TEMIC Motor Speed Control

T

TBFisher

Guest
I have a 12VDC brush type(?) motor with the
following label:
Temic
GP 62 A18
12V
17/00 082 085
It draws ~17amps @ ~13VDC
It has two power leads(+&-) and 3 leads that I assume
are tach leads.
It is installed as a blower motor in an Espar diesel
fired coolant heater. The motor's speed is controlled
from 300rpm to 7300rpm by the existing control module.
Does anyone know if this motor's speed be effectively
controlled using PWM or is it necessary to use linear
regulation? How is the speed monitored via the tach
leads?
I'm trying to build my own controller for this heater
using a Basic Stamp microcontroller and any help/ideas
will be appreciated. So far, I haven't yet been able to find
any info on this motor. I'm an EE but haven't done
any of this type of work in years and am very rusty
at best.
Thanks,
Tom Fisher
Dallas,TX
 
"TBFisher" <tbfisher@hotmail.com> wrote in message
news:_vk7c.883$Mg2.801@newssvr23.news.prodigy.com...
I have a 12VDC brush type(?) motor with the
following label:
Temic
GP 62 A18
12V
17/00 082 085
It draws ~17amps @ ~13VDC
It has two power leads(+&-) and 3 leads that I assume
are tach leads.
It is installed as a blower motor in an Espar diesel
fired coolant heater. The motor's speed is controlled
from 300rpm to 7300rpm by the existing control module.
Does anyone know if this motor's speed be effectively
controlled using PWM or is it necessary to use linear
regulation? How is the speed monitored via the tach
leads?
I'm trying to build my own controller for this heater
using a Basic Stamp microcontroller and any help/ideas
will be appreciated. So far, I haven't yet been able to find
any info on this motor. I'm an EE but haven't done
any of this type of work in years and am very rusty
at best.
Thanks,
Tom Fisher
Dallas,TX
Click to expand...
In general it's always easier on the motor to drive it with a linear
controller or a switching amp. Speed controllers for model airplanes PWM
the motor at around 1kHz, which ends up being more efficient than a linear
and less than a switching amp, but those motors aren't expected to have a
long brush life (and the el-cheapo ones are run hard enough to degauss the
magnets in a good flying season).

My guess is that the three-wire sensor is a pulse output to tell speed, and
that it's ground, +5V and output (which may or may not be open collector).
If it's a tach I'd expect to see two wires, but it may be two wires and a
case ground. If you connect a tach to a voltmeter and give the motor a good
spin you should see a reading.

If you're going to run the motor continuously and you want a long life you
should probably either use a linear controller or a switching amp (which
could run off of the PWM output on your PIC, if it's fast enough). Even a
linear controller could still be driven from your PIC PWM output if you
filter it. If the motor has replaceable and/or carbon brushes you might
want to run it with PWM but the only thing you'll gain will be a little bit
of circuit simplicity over a switching amp.
 
If you're going to run the motor continuously and you want a long life you
should probably either use a linear controller or a switching amp (which
could run off of the PWM output on your PIC, if it's fast enough). Even a
linear controller could still be driven from your PIC PWM output if you
filter it. If the motor has replaceable and/or carbon brushes you might
want to run it with PWM but the only thing you'll gain will be a little
bit
of circuit simplicity over a switching amp.

Thanks for the reply. The PWM controller is a PWMPAL
Click to expand...
http://www.parallax.com/detail.asp?product_id=28020
so I guess the max usable would be ~20Khz
Pardon my ignorance but what is a switching amp?
Could you point me to a good reference?
Thanks,
Tom Fisher
Dallas,TX
 
If you're going to run the motor continuously and you want a long life you
should probably either use a linear controller or a switching amp (which
could run off of the PWM output on your PIC, if it's fast enough). Even a
linear controller could still be driven from your PIC PWM output if you
filter it. If the motor has replaceable and/or carbon brushes you might
want to run it with PWM but the only thing you'll gain will be a little
bit
of circuit simplicity over a switching amp.

Yes, I need to run the motor continuously and control the speed from
Click to expand...
300 to 7300 rpm to provide combustion air flow in proportion to fuel flow.
The motor appears to be a sealed unit
Tom Fisher
Dallas,TX
 
"TBFisher" <tbfisher@hotmail.com> wrote in message
news:y%E7c.9520$f24.8794@newssvr22.news.prodigy.com...
If you're going to run the motor continuously and you want a long life
you
should probably either use a linear controller or a switching amp (which
could run off of the PWM output on your PIC, if it's fast enough). Even
a
linear controller could still be driven from your PIC PWM output if you
filter it. If the motor has replaceable and/or carbon brushes you might
want to run it with PWM but the only thing you'll gain will be a little
bit
of circuit simplicity over a switching amp.

Thanks for the reply. The PWM controller is a PWMPAL
http://www.parallax.com/detail.asp?product_id=28020
so I guess the max usable would be ~20Khz
Pardon my ignorance but what is a switching amp?
Could you point me to a good reference?
Thanks,
Tom Fisher
Dallas,TX
Click to expand...
Also known as a "class D" amplifier. Search for "switching amplifier" and
"class D amplifier" on the web. Also try Texas Instruments and Linear
Technologies for controller chips.

A switching amplifier is the business end of a switching power supply,
applied to other things (like driving a motor). Most of the same design
rules apply, except that you have to design for varying voltage, and you
often need to use synchronous rectification to allow the amplifier to pull
the voltage down as well as push it up. In theory you can make one that's
100% efficient (i.e. the amp itself doesn't burn up any power); in practice
you can't expect more than about 80% peak efficiency -- but that's still
much better than a linear amp.

In your case you could probably use a good switching supply circuit with
passive rectification, since you won't need to be slowing the motor down
quickly.
 
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