Limits on EbikeKit.com Motor/controller (Update)

[jc4291]

My trusty steed:

It is currently powered by EbikeKit.com's direct drive motor (model they had in 2012) and their 'upgraded' 72V controller they offered back then.

The battery is no longer the lead acid in the picture, but the straight-from-china special 48V 10aH lithium ion (as pictured here: http://www.alibaba.com/product-gs/844093031/48V_10Ah_e_bike_battery.html)

Surprisingly this pack has held up well, the bike has just passed the 1500 mile mark with it. However, my own personal ambitions have driven me to try and create a faster E-bike.

Currently the bike cruises at a respectable 27 mph (on flat terrain) with a 15 mile range (measured on the very hilly terrain of Northern California). My new goal is to create a bike that can cruise around the 40 mph mark (again, on flat ground).

I have done some digging and found some reports that the Ebikekit direct drive motor is a 9C 2807 clone (source: http://www.electricbike.com/9c/) However, I do not know how to verify this.

I hope to make the new pack out of these 6S packs (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=8582&aff=221230) because of their cost/watt, but I am open to suggestions.

To put it simply, what should my battery voltage and current goals be in order to hit the 40 mph flat ground cruising mark? What should the mAh be on the pack to achieve a (hilly) 20 mile range? With these requirements, will the EbikeKit.com controller I currently have handle these requirements or let out the magic white smoke? If not, what motor/controller combo would be a good choice?

Additionally, do you think the hard-tail hybrid commuter bicycle I have converted (pictured above: Schwinn Voyageur GSD link: http://www.performancebike.com/reviews/performance/power/pwr/product-reviews/Bikes-Frames/Bicycles-Frames/Cross-Comfort-Bicycles/SCHWINN/p/30__9536-2007-Schwinn-Voyageur-GSD-Comfort-Bike.html) can handle 40 mph without falling apart?

If you have any questions or if you need more information let me know and I will try to answer it as best I can. This forum is usually very good about answering these types of questions, thanks in advance.

 

[jc4291]

Just to give an update:

Just got off the phone with Jason from Ebikekit.com. It would appear that the motor is good up to 100V and the controller puts out 20A, he believes the motor can handle 2000W with little issue (not warrantied of course).

The controller I have (the 72V upgrade no longer offered) should be able to handle a 72V pack, assuming it has the correct capacitors inside (if not I'll blow them up and replace them with the correct ones). The controllers they offer now can only go up to 60V (63V capacitors inside, again not warrantied at this level).

I am leaning towards a 72V pack, do you think this will meet the goals I have laid out? Again, I'm now trying to figure out target AH.

Finally, what circuit should I implement for the cut off voltage? This controller isn't wired for a cycle analyst and is hard-coded to cut at 31V (something that would not go to well for a 72V pack).

 

[amberwolf]

Regarding the motor, there isn't really a voltage limit on those, for brushless motors, short of whatever the windings themselves are insulated for (type of magnet wire used and it's Insulation Class). It's the controller you'd need to deal with for that, and that depends on the FETs and caps in it, as well as it's low-voltage regulator. Unless you're willing to do what can be a lot of electronics work inside it, then replacing it with one designed for the voltage you want to use instead of upgrading it's internals is usually a lot easier and can be more reliable, especially if you intend to use regen braking.

Also note that if the caps blow up then other parts in the controller may be damaged or destroyed in the process, either by shorts caused by metal cap casings or by spikes no longer being absorbed by the caps. It is also possible for the caps to not actually explode, but rather to simply degrade quickly to the point they no longer do their jobs, and let the spikes thru that then damage the components, possibly making the controller unrepairable.


Cutoff voltage: If your pack has no cell-level BMS to do that for you, then pack voltage itself is not a really reliable indicator of health at low capacity anyway. You'd be much better off to have a watt meter (like the Cycle Analyst, among others) so you know how much of your pack's capacity has been used, either by Wh or Ah.

If you would rather have an actual pack voltage level cutoff, well, the controller doesn't have to have a CA connector on it to be used with a CA--just get the standalone version, which should be able to be set up to cut off the throttle signal if the pack drops below the LVC you set in the CA. The throttle would be plugge dinto the CA, and the CAs' throttle output into the controller's throttle connector. No special connectors needed on teh controller.


Alternately you can research (on the web or here on the forum) how to modify your controller's electronics or possibly programming so the built-in LVC is high enough for the pack you choose.


Regarding the bike and 40MPH, well, the first question: Can you stop safely and quickly from 40MPH on it right now? Repeatedly? With other traffic around you? If not, then that's the first thing you'd want to fix.

How rough are the roads you ride on? If they're not pretty smooth, you may need something with suspension designed for those sorts of speeds and road conditions, as it is possible to lose control and crash, or break wheels or even frames at those speeds when everything is perfectly fine at the lower speeds you're doing now.

Then, if you care about such things, you might check into the legal requirements/penalties for going 40MPH on an ebike in your locality. Some of them are pretty harsh.


Regarding voltage/power levels, you should play around with the http://ebikes.ca/simulator to see what is needed for your bike and conditions to do what you want. For capacity, you may need several times the pack size you have now to do the same range at the much higher speeds, because power usage isnt' linearly expanding. The added pack weight means it will take more power to accelerate from a stop, or climb a hill, so you may have to add even more pack (and weight) to make up for that if there's a lot of that on your path. At some point it becomes counterproductive to be adding more, because you end up with diminishing or even negative returns.

 

[Drunkskunk]

You may want to play with the Simulator on Ebikes.ca's site. The 9C can run at 40mph (44 peak) at 100 volts, but it will melt in 5 minutes per the simulator. With cooling mods, you might get 6 or 7 minutes out of it at those speeds. you're pulling over 3000 watts at that speed.

They can take 1500watts very reliably, and be pushed to 3000 watts for short periods with good results. There are many who push even more into them for very short periods of time.

If you run 72 volts (20S Lipo) you cut the peak speed back to 35mph, 31-32 cruise. You can run for 20 minutes at that speed and be pulling around 1700 watts, almost doubling your range.

You would need a battery size of 72V20A to run 20 miles at that speed, although the motor would melt before you got half way.

 

[jc4291]

Amberwolf, thanks for the reply. You bring up a good point about stopping distance needed at 40 mph, the bike has upgraded brakes/tires, but I fear that the suspension/frame would not hold up.
Perhaps the target of 35 mph, as suggested by drunkskunk, would be more appropriate.

I have been playing around with the simulator and see that it calculates the 'time to overheat'. Do you know how this number is derived/how realistic is it?
This was not something I had considered, but as drunkskunk pointed out, I may be at risk of melting something.

Drunkskunk, thanks for your reply. Could you elaborate why a 72V20A pack would melt the motor? 1500W should be able to be handled by it, or is there something I am missing?

Can a BMS, like the Cycle Analyst, monitor temperature and put a limit on draw after a set amount of time/heat?

As for the pack itself, I am thinking about a unit comprised of 9 packs of the 5000mAh 6S1P 20C (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=8582&aff=221230) to get 72V and 15AH, is this a reasonable starting point?

Thanks again for the help.

 

[amberwolf]

"1500W" is just a "power consumption" figure, if you mean that to do the speed you want it would take 1500W to do it. Or, if the motor is rated at "1500W" it means that it could deliver that much power.


However, depending on the speed you're going and the load you're putting on it, the motor may not be in it's efficient speed zone, and the power wasted as heat in the motor could be enough to damage it, because it would be more than it could dissipate to the air around it.


That's what the "time to overheat" part of the simulator helps to determine. As for it's accuracy, it depends on whether your real life situation is the same as the conditions the simulator data was gathered from--those are listed on the page in the definitions and instructions below the actual simulator.


If you were to take just about any typical ebike hubmotor and try to climb a steep hill with it at a slow speed, it would take a lot of current to do this, meaning a lot of wattage, and because the motor would be spinning slowly (probably a LOT slower than it's efficient zone) it would heat up quickly, and be unable to dissipate much of that heat to the environment because of the way hubmotors have to be made. (there are threads about how to help cool them for such situations, but the effectiveness of this varies).


EDIT (added The same is true of constant stops/starts in traffic or typical city streets, too. I've damaged at least a couple of motors this way, even though normally I only pull about 500W cruising around, startup from a stop with the controller I used allowed several times that, momentarily, and repeatedly doing this in a few minutes quickly overheated the motor, probably damaging the hall sensors in it (I haven't had time to troubleshoot the motors with all the events of this year, so far).


Playing with the simulator a lot will give you an education about how various things affect motors and how you use the bike, etc., once you have played with it enough to begin to see the relationships (or after you read a lot of the forum, and/or the wiki linked in my signature).



EDIT (added): Typically BMSs do not do anything except monitor cell-level voltages, and sometimes pack-level current, and shut off if either exceeds any of it's preset limits.


Regarding using the RC LiPo packs, unless you have experience with them already, and the safety procedures and precautions for using them and charging them and storing them, I highly recommend you read around the forum for a good while before choosing to use RC LiPo, to ensure you will have minimal problems with them, and no dramatic failures resulting in loss of life, limb, or residence. (these can happen with any battery but are more prevalent with inexperience combined with cheap RC LiPo, for a number of reasons that become self-evident with a bit of reading).


If you really need higher speeds, or higher power with hilly terrain, going to 2 wheel drive (2WD) might be a better option than a bigger motor. Check out Kingfish's various threads about that, including his trip documentation threads about riding from Seattle to somewhere in California and back.

 

[dogman dan]

You have a 72v 20 amps controller and an E-BikeKit 28mm type dd motor (like the 9c's).

So do I. So I won't talk simulator. I know.

You will be able to cruise 35 mph with a 72v, that is 20s, RC lipo battery. With that, you should see about 35v at the top of charge. Lico does drop voltage a bit more each mile than lifepo4, so you will start out with a 35 mph cruise, but at the very very end only see about 35 mph.

1500w, well within the limits for these motors to cruise farther than 10 miles without melting one. At 35 mph, you will be getting pretty poor wh/mi. 40-45 wh/mi something like that. I think you will need to carry more than 1 kwh. 72v 20 ah battery should do your 20 miles range fine.

It's a very workable plan to use what you have, but get a large 72v battery. You could get away with 22s with that controller, but I would not go much past 90v fully charged if I were you. 24s is pushing it.

18s, is less than 72v, but would take you farther, with speeds closer to 30 mph. 40mph on the 28mm cheap motors will fry them somewhere between 10 and 15 miles. Not speculation or simulation, I've done it. So have others.

Get a 72v 40 amps controller, and enjoy 40 mph if you want to. You'll be able to go 8-10 miles before you see the motor really overheating. 40 mph won't last long, most of the ride would be at 38 mph with 20 s lico. But for the price of a controller, you can legitimately say you have a 40mph bike. Just don't try for 20 miles at 40 mph with these 28mm motors.

Answering a question from awhile back, 72v 10 ah and a 40 amps controller will run dry at about 8-10 miles, just before smoke pours out of the motor. Carry 72v 15, or 72v 20 ah, and with a 40 amps controller you can easily go far enough to melt down. That's what Drunkskunk meant I think. I won't carry more than 72v 10 ah, when I run my 40 amps controllers. It helps me keep melted motors down to about one a year.

Enough stop and go with a heavy bike can fry a smaller motor. That's why I jumped at a chance to put a huge motor on my cargo bike.