Battery

The DF148 battery is manufactured by the Spanish company Amopack.  It has a recommended charge voltage of 58.8 volts and a maximum charge current of 12.5A.  It provides a very sophisticated diagnostic capability that's available to the end user via LEDs.  Cells are manufactured by Samsung and should be good for 500 charge cycles at 25° C. 

The following battery information was updated in January 2024.  Three batteries are presently available.  In all cases, energy capacity is rated at 58.8 volts.  Note that rating battery capacity hot off the charger yields the most favorable capacity values and is not representative of real-world conditions.

The standard 3.2 battery has a claimed capacity of 1882 Wh and is priced at $2,850.  This is the battery that comes with the 2023/2024 bikes.  There are 112 cells in this battery, so it's configured 14S8P.

The big 4.0 battery has a claimed capacity of 2352 Wh and is priced at $3,395.  There are also 112 cells in this battery, so again 14S8P.

The lightweight 3.0 battery has a claimed capacity of 1764 Wh.  It weighs 4.4 pounds less than the other standard battery and is priced at $3,395.  There are 84 high-performance cells, so a 14S6P configuration makes sense.

The battery's operating voltage range is 40 to 58.8 volts.  Below 50 volts, power output will decrease and performance will suffer.  At 40 volts, the battery will shut itself off to protect the cells.  Thus, discharge is allowed down to 2.85V / cell (which seems pretty low to me)

For the standard 3.2 battery, the maximum continuous discharge current is 80A.  Assuming 50 volts * 80A = 4kW = 5.3 horsepower.

Permissible “over-discharge” is as follows:

165A for 60 seconds, so 8.25 kW = 11 horsepower.

200A for 35 seconds, so 10 kW = 13.4 horsepower.

400A for 1.2 seconds (I doubt the controller is going to allow that).

Short-circuit detection and shutdown occur at a current of more than 500A for 400 microseconds.

Comparison with EM Race Battery

Both Electric Motion and Mecatecno rate the energy capacity at about 1.875 kWh.  During my capacity testing, I found them to behave very similarly (with EM having a slight advantage).  At the time of testing, the EM battery was less than a year old and the bike had seen about 50 hours of use.  The Dragonfly battery was about 18 months old and the bike had seen about 15 hours of use.  To learn more about my capacity testing method, refer the the EM ePure Race battery sub-page on this website.

Standard EM Race Battery

• Cell configuration: 14S12P

• Energy: 1610 Wh @ 10A constant draw down to 3.00V/cell

• Weight: 25 pounds

• Price: $4561 (US dollars)

• Life: Claimed 1000 charge cycles

• Advantages: Easier to connect charger, foolproof when connecting battery to system

• Recharge: Requires 175 minutes for a full charge

• Self-discharge: Negligible  

• Notes: Automatically charged to 58.86 volts

Standard 3.2 Dragonfly Battery

• Cell configuration: 14S8P

• Energy: 1547 Wh @ 10A constant draw down to 3.00V/cell

• Weight: 24.6 pounds (including fuse and cable to controller)

• Price: $2850 (US dollars)

• Life: Claimed 500 charge cycles

• Advantages: Easier to remove/replace battery, weight better distributed in bike, diagnostic display

• Recharge: Requires 190 minutes for a full charge

• Self-discharge: A loss of 0.1 volts per day considered normal

• Notes: Automatically charged to 59.0 volts

The “charged” voltages are measured external to the battery.  We don’t actually know what voltage the cells are experiencing.  The BMS and charging switch both have some internal resistance that will drop a bit of voltage.  If I had to guess, I might say the EM’s charge relay has a lower on-state resistance than the Dragonfly’s charge MOSFETs.  

I've been monitoring the self-discharged of the Dragonfly battery.  It's averaging a disappointing 0.1V per day.  At something under 52.4 volts, the battery put itself to sleep. (But this may be more related to days of inactivity than a specific voltage level.)   

The battery manual says the user can put the Dragonfly battery to sleep, but only if the voltage is below 50.4 volts.  The only way to get the battery out of sleep is to connect the charger.  This seems like it would be very inconvenient if something happens while out riding.

For comparison, last year my EM Race battery lost only a few tenths of a volt over winter and the EM 5.7 battery lost almost nothing.

Battery Alarms

The table below is adapted from Amopack's manual.  If you are familiar with the binary number system, it's easy to see that the alarm code is a 5-bit value with its least significant bit being represented by the 100% SoC LED.

This display is a huge benefit compared with EM's battery which tells the rider nothing.  However, I suspect this may be necessary partly because the Dragonfly's battery will be under greater stress than the EM's battery.  Only time will tell. 

We can also infer that modern solid-state devices (MOSFETs) are used in place of the charge and discharge relays employed by the EM battery.  MOSFETs are lighter than relays and have the potential to be more reliable (assuming they have been sized by engineers and not accountants). 

Battery Temporary Shutdown Procedure

The battery manufacturer calls this procedure “temporization” (which essentially means to introduce a delay into a process).

This procedure is necessary any time the battery is connected to the controller to avoid a large surge current and consequent arcing at the battery lead.

To temporarily shut down the battery, hold the battery “Test” button for at least six seconds and then release it. 

After a few seconds, the LEDs will start flashing in a particular sequence.  During the following minute, you may reconnect the power leads to the controller before the battery turns itself back on.

Presumably, when the battery restarts it does so initially in a current-limiting mode to facilitate a gentle pre-charge of the controller's capacitors.

Also note that if the battery voltage is less than 50.4V during the shutdown, the battery will go into sleep mode and will not restart automatically.  This would be ideal for storage.

Cell Packaging Estimate for 3.2 Battery

Excluding the bump for the BMS, the battery case has outside dimensions of approximately 490mm long x 120mm wide x 86mm tall.  See photo below.  Some volume is not available due to the diagonal corners.

Assuming the use of 21700 cells leaves ~8mm above and below each cell for container walls and interconnect space.

Plastic spacers for a rectangular array of 21700 cells typically have 23mm center-to-center spacing.  So 5 cells wide would be 115mm.  This seems reasonable.

But 23 cells in  the long axis is 529mm, which exceeds the length of the enclosure.  It is also totals 115 cells (3 more than Mecatechno says the battery uses).

So I think it’s likely the cells are packaged in a honeycomb rather than a side-by-side array.

Output / Input Efficiency

As part of battery charge and discharge testing, I kept track of the total energy extracted from the battery (down to 3.00 volts per cell) and how much energy it then took to recharge.  

The 3.2 Dragonfly battery delivered 1610 Wh at a constant 10A draw.  It then took 1652 Wh to recharge it.  That's an output/input ratio of 0.975.  This means that with a  constant 10-ampere load, the battery will return 97.5% of the energy that was put into it.  I think that's very good.

Waking-Up from Sleep

I've been thinking about what would happen if the Dragonfly's battery decided to go to sleep in the middle of nowhere.

The Installation and Operation Manual for Amopack's DF148 explains that the battery pack can be put to sleep using the temporization procedure if the voltage is less than 50.4 volts.  The manual further states in a bold red typeface, “After this temporization end, the battery is in sleeping mode, so the only way to wake up the battery again is by the connection of a charger.”

Maybe there is a translation issue or a misprint, but I have not found that to be the case.  So far, the battery I have for experimentation has “gone to sleep” (won't provide any power) twice.  One time was after sitting unattended for 17 days.  During those 17 days, the terminal voltage dropped from 52.4 to 50.8 volts (last reading before sleep).  This represents a self-discharge of ~95 mV per day.

Note that these experiments are with the battery disconnected from the controller.  Under this condition, the battery emits the waveform shown below at the end of the temporization period.  If the controller is connected, the pulsation would quickly cease and a steady DC voltage would be produced. 

Field Wake-Up Device

The adjacent photos show the testing of a simple wake-up device comprising an $8 Chinese adjustable DC-DC converter and a 20-volt power tool battery.   The DC-DC converter has 3 adjustment potentiometers.

This experimental circuit does wake-up the battery after being connected for only about a second.  A packaged version could be carried in a backpack.  Very little energy needs to be transferred.

The digital power meter is not necessary.  It was only used to gain an understanding of the circuit's operation.