Low Voltage Cutoff - Troubleshooting

[Bedmountain]

Hi Everyone

I'm now a proud owner of my first e-bike having bought an MP3 from GM Canada a couple of weeks ago. Thanks to Bikemad and e-lmer I was able to wire up the horn button as a cuttoff/regen switch and I'm now up and running.

I'm having a few issues with the low voltage cut off.

I initially set the battery voltage to 48V via the software and I found the controller was cutting the motor off at 22V according to my CA.

Today I tried the 24V setting and I found the battery BMS was cutting out. CA showing minV at 10.2V.
I will try the 36V setting tomorrow.

I'm not sure whether it is quite normal to have cutoffs regularly and it is just up to me to avoid over acceleration and full throttle? I'm 190lbs and the overall bike weight seems quite heavy to me so perhaps I am asking too much of the setup?

I'm using a 48V 10AH LiNiCoMnO2 battery from:

http://www.aliexpress.com/store/product/Bottle-Lithium-Ion-Battery-pack-48V-10AH-with-Free-charger-at-lowest-price/408567_538783246.html

Initially I thought there may be a problem with the cables that came with the battery as they were a little thinner than the +/- wires supplied with the controller. I replaced these with some of the excess controller cable but I don't think this has made any difference.

Could it be that my soldering of the wires between the battery/CA shunt/controller is not up to scratch and that could cause this problem?

The spec on the battery says it has a Discharge Cut-off Voltage of 32.5V. Should the voltage be dropping to 10.2V if that's the case? Should it be dropping to 10.2V anyway when pulling away after a full charge (shows 54V when fully charged).

Apologies - I'm very new to all this and have almost zero electrical knowledge. I can live with being very careful with the throttle and switching the battery on and off to get it going again but it's a bit of a pain (especially when pulling away in traffic).

Perhaps I made a poor choice of battery or the battery is not working as it should?

Any advice on how I can troubleshoot this would be much appreciated.

Thanks
Ben

(picture of bike included cos I couldn't help myself  ...)

[Gregor]

Hello Ben.  I was following your posts about using the horn button as a switch for the regen braking with interest.  I am awaiting delivery of my MP III and I too would like to keep my hydraulic brakes.  When you soldered the regen cable onto the horn switch, did it matter what colour went to which connector ?  Cheers.  Gregor.                                                                                                                                                                                    Yer bike's looking good.

[Bikemad]

Could it be that my soldering of the wires between the battery/CA shunt/controller is not up to scratch and that could cause this problem?

Hi Ben, I think the cutting out problem is most likely occurring because the current protection circuit inside the battery is being overloaded.

According to the specifications of your battery, it is set to deliver a constant current of 10 Amps and a peak current of 20 Amps, and your Magic Pie is probably trying to pull a lot more than 10 Amps of current from the battery on hills and during hard acceleration. If the current being drawn is more than the battery is designed to deliver then the internal Battery Management System (BMS) will automatically disconnect the power to prevent excessive current draw. When this occurs, the voltage will instantly drop until it falls low enough to activate the Low Voltage Cut-off (LVC) in the controller.

I suspect that the battery voltage will jump straight back up as soon as the controller cuts out, and the controller is only able to reset itself after the power has been turned completely off and then back on again.

Reducing the current settings in the controller should reduce (or eventually eliminate) the cutting out, but the assistance is going to be noticeably reduced too.

I think it will be a case of trial and error to find the highest settings that do not cause the battery's BMS to cut out.

I suspect that battery is easily capable of continuously delivering the maximum amount of legally permissible power under EU laws, but I think you may find that the motor's assistance will be very poor and disappointing with only 5 Amps of current.

When you soldered the regen cable onto the horn switch, did it matter what colour went to which connector ?

Gregor, those type of momentary switches usually contain a small copper disc:

The disc (or sometimes a springy metal strip) simply completes the circuit between the two contacts when the button is depressed.
As the switching operation is purely mechanical it is not polarity sensitive, so it does not matter which way around the two wires are soldered onto the two switch contacts.

Alan
 

[Gregor]

Can I ask you another dumb beginner question ?

I am going to run a 48V10AH LiFePO4 battery. If I was to run this battery with the controller set at 24V, would that double the distance of running with 48V ? Would that damage the battery at all ? Would top speed be affected ?

If it's too dumb a question(s), just go "TSSSSST" and delete.  How dumb. Two questions...Three.

Thanks again.

Gregor.

[Bedmountain]

Thanks Alan - top notch assistance as always...

So - in short - I made a poor choice of battery purchase.

Does the 48v lifeP04 battery supplied by GM produce the require Amps to run the motor without cutout?

I went for the water bottle battery as I was planning to put it within the frame - turned out to be 10mm too long though! so had to mount it on the top tube.

I'm reluctant to reduce the amp settings in the controller so will live with trying to keep it under the cutoff. Am I running the risk of damaging the battery doing this or can I rely on the BMS?

Can I ask you another dumb beginner question ?

I am going to run a 48V10AH LiFePO4 battery. If I was to run this battery with the controller set at 24V, would that double the distance of running with 48V ? Would that damage the battery at all ? Would top speed be affected ?

If it's too dumb a question(s), just go "TSSSSST" and delete.  How dumb. Two questions...Three.

Thanks again.

Gregor.

Hi Gregor

I'm pretty sure the only function of the 24v/36v/48v setting is to alter the voltage at which the low voltage cutoff comes into play in the controller to protect your battery.
I believe the general advice given on this forum is to set the value to 24V and allow the BMS of your battery to do the cutoff if required.

Hope this helps
Ben