Understanding Battery Voltage.

[Del Arthur]

O.k, Pressing the button on my battery, shows no green light at all, just a red on the 20% portion......the handlebar indicator shows 1 red light, meaning low battery.....the volt meter is showing 33/34 volts left in battery.....which is correct ?....in pedal assist mode two the bike is still pulling like a train......at what voltage will it cease to supply power to the motor ?..........

 

[WheezyRider]

O.k, Pressing the button on my battery, shows no green light at all, just a red on the 20% portion......the handlebar indicator shows 1 red light, meaning low battery.....the volt meter is showing 33/34 volts left in battery.....which is correct ?....in pedal assist mode two the bike is still pulling like a train......at what voltage will it cease to supply power to the motor ?..........

Depends on the low voltage cut off point of the controller. Usually 31 to 33V, then at that point it will cut off.

I would not run your battery so far down, it's bad for battery life.

 

[StuartsProjects]

which is correct ?

Depends on the battery, what does the label say the voltage should be.

A lot of eBike batteries are known as 36V batteries, and would show around 41V when fully charged. The displayed 33.1V would be quite low for such a battery, not far from motor cut off.

 

[saneagle]

None of them are correct, all of them are approximately right, and even if any one was correct, it wouldn't tell you when the motor was going to cut out.

When you're riding the bike, the power is going up and down all the time. When the current goes up, the voltage goes down in proportion.

When any cell reaches the low voltage switch off point (about 3.0v), the BMS will switch off, then the voltage will rise because there's no current and the BMS will switch on again.

When the battery voltage reaches the controller's low voltage cut off point (about 31v), the controller (control panel) will switch off and stay switched off. The battery voltage will rise because there's no current, and you can then switch on the control panel again.

Obviously, the further you go, the more frequent and permanent the cut-outs become. On most occasions, the first cut-out will happen when you're going slowly up a steep hill because that's when you're using the most current.

 

[Del Arthur]

None of them are correct, all of them are approximately right, and even if any one was correct, it wouldn't tell you when the motor was going to cut out.

When you're riding the bike, the power is going up and down all the time. When the current goes up, the voltage goes down in proportion.

When any cell reaches the low voltage switch off point (about 3.0v), the BMS will switch off, then the voltage will rise because there's no current and the BMS will switch on again.

When the battery voltage reaches the controller's low voltage cut off point (about 31v), the controller (control panel) will switch off and stay switched off. The battery voltage will rise because there's no current, and you can then switch on the control panel again.

Obviously, the further you go, the more frequent and permanent the cut-outs become. On most occasions, the first cut-out will happen when you're going slowly up a steep hill because that's when you're using the most current.

Thanks for that.....obviously there is more to it than I thought.......

 

[saneagle]

Thanks for that.....obviously there is more to it than I thought.......

Every bike, motor, battery and controller is slightly different. You get information from the voltage indicators, which have a slightly different meaning on different bikes, but should be consistent on yours. Eventually, you'll build your own understanding of what they mean, how they're affected by the way you ride and your type of rides, then you'll learn when your bike is likely to cut out.

Once you have that understanding, it's best not to let your bike run down that far if you have the choice.

 

[Del Arthur]

Every bike, motor, battery and controller is slightly different. You get information from the voltage indicators, which have a slightly different meaning on different bikes, but should be consistent on yours. Eventually, you'll build your own understanding of what they mean, how they're affected by the way you ride and your type of rides, then you'll learn when your bike is likely to cut out.

Once you have that understanding, it's best not to let your bike run down that far if you have the choice.

Thank you......now on charge !!.......

 

[Del Arthur]

Every bike, motor, battery and controller is slightly different. You get information from the voltage indicators, which have a slightly different meaning on different bikes, but should be consistent on yours. Eventually, you'll build your own understanding of what they mean, how they're affected by the way you ride and your type of rides, then you'll learn when your bike is likely to cut out.

Once you have that understanding, it's best not to let your bike run down that far if you have the choice.

So I will never get a correct voltage reading, from the volt meter I installed......it will never go below about 31v .......is that correct ?....

 

[WheezyRider]

So I will never get a correct voltage reading, from the volt meter I installed......it will never go below about 31v .......is that correct ?....

It's a case of how well calibrated it is as to whether it is giving a correct voltage reading.

Hopefully the Low Voltage Cutoff of the controller will cut in and shut the system down by 31V. The voltmeter you have added may still continue to display a voltage after the controller has shut down, if you have wired it in directly to the battery and you are not reading the voltage from a port on the controller. Best not to let it get to 31V though

 

[saneagle]

So I will never get a correct voltage reading, from the volt meter I installed......it will never go below about 31v .......is that correct ?....

There's no way of knowing whether your voltmeter is correct unless you check it against a known voltage or with another voltmeter that you know to be accurate. It might be spot on, but you don't know unless you check it.

 

[Emanresu]

Can anyone explain the physics (or electrics) about being able to charge a 500w battery to 80% in 90 minutes but the remaining 20% taking proportionately longer? A sure there will be logical explanation with formula, but can't think of one at the moment.

 

[StuartsProjects]

For single Lithium Ion cells see here;

https://batteryuniversity.com/article/bu-409-charging-lithium-ion

 

[Woosh]

Can anyone explain the physics (or electrics) about being able to charge a 500w battery to 80% in 90 minutes but the remaining 20% taking proportionately longer? A sure there will be logical explanation with formula, but can't think of one at the moment.

it's down to the diffusion of Lithium ions through a porous electrode.
You can push those ions more quickly with higher charging voltage up to 80% but It takes time to spread evenly so filling the remaining 20% will have to be slow. Pushing those ions too fast will result in fractures.

 

[saneagle]

Can anyone explain the physics (or electrics) about being able to charge a 500w battery to 80% in 90 minutes but the remaining 20% taking proportionately longer? A sure there will be logical explanation with formula, but can't think of one at the moment.

It's pretty simple really. There's a fair chance that the battery will catch fire or explode if you fast charge it at the top of the charge.

 

[Woosh]

It's a bit like traffic congestion on the M25. You can drive reasonably fast until 80% of capacity.

 

[Sturmey]

it's down to the diffusion of Lithium ions through a porous electrode.
You can push those ions more quickly with higher charging voltage up to 80% but It takes time to spread evenly so filling the remaining 20% will have to be slow. Pushing those ions too fast will result in fractures.

Very similar to pouring a perfect pint of Guinness.