At what voltage might battery cut out?

[HJ]

I've got a question. Ive had a KS – 18 for about a month now. I have the big battery, 1360, and  usually charge up again once I've gotten down to 50%.  But I was wondering, I notice my voltages will sometimes go as low as 58 when under load (that is, when I am starting out at 50% (about 60v), and going uphill.   I know, being a unicycle, it's always under load, but I'm speaking of when I'm going up a hill. Does anyone know exactly at what voltage you're in danger for motor  cut off? when fully charged up,  it's starts at 66 V.

H

[Cloud]

1 hour ago, HJ said:

I've got a question. Ive had a KS – 18 for about a month now. I have the big battery, 1360, and  usually charge up again once I've gotten down to 50%.  But I was wondering, I notice my voltages will sometimes go as low as 58 when under load (that is, when I am starting out at 50% (about 60v), and going uphill.   I know, being a unicycle, it's always under load, but I'm speaking of when I'm going up a hill. Does anyone know exactly at what voltage you're in danger for motor  cut off? when fully charged up,  it's starts at 66 V

if you are talking strivtly about the battery voltage operating  range, then according to the current firmware, you may not be able to ride the wheel below about 50v , it will beep, indicator will flash, and it may tilt back on you. 

However if you are talking about the motor cutting out due to lower power, there is not enough info to answer your question. If you have a 800w unit, you need to be careful when the battery gets below 56v or so. However this depends on your weight, speed, and riding style. Whenever you see 4 bars or less you need to be careful, especially on ks18 with 800w - dont go at top speed - the latest firmware may allow the wheel to cut out or lose balance under high load on low power without tiltback.

[esaj]

It depends, if it's the BMS cutting the power, they usually have some "threshold" voltage, below which the power will be pretty much instantly cut, and the lower the battery voltage is (in rest) the lower it will dip during high discharge (climbing, hitting a pothole, acceleration...). Some BMSs are really fast reacting, the voltage doesn't need to dip below the threshold but for a split second (like 1/100th of a second or so) and the power is instantly cut, whereas some might allow it to dip below it for a short while (half a second or so?) without cutting.

Don't know what sort of motor power cuts are programmed in the KS firmware, and at what situation(s) does it cut the power (ie. is there some voltage level at which it would cut the power).

[HJ]

When I get below 6 bars I tend to be real conservative with my riding style    

H

[Keith]

6 minutes ago, HJ said:

When I get below 6 bars I tend to be real conservative with my riding style    

H

With that much battery you can afford to!

A lithium Ion battery is fully charged at 4.2V ( arguably 4.25V but a bit lower gives a safety margin. Off load the cells have no capacity left at 3V, on load that could be as low as 2.5V. Off load much below 3V or more than 4.25V will do permanent damage. Multiplying this by the 16 series cells in KS wheels means the practical range is 67.2V to 48V.

Battery management systems need to be somewhat conservative, older KS wheels like mine alarm at 55V, @Jason McNeil knows more accurately but, I think, the newer wheels alarm at 50V. By 'alarm' I mean start beeping and then tilting back. Again, Jason has done some work on this but, if I remember correctly, the KingSong wheel will tilt further and further back the lower the battery gets until it is impossible to ride. It should not just suddenly fail on you.

I rode my 340Wh KS-14C wheel at a London roller skate run of 8 miles two weeks ago and with riding to get there, lots of stopping, etc. I was down to 2 bars, occasionally under load, no bars; at the end of it all it did was beep and start to tilt back at around 8-10MPH, other than that it was still fine. I'm confident the KS wheels behave like gentlemen under low battery conditions.

However, before the start, with a very fully charged battery, I accelerated to full speed (25kph on mine) and then braked to make a turn. None of my actions were aggressive and I run at full speed every week in my local park however this time , the peddles became floppy and I face planted. I'm convinced this was the regenerative braking having nowhere to go as the batteries were full so I lost all braking torque. I'm now less confident of the wheels full battery behaviour.

[HJ]

Thanks Keith, Esaj, and my boy Cloud. Excellent points.

H

[Jason McNeil]

On 4/2/2016 at 8:23 PM, HJ said:

I have the big battery, 1360,

That's four physical packs of 32 cells each, each of these 32 packs is daisy chained together, but has eight parallels of 16 cells in series. Even with the pretty mediocre LG MG1s, these can sustain between 5-7A each, that's 128 cells x 5A x 3v (to be conservative) =  1920W sustained from the battery pack, clearly this isn't going to be the bottleneck on power delivery.

If there is going to be a component heavily stressed, on something like acceleration up the Himalayan plateau, this is likely to be the control-board which can exceed 3500W output, but as the temperature hits 70°C you'll get tilt-back exceeding 15°, forcing you to get off. The good thing is it doesn't take long for the temperature to drop back down—under testing it's about 7°C/min from 70°C. 

On 4/2/2016 at 11:56 AM, Keith said:

newer wheels alarm at 50V. By 'alarm' I mean start beeping and then tilting back

Like Keith said, the early KS had the extreme-tilt-back voltage set to 56v & get off now at 54v. For my order, I asked that KS modify the firmware on the 64 cell packs, reducing the limp-home to 52v and get-off-now to 48v—the rationale was that with four parallels, there is more than enough juice left in the cylinders to extend the riders journey by about 20-30%