What causes lower top speed gains in this scenario?

[ebike11]

Here is my situation,
I have 2 separate battery packs with the same cells.
Each pack is 12S so around 50V fully charged.
Just for fun I connected only 1 pack and got a top speed of 90kph on a QS273 motor (high rpm motor)
The controller I have works from 48V~120V
When in series @100V fully charged, which is the voltage I normally use, I get around 110kph.
What causes the motor to gain less and less on top end speed with even with double the voltage compared to 50V in this case??
Is it resistance or heat??
What are some ways to resolve issues to reach even higher speeds?
Just add more voltage?
Wiring?

Thanks!

 

[neptronix]

You need more amps to develop the higher speed your voltage has now enabled.

 

[E-HP]

When riding or no load?

If when riding, then over 95% is wind drag and the rest is from rolling resistance.

Setting the wind drag to zero, comparing with a regular upright seating position in this example changes top speed from around 43 mph to 58 mph.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_72_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_72_0.05_24&hp_b=0&frame_b=cust_0_0.005

Then setting the rolling resistance to zero gains about another half mph or so.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_72_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_72_0.05_24&hp_b=0&frame_b=cust_0_0&mass_b=100

Once you set the rolling resistance to zero, the bike could be 500kg, and the top speed is the same, and the range stays to same at 1132 miles (compared to 21 miles with wind and rolling resistance)!

100V example in kph
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_100_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=kph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_100_0.05_24&hp_b=0&frame_b=cust_0_0

 

[ebike11]

When riding or no load?

If when riding, then over 95% is wind drag and the rest is from rolling resistance.

Setting the wind drag to zero, comparing with a regular upright seating position in this example changes top speed from around 43 mph to 58 mph.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_72_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_72_0.05_24&hp_b=0&frame_b=cust_0_0.005

Then setting the rolling resistance to zero gains about another half mph or so.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_72_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_72_0.05_24&hp_b=0&frame_b=cust_0_0&mass_b=100

Once you set the rolling resistance to zero, the bike could be 500kg, and the top speed is the same, and the range stays to same at 1132 miles (compared to 21 miles with wind and rolling resistance)!

100V example in kph
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_100_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=kph&frame=mountain&autothrot=false&throt=100&grade=0&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_100_0.05_24&hp_b=0&frame_b=cust_0_0

Ah...its while riding

 

[ebike11]

You need more amps to develop the higher speed your voltage has now enabled.

But i thought more voltage determined the top speed rather than amps

 

[MadRhino]

Voltage does make speed, but speed can’t be achieved with insufficient power. The faster the speed your motor wants to spin, the more power is required to fight resistance.

If you feed 200v, your motor will want to spin twice as fast, but all this extra speed will be lost in lag due to lack of power to overcome resistance. So, a target top speed requires not only sufficient volts for desired RPM, but also sufficient watts to make it possible.

 

[ebike11]

Voltage does make speed, but speed can’t be achieved with insufficient power. The faster the speed your motor wants to spin, the more power is required to fight resistance.

If you feed 200v, your motor will want to spin twice as fast, but all this extra speed will be lost in lag due to lack of power to overcome resistance. So, a target top speed requires not only sufficient volts for desired RPM, but also sufficient watts to make it possible.

But on 50V it goes all the way up to 90kph..but increasing 20+kph takes so much more voltage.
So frustrating haha

At the time, the controller was putting out the same amps power at 50V and 100V

 

[dogman dan]

I think its drag for a lot of it. Most of it is my thought. Since drag is exponential with speed, it increases a lot for little increase in speed. At lower speeds, I was quite amazed how much less current it took to go 18 mph, vs 20.

But there is a point where everything starts to suck your power into heat. Not one single thing, but your wires do resist, connectors may be resisting more than you'd think, controller is getting warm, and even big motors make heat when the voltage goes up. none of this helps any either.

So drag is the biggie, but then everything else slows you some too. Adding more amps would help of course, but only if your battery likes even higher amps.

 

[ebike11]

I think its drag for a lot of it. Most of it is my thought. Since drag is exponential with speed, it increases a lot for little increase in speed. At lower speeds, I was quite amazed how much less current it took to go 18 mph, vs 20.

But there is a point where everything starts to suck your power into heat. Not one single thing, but your wires do resist, connectors may be resisting more than you'd think, controller is getting warm, and even big motors make heat when the voltage goes up. none of this helps any either.

So drag is the biggie, but then everything else slows you some too. Adding more amps would help of course, but only if your battery likes even higher amps.

Thanks!
I will change to anderson and do only crimp connectors..would there be less resistance instead of soldering my connectors?
I am also using small short pieces of around 3cm and crimping packs in series rather than soldering also. Do you think its better?

 

[MadRhino]

But on 50V it goes all the way up to 90kph..but increasing 20+kph takes so much more voltage.
So frustrating haha

At the time, the controller was putting out the same amps power at 50V and 100V

Same Amps at twice the voltage is twice the power, but twice the power is not enough to achieve twice the speed because wind drag is not a linear equation. As Dogman said: wind resistance is exponential. That is why fast bikes are power hungry, and your controller/battery might not be up to the task right now, for either controller settings or battery C rate.

 

[ebike11]

But on 50V it goes all the way up to 90kph..but increasing 20+kph takes so much more voltage.
So frustrating haha

At the time, the controller was putting out the same amps power at 50V and 100V

Same Amps at twice the voltage is twice the power, but twice the power is not enough to achieve twice the speed because wind drag is not a linear equation. As Dogman said: wind resistance is exponential. That is why fast bikes are power hungry, and your controller/battery might not be up to the task right now, for either controller settings or battery C rate.

Yes im sure wind is a pretty big factor.
So what can i do to "slightly" overcome this? More amps and voltage?

 

[E-HP]

Yes im sure wind is a pretty big factor.
So what can i do to "slightly" overcome this? More amps and voltage?

Depends on how much you want it man. Personally, I don't need to go that fast. But the wind tunnel don't lie:
https://www.stickybottle.com/coaching/cyclists-shaved-legs-faster/

I guess you could ease into it by trying out one of those full body lycra suits and see if that gets you enough speed.
Good luck on your journey.

 

[E-HP]

Another more traditional route to go would be to test it, by buying these and a roll of duct tape. Ride out to the spot where you do your speed runs, and plug in series with your pack to see how 28S feels.
https://hobbyking.com/en_us/rhino-3300mah-4s-50c-lipo-battery-pack-w-xt90.html?queryID=8d5ff09512c7e02dbfeec8bb6580c6f4&objectID=86252&indexName=hbk_live_products_analytics
https://hobbyking.com/en_us/xt90-battery-harness-10awg-for-2-packs-in-series.html?queryID=534e37518128a39c85a49c2313081e2f&objectID=4019&indexName=hbk_live_products_analytics

 

[ebike11]

Another more traditional route to go would be to test it, by buying these and a roll of duct tape. Ride out to the spot where you do your speed runs, and plug in series with your pack to see how 28S feels.
https://hobbyking.com/en_us/rhino-3300mah-4s-50c-lipo-battery-pack-w-xt90.html?queryID=8d5ff09512c7e02dbfeec8bb6580c6f4&objectID=86252&indexName=hbk_live_products_analytics
https://hobbyking.com/en_us/xt90-battery-harness-10awg-for-2-packs-in-series.html?queryID=534e37518128a39c85a49c2313081e2f&objectID=4019&indexName=hbk_live_products_analytics

Yes that would be fun hehe 50C..but im wondering if its an accurate number. I read a lot of good and bad about hobbyking.
Do you recommend these or it was just a random choice?

 

[E-HP]

Another more traditional route to go would be to test it, by buying these and a roll of duct tape. Ride out to the spot where you do your speed runs, and plug in series with your pack to see how 28S feels.
https://hobbyking.com/en_us/rhino-3300mah-4s-50c-lipo-battery-pack-w-xt90.html?queryID=8d5ff09512c7e02dbfeec8bb6580c6f4&objectID=86252&indexName=hbk_live_products_analytics
https://hobbyking.com/en_us/xt90-battery-harness-10awg-for-2-packs-in-series.html?queryID=534e37518128a39c85a49c2313081e2f&objectID=4019&indexName=hbk_live_products_analytics

Yes that would be fun hehe 50C..but im wondering if its an accurate number. I read a lot of good and bad about hobbyking.
Do you recommend these or it was just a random choice?

Random choice, but I get lipos from them and haven't had an issue. Got one dud, took a picture of my meter showing a wonky cell, and they credited me and ordered a replacement. Took a few days to arrive and was good. If you were going to use it for more than testing, I'd get a better quality/brand one.

 

[MadRhino]

Smaller wheels are lowering your exposed surface to wind, and add a mechanical advantage that does lower the power required.

Controller tuning would help of course, but be careful not to exceed battery C rate.

Aero tuning does require building, or at least finding fairing parts that would adapt to your bike. It is by far the best way to improve efficiency and top speed, but also the most expansive in cash and labor.

 

[dogman dan]

Re soldering, a plug costing you amps is not likely to be the difference between a crimp and a solder, but between a bad crimp or solder, and a good one. Or just the thing is in the housing wonky, a common problem with andersons.

But drag is why my motorcycle accelerates quite quick from 0 to 90, but takes awhile to get to 120 mph. Even 1100 cc's hits the wall of air at the top speeds, with a really good, really slick fairing. Easy to make a fairing that looks ok, but lots of engineering to make one that is truly slick.

 

[ebike11]

Re soldering, a plug costing you amps is not likely to be the difference between a crimp and a solder, but between a bad crimp or solder, and a good one. Or just the thing is in the housing wonky, a common problem with andersons.

But drag is why my motorcycle accelerates quite quick from 0 to 90, but takes awhile to get to 120 mph. Even 1100 cc's hits the wall of air at the top speeds, with a really good, really slick fairing. Easy to make a fairing that looks ok, but lots of engineering to make one that is truly slick.

Do yoy mean the spring part of the Andersons are a bit wonky?

 

[ebike11]

Smaller wheels are lowering your exposed surface to wind, and add a mechanical advantage that does lower the power required.

Controller tuning would help of course, but be careful not to exceed battery C rate.

Aero tuning does require building, or at least finding fairing parts that would adapt to your bike. It is by far the best way to improve efficiency and top speed, but also the most expansive in cash and labor.

But larger wheels can give more top speed though. Maybe a tire in the middle size range like a 19 inch wheen would be good? With tire mounted it would be over 20 inches

 

[99t4]

Re soldering, a plug costing you amps is not likely to be the difference between a crimp and a solder, but between a bad crimp or solder, and a good one. Or just the thing is in the housing wonky, a common problem with andersons.

Do yoy mean the spring part of the Andersons are a bit wonky?

Especially with the counterfeit Andersons (too common), the plastic housing shaping and manufacturing tolerances are not tight and crisp, which allows the contactor to be improperly seated in the housing so it does not firmly contact with its mate.

 

[Chalo]

Here, play with this:
http://www.kreuzotter.de/english/espeed.htm

Set the baseline to "roadster", since that's how almost all of us sit on our bikes. Correct the rider height and weight, the bike weight, and the elevation. Set pedal RPM to 1, because it won't accept zero and because pedaling at normal RPM consumes more power as drag than pedaling produces at the speeds you're discussing.

Then put the power you have available into the appropriate box. If you don't know how much that is, take your voltage times your controller current and multiply by 0.75. That's an optimistic case in which the peak output power and the top speed are well matched. So it's probably realistic for a 44V battery but not an 88V battery. To get an idea what the 88V battery will do for you, assume the input power is volts x amps x 0.6. The efficiency might not be that high, but that's more plausible.

 

[MadRhino]

About the wheel size/speed relation. Suppose that you have a large wheel that would be doing 100 mph in theory for the voltage and motor, but it does only 60 because of lack of power to overcome résistance. If you build in a smaller wheel, although the potential top speed would be lower, the real top speed can be higher because it will fight resistance better. If you can’t add power, a smaller wheel is gearing down a DD drive thus requires less power for equal task. When the difference is big between theory and real life top speed, a smaller wheel is going to improve the results. In any case it will improve acceleration and ease the stress on your motorization. After you’ve achieved the best speed with the power that you have, the next step is feeding more power, which could mean battery and controller expenses. Only when your real top speed is getting close to theory, adding voltage does make sense.

Large wheels like slow motors. They are best when riding quality is preferred to performance. You know, when terrain does make a better bike finish ahead of a faster one.

 

[dogman dan]

Andersons, even the best, can be installed poorly for a number of reasons.

1. you used too big a wire for the connector, and the insulation on the wire jams on the connector, making it hard to click into the spring.
2. bad crimping caused the contact to be hard to insert into the housing, again making it appear locked in when it actually did not click into the spring. This can also happen if the contact gets bent for whatever reason.

Both those problems can make the wire pull out of the housing, resulting in poor contact and melted plug, or disconnect.

3. you have to put the contacts on the wire in the right orientation. When completed, the contacts have to be laying flat on the table, at the same angle. If the contact is rotated 90 degrees or more than the other one, then when you put them in the housings side by side, one or both wires will twist the contact within the housing, and it can result in a less perfect contact. Andersons can be put together side by side, or top and bottom, with the contacts in the same side by side orientation. But you really want to avoid having one facing up, and the other facing down, putting a twist on the contact in the housing.

4. never use a melted, crushed, or otherwise deformed housing.