I want more speed using 20'' wheels

[luisgouveia]

Hello guys,

I think that only Golden Motor staff will be able to help me in this particular issue.

I set up the maximum settings (250W motor):

Peak current: 50A
Continuous current: 30A
Speed: 100%

With these settings I can only get 19 Kmh (12Mph) using 20'' wheels.

My bike has great torque with these settings. The problem is the top speed. I feel that the motor has more speed to give but the controller can't go harder in frequency.

I am an electronic engineer and I guess this can be fixed by software. I'm writing this mail in order to advice you to prepare the next configuration program to 20'' wheel bikes.

I have no doubt that putting this hub in a 26'' bike would give me a 30Km/h (20Mph) top speed.

PS: Anybody in here riding 20'' bikes? Thank you for replying.

Thanks,
Luís Gouveia

[Bikemad]

I set up the maximum settings (250W motor):

Peak current: 50A
Continuous current: 30A
Speed: 100%

With these settings I can only get 19 Kmh (12Mph) using 20'' wheels.

My bike has great torque with these settings. The problem is the top speed. I feel that the motor has more speed to give but the controller can't go harder in frequency.

I am an electronic engineer and I guess this can be fixed by software.

I have no doubt that putting this hub in a 26'' bike would give me a 30Km/h (20Mph) top speed.

Luís,

The speed you are getting would seem to be about right for the power available from the 36V minimotor in a 20" wheel running at 24V. This motor will only produce more than 107 Watts of power if the motor is loaded to 207rpm or less (approx. 19km/h or 12mph for a 20" wheel). See performance figures.

I'm a bit concerned about the current settings for that motor, it will not survive very long at those settings if loaded too much.
I would have thought a continuous current of 10A and a peak current of 15A would be far more suitable, but still above it's rated capacity. With a 24V battery, this would still allow for 240Watts continuous and 360Watts maximum power consumption.

I don't think your maximum loaded speed is likely to see any improvement with just software modifications, but it can be increased considerably by using a higher voltage!

Incidentally, to achieve 30Km/h or 20mph would require a power output of approx 220Watts, but this motor can only produce this amount of power at a much lower speed of 23Km/h or 14.3mph with a 26" wheel. So although it may produce enough power, its gearing is too low to allow it to reach its theoretically achievable maximum speed.
(220 Watt power requirement obtained using Bike Speed and Power Calculator.)

Alan
 

[luisgouveia]

Hello Alan,

First of all, let me thank you for your answer.

In fact, I was affraid that the motor couldn't produce more than a certain amount of power (107 W) when its rotation is considerable (207 RPM).

However, I don't understand why you said that I can improve my top speed by using a higher voltage of, let's say, 36V insteed of 24V. Regarding what you said, once I reach 207 RPM, it's pointless to give more than 107 W to the motor. Why would I want to give it more voltage?

Thanks a lot once again Alan,
Luís Gouveia

[Bikemad]

I don't understand why you said that I can improve my top speed by using a higher voltage of, let's say, 36V insteed of 24V. Regarding what you said, once I reach 207 RPM, it's pointless to give more than 107 W to the motor. Why would I want to give it more voltage?

Luís,

In the eBike community it is pretty common practice to raise the voltage in order to increase the speed.

If you were to go from 24V to 48V, the unloaded speed should almost be double.  The actual top speed on the road will also increase, however it will not be twice the original speed due to the greatly increased drag produced at higher speeds.

If you wanted to double your speed, you would need four times the amount of power in order to overcome the additional drag and frictional forces.

The way I see it is like this:
Doubling the voltage (but keeping the same current draw) should double your power, which consequently should increase your top speed by 50%.
So if you use 48V instead of 24V your 19 km/h (12 mph) should increase to 28.5 km/h (18 mph).

The biggest problem with increasing the power is that the motor may not be able to cope with the additional heat that will be generated, and is very likely to become damaged if too much current is used.

I'm pretty sure that if you doubled the voltage, but halved the current, your maximum speed would still increase, because the 250 Watt power would now be available at a much higher speed.

Has anyone tried this yet?

Alan
 

[luisgouveia]

Thanks Alan,

I will buy two Zippy Flighmax 5000mAh 6S1P 15C 22.2V, put them in series to obtain something like 44-48V, and then I will run my bike at 30 km/h!

I am amazed with the price of these batteries. 50$ each in hobbyking.

Thanks,
Luís Gouveia

[Bikemad]

Luís, this should not apply to you, because your minimotor should have a freewheel device which prevents regen from working.

But if anyone with a Magic Pie is planning on using LiPo packs, please be aware of the amount of regen current that is actually generated, as it can easily exceed the maximum recommended 2C charge rate (10A) for those 5000mAh packs.
I used 2 packs in parallel for this exact reason and have still exceeded the maximum charge rate on several occasions.
These are my highest recorded regen readings so far with a 26" wheel, but these figures would be even higher for smaller wheels using regenerative braking at the same road speed:
            23.35 Amps (681.5 Watts) using a 7 cell LiPo pack (25.9V 10Ah).
             9.65 Amps (525.8 Watts) using 14 cell LiPo pack (51.8V 5Ah).

It's a good idea to have an additional switch wired into the brake switch wiring, so you can turn off regen when braking from excessive speeds.

If you live at the top of a steep hill and set off with a freshly charged LiPo pack, the regen can easily provide too much charge, which could actually result in your LiPo battery pack exploding into flames!

Now you can't say that you weren't warned.
 
Alan
 

[Leslie]

No use having all that current is you have no vollts to push it anywhere.


The two properties we talking about are magnetic intensity and magnetic density.  Both are intertranferable but you need at least one part current and one part voltage for any good things to happen. .


The motor has many electro magnetic coils and nearly as many magnets,  When you consider some of the relevant properties of magnetism and the ones you need to know for this answer are the two called magnetic intensity and magnetic density.

The two properties can be related to their relatives Voltage and Current by their distinct attributes.


Intensity = Voltage = Speed

And
.
Density = current. = Torque

They almost hold hands and kiss.


one way to get an idea how voltage works is looking how electricity arcs, at high volts it will arc further comparing to pressure. With high currnet the arc is thicker giving more stuff at that pressure.  

The nature of induction can be EZ expressed by this senario,

Spray an object along the ground with your  garden hose.  You cant stop the water with your finger you can make the pressure more and amount of flow less, the hose expands (induction) and pushes back on your finger (diode), and the water comes out faster,  It will push the object further and faster where as the hose with no pressure put into it will push larger objects but more slowly. This is the inductive model almost in a nutshell.



Like a fire hydrant hose will blow you off your feet and down the road 30 meters yet the pressure from a spray bottle at a similar pressure (voltage) attempts to blow down the road but there isnt enough mass behind it to move nothing but your skin.  You will even notice that a thicker hose at the same pressure sprays further, just like the magnetic denity holds up the intensity so to the thicker hose in this senario holds up the presssure.



High volts low current will create a intense but unreliable field

And low volts with high current will create a less intense but more reliable field.  

Fish for both and you have an intense relaible field that will resist colapsing under load..

[Bikemad]

I will buy two Zippy Flighmax 5000mAh 6S1P 15C 22.2V, put them in series to obtain something like 44-48V, and then I will run my bike at 30 km/h!

I would fit one of these battery monitoring units to one of the batteries to indicate when the batteries are starting to run low:


When it's first connected it gives a single beep and after a few quick flashes, the  Blue LED lights up brightly.
When the battery voltage falls below 22.2V the Blue LED will start to flash.
When the battery voltage falls below 20.4v the Red LED lights up constantly.
If the voltage drops below below 19.8v the Red LED flashes and the beeper sounds.

For just $3.49 I think it's great value, and the noisy beeper should alert you before damage occurs to the battery when you've accidentally left the power turned on and the battery voltage falls too low.
Being woken up at 3:00 in the morning by a high pitched beeping noise is much better than finding a completely ruined LiPo pack several days later.
(Don't ask me how I know).

I always make sure I connect mine to one of the balance leads before I connect the main battery power leads. By doing this, I don't forget to use it.

Alan
 

[luisgouveia]

Hello again Alan,

Thanks for your advice. I will certainly buy that monitoring unit.

I have one last question for you: Is it important for a charge controller to have discharging capability? Why would I need that?

Is there anything wrong with charging a LiPoly battery that is still 50% charged?

I'm looking forward to buy the 18.99 $ charger from HobbyKing but it doesn't have that capability and I would like to hear from you regarding this. 

Thanks!

[Bikemad]

I have one last question for you:
Is it important for a charge controller to have discharging capability?
Why would I need that?
Is there anything wrong with charging a LiPoly battery that is still 50% charged?

One last question? I counted three.

The discharge function is used mainly to determine the actual usable capacity of a NiCd or NiMH battery pack, and can also be used to improve the capacity of NiCd and NiMH packs, which can suffer from so called memory effect if they are only partially discharged each time.
This function is not generally used with LiPo packs which do not suffer from this memory effect, so it would just be a complete waste of an otherwise usable discharge cycle of the battery.

If a fully charged pack is not going to be used for a long time, it is suggested that it may be beneficial to discharge the battery to a reduced level (usually 3.85V per cell for LiPo packs) and this is probably the only time you would want to use a discharge facility.
Without the discharge capability, you could just use the bike until the battery had been run down to the required voltage instead.

The Lithium battery prefers a partial rather than a full discharged. Frequent full discharges should be avoided if possible. Instead, charge the battery more often or use a larger battery

So charging a LiPoly battery that is still 50% charged will be much better for the battery.
Most of my rides are usually around 3-4 miles long, which uses less than 20% of my battery's capacity, and I always charge it fully after each ride.
I hope this answers your question(s).

Alan

P.S.
In case you hadn't realised, the charger you have in mind requires a separate power source. Although it can be powered from a car battery, a mains powered voltage supply of between 11 and 18 Volts and at least 5Amps might be better.
(The +12V output from an old PC power supply should be ideal)

[luisgouveia]

Thank for all Alan!

Finally I will ride at 36V, the motor doesn't allow me 48V (apparently it is possible to use 48V but only for a few hours till it brokes). I will put in series 2 batteries of 5 cells each.

I will post here my top speed with 20'' wheels.

Thank you again,
Luís Gouveia

[luisgouveia]

Hello guys!

My new top speed: 18mph / 29 km/h

Config:
250W mini motor
Magic controller
2 lipoly batteries (18.5V 4.400 Ah each)

Peak current: 15A / Continuous current: 10A

The motor is not getting warm. I will try to increase the continuous current to 12A.