KT-LED880 low-voltage cut-out

[theWoosh]

Hi I have just converted my MTB with a Chinese 36v hub motor kit and a KT-LED880 handlebar controller...
I am using some old batteries from my previous e-bike, including one LiFePo4, 12 cell, which I am getting at rest voltage of 3.32v per cell and overall 39.9v.
This does not work on the e-bike, with the controller cutting out and giving a low voltage indication. My other battery pack (a Li-Pox10 giving out 42v), works fine (though it doesn't show full voltage indicator on the KT-LED880).
The KT-LED is marketed as a 36v/48v controller and I am wondering how intelligently this works - does it have any way to set or detect the actual battery voltage? or does it just cut out below 40v (i.e. to protect a 48v battery)?
If this is the case, is there any way to set the cut-out voltage (which I would rather have at least at 36v!) or do I need to replace it with a controller that actually is designed for 36v or is smarter? If so suggestions are welcome...
Thanks

 

[vfr400]

Please explain "doesn't show full".

 

[theWoosh]

IT shows just 3 LEDs lit up not 4...

Please explain "doesn't show full".

 

[vfr400]

If it was set to 48v, it would show one or none.

Measure that battery voltage whole the display is showing 3 lights, then you have your answer.

 

[theWoosh]

Thanks for replying - good point ...
But since the voltage level drops so quickly on Lifepo4, I have not found cheap battery level indicators to be very useful + we have no idea what voltage levels will trigger each led...

If it was set to 48v, it would show one or none.

Measure that battery voltage whole the display is showing 3 lights, then you have your answer.

 

[vfr400]

Thanks for replying - good point ...
But since the voltage level drops so quickly on Lifepo4, I have not found cheap battery level indicators to be very useful + we have no idea what voltage levels will trigger each led...

That's the point of using a voltmeter. It'll tell you all you need to know.

 

[theWoosh]

Does anyone have any info about how the KT-880 'knows' whether the supply is rated 36v or 48v?

 

[theWoosh]

I found a guide here http://www.szktdz.com/upload/file/20140813/20140813081138_34669.pdf for setting up the KT-LED890 which I am assuming is similar. It says:
...5. P5 parameter setting After entering P5 parameter setting interface, four battery indicator and 6KM / H function indicator will flash simultaneously. P5 is power monitoring mode, when P5 setting is 0, the power monitoring is the "real-time voltage" mode. Namely, it is the method to determine the battery capacity based on real-time battery voltage. When P5 equals to a specified parameter, the power monitoring is the "smart power" mode (this parameter is determined by the battery characteristics, ordinary 24V lithium is generally is 4-11, 36V lithium is between 5_15). P5 setting ranges from 0-15, short Press ON / OFF button or MODE button to select. P5 parameter setting method is the same to that of P2...
Sounds like there is a real risk of this not working at all if I get the settings wrong so any experience of setting 'smart-mode' or explanation about what that means would be useful. What I am aiming to do is set the cut-out below 36v if possible!

 

[Nealh]

4 led's will only light up once battery is greater then 80% .
At 39.9v the 880 probably is confused and doesn't know if it is reading a low 48v battery or a higher voltage 36v battery, my guess is the former due to it's differing chemistry. However the displays can't differentiate the chemistries and is simply going by voltage.

 

[Nealh]

Set P5 to value #12 to see if it helps.

 

[vfr400]

P5 doesn't do anything.

There's a bit of a quirk with KT battery displays, where they don't respond immediately, but settle down as soon as you start riding the bike. Have you tried it yet?

 

[theWoosh]

This is interesting - the problem is not to do with how accurate the display is though , it's just that the bike won't run at all! My original question was - is the KT880 shutting down the motor because it thinks I have a low battery (Can it do this or is it just a display)? Or is the issue something to do with a faulty BMS on the battery itself (or that the cell voltage is dropping super-low when a load is applied)
?

P5 doesn't do anything.

There's a bit of a quirk with KT battery displays, where they don't respond immediately, but settle down as soon as you start riding the bike. Have you tried it yet?

 

[vfr400]

This is interesting - the problem is not to do with how accurate the display is though , it's just that the bike won't run at all! My original question was - is the KT880 shutting down the motor because it thinks I have a low battery (Can it do this or is it just a display)? Or is the issue something to do with a faulty BMS on the battery itself (or that the cell voltage is dropping super-low when a load is applied)
?

You can run without the display to test the controller. Disconnect it and bridge the blue and red wires to it. That should give normal throttle and levl 1 PAS. You might have to bridge the two data wires to each other. That's the two that aren't blue, red or black. Sometimes, you get a special bridge connector with KT controllers specfically for that, so have a look to see if it's in the box.

 

[theWoosh]

Thanks vfr400 that's what I was thinking of trying and that info will help

You can run without the display to test the controller. Disconnect it and bridge the blue and red wires to it. That should give normal throttle and levl 1 PAS. You might have to bridge the two data wires to each other. That's the two that aren't blue, red or black. Sometimes, you get a special bridge connector with KT controllers specfically for that, so have a look to see if it's in the box.

 

[theWoosh]

I just tried the battery again on the bike (prior to trying to bypass the KT controller) and it worked! It gave me 3 LEDs (out of 4) and I rode it hard for a few miles up a very steep hill with no problems - LEDs dropped to 1 at one point but then went back up to 2. Voltage at end was 38.4v. Weird. Is it anything to do with the fact that previously I'd plugged in this pack (on two occasions) only after having ridden on a Li-ion pack? Did it detect the voltage of that and use it as a basemark or something? Who knows.... moral is maybe that the KT-808 is a bit random...