Battery indicator showing Empty, Battery more than half Full

[EasyRide]

Hi there,
I'm new to the forum and have run into an issue. I have been building an eBicycle from scratch and chose the MP3 to power the bicycle.
I bought the motor in Aug 2012, and by Dec 2012 I got it running. I'm running a 36V system and initially the motor would cut out at load, but I suspected that my battery BMS was cutting the power (I built my own battery pack). I had the BMS upgraded to a higher current rate (40Amp continues) then my maximum motor/control setting of 35Amp.
I have just installed the new BMS and reconnected up everything again. When I first switched on the power, the half and empty battery indicator lights on the throttle lights up (the battery was at 36.4V). I managed to ride it but noticed that I was struggling up a hill which I could go up before (not cutting as previously though). I left it for the rest of the week, and now when I turn on the key, the half and empty lights go on but the half light fades away after a few seconds and only the empty light is on, the battery power is @ 31.6v though. Obviously nothing happens as I assume the controller things the battery is flat and turning the throttle does nothing.
Could you assist me with what could be wrong? 

[Bikemad]

Hi EasyRide andto the forum.

Before I go any further, I would just like to clarify things by pointing out that "31.6V" is nowhere near high enough for a 36V battery which is supposedly "more than half full".
If you're "running a 36V system" I would also expect the battery voltage to be considerably higher than "36.4V" for a fully charged pack.
For example, a 10 cell Lithium pack (commonly referred to as a 36V pack) would have a nominal voltage of 37V, but would be nearer 42V fully charged.

During use, the pack voltage will gradually decrease until it falls low enough to trigger the Low Voltage Cutoff (LVC) on either the battery's BMS or the controller itself (dependant upon which is set the highest).

If you take a look at the discharge graph for a single cell below you should notice that the cell is fully depleted when its voltage falls to around 3V (~30V for a 10 cell pack).

If your 36V pack is down to "31.6V" (presumably measured under a no load condition) the BMS should prevent any further current from being drawn from the pack.



Over discharging lithium cells will result in permanent cell damage, and this is just one of several problems that the BMS is supposed to prevent.

I suspect your battery pack is not being charged to anywhere near the correct level. This would mean that the battery's usable capacity would be very low, even after charging, and this could also explain why the third LED on your battery gauge does not light up.

Having said that, it's worth considering that a similar operation of the gauge lights would also be observed if you were using a 48V throttle unit with a 36V pack.
If your throttle does not have a voltage printed on the casing, it will be a 36V throttle, as the other throttles are marked accordingly with either 24V or 48V in white, as you can see on this thumb throttle:



If you can give us some more details of your BMS unit and the battery pack (number of cells, type, nominal voltage,  etc.) it would make it much easier to properly diagnose the problem.

If your controller has been programmed for 36V operation, I would not expect the motor to run if the battery voltage was as low as 31.6V, as the Low Voltage Cutoff on the controller would probably be triggered.

Please let us know if a low charging voltage is causing your problem.

Alan
 
 

[EasyRide]

Hi Bikemad,
Thanks for your reply  . I suspected that the battery was to low.
One of the issue I have is that the charger won't charge the batteries when connect through the BMS/PCM. I have managed to connect the battery pack direct to the charger and have managed to get the battery pack up to 39.6V.

Here are my specs for the Battery and PCM:
12 * Headway LiFePO4 38120 3.2V, 10 Amp cells connected in series giving me 38.4V
1 * PCM-LFP12s40a protection circuit module.
http://www.batteryspace.com/pcmwithequilibriumfunctionfor12cells384vlifepo4batterypackat40alimited.aspx

Like I said above it won't charge via the PCM but connecting the battery directly to the charger, charges it perfectly.

Cheers,
Easyride

[OzGeeksGarage]

Interesting stuff, when I purchased my Smart pie I didn't see any options for voltage 24v, 36v or 48v buying the kit, so just assumed they were all the same, so my throttle charge indicator shows flat because I've only got 24v LiPO4 currently, will get another and upgrade to 48v eventually, so now I know there are different voltage units available. I didn't notice any voltage markings so must have the 36v unit, I'll have to upgrade it or see if I can put a resistor in series if I got to 48v, but maybe the throttle potentiometer needs changing or a resistor too. I've also been half thinking of changing batteries to 3x 12v LiPO4 because I realised I can't run my 12v air compressor & lighting off 24v easily

[EasyRide]

Oh Bikemad, in my reply I forgot to mention that after I got the battery charged to 39.6V all the LED's were alight and I have managed to get the motor running. Now I just need to figure out the charging issue.

[GM Canada]

The motors are all the same. You can run them at 24, 36 or 48 volts. All the throttles are the same too except for the led read out. For the LED to work right you need the throttle to match the battery voltage. I usually use black tape over the leds anyway and just use my cycle analyst to judge remaining power. I think I actually have a 36 volt throttle on my townie and it uses 48 volt batteries. I see Alan is online right now so I am sure his post will be much more informative then mine.

Gary

[GM Canada]

Like I said above it won't charge via the PCM but connecting the battery directly to the charger, charges it perfectly.

Cheers,
Easyride

I have seen this a few times. I have fixed this issue two different ways. On one pack a cell was completely dead and it did not allow the pack to charge. I assume the same thing would happen if a wire from the BMS to the cell was disconnected. The other way to fix this was replacing the BMS. Lets hope for a loose wire.

Gary

[Bikemad]

I have managed to connect the battery pack direct to the charger and have managed to get the battery pack up to 39.6V.

39.6V is only 3.3V per cell, which is well below the typical charge voltage for a 3.2V LiFePO₄ cell.

Headway recommend a Maximum Charge Voltage of 3.65 ±0.05V per cell, which is 43.8V ±0.6V for your 12 cell pack.

I reckon that you are missing out on at least a third of your battery's available capacity by not charging it to the correct voltage, so the stated 10Ah capacity will probably be nearer 6Ah in reality until you rectify the charging problem.

I didn't notice any voltage markings so must have the 36v unit, I'll have to upgrade it or see if I can put a resistor in series if I go to 48v, but maybe the throttle potentiometer needs changing or a resistor too.

As Gary has already mentioned, the throttle electronics (a hall sensor is used instead of a potentiometer) are all the same and use the same 5V input and variable 0-5V output voltage and it's just the battery gauge that differs.
Simply placing a resistance in series was much easier to do on the earlier throttle units as the battery gauge and the lighting switch each had their own supply wires.

Unfortunately, the MPIII and Smart Pies use a single wire to supply power to both the battery gauge and the light switch, so it is not a good idea to fit a resistor into this shared wire if you are also using the light switch to supply the power for your lighting as this will create a much larger voltage drop (and extra load) across the resister when the lights are turned on.

The resistor would need to be fitted inside the throttle unit, ensuring that the supply wire goes direct to the light switch before passing through the resistor and on to the battery gauge, but there is very little room to spare in there.

I simply use my battery gauge on the throttle as a "power on" indicator and rely on my wattmeter to indicate the amount of battery capacity that has been used.

Alan
 

[EasyRide]

Thanks everyone for you reply.

Alan, just to let you know that the charger does charge @ 3.65V, I mentioned 39.6V is what I let it charge to before I disconnected it and tested the Battery indicator.

I'm checking all the connection to the BMS and hopefully that will solve it. This is my second BMS so I hope I do not have to change it.

I'll post what the results are.

Cheers,
Jeetesh

[EasyRide]

Hi Alan,

Just a quick update on the issue I have been having.

1. I checked all the sensor wires to each cell and there were two wires that were crimped to the insulation. I however have two cells running down faster then the rest of the cells. Need to get two new cells.
2. The charger issue was a combination of a faulty wire and some wonking connection instructions, but after some trial and error finally got that resolved.

Going forward I nee to get at least two more cell to replace the two weak cells.

Thanks for all your assistance and for all the replies from everyone else.

Cheers,
Jeetesh

[Bikemad]

It's good to hear you've nearly got it sorted, hopefully the new cells will put it right.



Alan