E-Bike efficiency high inflated

[Teh Stork]

Tested one of our ebikes to 64% total system efficiency when going on a trip from about 0moh to a location known to be 520 moh. No human input. BBS02 around 500W, 1C discharge on ~3C capable battery.

With 85% motor efficiency, 90% battery efficiency the system is already at 76% theoretical efficiency. The unknowns (air resistance and friction (tires and chain)) coming in at around ~15-20% seems reasonable since the climb is very steep and done at a relatively low speed (do not have the numbers here, around ~20kph).

I'd say the coolaid is real

 

[flat tire]

Your motor may well get 80+% efficiency at peak. You don't state what motor you have, what the KV of the winding is, what controller you have, how much you weigh...we have no idea what's going on besides some wattage claim you make but don't even show the math for. Nice.

Now, what's probably happening is your motor is way off the efficiency curve at 6MPH with the torque required to climb the hill. Efficiency for a given electric motor varies incredibly widely depending on speed and throttle input. Low speed, high throttle input generally gives the worst possible efficiency.

 

[spinningmagnets]

Direct drive efficiency? There is no mention of the RPMs that were maintained on the hill-climb. If you bog a motor down, it will suck a lot of amps to try and get back up to its designed top-speed. The diameter of the tire plays a role too. A large diameter DD hub and a small diameter wheel that is running high volts will take hills much more efficiently than a small diameter hub in a large diameter wheel using lower volts.

When the electricity needed to charge an ebike battery to travel ten miles is incredibly cheap, a system with low efficiency is much better than a car, by a huge margin.

From another perspective, I am shocked...SHOCKED I SAY!...to find out that a vendor on the internet has over-inflated the power, range, and efficiency performance specs of their products. Thanks for informing us.

 

[justin_le]

From another perspective, I am shocked...SHOCKED I SAY!...to find out that a vendor on the internet has over-inflated the power, range, and efficiency performance specs of their products. Thanks for informing us.

I know this was said with some sarcasm/humor, being quite true of many vendors. But to the defense of the industry, one of the things that has really surprised me is how honestly and accurately most actual ebike motor manufacturers (not just ali-express resellers) are on the specifications of their hub motors, both in terms of peak efficiency and nominal power capability. Most geared motor manufacturers specify around 80%-82% peak efficiency, which is exactly what I measure on the dyno, and direct-drive motors are typically advertised as 84-86% efficiency, which is again pretty much exactly what an independant dyno test what will show.

And a surprising number of manufacturers include a printout of the actual dyno test curves of their hub motors, and I've never seen one of these that looked suspicious or didn't jive with my own measurements. And for power ratings, where they'll usually list smaller geared hub motor as say 250 watts, while by RC hobby standards that exact same motor would be called 2000 watts.

You can have beefs about a lot of things, but the overseas motor manufacturers have been pretty straight up honest about performance expectations.

We don't know the motivations of the OP, but it's a valid question or observation with a straightforward answer. On a hill climb, you've got more than just gravity to overcome, so add rolling and wind drag and you might need more like 200 watts to climb that hill at 6mph. And at just 6mph putting out substantial torque, most direct drive motors will be running at less than 50% efficiency, as any torque/speed curve (or the motor simulator) will show you, hence needing 400-500 watts from the battery. You'd have much better motor efficiency using 1000 watts and climbing that hill at 20mph instead of 6mph, and would consume fewer Ah to get to the top too.

 

[dogman dan]

I'm shocked, shocked I say, that a motor designer would think a typical dd motor would be efficient going up a hill under full load, at 6 mph rpm.

 

[spinningmagnets]

Thanks for clarifying about the manufacturers, Justin. My immediate thoughts about efficiency claims were the 50-mile batteries from HPC a few years ago.

 

[dogman dan]

Remember Wilderness Energy? They had me thinking my first brushed motor kit would go 20 miles, at 20 mph, on 36v 12 ah slas. In fact, it was 6 miles at 20 mph, pedaling as hard as I could. I suppose somebody was capable of pedaling a bike with a 30 pound battery load 18 mph, but I wasn't.

That seller is gone now. They did actually have pretty good customer service, on the stuff they sent me that did not work at all.

You still see lots of range claims from vendors, 40 miles from a 400 wh pack. It's not impossible, just impossible at 20 mph unless you have a good EPO connection. Range tests that ad text is based on need to be done with the rider putting out 100w, not 400w. But that's a whole different topic, not motor efficiency. If real world efficiency of the whole bike is only 70% or so under ideal load and speed conditions, it still beats ICE efficiency.

I don't see a real need to keep this thread locked, if the motor designer is gone.

 

[MadRhino]

A bike may be efficient, yet not effective. I mean, I don't care much about efficiency when power is required to climb. I want the bike to effectively climb the hill, not at 6 but 60 Kmh when the trail is good. Then, I realized that building a bike to be effective in the extreme, is making it pretty efficient in most situations.

Now about 'high inflated': You might find slightly lower rolling resistance in overinflating your tires, but it will be at the cost of poor grip and traction. This handicap will not let you ride the bike at it's best efficiency anyway, no matter how good the optimal efficiency can be.

One must build a bike to do the task effectively first, efficiency is coming next and only a matter of optimisation. Efficiency can be improved with riding behaviour, but effectiveness has to be planned and built to meet performance expectations.

 

[Triketech]

Over the years my job has given me ample opportunities to test efficiencies of motors from tiny steppers to 3 megawatt AC Mining Truck motors.

Ergo, any motor operating at 0 RPM under power has 0 efficiency. Velocity whether RPM or linear (in the case of a linear motor) is probably the most influential factor of efficiency.

Despite all the good stuff that goes into design, the motor efficiency will always be highest at a particular speed, and the closer to 0 velocity the lowest.

When I decided to electrify my trike I chose a handful of motors to test; rather than focus on efficiency I chose to measure total watt-hour averages on a consistent route with consistent average velocity. Hardly the scientific solution of exact science, the tests were run for a series of articles I'm writing at Triketech to help them select a system most suited to their needs.

Not surprisingly the BBS02 consumed the lowest Watt-Hrs by a significant margin. Changing gears to keep the cadence at about 80 RPM maintained a more uniform speed that's probably pretty close to its efficiency sweet spot.

The MAC 10T sort of surprised me, only consuming about 15% more power then the BBS02.

Both the Golden Motor Magic Pie 4 and Smart Pie 4 consumed over 50% more power then the BBS02. As there is some climbing involved the Smart Pie was slower up hills, and always hit scale back on the final ascent. To even out the speed average I had to go faster on the longer downhills (~30 vrs 20) which reduced regen, but there really wasn't that much regen from either motor.

That's not to say the BBS02 was my motor of choice. There are other factors that for me made the BBS02 less desirable.

Literally your mileage may vary. It would make perfect sense that on a flat with minimal stops, maintaining speeds in the 25 MPH range a direct drive would probably deliver awesome efficiency. However for my intended audience, "recumbent trike riding geezer larva" the course is similar to what most of them tend to ride.

The point is stated efficiencies are based on peak values but the actual efficiency will vary with the nature of your ride.

 

[amberwolf]

Range tests that ad text is based on need to be done with the rider putting out 100w, not 400w. But that's a whole different topic, not motor efficiency.

To stay for a moment on that OT: Ads ought to show the range with zero pedal input, and state the exact test conditions (or use a standard set shared by everyone, which is unlikely to ever happen). Then they can state that range and/or speed can be improved depending upon the rider's input.


But we all know how marketing departments work, and that very very few don't stretch the truth, if not actually outright lie, no matter what the product is.


Back to your irregularly unscheduled discussions.

 

[dogman dan]

Nothing really wrong with his original questions. We just have a really good spam checker here.

Would it be theoretically possible to rig a motor lab test to gain 10% efficiency? What I mean is like run it as close to no load as physically possible, use all gold wiring, special controller, etc? Then have an 85% efficiency motor test to 95%?

Not saying anybody does this. Far easier for a salesman to just lie if they really want to cheat it.

I get the efficiency question at work all the time, from the eco marathon competitors. Hard question to answer, since real world efficiency of a hub motor is so dependent on many variables of load, wheel size, etc. I just point them to the Grin Technology simulator.

 

[Miles]

Would it be theoretically possible to rig a motor lab test to gain 10% efficiency? What I mean is like run it as close to no load as physically possible, use all gold wiring, special controller, etc? Then have an 85% efficiency motor test to 95%?

Nope. At no load you're back to 0%

Maximum efficiency is the point where copper losses are at parity with parasitic losses (iron losses etc.).

Maximum efficiency is dependent on rpm, of course...... (as said above).

 

[markz]

I've learned a little something-something from this thread as I hack, cough flem, and sniffle.

Efficiency for a given electric motor varies incredibly widely depending on speed and throttle input. Low speed, high throttle input generally gives the worst possible efficiency.

Everytime, before, I would go to the motor simulator, punch in my specs and always have the throttle at 100%. Then I'd move the cursor to a different speed and see the efficiency fall. But we dont actually ride all the time at wide open throttle right, so it makes sense. When riding I'd never really go wot cuz I was always scared of the power 72V Lipo gave my MXUS 3kW V2. So I was making another thread just now on how do I properly guage battery needs, to motor/controller and bicycling habits. So that statement cleared a few things up.

BTW I am always suspicious of someone with 1 or 3 posts, posting and then another low post count dude responds as "Im an engineer and blah blah blah"

Motor diameter discussion was here. This thread is what I remember reading about.
https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907&p=1095975&hilit=hub+diameter#p1095975

 

[Triketech]

Motor diameter discussion was here. This thread is what I remember reading about.

How's this for motor diameter?

That's a 1700 VAC 2000A continuous duty motor with a 42:1 triple reduction box. The motor comes from Skoda in Pilzn and was originally designed as a windmill alternator; it's been a bit modified in design to spin 3600 RPM without ejecting the rotor bars. This one has been running at Syncrude in Ft. Mac for over 5 years now.

The gearbox, controller, software, alternator is what my team developed for the trucks. It has 150 HP blower to cool both motors and uses an MTU 20 cylinder diesel to drive the Kato alternator. We have several patents on the control software including traction control, retard to zero, and high torque start.

The red lift bracket is attached to the hub, and a pair of Rimex rims are clamped to the hub with 6300 size tires.

Larger motor diameter offers a huge advantage to lower speed efficiency but at the cost of weight and rotary inertia.

If ever there was a more aptly named forum than "Endless-Sphere" on the topic of electric motors, I can't think of it. Electric motors are an endless spectrum of compromise in the characteristics needed.

 

[Lurkin]

What is it actually used for?

 

[Triketech]

Terex MT6300 Mining Truck. This one is currently in Ft Mac at the Syncrude oil sand mine, at least that's where it was about 5 years ago.

There are another 30 in Karratha at he China Pacific Iron Mine.

Two per truck.

Retail price as a spare is a million bucks.

 

[Punx0r]

I can only imagine the power required to push one of those motors to saturation or a ~10-second thermal limit. I bet there's not a standing quarter-mile record for those trucks

There was some discussion a while asking why these trucks don't use regenerative braking and a battery pack rather than dumping the energy to a resistor bank. It would be heavier/bulkier and more complicated/less reliable but with mines having to truck in diesel fuel to remote areas it seemed a large potential saving in running cost. Perhaps you could offer some enlightenment based on your experience of the industry and hardware?

 

[Alan B]

I wish I had photos of the motor-generators we used to run the Bevatron. I suppose I could dig some up from the archives at the Lab. A pair of 3600hp motors, running on 4kv three phase at 200A idle current. Efficiency must have been pretty high since we energized the field of the main magnet, and then after the pulse reversed that energy back into the AC line, recovering a significant percentage of the energy. Output power from the pair of these motor-generators was up to 15kv 5000A dc to the main magnet.

https://en.wikipedia.org/wiki/Bevatron