Special bike (old trial) converted but weak

[Triad]

Hello! New member here, total ignorant when it comes to electricity and batteries 
I've just acquired a special bike, basically a 70s trial converted to electric with a 5kw Golden Motor and, as far as I know, a 20amp battery pack.
It's very very nice looking but the engine is really really weak, and the guy says if you floor it, the engine (or the battery) will turn off for protection.
There isn't much room on that frame for a bigger battery, and the bike has a nice reduction pulley so the movement doesn't go directly from motor to wheel.
The transmission works with belts.
I've got the battery charger and a cable to set the ecu/controller parameters from my computer. Hope the pictures will be visible.

[Bikemad]

Hi Triad andto the forum.

If the motor is cutting out under load, I would say that the battery (or the battery's BMS) may be unable to deliver the required power under maximum load, and the BMS is simply cutting the power going to the motor to protect either itself or the battery.

If the battery has one or more weak cells, the weakest cell voltage can be pulled low enough under load that it reaches the minimum permitted cell voltage setting in the battery's BMS, which would trigger the BMS to instantly shut off the power going to the motor.

If the maximum current output of the battery's BMS is being exceeded under heavy load, it is possible that the BMS will also cut off the power to protect itself from being overloaded.

A suitable voltmeter attached to the battery connections on the controller would allow you to see what is happening to the supply voltage under load.
If you have a 48V battery and the voltage at the controller drops to 42V (52V for a 60V battery or 63V for a 72V battery) just before the motor cuts out, it is likely to be a weak cell/cells in the battery.
A new battery of a similar size, but with improved cells that can deliver at least 120 Amps, may be required to extract maximum power from the motor.

If you don't want to purchase a higher power battery, you should be able to gradually reduce the Battery drawn current (A) setting until the battery no longer "turns off" under full throttle.
However, if it's weak cells that are causing the problem, these cells will probably continue to weaken, causing the cutting out to eventually return even with the reduced battery current settings.

If the voltage at the controller does not drop as low as 42V (or 52V/63V for 60/72V battery) before the motor cuts out, it could be the BMS that is causing the problem. It could be faulty, or it may need to be upgraded with a BMS that has the required current output (provided the cells in the battery are able to deliver the increased current.)

If the voltage at the controller does not drop when the controller cuts out, it could simply be that the stall protection is being activated by the controller itself.
If this is the case, try increasing the stall protection time (s) setting in the controller to see if it improves the cutting out.

Alan
 

[Triad]

Hello, thanks for your reply! Please be patient as I'm really really a total newbie in this field, know next to nothing.
The builder said that the bike has this problem but I didn't even experience it 'cause it's so weak at low speed that a relatively easy uphill will stop it.  :'(
He gave me a cable to connect the bike to the computer to check the various settings... how do I check the BMS parameters?
I might also have a problem with dimensions if I decide to replace the battery, as the frame won't allow to use a longer pack, could only use one that's a bit taller or maybe wider.

I might live with it cutting out at "high speed" (note the quotes) but if it can climb up easy uphills, then it's just a nice static model.

As I said, I can basically stop it with my feet when I take off but it feels like it gradually gets better in a few meters... the problem is, if the throttle response is so poor, you can only use it uphill if you have enough momentum.

[Bikemad]

He gave me a cable to connect the bike to the computer to check the various settings... how do I check the BMS parameters?

The BMS is unlikely to be user configurable unless it has Bluetooth connectivity which allows user to change certain parameters. Most BMS have a sticker on them stating the maximum and continuous current figures and voltage etc.. As the BMS is usually hidden inside the battery casing, there may be a sticker on the battery casing with the voltage and current figures etc. if you're lucky.

I can basically stop it with my feet when I take off but it feels like it gradually gets better in a few meters... the problem is, if the throttle response is so poor, you can only use it uphill if you have enough momentum.

I have just been looking at the dynamometer data for the 48V version of that motor and it shows ~24Nm of torque with a 176 Amp current draw. Unfortunately, I suspect that your bike may have the VEC300 controller that is only rated for 120A @ 48V or 100A @ 72V. The 48V 5kW motor is only likely to produce ~ 13Nm of torque with a 120 Amp current draw.

The gear reduction on your bike is similar to the original Electro-Motion trials bike, which also had a two stage gear reduction. 
The primary stage was via a toothed drive belt, but the secondary stage utilized a more convention chain and sprocket drive:


The primary belt reduction ratio was ~2:1, and the secondary chain and sprockets gear ratio was 6.45:1 (9T:58T):


This provided a combined total gear reduction of ~12.9:1.

After carefully studying your previous picture, your bike appears to have a 3:1 primary reduction (14T:42T), but as the rear sprocket is not shown I can't tell what the secondary reduction is (14T:??T).
If yours has a 42 tooth sprocket on the rear wheel, that would give a 9:1 overall gear reduction ratio, which (according to my calculations) means the torque at your rear wheel should be ~117Nm @ 120 Amps.
If it's a 56 tooth sprocket on the rear wheel, that would be a 12:1 overall gear reduction ratio, which should provide ~156Nm of wheel torque @ 120 Amps.

I've guessed that your rear tyre's outer diameter is likely to be ~600mm (24"), in which case a 42 tooth rear sprocket should provide a forward force of ~384N (39kg or 86lbs), which I reckon should be sufficient to propel a combined 250kg load (bike and rider) up a 11% slope.
If your rear sprocket had 56 teeth it would provide a forward force of ~512N (52kg or 114lbs) that should be sufficient to propel the same 250kg load up a 19% slope!
In ether case, your motor is obviously not drawing anywhere near 120 Amps from a standstill, because you would not be able to stop it so easily with your feet if it was.

You should be able to use the PI-800 programming software with the USB programming cable to read the parameters from the controller. If you can then attach some screenshots (or the exported *.FOC file) I will take a look at your existing settings to see if there is anything obvious that needs to be changed to hopefully improve the low speed torque/power.
       
If you need the USB Driver, it can be download from here.

Alan

P.S. I don't know what voltage your battery is, but I'm guessing that it's a 20Ah pack (Ampere-hour = storage capacity) rather than 20Amp (Ampere = unit of electric current).
 

[Triad]

Thanks a lot for your time and your impressive guesswork! The rear is a 18" rim, I guess 24" outer diameter is a good guess.
The rear "sprocket" is still a pulley but I still have to count the number of teeth on it.
I have no idea of what controller's under the fake tank of the bike, but for sure the battery is too small.
The bike is very weak from a stop, but it feels like in a few meters it gains some momentum. The guy gave me a cable to connect the controller to a pc via USB and change the parameters, but I'm still trying to work on the "hardware" by replacing the front pulley of the primary from Z16 to Z12 to increase the torque. Replacing the rear pulley on the wheel is also a possibility.
The bike doesn't really have much room for improvement in the battery compartment, so I'll just try to work with what I have.
I attach a picture of all the parts of the bike, don't know if you can recognize motor, battery pack and controller.

[Triad]

Ordered the pulley from the primary, 12 teeth is the smallest I could find... hopefully it will make a sensible difference (the stock one has 16 teeth).
I still haven't found time to remove seat and tank and check the controller, though  :'(

[Triad]

Got the 12Z front pulley... definitely much better torque. I had to put together a very very very very ugly belt tensioner as the original 500mm belt is now, obviously, too long.
I'll try to check the controller settings tomorrow... but isn't there an "automatic" setup for these controllers?

[Triad]

Tried my hand with the program... tried to up the boost, the maximum drawn current etc. but the bike now will go into protection as long as the throttle is twisted fast.  :'(
I also checked the controller model: 48V300L, item type VE C300/48Vdc.
I'll have to order a belt from aliexpress as those measurements are impossible to find here in Europe.

Any advice about how to make it better from dead stop without making it "stall" into protection mode?

[Bikemad]

Apologies for the delayed reply but I missed the notifications for your previous replies as I'm still experiencing major grief with all of my Hotmail email accounts on my Windows PC and on my Android phone.

I'll try to check the controller settings tomorrow... but isn't there an "automatic" setup for these controllers?

There is no automatic setup for these controllers, just the ability to load the factory default settings, which may not be correct for your setup.

Tried my hand with the program... tried to up the boost, the maximum drawn current etc. but the bike now will go into protection as long as the throttle is twisted fast.  :'(

Any advice about how to make it better from dead stop without making it "stall" into protection mode?

Could the fault be happening when the throttle is being twisted fully, rather than just being twisted fast?
I'm wondering whether you may be experiencing a problem caused by the throttle signal voltage exceeding the Throttle maximum allowed voltage (V) value at full throttle, but this would usually be accompanied by the 12 beep/flash error code from the controller if this were the case. 

If your throttle is a potentiometer type (not a Hall Sensor type) it could be triggering the Throttle voltage range protection if the throttle signal voltage output exceeds 4.0V at full throttle with the default throttle voltage protection values.

If you are not sure on the throttle type, try temporarily setting the Throttle voltage range protection enable value to 2:Disable and see if it cures the problem.

Check out this post for further information on the Throttle voltage range protection values and why it should be enabled.

Alan
 
EDIT: Faulty link repaired

[Triad]

Thanks for your reply. Not sure of the type, externally it's a normal throttle like on a motorcycle but it's got a small "dimple" on the grip. I see it turns off if I twist the throttle too fast, but before I modified the settings, it did it (as far as I know) if the rider tried to reach top speed. Can't open the link you provided for some reason.
Is it possible/safe to raise the protection limit? Would it be risky?

[Bikemad]

The previous link should now be working properly, and that post explains what could happen without the throttle voltage range protection being enabled.

If you have a potentiometer type throttle, raising the protection voltage to allow its maximum signal voltage (~5V) would basically have the same effect as disabling the throttle voltage range protection.
So you could still end up with the motor stuck on full throttle if any of the connections or wires on the ground circuit of the throttle failed due to fatigue or suffered physical damage etc.! 

If temporarily disabling the throttle voltage range protection cures the cutting out at full throttle, you should add some resistors and re-enable the throttle voltage range protection for safety reasons.



Alan
 

[Triad]

I can turn the bike off with a switch on the fake tank... so if there's no chance of harming battery or motor, I'd go for it.
It got worse after I altered some of the values, though. So I guess I'll have to put it back to default settings and then disable the throttle voltage protection.
I activated the "turbo mode" or something like that, as it should help the motor from take-off... I'm not very interested in top speed but I'd like more torque/power down low and from a dead stop.

[Triad]

Ok, another update: I finally put the bike back together after altering the primary belt and pulley. It's definitely way more powerful from a dead stop, but even after disabling the protection voltage it will still "freeze" if I give full throttle. Why and how can I fix this?

[Bikemad]

If it's not the throttle voltage range protection causing the cutting out (and you're not getting any error code beeps from the controller) then I'm thinking that it's probably the battery/BMS that is cutting the power because too much current is being drawn (or a cell voltage is being pulled too low) under high load.

You should be able to gradually reduce the Battery drawn current (A) setting until the battery no longer "turns off" under full throttle.

Tried to up the boost, the maximum drawn current etc. but the bike now will go into protection as long as the throttle is twisted fast.

Did you try reducing the Battery drawn current (A) setting to see if it made any difference?
You might not be able to pull the higher current required from the battery for increased torque if your battery/BMS is unable to supply it. 

Alan
 

[Triad]

Just for others having similar issues, lowering the maximum drawn current did the trick but I had to lower it to 100 (default setting was 250!).
Now the bike won't cut off but it's pretty weak if compared to how it was. Yeah, I can twist the throttle completely but I can feel it lacks the torque it had before at half throttle from a dead stop.