Is the "Volt-Up, Gear-Down" Theory Justified???

[The Mighty Volt]

Hi.

I've been doing some basic tricking around on the very entertaining Ebikes.ca simulator II

http://ebikes.ca/simulator/

The general theory is to volt up, keep the amps down.

According to the sim, An X5303 needs to reach 28 Mph to enter a state where it will "Never" overheat, when a system of 59v and a 40A controller are used with a 20" wheel and 220lb rider,on an 8.5% grade. Consumption is 71.6Wh/Mile at that speed, 28.5Mph. Range is 7.1miles at that speed from a 10Ah pack.

However, according to the same sim, once a switch is made to 72v, the same rider must bring the bike up to around 36 MPH in order to avoid overheating. Energy consumption at that point is 69.7 Wh/Mile. Under the same system, Consumption is 88 Wh per mile at 28 MPH.

Am I missing something here???

 

[liveforphysics]

No amount of re-winding can have any gearing-like effect on a motor. This is one of the biggest misconceptions on this forum.

Secondly, a motor never see's battery current, it sees phase current, which you have no way of comparing.

Thirdly, regardless of voltage or wind (assuming the slot ends up stuffed with the same amount of copper in the end), a motor has the same continuous torque limit that is totally irrelevant to battery voltage or battery current. It's a property of the motor alone.

 

[Russell]

When I run the simulation changing just the battery voltage and throttle settings I get the same power consumption for each.

 

[dogman dan]

Well, just to nit pick ya, I'd never choose a 5303 for a steep grade. To me the key to not overheating is to keep that motor in the happy rpm, which you refer to. So since wattage needs to be limited to what the motor can radiate fast enough, and since the motor will be slowing down climbing that grade if wattage is limited, choosing a slower winding gets that motor closer to being in that happy zone. Very hard to make a 5303 happy on an 8% grade for sure.

This is how I get away with long duration rides up very steep grades in summer desert heat. It's 1 not overwatting it and 2 choosing a motor that makes less heat at 10 mph than faster winding. The slow motor does need more volts to keep from being a completly slow pig, so right now I'm running 72v. In order to not be making 1500 watts into heat, I lower the amps to where there is only 1500w avaliable. Double the motors intended wattage is not so bad. But adding another 1000w would just be adding 1000w of heat when the motor is stalled. And riding those hills, it will be stalling some.

It's far from perfect, and not particularly fast. But I do get up steep hills, and never melted a motor this summer. And I don't have to make short 20 min rides. I can go out and take an hour, and drain my whole battery. Twice the amps would ride better, I garantee it, but that's how I melted the last one. More amps simply made heat the motor could not radiate fast enough. It was 50 F when I melted that motor too.

In the end, it's all compromises till you just go get a motor designed for more watts. Do you want a fast short ride? a very long slow one? or what I chose? a medium fast, but long enough ride.

You definitely don't get a lower gear, or more torque by changing windings and voltages ( if wattage remains the same). But you can go with combination A that makes 1000 watts of your power into heat, or combination B that makes 200w into heat. Should be a no brainer which works best. The tricky bit is that there is no one combination that works best for all kinds of riding. That's why the simulator is so great, you can look at various strategies before you buy. 8)

 

[The Mighty Volt]

Well, just to nit pick ya, I'd never choose a 5303 for a steep grade. To me the key to not overheating is to keep that motor in the happy rpm, which you refer to. So since wattage needs to be limited to what the motor can radiate fast enough, and since the motor will be slowing down climbing that grade if wattage is limited, choosing a slower winding gets that motor closer to being in that happy zone. Very hard to make a 5303 happy on an 8% grade for sure.

This is how I get away with long duration rides up very steep grades in summer desert heat. It's 1 not overwatting it and 2 choosing a motor that makes less heat at 10 mph than faster winding. The slow motor does need more volts to keep from being a completly slow pig, so right now I'm running 72v. In order to not be making 1500 watts into heat, I lower the amps to where there is only 1500w avaliable. Double the motors intended wattage is not so bad. But adding another 1000w would just be adding 1000w of heat when the motor is stalled. And riding those hills, it will be stalling some.

It's far from perfect, and not particularly fast. But I do get up steep hills, and never melted a motor this summer. And I don't have to make short 20 min rides. I can go out and take an hour, and drain my whole battery. Twice the amps would ride better, I garantee it, but that's how I melted the last one. More amps simply made heat the motor could not radiate fast enough. It was 50 F when I melted that motor too.

In the end, it's all compromises till you just go get a motor designed for more watts. Do you want a fast short ride? a very long slow one? or what I chose? a medium fast, but long enough ride.

You definitely don't get a lower gear, or more torque by changing windings and voltages ( if wattage remains the same). But you can go with combination A that makes 1000 watts of your power into heat, or combination B that makes 200w into heat. Should be a no brainer which works best. The tricky bit is that there is no one combination that works best for all kinds of riding. That's why the simulator is so great, you can look at various strategies before you buy. 8)

Heh? :lol: :lol:

I know all that

I guess my problem is Russells.........conflicting information from the Sim, suggesting that, in my case, an X5303 might be happier at 60v than at 72v.

 

[liveforphysics]

I guess my problem is Russells.........conflicting information from the Sim, suggesting that, in my case, an X5303 might be happier at 60v than at 72v.

Did you know, that a motor turning at the same speed getting the same number of watts of power has no idea if it's pack voltage is 1,000v or 10v? What it see's is exactly the same phase current, which is all the produces the flux in the motor. The difference is that the 1,000v setup would be able to spin the motor up to a higher RPM, but in a hubmotor situation, your motor speed is your vehicle speed, which is aero-drag power limited, so you quickly reach a point where higher pack voltage only places more stress on the controller and has no effect on vehicle performance.

 

[Russell]

TMV simply made an error interpreting the simulator, that's all. The 5303 on 72V will definitely make more power, have a higher top speed and climb hills faster than at 59V. Of course if a person uses that extra power the motor may overheat which it may or may not do at the lower voltage.

 

[John in CR]

You left out the "gear down" part in your example, which requires a smaller tire. The resulting benefit will be more power potential with little change in efficiency.

 

[The Mighty Volt]

TMV simply made an error interpreting the simulator, that's all. The 5303 on 72V will definitely make more power, have a higher top speed and climb hills faster than at 59V. Of course if a person uses that extra power the motor may overheat which it may or may not do at the lower voltage.

Probably. The simulator simply gave me the impression that at 72v, I would have to keep the bike at 35mph to avoid overheating, whereas with the 60v system I would only need to hold it at 28mph.

Of course what LFP says is also true....the motor has no idea what the voltage of your pack is.

 

[The Mighty Volt]

You left out the "gear down" part in your example, which requires a smaller tire. The resulting benefit will be more power potential with little change in efficiency.

20" is as small as I can go man!

 

[LI-ghtcycle]

You left out the "gear down" part in your example, which requires a smaller tire. The resulting benefit will be more power potential with little change in efficiency.

20" is as small as I can go man!

Unless you get a monster scooter hub motor and just attach the wheel to the rim!

 

[liveforphysics]

You left out the "gear down" part in your example, which requires a smaller tire. The resulting benefit will be more power potential with little change in efficiency.

Yep, that's right. For a hubmotor, going to a smaller size wheel and a higher voltage pack does work, and is like a gearing change. If you want power with a hub, running the smallest sized wheel you can find is a way to get higher continuous power from a given hub.

Drilling big holes in the sides or adding internal fans etc are other options.

 

[Russell]

TMV simply made an error interpreting the simulator, that's all. The 5303 on 72V will definitely make more power, have a higher top speed and climb hills faster than at 59V. Of course if a person uses that extra power the motor may overheat which it may or may not do at the lower voltage.

Probably. The simulator simply gave me the impression that at 72v, I would have to keep the bike at 35mph to avoid overheating, whereas with the 60v system I would only need to hold it at 28mph.

Of course what LFP says is also true....the motor has no idea what the voltage of your pack is.

TMV,

Your logic is just a bit backwards. At 28 MPH you need 'X' amount of power and whether you're powered by 60V or 72V that's going to be the same which you can see graphically in my post above. At 28 MPH the motor may never overheat up the grade. Now at 35 MPH the motor will be consuming significantly more power, which of course means more heat and a better chance of overheating.

-R

 

[The Mighty Volt]

TMV simply made an error interpreting the simulator, that's all. The 5303 on 72V will definitely make more power, have a higher top speed and climb hills faster than at 59V. Of course if a person uses that extra power the motor may overheat which it may or may not do at the lower voltage.

Probably. The simulator simply gave me the impression that at 72v, I would have to keep the bike at 35mph to avoid overheating, whereas with the 60v system I would only need to hold it at 28mph.

Of course what LFP says is also true....the motor has no idea what the voltage of your pack is.

TMV,

Your logic is just a bit backwards. At 28 MPH you need 'X' amount of power and whether you're powered by 60V or 72V that's going to be the same which you can see graphically in my post above. At 28 MPH the motor may never overheat up the grade. Now at 35 MPH the motor will be consuming significantly more power, which of course means more heat and a better chance of overheating.

-R

Yeah I think I need to give it more thought.....the simulator seemed to be "saying" to me that higher voltages need to be "used", once you apply them. Ironically, it seems to be suggesting that you MUST stay at higher speeds in order to avoid overheating. In other words, at 60v, you need to hit 28MPH and at 72v you need to hit 35MPH.

Now I know that makes no sense.

Anyways I will keep trying.

 

[John in CR]

That is correct. The higher the voltage the higher the speed you need to maintain at that throttle position to avoid overheating. If you're looking at sims, then you want cruising to be at or above the point of peak power to be in the band of better efficiency for the motor, and out of currently limiting to make life easier for the controller. Especially with the higher Kv scooter hubbies, you want to avoid partial throttle under heavy loads like big hills, because it's a quick death for controllers unless you can get above the safe point of speed. If you don't maintain that safe speed, partial throttle just chops of the phase pulses even more, which is harder on the controller.

 

[wineboyrider]

A watt is a watt no matter watt. 8)

 

[The Mighty Volt]

That is correct. The higher the voltage the higher the speed you need to maintain at that throttle position to avoid overheating. If you're looking at sims, then you want cruising to be at or above the point of peak power to be in the band of better efficiency for the motor, and out of currently limiting to make life easier for the controller. Especially with the higher Kv scooter hubbies, you want to avoid partial throttle under heavy loads like big hills, because it's a quick death for controllers unless you can get above the safe point of speed. If you don't maintain that safe speed, partial throttle just chops of the phase pulses even more, which is harder on the controller.

Okay then! Now I know I am not cracking up!!! :lol:

Thats why I asked about the "Volt Up, Gear Down" philosophy.

Clearly the user has to be prepared to match their system with a particular style of riding to avoid damage to the system.

In other words, there is no point in having an X5303 with 72v unless you have the guts to open the taps and hang on in there.

This is news to me. I confess...with my X5305 I like to travel up very steep hills with a partial twist, at 500w or so, watching, as I travel up the hill, the watts rise to around 1500 or so.

But by rights I should be attacking that hill flat out, and letting the motor hit the top speed??

Cheers. 8)

 

[The Mighty Volt]

A watt is a watt no matter watt. 8)

It is....but the duration of time for which the system "see's" the higher Watts is critical.

It seems now that this "gently gently" philosophy could be false, especially in the area of steep hills.

 

[dogman dan]

Re my nit pick. I figure you do know what I was saying, as well as the others posting. I just repeat stuff ad naseum because 90% of the readers don't know, didn't understand another similar post, or are just noobs. Sorry, I do get tedious and clutter up threads. But for every time I repeat myself, ther'es 50 ads that talk about a speed model and a torque model. No such critter. Want more torque, either watt up or gear down ( smaller wheel). Or both hee hee!

Another nit pick though, Somebody mentioned cruising at 72v. But the sim you showed was no cruise. 8.5% grade will never be a cruise. So of course that produced conditions of heating that are waaaay different than a cruise on flatter terrain.

On hills, it's a matter of can the motor radiate the heat fast enough to not overheat. Slower windings help keep the motor from stalling at such a fast speed. Less stalling, less heat. This works fine if you also limit watts somewhat. At some point on a really steep grade, more watts doesn't get enough faster, it just makes more watts avaliable to the heater. The key on a long hill is keeping the heat produced balanced with the heat you can radiate in that days weather, somehow. If you can keep watts really low, and use the motor as just an assist to pedaling, you can slowly climb a long hill with just about any winding. Even if the motor is making 400 out of 500w into heat, it still can keep up with radiating that 400w of heat. The 100w left is sure a lame assist though.

More watts in the form of more volts can keep the motor from stalling as much by speeding up. Your example quite correctly points out the problem with this approach, stalling speed gets faster. This could be part of why my DR motor smoked. The speed up the hill approach does work great on a shorter hill. Anything under 1 mile length, charge it WOT, if you have time for the motor to cool before the next one.

I played with the new sim for awhile this summer. I put it the conditions of all the stuff I have personally tested, and found it quite right on. It seemed to really confirm everything that I saw actually happen. Some of the seat of the pants rules of thumb I've been using to climb hills seem to be confirmed. For example, you mentioned limiting watts to 1500 climbing a big hill. That's just about where I am too. I think in most weather, motors can radiate the heat ok at 100-1500 w. Above that, you start having to look at limiting duration. Cover holes help, but only up to a point. Past a certian wattage, they mainly let the smoke out better.

 

[wineboyrider]

Well put Dogman. That's why I limit my watts to my 9c to around 1200 and I haven't had any problems with it yet. But, my BMC motor has a fried hall wire somewhere, because I was running it a little over 1500w. The winding doesn't help either as it is wound for more efficiency at speed and not climbing....?

 

[John in CR]

Dogman,

No wonder you continue to melt hubmotors. I've never melted one... not even darkened the color of the varnish on the windings, and 95% of the time I ride a bike with a sealed hubmotor.

After the last debate on this topic, I tried partial throttle on one of my regular climbs. Luckily I stopped to check the motor after just a few hundred yards, because it was much hotter than it gets at WOT on the same climb, and I hadn't even gotten to the steepest segment yet.

Speed is the target not some power level. I could melt my motor at 1000W if I was so inclined, however, if I can maintain 30mph on my primary bike, the motor can handle multi-kilowatts as long as the battery will last regardless of the grade or how much extra weight the bike is carrying. The minimum safe speed at WOT factors in everything but the ambient temperature.

For those playing with the simulator, Justin is still working it, and since it doesn't factor in the fact that cooling is better at higher rpms and higher speed, those overheat times can't be relied upon to make valid comparisons.

 

[miniebiker]

I guess this is the answer.

http://www.youtube.com/watch?v=EZ2_sXwdaiw

 

[John in CR]

I guess this is the answer.

http://www.youtube.com/watch?v=EZ2_sXwdaiw

Variable gearing is definitely better for hills, but only at moderate and lower power can "through the gears" using bicycle components be reasonably reliable.

What we really need is a proper multi-speed geared hubmotor with proper metal gears and cooling system for the smaller motor enclosed. The reasons we don't have them already are:
1. I'm not a mechanical engineer
2. Ebike design is dominated by pedalists
3. Motorcycle companies either don't understand how fun 5-10kw can be with a lightweight silent bike, or they're stuck in the box with a motor driving a chain because that's what they know. At least we have a member inside one plugging for what's really needed and being ignored.

I have no doubt that a 5kw 2 speed actively cooled hub motor is possible in the 5-8kg range, and if I could, I'd build one to prove it.

 

[dogman dan]

I'd like one of those too I'm sure.

I'm not quite sure what you meant, but every time I ever melted a motor I was definitely riding it WOT up steep hills or racing. My guess is your motor got hot because it slowed into that stalling speed range. The less throttle trick only works when you pedal till you puke keeping the bike traveling fast enough after lowering motor watts. In other words, replace motor watts with equal human watts. No fun, but it can be done. It's a trick for those who use a motor just as an assist.

I think it's quite possible your motor was still making more heat than it could radiate. For the slow down to climb thing to work, you have to lower watts to at least no more than 500-800w. Otherwise the hub can't radiate it as fast as it gets made.

My best bikes so far have been slow winding motors run at 1200-1500w. Slow but steady, and I can climb all I want WOT with few worries. Same motor on 3000w melted fairly quick.

I bet a motor designed to the same speed but built for 5000 w would very quickly become my favorite! It's not that I like low watts, it's just that these bike motors are designed for low watts.

 

[John in CR]

The point was that it's not the power you have to watch, but the speed you have to maintain. The race bike meltdown was different, and the repeated accelerations bit you. What you needed there was a second motor.