[Solved] Magic Pie III Amp drop

[Amund]

Hi,

I have a problem with my newly purchased Magic Pie III (I am suspecting it is in fact a Pie 4, but that may be a separate thread)

I have connected it to a 48v/13Ah battery.

It runs very well when the battery is fully charged. But as I empty the battery, the peak amperes (when accelerating or uphill) drop proportionally:

100% - 26A
1Ah - 20A
2Ah - 18A
5Ah - 15A
9Ah - 8A

I have asked a lot of people, and googled a lot. The only similar case I've found was in this forum, and his answer was this:

ksotar
Hello!

Yes, it was faulty controller, and it was replaced by goldenmotor support, when they started to answer e-mails

It was MP2, though.
Good thing is that MP III is much easier to replace controller.

Before that I would check all the power line for faults, loosy contacts, etc. I've had issues with that as well, with the same symptom, easy to fix.

I've since tried to get help from BMSBattery.com, where I purchased the pie, they blame the battery, and stopped replying when I told them I've tested other batteries with the same results (10-20C 10Ah lipo - delivering 200 amp burst). I've also tried goldenmotor.com support, still waiting patiently for a reply.


Can anyone help me get further with this problem? I am not sure if my controller is to blame, and I am not ready to order a new one, in case the problem lies elsewhere.

I am also suspecting I recieved a MP4 instead of MP3, mostly because it's dead quiet, and people seem to attribute the MP III with a fair bit of noise. Also, my brake handles have 3 pins, which according to a post in this forum is a great new feature of the MP4.

[Bikemad]

Hi andto the forum.

I have experienced something very similar on an MP4 with a faulty battery, so if your motor is actually an MP4 instead of an MPIII, it could be that the Low Voltage Protection value is set too high for your battery (or perhaps a weak battery).
As the battery voltage reaches the Low Voltage Protection limit under load, the current is automatically reduced to prevent the voltage from dropping below the set protection level.

Are you able to monitor the minimum voltage at maximum current throughout the different stages of the battery's capacity?

100% - 26A  ?V
1Ah - 20A    ?V
2Ah - 18A    ?V
5Ah - 15A    ?V
9Ah - 8A     ?V

The speed of the bike will also affect the maximum current draw, so it might be better to check the maximum current draw while fully accelerating up the same incline from a standing start each time for consistency.

If the problem was temperature related it would be interesting to test a part used battery with a cold motor/controller to see if the current starts off limited.
i.e. If you had used 5Ah from the battery and then tried it the following day without recharging the battery, would it still be limited to 15A maximum instead of 26A?

Do you have anything externally attached to the throttle that might affect the power output like a Cycle Analyst etc.?

If your motor is an MP4, it will not run at very slow speeds (below 20~30rpm) whereas the MPIII can run as slow as 2~3rpm.

Alan
 

[Amund]

Thanks!

When you say low voltage protection, I thought that would cut power instantly, not gradually?
Anyways that point can not be relevant, since I've tested with my friend's Tower Hobbies 10-20C 10Ah lipo - delivering 200 amp burst, and no BMS - bike showed EXACTLY the same ampere drop.

I think I need som better numbers, I will have to rig my gopro to record the watt meter.

I have tried the cooldown trick, I used 2Ah and let the bike rest outside for about 5 hours. It continued right at 18A peak.

The cruise control stopped working recently, maybe the wire is broken, I haven't cared yet as I did not use it much.

I have nothing attached except a DX wattmeter on the power wires from the battery.


I do however have one theory that I haven't followed up on completely:
I noticed the voltage drop under full load was very low in the beginning, maybe just 2 volts.
I had some car style flat lug connectors in my circuit, and started pondering what would happen if I had a poor connection AFTER the watt meter. I would not see the voltage dropping, but maybe the amps?
I swapped all lugs for screwed connectors - result was MORE voltage drop, like 5 volts under load. But same amps. Bike seems to run better, but it could be placebo.
The only poor wiring left is the stock plug and cables out of the battery, short wires but they seem very thin. But in any case they are BEFORE the watt meter, so if they caused a big voltage drop I would see it.

I've also ordered a new watt meter, just to see if there is something wrong with it (cheap turnigy copy from DX). However that would not solve the problem, I felt the bike running slower as the battery got lower before I had a watt meter, that's why I ordered it, to get some numbers on what was going on.


Another theory would be - what if something is WRONG with the ampere shunt in the controller, causing it to be disturbed by voltage?
What if there is something wrong with the minimum voltage cut-off circuit, so it is way too sensitive of voltage drop?

[Amund]

Hi andto the forum.

I have experienced something very similar on an MP4 with a faulty battery, so if your motor is actually an MP4 instead of an MPIII, it could be that the Low Voltage Protection value is set too high for your battery (or perhaps a weak battery).
As the battery voltage reaches the Low Voltage Protection limit under load, the current is automatically reduced to prevent the voltage from dropping below the set protection level.

Are you able to monitor the minimum voltage at maximum current throughout the different stages of the battery's capacity?

100% - 26A  ?V
1Ah - 20A    ?V
2Ah - 18A    ?V
5Ah - 15A    ?V
9Ah - 8A     ?V

Alan

Your line about voltage cut-off might have been more helpful than I realized. I made a video today, filming the watt meter during a ride. Studying that video I realized the amps are not dropping in the beginning, but staying completely flat, until a point where it starts dropping. Looks like that point is about 44v (voltage under load). Which I hit after using a little over 1 Ah.

I downloaded the MP4 config program, and guess what - when selecting 48V - it seems to have a default 'low voltage triggering current reducing' starting at 44v! Now I just need a USB cable to get cracking.

Thank you so much for giving me these hints, I was almost pulling my hair out. Looks like instead of having been sent defective stuff from china and talking to the wall, I have actually recieved a MP4 for a pretty good price. I can see that the setup utility for MP4 really has a lot to offer, compared to the MP III software. This is great!