Smart Pie 4 and NMC 24V 20Ah Battery

[haase]

Hi Everyone,

I am new to the ebike scene and would like to know if anyone has experience of the Smart Pie 4 or even the Magic Pie 4. They are cheapish Chinese ebike conversion kits. I understand they have sine wave controllers, regenerative braking and the quitest direct drive brushless hub motor. The Smart Pie 4 is 240-400W, whereas the Magic Pie 4 is 750-1000W. I am going for the Smart Pie 4 to be within regulation limits.

Secondly I have ordered a battery from China using NMC chemistry and rated at 24V 20Ah with a high current BMS, continuous discharge rate as high as 10C and burst discharge rate 15C.

What will the high discharge rate give me over and above a lower rated 24V battery?

I understand NMC is the chemistry chosen by Tesla, Nissan and Zero bikes to name a few.

Thank you in advance.

 

[cwah]

No tesla purposely avoided NMC because of the poor calendar life.

They choosen NCA instead, which are the ncr18650 range cells

 

[trex]

@haase: can you explain the reason or reasons why you chose the Golden Motor's Smart Pie 4 and a 24V battery?

 

[haase]

From what I have seen in various reports, almost all ev cars are having NMC battery packs. Since NMC has high energy density and low weight it makes sense and seems the safety is acceptable too. Time will show which battery chemistry will rule. As far as I see it, NMC is the one presently.

I believe Tesla will start their own battery manufactuing in Nevada with NMC or whatever is their choice.

In short for outright performance, NMC and for longer life LiFePO4. For me these are the two that matters at the moment.

 

[haase]

@haase: can you explain the reason or reasons why you chose the Golden Motor's Smart Pie 4 and a 24V battery?

I chose Golden Motor as they are a big manufacturer with lots of experience with brushless motors upto 20KW power output. The ebike hub motors have the controller built into the hub which makes the motor very quiet. Built-in cooling with a fan. Programmable motor power and battery voltage and regenerative braking.

This is the fourth generation kit and most likely more refined than earlier versions. The motors can be connected to a PC and set to higher power levels from 250-400W. I honestly think the Golden Motor range is probably the most sensible choice if I understood the market. The 24V battery will be using a NMC battery at 24V 20Ah with continuous discharge rate at 10C and burst rate at 15C. At least the battery manufacturer is claiming these figures.
I also have 24, 36 and 48V 10Ah LiFePO4 batteries for testing from OptimumNano which is a top company that so far has concentrated in Chinese domestic market with over 3000 employees.

There are many grades of LiFePO4 and buying from unknown sources is a risky business. My batteries are coming with 2 years manufacturer's guarantee.

People have used much higher voltage with these motors without damage. Also have a Magic Pie 4 on the way with 1000W brushless motor.

I have just bough a Cadex C7400ER battery analyzer and hopefully will be able to check out the performance of the batteries and confirm these claims if true. I am taking this subject seriously and do have an electronics background. It won't take too long to get to grips with it. I would also like to draw everyones' attention buying from Chinese sources or UK sources with unbranded batteries. Headway claims that all batteries bought in China are grade B and C and that Grade A for export markets are only available through official Headway distribution centres. I understand this practice is common amongst top Chinese battery manufacturers.

I am taking this up as a sideline to my business as I like it a lot. Will have a 250J professional capacitive discharge welder to tab 18650 or other batteries including pouch NMC 3.7V 10Ah very soon. If any board member needs tab welding to their batteries, I would be happy to oblige.

 

[cwah]

From what I have seen in various reports, almost all ev cars are having NMC battery packs. Since NMC has high energy density and low weight it makes sense and seems the safety is acceptable too. Time will show which battery chemistry will rule. As far as I see it, NMC is the one presently.

I believe Tesla will start their own battery manufactuing in Nevada with NMC or whatever is their choice.

In short for outright performance, NMC and for longer life LiFePO4. For me these are the two that matters at the moment.

No, Tesla chemistry is NCA, which is why they are dealing with Panasonic NCR18650 type cells.

Nissan used NMC and had massive capacity loss over a short period of time and filed a lawsuit against Leaf. See video here:

Here is the comparison between chemistry:

https://www2.unece.org/wiki/download/attachments/8126481/EVE-06-05e.pdf?api=v2

NMC have usually higher discharge rate but much lower calendar life than NCA.

 

[haase]

No tesla purposely avoided NMC because of the poor calendar life.

They choosen NCA instead, which are the ncr18650 range cells

Here is a news clip from a news site:

"To make ion batteries a little safer, manufacturers have replaced the lithium cobalt oxide with either lithium iron phosphate, lithium manganese oxide (one oxygen atom as opposed to dioxide’s two atoms), or lithium nickel manganese cobalt oxide. This latter one (NMC) is the favored configuration for electric cars.

The need for NMC batteries is so huge that Tesla Motors announced last month that it will build its own lithium battery factory — the world’s largest. The company is gearing up to begin production of its next generation electric car in three years’ time, and it doesn’t want any battery shortages to interfere with production."

 

[cwah]

Up to you what you want to believe.. I prefer to believe in the scientist talk working for Tesla, but if you consider the news site is the truth, then so be it

 

[haase]

Up to you what you want to believe.. I prefer to believe in the scientist talk working for Tesla, but if you consider the news site is the truth, then so be it

I don't disbelieve you and I am aware of all the points you raise. You make valid points and I respect that. But in this industry nothing is for certain for too long and I am putting my faith in to NMC given all its imperfections.

We will see what Tesla will decide on as I understand it, there hasn't been a decision as to what will be manufactured in their new factory when it is built.

 

[trex]

thank you cwah for the long but excellent video.
It explains very well why batteries die when slowly discharging.

 

[trex]

I chose Golden Motor as they are a big manufacturer with lots of experience with brushless motors upto 20KW power output. The ebike hub motors have the controller built into the hub which makes the motor very quiet. Built-in cooling with a fan. Programmable motor power and battery voltage and regenerative braking.

This is the fourth generation kit and most likely more refined than earlier versions. The motors can be connected to a PC and set to higher power levels from 250-400W. I honestly think the Golden Motor range is probably the most sensible choice if I understood the market. The 24V battery will be using a NMC battery at 24V 20Ah with continuous discharge rate at 10C and burst rate at 15C. At least the battery manufacturer is claiming these figures.
I also have 24, 36 and 48V 10Ah LiFePO4 batteries for testing from OptimumNano which is a top company that so far has concentrated in Chinese domestic market with over 3000 employees.

There are many grades of LiFePO4 and buying from unknown sources is a risky business. My batteries are coming with 2 years manufacturer's guarantee.

People have used much higher voltage with these motors without damage. Also have a Magic Pie 4 on the way with 1000W brushless motor.

I have just bough a Cadex C7400ER battery analyzer and hopefully will be able to check out the performance of the batteries and confirm these claims if true. I am taking this subject seriously and do have an electronics background. It won't take too long to get to grips with it. I would also like to draw everyones' attention buying from Chinese sources or UK sources with unbranded batteries. Headway claims that all batteries bought in China are grade B and C and that Grade A for export markets are only available through official Headway distribution centres. I understand this practice is common amongst top Chinese battery manufacturers.

I am taking this up as a sideline to my business as I like it a lot. Will have a 250J professional capacitive discharge welder to tab 18650 or other batteries including pouch NMC 3.7V 10Ah very soon. If any board member needs tab welding to their batteries, I would be happy to oblige.

don't you agree with the general consensus that DD motors are heavy, have drag and consume too much battery for legal bikes? with regard to the 10C discharge rate, that's 10 * 20A = 200A, your BMS can't take that much surely?

 

[haase]

don't you agree with the general consensus that DD motors are heavy, have drag and consume too much battery for legal bikes? with regard to the 10C discharge rate, that's 10 * 20A = 200A, your BMS can't take that much surely?

I have yet to hold a motor that is light. Direct drive brushless motors are my choice. The Smart Pie 4 Vector controller can withstand 18A continuous current and safely upto 63V can be applied. The motor can be programmed for 24, 36 or 48V operation through USB with rated power of 250-400W and peak power at 700-800W. For a $350 kit that is not a bad specification. I will make a giant killer out of it. The Lotus 7 of ebike kits. The guys at Golden Motor are keen listeners. They are a proper manufacturer capable of producing multi KW BLDC and controllers for heavy use. The Smart Pie 4 vector controller is a scaled down version of the controllers costing $1000+. I will have a customized kit at some time in the future exclusively made to my spec. when I am clued up enough.

The high C rate is simply the ability to provide burst of high current for short periods. It is wise to demand 0.5C or less if you want the battery to last. My view is that the battery should have at least twice the capacity such that the batteries are never discharged below 50% DOD. The life cycle of a battery can be improved dramatically by avoiding deep discharging a battery.

The high C rate is important for short bursts of high current that a motor may demand under heavy acceleration or loading. In RC batteries 65C and 70C are common and I am assuming that what applies to RC equally applies to ebikes. Continuous 10C discharge would exhaust the battery 10 times faster but the point is the battery can safely be discharged at this rate if and when required.

 

[trex]

In RC, the pack does not have a BMS. Don't you agree with the consensus that 36V is better than 24V because you can pull the same amount of power from the battery at lower current and the heat generated by the 36V controller is less than a 24V controller for the same power?

 

[trex]

I think the guys at GoldenMotors are nice to talk to but most manufacturers use 8-Fun motors because they have the best quality control and performance / price ratios. A BPM motor costs about $120 and give the Pie 4 a run for its money any day.

 

[cwah]

I don't disbelieve you and I am aware of all the points you raise. You make valid points and I respect that. But in this industry nothing is for certain for too long and I am putting my faith in to NMC given all its imperfections.

We will see what Tesla will decide on as I understand it, there hasn't been a decision as to what will be manufactured in their new factory when it is built.

What tesla is going to decide has no impact on the current NMC chemistry.

They may be able to extend NMC shelf life by adding new additive, then use it.

But NMC as it is now doesn't have a good shelf life. Period.

So, if you buy now, don't get NMC if you want to keep them for few years.

And maybe in few year time when technology evolved you may get a new version that has desired shelf life.

 

[haase]

In RC, the pack does not have a BMS. Don't you agree with the consensus that 36V is better than 24V because you can pull the same amount of power from the battery at lower current and the heat generated by the 36V controller is less than a 24V controller for the same power?

It is not common to find a BMS in RC packs simply to save weight and allow the controller to use as much of the available current. Voltage is related to the speed of the motor and the current is the torque element if I understood the fundamentals of a motor. Increasing the voltage to 36V will provide more speed but reduce the acceleration. The Smart Pie 4 motor can be programmed to use 24, 36 or 48V and the controller will will stand up to 60V. Using higher voltage would mean a reduction in the current with less torque. The aid is to provide a sensible bike with a hub motor with plenty of torque and be within the 250W power limit. It is also a lot easier for anyone to convert an ordinary bike to an ebike in less than an hour. The controller is built into the hub motor and is cooled by a fan and is tidier than an extenal conroller. The maximum current is 18A for the controller. The flexibility of the Smart Pie 4 is unique as a programmable hub motor. At this time it is my choice for a "peoples'" ebike.

 

[trex]

the sine wave controller has a slow power ramp and is limited to 18A, that means that you get at most 24V * 18A = 432W. In addition, DD motors are not good at low speed unless you throw 40A at them at start. Trust me, this combination is not going to be the best bike on the market. If your plan is to make easy to fit kits, there are other people making easy to fit kits like this one:

it weighs a quarter of the MP4, uses less battery and takes 30 seconds to fit.

 

[haase]

Thank you for the advice. I am willing to risk it and make it the best kit on the market. Golden Motor is a big company with massive resources. The kit sells well world wide and they can't all be wrong.

Still I appreciate your comments.

 

[haase]

the sine wave controller has a slow power ramp and is limited to 18A, that means that you get at most 24V * 18A = 432W. In addition, DD motors are not good at low speed unless you throw 40A at them at start. Trust me, this combination is not going to be the best bike on the market. If your plan is to make easy to fit kits, there are other people making easy to fit kits like this one:

it weighs a quarter of the MP4, uses less battery and takes 30 seconds to fit.

Here are some facts and figures for the Golden Motor hub motors:

Smart Pie 4
Max phase current: 50A
Continuous current: 18A
Open Voltage: 20V - 60V
Rated Power: 200-400W

Magic Pie 4
Max phase current: 80A
Continuous current: 30A
Open voltage: 20V-60V
Rated power: 500-1000W

 

[trex]

have you checked their motor performance curve? what' the efficiency at under 100 RPM? on a 26" bike, 100 RPM corresponds to 7.5mph, below 100 RPM, most of what you put in the motor turns to heat. DD motors are so inefficient at anything less than 150RPM that makes them totally unsuitable to climb hills.
1:4 geared motors for example shift the max torque/rpm 4 times to the left, that makes them efficient hillclimbers above 4mph. CD motors can even do better, their gearbox reduction ratio is 1:16.

This is the performance curve of the MP3 DD motor @ 24V: