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

[cwah]

Hello there,

I have a brompton with the mini-hub from Conhismotor:

The motor is this one: http://www.conhismotor.com/ProductShow.asp?id=76
And I tried the high voltage controller from Lyen and the Hua Tong controller.

My battery is a 4 x 5s8AH (total of 74V8AH) zippy battery:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16227

I adapted the wiring system in order to have a 1 clip removal of the controller with an ATX power supply plug:

I use a lot of energy when running with this motor:
- Around 400W at 20kph (or 12 mph) continuous speed (With Lyen controller)
- Around 1000W at 30 kph (or 18mph) continuous speed (With Lyen controller)

And this yesterday, with Hua Tong controller, I did 8 km (5 miles) and used 200wh. So around 25wh/miles at 30-35kph (around 20 mph).


The amount of energy used is huge. I don't know how I can use that much. The controller isn't that warm and neither is the motor. The wire haven't melted.

So what's wrong with my set up?

 

[heathyoung]

I'd be checking your no-load current - and no-load speed as well.

 

[SamTexas]

Trying to be helpful:

Who put the RShunt value into your Cycle Analyst? What is that value? What is the RShunt value of the controller? Show pictures.

What is the circumference of your wheel? What is the value entered into your Cycle Analyst?

What are the individual cell voltages at the beginning of the ride? What are they at the end? How many Whs did your Cycle Analyst say you used during the ride.

 

[Drunkskunk]

25Wh/mile at 20mph isn't that bad for a geared motor. and you're running a 12 adaptor, which is eating a few watts as well.

 

[SamTexas]

And this yesterday, with Hua Tong controller, I did 8 km (5 miles) and used 200wh. So around 25wh/miles at 30-35kph (around 20 mph).

It's 40Wh/mile. No idea how he came up with 25.

 

[cwah]

Yeah, it's 40wh/miles. Sorry for the typo.

At no load the motor uses 2 amps (160w), the wheel circumference is 1250mm (brompton 16 inch). The cells voltage depending on the ride go from 4.1V/cell to 3.7V/cell. But I really use the pack max wh (between 200wh to 400wh).

Will check other data later as I can't now (at work)

 

[miuan]

drain your batt from full to low at constant speed, measure the distance, estimate the Ah used.

 

[cwah]

Ok, will try to drain it from 4.1 to 3.7 and see the results.

 

[adrian_sm]

What gets hot when you ride?

The power has to be going somewhere.

 

[Jeremy Harris]

As we've already said in your other thread, and as adrian_sm has said above, something has to be getting hot if you really are drawing that much power continuously for that speed.

12mph with no wind on the flat should need around 100 W at the road when sitting upright and with MTB tyres, around 70 W at the road if using smooth tread tyres. Allowing for a motor and controller efficiency of 70% then I'd expect to see an electrical power of around 100 to 140 W for 12 mph for your bike running on Marathons.

400 W is a lot of power, so either your power readings are well off or something is getting pretty hot.

 

[dogman dan]

I thought it was just heavy handed starts whacking your average wh/mi.

But if you are seeing 400w when cruising 12 mph, something is seriously wrong. I suspect you CA is whacky.

Using an RC charger? It will tell you how many mha were used, which won't be hugely different from the mha that acutally went into the battery. Use that, and a calibrated speedo, or accurate map distance ridden to see how far from reality your CA is.

Wrong phase and halls wiring is known to cause this kind of problem too. 160w no load is waaaaay too much.

 

[miuan]

160w no load is waaaaay too much.

not really at that voltage.

 

[Jeremy Harris]

160w no load is waaaaay too much.

not really at that voltage.

Would you like to explain that, please?

160 W is, as dogman rightly says, a massive amount of power just to turn the wheel with no load, power that, if it really is going to the motor, will just be creating a lot of heat, as no useful work is being done.

 

[joe tomten]

& if nothing is getting hot, then power isn't being wasted and we are back to being suspicious about the Rshunt number programmed into the cycle analyst giving the overstated power usage value.

 

[miuan]

160w no load is waaaaay too much.

not really at that voltage.

Would you like to explain that, please?

That's 2A. At 36V it would be a little less I think. But it turns very fast at this voltage, so it needs much more power than your typical 36V setup. but yeah... the shunt value seems off anyway. As I suggested before, doing a full charge/discharge cycle should solve the puzzle.

 

[d8veh]

I use that same motor for testing my batteries and the no-load current is about 0.8 amps. so I suggest that you have the wrong R-shunt value in your Cycle Analyst, which is therefore give you the wrong values for current, watts, wH, etc. If you still have your old watt-meter, try it and see if you get the same results.

 

[dogman dan]

True, it will take some watts to spin a wheel really fast. Perhaps I don't understand just what the no load speed rpm of his motor is.

I just went out and slapped a stand alone CA on my 48v 20 ah bike, and it's no load watts is 67w. I thought it would be closer to 37w actually. I didn't get the wheel speed because I didn't put the speedo sensor on the bike. Likely 35 mph or so.

So maybe 160w is not crazy high, if he's spinning a motor twice as fast. I don't recall ever looking at the no load wattage on my racing bike, which has a 100v at 40 amps, or 72v at 40 amps. Could be 200w I suppose.

I think something, the motor, is getting hot. Or your CA is whacky. But it shouldn't be getting hot going slow, or using that much power. Going 20 mph on my racing bike, with 100v 40 amp controller takes, you guessed it, 400w.

 

[cwah]

Thanks guys. Going to take my turningy wattmeter and check that first.

Will post the result when that's done

 

[Jeremy Harris]

Thanks guys. Going to take my turningy wattmeter and check that first.

Will post the result when that's done

Be careful! The Turnigy isn't rated for 74V, IIRC.

 

[cwah]

Damn, I forgot. The turningy is limited to 60V. It doesn't work with my system

 

[NeilP]

I'd like to see more of the power wires from battery to controller. Just look at the number of connections visible in that second pic with the red power lead.

From controller to the 4mm bullets...is taht a bit of blac insulating tape just before there..then on to those horid blue crimp terminals...no I then see a fuse block ( Maxi Fuse style).
I am wondering about the resistive losses and voltage drop between battery and controller. An what of the rest of the connections?

 

[cwah]

Going to take a picture of that. How do I measure the electrical loss between the battery and the controller?

 

[NeilP]

Well any connection, crimped or soldered, and the junction between the two halves of any connector all create a small resistance and therefore a small voltage drop.
This may be nothing and totally irrelevant, but all worth looking at.

 

[cwah]

Is there a simple way to measure the electrical loss? Can I do that with a voltmeter?

The RShunt displayed on my Cycle analyst is 1 mOhm. don't know what that mean :lol:

 

[SamTexas]

The RShunt displayed on my Cycle analyst is 1 mOhm. don't know what that mean :lol:

There you go. I think that's the answer. I'm willing to bet that the RShunt value of your controller is around 3 mOhm.