Is kt36 controller safe with 48v battey

[neixian]

Hi guys,

Tried searching but no results.

Is it safe to do so? My ebike is 36v 350w hub drive with kt36zwsr controller and kt-lcd5 display.

Now I have a 48v 15ah battery and want to mix batteries.

It appears that kt-lcd5 can sense the voltage but I am not sure.

Thanks in advance.

 

[docw009]

The first showstopper is whether the controller can work with 48V. What I've done is pull off a rear cover on the controller and look inside. The long tubular components are electrolytic capacitors, and their maxi,mum working voltage is marked on them. It's going to be either 50V or 63V. The one in this picture is 63V.



If it's 50V, you should not go with a 48V battery because full charge on a 48V battery is 54.6V, Long term, that will cause a 50V capacitor to fail early. In addition, KT controllers that support dual voltage will usually say that on the label.




I do own one 36V KT controller, and it did not surprise me when I peeked inside. It has 50V capacitors. I don't mix batteries on it. It is convenient to do so with my dual voltage controllers.

A 20A dual voltage KT controller is around $35-45 shipped.

 

[neixian]

The first showstopper is whether the controller can work with 48V. What I've done is pull off a rear cover on the controller and look inside. The long tubular components are electrolytic capacitors, and their maxi,mum working voltage is marked on them. It's going to be either 50V or 63V. The one in this picture is 63V.

View attachment 342635

If it's 50V, you should not go with a 48V battery because full charge on a 48V battery is 54.6V, Long term, that will cause a 50V capacitor to fail early. In addition, KT controllers that support dual voltage will usually say that on the label.


View attachment 342637

I do own one 36V KT controller, and it did not surprise me when I peeked inside. It has 50V capacitors. I don't mix batteries on it. It is convenient to do so with my dual voltage controllers.

A 20A dual voltage KT controller is around $35-45 shipped.

Thank you very much. I will open it to see if it 50v or 63v.

 

[slaphappygamer]

I googled your controller. I found this.

It’s listed only as 36v. The low voltage cutoff would be 30v. If you use a 48v battery, the low voltage cutoff of the controller will still be 30v. It is bad for a 48v battery to be so discharged. You’d have to rely on the battery bms to manage the low voltage cutoff.

 

[docw009]

That's a good point, SlapHappyGamer. I forgot about the low voltage cutoff. I think many KT LCD displays detect the battery voltage on powerup , picks the LVC and shuts off the controller. Some of them allow you to adjust the LVC up/down by a few volts. Some, like the KT LCD1 don't have any voltage settings at all.

But if the above doesn't happen, then you're using the controller's built in LVC, and if it's 30V, that's well below the 40V usually used for a 48V battery. Your 48 battery BMS should trigger at 3V/cell, which will be 39V, if it has a working BMS.

I used to run a 52V battery on my 48V KT controller. I did not change the LVC settings on the LCD5 display, so it would try to run the 52V battery down to 40V. but the battery BMS would shut off around 42V. I had a 52V Luna changer that did not always start if the battery got down that low. That was a Luna problem. Other 52v chargers would work,

Kt controllers also use a power resistor to drop the voltage in front of their DC-DC converter circuits, I've never seen one fail, but have seem pictures of ones that overheated. This would be aggravated by overvoltage.

 

[neixian]

I googled your controller. I found this.

View attachment 342649 It’s listed only as 36v. The low voltage cutoff would be 30v. If you use a 48v battery, the low voltage cutoff of the controller will still be 30v. It is bad for a 48v battery to be so discharged. You’d have to rely on the battery bms to manage the low voltage cutoff.

As Docw009 said here, I believe that the KT LCD5 manual does say that it sense the voltage therefore LVC is not an issue but the component voltage limit is realy a concern.

 

[E-HP]

As Docw009 said here, I believe that the KT LCD5 manual does say that it sense the voltage therefore LVC is not an issue but the component voltage limit is realy a concern.

No, docw009 and slaphappygamer said the same thing:

"But if the above doesn't happen, then you're using the controller's built in LVC, and if it's 30V, that's well below the 40V usually used for a 48V battery. "

"The low voltage cutoff would be 30v. If you use a 48v battery, the low voltage cutoff of the controller will still be 30v. It is bad for a 48v battery to be so discharged. "

 

[neixian]

No, docw009 and slaphappygamer said the same thing:

"But if the above doesn't happen, then you're using the controller's built in LVC, and if it's 30V, that's well below the 40V usually used for a 48V battery. "

"The low voltage cutoff would be 30v. If you use a 48v battery, the low voltage cutoff of the controller will still be 30v. It is bad for a 48v battery to be so discharged. "

Yeah. I think the LCD5 detects the voltage and set up the controller accordingly.

But anyway, I can read the voltage on the display to see if it falls too low.

Thanks for your help!

 

[slaphappygamer]

The low voltage cutoff is set by the controller. The voltage setting, of the display, will only display the battery voltage. This setting will not change the low voltage cutoff. Only the displayed voltage will be changed.

Watching the battery voltage will help you avoid running your battery too low, thus making more heat. I find that 46v is a good voltage, for me, to charge my battery. Under heavy load/steep hill, I can see up to a 4v voltage sag, so if my battery drops under 44v, I could hit my low voltage cutoff. Good to keep an eye on it.

 

[neixian]

The low voltage cutoff is set by the controller. The voltage setting, of the display, will only display the battery voltage. This setting will not change the low voltage cutoff. Only the displayed voltage will be changed.

Watching the battery voltage will help you avoid running your battery too low, thus making more heat. I find that 46v is a good voltage, for me, to charge my battery. Under heavy load/steep hill, I can see up to a 4v voltage sag, so if my battery drops under 44v, I could hit my low voltage cutoff. Good to keep an eye on it.

yes. Display usually set up the controller. I hope by sensing the voltage, the display will set up the controller accordingly.

 

[E-HP]

yes. Display usually set up the controller. I hope by sensing the voltage, the display will set up the controller accordingly.

No, the controller senses/guesses the voltage, not the display. KT controllers don’t even need a display to operate or to set the input voltage. What was the rating of the caps?