400W for 12mph: Why is my bike so inefficient?

cwah said:
I have a direct plug from CA. So I suppose I don't have any shunt wire? I don't know how to recognize them.
Click to expand...

The shunts are inside the controller. The direct plug in CA needs to be calibrated (using the procedure that Justin has outlined in the instructions I quoted earlier) to suit the value of the shunt in the controller.

If Lyen has told you that your controller as a 2 mohm shunt, then that is the value you program in to the Rshunt field in the CA.
 
Jeremy Harris said:
NeilP said:
i tried riding at 12mph today, and ended up with a constant reading of about 120W on my bike, and that is with 26 inch wheels at about 35psi, smooth road tyres
Click to expand...

Pretty much exactly the figure I predicted when this first came up! Nice to know that theory can match reality now and again.....
Click to expand...
Must have been a fluke ...I'll test again tomorrow ;)

Sam, you are too late with the warning about opening it up...it has already been done...see cwah's other thread
http://endless-sphere.com/forums/viewtopic.php?f=3&t=39942&p=584370#p584370



Shunt wires are the 4 straight wires you can see in the middle of the next pic, just above the red and below the thick black.......two wires at either side of the shunt will go to the CA -DP plug


IMG_0185.jpg
 
Heh, you could just put a turnigy watt meter inline with 10S of the battery and measure the amps that way. That's how i figured out how much juice i was dumping into my 125v 30S setup, as the cycle analyst was WAY off :)
 
NeilP said:
Sam, you are too late with the warning about opening it up...
Click to expand...
Oh well... In that case I'm interested in knowing the number of shunt wires too. Shall we expect to see 2 of them or more than 2?
 
guys, here is the picture of the shunt:
lyen_controller_shunt.jpg


So that's 2 mOhm?


Neptronix, the problem is that my controller doesn't work at 37V. I'm trying to remove a small resistor in order to make it work then I should be able to test it.
 
cwah said:
Neptronix, the problem is that my controller doesn't work at 37V. I'm trying to remove a small resistor in order to make it work then I should be able to test it.
Click to expand...

No, you run it at 72v, but you put the watt meter inline with part of your battery. Like if you are using RC Lipo for example, and you have 20S.. then you have a series connection somewhere that will be at only 19-38 volts or so. You hook the watt meter inline there, and only measure part of your battery pack. It's the amps you will be looking for to see if they match up with the amps that your cycle analyst is displaying.

You are using RC Lipo, right?

Also you can program your controller for a lower LVC to get around the 36v issue.
 
yes, lipo I do use neptronix :)

Finally, I desoldered the little resistor and it's working at 37V now so no need to do the trick :)

When plugged without any current I have -4W on the cycle analyst:
conhismotor_no_load.jpg


When I activate the throttle, I have this:
conhismotor_no_load2.jpg


25W at 37V on a 16" wheel. All good?

Will test the bike tomorrow :)
 
Ok, just cycled to work at 15mph. no peddaling, on flat road, continuous speed, I use around 250-300W to maintain 15mph. And do 12wh/km at 25kph (15mph)
 
But fairly normal actually. Sounds like you are getting " close enough for government work" readings now. You could be up or down 50 watts on your 15 mph on many things. Pavement surface, tire choice and pressure, the clothing you wear. Pedaling good on a 26" bike, I could often get 15 mph down below 250w provided my panniers didn't have headwind.

I was watching the Giro the other day, and they said a fit cyclist putting out 200w continuous is making 800w of heat in his body. So a pedaler has a lot worse efficiency. Only 20% :shock:
 
dogman said:
But fairly normal actually. Sounds like you are getting " close enough for government work" readings now. You could be up or down 50 watts on your 15 mph on many things. Pavement surface, tire choice and pressure, the clothing you wear. Pedaling good on a 26" bike, I could often get 15 mph down below 250w provided my panniers didn't have headwind.

I was watching the Giro the other day, and they said a fit cyclist putting out 200w continuous is making 800w of heat in his body. So a pedaler has a lot worse efficiency. Only 20% :shock:
Click to expand...

Don't tell people about this, before you know it cycling will be forbidden because of it's low efficiency and high CO2 production.
I once read somewhere that a jogger has about the same CO2 per km as a modern small diesel car....
 
cwah said:
hmm.. just checked the simulator. At 15mph and 300W power usage, it means 65% efficiency for a direct drive.

Actually a bit low. :(
Click to expand...
Not quite sure why you put a sad face up there. Your reading was 100% off before. Now it's in the acceptable/normal range. As I hinted earlier, the 2mOhm controller RShunt value given to you might not be exactly correct, a reference calibration as mentioned my Jerry twice earlier can be performed to get a more accurate reading. But that's optional now.

The 65% efficiency you calculated above is only correct if you had a non-stop ride at cruising speed all the time. No stopping, no slowing down, no speeding up. No incline in the road, however slightly. Is that the case for your ride to work today?

BTW, how did you come up with 65% figure? It only takes around 150W to cruise at 15mph. So if your average power is 300W then you're getting 50% efficiency, not 65%.
 
Ok I think you're right. I did stop and start a lot. Probably the main cause of the low efficiency.

I am a bit disapointed because the consumption is identical to my 26'' bike that does the same distance at 34kph (22mph) and also uses 12wh/km when I cycle to work
 
cwah said:
I am a bit disapointed because the consumption is identical to my 26'' bike that does the same distance at 34kph (22mph) and also uses 12wh/km when I cycle to work
Click to expand...
You can't compare apples to oranges. You did not pedal today, and you were pedaling on your 26" bike.
 
The shunts on the Xiechang/Lyen/Infineon controllers are typically between 4 and 5 mohm each - the one in my folding bike controller, for example, is just under 5 mohm. Two shunts in parallel could therefore be anywhere between 2 mohm and 2.5 mohm. As Justin says in that calibration sections from the CA FAQ that I posted previously in this thread, you can have a wide variation in value from controller to controller.

Also, the Turnigy watt meter current readings are none too accurate either, particularly at relatively low current. I have four of them and they all read differently when I first got them (but are better now as I've calibrated them, see this thread: http://endless-sphere.com/forums/viewtopic.php?f=2&t=21976&p=368124&hilit=Turnigy+calibration#p368124).
 
Ok thanks guys. I suppose I'm on normal power consumption and I'm still using quite a lot of power. Jeremy, I think I'll just leave it at 2 mohm as if I change anything it would just be random.


I cycled today something like 20 km and I had a huge range anxiety with my 74V8AH lipo. I limited to 300W max after 10 km to be sure I can go home without killing my lipo :lol:

Damn, I'm going to move shortly at 7 miles from my workplace very soon. Would need around 800-1000wh lipo.. or maybe get some A123 for the lifecycle as I'll cycle everyday.
 
The only way you could change it to anything else other than two is to have a more accurate reference, the easiest being a Standalone Cycle analyst and its external shunt.

I bought one in the end, as a spare, to use on my bulk charger and job like this. Worth getting one if you plan on doing lots of other jobs with e-bikes in the future. Buy it as a tool rather than a piece of kit to fit to a bike
 
I actually do have a stand alone cycle analyst. I purchased it when the controller from Lyen stopped working.
I'll see what the power consumption with the stand alone cycle analyst.
 
Do it under load rather than no load

So set it up between pack and controller and try and find a bit of road where you can sit at a stable speed, and compare current readings, then adjust your bike main CA-DP shunt reading to that it reads some current

You will notice that they change current displayed every few seconds, but they will both update at different times, unless you manage to power them both on at exactly the sand time. Your standalone will come on when plugging in battery, And DP When you power on the controller, so either set averaging to a lower figure on both, use Cruise control, or leave controller on, then connect battery, to get both CA's to power up at same time

Your Stand Alone unit is probably the most accurate way to calibrate theDP
Justin at Ebikes.ca does great job of accurately calibrating them to the actual shunt fitted,
Lyen will just give you the published figures for the shunt (s) used
 
Ai chihuahua! You coulda just checked with the other CA all this time? Definitely a great way to calibrate the other one. You'll need a very repeatable ride, on a nice long flat straight section with the same weather. No ride full of starts and stops. one start, then look at watts at a given speed.

The stand alone CA speedo needs to be calibrated to the wheel it's on.
 
Yes, that is the other way , I tend to use them in Amp mode and compare instantaneous current, with both connected at same time
 
Right, ten ways to do the calibration that work I'm sure. The key thing is the same ride, and it never popped into my mind you could run both CA's simultaneously. Of course you can.

Just wanted to make sure he didn't have extra variables when he calibrates it.
 
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