EBIKE LIFEPO4 BATTTERY UNDERVOLTED

[Supreme Kay]

Hello I own an electric bicycle. I recently bought a LIFEPO4 36Volts 10AH for my bicycle. My ebike controller is rated at 22Amp and 36V. I have a lcd screen SW900, it display the speed, milles travel, the watt and battery consumption. However, I have an issue the battery indicator has 5 bars to indicate the battery level. The bar disappear as the battery discharge. My issue is that when I ride my bike I have 4 bars after about 20 miles of riding I rely on the battery indicator and keep riding. next thing I know I see error 06 (Battery Undervolted according to lcd display user manual) and then I have one bar and the lcd display shutt off I am left with no power from the battery to ride my ebike. I then have to pedal the old fashion way to get where I want to go. I checked the battery with my multimeter at home and I have 36.8 volt, I am assuming that I should still be able to ride . The battery cut off voltage is 25.2 volts, Rated Discharging Amperage:is 15 Amps, Max. discharging current is 35Amp and Max Continuous Discharging Amperage is 20 Amps. My thought is that perhaps the lcd screen may be defective. I mostly use pedal assist, I would appreciate any help to point me in the right direction

 

[bobc]

To be honest it all sounds sort of right:- lifepo4 cells output 3.2V unless very full or very empty so battery voltage is not a good indicator of charge level.
20miles range sounds reasonable for 10Ah of battery. The empty cells could easily be drooping to 25V on load then recovering to a higher voltage when the load has been shut off for a short time. (though 36.8V sounds high for an empty 36V battery.....

 

[amberwolf]

Not really; under load it probably sags lower than that, then recovers a little after the battery has sat for a bit--and there is probably one or more cells that are a bit lower than the others.


to the OP: It's possible you'll get more range if you leave the battery on the charger for a long time (days to weeks) so that it's BMS can balance the cells.

But 20 miles on 10Ah, depending on speed, terrain, wind, how much pedalling you're doing vs how much assist the motor has to do, sounds about right.


FWIW, I have a feeling most of those battery-bar-meters not only use simple voltage for the display, rather than actual power left, but they are probably calibrated for other battery types than LiFePO4, which has a pretty flat discharge curve for the most part. So what you're seeing is the first bit of charge "burn off", then it runs in the flatter part, so the bar seems to stay the same, and then it hits the very last bit of charge the battery has in it so it drops suddenly and stops.


If you were to use a wattmeter, it would show you how much actual charge has been used (watthours, Wh; amphours, Ah), and be more helpful in estimating remaining range. There are a bunch of htem out there, but the best one I've used is the Cycle Analyst by http://ebikes.ca . There are also others, like the WattsUp (which is much more basic, and there are dozens of clones of it out there that are less reliable or accurate to one degree or another).

 

[Supreme Kay]

I purchased a ebike conversion kit on Ebay from ebikelyng on eBay. The kit was advertised as 36 volt - 500w motor. Upon receiving the kit I spent a great part of the night mounting the kit, The LCD display that came with the kit is a SW900. When I ride the bike the battery indicator shows the battery as full I rely on that and keep going next thing I know the bike drop me in the middle of nowhere and I read on the lcd display error 06 (According to lcd display user manual it means battery undervolted) Then I see only on bar left on the lcd display and the lcd display screen turn off . I then have to either walk or ride the bike the old fashion way. The lcd display sw900 also has a future to show how much watt is being consumed and to my surprised the wattage goes up to 780 watt. The battery indicator is incorrect and get me most of the time in the very inconvenient situation. I would appreciate any suggestion toward solving this issue, I will also gladly accept recommendation for better ebike lcd display that has a more accurate battery indicator.

 

[dogman dan]

It's not the screen, it's the battery. But don't panic,, getting 20 miles out of 10 ah tells me you are not having a big problem with your battery.

Lifep04 has a pretty flat discharge curve, so it shows 4 bars way past 50% discharged. When you are at the end, one set of cells drops voltage enough to trigger the bms to shut off the pack.

If this is happening more abruptly than normal, it's because your battery is not fully balanced. One set of cells never gets a full charge. Try leaving it on the charger for long periods, if that does not help then try charging full, then a short ride, repeatedly. A more balanced battery might show a less abrupt end, but it will still show four bars till about a mile or two till the end.

But again,, all sounds good to me. 20 miles from a 10 ah pack is doing ok for sure.

Add a simple voltmeter, if you want to keep track of actual voltage, but even then, it's still lifepo4. Your odometer might be the best thing to go by,, head for home when you get 10 miles from home.

 

[999zip999]

Depends on style of riding. Wot starts, hills ect.

 

[docw009]

Maybe the display is set for a 24 volt battery? Then it would show 5 bars all the time. If so, hopefully, it was the low voltage alarm in your battery triggering the shut-down of the bike. If that was your first ride, 23 miles might be about as far as you can go on light or no pedals..

 

[rote]

I used to use that display. If I recall you set the battery voltage in Parameter 03; for you, set it to 36. But even with setting the correct voltage I had similar problems like you. Plus I recall you can't adjust LVC with the display so you're stuck with the relatively high LVC set by it (eg, 48v has LVC of 42v). The wattage scenario is likely normal (eg, 36v x 20amps from a zero start).