Ebike Shuts Down Under Load or High RPMs Without Load

Batteries, Chargers, and Battery Management Systems.
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Ryan Saldanha   1 µW

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Ebike Shuts Down Under Load or High RPMs Without Load

Post by Ryan Saldanha » Sep 06 2019 11:21am

EBike Specs:
I have custom built a mid drive ebike with a frame mounted motor and controller (components linked at bottom). I built a 48V 13S battery pack with 3 cells in parallel. A 48V BMS is installed on the battery. The battery is connected to the controller with an XT60 connector. All the battery components including the compatible 48V charger were purchased from VRUZEND.com. I installed a twist throttle that came with the motor and controller.

Issue:
When I ride the bike and open the throttle, the motor drives the rear wheel, accelerating the bike, but as soon as the bike reaches a few MPH all power is lost and the system shuts down. The motor stops and the throttle display fades to black, suggesting that the battery as fully stopped supplying current. If I very lightly feather the throttle, I can sustain the power nearly indefinitely, but if the throttle opens too much, only a fraction of its full range, the bike loses power. When I raise the back wheel of the bike off the ground and open the throttle, the back wheel reaches very high RPMs and can be sustained indefinitely with almost a fully opened throttle, but the bike does shut down in a few seconds if the throttle is fully opened. In the both the test with load and without load, I can use the system again by disconnecting and reconnecting the connector between the battery and controller.

Current Theories and Questions:
Because the power is lost at a certain level of throttle use, it seems the issue could be related to amp draw, suggesting that the BMS may be shutting down the battery when too many amps are being drawn. The BMS is rated for 30A continuous draw while the controller is rated for 33A continuous draw. I have heard that this should not be a major issue, because the BMS should be able to temporarily handle 33A and all 33A are not being drawn continuously for general use. Is this reasonable? What are the most effective methods of measuring amp draw from the battery? Could I install a resistor between the connectors and then measure the voltage drop over the resistor? Will a general multimeter be able to measure between the positive terminal and positive lead of the battery measure the draw?
I have measured the voltage of the battery as the motor is running with the wheel off the ground and the power is lost with the voltage dropping from around 47V to 45-46V which I do not believe is enough for the BMS to shut down the battery, correct?
What are the other variables that may cause this issue? Is there a possibility of the electrical components in the controller having issues? Is it possible that the connectors are not the right gauge to support the current coming from the battery? I would appreciate any thoughts on this issue.

Components:
Motor/Controller/Throttle- https://www.amazon.com/Electric-Brushle ... way&sr=8-4

Battery Cells- https://vruzend.com/product/set-of-two- ... ery-cells/

BMS- https://vruzend.com/product/48v-13s-bat ... ystem-bms/

Charger- https://vruzend.com/product/48v-lithium ... er-3-amps/

Connector: https://vruzend.com/product/xt60-connec ... ire-leads/

BlueSeas   1 W

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by BlueSeas » Sep 06 2019 1:40pm

I think it's unlikely you are exceeding 30A. In addition to the BMS and Controller, the problem could be a poor connection anywhere between the battery build connections to the controller.

Here are some steps to follow for troubleshooting. Depending on the results, you may find the problem or the results of the testing will help figure out the next steps.

1) Double check all connections starting at the taps on the pack for anything not making good contact. Gonna assume that's all good now.

2) Determine if there is an overload -- Measure the current flow out of the battery. Before the BMS. See the max amps drawn while running full speed. The easiest way to do this is with a DC clamp meter. Here is an example (be careful if you buy one, the less expensive ones only do AC current):

https://www.amazon.com/Meterk-Multimete ... B0721MKXBC

If you aren't seeing anywhere near the 30A limit when it stops, something is breaking down under load. If you are seeing near 30A, stop here and post again.

3) Measure the voltage at the outputs from the BMS under load. If that voltage isn't dropping out, the BMS and the pack are probably OK. The controller is suspect. Stop and post the results.

4) If there is a substantial voltage drop at the BMS output, this clears the controller for now.

5) Now check the voltage at the inputs to the BMS. If the input to the BMS is also dropping, the problem is the pack. Go to step 7). If the input isn't dropping, it's likely the BMS.

6) If the BMS is suspected, temporarily bypass the BMS and feed the controller directly from the battery to see if that resolves the problem. If so, stop and post results.

7) The BMS input voltage is dropping out under load, so the battery pack is suspected. Check the voltage at the battery pack taps. If dropping here, it's the battery pack/build. If not dropping, here the battery pack is probably OK and there is faulty wiring between the BMS and the Pack.

8) Stop and post results.

BlueSeas   1 W

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by BlueSeas » Sep 06 2019 1:50pm

A couple more comments...are you using the new high current version of the VRUZEND caps? You will need those.

All the wire from the pack taps to the controller, and also the phase wires to the motor should be a minimum of AWG 14, but I would be using at least AWG 12.

Bas   10 W

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by Bas » Sep 06 2019 5:45pm

Hi,

I have had the exact same symptoms like you..
After months and months of searching, I found the cause, which you can see in the photo..
Burned because of playing with too many amps..
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AngryBob   10 W

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by AngryBob » Sep 08 2019 4:34am

How old is the kit? Did it EVER work correctly, or has this been a problem from day one?

Is that tiny little gear on the motor driving the bike directly thru magic, or are there perhaps some intervening gears and chains and whatnot that just MAYBE could be having an effect on the problem?

Which Vruzend kit are you using, and did you use the large wooden mallet to construct your battery?

Do you know the LVC for both BMS and controller? The fully charged voltage for a 13S pack should be 54.6. Your measurement of 47V starting voltage is quite low. Describing how you got there might provide some useful diagnostic information.

Describing what happens when the battery is fully charged might be even more useful.

Providing accurate data in answer to ALL questions would be ideal.

Ryan Saldanha   1 µW

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by Ryan Saldanha » Sep 10 2019 12:24pm

AngryBob wrote:
Sep 08 2019 4:34am
How old is the kit? Did it EVER work correctly, or has this been a problem from day one?

I finished custom building this prototype system this past April. When I tested it at that time, this issue was present. I did not work with the project for a while, but upon revisiting it, the same issue was there.

Is that tiny little gear on the motor driving the bike directly thru magic, or are there perhaps some intervening gears and chains and whatnot that just MAYBE could be having an effect on the problem?

Unfortunately, I do not have access to the bike or a picture of the system right now, but I can reply with one later if necessary. I replaced the little gear with a small bike sprocket. A chain runs from this motor sprocket to a large drive chain ring which is bolted the normal front chain ring of the bike. In this way, when the motor runs the motor sprocket indirectly drives the center chain ring of the bike which drives the rear wheel normally. I did some calculations and set a gear ratio with considerable torque advantage. It seems like the issue is electrical because the entire system shuts down before the motor accelerates the bike above a few MPH although I would appreciate any thoughts on hardware involvement in the issue.

Which Vruzend kit are you using, and did you use the large wooden mallet to construct your battery?

I am using the 2.0 kit with the upgraded components. I am not sure which wooden mallet you are discussing.

Do you know the LVC for both BMS and controller? The fully charged voltage for a 13S pack should be 54.6. Your measurement of 47V starting voltage is quite low. Describing how you got there might provide some useful diagnostic information.

I could not find the exact LVC for the components, but the typical LVC for 48V lithium ion batteries is around 36V. For the 54.6V you mentioned, were you looking at the charging voltage on the BMS page? This should just be the voltage at which the battery is charged. Each cell is around 3.7V when fully charged resulting in 3.7 x 13s = approx. 48.1V. I measured the voltage from negative to positive terminal of the battery pack.

Describing what happens when the battery is fully charged might be even more useful.

The situation when running the bike is the same when the battery is fully charged. The charger light turns from red to green although at times it alternates between the two after a while of charging. This could just be a result of the battery hovering around being fully charged, but I am not certain.

Providing accurate data in answer to ALL questions would be ideal.

AngryBob   10 W

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by AngryBob » Sep 11 2019 7:33am

OK, so it has had the problem from day one.

The large wooden mallet was in the early construction videos for the Vruzend kit. This used a pressure fit ONLY for contact. There was an upgrade, then later bolts were added, which I believe was the Third revision.

Does your battery kit have bolts for retaining contact pressure? Pressure fit alone was just not good enough. Contact was not uniform and not consistent. IMPORTANT to answer whether or not the bolts are present.

On the gearing - not familiar with your chosen motor. Mismatch between motor RPM and torque and selected gear ratio can cause very high amp draw, which could lead to major voltage drop, and trigger shutdown. When such a voltage drop happens, as soon as the load is removed, voltage will quickly rebound, such that using a meter to check voltage AFTER the shutdown is not really useful.

THE CHARGING VOLTAGE - your number of 3.7 per cell when fully charged is incorrect. The accurate number is 4.2V. It is listed in the specs for the charger you have, which you posted. Your battery is NOT repeat NOT fully charged, and the cells likely not all balanced at the same level. Combined with possible not fully seated connections, this may be the problem.

The charger alternating between red and green should indicate a balance charge is happening. Low-power charge is applied while higher voltage cells are drained, in order to get all cells to matching voltage. If this is happening with a metered voltage around 48 and not 54.6, the charger is defective. You can meter the outputs to make certain. If the charger output is indeed 54.6, and the battery measures 48, then you need to let the red-green cycling continue for an extended period of time, WHILE YOU WATCH, possibly for many hours to several days.

Did you test the individual cells for voltage before assembly? You may have one or more dead or severely depleted cells in the group. Hopefully you bought a few extra, and/or the vendor will replace any defective cells. If you have the above situation where the charger output is indeed correct and the battery is severely low, you should probably check each individual cell for voltage.

John in CR   100 GW

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by John in CR » Sep 11 2019 6:24pm

If all the connections are good (motor, controller, battery and bms) throughout the system, then another possible culprit is an incorrect hall/phase wiring configuration which will cause a high amp draw and kick the bms into an over-current shutdown. With the wheel safely and securely off the ground measure the no-load current at full throttle.

Ryan Saldanha   1 µW

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Re: Ebike Shuts Down Under Load or High RPMs Without Load

Post by Ryan Saldanha » Sep 12 2019 10:51am

BlueSeas wrote:
Sep 06 2019 1:50pm
A couple more comments...are you using the new high current version of the VRUZEND caps? You will need those.

All the wire from the pack taps to the controller, and also the phase wires to the motor should be a minimum of AWG 14, but I would be using at least AWG 12.

I am using the V2 high current VRUZEND kit. I will have to verify the wire gauges, but many wires are of course just part of the controller/motor etc. Thank you for letting me know all of these courses of action to take in order to find and solve the problem. I will take those steps as soon as I get the chance and reply with the outcomes. I need to see where I could access the DC clamp meter or buy it as well as look into some other electrical considerations such as the proper fully charged voltage noted by AngryBob, another person who responded.

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