Coast -> throttle apply -> dead. KT72SVPRK + KT-LCD3

Hey there,

I have a strange phenomenon with my Kunteng sine wave controller KT72SVPRKD-LCD + KT-LCD3 running on 72V and would be interested to hear your opinions.
Very sporadically when I reapply throttle from coast condition there is no power and the display goes blank. It feels like a short or the motor tying up. Releasing the throttle and applying it again it works well.
Can it have something to do with the settup? There are some parameters regarding the motor programming in the controller that I am not sure about.
It's a sinewave controller but in a discrete riding condition it makes the humming noise: low speed with little load.

Any ideas?

If the display goes blank, the battery supply to the controller has been interrupted. The display works independently from the controller and is connected directly to the battery from a wire that branches off the main battery wire inside the controller.

good info!
next time i will try what happens when i disconnect the display.
battey voltage (SOC) is good. it only happens when i apply the throttle bit. the motor delivers negative torque then.
maybe some setting is so off that i pull down battery voltage below what the display can handle.

AFAICS, it's not a setting, it's a supply issue.

If it's dropping so low that it stops working and blanks the display, your battery is sagging in voltage so much that the system cannot operate at all.

That either means that the battery's BMS is shutting the pack output down due to cell LVC/etc., or if there is no BMS that the battery is simply incapable of supplying hte amount of current you need.

The latter could be because it's not big enough or it's defective or connections between cells or the outside world have too much resistance, etc.


Or the battery could simply be too discharged and needs to be charged back up again. Or unbalanced, with one or more cells much lower than the rest, either because they're old or defective or simply not fully charged vs the rest of them.

joe81 said:

the motor delivers negative torque then.

Click to expand...

"negative torque" :?

Do you mean the motor spins backwards?

Or do you mean that it holds itself in one position and resists motion?

it only happens sporadically when in the transition from coast. so it's still spinnng forward but i think it's braking a bit.

battery seems okay. the next seonds i can accellerate strongly (stronger than the request when the issue happened).

If it's intermittent and works most of the time then I'd suspect a connection, either inside the battery or from the battery to the controller, or controller to display, etc.

joe81 said:

good info!
next time i will try what happens when i disconnect the display.
battey voltage (SOC) is good. it only happens when i apply the throttle bit. the motor delivers negative torque then.
maybe some setting is so off that i pull down battery voltage below what the display can handle.

Click to expand...

It's not the LCD that's faulty. It's just showing that your battery supply is faulty. Three possibilities I can think of:

Bad conection somewhere on the main power from the battery;
Battery not able to give enough current for the demand;
Intermittent short circuit.

Did you ever sort this out joe81
I have the same controller doing the same thing :?

The issue should be when the firmware increases duty-cycle from zero (motor coasting) up to throttle value, and motor brakes a bit before running at speed that wad coasting.

I suspect the issue is about to much current asked frim the battery pack on that situation. Try to reduce the controller current with C5 and see if it helps.

The controller can control 2 types of currents: motor phase current and battery current. Motor phase current can be a big value and I think it is a value hardcoded on firmware and depends on the motor resistance you use, a powerful motor should have a lower resistance.

With our OpenSource firmware, the user can configure both motor max phase current as also max battery current. Also, the increase step of duty-cycle, with a slower value both current will increase slow and help avoid shutdown of the BMS, etc.

I'm experiencing a similar thing after coasting and it's not the battery causing the power fade. I've tried it with a fully charged lipo pack so there's no way it can't deliver the power a small controller is asking of it. When trying to configure the motor P settings it would also cause a dimming of the display and a similar power down with anything more than gentle throttle application. With the correct P setting you could mash the throttle and constantly and have no issues. So I can only assume that something in the controller / firmware is telling it to pull down the voltage to the display and thus power it down.