KT Controller maximum wattage limit.

[Zoi]

I recently installed a Cyclotricity 250w/36v front wheel conversion kit on a hybrid bike. All works fine.
Not happy with the LED display, primarily because you have to cycle through assist levels rather than being able to change up or down, which is way more user friendly when coping with undulating terrain.
So I replaced the LED display with a KT-LCD6. All works great except !!.....
When I selected assist level 5 the power reading was way over 250w, sometimes peaking 400wts.
I originally suspected that the controller was rated 350w so I re-programmed the KT unit with C5 set to 4, which adds a divisor of 1.5 to the maximum wattage.
Sure enough, the KT display now limits the maximum wattage value around 250w. ( I also noticed that the power levels were also reduced for assist levels 1-4).
However later, I check my controller and it is labelled 36v/ 7amps, which is 250w. So why do I have to change C5 to get the correct wattage limit and display?
Can anyone out there, make sense this, I can't ?
Its odd that there isn't a precise wattage limit setting in the KT programming ?

 

[Nealh]

You need to ride my bike, the KT controller is 12a rated with 25a peak over 900w at the wheel if needed. Happy days.

Your controller although 7a rated has a max current rating of 15a so about 430w at the wheel, not illegal as there are no stipulations for controller current .
As long as the motor is 250w rated you can plonk as much current as you like through it.

 

[vfr400]

As Above, and to confirm, 7 amps is the rated current, which is fairly meaningless. The maximum current allowed will be 14a or 15A. there is no legal limit on power from the controller, so you should set it back to where it was unless you actually didn't want that much power.

You should set P3=1 for current control to get a different power level in each level on the LCD, which will give you a better ride and allow you to cut down power when you want without having to go to the settings.

 

[Zoi]

I do have P3=1. I was just pointing out if you set C5 to reduce the maximum power, then intermediate power levels (1-4) are also reduced by a similar percentage.
Where these assist levels are derived puzzles me. I would have thought it should be based on a percentage of the maximum motor rating because then you could get sensible power steps ... but the display unit does not know the maximum motor rating. So do you get full welly on level 5 with no safety valve to prevent overcooking???
My main concern was not so much the legality of pumping more than 250w into the motor, rather a desire to run the system within the manufacturers specification, for reliability etc.

 

[anotherkiwi]

I do have P3=1. I was just pointing out if you set C5 to reduce the maximum power, then intermediate power levels (1-4) are also reduced by a similar percentage.
Where these assist levels are derived puzzles me. I would have thought it should be based on a percentage of the maximum motor rating because then you could get sensible power steps ... but the display unit does not know the maximum motor rating. So do you get full welly on level 5 with no safety valve to prevent overcooking???
My main concern was not so much the legality of pumping more than 250w into the motor, rather a desire to run the system within the manufacturers specification, for reliability etc.

Don't worry you are. 14-15 Amp peak controller is standard for 250W nominative motors and many motors have been running happily for years with them. A 250W nominative motor can handle 1 kW without issues. They don't like those power levels for long periods of time on very steep gradients.

I live on the bottom of the mountains and have ridden up a couple of Cat 3 climbs that figure in classic bike races at full power (540W), the controller gets warm but the motor doesn't.

Because one has to experiment I have tried my 250W motor with a 24 Amp controller which peaks at over 980 Watts with a fully charged 36v battery (or 1 kW with a 43v battery). Hills around here are pretty brutal - up to 17% - but short, nothing over 400-500 metres long. Nothing has the time to get warm because at 25+ km/h it takes less than a minute to climb most...

 

[Nealh]

PAS 1 gives approx. 13% of set current.
PAS 2 approx. 20%.
PAS 3 approx. 33%.
PAS4 approx. 50%.
PAS 5 100%.

 

[vfr400]

So do you get full welly on level 5 with no safety valve to prevent overcooking???

Can't you select level 4 or 3, 2 or 1?

Level 5 only allows full current when you're going slow. When you get up to a certain speed, you will see the power start going down. the only thing that causes over-cooking is going too slow up long hills, unless you have a high-speed motor.

 

[Zoi]

No problem with levels 1-4, it was only at level 5 where the power greatly exceeded the 'nominal' 250w that I was concerned about. Anyway, thanks for all the replies, I have a much better idea now about power levels.