Dual Mini 700 c. It Begins! I can't sit on my hands anylonger!!

[Perbear]

Gary, don't forget these minimotor are only 250 Watt motors, and are therefore 4X less powerful than a 1000 Watt Magic Pie.

At 80% efficiency they would require 312 Watts to output 250 Watts at the wheel. So limiting it to 9 Amps @ 54V (486 Watts) would mean that under heavy load, they could be producing 1.55 x more power than their actual rating.

To put it into perspective, a 9 Amp limit on a minimotor would be comparable to putting a 36 Amp limit (1,944 Watts @ 54V) on a Magic Pie!

So 9 Amps is not really "very low" when you stop and have a good think about it.

Alan
 

Actually, limiting phase current would be a better solution to protect the gears and the motor windings than limiting battery current. At low speed the winding current is much higher than battery current so at low RPM and high torque the motor could burn even at only a couple of Amps of battery current. Phase current control is normally implemented in the motor controller but I don't know if GM has such a feature. If they do, the winding current limit threshold should be adjustable on the Magic controller, preferably with some time constants to allow some overcurrent for a few seconds.

Something you could easily implement yourself is a temperature sensor in the motor. Since the torque is proportional to the winding current, and heating of the winding is related to the square of the current (P=I*I*R), a temperature sensor glued on the windings could easily protect the motor. So you could use high current in short burst but limiting current when the winding starts to get hot.  Then a higher phase current could be allowed and still avoiding burnt windings and damaged planet gears. Winding temperature sensors are standard in larger motors used for electric vehicles.

This is somehow built into the Magic Pie controller, probably using a common temperature sensor for stator and controller.  

[MonkeyMagic]

Not sure if the temp sensor would make a difference as if the heat is sustained even for a minute amount of time is enough to melt/destroy the plastic gears. Same goes for exceeding the RPM

And correct me if I'm wrong, but should you limit a given battery current would therefore limit the PWM phase current, no matter the current, correct?



I'm thinking of a small air compressor that uses 12V input. It has a plastic cog that gears the air piston. When I pick it up it's cold, but if I put say 24-30V through it (with the same current) either the motor will burn out or I will snap the plastic gear cog. However if I consistantly limit the current from stop start, then it will be fine upto the rated current/RPM. The temp sensor, if I had one in there - would cause erratic behaviour from the motor that I assume is better controlled by a limited current.

Lol the bottles surrounding my desk are telling me to stop now







 

[Perbear]

The PWM plus the controller capacitors and motor inductance works together as a DC/DC step down converter. The battery feeds more or less stable current into the motorcontroller (ESC) capacitor bank. These capacitors feeds burst of current into the coils when the MOSFET's conduct but the coils also conduct current when the FET turn off thru their freewheeling diode (often external schottky diodes in parallel for lower losses).

The best way to check this by using a four channel oscilloscope with current and voltage probes on a phase and on battery at the same time.

[GM Canada]

The PWM plus the controller capacitors and motor inductance works together as a DC/DC step down converter. The battery feeds more or less stable current into the motorcontroller (ESC) capacitor bank. These capacitors feeds burst of current into the coils when the MOSFET's conduct but the coils also conduct current when the FET turn off thru their freewheeling diode (often external schottky diodes in parallel for lower losses).

The best way to check this by using a four channel oscilloscope with current and voltage probes on a phase and on battery at the same time.

Hi Perbear,

I haven't got a clue what you just said there but it certainly sounds impressive!

Gary

[GM Canada]

Second test with a Cycle Analyst.

 If you watch it in 1080p you can read the numbers, pretty good this time. Except when im heading into the sun for a short time. I deleted the post of my first video attempt with the CA. I think I will do some limiting with the usb cable on the controllers before using any of the CA limiting features. Most people don't have a Cycle Analyst anyway. I think the first thing would be to just set the controllers to 48 volts. I'm sure they are factory set at 24 volts right now. Obviously I cant run these motors forever like this. I just wanted to see what they can do. Right now it is very cold and Im only doing short rides.

http://www.youtube.com/watch?v=jdRbWYxcKrw&feature=youtube_gdata

You can see at some points I am actually hitting 38 amps. Also top speed seems around 37-38kph. That is why I still feel setting it at 9 amps is very low. Do you actually mean I should be limiting it to 9 amps total or 9 amps each?  If I was running a 36 volt battery with no limiting I still think the amps would be quite high.

Gary

BTW all the snow was gone here. What you see in the video just fell two days ago. But its melting 

[GM Canada]

Your bike is looking really neat and tidy now Gary, but I'm now having serious doubts about you:

A little peddling at take off then the rest the mini's are haulin azz!

A little peddling for a little guy!


All those comments you've made about your size have obviously been carefully slipped in to throw us off the scent. You even had me fooled for quite a while, but now we have photographic evidence of your true size...you're actually mini sized, just like those hubmotors. The flag you have on the rear of your trailer is presumably there so that oncoming traffic can actually see you because you're so small.

It also accounts for the very low crossbar on your Joy bike.

Now I'll try being serious for a minute (which is quite a long time for me) as I have a couple of questions for you:

Are you running those 36V minis on a 36V or 48V pack?

How many of the 18 gears do you actually use?

Alan
 

lol, it was just pointed out to me that I am starring in one of my videos. If you can find it you will see me riding my joyebike when it was a 500w hbs motor (pro901). If there is any doubt of my size, in this video you can hardly see my bike!

Gary

[GM Canada]

I Just realized the speed is off in the latest video. I forgot to set the tire size to 700c instead of 26 inch. That would make quite a difference in top speed.

Gary

[cagatay]

   Hi 
could you guys say the 250 watt hub diameter?

[Andrew]

Hi gary,  anymore to report, a second test with correct parameters, and further advice on a safe reliable set-up.   I hope to run a minidual set-up with a 54v pack on my new bike buit only once I know how best to set the controllers

[GM Canada]

Sorry, nothing yet. Just had a weeks vacaton. Did anyone notice I was gone?

Hope to be riding again soon! Its almost nice enough.

Gary

[GM Canada]

More snow ... 8 more inches.. I refuse to shovel it this time. It is melting.

Gary

[GM Canada]

Ok FINALLY! Some real stats!

I set the controllers to 48v and 40 different amp settings and did the same run on the same street 4 times.

30amps continuos 50 peak
20amps continuos 30 peak
10amps continuos 20 peak
5 amps continuos 10 peak

At the 5 amps continuos 10 peak setting a scooter style ebike went by, I followed him and we had the same power! Didnt get him on video though. Couldnt see around the cycle analyst.

Anyway take a look at the video let me know what you think and what I should set the continuos and peak to by reading the CA stats.

http://www.youtube.com/watch?v=4yrj9JdTDx0&feature=youtube_gdata

At least I hope its the right address, it says "video is being processed" I waited as long as I can, I'm off to bed. Work in 5 hours..

ZZZZZZZZZZZZZZZzzzzzzzzzzzzzzzzz

Gary

[LOLO]

Hi Gary,
I have post a question on you tube but I think it's better here..
You realese this different test whitout pedal assist ?
I'm interessing to install two mini motor on a "single style".. 

[GM Canada]

All 4 tests are from a rolling start with no peddling. I was quite surprised that even on the lowest setting I tried I was still able to go over 30 kph.

Gary

[Andrew]

Hi Gary, I have studied the video several times and am too very impressed with the performances. With 5 amp Cont and 10 max the motor is obviously slower to wind by quite a bit but it still reaches a respectable 19mph/31kph.    As you know I am just a novice when it comes to electricals but with the magic controllers set higher than 5 cont/10 max will this burn out the motor or kill the gears I'm just going from Alan's previous posts about wattage and GM's own performance chart.   Is the total wattage generated by the volts and amps shared between the two motors.  For example 48v x 10amp = 480w, is this divided in half and shared between the motors?? Please go easy, I'm sure there is a very simple curcuit diagram to explain this