Thanks. I have been web searching for a bit, and they generally say
it's feasible to reverse a compound DC motor. To pick just 1, this one
[http://www.industrial-electronics.com/elecy4_3.html] shows a schematic
that says if you reverse the armature leads, that reverses the motor,
and all is good. (I'm ASSUMING - and I know the phrase that triggers -
that the series and shunt windings are cumulative, as this is a traction
application and we would want the extra grunt.)
On the other hand, the actual motors have an arrow on them indicating
only CCW (as viewed from the sprocket) operation. I also recall a motor
repair guy many years ago telling me that compound motors should not be
run in reverse (no reason given). So, I figured I would consult the
collective wisdom of this list before doing anything potentially dramatic.
Just back in from checking the posts and polarity. My recollection was
that there are no markings on the posts, which is true. (On series
motors they are usually marked A1, A2, S1 & S2). On one compound motor
I had years ago, they were marked A1, A2, S1, S2, F1 & F2 - but posts F1
& F2 were smaller which indicated they were the shunt field.)
I misremembered the posts on this motor. There are 5, not 6, and they
are all the same size. There are only 2 power connections to the motor,
but there are jumpers across two pairs of posts. Some ASCII art below
(use a fixed width font). Think of this as a 'Top View' where bottom is
defined by the base plate.
(Negative (Positive
Connection) Connection)
Post1 Post2 Post3
============ Jumper
___________________________________________________
| |
| |
| |
* | Motor body |
Shaft *==| (base below - not visible |
and * | |
Sprocket | |
| |
| |
___________________________________________________
============ Jumper
Post5 Post4
(No external
connections)
(In hopes of providing some clarity in further discussion, I have
arbitrarily numbered the 5 posts CW from top left, but there are no
markings on the motor itself around the posts.) The jumpers are fairly
thin metal, which suggests to me they aren't intended to carry as much
current as the main power wires, but that's just a guess.
I have never taken one of these apart, but commutator and brushes
(armature power) is usually at the external shaft end (no tail shaft on
this motor), right?
So, with only one connector post at the shaft end of the motor, which
are the armature connectors?
Darryl
On 9/5/2019 2:22 PM, RJ Kanary via Elec-trak wrote:
Not authoritative, but a start.........
https://www.quora.com/How-can-the-direction-or-rotation-of-a-DC-compound-motor-be-reversed
RJ
Wishing his Dad was still alive to answer that question.
On 9/5/2019 1:35 PM, Darryl McMahon wrote:
I have been using a spare ET snowthrower motor over the summer to
power some test rig contraptions over the summer, and it's worked
like a charm.
Last week, I was asked to try powering something new (possible
amphibious drive 'tire'), but the new wrinkle is they want to be able
to move forward and reverse.
As I understand it, the snowthrower motors are compound wound -
strongly series but with a weak shunt field to prevent motor speed
runaway. On the blowers and tillers, there are jumpers between what
I expect are the 2 sets of field windings. (I don't have a schematic
for these motors.) Which posts do what on these motors (there are
six external connection posts). For ET use, only two connections are
used (pack positive and pack negative).
On a series motor, this can be done by reversing the field or
armature connections (but not both).
I'm looking for guidance on the possibility of reversing one of these
motors. If that's doable and not going to damage the motor, I expect
I would be putting a set of contactors in place to be able to do this
conveniently and repeatedly. I need the motor to survive so it can
go back on a snowthrower in a couple of months.
Thanks in advance for any documentation or guidance,
Darryl
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