It seems that the battery capacity has decreased

After several weeks not using the E-Bike, we have discovered an (aparent) important lost of capacity in the battery.

The logical hypothesis is that the cells are unpaired.
This means than the 16 serial battery needed to give the nominal 48 volts have diferrent electric charge.
Then when we discharge (using the bike) the battery:
a) When the cell less charged arrives to the minimum admited voltage. The BMS (battery management system) cuts the power. But there are still cells with near 50% of residual charge.
b) When we recharge the battery, the cell with more charge arrives to the maximum admited voltage. The BMS cuts the power. But there are still cells charged near of the 50% of its capacity.

But this 'never-end loop' has a solution:
The battery charger during the charging process gives a current of 2.6A but it really doesn't cut totally when the most charged cell reaches the max cell voltage. Then it just gives a standby current near 0.085A.
This means that this standby current doesn't overheat the already loaded cells, but let the not full charged cells arrive to be loaded. This process will pair again the cells.

What is the problem:
This is a slow process for a 20AH battery. If our battery has some cell charged at 50% of the other, this means that we will need to recharge 10AH with a source of 0.085A.
In other word we'll need 117hours (near 5 days) to finish the process.
By now we have recovered 2.5A, we will need to be patient.

Lesson learned: If you don't use the E-Bike for a long time, connect the charger at least 24h every 2 weeks ;)


BMS example:
http://www.conhismotor.com/ProductShow.asp?id=132

Some pictures of our first prototype

Until we get the necessary torque arms for the new bike with front wheel motor (the wheel jumps off the fork every time we accelerate) here you have some pictures:

From the Volttour meeting (http://www.volttour.net)

And from the Mussara and Albiol trips:

First tests with the 500W motor

From our friend XaviTa:

Saturday night (everyone has a different sense of party) I mounted the electrical kit in my wife's bicycle and I gave a tour... 3am till 3'30am...
Sunday morning I decided to go breakfast's 'Croissants' shopping to Cànoves, 5 km from home... no pedaling at all... came back at around 50km/h!!!
When arriving home something made me a kind of 'Castanyada flight'... scratches on knee, hands... that's what R&D is, isn't it?

I'm really glad to say it's heaven!!!!!!
The only thing is the battery weight... 9.5kg on shoulders... the motor, 48V 500W, needs 15A...

• I don't really know how the front wheel went out of the frame... dangerous!!!
• Fuse wire solder melted, needs to be rewired assuring good contact.
• Battery wire was pretty hot (good for in-jacket heating?).
• Pay attention to front traction wheel in slippery track.
• Internal motor friction is quite high... investigate.

Next:

• Spare 20A fuses or change for DC magnetothermal protection.
• Concentrate wires in a single connector. (maybe iron frame could do negative path, to 'save' one or more wires)
• Mount back solid rack for batteries, too heavy in a backpack.
• Mount regenerative controller.
• Buy confortable seat with suspension as 50km could become long!
• Use full suspension bicycle as motor/battery weight reduces quite a lot comfort.

Ideal: 48V, 1kW motor, 15A 4kg or less batteries, boost converter (from 24V to 48V) with current limitter (battery protection).

Other: Mount traction on a back trailer instead of bicycle.

500W Kit received

We have just received the 48V500W kit. This time, it took about 25 days, from China to Spain.
















Battery 48V, 15Ah, LiFePO4, 9.5Kg, 31cm x 15cm x 15cm. Charge at arrival 52.7V.
















Battery bag. Much better quality than previous one, but still too small (Battery doesn't fit inside), so it's useless.
















Regenerative Controller

EValbum.com

We have added our bike in EV Photo Album (great page where you can find details of over 2600 electric vehicles):
http://www.evalbum.com/2954

Performance of the first kit

After several months using the bike, we can sum up the main features:

• Maximum Speed: about 50km/h (downhill, I've seen 58km/h ;)
• Range: from 50km (at full speed without pedalling) to 75km (pedalling)
• Charge time (with 3A charger): 7 hours

We have ordered 3 new kits

After the great experience with the 1000W motor with 48V20Ah battery and regenerative controller, we have ordered:

• Another 1000W motor for the front wheel (yes, we will try with 2 motors in the same bike ;)
• A 250W kit with 36V 10Ah battery (LiFePO4), we want to see how a street legal version performs.
• A 500W kit with 48V 15Ah battery (LiFePO4), we want to try this battery with the 1000W motor, too.

Installing the Regenerative Controller

The only documentation that came with the regenerative controller was a sheet of paper written in Chinese, so we requested some info in English to the seller. This is what we received: http://dl.getdropbox.com/u/367893/Regenerative%20Braking%20Controllers.doc

There are several differences between the connectors of the Standard Controller and this one:

• no input for the Pedelec Sensor (not a problem as we don't use it).
• no input for the On-Off switch (button in the throttle). Instead, there are two orange wires (connector 2 in the document) for the same function.
• there are 2 additional connectors (number 10) to supply an external alarm device (we haven't tried it yet).
• there are 2 blue wires (number 3) needed when installing the controller for the first time.
• there are 2 white wires (number 5) to activate the Cruise Control function.

First, we have connected all the wires excepting for number 5 (Cruise Control). The motor should turn in one direction (forward or backwards) and each time the throttle is pushed, the wheel should turn in the opposite direction. In our case, this was not happening. It was always running forward, but with some noise, low torque and the controller and wires were very hot. After connecting and disconnecting everything several times, we saw the expected behaviour. Then, we disconnected the blue wires (just after the motor was going forward), to keep the configuration.

Regeneration starts only when the brake levers are pressed. The braking caused by the motor is quite powerful, but not excessive. Actually, the original brakes of the bike were not powerful enough due to the increase in weight and speed, and the regenerative braking is a great help. In fact, most of the time, we don't even use the brake pads. We just push a brake lever slightly, so that the regeneration kicks in and stops the bike quite quickly.

The Cruise Control function is great. If the throttle is fixed for 8 seconds, then it can be released and the power is maintained until the brakes are used. The only problem is to keep the thumb throttle completely still for 8 seconds. Any vibration or slight movement is detected.

To sum up, the Regenerative Controller is highly recommended: it helps braking, and recharges the battery noticeably (we are now taking some measurements).

LogBook and Gauge tuning

Here we have a report to show how the bike is working.
We've made a basic correlation to have an idea of the residual energy.
We've also tried to check the energy loaded to validate the estimation.

This is the link to the document: EBike.logbook

We also detected that the gauge was not adjusted for our battery.
It seems that our battery produces 90% of the energy between 54V to 51.5Volts.

But the green and orange LEDs were ON even when the battery was discharged (below 51V). The gauge was probably designed to detect voltages from 43V to 49V, not for a LiFePO4 battery pack.

We've slightly modified the circuit:
1st) A 5.1 zener diode has been added to make the green LED switch off at 53.2V
-> Now it indiacates that there is more than 66% of energy left.
2nd) For the orange LED it has been a bit more complex.
A TL431 chip turns on the LED when the voltage in reference pin is over 2.5V.
Originally this pin had a voltage divider with 3 resistors: 100K + 5600 + 590 (ohms). The comparison voltage was fixed too low. We have shortcircuited the 590 ohms resistor, and now the comparison voltage has increased to 52.3V.
-> Now it indicates that there is more than 33% of energy left.

The references are approximate, and visible when you release the throttle.

New connector for the Regenerative Controller

We have a second regenerative controller.
This one has been tuned up: the original bike wiring has been concentrated into a DB37 connector to simplify the connections.

Now we have only a connector to the battery and a second connector to the bike.






This is the pin-out that we have adopted: