Randy Day
Guest
Mon Dec 12, 2011 6:54 pm
In article <jc5dfa$gqp$3_at_dont-email.me>, wolftracks_at_invalid.com says...
[snip]
Quote:
If you still want DC, you might find
some power window motors at an auto
scrapyard, or even a car starter motor,
though that might be overkill...
Doubtful. The dome weighs 1500 pounds and the shutter about 400 pounds.
The dome rotates on rollers though.
A clerk at an auto show mentioned the window motors, but then thought
differently about them.
A 12v electric winch motor might work, but
you'd have to check the current required.
Sounds like relays running your present
motors are still your best bet, though...
W. eWatson
Guest
Mon Dec 12, 2011 8:27 pm
As it turns out, I will need at least one DC motor. The one that
operates the shutter. Right now a power cable runs from it to the power
outlet on the apron. I need to remove the cord to prevent entanglement
with me or the telescope.
Randy Day
Guest
Mon Dec 12, 2011 9:05 pm
In article <jc5kj9$49i$1_at_dont-email.me>, wolftracks_at_invalid.com says...
Quote:
As it turns out, I will need at least one DC motor. The one that
operates the shutter. Right now a power cable runs from it to the power
outlet on the apron. I need to remove the cord to prevent entanglement
with me or the telescope.
A 12v electric winch for mounting on
trucks/ATVs should do the trick.
HTH
ehsjr
Guest
Tue Dec 13, 2011 7:11 am
W. eWatson wrote:
Quote:
On 11/16/2011 10:29 PM, ehsjr wrote:
W. eWatson wrote:
I have a domed observatory. Presently, it has two a/c motors that
operate the rotation of the dome, and the shutter. The latter opens to
the sky as the shutter is raised. I must move either manually with a
lever.
Assuming that the existing a/c motors move the dome & shutter with
whatever degree of accuracy/speed/precision you need, there is no need
to change them. Literature for the new controller says:
"It is possible to connect other types of motors, such as AC motors,
using external relays."
Good find. I guess you found that in the pdf manual. Yes, I see it.
Interestingly though, the president of the company suggested DC on their
Yahoo Group, but gave no explanation why.
Well, I'll take a guess at that. It may be that the new controller
was designed to provide more precise rotation increments to a DC
motor than it can to an AC motor via a relay. The controller can
time *exactly* how long current is applied to a DC motor. With an AC
motor, the controller must operate a relay, and the controller cannot
control how long the relay takes to transfer. When the controller
tells the directly connected DC motor to move, current through the
motor starts immediately. When it tells a relay connected AC motor to
move, there is a delay while the relay contacts transfer. The
controller can't "see" that delay so it can't be as precise in
controlling how much rotation you get at the motor shaft.
We are not talking about a large amount of error. In fact, a relay's
transfer time is likely to be much faster than the time it takes
you to operate your existing lever switch. Therefore, it should be
more precise in controlling motor rotation than your manual lever
switch. The fact that the error the relay introduces is likely
much less than the error the manual lever switch causes is one reason
to go with your existing AC motor setup (assuming it meets your needs
at present) and relays when you install the new controller. The
other is cost: you'll be able to buy relays for way less than
it would cost to replace your motors.
Quote:
Assuming that the lever you use now operates a switch, you will
replace that switch with relay contacts. In fact, you may be able
to retain the lever setup as is, and just wire the relay contacts
in parallel with the existing switch. Retaining the lever setup
will allow you to manually operate just as you do now, if you
need to.
I understand the concept of a relay, but how does it work in the case of
motors here?
Ok, here's a schematic representation of your present setup
showing your lever operated switch and the motor it controls:
-------- /
| AC |-----o o-----[Motor]---+
| Source | |
| |-----------------------+
--------
Here it is again, except this time it shows the addition of
the relay that your new circuit will control:
/
+--o o--+ <== added relay contact; new controller
| | controls the relay, opening or closing
| | the contacts as needed.
-------- | / |
| AC |--+--o o--+--[Motor]---+
| Source | |
| |-----------------------+
--------
By wiring the relay contacts in parallel with the lever switch
contacts, the motor can be controlled by either the relay or
the lever switch. You need to check that the relay contacts are
rated to carry *AND* switch the power to the motor - which means
you need to know the amperage and horsepower rating of the motor.
Quote:
If you do operate the dome manually with the new controller
powered off or not functioning, you need a means of letting the
controller "know" the position of things. Since it didn't control
the movement and couldn't "see" the movement, it won't know the
position. You would have to tell the PC where the thing is currently
aimed so that it can move the proper distance & direction to the new
aiming point.
Pages 12-15 of the manual talk about optical rotation sensor. I think
I'd better read that. I see they provide one sensor.
I'm about to replace the manual operation with two circuit boards (not
yet purchased) that will be attached to the dome and the circular
support holding it up, sometimes called a skirt. The dome moves on
wheels. The two boards communicate wirelessly. Solar cells will
provide power to the boards. The electric motors used for manual
operation, I think, will no longer be of use.
They will work as well as they do now if you use the external relays
with the new controller.
"new controller"? A circuit card.
It looks like they will have to be replaced by DC batteries. I'm kind
of guessing here. However, according to the manual for the two boards,
relays will be provided. I'm guessing they will somehow be needed to
go between them and each of the circuit boards.
Does this latter part make any sense? Comments welcome. I'm just
trying to get a feel for what I may need beyond the two circuit
boards, and a few minor accessories provided with it. No batteries
included!
You need a battery, and the external relays. According to the list
you posted below, the relays are not included.
If I go DC, then I'll need two 12v batteries, and two solar cells.
And some form of battery monitoring/charge control, unless that is
already built into the new controller.
Ed
< snip >
Randy Day
Guest
Tue Dec 13, 2011 6:26 pm
In article <jc6qan$bm6$1_at_news.eternal-september.org>,
ehsjr_at_nospamverizon.net says...
[snip]
Quote:
Well, I'll take a guess at that. It may be that the new controller
was designed to provide more precise rotation increments to a DC
motor than it can to an AC motor via a relay. The controller can
time *exactly* how long current is applied to a DC motor. With an AC
motor, the controller must operate a relay, and the controller cannot
Another possibility occurs to me; if the
controller uses an H-bridge configuration
to provide DC forward-reverse direction
control, AC control would be a bit
different.
W. eWatson
Guest
Thu Dec 15, 2011 2:51 pm
I'm going to call the mfger of the boards this morning, and ask if
modeling the use of the boards is safe. That is, start with hobby DC
motors to learn the ropes, then graduate to maybe a motor that would
raise a garage door or window.
