Author Topic: AC powered PWM controller for DC NPC Black Max motor?  (Read 3077 times)

0 Members and 1 Guest are viewing this topic.

Offline muniorbustTopic starter

  • Jr. Member
  • **
  • Posts: 17
  • Helpful? 0
AC powered PWM controller for DC NPC Black Max motor?
« on: December 14, 2010, 12:22:59 PM »
I'd looking at the NPC Black Max motor (NPC-4200) for a project.
(24V to 36V, draws 200 amps normal use, 470 amps at stall)
It's an indoor, non-mobile application, so I want to use AC for power.
I'll be using PWM from a microcontroller.

I'm not smart enough to choose a motor speed controller.
Should I be looking for an AC powered controller that outputs DC?
Or a DC powered controller and use a AC/DC power supply?

Thanks for any help.
Buzz

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: AC powered PWM controller for DC NPC Black Max motor?
« Reply #1 on: December 14, 2010, 11:48:04 PM »
Hi,

I'd looking at the NPC Black Max motor (NPC-4200) for a project.
(24V to 36V, draws 200 amps normal use, 470 amps at stall)
I don't mean to imply any stupidity in your question, but are you absolutely sure you need a motor taking up to more than 7kW and outputting roughly 3kW (3.8HP)?
If it's for your unicycle project, it's gross overkill (and I mean really-really gross).


It's an indoor, non-mobile application, so I want to use AC for power.
I'll be using PWM from a microcontroller.
If you insist that you either go super fast or have an extreme acceleration/deceleration (or both) warranting such a powerhouse, I'll pretend to believe ::) you and tell you how a radio amateur with a large "after burner" (PA stage) would solve large but intermittent current demands...
3 lead-acid "marine" batteries connected in series - fed from a charger that can make up for the average demand (and a little more) over a day (or whatever your timeframe is) and things should even out without making the supply hideously expensive.

The (DC) motor controller needs to be able to handle the stall current and will be very expensive, but shop around - the same capacity may cost more than double the "cheapest".
(Or build it yourself).


Edit: motors for electric assisted bicycles comes in powers from around 200W to 1500W. Only 250W is allowed in DK and only as assist (i.e. when the pedals are used) up to 28km/h.

Since I'm in the process of selecting a motor for a friends cargo bike, I have recently studied the subject in detail and have seen some seriously crazy stuff - like two 1500W motors on a bicycle, when a single 1500W motor is spec'd to be able to go close to 80km/h IIRC with an average adult rider (and no pedaling at all).

We're planning on gearing the cargo bike for a top speed of 15..20 km/h. Unloaded, it's about the top speed to go on those (they become unstable if you go too fast) and perhaps we'll ad a second (mechanical) gear for when it's loaded with up to 100kg and going uphill, as you need torque over speed when the bike with load and rider can net around 220kg+ (and it's inherently unsafe going just 15km/h with the bike fully loaded anyway).

The 250W motors alone should be able to take the average two-wheel rider to 50..60km/h (don't remember the exact speed) without pedaling and, judging from some avi's I've seen, with a fairly decent acceleration.
I have a hard time imagining a one gear, one wheeler touching this (and the rider living to tell).
« Last Edit: December 15, 2010, 12:12:05 AM by Soeren »
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline muniorbustTopic starter

  • Jr. Member
  • **
  • Posts: 17
  • Helpful? 0
Re: AC powered PWM controller for DC NPC Black Max motor?
« Reply #2 on: December 15, 2010, 07:53:34 PM »
I don't mean to imply any stupidity in your question, but are you absolutely sure you need a motor taking up to more than 7kW and outputting roughly 3kW (3.8HP)?
If it's for your unicycle project, it's gross overkill (and I mean really-really gross).
The only thing I'm absolutely sure about is that I'm not absolutely sure about anything.  ;D
Yes, it's for the treadmill unicycle project we were talking about here.  There is a lot of stupidity coming from me.  I wish I already had the necessary motor knowledge.  I'm a software engineer by day.

Here's some of the logic (good or bad) that led me to that motor:

VegaObscura helped me with how to determine the torque I need.
I put that in a spreadsheet, here it is:
mass (lbs)   160
acceleration (ft/s^2)   11
wheel diameter (ft)   0.66666666666667 (previously I thought it was 0.5 ft)
   
mass (kg)   72.5747792
acceleration (m/s^2)   3.3528
force (n)   243.32871970176
wheel radius (cm)   10.16
torque (n-cm)   2472.21979216988
torque (lb-ft)   18.234157434005
   
double torque (lb-ft)   36.4683148680099

For the wheel radius I am measuring the existing pulley on my treadmill's drive roller.  It has an 8" diameter.  Maybe it's the roller itself that I should measure here?
This value effects the results significantly.  PLEASE let me know if this or any other values don't make sense.  It's confusing to me.

I saw a self balancing unicycle project online.  But then, I'm not sure how fast his uni accelerates or his top speed.  He used this A28-150 motor.
The specs for this motor from that link are:
24V (can be run higher)
3 horsepower
1970 oz-in Torque
Max current 285 Amps
82% Efficiency
6000 rpm

To convert 1970 oz-in to lb-ft I divide by 16 to get lb-in, then divide by 12 to get lb-ft.
1970/12/16 = 10.26 lb-ft
Hmm.  Less than the 36.5 lb-ft I'm after?
But I learned that Torque in lb-ft = (horsepower / RPM ) * 63025
Using the specs: T = (3 / 6000) * 63025 = 31.5 lb-ft
Hmm.  Completely different than the 10.26 lb-ft spec, and still less than the 36.5 lb-ft I'm after.
I certainly feel stupid here.
But maybe it's close enough?  I don't have any past experience to make a judgment.
What happens if I gain weight or my 200 lb friend tries it?
Then my spreadsheet says I need 45.6 lb-ft.

Looking at the A28-150 motor, it costs $300 and I'll need the $30 motor mounts for a total of $330.

Looking further I found some motors at robotmarketplace that had more torque but cost more, and some the would require some kind of L-bracket for mounting.  Then I saw the NPC Black Max motor that has the mount I'd like, is cheaper than the A28-150 and has way more torque.

I figured it was a good value and would remove any doubt I had about power.
It sounds like it's way overkill.
But again I ask, is there an alternative that is going to be better?
I haven't found a source of motors that ends up cheaper for me.

In the back of my mind I figure I might be happy to have such a powerful motor for some future application.  I think of it as an investment.
But at the same time I'm worried a bigger motor will require a more expensive controller.  But I have no frame of reference.  Yes, I'm stupid.  If the motor is going to be more trouble than it's worth, despite what seems like a good value, please let me know.

If you insist that you either go super fast or have an extreme acceleration/deceleration (or both) warranting such a powerhouse, I'll pretend to believe ::) you
I generally ride a max speed of 10 mph (16kph) and average about 6mph (10kph), but I own a geared hub that I'm not yet good with, but I expect to go up to 15mph (24kph).  But riders have gone 24mph+ (39kph) with that hub and my current wheel size (24").  Unicycle wheels are made as big as 36", and I've read of people riding near 30mph (48kph).  I may own such a ride in the future.
I'd currently be happy to ride about 15mph (24kph).
What's my acceleration?  I admit I haven't really measured that... just imagined.  I can get up to normal speed (6mph (10kph) ) in a few seconds.
What might be more important is deceleration.  If I get tripped up and have an unplanned dismount, ideally the treadmill will come to an instant complete stop.  (Failing to detect a dismount and false detection will both be dangerous... but that's a different problem to solve)

3 lead-acid "marine" batteries connected in series - fed from a charger that can make up for the average demand (and a little more) over a day (or whatever your timeframe is) and things should even out without making the supply hideously expensive.
I've grown to think of batteries (and unrelated to this conversation, combustion engines) as needy dependents that I'd prefer to avoid around the house.  I figured some kind of AC solution would be available, and since my treadmill isn't mobile, I hoped to take advantage of AC.
It must be possible.
Is it not practical?  I'm stupid here too.

The (DC) motor controller needs to be able to handle the stall current and will be very expensive, but shop around - the same capacity may cost more than double the "cheapest".
(Or build it yourself).
Honestly, I'm too stupid to build it myself.  I'm sure I have the brain capacity and dexterity, just not the knowledge and time.  I'll have to buy one.
But of course, I need the motor choice before I can choose this.

I'd also like to know how I could power the motor controller with AC.  Aren't there AC powered DC motor controllers?  Or, aren't there DC motor controllers that can be powered with a AC-to-DC power supply?
AC-to-DC-to-battery-to-controller is one way... but why can't we remove the battery part?

The 250W motors alone should be able to take the average two-wheel rider to 50..60km/h (don't remember the exact speed) without pedaling and, judging from some avi's I've seen, with a fairly decent acceleration.
Can you point me to one of these motors?  Are you suggesting it would be good for my application?

I have a hard time imagining a one gear, one wheeler touching this (and the rider living to tell).
Don't forget, in my case the rider is controlling the speed.  Unless there is a problem with my system, the treadmill will only move to match the rider's speed.  Still... it will be dangerous until all the inevitable bugs are worked out, but even then it will never be completely without risk.

Offline muniorbustTopic starter

  • Jr. Member
  • **
  • Posts: 17
  • Helpful? 0
Re: AC powered PWM controller for DC NPC Black Max motor?
« Reply #3 on: December 18, 2010, 12:37:58 PM »
I'd really love some help here.  Can anyone help me?

Offline muniorbustTopic starter

  • Jr. Member
  • **
  • Posts: 17
  • Helpful? 0
Re: AC powered PWM controller for DC NPC Black Max motor?
« Reply #4 on: December 21, 2010, 09:28:01 PM »
Hmm.

@Soeren - Will you be coming back to help me?

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: AC powered PWM controller for DC NPC Black Max motor?
« Reply #5 on: December 23, 2010, 02:02:06 AM »
Hi there,

Sure, but it's been a busy month (socially) and posts that take a massive amount of time to answer has been prioritized a bit low.
I'll be back from Germany late on the 25th, so I'll probably not get around to your questions until the day after as the earliest.

Merry X-mas.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


Get Your Ad Here

data_list