I've commented on the pedelec system with these kits before. There is motor speed control via cadence but the ramp is so steep between nothing and full speed that its useless in practice. These motors are voltage and therefore speed controlled, the throttle, pedelec etc control motor RPM not power. Power is a function of Torque and RPM, Tillson made an excellent post a while back how the three relate but I cant locate it right now...
Photo guide (3 of 3) for 8Fun kit conversion of Specialized Hardrock Sport Disc
- Thread starter IanA
- Start date
Ian
This was a great help when I was converting my bike though we took different paths and I opted for single chainwheel RH mounted pedelec. I was told that 8fun didn't offer the bottle battery but in fact I am very happy with my carrier mounted battery as I only want a shopper/tourer bike and usually have at least one pannier fitted.
A point about the brake cut out. My kit had a cut out on both brakes. They are wired in parallel to a single two terminal plug and closing either switch cuts off the motor. The switches are normally closed push buttons held open by the brake lever. I rearranged things on my installation so the cut out is operated by the brake caliper, not the lever and this meant using a normally open switch.
If you would like the original 8fun brake lever and switch you are welcome to it foc except for postage, send me a pm if you want it.
Thanks also for the information on how the power management works, I have been trying to figure it out and I think your description is probably pretty accurate.
This was a great help when I was converting my bike though we took different paths and I opted for single chainwheel RH mounted pedelec. I was told that 8fun didn't offer the bottle battery but in fact I am very happy with my carrier mounted battery as I only want a shopper/tourer bike and usually have at least one pannier fitted.
A point about the brake cut out. My kit had a cut out on both brakes. They are wired in parallel to a single two terminal plug and closing either switch cuts off the motor. The switches are normally closed push buttons held open by the brake lever. I rearranged things on my installation so the cut out is operated by the brake caliper, not the lever and this meant using a normally open switch.
If you would like the original 8fun brake lever and switch you are welcome to it foc except for postage, send me a pm if you want it.
Thanks also for the information on how the power management works, I have been trying to figure it out and I think your description is probably pretty accurate.
Pedalling will be the same, but the assist will cut out at a lower speed, 9mph i believe. Medium assist around 12mph and top assist around 15mph
OK. I have a 8fun with the TFT screen and that gives you a percentage of power.
So pedalling at setting 3 is far easier than setting 1 (ignoring top speed but say uphill at 4mph) just that I am building a bike for the wife and wanted to keep it simple. however that percentage power thing is great.
Mart
So pedalling at setting 3 is far easier than setting 1 (ignoring top speed but say uphill at 4mph) just that I am building a bike for the wife and wanted to keep it simple. however that percentage power thing is great.
Mart
Precisely what I was going to post but you beat me to it by 2 mins!
HOWEVER, I have just been for a ride today and played around with the 3 settings and now don't think it's as simple as this and quite confusing when riding.
The 4mph test is hard to pull off - it's a very slow speed so requires a contant hill of the right gradient. That said, I believe I got it to work once and all three assist levels seemed to deliver the same power.*
I think the issue is the way the power tapers off rather than hitting a wall at the limit. This means that at most speeds one or two of the assist levels will be offering reduced power and the higher setting(s) will therefore give more power.
I had believed until today that the taper for Medium assist was from about 9 to 12mph but since I can feel a boost in power from medium to high assist at speeds as low as 7mph the taper for Medium assist must start below 7mph (more testing needed). If that's the case then the taper for Low is likely to start below 4mph and that would mean I was wrong about all 3 assist levels delivering the same power at 4mph (* above)!!!
I found 7mph was a good test speed but still requires a constant gradient. All three assist levels are available. Low is at very much reduced power because it's only 2mph off cutting out altogether. Medium is only slightly reduced as it's only just starting to taper off and I presume High is at full power.
This starts to shed light on why I am getting such different distances out of the battery on the same route on High assist. Not only do I save power the more time I go over 15mph but I also save power the faster I go between about 9mph and 15mph.
Lots more testing needed!
Maybe one of the electronics gurus can explain this (in layman's terms PLEASE!! ).
I shall now put on my tin hat and retreat to the bunker ready for my theory to be shot down in flames!
I too tested this on the weekend. I now think that the power increases, not just the top speed! THere was definitely more torque at low speed on 'Hi' setting than low speed on the 'Lo' setting!
Ian, Thanks for such a comprehensive 'walkthrough' of your conversion, your solutions to various problems are very useful, you've inspired me to do a similar job on the wife's Specialized. Wondering if you'd tackled the 'long cable syndrome' at all?
Not weird at all, these motors are voltage controlled, to control 'power' you would need to vary the current delivery, only a few controllers can do this AFAIK...
Not quite as the controllers use PWM to control motor speed, they act like a buck converter: Buck converter - Wikipedia, the free encyclopedia
IE to maintain forward progress at a certain speed a certain amount of power is required if lets say you are climbing a hill at 8 mph and drop the voltage (close the throttle slightly) but not enough to go lower than 8mph you still require the same amount of power to climb that hill but the voltage has dropped ...so the only thing the controller can do is scale up the phase amps to compensate so you continue to climb at 8mph.
Theres an excellent thread on ES about this...somewhere!
Edit: I should also have stated the current draw from the battery is not the current the motor sees, these are three phase BLDC motors so Phase current is linked to but different from battery current.
IE to maintain forward progress at a certain speed a certain amount of power is required if lets say you are climbing a hill at 8 mph and drop the voltage (close the throttle slightly) but not enough to go lower than 8mph you still require the same amount of power to climb that hill but the voltage has dropped ...so the only thing the controller can do is scale up the phase amps to compensate so you continue to climb at 8mph.
Theres an excellent thread on ES about this...somewhere!
Edit: I should also have stated the current draw from the battery is not the current the motor sees, these are three phase BLDC motors so Phase current is linked to but different from battery current.
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Shortening the power cable...
Yes I did shorten the power cable. The easiest way would be to replace the crimp connection at the control box end but I didn't have any new connectors and was impatient so I decided to re-soldered at the main battery connector end. It was tricky but I managed it and also added some extra insulation to prevent a short circuit. I'm not that great at soldering but even I can make a better job than the original soldering - very shoddy work that was only 1-2mm from shorting out.
After seeing the state of the soldering I got concerned about the quality of the workmanship and taped up the control unit box and the handlebar switch/display (where there are joins in the plastic) to be sure that water wouldn't get in - used black tape and can't even see it. I've also started covering the battery with a plastic bag and large rubber band when it's raining as a temporary measure until I one day get around to making a proper waterproof cover for the battery.
It's been outside for 30 mins in a torrential downpour without any of this and survived okay so I'm probably worrying over nothing.
Hope this helps and that my reply isn't too late!
For some reason I've not been notified of new messages to this thread so only just seen your question.
Yes I did shorten the power cable. The easiest way would be to replace the crimp connection at the control box end but I didn't have any new connectors and was impatient so I decided to re-soldered at the main battery connector end. It was tricky but I managed it and also added some extra insulation to prevent a short circuit. I'm not that great at soldering but even I can make a better job than the original soldering - very shoddy work that was only 1-2mm from shorting out.
After seeing the state of the soldering I got concerned about the quality of the workmanship and taped up the control unit box and the handlebar switch/display (where there are joins in the plastic) to be sure that water wouldn't get in - used black tape and can't even see it. I've also started covering the battery with a plastic bag and large rubber band when it's raining as a temporary measure until I one day get around to making a proper waterproof cover for the battery.
It's been outside for 30 mins in a torrential downpour without any of this and survived okay so I'm probably worrying over nothing.
Hope this helps and that my reply isn't too late!
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