip information. The % Regen tells you by what percentage your range has increased to to regenerative currents flowing back in the battery. This is calculated as the regen amp-hours divided by the net (fwd - regen) amp hours.

The watt-hours tells you exactly how much energy has been taken out of the pack. In general, the total watt hours once you have drained the battery should be equal to the voltage of the battery times its capacity in amp-hours. However, the actual value will depend significantly on how loaded the pack is. As well, a 36V lithium pack will generally give more watt-hours than a NiMH or Nicad pack of the same capacity, because the average voltage during discharge is higher. Note also that this only records the watt-hours pulled out of the battery. Watt-hours does not decrease during regen even though the watts are negative, this was done deliberately.

Finally, the last display shows you how many total amp-hours have been extracted over the life of the battery and how many times it has been charged and discharged. Every time you reset the device, the forward amp-hours are added to the total amp-hours, and if more than 2 amp-hours were pulled then the number of cycles is incremented too. This information will be especially useful when the battery is at the end of its life, since you'll be able to look back and calculate exactly how many cycles and how much energy you pulled out of it. From there you can evaluate the battery economics, answer that age-old question of NiMH vs. lead acid, figure out your net cost/km, and provide useful battery information back to the ebike community.

When you do upgrade to a new pack, these values can be reset to zero by holding the button for 10 sec.

Specifications
This unit was designed with parameters that would be ideal for 24-72 Volt crystalyte or wilderness energy bicycle conversion kits using the standard 20 amp controllers. For other conversions, the 30 Amp model can be readily wired into place. Listed below are the display specs:

14.0 to 99.9V with 0.1V resolution
-40 to +40 amps peak with 0.1A resolution (continuous current of 20A max) for Trailer Hitch Model
-60 to +60 amps peak with 0.1A resolution (continuous current of 30A max) for model with inline wires
-4000 to +4000 watts, with 1 watt resolution
-99.9 to 99.9 amp-hours, with 0.01 Ahr resolution
0 to +2000 watt-hours, with 0.1 Whr resolution
0 to 99999 total battery amp-hours, with 0.1 Ahr resolution
0 to 65000 battery cycles
The meter draws 7mA of current from the battery pack to keep powered, which is 5-6 times less than the quiescent current of the controller. It can withstand up to 100V before suffering permanent damage. There is reverse polarity protection so if it is accidentally plugged in backwards, no harm will ensue.
 

The Speedometer Option:

The DrainBrain - Speedometer model finally brings all the stats an e-cyclists wants to know into a single unit. In addition to the battery information of the original DrainBrain, it also shows your speed, max speed, average speed, trip distance, total distance, trip time, and watt-hours per kilometre, the ultimate metric for measuring the 'mileage' of an ebike. Below are some samplings of a few of the different display screens that can be selected.

On power-up, the DrainBrain-S shows the four most important pieces of information you would want while riding. The electrical power in watts, the net amp-hours pulled from the battery, your instantaneous speed, and the trip distance. Both the distance and amp-hours have moving decimal points. Initially they show the 0.001 Ars and 0.001 kilometers, but will display up to 199.9 Ah and 199.9 km. How does it achieve a distance resolution of 1m when the typical bike tire is 2m around? The meter actually interpolates between the magnets passing the sensor. Not often do you really need to know the nearest meter, but its sure fun to watch the numbers fly up.

The watt-hours per kilometre is the key figure for estimating what your expected range will be for a given battery pack. It is calculated while taking into account the regen amp-hours put back into the battery and is not simply the net forward watt-hours divided by the total distance. The actual formula is as follows:

whrs/km = (fwd whrs)*(fwd Ahrs - Regen Ahrs)/(fwd Ahrs)/(distance)

This way it reflects as accurately as possible the net energy pulled from the battery pack over the total distance travelled. For bikes that don't do regen this is of no consequence, but for those that do it is nice that the meter does the calculation correctly.

The final additional screen shows the typical trip statistics, average and maximum speeds as well as total trip time in hours, meters, and seconds. Like most bicycle computers, the trip time stops incrementing when the wheel is not spinning. It records up to 18 hours.









At last, total odometer info was squeezed in with the total amp-hours and total battery cycles screen. Now when your thousand dollar battery pack is finally dead, you can scroll through and see just how many kilometres it got you. 10,000? 100,000? We can't wait for this real-world information to start trickling in.









By default, the units are programmed assuming a wheel circumference of 2075mm, typical for a 26" tire. This is readily changed by holding down the button when the meter is being powered up. The screen "Set Wheel Circumference" will appear, and by pressing the button the highlighted digit will scroll in circles from 0 to 9. Hold the button for one second to save and move on to the next digit. Once all digits are input, the new circumference is stored to memory and the meter resumes normal operation

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Copyright  © 2007 JV Bike Sales and Rentals Ltd.
Last modified: 14-Jul-2007