Magic Pie VS "Older" model

[GM Brazil]

And that is the CONSUMED power, you need to take in account the efficiency to know the DELIVERED power, but stills something close to 350W (considering an average efficiency of 75%). witch is more than 250W anyway!

My pie reads 30A and 1300W of power with the watt meter, but this is the CONSUMED! But actually deliver something close to  975W of power.

[Bikemad]

becuz 250w is mostly continious and that's a legal limit, but they don't say anything about max burst power and how long a burst power last... nobody knows about that so it's legal but more powerfull.

According to the performance data chart for the 24V Magic Pie, to produce an output of 250Watts, the wheel must rotate under full load at 143rpm. With a 26" wheel that's approximately 18km/h or 11mph.
As the motor is 72.4% efficient at this speed, it requires an input of 345.86Watts and will draw approx 14.5Amps whilst producing 16.78Nm of torque which equates to 5.19kgs (11.41lbs) of forward force.

As it starts to exceed 143rpm with full throttle, the power it's producing will actually reduce.

As the maximum power (and maximum torque) is only produced at minimum speed, therefore at full throttle, the motor is working at its hardest when pulling away from a standstill on inclines, and as the speed increases, the load on the motor is reduced!
So, if you're climbing a steep incline at full throttle, and the motor is loaded enough to pull its speed down below 143rpm, it will then start to produce more than 250Watts.

The way I see it is this; if your legal power limit is 250Watts continuous, when you're running on the flat at speeds above 18km/h or 11mph it will definitely be running below the legal power limit. Travelling below this speed by reducing the throttle will obviously reduce the amount of power.

I hope some of this makes sense.

Alan
 

[Bikemad]

I've already had one cell die on me after trying some similar tests earlier today, but fortunately it didn't catch fire or explode!
Two of the three Cells are still reading 4.1V, but the other ballooned cell is only reading 0.04V!

I'm not very happy about this failure as the pack is only two months old, and this was the first time I had used it!

I think I'll just pull it apart and convert it into a 7.4V pack for my son's R/C car instead.

Mission accomplished
I made up an adapter so that I could use the discharge function of my charger (through the balance lead) to drain the good cells to just over 3 Volts each, so it would be less likely to catch fire or explode while dismantling.
By carefully trimming the end of the heatshrink wrapping, I managed to persuade it to slide off, so I could re-shrink it back onto the much thinner pack after the faulty cell had been removed, and here is the end result:




Above is the converted pack, with the swollen faulty cell on the left and a normal 3 cell pack on the right for comparison.
The faulty cell had ballooned to almost twice the original thickness.


My IMAX B8 LiPro balance charger is supposed to charge 1 to 8 lithium cells, but for some unexplained reason, it doesn't have a 3 pin balance socket suitable for a two cell pack.
So I've kept the four pin balance plug and simply rearranged the three leads and it works fine.

I'm all for recycling whenever possible, and this battery was no exception, I now have a good two cell pack that I can use, which has got to be better than a faulty three cell pack that I couldn't.

Alan