Magic Pie 4 regen problem

[Mancuz28]

Hi, new member here.  Hoping for some help getting my Magic Pie 4 regen working properly with a new battery.

I purchased my MP4 2.5 years ago with a 36V golden motor battery and everything worked flawlessly, including strong regen.

I recently decided to upgrade the battery to a 50V 14.7Ah battery from em3ev.  The battery is awesome, and really gets good power out of the MP. The only issue is that regen only works when the battery is under 55V or so. Full charge is up over 58V, so I need to ride for many miles before I can use regen.  This is especially annoying because I live at the top of a large hill...with my old battery it was nice to be able to regen on the way down, but that is no longer possible unless I only charge to 60% or so.

I can't figure out why this would be happening.  I tried programming (see specs attached) to make sure the the overvoltage protection was high enough.  It's at 62V so that should be OK.

I have a Cycle Analyst so I can see exactly where it cuts off...if the battery is around 55V and I hit the ebrakes, V will spike up to around 56V and I get no regen.   If the battery is a little lower and the Voltage spike is like 55.8 V I will get some weak regen (-100W or less), but not much.

If the battery is much lower...like under 54V, then I get full regen (-600 or more W). 

Could there be some controller setting I'm missing?  Or something hardwired in the MP controller to prevent regen over 56V? Or perhaps a limitation of the battery BMS?  Does anyone else have a 50V+ battery hooked up getting regen?

Thanks for any assistance you can provide.

[Bikemad]

Hi andto the forum.

It sounds like the battery's BMS may be causing your lack or regen above 56V.
Your GM battery was probably a LiFePO₄ battery, in which case the cells can accept slightly higher charging voltages without any major problems apart from a reduction in the battery's lifespan.

Your new 51.8V, 14S7P Battery Pack uses the more common 18650 lithium Ion cylindrical cells instead of the safer (also heavier and usually more expensive) LiFePO₄ cells, therefore it would be potentially dangerous to overcharge the battery with an excessive amount of regen energy, but I would have expected the maximum acceptable voltage to be exactly the same as the maximum charger voltage (14 cells @ 4.2V/cell = 58.8V).

The Magic Pie can produce more than 22 Amps of regen current:



But fully charged 18650 lithium cells would not be able to safely absorb that amount of additional energy without the maximum charging voltage being exceeded, and this is why the BMS prevents the excess energy from reaching the battery.

Your controller settings all look correct to me, and I think it is probably due to your battery's BMS doing it job correctly.
Although, it might be worth raising the overvoltage protection a couple of volts to see if it has a noticeable affect on the regen.

As long as your maximum recorded voltage on the Cycle Analyst does not exceed 58.8V, your controller and battery will be fine. 

Alan
 

[Mancuz28]

Thanks for the input.  I was figuring it was either battery BMS or something "hard coded" in the MP4 controller.  Just seems unnecessarily low for the battery to cut off there since I can charge it up to 58.8V.

Oh well...I can probably work it out with a timer to only charge up to 55V so I can get some regen on my trip down the hill, not the end of the world!

[Kneedeep]

Have you tried to lower regen to 20 amps on the controller. The lower amps will lessen the initial burst and allow the -.600 at the higher voltage level. If you have the time do 5 amp increments and test your best results 15amp, 20amp, 25amp and so on. my controller on MP5V only take multiples of 5 I think but not sure. you might achieve more regen with it lower setting and stay away from bms limits.

[Mancuz28]

Have you tried to lower regen to 20 amps on the controller. The lower amps will lessen the initial burst and allow the -.600 at the higher voltage level. If you have the time do 5 amp increments and test your best results 15amp, 20amp, 25amp and so on. my controller on MP5V only take multiples of 5 I think but not sure. you might achieve more regen with it lower setting and stay away from bms limits.

Thanks for the thought...haven't tried this yet, but will let you know.  Theoretically if lowering the regen Amps decreases the voltage spike (which it should) I would think it would let me start getting regen at a slightly higher voltage.  I'll try it out when I next have the controller hooked up.