Efficiency of old verses new

[cgbjake]

For years I've been running an 800 watt brushed motor from from a scooter and adapted it to my bike. I used a Curtis Controller with no real limits on Amps. I ran SLA for a long time and then used a NIMH pack. Both packs died and I had to take a break for relocating to the East Coast. I'm building a hub motor kit bike for my wife, but would like to get mine going again, but wonder if I should stick with my 9 year motor. I plan on using some 36V Lipo packs at 10 or 15 AH, but keep eyeing up the newer RC motors. Anyone have an idea how much I'd gain from going to a newer motor? I'm nearly certain I could get something from it, but just don't know how to figure it out. The newer battery technology is so good, I'm wondering if the motor comparison is the same. Thanks for any info on this...and if there is already a topic on this one, I'll read if you can point me in the direction....

[SamTexas]

All other things being equal a brushless motor is at least 10% more efficient than a brushed motor. There are several threads discussing the pros and cons of brushed vs brushless motors but I don't remember the threads' names. Here's a quick summary off the top of my head:

Pros and cons for brushed:
Simple: Only 2 wires
Maintenance: brushes must be replaced in time
Cost: cheaper motor, cheaper controller
Efficiency: Bad compared to brushless

for brushless:
Simple and longevity: No mechanical parts to wear out (for Direct Drive motor)
Efficiency: No sparks, no wasted energy
Cost: controller costs more, motor costs more
Complexity: a lot more wires between motor and controller

[cgbjake]

10% is nice, but not enough to jump off yet. I'll wait just a bit more and get used to these LIPO's first. Thanks!

[SamTexas]

10% is nice,

10% is the minimum to expect.

[TylerDurden]

10% is the minimum to expect.

Got evidence?

[SamTexas]

No. You have evidence to the contrary?

[TylerDurden]

No. You have evidence to the contrary?

I'm not making any claims... where do you get that idea from?

These guys have been doing fairly well with brushed motors:


http://www.agnimotors.com/home/index.ph ... &Itemid=60

[SamTexas]

These guys have been doing fairly well with brushed motors:

Is that supposed to mean something?

Here's one of many references in regard to brushless motors being more efficient than brushed.
http://en.wikipedia.org/wiki/Brushless_ ... shed_motor

You have been hanging around here for a gazillion years and you are still asking if brushless motors are more efficient? It did not sound like a question. It sounds like you want to start a fight. Well, bring it on.

[TylerDurden]

<Yawn>

Wikipedia?... Right.....

Show us some data.

Agni brushed get up to 93% efficiency... so on planet Sam Texass 10% more efficiency would be 102.3% efficient.

The OP should get one of those.

[SamTexas]

You have evidence that Agni motor is 93% efficient? Or are you just eating all the garbage they feed you? Don't compare yourself with Wikipedia, you are no where near it. Yawn as much as you want, but don't for a minute think you know better.

[John in CR]

...anticipating Sams weak jab TD easily slips it, and steps in countering with a devastating right cross that knocks Sam out in one punch.

cbgjake,
The weakness of your brushed motor is the brushes themselves, which are subject to wear. If you're happy with the performance, then I would at least open up the motor to inspect the brushes, their holders (I've heard of heat related failures in brushed hubmotors where plastic pieces holding the brushes failed.), and the commutator. I'd expect replacement parts to be quite difficult to find.

With a brushless hubmotor, the only parts subject are the bearings, which are easily found locally, giving brushless motors a nearly indefinite life.

John

[neptronix]

I had this image on my server just for this occasion that he had yet another flare up

Yeah. brushed can super duper efficient, but when those brushes wear out, it can suck pretty bad.

[SamTexas]

...anticipating Sams weak jab TD easily slips it, and steps in countering with a devastating right cross that knocks Sam out in one punch.

Coming the stupid guy who still eats all the shit about Konion cells capable of self balance. Go eat some more shit and so you can sink to the bottom and join the scum.

Coming from the idiot who believes that his ebike is faster and safer than a car.

Coming from the dumber than dirt who let the low life scum sangef scam his money.

[Miles]

Please......

[Jeremy Harris]

I've been away from here for a fair while, and it looks as if things have gone a bit downhill...............

To answer the OPs question about motor efficiency between brushed and brushless DC motors (from someone who's measured many motors in the quest for best overall efficiency over the years):

It depends. Some brushed motors are more efficient than some brushless motors and vice versa. Both brushed and brushless DC motors work the same way, the only difference is the device used to switch the current through the windings. In a brushed motor that device is a commutator and brushes (in other words a mechanical switch) in the brushless motor that device is an array of FETs in the controller (in other words an electronic switch). Both have resistive and switching losses.

Overall efficiency will depend very much on how well the controller is designed for a brushless motor, and both how well the controller is designed and how the brushes and commutator are configured for a brushed motor.

Most ebike brushless motors are probably as near as dammit identical in terms of efficiency to equivalent power/rpm brushed motors, at around 85% or so (on a good day, some will struggle to get 80%). Some brushless motors can get to 90 to 95% or more (with a good controller) as can some brushed motors. Any efficiency difference between the two at ebike power levels is likely to be lost in the noise of other losses and is very unlikely to be noticeable in normal use (my guess is that the practical difference may be 1 or 2% tops).

The big (and probably only significant) advantage of brushless motors has already been mentioned, freedom from brushes that wear, produce ozone and sparks and create a mess. The brush wear rate on a high power brushed motor can be pretty high, resulting in a relatively short service interval before replacement is needed. Brushes are also subject to rapid degradation if they get wet or oily, something pretty likely if they are in on a bike.

Jeremy

[Miles]

I've been away from here for a fair while, and it looks as if things have gone a bit downhill...............

Thank you Jeremy. Good to hear from you!

Just a blip, I think....

[Brentis]

I've been away from here for a fair while, and it looks as if things have gone a bit downhill...............

Thank you Jeremy. Good to hear from you!

Just a blip, I think....

+1


While there is an increase in shit flinging as of late.
Things are still pretty open and helpful here.
Wonderful to see someone with your knowledge & class coming back to clean up the joint a bit.

Hope you have the time to hang with us some more.

[salty9]

It's good to see you are back, Jeremy.

Chuck

[Ypedal]

Jeremy !!!.. woot !.. great to see you posting again !

(* yeah.. as with all forums.. we get the special one's once in a while.. lol.. 10% ? )

---

Ther over-all efficiency of the bike needs to be considered, power used vs distance delivered, chains, idlers, tires, beer bellies, all contribute to how far you can go on a charge.. if the brushed motor gets the job done with power to spare.. you win the prize !.

[dnmun]

great to see jeremy back, the return of common sense.

i thought the use of electronic commutation resulted in higher efficiency because the sparking from interrupting contacts with brushed motors would result in power lost to heat at the brushes. jmho

jeremy, we are all dying for you to post up a thread about your house project. i am in the middle of double insulating mine and replacing all the old windows with large thermopane units to make the house brighter and add solar gain in winter.

[Jeremy Harris]

Thanks for the warm welcome back folks - the house project has been a nightmare, when I get time I'll post details on another thread.............

The brush losses on a brushless motor (which are mainly from the resistance of the brushes, I believe) are to some extent balanced by the resistive losses in the FETs of a brushless controller, as it's pretty commonplace for off-the-shelf ebike brushless controllers to have FETs that have a fairly high on resistance (and pretty high switching losses). There are also FET losses in a brushed motor controller, but because they only need 1/3 the number of FETs (or even 1/6 the number plus a diode) the economics seem to mean that they often seem to have better/more FETS and lower losses.

Add in that there are a lot of pretty poor brushless motors around, with excessive winding resistance and poor configuration (from an efficiency perspective) and the comparison gets pretty tricky, as there will be no hard and fast rule that says one type will be better than the other in practice.

Jeremy

[TylerDurden]

Welcome back JH!


My highly uniformed reply to the OP's query, would address more specifically his application(s):

AIUI,

You can get good efficiency in brushed or brushless. The curb-appeal of the RC motors is good efficiency and power in a small package, but there are tradeoffs.

Brushless RC motors for bikes have been somewhat problematic, since they are designed for near constant high rpm, with constant airflow for cooling. RC motors are commonly sensorless, which can be an issue for low rpm, high torque responsiveness. ES member Burtie makes a kit for adding hall-sensors to RC motors. Larger RC motors may have low inductance that damages controllers.

See topics by: Luke, Thud, Burtie, Arlo1, Dontsendbubbmail, Aussiejester, Adrian_SM, Kepler...


Brushless motors are the norm these days for hubmotors, since changing brushes is a hassle when they are in a wheel (brushed hubbies may be getting rare). The downside is most hubmotors use hall-sensors for position sensing, which can fail and damage the controller... Failures are commonly caused by damage to wiring where it enters the hub, overheating or ingress of water. Controllers that switch from sensored to sensorless are becoming more common.

Search ES for: failed hall sensor.


I generally trot-out the agni motor example when unsupported declarations of brushed-motor inferiority are casually disseminated. In recent history, agni brushed motors have been the choice of professionals for their power and efficiency - as of late, brushless motors are emerging and winning in competition.

A safety note on brushed motors: throttle failures usually result in full power to the motor - a mains kill-switch is strongly suggested.


YMMV

[neptronix]

http://www.electricmotorsport.com/store/ems_ev_parts_motors_pmg132.php

The perm motor is another example of high efficiency, and high output in a brushed configuration;
upper 80% efficiencies.
24lbs and 7kW constant output is pretty damn good too. That's higher output per weight than many brushless motors in it's class ( mid-rpm, non-hub )

To the OP: for your bike, I would give the brushes a look. They may be worn.

To Jeremy: i am happy to see you here as well, as i learn more and more about motor theory and electronics, i appreciate the little bits of gold you've left here and there on the forum in the past. When you left, the brain drain was felt.

[TylerDurden]

Another data point:

"Chretien had been given a target of 10 to 12 minutes' flight time by Solution F, so the most critical part of the aircraft design was working out how to store enough power for this kind of flight, as well as how to use that power most efficiently. Early on, he sought the help of Lithium Balance , who supplied the battery management system and consulted on power storage issues.

Chretien chose brushed DC motors for the rotor shafts, even though the required power output was "just on the edge of what can be achieved with brushed motors" - because brushed motors are exceptionally efficient, and their simple controller units are significantly lighter than those of more powerful, less efficient brushless motors.

With these in place, Chretien was able to achieve an 87.5% energy efficiency between the battery terminals and the rotor shafts."

first-successful-manned-electric-helicopter-flight.jpg (37.91 KiB) Viewed 258 times

http://www.gizmag.com/first-successful- ... ght/19716/

Notes:

Weight: Empty weight 170Kg (374 lb0. Takeoff weight 247 Kg (543 lb)
Airfoils: NACA 0012. 8-H-12. A lift test with the machine resting on 4 scales and stabilized by sandbags revealed that the thrust was 260 Kg with NACA0012 airfoils, which were later replaced by 8H12 airfoils. In the later test the lift went up to 310 Kg. With an all up weight of 247 Kg, the power margin was sufficient for takeoff.
Rotor: 710 RPM.
Motor: ELECTRAVIA http://www.e-motor.fr/welcome.php Lynch Motor. It is made in India. It is brushed.
AGNI Motors
Reduction: Cog belt. Ratio approximately 5.25:1. Check with Pascal
Battery: LiTHIUM BALANCE.

http://www.unicopter.com/2071.html

[circuit]

10% is nice,

10% is the minimum to expect.

FALSE. 10% is an absolute maximum when comparing PMAC (BLDC) motors with series-wound motors (SepEx, etc.). Since OP is using PMDC motor, it's efficiency is lower only like by 1-2%, when compared to BLDC alternatives used in ebikes. Also, AC controllers are complex, expensive and very unreliable. I have blown three (18fet lyen among them) controllers last week with my crystalyte motor.
If you are happy with your brushed motor and curtis (probably the only good and affordable controller) - do not go sideways and stick with it. I tend to use BLDC where I can, but sometimes its just not worth it.