Help! Slight tweaking question

[Grafix01]

I'm happy with my new E-go MAX bike but note that its LCD (a Kunteng LCD 5) is locked and so no tweaking of any parameters is possible. I get that but I'm an engineer and born to tweak!

If I was to buy a std LCD 5 and swap it in would I actually have any real room for modification of the bike's performance though?

It's a 20" wheel bike with a 36V LG branded 14ah battery and a MXUS XF08 250W rear hub motor. Am I right to think that pretty much limits it to the legal UK numbers anyway and so it's not got any untapped performance that could be used off the road even if I had an unlocked LCD? (I've yet to look at the KT controller in the frame so am not sure of its specification yet).

Cheers!

 

[saneagle]

A standard LCD5 or any other of the KT displays will work and give you access to change the settings. There should be a bit more speed to come if that's what you want. 20" wheel motors normally spin to 21mph with the battery at 36v, so maybe 18 mph on a flat road with light pedalling, and a couple more mph with a fully charged battery.

 

[Grafix01]

A standard LCD5 or any other of the KT displays will work and give you access to change the settings. There should be a bit more speed to come if that's what you want. 20" wheel motors normally spin to 21mph with the battery at 36v, so maybe 18 mph on a flat road with light pedalling, and a couple more mph with a fully charged battery.

Much appreciated - thank you!

 

[Grafix01]

Having had a squint at the controller now its a KT model with rated current of 7A and max current of 15A.

To follow up on my query and the info received does this basically mean the motor is limited to continuous 250W by the combination of 14ah 36V battery and this controller since 7A*36V = 252W - but peak power reaches 500W? (14A*36V).

I assume there is no easy way to raise the rated current from the controller to 8/9/10A?

I also see the motor I have (MXUS XF08) listed with various rated rpm - anything from 270 to 350rpm. Am I right to think that if it was only 270rpm I would struggle to get any higher speeds - as with my 20inch wheels that is only 26.2kph? It would take higher voltage than 36V to over speed the motor - and probably break it!?

Cheers for any pointers!

 

[saneagle]

You won't know anything about the speed of the motor until you test it unrestricted.

Higher voltage won't break the motor. It just makes it spin faster. It's current that burns motors. A Mxus XF08 can easily handle 48v, especially in a small wheel. bear in mind that a 20" wheeled bike without suspension won't be pleasant above 20 mph, and the frame and folding mechanism isn't designed to take the shock loads.

15A max with a 36v battery will take a maximum of 15 x 40 watts from the battery, which is 600w. At peak efficiency of around 70% at 75% max speed, that's 420w output power.

The current is set by the levels on the LCD, assuming that it's set to current control. On level 5, you get 15A.

Some versions of the software allow you to turn up the current in the sttings, but most versions now only allow you to turn it down from the maximum 15A.

You can change the maximum current without using the settings by adding solder to the shunt inside the controller. Each 10% of it's length you add solder to increases the current by 10%. Do not solder more than 30% otherwise the controller will get too hot.

 

[Grafix01]

You won't know anything about the speed of the motor until you test it unrestricted.

Higher voltage won't break the motor. It just makes it spin faster. It's current that burns motors. A Mxus XF08 can easily handle 48v, especially in a small wheel. bear in mind that a 20" wheeled bike without suspension won't be pleasant above 20 mph, and the frame and folding mechanism isn't designed to take the shock loads.

15A max with a 36v battery will take a maximum of 15 x 40 watts from the battery, which is 600w. At peak efficiency of around 70% at 75% max speed, that's 420w output power.

The current is set by the levels on the LCD, assuming that it's set to current control. On level 5, you get 15A.

Some versions of the software allow you to turn up the current in the sttings, but most versions now only allow you to turn it down from the maximum 15A.

You can change the maximum current without using the settings by adding solder to the shunt inside the controller. Each 10% of it's length you add solder to increases the current by 10%. Do not solder more than 30% otherwise the controller will get too hot.

Fantastic info - thanks for putting it so clearly.

I understand your point about the speed too by the way - it's 'happy' at 15.5mph but you can sense the motor has more to give - as it cuts 'thrust' quite obviously when it hits that speed on the flat. I don't want to make the bike feel squirrelly as you say - but 2-4mph more would be good.

Really appreciate all the info you've laid out for me - thank you!

 

[saneagle]

Fantastic info - thanks for putting it so clearly.

I understand your point about the speed too by the way - it's 'happy' at 15.5mph but you can sense the motor has more to give - as it cuts 'thrust' quite obviously when it hits that speed on the flat. I don't want to make the bike feel squirrelly as you say - but 2-4mph more would be good.

Really appreciate all the info you've laid out for me - thank you!

20 mph will be OK, but it starts to get dodgy after that the faster you go. 30 mph would be good if you're tired of living and have left everything to me in your will.

 

[Grafix01]

20 mph will be OK, but it starts to get dodgy after that the faster you go. 30 mph would be good if you're tired of living and have left everything to me in your will.

Deal!

 

[Grafix01]

Could I ask. Would the XF08 hub motor cope OK with some higher current? I'm seeing there is a KT 6-mosfet controller the same size as mine but with rated 10A output and 20amp max - versus my controller's 7A/15A spec.

 

[Nealh]

With KT the current rating relates to the power use in PAS level 4, pas level 4 is 50% current power. It is only PAS level 5 or throttle use that will deliver the max rated current of 15a.
Typically with KT one will see the following max current % in each PAS level.
PAS1 13% /1.95a, 70w.
PAS2 20%/ 3a, 110w.
PAS3 33%/ 4.95a, 180w.
PAS4 50%/ 7.5a, 270w .
PAS5 100%/ 15a, 540w.

The watts are the lcd displayed and doesn't take into account the inefficacy of the power lose /conversion.

As can be seen PAS 1 or 2 are the most economical PAS levels to use if wanting to eke out range. They don't equate to max speed as max speed is attained in any of the five PAS levels, PAS level simply eqautes to how much power is provided and how quick the acceleration /torque is felt at the pedals.

 

[saneagle]

Could I ask. Would the XF08 hub motor cope OK with some higher current? I'm seeing there is a KT 6-mosfet controller the same size as mine but with rated 10A output and 20amp max - versus my controller's 7A/15A spec.

It should be fine at 20A and 36v, and maybe 17A at 48v.

Your controller is only rated for 7A. If you run it above 10A for prolonged periods, it will overheat. As your motor speeds up, the back emf opposes the battery voltage, so no matter how much the controller allows, you cannot get maximum current at high speed. The current ramps down to zero when the motor reaches its maximum speed, so a typical ebike with a motor maxing out at 20mph and cruising along at 15 mph will not be getting more than 10A.

This is one problem with going to a higher voltage. The higher battery voltage will keep the net voltage high enough to keep pushing the maximum current at higher speeds, so that typical ebike just mentioned, now maxing out at 25 mph, will get the 15A all the way to about 18 mph, which will cause the controller to overheat, not the motor. What people don't realise is that speed can be good for the battery, motor and controller because it restricts the current.

 

[Grafix01]

It should be fine at 20A and 36v, and maybe 17A at 48v.

Your controller is only rated for 7A. If you run it above 10A for prolonged periods, it will overheat. As your motor speeds up, the back emf opposes the battery voltage, so no matter how much the controller allows, you cannot get maximum current at high speed. The current ramps down to zero when the motor reaches its maximum speed, so a typical ebike with a motor maxing out at 20mph and cruising along at 15 mph will not be getting more than 10A.

This is one problem with going to a higher voltage. The higher battery voltage will keep the net voltage high enough to keep pushing the maximum current at higher speeds, so that typical ebike just mentioned, now maxing out at 25 mph, will get the 15A all the way to about 18 mph, which will cause the controller to overheat, not the motor. What people don't realise is that speed can be good for the battery, motor and controller because it restricts the current.

Perfect - all understood - many thanks!

 

[cyclebuddy]

If upping the speed, the OP maybe needs to consider gearing too. The e-go looks fairly similar to my own 20" folder; 52t/14t, 7sp Tourney. Spinning gets pretty frenetic at/beyond 20mph.

 

[Grafix01]

If upping the speed, the OP maybe needs to consider gearing too. The e-go looks fairly similar to my own 20" folder; 52t/14t, 7sp Tourney. Spinning gets pretty frenetic at/beyond 20mph.

Definitely agree! It's pretty spinny at 17/18 going downhill so that would need some thought as you say.

 

[saneagle]

If upping the speed, the OP maybe needs to consider gearing too. The e-go looks fairly similar to my own 20" folder; 52t/14t, 7sp Tourney. Spinning gets pretty frenetic at/beyond 20mph.

That's always the problem on bikes with 20" wheels. If you have a 52T chainring, and freewheel gears, you can always fir a DNP freewheel to get 25% less pedal speed with its 11T top gear.

 

[Peter.Bridge]

Don't know if they have different motor windings for different size wheels but my XF08c on 700c wheels maxes out at 19mph on the flat with me pedalling

 

[Grafix01]

With KT the current rating relates to the power use in PAS level 4, pas level 4 is 50% current power. It is only PAS level 5 or throttle use that will deliver the max rated current of 15a.
Typically with KT one will see the following max current % in each PAS level.
PAS1 13% /1.95a, 70w.
PAS2 20%/ 3a, 110w.
PAS3 33%/ 4.95a, 180w.
PAS4 50%/ 7.5a, 270w .
PAS5 100%/ 15a, 540w.

The watts are the lcd displayed and doesn't take into account the inefficacy of the power lose /conversion.

As can be seen PAS 1 or 2 are the most economical PAS levels to use if wanting to eke out range. They don't equate to max speed as max speed is attained in any of the five PAS levels, PAS level simply eqautes to how much power is provided and how quick the acceleration /torque is felt at the pedals.

Really interesting - thank you - I had wondered at the various PAS levels versus current and this explains it really well.

 

[saneagle]

Really interesting - thank you - I had wondered at the various PAS levels versus current and this explains it really well.

That's only if it's set to current control (P3 =1). It can also be set to speed control, where you get a different speed in each level and the same current (P3=0).

 

[Peter.Bridge]

Don't know if they have different motor windings for different size wheels but my XF08c on 700c wheels maxes out at 19mph on the flat with me pedalling

Just tried holding the backwheel off the ground and turning the pedals with my hands - showed 21 mph (obviously with no load)

 

[Grafix01]

That's only if it's set to current control (P3 =1). It can also be set to speed control, where you get a different speed in each level and the same current (P3=0).

Yep - understood - it is set as P3 = 1 and looking at the LCD5 user manual I'd realised the difference between that and setting P3 to 0 where it would change to speed threshold related cut-off in each level.

Do you happen to know what those speed thresholds are in levels 1 to 5?