Need help with my e bike

[Sami fouad]

I am trying to ensure that Sami understands that more current is drawn as the motor works harder. Regardless of the type of controller, as far as I know neither Ohms nor Kirchoffs principles have been rescinded but if your saying that the motor will draw maximum current when completely unloaded I’m learning something new. I do find it surprising that the peak of current at start up when the motor is completely unloaded is sufficient to make the battery fail yet by Sami’s description the cycle is often able to progress along the road normally under low demand. I would have presumed that if the battery was so far gone it would be on able to move the weight of the bike and cyclist at all? The only way I can see that being the case is if there was a significant resistance in series with the battery thereby dropping a significant voltage at start-up.

Taking all that aside, Sami needs to load the motor and it’s battery's compared to simply freewheeling it upside down in the air. In the context of this fault finding exercise I don’t believe my explanation nor suggested testing is incorrect.

I did consider earlier on whether I needed to mention that there may be brake cut-off switches, so my testing method may fail if that is not disabled but at this stage I’m beginning to wonder whether we will ever get to the bottom of this

Helll thse

Okay, So far all we really know for sure is that the voltage that you are measuring changes as you start to pedal (or use the throttle)

A few things can be causing this problem and it’s frustrating when only some of the symptoms are given but I know remote testing is hard sometimes.

I’m going to give a bit of background which might help explain, I hope it doesn’t make it more confusing for you. The mathematics behind this isn’t complicated but if it isn’t your knowledge then it’s confusing so no maths I promise ;-)

Because of the way electrical circuits work pedal assist one only needs a small amount of current whereas pedal assist three needs a lot more current, also when you go uphill or ride faster you need more current.

When you draw current from the battery the voltage will drop, this is because the battery and all of the wiring and switches have a property called resistance.

If the resistance of any of the wires, switches or the cells inside the battery is higher than it should be then too much voltage will be lost. Your tests so far tell us that you are losing voltage when pedalling or using the throttle so the only conclusion is that somewhere you have a high resistance.


At the moment you don’t know where and whilst it’s probable that the battery is faulty I don’t want you to buy a battery and still have a fault.

The voltage will reduce as you have described if the battery is bad or there is a resistance in the wiring between the battery and where you make the measurement.

If the key switch is not working properly there is a risk that rather than being an on off switch it is failing and when the switch is in certain positions it is introducing a resistance in series with the battery. We don’t know that because the testing that you have done so far is after this switch .

What I suggest you do is as follows:

First prove that you can reproduce the fault when testing. Stand the bike so that you can spin the wheel with the throttle and apply the brake to that wheel and guarantee that you can make the fault occur every time.

Measure the voltage at idle, ie motor not running and write down the voltage.

Next measure the voltage right at the battery terminals when the motor is running and the brake applied, measure the voltage as you gradually apply the brake and watch it slowly drop. Remember the voltage just at the point that the motor cuts out, not after it cuts out but just before it cuts out and write that voltage down.

Next measure the voltage after the key switch when the motor is running and the brake applied, measure the voltage as you gradually apply the brake and watch it slowly drop. Remember the voltage just at the point that the motor cuts out, not after it cuts out but just before it cuts out and write that voltage down.

Repeat the measurements a few times to be sure that the test results are consistent.


If the voltage measurement right at the battery drops suddenly then the problem is almost certainly inside the battery,

If the voltage at the battery remains relatively constant the problem is in the wiring or the switch, I hope those tests above should pinpoint where you need to spend your money.
[/QUOTE

 

[Sami fouad]

H

I am trying to ensure that Sami understands that more current is drawn as the motor works harder. Regardless of the type of controller, as far as I know neither Ohms nor Kirchoffs principles have been rescinded but if your saying that the motor will draw maximum current when completely unloaded I’m learning something new. I do find it surprising that the peak of current at start up when the motor is completely unloaded is sufficient to make the battery fail yet by Sami’s description the cycle is often able to progress along the road normally under low demand. I would have presumed that if the battery was so far gone it would be on able to move the weight of the bike and cyclist at all? The only way I can see that being the case is if there was a significant resistance in series with the battery thereby dropping a significant voltage at start-up.

Taking all that aside, Sami needs to load the motor and it’s battery's compared to simply freewheeling it upside down in the air. In the context of this fault finding exercise I don’t believe my explanation nor suggested testing is incorrect.

I did consider earlier on whether I needed to mention that there may be brake cut-off switches, so my testing method may fail if that is not disabled but at this stage I’m beginning to wonder whether we will ever get to the bottom of this

Hello, these are the measues that i took.
- only the battery 39,7v
- in the controller with switch on 39.4v
- in the controller +throttle 39, 1
-in the controller +brake +throttle 38,9v


After cuts out that i made by the throttle
-in the controller with switch on 39,3v
-in the controller brake+throttle 38,8 v

 

[Sami fouad]

After 2 cuts out i took measures
in the controller with switch on 39,2v
- in the controller + only throttle 38,8 v
-in the controller +brake +throttle 38, 7v


in the controller with switch on 39,2v
- in the controller +only throttle 38, 7v
-in the controller +brake +throttle 38,6v

 

[Sami fouad]

I wanted to add that measure had been taken with wheels in the air.. Not on the ground

 

[gw8izr]

The starting voltage is a little low, I presume that you have not fully charged he battery but regardless the amount of voltage drop under load and as the motor stops does not suggest to me that you have a battery problem. It also does not suggest a problem with the key switch.

Whilst there could be some error in the measurement and testing I wouldn’t yet replace the battery on that evidence.

Does anyone else disagree so far?

 

[BazP]

I think the op could be winding us up so tightly we could be good for 50 mile or more.

 

[gw8izr]

I did wonder the same, 85 posts to get some voltage readings but there we go.

 

[D C]

Whatever else is going on with this thread and even if it's a wind up, the positive result has been to demonstrate what a helpful and patient group of contributors we have on the forum.
I don't think there's a solution available here but if Sami would say where he lives maybe someone could physically look at the bike for him.
How about it Sami, where are you?
Dave.

 

[Deleted member 25121]

The starting voltage is a little low, I presume that you have not fully charged he battery but regardless the amount of voltage drop under load and as the motor stops does not suggest to me that you have a battery problem. It also does not suggest a problem with the key switch.

Whilst there could be some error in the measurement and testing I wouldn’t yet replace the battery on that evidence.

Does anyone else disagree so far?

That depends on what the problem is, who knows....

I think the answer is probably 42.

 

[Sami fouad]

 

[Sami fouad]

So aftr i took measures now i can see nothing from you

 

[Nealh]

I'm going to throw this one in to see if we get an answer or simply played with.
Charge the battery fully and tell us the voltage it sits at.....

 

[Sami fouad]

Hi i have charged the Battery and it shows 40,4 v

 

[Sami fouad]

I can see that it can't go further than 40, 4

 

[Nealh]

40.4v isn't good fully charged so that changes things now, shame this wasn't mentioned in the first place. Though your issue is still battery related we should be able to aide you and assess how bad the problem might be.
It suggests the battery is unbalanced and that at least one cell group is low or weak and is the reason for the bike cutting out, voltage sag hitting lvc is likely coming into play.
What you need to do now is open the battery to access the BMS and sense wires so we can direct you to take a series of voltage readings to see how bad the issue is.

Take some pics and post them so we can direct you in taking the readings.

If it is down to a low cell group voltage we can guide you on how to manually raise any low cell group voltage so it at least can be raised to match the others then you can see if the whole battery will balance charge better.

You have a volt meter and know how to use it, so no reason you can't take more readings with our guidance.

 

[Nealh]

That depends on what the problem is, who knows....

I think the answer is probably 42.

If the battery is only charging as we have found now to only a little above 40v then the battery is certainly toast I believe and is currently in a worse state then I mentioned my pair of ageing ones are in #42. At least with my pair I can coax them with good current control into providing up to 40miles on fairly flat terrain with some small inclines.

 

[Nealh]

Further more to Sami's battery problem at 40.4v max charge I would say possibly one cell group at least may only be charging to about 38v - 39v or so and this one is the one causing the battery BMS to cut out as the one cell group hits lvc so much sooner then the others.
Only opening the battery and taking 10 voltage readings from the cell groups will we know what is occurring.

 

[Deleted member 25121]

If the battery is only charging as we have found now to only a little above 40v then the battery is certainly toast I believe and is currently in a worse state then I mentioned my pair of ageing ones are in #42. At least with my pair I can coax them with good current control into providing up to 40miles on fairly flat terrain with some small inclines.

Yes, the battery is on its last legs but I also suspect that there's a problem with the display or controller given the way the motor apparently / possibly / maybe cuts out so abruptly. The question then would be whether it's worthwhile trying to fix the various bits or just giving up on the bike.
But it's difficult to say because I've given up on trying to understand what's going on when the bike goes wrong

 

[Deleted member 25121]

Further more to Sami's battery problem at 40.4v max charge I would say possibly one cell group at least may only be charging to about 38v - 39v or so and this one is the one causing the battery BMS to cut out as the one cell group hits lvc so much sooner then the others.
Only opening the battery and taking 10 voltage readings from the cell groups will we know what is occurring.

Ah yes, that's a possibility. It's a pity we don't know what happens to the battery voltage when the motor cuts out.

 

[gw8izr]

Further more to Sami's battery problem at 40.4v max charge I would say possibly one cell group at least may only be charging to about 38v - 39v or so and this one is the one causing the battery BMS to cut out as the one cell group hits lvc so much sooner then the others.

That certainly sounds very plausible to me, it will be interesting to see what the individual cells measure like