KT display battery level accuracy

I have a KT controller/display on my Bafang 500w rear hub drive. I recently switched to the KT system from the stock Bafang controller/display. Everything works well with the exception of the battery status indicator. The four bar battery indicator on the display does not correspond to the one on the Hailong battery. The difference can be as great as 50%. With the Bafang controller/display, both the display and the battery indicators were in sync.

With the KT setup, the display shows 4 bars when the 48v battery is fully charged, but it rapidly decreases as I ride. Checking the difference when the display showed 2 bars, the indicator on the battery still displayed 3. Checking again when the display showed just 1 bar, the battery still showed 3, but soon after dropped to 2 bars. Currently I have no bars on the display, but still show 2 on the battery indicator.

I have learned to watch the voltage shown on the display instead of the battery life indicator. Currently I have 0 bars on the indicator but the voltage shows 45.1v. It still show 2 bars on the battery's indicator which would translate to about 50% battery life. Based on this, I'm not sure how accurate the voltage shown on the display is. The problem is that even if there is plenty of battery left, the motor may shut off since the display thinks it is at the LVC. I have read that the LVC is around 40w?

I probably should check the voltage coming from the battery to see if it is the same as the display, but I don't have a meter or how to use one on the battery. That also would not resolve the problem if the battery and the display show different voltage. There seems to be no setting to sync the battery and display. Am I correct about this? Have others had similar problems, and were you able to resolve them?

rocketman58 said:

Currently I have 0 bars on the indicator but the voltage shows 45.1v. It still show 2 bars on the battery's indicator which would translate to about 50% battery life. Based on this, I'm not sure how accurate the voltage shown on the display is. The problem is that even if there is plenty of battery left, the motor may shut off since the display thinks it is at the LVC. I have read that the LVC is around 40w?

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Actually, that's the voltage that I would be charging the pack at anyway, given my charging routine. I charge to 4.15V per cell and discharge to 3.6V-3.7V. So on a 13S pack, that would be 54V down to 47V.

Those LED bars have no usable information, I always use the voltage readout to estimate the charge level.

Once you decide what type of charging routine you want to use, you can figure out what voltage you want to charge to, and discharge to. After that it's pretty simple math to know that full, half, or empty is represented in pack voltage. After a while you'll just look at the voltage and know pretty much how much range you have remaining.

Thanks for the reply.

I guess I just became used to the Bafang setup where when it reached one bar, it was time to recharge. I honestly do not remember what the exact voltage was at that point. Now I will have to switch to reading the voltage instead, which I guess is probably better. It's just annoying that the battery status bar isn't even close to being accurate.

You stated that you normally recharge your battery at around 45.1v. Is it save to go down a bit lower to say 43v? Can you confirm that for a 48v system that the LVC if 40v?

thanks

rocketman58 said:

Thanks for the reply.

I guess I just became used to the Bafang setup where when it reached one bar, it was time to recharge. I honestly do not remember what the exact voltage was at that point. Now I will have to switch to reading the voltage instead, which I guess is probably better. It's just annoying that the battery status bar isn't even close to being accurate.

You stated that you normally recharge your battery at around 45.1v. Is it save to go down a bit lower to say 43v? Can you confirm that for a 48v system that the LVC if 40v?

thanks

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LVC on a BMS or controller is usually set too low for battery health, but high enough to shut things down before it gets dangerous. I've actually never hit the LVC, ever. It's better for the battery to stay away from full charge or full discharge, if you want the battery to last and stay healthy. What range you use, should be whatever you're comfortable with, knowing that. If I ever go to full charge, I ride the bike immediately so it doesn't sit at full charge for more that a few minutes.

I'm running 72V, so I charge to 83V and discharge to 72V or so, but usually before that. I have plenty of battery, so that's still a lot of range, and if I really needed to, I could keep riding quite a ways. Even when charging to 83V, I usually go out and ride right away. Everyone has their own routine. Some are more conservative on their "full charge" side, and less on the discharge side, with the main goal of staying away from the extremes. 40V seems about right for LVC on a 48V pack.

I generally charge my battery to full the night before leaving on a ride of 30 miles or so. I can typically get in around 70 miles before I get down to about 45v, so that's about two 30-35 mile rides on my 17.2Ah battery. I know you should not charge it up to full capacity as it is not healthy for the battery. I need to get a charger that allows you to control the charging level, right now I'm using the stock charger.

It sounds like charging the battery to 90% and not running it down much lower than 45v would be the preferred thing to do. I might need to get a larger battery in the future.

I charge at 45-46v too, and for the same reason. I don't NEED the capacity below that, so I don't use it for better battery health.

I just wanted to add that there's nothing wrong with charging a battery fully. What you want to try to avoid is STORING them that way! Overnight or a couple of days is fine. A couple of weeks or months, not so much...

rocketman58 said:

I generally charge my battery to full the night before leaving on a ride of 30 miles or so. I can typically get in around 70 miles before I get down to about 45v, so that's about two 30-35 mile rides on my 17.2Ah battery. I know you should not charge it up to full capacity as it is not healthy for the battery. I need to get a charger that allows you to control the charging level, right now I'm using the stock charger.

It sounds like charging the battery to 90% and not running it down much lower than 45v would be the preferred thing to do. I might need to get a larger battery in the future.

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Sounds like you have a routine at least. Many generic chargers have a small adjustment potentiometer to set the charging voltage to. I have a one that I've adjusted to "90%", and another smaller one that I use if I want to fully charge and balance the pack. However, you need at least a cheap voltmeter/multimeter to measure the voltage; even a $10 one would be good enough though. If you adjusted your charger, at least you could stick with the same routine. On the other hand, if you're not detecting much range reduction from when you got the pack, then sticking with what you're already doing is an option.
https://www.youtube.com/watch?v=ViORzKrOfHU

If your KT display jas the voltage display option, use that. However, I have several bikes with LCD3's and they never read the same voltage for a fully charged 10S that I can move around. Up to 3/4 volt difference.

However, they all have the P5 option which controls how the bar gauge is updated. It must look at the voltage sag and take a some combo of the mean value and minimum value for voltage. I set it to 15 which I read somewhere works for 36V.