When to replace the battery cells?

[Bikemad]

Dmitryl, I currently use three different voltage packs:
The 7 Cell LiPo pack which is 25.9V nominal and charges to 29.4V
The 8 Cell LiPo pack which is 29.6V nominal and charges to 33.6V
The 14 Cell LiPo pack which is 51.8V nominal and charges to 58.8V 

All my controllers are programmed to the 24V setting so that I can use whichever pack I want without having to alter the settings.

When these cells explode as a direct result of physical damage, it is usually a sharp metal object that has pierced right into the battery and shorted out the anode and cathode layers within the cell. I haven't tried puncturing a cell with a non metallic object, but I'm guessing it would be less likely to result in the cell igniting.

I don't use a BMS on my packs, but it would be possible to wire up the alarm function of my cell monitor to automatically close the throttle as soon as any of the cells reaches the pre-set minimum voltage if I didn't want to simply rely on the beeping.

LiFePO₄ cells are typically heavier than similar LiPo cells. Check out this post to see a comparison between similar LiPo and LiFePO₄ packs.

Alan
 

[Just]

Very interesting... Is a Controller, which is programmed to 24V, able to work with 36V and 48V batteries? How is so? Wasn't burn? How does it exactly work? What about the motor? Does it also work with all voltage ranges (from 24V to 48V)?

Could I ask you to provide a schematic shown how is it possible to wire up an alarm function of the cell monitor to the throttle so that it will allow to deactivate the throttle once a voltage over one of the battery cells drops below a preset alarm value?

Thank you

[Bikemad]

The GM Controllers will work with any voltage between 24 and 48, the maximum charged battery voltage must not exceed 60V.
The voltage selection in the programming software is there to set the Low Voltage Cut-out (LVC) to suit the battery voltage being used.
As most batteries have a Battery Management System (BMS) which includes its own LVC, the voltage setting in the controller can be left on the 24V setting without causing any problems.
All Magic Pies and Smart Pies can run on 24, 36 or 48V, as the motors can cope with the higher voltage, but it might not be a good idea to run a standard 24V motor on 48V.

Here is a basic diagram showing how to easily connect the alarm port wiring on either the CellLog 8S or the 8M to cut the throttle when the alarm is activated:



As the alarm function can be set to operate on both minimum and maximum user defined voltage levels, a more complex system could be designed using a miniature crossover relay to simultaneously cut the throttle and disable the regen. This would also prevent overcharging when you set off from the top of a steep hill with a fully charged pack that isn't equipped with a BMS.

Check out this post for more information on the CellLog 8.

Alan
 

[Just]

Thanks for the schematic! BTW, what application do you use for drawing so nice pictures?

All Magic Pies and Smart Pies can run on 24, 36 or 48V, as the motors can cope with the higher voltage, but it might not be a good idea to run a standard 24V motor on 48

Hmm... So, when manufacturers rate their motors for 24V, 36, 48V and so on, what do they mean? What's OVER voltage is safe to apply to the motors? Let's  say for the 48V motors, would it safe to let them working on the 60V batteries? As for the Controllers, will they supply the same amount of current with no relation to the supplied voltage?

Thank you!

[Bikemad]

I used the Windows 7 Snipping tool to grab the required images from screenshots etc. and then edited it with my favourite free drawing program called , which I find a lot less complicated to work with than Photoshop. Although it's a pretty basic drawing package, it does however have the layer function, which I find particularly useful for the type of diagrams that I create.

Specified motor voltages are not always as you might expect with brushless motors, the Magic Pies will actually run on much higher voltages (60V, 72V, 84V, 96V etc.) as long as the current is controlled to prevent the motor from being cooked, but this would require a suitable brushless controller that is specifically designed to handle the higher voltage being used.

I find that the GM controllers generally draw a similar current, regardless of the voltage being used.

Alan
 

[Just]

Thank you Alan! Very useful App!

[Just]

As for the CellLog8S, does it keep logs for all 8 monitored cells or only for one of them or for the overall battery pack (8 cells in serial)?

As for spec, it's able to keep the log for 36 hours... What does happen then? Will it be fully overwritten?

Thank you!