Speed limiter - trap for young players....me

[mingonn]

Hi all,

Just thought I would share my embarrassment. I have only just go into e-biking having converted my 20" folder with a 36v brushless DD kit (wound for a 26" but spoked in a 20" rim and running a 44.4v 3800mah RC lipo pack)

The controller that came with the kit has a speed limiter jumper.....I thought the wiring diagram said if connected it was unlimited... .... thought I would try it disconnected just in case I misread the instructions......30 km/h later I think I got it the wrong way round.

I have done 100 km so far wondering why the wheel would only spin up to 22 km/h on the flat and barely taking 35% out of my battery pack.

With the limiter off and 20" wheels my little folder pulls like a truck, I think I might need to look into a current limiter to keep me under our crazy 200w limit now. It will be interesting to see how the lipo pack holds up under the load.

Derek

 

[deecanio]

Hi Derek,

sounds like you've found the missing power and it's making you smile?
i dont understand your power limiting to 200w though? you do realise 200w wouldn't pull the skin off a cold bowl of custard?
If its a legal thing, any bike that goes well is normally way over the limit anyway (few exceptions) - if you run 44v by my reckoning to be legal (in your case under 200w) you would only be able to run 5amps ? (please let that be right) :lol: .
one thing that strikes me as a possible "limiter" would be if you connect up the controller jumper to a switch? so you can limit/unlimit with a bar switch? - you would have to ask the guys if there was any problem doing this but it seems workable to me? anyone ?
also i wonder does anyone how low CA goes as a current limiter? can you use ca to let your output to be say sub 250w? that would be very useful


Cheers,

D

 

[Anonymous]

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[mingonn]

The extra power was amazing, even more so given the 1kg 3800mah lipo pack I am using. I think I will be using a bit more capacity than I have been using so far to get to work.

The 200w thing is a both a legal thing and a challenge. I am a big fan of getting more out of less especially in this day and age where the solution to everything seems to me more despite the environmental consequences.

I only have a multimeter that goes up to 10A but I will give it a go to see what current draw I now get WOT on the flat. Previously on 36v at 20km/h I was only pulling 2A which is a measly 72W. I am hoping that at 28-30 km/h it will under 5A which still makes me legal on the flat and questionably legal under load. Even a small 540 RC car motor can pull 30A at 7.2v which would break out Australian laws if used in an ebike, so I am applying a bit of common sense to my interpretation and making it 200w WOT and full speed on the flat with a 70kg rider.

Even so the ideal solution would be a 200w power limiting circuit. An inline throttle override based on the battery voltage and current drawn to limit the throttle signal to keep within the nominated power limit....with an override of course. That way, hopefully I still get a unrestricted top end on the flat but 200w limited acceleration and hill climbing.

I don't mind pedaling a bit, keeps me warm this time of year. I think CA will limit current but at $150, its a bit overkill for what I am after.

Derek

 

[Anonymous]

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[Link]

↑ Seconded. My 72V BD36 uses about 1.3A just freewheeling. No way you're using less than an amp to actually move.

 

[mingonn]

Hi guys,

That was 2A at 36v doing (speed limited) 20 km/h dead flat road, no wind with an all up weight (rider and bike) of 90 kg and tyres at 80 psi. I have since been using a 44.4 v lipo pack but until yesterday it was unbeknown to me speed limited. All that is about to change now I unplugged the limiting connector.

I have been putting 1300 mah after each leg of my 12 km (each way) ride to work, I pedal whilst easing the throttle in until i hit the speed limited 22 km/h, throttle off and coast down hills, and WOT and pedal to maintain 22 km/h up hills. Its a pretty flat ride. Takes about 40 minutes, assuming 30 minutes under power that gives me 2 x 1300 mah = 2.6 A average current draw.

Doesn't surprise me that you pull 1.3 A no load at 72 volts Link that wheel must howl. Will connect up the multi meter and get some no load and load readings, unfortunately I don't have a CA or watt meter so I hope I don't blow my 10A multi.

Derek

 

[Link]

Will connect up the multi meter and get some no load and load readings, unfortunately I don't have a CA or watt meter so I hope I don't blow my 10A multi.

Go easy on the throttle and you should be okay with the no-load tests. I wouldn't try it loaded.

 

[Anonymous]

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[mingonn]

Wired the multimeter in this morning and unloaded (wheel off the ground) it spins at 34 km/h at .96A. On the flat 30 km/h steady (no pedaling) it varied between 4-4.5 A, up a slight incline speed dropped to 27km/h and current went up to 6.5-7A.

So at 44.4v nominal (I didn't measure the voltage under load) that should work out at 44.4 x 4.5 = 199.8W on the flat at 30 km/h, which is legal here in OZ. Now if I can just work out how to limit my current to 4.5 A I will be set.

There are a couple of topics that cover this but my circuit knowledge is a bit basic so I might have to take the plunge and buy a CA.

Wish we had the 750W limit / 20 mph law here.

Derek