Discussion:
Supressing an electric motor
(too old to reply)
Andy
2003-12-26 05:53:36 UTC
Permalink
I have almost completed building an electric on-board starter for my Biglift
glider tug with Moki 180.
I am using a standard 05 type electric motor to power the device and would
like to know how I go
about suppressing any electrical noise that will be generated when I
activate the starter. One usually
uses capacitors soldered across the electric motor's terminals, but how does
one calculate the correct
value of the capacitor ?? How actually does the capacitor suppress the noise
and is there a better way ??
Another aspect that interests me is how capacitors assist electric motors
with start up torque. If one
of you guys can give me a short exposition on this or refer me to some
source, I would be most grateful.

Regards
Andy in South Africa
The Natural Philosopher
2003-12-26 10:20:58 UTC
Permalink
Post by Andy
I have almost completed building an electric on-board starter for my Biglift
glider tug with Moki 180.
I am using a standard 05 type electric motor to power the device and would
like to know how I go
about suppressing any electrical noise that will be generated when I
activate the starter.
One usually
uses capacitors soldered across the electric motor's terminals, but how does
one calculate the correct
value of the capacitor ??
Its not crirtical. Its there to short teh 72Mhz, but leabeve teh 8Khz or
so un marked...pleanty of difference between the two.

Normally about 10-50nF is ideal, use small ceramics, soldered right
across teh brushes and between each brush and teh motor case.
Post by Andy
How actually does the capacitor suppress the noise
and is there a better way ??
It short circuits teh high frequency radio noise from the brush sparks,
before it can get into the motor wires and radiate as radio signals.

Other thigs to do are

(i) Schottky diode across the motor. This helps clamp flyback spikes.

(ii) Keep motor wires very very short, and twssit together.

(iii) Keep radio as far away from the motor and ESC as the wires allow.

(iv) sometimes and extar capacitor right across teh receiver + and -
helps too.

(v) sometimes ferrite beads or chokes in teh servo wires help.
Post by Andy
Another aspect that interests me is how capacitors assist electric motors
with start up torque. If one
of you guys can give me a short exposition on this or refer me to some
source, I would be most grateful.
They don't in our applications. I suspect you are thinging of AC motors
and the starting capacitor. That doesn't help start up torque - its
there to make sure the motor starts in the right direction on a single
phase AC motor, but thats a whole other story.
Post by Andy
Regards
Andy in South Africa
Thomas Scherrer
2003-12-27 02:21:38 UTC
Permalink
go to the end of this page:
http://www.webx.dk/rc/sp540/sp540.htm
Post by The Natural Philosopher
Post by Andy
I have almost completed building an electric on-board starter for my Biglift
glider tug with Moki 180.
I am using a standard 05 type electric motor to power the device and would
like to know how I go
about suppressing any electrical noise that will be generated when I
activate the starter.
One usually
uses capacitors soldered across the electric motor's terminals, but how does
one calculate the correct
value of the capacitor ??
Its not crirtical. Its there to short teh 72Mhz, but leabeve teh 8Khz or
so un marked...pleanty of difference between the two.
Normally about 10-50nF is ideal, use small ceramics, soldered right
across teh brushes and between each brush and teh motor case.
Post by Andy
How actually does the capacitor suppress the noise
and is there a better way ??
It short circuits teh high frequency radio noise from the brush sparks,
before it can get into the motor wires and radiate as radio signals.
Other thigs to do are
(i) Schottky diode across the motor. This helps clamp flyback spikes.
(ii) Keep motor wires very very short, and twssit together.
(iii) Keep radio as far away from the motor and ESC as the wires allow.
(iv) sometimes and extar capacitor right across teh receiver + and -
helps too.
(v) sometimes ferrite beads or chokes in teh servo wires help.
Post by Andy
Another aspect that interests me is how capacitors assist electric motors
with start up torque. If one
of you guys can give me a short exposition on this or refer me to some
source, I would be most grateful.
They don't in our applications. I suspect you are thinging of AC motors
and the starting capacitor. That doesn't help start up torque - its
there to make sure the motor starts in the right direction on a single
phase AC motor, but thats a whole other story.
Post by Andy
Regards
Andy in South Africa
Andy Z
2003-12-27 18:24:19 UTC
Permalink
OK,
Mr. Sherrer, I have to ask; had you already sometime in the past completed
that investigation, or did you "whip it up" that day since your reply is
dated 8 hours after the post?
Either way, your work is impressive for clearly (and in a simple manner)
demonstrating to me for the first time in 20 years why installing capacitors
are a must on electric motors. All of these years my avionics buddies have
never been able to explain to a former jet engine mechanic like me what the
capacitors actually do as effectively as you just did.

Thank-you from a different Andy.....than the orginal post.
Post by Thomas Scherrer
http://www.webx.dk/rc/sp540/sp540.htm
Post by The Natural Philosopher
Post by Andy
I have almost completed building an electric on-board starter for my
Biglift
Post by The Natural Philosopher
Post by Andy
glider tug with Moki 180.
I am using a standard 05 type electric motor to power the device and
would
Post by The Natural Philosopher
Post by Andy
like to know how I go
about suppressing any electrical noise that will be generated when I
activate the starter.
One usually
uses capacitors soldered across the electric motor's terminals, but
how
Post by Thomas Scherrer
does
Post by The Natural Philosopher
Post by Andy
one calculate the correct
value of the capacitor ??
Its not crirtical. Its there to short teh 72Mhz, but leabeve teh 8Khz or
so un marked...pleanty of difference between the two.
Normally about 10-50nF is ideal, use small ceramics, soldered right
across teh brushes and between each brush and teh motor case.
Post by Andy
How actually does the capacitor suppress the noise
and is there a better way ??
It short circuits teh high frequency radio noise from the brush sparks,
before it can get into the motor wires and radiate as radio signals.
Other thigs to do are
(i) Schottky diode across the motor. This helps clamp flyback spikes.
(ii) Keep motor wires very very short, and twssit together.
(iii) Keep radio as far away from the motor and ESC as the wires allow.
(iv) sometimes and extar capacitor right across teh receiver + and -
helps too.
(v) sometimes ferrite beads or chokes in teh servo wires help.
Post by Andy
Another aspect that interests me is how capacitors assist electric
motors
Post by The Natural Philosopher
Post by Andy
with start up torque. If one
of you guys can give me a short exposition on this or refer me to some
source, I would be most grateful.
They don't in our applications. I suspect you are thinging of AC motors
and the starting capacitor. That doesn't help start up torque - its
there to make sure the motor starts in the right direction on a single
phase AC motor, but thats a whole other story.
Post by Andy
Regards
Andy in South Africa
Andy
2003-12-28 04:38:24 UTC
Permalink
Thanks guys for the info. Its much appreciated.
Regards
Andy in SA
The Natural Philosopher
2003-12-28 23:32:32 UTC
Permalink
Post by Andy Z
OK,
Mr. Sherrer, I have to ask; had you already sometime in the past completed
that investigation, or did you "whip it up" that day since your reply is
dated 8 hours after the post?
Either way, your work is impressive for clearly (and in a simple manner)
demonstrating to me for the first time in 20 years why installing capacitors
are a must on electric motors. All of these years my avionics buddies have
never been able to explain to a former jet engine mechanic like me what the
capacitors actually do as effectively as you just did.
Thank-you from a different Andy.....than the orginal post.
Yes, nice scope traces. Fiest time I had seen what a Schottky does tho
its what I guessed amnd borne out by my practical experiments - i.e.
knocks off a fair bit of stiff that teh caps don't.
Post by Andy Z
Post by Thomas Scherrer
http://www.webx.dk/rc/sp540/sp540.htm
Post by The Natural Philosopher
Post by Andy
I have almost completed building an electric on-board starter for my
Biglift
Post by The Natural Philosopher
Post by Andy
glider tug with Moki 180.
I am using a standard 05 type electric motor to power the device and
would
Post by The Natural Philosopher
Post by Andy
like to know how I go
about suppressing any electrical noise that will be generated when I
activate the starter.
One usually
uses capacitors soldered across the electric motor's terminals, but
how
Post by Thomas Scherrer
does
Post by The Natural Philosopher
Post by Andy
one calculate the correct
value of the capacitor ??
Its not crirtical. Its there to short teh 72Mhz, but leabeve teh 8Khz or
so un marked...pleanty of difference between the two.
Normally about 10-50nF is ideal, use small ceramics, soldered right
across teh brushes and between each brush and teh motor case.
Post by Andy
How actually does the capacitor suppress the noise
and is there a better way ??
It short circuits teh high frequency radio noise from the brush sparks,
before it can get into the motor wires and radiate as radio signals.
Other thigs to do are
(i) Schottky diode across the motor. This helps clamp flyback spikes.
(ii) Keep motor wires very very short, and twssit together.
(iii) Keep radio as far away from the motor and ESC as the wires allow.
(iv) sometimes and extar capacitor right across teh receiver + and -
helps too.
(v) sometimes ferrite beads or chokes in teh servo wires help.
Post by Andy
Another aspect that interests me is how capacitors assist electric
motors
Post by The Natural Philosopher
Post by Andy
with start up torque. If one
of you guys can give me a short exposition on this or refer me to some
source, I would be most grateful.
They don't in our applications. I suspect you are thinging of AC motors
and the starting capacitor. That doesn't help start up torque - its
there to make sure the motor starts in the right direction on a single
phase AC motor, but thats a whole other story.
Post by Andy
Regards
Andy in South Africa
Ron van Sommeren
2003-12-30 13:21:05 UTC
Permalink
Hi Thomas, Natural and all,
Post by The Natural Philosopher
Yes, nice scope traces. Fiest time I had seen what a Schottky does tho
its what I guessed amnd borne out by my practical experiments - i.e.
Thomas, you don't state you're using a Schottky, the 1N5401 is a normal
diode, rated at 3A. Have you noticed a difference between normal and
Schottky diodes? Did you/can you make scope traces for Schottky's?

Met vriendelijke groet ;-) Ron van Sommeren
near Nijmegen, the Netherlands
The Natural Philosopher
2003-12-30 13:42:21 UTC
Permalink
Post by Ron van Sommeren
Hi Thomas, Natural and all,
Post by The Natural Philosopher
Yes, nice scope traces. Fiest time I had seen what a Schottky does tho
its what I guessed amnd borne out by my practical experiments - i.e.
Thomas, you don't state you're using a Schottky, the 1N5401 is a normal
diode, rated at 3A. Have you noticed a difference between normal and
Schottky diodes? Did you/can you make scope traces for Schottky's?
Shottkys are simply faster, and have less forward drop. So they do a
better job with RF.

A normal diode takes a bit of time before it starts to clamp, so you get
some spikes. Shottkies clamp earlier. A normal power diode is, for
example, fine at 50/60hz for rectifying mains, but shottkies are widely
used in switched mode supplies running at several (tens?) of Khz.

Since our controllers run at those sorts of speeds, schottkies are
better, but any good diode is likeley to be better than none.
Post by Ron van Sommeren
Met vriendelijke groet ;-) Ron van Sommeren
near Nijmegen, the Netherlands
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