ok guys
i figure someone here is connected to the RC hobby or knows someone that is
from what i gather some of those guys are converting small frame alternators into high output
motor using a electronic box known as a ESC (electronic speed control)
from what i have been able to learn the ESC produces a three phase current from the DC battery buss and it is fed to the alternators stator along with some sort of connections to the rotor field and the result being a motor powered by a battery.
they have sensor and sensorless ESC units, and from what i gather the sensorless is the way i want to go.
so where do i find such a ESC that is capable of driving maybe 120amps max, or maybe that is what they refer to as input of 120amps? i don't know, but i want to find out more.
fwiw, my understanding of the sensorless design, the unit monitors the shift in inductance to know when to trigger a phase, otherwise the sensor design uses hall effect or optical sensors to monitor where the rotor poles are in reference to the stator poles and then knows when to fire the phase.
anybody know anything about these things? or anyone that does? or any good links? or other references?
i got a really cool project in mind if i can locate the right ESC that will do what i need done.
thanks guys
bob g
Hey Bob,
Wouldn't the tail end (DC section to PWM AC) of a three phase VFD (Inverter) Do what you need? Their DC Level is usually quite high, but hey, most anything can be worked with or around.
Terry
It sounds like they are using a standard brushless DC motor ESC. Clever to use an alternator as a cheap motor.
You're not thinking to use the alt as a starter motor and then as a generator are you Bob? ;D
That would be great for starting stationary engines and then using them to provide power nice and cheaply.
goldenmotor.com have some motor controllers for Brushless DC motors, though, they're ment for permanent magnet DC motors...
Turnigy makes a 100A brushless motor ESC for $64 sold at online RC hobby stores. It's a sensor type, comes with external sensors. Don't know if that's enough to enough to run an auto alternator.
Goldenmotor's controllers are certainly enough to handle an alternator.
Glort:
that is exactly what i have in mind! you win the cigar! :)
EBI-WPO:
i have tried to feed the stator three phase power and it just doesn't work as expected when i energize the rotor field, it just sits there and pulsates/growls
now when i put a reostat across the field/rotor the thing will motor, just not with much power
as it makes for a very inefficient induction motor with its solid rotor poles...
Cornelius and Bruce, i will check out the two sources and see what they have to offer.
thanks
bob g
Quote from: mobile_bob on June 30, 2013, 01:14:43 PM
Glort:
that is exactly what i have in mind! you win the cigar! :)
Oh goody!
I hope it's one of those good, fat Cuban ones.
I was given one of those years ago and the thing lasted for hours. Not a smoker but that was good! ;D
Whatever you come up with, please make it an off the shelf and affordable thing Bob.
It's OK for these electronic geniuses here to do all these wonderful projects but a real bummer for those not so intelligent that want the same thing but don't have the smarts to build it.
bob g,
FYI, this is what most of us use as a speed control in our 1/8, Tekin RX8. I just received the new 2nd generation and according to their site this poppy delivery 220 amp per phase, price is around $200.
You can contact them for any question, the tech support is really good. Sorry I can help you more, but on the ESC all we care is to have the same punch from start to finish on the race and without frying the motor. I hope these help...
http://www.teamtekin.com/rx8.html
Really nice idea for a starter on the listeroid...
Interesting thread on converting an alternator to power a 2 seat buggy.
http://endless-sphere.com/forums/viewtopic.php?f=30&t=16328&sid=24adc8e3466209fd76e8f6991ed1a6d6
Michael
Here is another source for speed controllers. Many of them stocked in the USA warehouse.
http://www.hobbyking.com/hobbyking/store/__455__182__speed_controllers-above_80_amp.html
I'm reading the threads but getting a bit lost in all the questions and modifications.
Can anyone give me the real short version of this. From what I understand, you get an alt, take out the diodes, hook a wire to each phase and then couple that up to one of these speed controllers and off you go?
Am I missing anything?
Do the controllers need programing or adjusting? How do they throttle/ ajust the alt speed?
Any other intricacies to making this work?
I'd like to give one of these a go but just trying to understand the complications and pitfalls before I try and realise it's over my head.
If I understand correctly they are similar to a 3 phase variable speed drive used in industrial applications.
I agree that the alternator becomes similar to industrial 3 phase motors. The main difference is the industrial motors use induction, instead of field windings on the armature. Standard VFD (variable frequency drives) take AC, convert to DC, and then recreate the AC at the needed frequency. Speed is controlled by the frequency.
To use the alternator as a motor, you would disconnect the diodes, connect a separate wire to each phase, and provide a field current. The greater the slip (difference between AC frequency and motor rpm/frequency) the greater the current. If you use one of the RC ESC, I believe they will vary the frequency to accelerate up to speed, so no large startup draw.
I think (haven't seen a manual) that the RC ESC's should have a default mode. You don't have to tweak the settings if you don't want to. The problem I see, however, is that you need a servo signal to control the speed. I may be off the wall, but since it's RC equipment...
Something I'm wondering about is how fast would a 555-110 turn using 60hz power? If it was fast enough to start an engine, you could use a static phase converter to make 3 phase out of simple single phase from an inverter, and feed that to the alternator. Use transformers to get the voltage down to an acceptable level...
Michael
For 60Hz, divide 7200 by the number of poles in the motor/alternator. That will give you RPM at the theoretical, no-slip point.
2 poles ==> 3600 RPM
4 poles ==> 1800 RPM
6 poles ==> 1200 RPM
8 poles ==> 900 RPM
12 poles ==> 600 RPM
Then you have to figure out the pulley ratio to get engine RPM.
The easier way is to measure it - run the engine, measure engine and alternator RPM, and measure the frequency at the point where the stator connects to the diodes. Many of the digital meters will measure frequency.
I was messing with an old 7.3 liter (non-turbo) Ford diesel once, and determined that the frequency of the alternator (in Hz) was almost exactly the RPM of the engine. That made for an easy tachometer! I don't know how the pulley ratios and # poles worked out, but it did.
alternators will not run simply by applying 3 phase power to the stator and a current to the field (rotor), they will just sit there and do the jitterbug
they will however run as induction motors, although with very poor efficiency
all you have to do is short the field windings at the brushes and apply the three phase power and off to the races it will go... just not with a lot of power.
these sensorless ESC units sense the shift in inductance as the poles pass each other and trigger the phase pulse, this provides for sync/timing and increased torque.
the sensor type ESC of course uses a sensor(s) to determine the pole position relationship, and in doing so allows for control to the phase timing.
the amount of field current then is used to dial in the rpm, and some other characteristics such as power factor.
thanks for the links btw...
some of these are priced low enough to take a shot with and try it out.
bob g
Quote from: mobile_bob on June 30, 2013, 01:14:43 PM
Glort:
that is exactly what i have in mind! you win the cigar! :)
EBI-WPO:
i have tried to feed the stator three phase power and it just doesn't work as expected when i energize the rotor field, it just sits there and pulsates/growls
now when i put a reostat across the field/rotor the thing will motor, just not with much power
as it makes for a very inefficient induction motor with its solid rotor poles...
Cornelius and Bruce, i will check out the two sources and see what they have to offer.
thanks
bob g
Need to enegize the rotor with approx 6V DC. Can't leave the rotor field open. It will just become the secondary of a transformer. 60Hz is pretty slow to drive an automotive alternator with.
Thob,
".........he frequency of the alternator (in Hz) was almost exactly the RPM of the engine. That made for an easy tachometer"
I have a 6.5 Turbo Chevy Suburban that uses the alternator for the tach. A common problem is people replacing a bad alternator with a gas motor version (different size pulley) and then wonder why their tach isn't reading correctly :D