Battery problem?

[User1]

Hi,

I have just bought Magic Pie III with 48 V LiFePO4 battery. The problem is that when the battery voltage is about 50.5 V, the motor turns off and the output voltage of the battery drops to about 1 V. Unlike some other cases described on this forum, all 3 lights on the throttle turn off too. The wheel can turn easily by hand. When I disconnect the battery, the voltage gets back to 50.5 V. The voltage drops also when I connect the battery to the motor disconnected from the rest of the components (brakes etc.) so it looks like it's the problem with the motor itself. Any ideas how to fix it?

EDIT: I've forgotten to add that battery is charging only 1 hr 20 mins (instead of 5-8 hrs) so it's definitely not fully discharged at 50.5 V.

[Morgen 3Eman]

Hi User:
Welcome to the group

The reason the battery output drops to zero is that the battery needs to be charged.  The BMS is shutting down the output to protect the cells.  I have no idea what so ever  why the 56VDC battery is labeled as 48 V, but it is.    Plug in the charger and be happy the system is protecting itself.  By the way, how do you like the MP III performance? 

[User1]

Hi User:
Welcome to the group

The reason the battery output drops to zero is that the battery needs to be charged.  The BMS is shutting down the output to protect the cells.  I have no idea what so ever  why the 56VDC battery is labeled as 48 V, but it is.    Plug in the charger and be happy the system is protecting itself.  By the way, how do you like the MP III performance?

Thanks for your answer
However, I'm sure that something is wrong, because all 3 leds go out simultaneously (instead showing "full", then "half", and then "empty"). Also, 1 hr 20 mins charging time seems too short for me, comparing to 5-8 hrs given in my user manual. Do you think it's possible to charge the battery in such a short time?
Except from this, I like MP III very much In my country (Poland) e-bikes are very unpopular (probably I haven't seen any "live", it's also impossible to buy one in most bicycle shops), so I guess drivers behind me must be very surprised when I go uphill without much effort so fast that they can't overtake me

[Morgen 3Eman]

Hi User,

I wrote my reply before your added information was available, so thanks for the extra data.  When the BMS shuts down the output to protect the cells, the LED status lights have no source of power, so they all go out together.  But the short recharge time would seem to be an indicator of something wrong with either the BMS or the battery itself. I don't think it will hurt the battery to keep using it, but Alan (Bikemad) is clearly the best resource you have on this subject, so I'm going to drop out of the conversation. 

TTFN,
Dennis

[Andrew]

Sounds like the low voltage cutout is set too high on the bms. I do not really know anything about this battery type but I would have thought that something like 42v would more normal for  the motor to cut out while you are on the move.

Other than that you may have a bad cell in the pack?

I am just guessing.

How long are you riding for before it cuts out?

[User1]

I think that it's bad BMS too. At first I thought that it's a problem with the battery, but then I discovered that a voltage drops only after connecting to the motor, so the battery seems OK.

My battery is 10Ah from Golden Motor. I can ride about 60 km (or 40 km - if I ride faster), but I turn the motor on usually only when going uphill However, I usually ride the same distance uphill as downhill, so perhaps I could as well go 60 km on a flat surface with motor on all the time.

The first time it cut out when I tried to push the bike on a very steep incline with a help of the motor, so maybe then something went wrong.

[MAGICPIE3FOCUSPOWER]

Check all cells independently when battery is cutting off.

[User1]

You mean opening up a battery? Well, I'd rather try sending the motor and the battery back to the dealer first I couldn't fix anything in the battery anyway.

[MAGICPIE3FOCUSPOWER]

Yeah that's a better idea if you have still warranty

[User1]

Yes, I've bought it just few weeks ago But I'm just asking you, because maybe there is a simple fix about which I don't know

I had many problems before, which turned out not to be serious. For example, when I first tried to turn the motor on, I turned the key in the battery, but nothing happened - leds on the throttle were off. It took me many hours to find out that I have to turn the key once again It would be good to have a user manual with described such things as "how to turn the battery on", because they are not obvious, really

After that, although lights were on, I didn't manage to start the motor either. And when I did, then cruise control button didn't work etc. So far, the only parts I had no problems with were the brakes So I hoped that I can solve this problem easily as I did with previous ones, but it seems like not this time

[Andrew]

When pushing up hill the motor will use the most amps  and draw the most power from the battery in order to keep up the designed rpm of the wheel/motor. Voltage tends to drop when used for a prolonged period.  It could be you are using too many amps up the hills and causing a voltage sag which leads to a cut off.  Though cutting out at 50v is not right.

Can I ask how you are measuring the voltage and amps on your vehicle while you are using it?

[User1]

I can completely understand why it cut off for the first time. But after that it cuts off at 50 V even if I go at 7 km/h on a flat surface.

I can measure the voltage easily by putting the bike on a stand and inserting wires from a voltmeter into the plug here:

I tried to measure it also while actually riding, but this wasn't very convenient I didn't measure amps so far.

Now I've found this post:

Unfortunately, it sounds like your cutting out problem is being caused by the battery, not the controller.

Do the LEDs on the throttle control go out completely when the motor cuts? if so it could be a poor connection on the battery plug, or possibly a faulty group of cells within the battery.

Your 36V battery consists of 10 groups of cells which are individually monitored by the battery management system (BMS).  If the voltage across any of the groups of cells falls below a predetermined level, the BMS will automatically disconnect power to prevent the cell voltage from going too low and causing permanent damage.  Normally, this would only happen when the battery was almost completely discharged. But if one of more groups of cells has become faulty, this could easily cause the voltage to fall too low on the faulty group/s of cells when the motor was under load, even with a fully charged battery.

As you've mentioned that this problem only started after being used in heavy rain, I'm wondering whether water may have got inside the battery and somehow affected the BMS circuit board, producing a similar effect, or perhaps the water might have somehow affected the cells themselves.

In order to try and confirm the cause of the problem you would need to check the voltage across each of the cell groups while the battery was under load, to see if one group was reading significantly lower than the others, but that's not going to be an easy thing to check.

Alan

So it can be a bad cell in the battery in deed... but if the BMS is located in the battery, how does it "know" that it's connected to the motor (because the voltage drops only after connection)? It can detect such small amounts of power taken from the battery?

[Andrew]

Check that the anderson connector spades as shown in your photo are staying in place when you plug it in.  Sometimes the GM plastic plugs let the metal spades slide backwads when you push into place or into other same size connectors. This will lead to a poor connection. It has happened to me in the past and to others.

   Make sure the spades on the cables cannot come out of position easily in the plastic connector by pulling on the cables going into the connector.  If they come out or there is a lot of movement on the spade/spades  then buy a  genuine 50amp anderson plastic connector.


Its worth a try, it will only take two minutes.  I had poor voltage due to this happening. This could also cause poor charging

[User1]

I've checked this connector (and other connections too), but everything seems fine.
When I measured the voltage, I also disconnected the cable in this place:

(this time the photo is mine, the previous was taken from here )
then plugged the connector into the battery, put the wires from the voltmeter to the connector and measured the voltage (it was about 50 V). Then, without touching the connector, I connected the cable to the motor again (voltage dropped to 1 V). So I think that it's not a problem with bad connections.

Anyway, thanks for your post - any other ideas are much appreciated

[Bikemad]

It would appear to be a faulty battery, unless the controller is drawing an unusually high current causing the BMS to shut down.

If you can measure the current draw when the battery is connected this might indicate a controller problem if the current was over 5 Amps with the throttle released.

If you don't have a suitable ammeter, you can try disconnecting one of the battery lead bullet connectors and placing some 5A fuse wire between the unplugged connectors to complete the circuit.
If the fuse wire blows when the battery is switched on it is most likely to be a faulty controller.
If the fuse wire does not blow, but the battery voltage still drops to 1V it will probably be the result of either a faulty battery cell or BMS.

Alan