Does voltage affect range?

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forcefed   10 mW

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Does voltage affect range?

Post by forcefed » Mar 13 2018 9:17pm

If you run the motor at 40v with a 10ah battery and ride at a constant 20mph, will the range be similar if you ran it at 20v with 20ah battery and the same speed? I'm guessing nothing will change, except top speed and acceleration, range should be similar right?

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Re: Does voltage affect range?

Post by amberwolf » Mar 14 2018 3:30am

You can use the http://ebikes.ca/simulator to see how this works out, using any system similar to your own (it doens't have to be exact).

Mostly it depends on how you ride--if you ride exactly the same way, same accelration, same speed, then the range should be about the same.

But you won't, most likely. You'll use the quicker acceleration and faster speeds once you have them, and range will drop. ;)


One other thing that will affect range is the battery pack itself. As long as it's made of cells that can handle the required currents no matter how many parallel there are, it'll operate the same whether it's lower or higher Ah.

But if ti's made of cells that require a certain number of parallel cells to handle a certain amount of current, then as the number of paralle cells (and total Ah) drops, the votlage sag will increase, and the cells will have a rougher time handling the load on them.

So depending on the current draw of the system, the higher Ah pack (regardless of voltage) might last longer than the lower one.

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Re: Does voltage affect range?

Post by forcefed » Mar 14 2018 4:05pm

amberwolf wrote:
Mar 14 2018 3:30am
You'll use the quicker acceleration and faster speeds once you have them, and range will drop. ;)
Yup most likely, i guess setting it to 20v would ensure i would get longer range than trusting my lead foot... hand :)

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Re: Does voltage affect range?

Post by billvon » Mar 14 2018 4:53pm

forcefed wrote:
Mar 13 2018 9:17pm
If you run the motor at 40v with a 10ah battery and ride at a constant 20mph, will the range be similar if you ran it at 20v with 20ah battery and the same speed? I'm guessing nothing will change, except top speed and acceleration, range should be similar right?
The 20V system will be slightly more efficient because you are dropping less voltage across the motor controller, assuming no phase advance in either system. But it's pretty small; perhaps 1-2%.
--bill von

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eCue   10 kW

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Re: Does voltage affect range?

Post by eCue » Mar 14 2018 11:43pm

The amp output will be a challenge for the batteries
20v x 35A makes for 700 watts.

I use 48v 14A / 700w with a 350w mxus hub but you would not know it as on the hills it needs plenty of leg action or its dead in the water.
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dogman dan   100 GW

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Re: Does voltage affect range?

Post by dogman dan » Mar 15 2018 7:35am

Assuming other problems don't crop up, range will be same, or at least very similar, ( 1% is similar in my world) when the ride is continuous and flat, and the motor is not overloaded. Here is why.

A similar ride will use the same watt hours per mile no matter what. 20 mph takes about 500w, whatever the voltage. Up the voltage, and it won't take more watt hours, until you go faster. Physics says 20 mph on a bike has a certain wind drag, and changing stuff never changes that.

But if lowering or raising the voltage makes it run shitty for any reason, then you just lost efficiency. Anything that would make the motor run hot for example, would mean 20 mph takes more wh/mi. Often this would be overloading, too steep hill, too fat a rider, etc.

Same lack of effect happens with different types of hub motors. in general, differences matter little for wh/mi when cruising. Different voltages, or motor, or weather, or whatever can have huge effects when the motor has to climb hills, or do lots of starts and stops. That again, is different load.

Small differences like spoken about in previous posts don't matter. To make up 1%, pedal with the motor off one block, or less. Yes, its measurable, but no, it is not going to get you another mile.

To reallllllllllllly increase range, slow down 2 mph. Its truly unbelievable the difference between a 20 mph cruise, and an 18 mph cruise. Now you are well into difference above 10% more.

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Re: Does voltage affect range?

Post by amberwolf » Mar 15 2018 1:03pm

dogman dan wrote:
Mar 15 2018 7:35am
20 mph takes about 500w, whatever the voltage.
Generally true for most ebikes; though there are exceptions, mostly due to aerodynamics (assuming an all-on-the-flats no-stop/starts ride).

Something big and boxy like SB Cruiser takes about twice that wattage to maintian 20MPH. :(

Something long and unstreamlined like CrazyBike2 takes about 600w+.


But the rest of what you posted is applicable even to those. ;)

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Re: Does voltage affect range?

Post by DRMousseau » Mar 15 2018 2:17pm

In "pure theory",... Yes! There would be no discernable difference, IF ALL ELSE remains constant. I think Dogman Dan best explained this. Not accounting for tiny variable losses of efficiency, it will take "X" amount of energy to do "Y" amount of work over time. Unless you can vastly improve efficiency, you won't see any significant increases.

In "reality" though,... your likely to see a significant loss with the higher voltage due to "performance" matters. You'll likely use more as you accelerate from a stop to that 20mph speed unless you carefully match the power draw (watts) of accelerating with the lessor voltage, or at the very least, expend no more or no less energy to reach the desired speed. Once that speed is attained and maintained, power draw should be the same. So that slight performance matter, which will be easily noticed by you, will become a significant mileage liability if not consciously and purposely reconciled.

Many ask, "What kinda mileage do ya get with that setup?"
And I kinda liken it to something they can more easily relate to. "Remember drivin' those old cars with V-8 4-barreled engines?" (yes, I have to consider that many today never had such experience. :roll: so sometimes I consider other examples)
"Kinda pretty much the same. If I ease into the throttle, never opening the back barrels, and drive cool and reasonable,... I can do great! If I have some fun, raisin' daylights from every stop at full throttle all four barrels suckin' and screamin' at top speed,... I'll really eat it up!" Sure, I could use a lessor motor, or lower voltage, or limit to slower speeds,.... but what fun would be left!?! So if I'm planning a bigger trip with maximum range expectations,... I do jus as Dogman Dan says. And enjoy the fun at the end of my journey,... if I still have some battery left. :lol:

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eCue   10 kW

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Re: Does voltage affect range?

Post by eCue » Mar 15 2018 3:40pm

My display does not have a watt meter so I im unsure what it draws. The ebike.ca calculator suggest the mxus xfo7 350w consumes about 300 watts with 220lb ride weight 100% throttle 37 Kph on level ground @52v.

By everyone's account that is not going to happen

I want to pick up a cheap multimeter that measures power to test the wheels power input. I want to know what it consumes on the flats and the watt strain on hills at various speeds then Im good and will disconnect it.
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forcefed   10 mW

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Re: Does voltage affect range?

Post by forcefed » Mar 15 2018 7:24pm

eCue wrote:
Mar 15 2018 3:40pm
I want to pick up a cheap multimeter that measures power to test the wheels power input. I want to know what it consumes on the flats and the watt strain on hills at various speeds then Im good and will disconnect it.
I picked up one of these https://www.ebay.com/itm/231739352971 will be interesting to see what it shows at the two voltages, but judging from all the answers here it shouldn't be much of a difference at steady speeds except under certain circumstances.

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dogman dan   100 GW

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Re: Does voltage affect range?

Post by dogman dan » Mar 16 2018 7:11am

FWIW, in the sim, there is no wind. Many get 20 mph with only 400w from motor. Often this means they pedal 100w or more. I don't. lots of people don't. And then there is weather.



After somewhere greater than 20,000 miles riding looking at a wattmeter, I typically run 500-600w on flat ground. And,,, there is never much flat ground around here. So I can pull 200w, or 1000w. But my average on very heavy bikes is closer to 600w. With my pedaling being 50w, or less. ( not healthy) Others do better because my bike is heavy, and not even close to aero. Its a tank with big panniers.

For sure,, Its very hard to ride slow and efficient, at 20 mph or less, when your 48v bike can go 25-30 mph!!! So realizing better efficiency when the voltage is high is quite difficult to do. But if you live in the rocky mountains, low power low voltage bikes just fail on the hills. The answer to extending range is to use all you can get going uphill, and get up the hill efficient. The motor off, pedal as far as you can on the other side of the hill.

If I lived on the gulf coast, then I'd be running a lot less watts, and no more than 36v.

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Re: Does voltage affect range?

Post by DRMousseau » Mar 16 2018 8:01pm

I built mine as I lived along the Emerald Coast of Florida by the Gulf,... summers are now spent in north Michigan. Most typically average I jus over 25mi per charge on an 11.5ah 52V of my 1500w cruiser. I'm usually only pedaling to maintain PAS activation, no efforts at all unless I'm passing thru a deep valley or maybe climbing up a highway overpass or an ICW bridge. I built specifically for that bit of "extra PoP" to be available when needed. Didn't really expect the 40mph speed it was capable of, and not so comfortable with that. I typically have my speed limited to 30mph, and pedal the PAS set to maintain about 20mph. This allows me to grab the throttle while passively pedaling and get outa folks way quickly, and keeps me at a reasonable speed to quickly stop to avoid folks as well.

I do notice some slight differences between the PAS, steady throttle, and cruise settings,... but that 500w @ 20mph is most typical. It's actually surprising to see the difference a slight rise of maybe a foot or two over a 1/4mi or 1/2mi can make. Visually it's hardly noticed at all, but it can make 100w difference for a few moments! And those breezes do to! Those 10mph tailwinds when hittin' 20mph go somewhat unnoticed, with a breeze is still in your face.... but it is significantly shown in the watt meter.

Should I decide to put together a lessor build for a grandkid, I might jus borrow the battery and run a 36V or 48V on my current setup for a bit, jus to see the noticeable difference, and if I actually made a decent choice in regard to my desired performance and range.

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Re: Does voltage affect range?

Post by Alan B » Mar 16 2018 8:29pm

Incidentally, if the battery uses the same cells, the pack power capacity will be equal, each cell will see the same current at the same power level whether arranged for 40V or 20V. At the lower voltage they will be paralleled twice as much, but they will need to supply twice the current for the same power.

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Re: Does voltage affect range?

Post by eCue » Mar 16 2018 10:40pm

I thought of that one after the earlier post I made about 20v batteries and Amp output. Its true :) the 20AH 20v cells have the same amp pull on them as cells in a 10AH 40v pack.
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Re: Does voltage affect range?

Post by John in CR » Mar 17 2018 8:03pm

Running a controller at a higher voltage but at same speed (assuming same motor) is less efficient. That's because running at partial duty is less efficient for the same power, primarily in the controller itself. I see it first hand all the time, because I run high enough voltage that I don't ride around at WOT, and when I ran lower voltage but the same speeds my controllers ran cooler. Motor temp seem unaffected in long-term comparisons, so it's not a matter of using the greater performance available when running higher voltage, but the effects of partial throttle on a controller are significant enough to note the lower efficiency in the form of a hotter controller and some increase in consumption wh/mile or wh/km.

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Re: Does voltage affect range?

Post by DRMousseau » Mar 17 2018 9:29pm

John in CR wrote:
Mar 17 2018 8:03pm
Running a controller at a higher voltage but at same speed (assuming same motor) is less efficient. That's because running at partial duty is less efficient for the same power, primarily in the controller itself. I see it first hand all the time, because I run high enough voltage that I don't ride around at WOT, and when I ran lower voltage but the same speeds my controllers ran cooler. Motor temp seem unaffected in long-term comparisons, so it's not a matter of using the greater performance available when running higher voltage, but the effects of partial throttle on a controller are significant enough to note the lower efficiency in the form of a hotter controller and some increase in consumption wh/mile or wh/km.
OH YES!!! It's sort of drawback to my 52V 1500W cruiser,... since I'm rarely at full speed where it's most efficient. But this has been an acceptable sacrifice for having the extra "PoP" available when desired. The other error I made was that my cruiser is a 29er,... motor is specifically designed and most efficient for a 26" wheel. My new build (under construction) has more consideration for this, as I try to balance other sacrifices I can live with and accept.

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Alan B   100 GW

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Re: Does voltage affect range?

Post by Alan B » Mar 18 2018 1:25am

John in CR wrote:
Mar 17 2018 8:03pm
Running a controller at a higher voltage but at same speed (assuming same motor) is less efficient. That's because running at partial duty is less efficient for the same power, primarily in the controller itself. I see it first hand all the time, because I run high enough voltage that I don't ride around at WOT, and when I ran lower voltage but the same speeds my controllers ran cooler. Motor temp seem unaffected in long-term comparisons, so it's not a matter of using the greater performance available when running higher voltage, but the effects of partial throttle on a controller are significant enough to note the lower efficiency in the form of a hotter controller and some increase in consumption wh/mile or wh/km.
You can make a pretty good estimate of the switching losses in a controller. Each PWM cycle the FETs switch they pass from off to on, and then again from on to off. So twice per cycle. During this switching time their power dissipation goes from near zero to max to near zero again. The worst moment is when they are halfway, at which point they see half the battery voltage and the full motor current. The power dissipation is basically a triangle shape with the peak being the halfway point. The area under this triangle is one half, so the average power dissipated during this switching event is half the max power times the time duration of the switching.

Better FETs don't help much here, the problem is the time to switch. Better drivers to switch the FETs faster does help, but it also causes larger transients which require better capacitors and more engineering and more expensive parts and better drive circuitry.

So let's take a simple case. Assume 1000W continuously to the motor, 100V battery, 1 microsecond switching time, 10 khz switching frequency, and half throttle.

So the motor is seeing 50 volts effective because we are at half throttle 100 * 50% = 50V, and we're traveling at about half max speed.

We know the motor power is 1000W so the motor current is 1000/50 = 20A.

The peak power dissipated during switching is 100V times 20A or 2kW. The average during this switching time is half that, or 1kW.

This loss occurs for one microsecond, times 10khz PWM times twice per PWM cycle, which is 0.02 times the average switching power, or 20W.

So the loss in the controller is 2% while we deliver 1kW to the motor, which doesn't have much effect on range.

Dropping the system voltage to 75V would mean we'd run at about 67% throttle, the motor current and voltage would be the same of course to travel the same speed and the same power. The result overall would be the switching loss would drop by the ratio 75/100 or about 15W, for a savings of 5W in the controller from switching.

This is switching loss only, the I squared R loss in the FETs from motor current is not related to switching and not included. It is also not changing if the same controller is used as motor current is the same and motor current dominates FET I squared R loss.

If you lower the switching frequency, or reduce the switching time the loss will drop. Well engineered controllers can reduce losses, but it does come at a cost.

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Re: Does voltage affect range?

Post by John in CR » Mar 18 2018 10:16am

Thx for that analysis Alan, but it sure seems like there's a lot more going on that's bad during partial throttle situations. Maybe it's just tiny pulses of the throttle that are short enough duration to not feel acceleration, and that's shooting phase current through the roof. My box of blown controllers, other than a few not properly tested by the seller and a handful that I pushed to excessive power, the box is full of controllers blown at partial throttle. 2 were blown at extra low power and low speed (about 5mph on flat bumpy road), which I attribute to short throttle pulses. I've blown exactly zero controllers at above 50% speed even under high load, as well as none blown during WOT while the motor was being tortured on steep hills down to a stall (before I learned better and had motors to powerful to bog down.

Switching losses wouldn't seem to be the cause of these failures, since switching frequency doesn't change and they survive fine switching higher power. I always thought it was phase currents spiking out of hand at low % throttle, and running a higher voltage means lower % throttle. What am I missing?

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Re: Does voltage affect range?

Post by dogman dan » Mar 18 2018 12:21pm

If the load is light, I see no big penalty for running half throttle a lot. Basically, if the load is light you get away with everything.

Its when the load is heavy that you might be better off tuning a hub motor system to cruise the speed you like WOT. start with a smaller wheel if its a hub motor, and then adjust rpm with voltage. Then ride wot most of the time so its not cooking your controller.

Having that extra speed if you need it is nice, but maybe just don't over do it. Or have another bike, you don't mind stressing so hard. that's a fun bike, for the race, or whatever. Daily driver that packs a big load, tune it to last.

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Re: Does voltage affect range?

Post by Alan B » Mar 18 2018 2:26pm

I'm working on an analysis of the zero back EMF startup conditions where I've had five controller failures, but it isn't ready to publish here yet, and the laptop's battery is low so I'll finish that later.

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Re: Does voltage affect range?

Post by Alan B » Mar 18 2018 6:52pm

I think that's a different problem, one which I have also experienced. Let's see if I can estimate my situation there.

I blew one 24FET controller 5 times, every time was at low speed throttle onset, or while climbing a steep hill early in the commute.

In these conditions there is nearly zero back EMF. I had a low resistance motor (Cromotor), with short, low inductance and low resistance wiring, and low resistance Lipo pack with 4 parallel bricks at 18S so 75V max charge voltage. The controller was a name brand 24 FET Xie Chen type rated for 10KW and 100V.

The FETs were 4110's, and with a 24 FET there are four FETs in parallel in each of the six switches. Cold resistance of the 4110 is said to be about 3.5 milliohms, wired four in parallel and two in series so net is half of that, or 1.75, let's call it 2 milliohms to allow for some stray resistance in the controller.

Turnigy 18S4P 5AH 25S bricks.. I don't have a lot of data here, looking around I'm going to use 3mohm per cell. 18 cells series multiply this, and it is divided by four in parallel for a net resistance of 3*18/4, I'll round that up to 15 milliohms.

Wiring is just a few feet of #10 and big Anderson connectors, #10 wire is 1 milliohm per foot, total maybe 10 milliohms.

The CroMotor Info
measured inductance (star configuration): 133.6 uH
total motor 'resistance' (star configuration): 93.3 mOhm, this includes motor cabling.

System resistance is battery resistance plus cable/connectors plus controller/FETs, plus motor. 15 + 3 + 10 + 93 = 121

During the initial application of torque the current flows from the caps through the FETs and the motor windings. So the resistance is the caps effective series resistance ESR, plus the controller and the motor resistance.

The inductance is dominated by the motor at 134uH

So the FETs turn on at zero speed with no back EMF and apply the full 75 volts through 2+93 milliohms. The current heads for 75/.095 = 789 amps, slowed by the time constant. That's 789/4 = 197 amps per FET, if they are perfectly balanced, but there will be some mismatch so we can expect one FET to carry perhaps 50% more than average or perhaps 296 amps. This is a lot of current for those tiny legs to handle. Too much, if it ever gets there. Now the inductive time constant will slow the rise of the current to 67% at L/R = 134/95 = 1.4 milliseconds. During this period the controller (assuming 10 khz switching) will look at the battery current 10 times each millisecond, so it has the opportunity to see it rising and react, but how much does it rise? Remember the capacitor bank is feeding these currents, so the amount that the controller can measure is a function of the power consumed, as it's sensor is in the battery to capacitor side. It also has a time constant slowing the response. We could estimate that but I don't think the controller can see much this early unless it has current sensing in the motor side, which we generally find only in FOC controllers.

Another feature of most Xie Chang controllers is "block time", during which the controller ignores the battery current for a time after the initial throttle opening. On many controllers this value can be set, but in some cases zero is not available as a choice. This could also be a factor.

I'll let people draw their own conclusions, but in my case the controller survived for varying amounts of time. When new it lasted for a few rides, then failed on modest throttle application on a grade. On the first repair it spun the motor and wheel just fine, then failed instantly on first throttle with the bike wheel on the ground, taking off with a mild throttle. After that the repairs were more thorough and I suspect that more FETs were replaced, perhaps all of them, and perhaps they were actually selected for balance, and the testing was more thorough before it came back to me. I didn't do the repairs, so I don't know. The fourth repair in this series involved replacing the entire PC board, and it lasted a long time before it failed on while going up 15% grade, which was a daily return home start of commute event. The controller was never more than barely warm, ever. When it failed in particular it was cold, I always checked that. Note that the period between was over a year between the fourth and fifth. The others occurred in the first couple of months. I had two spare controllers set up for this bike, a 12 FET 100V and an 18 FET 150V. Both of these controllers did get quite warm, and develop less power, but they never failed.All of these controllers were as-delivered, supposedly with common mods already installed.

After the fifth failure the controller was sold (for a bargain price), repaired again and used on a higher resistance motor, in a system with a BMS (so more resistance there and less peak battery current), and didn't fail again, and was eventually sold again so I lost track of it.

The Sabvoton FOC controller I replaced it with has had no trouble with this low resistance system.

If you build a system with low resistance and high voltage it will stress the controller. It is best to have a controller with motor current and FET temperature sensing to properly keep the current in a safe region for the FETs under all conditions.

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