[TF] Ideal Power For a Heavy E-bike: Amps vs Voltage

[deerfencer1]

I have thought for a couple years now that 48V is THE ideal power
level for heavier e-bikes and/or riders. Why? Lower amp demands on the
pack (compared to 36V) makes me think they will suffer less under
loading, but I'm no EE so would appreciate any informed input on this
topic.

I will say from personal experience that I have ridden several 24V e-
bikes (Currie-based) and found them more than wanting. OTOH my TF SX
kicks serious butt at 36V (actually 36-39V under load off a charge
with my low sag lipolys) but a steep hill will push the amperage to
33A average and risk thermal power drawdown if the hill is a few miles
long without a break.

The main issues here IMM (besides the obvious need for a certain
amount of power) are 1) battery pack stress/longevity and 2) motor
(over)heat issues, and I'm guessing a 48V bike motor running @ 25A
(producing 1200W average) is simply a kinder setup for both battery
and motor than a 36V motor @ 33.3A.

Maybe DC, Jeff, Dermot and the other talented engineers we have here
can weigh in on this question, namely does a higher voltage/lower amp
setup produce less heat than the opposite?
Any efficiency tradeoffs?

LH


--
Subscription settings: http://groups.google.com/group/tidalforce/subscribe?hl=en

[remf]

Well I'm no engineer either but I agree, 36V is too low for a heavy bike. I came to this conclusion after test riding the 72V Stealth Bomber. With a combined total weight of bike & me at 275 lbs, a lot of torque is required. It seems to be well in excess of 100 N-m at low speed, getting you off the mark _really_ quickly. At 3,000W @ 72V, probably operating at ~40A. Battery longevity is managed by a quality BMS & very solid LiFePO4's. As far as I can tell, motor overheating issues are non-existent and I gave it a workout.

[deerfencer1]

The Bomber's an e-moto, so substantially heavier than the TFX bikes
and probably not a useful comparison to e-bikes since the motors on
these beasts are usually much bulkier and more thermally capable than
most compact e-bike motors, so kind of an apples to oranges comparison
IMO.

Separately, one point I neglected to make in my initial post is that
in arguing for 48V I'm assuming my own significant power needs, much
of them due to the very hilly terrain in my area. Someone riding the
same bike in Florida on flat blacktop OTOH would most likely be more
than happy with 36V, which is why the ultimate e-bike might someday
have switchable variable voltage input.

In fact the Powerpack motor/controller upgrade I bought for my wife's
Lashout a couple years ago offered exactly that: with the turn of a
keyswitch and an extra battery pack you could step the voltage up from
24V-36V-48V-60V, (though I was cautioned that 60V was likely
overkill). Very cool and brilliant tech tweak added by the EE's behind
the Powerpack, which was a bargain at around $300 if I recall (that
included a new motor and controller). At 48V the Lashout had tons of
torque and easily outclimbed Uma. SOmeday I'll have to plug in my 37V
lipolys and see how she runs.

The current model advertises 36-48V range or about 1000W but the BMC
motors are known for their torque, so that's probably all the current
most riders would need with that particular motor.


http://www.thesuperkids.com/10wabmc36vor.html



LH

On Apr 16, 2:52 pm, remf <optibi...@gmail.com> wrote:
> Well I'm no engineer either but I agree, 36V is too low for a heavy bike. I
> came to this conclusion after test riding the 72V Stealth Bomber. With a
> combined total weight of bike & me at 275 lbs, a lot of torque is required.
> It seems to be well in excess of 100 N-m at low speed, getting you off the
> mark _really_ quickly. At 3,000W @ 72V, probably operating at ~40A. Battery
> longevity is managed by a quality BMS & very solid LiFePO4's. As far as I
> can tell, motor overheating issues are non-existent and I gave it a workout.
>

[deerfencer1]

P.S. Also, that 1000W rating on the BMC motor is no doubt nominal.
Fact is 35A v 48V = 1680W, more than enough juice for any hill.

LH

[rem f]

You mentioned voltage in respect to heavy bikes. I think the Bomber
illustrates that heavy bikes need more voltage. I wasn't comparing it
but now that you mention it, how much does a TFX weigh?

[remf]

"The Bomber's an e-moto"

It's got pedals. I agree it's heavier than a TFX with a big battery but not by much, especially after the Bomber recently shed a few kilograms with new batteries.

Here's someone else who says it isn't. 

Quick, what has two wheels, handlebars, a motor and goes over 40 mph?

A motorcycle – wrong!

Sorry, that was not fair. I left out pedals and crank arms. So OK, now guess what it is?

A moped – wrong again!

Ok, enough with the semi-cleverish intro. I’m talking about electric mountain bikes. Big travel downhill mtb’s with an electric motor, batteries, cranks and motorcycle like top speeds. Why bother with pedals on a bicycle that does 50+ mph and weighs 100+ pounds?

Find out why after the break.

First off all that power can be hidden inside what looks exactly like a bicycle. If you are in an urban area a bicycle can be ridden on sidewalks, bike paths and on the street. In big cities it can also be locked to a bicycle rack when parking is at a premium. Second you may get more exercise. I think offroad motorcycles are underrated in their physical strength requirements but theoretically you can get a better workout on a motorcycle with pedal assist. Lastly, if you do run low on power you can pedal which lessens range anxiety. Granted, you are gonna be feeling the burn when you get home.

Stealth Electric Bikes Bomber

The Stealth Bomber and Stealth Fighter by Stealth Electric Bikes in Melbourne, Australia are “mountain bikes on steroids”. The 72 Volt Bomber uses a Crystalyte X5 hub motor in the rear wheel and a 9 speed Suntour v-boxx crank. The RST front suspension provides 9 inches of travel and the DNM rear almost 10 inches. Most of the components are upgradeable through Stealth. The all steal monocoque framed bike weights close to 130 lbs but it will do almost 50 mph without pedaling. Have a look at the video below to see the Stealth Bomber doing hot laps to get an idea of how fast it moves. Also be sure to read through Potatoho’s first hand report of life with the Stealth and how it compares to his Zero X.

Bottom line is the Stealth Bomber proves that an identity crisis can be a good thing. Now what is this blog about again? Aww whatever, let’s ride.

from http://plugbike.com/2010/01/13/stealth-electric-bomber-a-two-wheeled-identity-crisis/

[Jim_Kirk]

Remf,
You got the Bomber now? Looking for a ride report :).
-Jim

> fromhttp://plugbike.com/2010/01/13/stealth-electric-bomber-a-two-wheeled-...

[deerfencer1]

You can put pedals on anything but even @ 125 lbs I would still call
the Stealth an e-moto. These power e-hogs occupy a whole different
category IMO, and are obviously designed for much more extreme offroad
riding than any e-bike. My Denali e-moto is 30-35 pounds lighter then
the Stealth and has pegs, not pedals, but I can't imagine much point
in pedaling it even if I could. Sure, they can be ridden on blacktop
but one look at the tires and suspension tells the real story, namely
that these are basically electric downhill/XC trail bikes. LOTS more
juice required for this kind of riding than macadam cruising.

And with the Stealth about 45 lbs (or 50%+ heavier) than the TFX
bikes, the battery power requirements are obviously much greater, so
still an apples to oranges comparison IMO.


LH

On Apr 17, 10:38 pm, remf <optibi...@gmail.com> wrote:

> fromhttp://plugbike.com/2010/01/13/stealth-electric-bomber-a-two-wheeled-...

[plasmadust]

Run a BMC at 1600W for any amount of time and you get a fried motor.
We tried to solve some of the BMC problems by double wrapping the
windings, instead of one largeer dia. winding. Read, more flux, less
current.
We can run at 1000W (power is power kids, volts up and amps down or
the inverse) but the amount of heat is Watts. Do you seriously think
you can generate 1600W of heat in a closed case motor and not have
problems????
DC

[Joe]

With luck, some (hopefully most) of the energy (Watts) is converted
to use moving the bike forward and most of what we call wasted is
converted to heat. I think most electric motors convert 80% or more
to useful non-heat energy but there are a lot of variables. ICE
motors much lower efficiency of around 18% (82% of the stored energy
in the gas is wasted as heat.)

[deerfencer1]

DC,

Thanks for the frank post--exactly what I was looking for.

If I understand I think you're saying the whole amps vs voltage thang
is not the point, just total watts? Please inform.

LH

[remf]

Hi Jim - not yet. Shouldn't be more than a few weeks away now.

Larry...I've ridden many MX bikes...for example the KTM 150SX weighs about 200 lbs, even pit bikes weigh close to this, all with much more power & no pedals. Then look at real e-motos & see how much they weigh with about 4 or 5 times the power of the Bomber.

Zero MX 172 lbs 17 kW

Zero X 161 lbs 17 kW

Quantya 195 lbs 12 kW

Bomber 120 lbs 3 kW

I do not believe it's credible to say it's an e-moto. It may not be directly comparable to an Opti or E+ and it is a power e-hog but after riding it, it's definitely still an e-bike...you use the pedals a _lot_ & you can still lift it. Cranks also allow you to take the bike places you could never go on a Zero.

[Bike_on]

I concurr with Doug. At 80% eff and 1000W from the battery, that is
200W of heat. The move to increase power density - ie reduce motor
size and weight but keep up the power, has it's physical limits. The
small Opti motor is rated at 850W, but probably draws 500-600w
average. If it ran at 23.5A, 850W, and 72rpm pedal speed, it would
not take long for the thermal protection to kick in and start phasing
back on the drive.

I also ran the new E+ motor very hard for 11 miles and got some
thermal cut out. There, I was running 1000-1200W average from the
battery. The motor has more surface area than the Opti, but still had
it's limits.

The X5, at 23lbs, has more mass to move the heat, and seems to fit the
1500W+ needs.

I wonder about Hi-Power cycles and Betterbikes who are selling BMCs,
and advertising 1800W-2400W operation. That is a very attractice
48-51V system, weighing less than 80 lbs, but will it survive?


Dan

> >http://groups.google.com/group/tidalforce/subscribe?hl=en- Hide quoted text -
>
> - Show quoted text -

[plasmadust]

Larry,
Yes, it is a Watts thang.
The brushless motors WILL run faster at higher volts, but you better
mind your amps.
When we rate a motor, it is based on a lot of things. First, how much
output power (torque), in both sustained and max, short burst.
Generally motors have a 100% max over sustained watts. I.E. 500W motor
CAN pump 1000W, but for how long. Any energy that is not converted
into mechanical rotation is dissipated as heat. Increase the load on
the motor (torque) and you get... more heat due to less rotation and
more torque. This is why a motor with 85% efficiency runs hotter than
a motor rated at 95%. The 95% motor converts more energy into work.
Now for the quickie lesson.
Take a 36V battery and a 25 amp controller. Ideally that equals 900W
of energy (power). IF the motor is rated at that much power, then
everything is good to go. Now take that same motor and 25A controller
and bump it up to 48V and you get 1200W of energy delivered to the
motor. IF the motor is not designed to produce that much output
torque, you get mucho caliente built up inside the windings and
effectively have a nice space heater until the windings burn out.
The C-lyte motors were made to take lots of power and turn it into
rotational torque. The down side to that is the amount of battery
necessary to feed the motors. That has been a real problem for them. A
$300-500 motor, which is a good motor, but then you need batteries
that are stratospheric in cost to keep up with the motor and
controller.
I hope you can see the relationship between Volts and Amps now a
little better.
We all know about the voltage sag under a load from previous post. As
the load goes up, so do the amps. The voltage will sag because the
power is up. V x A = I (power) get it.

[OptOut]

Nice explanation Doug.

Another variable with strong influence on voltage sag is internal
battery resistance. Ie typically NiMH have greater internal resistance
than lithium which explains larry's observations of low V sag with his
lipo's compared to Nimh and also explains why NiMH packs get hotter
during use than lipos. Resistance always means electric energy
converting to heat.

Best,
Joe (mobile)

[Bike_on]

Doug gave a good synopsis, but needs some clarification on the units
of measure. Power is related but not the sme as energy.

Power (Watts), Energy is POWER * time (watt-hours).

There has to be work for a power measurement. Energy is already there
either as potentialor kinetic.

If I stand on top of a pedal with my brakes applied, I do not move and
produce zero power. I have potential energy (mass*gravity force)

Motors have no energy limit, just a power limit.

Batteries are finite in energy (Ahrs ==> Whrs = V*Ahrs) and are
limited in peak power by its peak Amp output due to resistance.

Doug - can you give some real world power limit numbers on the BMC
motors? Is th enew 1000W unit for real?

DR

On Apr 19, 1:08 pm, OptOut <optib...@gmail.com> wrote:
> Nice explanation Doug.
>
> Another variable with strong influence on voltage sag is internal  
> battery resistance. Ie typically NiMH have greater internal resistance  
> than lithium which explains larry's observations of low V sag with his  
> lipo's compared to Nimh and also explains why NiMH packs get hotter  
> during use than lipos. Resistance always means electric energy  
> converting to heat.
>
> Best,
> Joe (mobile)
>

> > Subscription settings:http://groups.google.com/group/tidalforce/subscribe?hl=en- Hide quoted text -

[deerfencer1]

remf,

Point taken re these heavier "real e-motos" you mention, but keep in
mind this is a category that didn't even exist a few years ago, which
accounts for much of the debate here.

And since you've ridden both an Opti and the Bomber, I'll take your
word for it that the latter is an e-bike and that the pedals are
actually functional. My Denali OTOH I think is best described as an
electric dirt bike.

Looking forward to your ride reports on the Bomber--what's it costing
and where will you be riding it?


LH

On Apr 18, 7:21 pm, remf <optibi...@gmail.com> wrote:

[rem f]

Larry, totally agree, it is a new category. Maybe even a new sub-
category, for the moment totally owned by Stealth. Something tells me
it won't be long before there are others. Rumors of a new Opti police
bike are interesting in this regard; if true, unless it's a major
redesign, it's not going to be in the same power & weight category as
the Bomber but it will be amazing, no doubt about it

The Bomber costs around $7,500 fully optioned. I plan on riding it on
local fire trails & singletrack. There's also a new custom hitch that
allows for easy transport on the back of any vehicle with a tow-
ball...opening up a world of dirt a bit further afield. Recent
developments may make it possible to ride it on public roads legally.

Very interesting what DC says about Crystalyte motors like the X5 that
powers the Bomber..."made to take lots of power and turn it into
rotational torque. The down side to that is the amount of battery
necessary to feed the motors...". Absolutely and it seems that no
manufacturer, apart from Stealth, has yet managed to design a durable
bike that can elegantly carry 20 Ahrs of batteries running at 72V, or
anything close.

[OptOut]

Whatever happened to the $7,200 brammo enertia e motorcycle. Anybody
riding one here? They're $6000 in CA.

Best,
Joe (mobile)

[deerfencer1]

remf,

Interesting that Stealth is Clyte-powered--I didn't know that--and
furthermore that they may well be the first to exploit the power these
motors afford--very exciting!

It will be interesting to see how these pups hold up to all the abuse
that this category implies. Kudos to Stealth for pushing the power
envelope here!

LH

On Apr 19, 6:55 pm, rem f <optibi...@gmail.com> wrote:
> Larry, totally agree, it is a new category. Maybe even a new sub-
> category, for the moment totally owned by Stealth. Something tells me
> it won't be long before there are others. Rumors of a new Opti police
> bike are interesting in this regard; if true, unless it's a major
> redesign, it's not going to be in the same power & weight category as
> the Bomber but it will be amazing, no doubt about it
>
> The Bomber costs around $7,500 fully optioned. I plan on riding it on
> local fire trails & singletrack. There's also a new custom hitch that
> allows for easy transport on the back of any vehicle with a tow-
> ball...opening up a world of dirt a bit further afield. Recent
> developments may make it possible to ride it on public roads legally.
>
> Very interesting what DC says about Crystalyte motors like the X5 that
> powers the Bomber..."made to take lots of power and turn it into
> rotational torque. The down side to that is the amount of battery
> necessary to feed the motors...". Absolutely and it seems that no
> manufacturer, apart from Stealth, has yet managed to design a durable
> bike that can elegantly carry 20 Ahrs of batteries running at 72V, or
> anything close.
>

[deerfencer1]

Wow Joe--that's 50% less than the original price point, no? Is the $6K
price due to CA state credits? Either way it's a tempting buy at that
price for anyone looking for a purely local commuting bike.

LH

On Apr 19, 8:05 pm, OptOut <optib...@gmail.com> wrote:
> Whatever happened to the $7,200 brammo enertia e motorcycle. Anybody
> riding one here? They're $6000 in CA.
>
> Best,
> Joe (mobile)
>

> On Apr 19, 2010, at 6:55 PM, rem f <optibi...@gmail.com> wrote:
>
> > Larry, totally agree, it is a new category. Maybe even a new sub-
> > category, for the moment totally owned by Stealth. Something tells me
> > it won't be long before there are others. Rumors of a new Opti police
> > bike are interesting in this regard; if true, unless it's a major
> > redesign, it's not going to be in the same power & weight category as
> > the Bomber but it will be amazing, no doubt about it
>
> > The Bomber costs around $7,500 fully optioned. I plan on riding it on
> > local fire trails & singletrack. There's also a new custom hitch that
> > allows for easy transport on the back of any vehicle with a tow-
> > ball...opening up a world of dirt a bit further afield. Recent
> > developments may make it possible to ride it on public roads legally.
>
> > Very interesting what DC says about Crystalyte motors like the X5 that
> > powers the Bomber..."made to take lots of power and turn it into
> > rotational torque. The down side to that is the amount of battery
> > necessary to feed the motors...". Absolutely and it seems that no
> > manufacturer, apart from Stealth, has yet managed to design a durable
> > bike that can elegantly carry 20 Ahrs of batteries running at 72V, or
> > anything close.
>

[Joe]

Yes in CA they get $2000 off total. Fed national credit is $800 off
the 8000 sticker list price. "42 mile average range, top speed over
60 MPH"

[Joe]

read all about it at brammo.com

On Apr 19, 2010, at 9:01 PM, deerfencer1 wrote:

[plasmadust]

So much for being in a hurry.
I was trying to finish the little lesson as the Admiral walked in to
go over some specs on the EVSE boards we are designing.
Yes indeed energy is power over time. Was just trying to get the
relationship across in as little time and detail for all to grasp.

BMC, can't say much about them anymore. We severed the ties more than
two years ago and never looked back.
The point is valid though. We are building brushless motors for bikes,
and other vehicles as well, but we tend to keep everything matched up
in the power and performance end of things. We know we can push our
motors that we rate at 500W to 1000W and hold it there for as long as
we have battery to feed it. So far, no smoke. But is it a good idea to
push it that hard ALL the time? My guess would be no, as with any
motor.
E-bikes or e-cars, the point would be to determine what you need it to
do, rather than what you want it to do.