Help! My pedelec suddenly got faster (SameBike JG20, YSDX20, XW-20ZC) - long text!

[Craigs]

@sjpt:
None of the documented tweaks for setting changes (brakes, buttons, switches) seems to work.
At least I feel vindicated that my original observation (higher speed after 3 charges) was NOT accidental, but a planned run-in by the manufacturer. I did find several similar comments in reviews at the dealer's site. Someone is counting 1-2-3-GO! somewhere in this funny bike.

It does not tell HOW TO RESET this counter though. I wish I had another battery canister to see whether the controller would 'sense' the change and start all over.
As said in my final report I am set, my 'solution' is better than the manufacturer's. My bike runs longer ranges than any other JG20, thanks to the PAS on/off-modification.

 

[sjpt]

36v is a nominal voltage, from 10 series 3.6 v nominal. It is usual for these to be 42v/4.2 v fully charged.

250w is a nominal continuous rating for a motor. It is standard for them to draw about double that under full power with fully charged motor. Most 350w motors are pretty much identical to 250w ones; the difference being to cater for legal requirements (call it 250w in UK/EU) and customer perception (call it 350w in US).

I agree that the way batteries work is not ideal for people that live at the top of a large hill. Actually, it is not ideal for non-battery ebikes either; person power drops during a ride too and a hill near the start is easier than one near the end.

Most energy lost is lost in the battery (internal resistance, hence the drop in voltage under load), and the motor (inefficiencies). You can see lots about motor behaviour at https://www.ebikes.ca/tools/simulator.html and about battery behaviour at https://www.pedelecs.co.uk/forum/threads/is-the-extra-5-amps-chewing-up-my-range.35664/#post-520066

 

[vfr400]

Sorry, I have not updated this topic for a while, was too busy fiddling and riding...

Here is how I solved my issue with this ONE-POWER-MODE controller, as I could not reset it to the factory mode of Vmax=20km/h:

As the PAS would always trigger the full power mode whenever pedaling I made it optional, adding a switch to the handle bar. This way I can disengage the PAS and control the electric power manually at will and ANY level, using the handle bar gas grip.
Meaning I can adjust the power output for any desired speed up to Vmax, but have to hold the gas grip, like on a motorcycle, while pedaling along.
Range of the 288Wh pack is now back to 55-60km for a single charge (from around 40km with PAS active), around 5Wh/km, cool! I did some very nice trips with the modified bike, at avg speed of 20km/h, perfect for the 20inch wheels and high cadence gearing.

I also invested into a GTC power meter to watch over power output, true battery voltage, power consumption etc. It allows to see the actual wattage, the accumulated Wh consumed, the battery voltage and amps under load etc.
The cheap meter (which is usually bought and installed for solar panel monitoring) is very accurate (home bench testing) and very useful for this bike with its anemic 3LED power display.

But I found a few very surprising facts when observing the readings during my rides:
- a 36V battery really has around 42V when fully charged, so it contains TEN elements of 4.2V?
- even during regular rides the battery operates way above 36V
- under load the battery on this 250W bike is drained with up to 13Amps, around 480W!
Why a 250W bike will operate at almost twice the power (at regular speeds below 25km/h) I cannot explain, but it is a fact for my JG20. Does the full power get to the motor, or is it partly consumed by the controller FETs? Cannot say.

Also interesting is the significant voltage drop of the battery under load, a typical effect of these Li ion packs: at full throttle and power the voltage may drop from 39V to 36V or lower, recovering quickly when the load is released.
This behavior is very unfortunate for folks like me who live on TOP of a steep hill. After a trip the battery may be down to 35V already, still containing 'juice' for another 10km or so. But a steep hill climb will squeeze the voltage below the shut off trigger point (around 33V?) and will NOT allow to restart the motor afterwards, bummer. I ended up pushing the bike uphill more than once..

The season is over; I rode about 550km with this weird Samebike JG20. It IS fun and WAS cheap, it DOES work, but needed the special TLC and mods to become a useful vehicle.
Would I buy it again? Not with the simple and poor controller and display it uses, not with the bad gearing ratio of the Shimano set.
A conversion of all controller electronics or the Shimano sprocket sets would cost more than the bike is probably worth.
My own solution set me back by 7Euro for the PAS shut-off switch and the GTC power meter - well spent!

Thanks for reading and your suggestions; I learned a lot about pedelecs this year!

Everything you report is normal. 250w is the motor's rated output power, not how much you put into it. You will see that the current and power goes down when you ride fast, so you will only see 480w at low speed where the motor's efficiency is low (say 60%) and output power would be around 290w. The "rated" power means the output power the motor can run at continuously without overheating when running in its most efficient band, which will be at about 75% of its maximum RPM. You can see how efficiency and power work here.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

www.ebikes.ca

You probably have a freewheel on the motor that has 14 teeth on the top gear. If so, you can change it for one that has 11 or 12 teeth to reduce your pedal RPM at 25km/h.

 

[Craigs]

As said I do not want to change the gears at either end, also because I find 25km/h too fast on a wobbly 20" folding bike. The 20km/h are very comfy for my old age and non-existing excercise level. I have no clue why anyone wants to 'hack' these bikes to run 20mph (32km/h); ridiculous.
That's why I was happy as a clam when it ran only 20km/h 'out of the box', until it changed its mind after the suprising "run-in" phase...

For the fun of it (sun was out, 20C) I did a last test ride on my slightly hilly 'home track' near my home:
- PAS disengaged, manual power control as needed: 32Wh for 9km on a semi hilly track, avg=18km/h
- with PAS active (i.e. full power whenever moving pedals): 67Wh for the same trip, avg=21km/h

Since the motor kicks in about 3sec after starting to pedal and opens 'full throttle' (350W and more) this is extremely inefficient, and accelerates above 20km/h each time so I need to stop pedaling to ´get the motor "off my back". Crazy.


I also clocked the steep incline to my home after doing these two countryside laps:
for the 300m uphill the motor 'eats' a whopping 7Wh, the voltage dropping almost 3V during this load cycle (37.5->34.7V), power peaking around 440W; probably limited by the max amperage of 13A and the already depleted battery voltage. Had I started around 34V the system may as well have shut down halfway up.

Thanks for the charting tool! Mkes perfect sense, torque and all, matches my GTmeter quite well under the various conditions. I am suprised that the Chinese are FOR ONCE honest and specify the true OUTPUT rating of their hub motors. Usually they exaggerate capacities, speeds, powers and sizes by a factor 2 or more... I might as well ride a '500W' bike based on my own meter readings

I think it is a good idea to store the semi-charged battery (1/3 down after these tests) for the upcoming winter. One should NOT leave them fully charged for long periods of time, right?
Spring is far, far away..

 

[Andy-Mat]

36v is a nominal voltage, from 10 series 3.6 v nominal. It is usual for these to be 42v/4.2 v fully charged.

250w is a nominal continuous rating for a motor. It is standard for them to draw about double that under full power with fully charged motor. Most 350w motors are pretty much identical to 250w ones; the difference being to cater for legal requirements (call it 250w in UK/EU) and customer perception (call it 350w in US).

I agree that the way batteries work is not ideal for people that live at the top of a large hill. Actually, it is not ideal for non-battery ebikes either; person power drops during a ride too and a hill near the start is easier than one near the end.

Most energy lost is lost in the battery (internal resistance, hence the drop in voltage under load), and the motor (inefficiencies). You can see lots about motor behaviour at https://www.ebikes.ca/tools/simulator.html and about battery behaviour at https://www.pedelecs.co.uk/forum/threads/is-the-extra-5-amps-chewing-up-my-range.35664/#post-520066

Depending upon how easy your battery is when doing a removal/replacement, a good alternative I find, is to have a second battery with you.
On my bike there are 3 different capacities, so I bought a small one as an extra help.
I do realise that some batteries are a pain to change, please ignore this post if yours is, but I am lucky,I can change mine out in less than a minute.
Furthermore, you can ride the bike till the battery shuts down, which is a great "place" to start a recharge, IMO.

As said I do not want to change the gears at either end, also because I find 25km/h too fast on a wobbly 20" folding bike. The 20km/h are very comfy for my old age and non-existing excercise level. I have no clue why anyone wants to 'hack' these bikes to run 20mph (32km/h); ridiculous.
That's why I was happy as a clam when it ran only 20km/h 'out of the box', until it changed its mind after the suprising "run-in" phase...

For the fun of it (sun was out, 20C) I did a last test ride on my slightly hilly 'home track' near my home:
- PAS disengaged, manual power control as needed: 32Wh for 9km on a semi hilly track, avg=18km/h
- with PAS active (i.e. full power whenever moving pedals): 67Wh for the same trip, avg=21km/h

Since the motor kicks in about 3sec after starting to pedal and opens 'full throttle' (350W and more) this is extremely inefficient, and accelerates above 20km/h each time so I need to stop pedaling to ´get the motor "off my back". Crazy.


I also clocked the steep incline to my home after doing these two countryside laps:
for the 300m uphill the motor 'eats' a whopping 7Wh, the voltage dropping almost 3V during this load cycle (37.5->34.7V), power peaking around 440W; probably limited by the max amperage of 13A and the already depleted battery voltage. Had I started around 34V the system may as well have shut down halfway up.

Thanks for the charting tool! Mkes perfect sense, torque and all, matches my GTmeter quite well under the various conditions. I am suprised that the Chinese are FOR ONCE honest and specify the true OUTPUT rating of their hub motors. Usually they exaggerate capacities, speeds, powers and sizes by a factor 2 or more... I might as well ride a '500W' bike based on my own meter readings

I think it is a good idea to store the semi-charged battery (1/3 down after these tests) for the upcoming winter. One should NOT leave them fully charged for long periods of time, right?
Spring is far, far away..

Check the SOC of the battery, every 4 weeks at first, till you get a "feel" for the rate of "self discharge"...
I set a date and time on my smart phone so that I do not forget it!!
best wishes
Andy