Moving an observatory dome

[W. eWatson]

Back to my domed observatory. I brought up this topic here around 12/12,
and at one point directed the thread to a users manual that gives
details on the circuit board kit that I plan to use. Here's what I said.
-------------
I'm not sure it (the manual) will be helpful, but look here
<http://www.cyanogen.com/help/maxdome/MaxDome.htm>. There's a 66 page or
so pdf for it somewhere on their site.
------------

The dome has two A/C motors that operate the rotation of the dome, and
the shutter. The latter opens or closes the shutter to the sky. I must
move either manually with a lever, which is probably a switch with three
contacts (reversible motor). The two circuit boards are identical, but
via a jumper or switch can be used for the shutter and rotation
(azimuth,az) A fellow I know who is familiar with the dome and circuit
boards says, that it would be wise to keep the AC motors and use an
inverter between the A/C motors and a 12v battery (maybe 2). The motors
are already matched to do what they need to do. The motors are both
reversible. What's not clear to me at the moment, is how the circuit
board can change the direction of the motors. There are Mot1+, Mot1-,
Mot2+, Mot- screw connections on the cards. Maybe a relay to the switch?

I would like to try out the card out for dome rotation as an experiment.
That is, putting the circuit board, battery and inverter on a table
inside the dome. The az motor is a Dayton 6K974. You can read the specs
on Grainger's site.

<http://www.grainger.com/Grainger/ww...uery=6K974&op=search&Ntt=6K974&N=0&sst=subset>

I have no idea what inverter would be useful, or if a relay would be a
better way. I have a 12v Xantrex battery. So what inverter do I need to
make sure I don't mess this up, but can operate the az motor to rotate
the dome?

 

[Randy Day]

(azimuth,az) A fellow I know who is familiar with the dome and circuit
boards says, that it would be wise to keep the AC motors and use an

The consensus around here was that this would be
the way to go, as well.

inverter between the A/C motors and a 12v battery (maybe 2). The motors
are already matched to do what they need to do. The motors are both
reversible. What's not clear to me at the moment, is how the circuit
board can change the direction of the motors. There are Mot1+, Mot1-,
Mot2+, Mot- screw connections on the cards. Maybe a relay to the switch?

IIRC, the controller is for use with DC motors,
so it likely reverses the polarity of the DC to
reverse the motor. If that's the case, you can
still use the controller for your AC motors,
but you'll need 2 relays and 4 diodes for *each
motor*:

<view with monospaced font, i.e. courier>

motx+ +--|<------+-R
+-->|-+-R | e
| e | l
| l | a
- a v y
^ y - 2
| 1 | |
| | | |
motx- ------+-+--+-+

When Motx+ is positive, relay1 activates, and
when Motx- is positive, relay2 activates. Use
the relay contacts to activate the appropriate
motor circuits.

I would like to try out the card out for dome rotation as an experiment.
That is, putting the circuit board, battery and inverter on a table
inside the dome. The az motor is a Dayton 6K974. You can read the specs
on Grainger's site.

The inverter will need to be able to supply
enough power to run both motors at their rated
capacity.

Amazon lists the full load amperage for that
motor as 5 amps. Double that (at least) for 2
motors, and you're in the ballpark.

<http://www.grainger.com/Grainger/ww...uery=6K974&op=search&Ntt=6K974&N=0&sst=subset>

I have no idea what inverter would be useful, or if a relay would be a
better way. I have a 12v Xantrex battery. So what inverter do I need to
make sure I don't mess this up, but can operate the az motor to rotate
the dome?

1200 Watt inverters are $100-250. Most of the
ones I saw are 1200W peak, not continuous.
You want 1200W continuous.

Oh, one more thing. 1200W/12v = 100Amps coming
out of your battery. You won't get much
observation time from a car battery. Granted, you
won't be running both motors full-time, but even
one is asking a lot from a car battery. Maybe if
you connect the car...

 

[ehsjr]

Back to my domed observatory. I brought up this topic here around 12/12,
and at one point directed the thread to a users manual that gives
details on the circuit board kit that I plan to use. Here's what I said.
-------------
I'm not sure it (the manual) will be helpful, but look here
<http://www.cyanogen.com/help/maxdome/MaxDome.htm>. There's a 66 page or
so pdf for it somewhere on their site.
------------

The dome has two A/C motors that operate the rotation of the dome, and
the shutter. The latter opens or closes the shutter to the sky. I must
move either manually with a lever, which is probably a switch with three
contacts (reversible motor). The two circuit boards are identical, but
via a jumper or switch can be used for the shutter and rotation
(azimuth,az) A fellow I know who is familiar with the dome and circuit
boards says, that it would be wise to keep the AC motors and use an
inverter between the A/C motors and a 12v battery (maybe 2). The motors
are already matched to do what they need to do. The motors are both
reversible. What's not clear to me at the moment, is how the circuit
board can change the direction of the motors. There are Mot1+, Mot1-,
Mot2+, Mot- screw connections on the cards. Maybe a relay to the switch?

I would like to try out the card out for dome rotation as an experiment.
That is, putting the circuit board, battery and inverter on a table
inside the dome. The az motor is a Dayton 6K974. You can read the specs
on Grainger's site.

<http://www.grainger.com/Grainger/ww...uery=6K974&op=search&Ntt=6K974&N=0&sst=subset>


I have no idea what inverter would be useful, or if a relay would be a
better way. I have a 12v Xantrex battery. So what inverter do I need to
make sure I don't mess this up, but can operate the az motor to rotate
the dome?

As I recall, you already have a working dome drive with AC motors.
If that's right, you have no need for an inverter, because you
already have an AC source capable of driving the motors. All you
need to do is use the new controller to activate relays. I posted
the solution way back. Here it is again, in a diagram:

+---New added wiring---+
Existing switch | |
---Forward contact--> o Forward relay contact
|
+-----Common contact> o +--------+
| | |
| ---Reverse contact--> o Reverse relay contact |
| | | |
| +---New added wiring---+ |
| |
o o----------------------------------------------------+
\
o--------existing wire to common of existing switch
Added
interlock
switch

You do not change the existing wiring, you just add to it.
You must either mechanically lock your existing switch
in the off position, or remove it - or you can use the
interlock switch shown to give control either to the relay
contacts or the existing switch. That is to prevent having
the controller drive the motor in one direction while the
existing switch (inadvertently, one hopes) is use to drive
the motor in the opposite direction.

The wiring you add is the same gauge as your existing
wiring as it will carry the same AC you are already using
to drive the motors. The wiring to the coils of the
relays must be as specified for the new controller relay
output.

Ed

 

[Randy Day]

[snip]

As I recall, you already have a working dome drive with AC motors.
If that's right, you have no need for an inverter, because you
already have an AC source capable of driving the motors. All you
need to do is use the new controller to activate relays. I posted
the solution way back. Here it is again, in a diagram:

IIRC, his idea was to run the thing off
solar, charging a battery with a panel,
then to the inverter. I don't think he's
crunched the numbers, though. He'll
need something like a week of good
sunlight to charge up for maybe an hour
or two of observing.

1/4hp motors suck a lot more
Kilowatt-hours than I think he realizes.

Still, your advice is good for when he
finds himself back on the grid...

 

[W. eWatson]

The consensus around here was that this would be
the way to go, as well.


IIRC, the controller is for use with DC motors,
so it likely reverses the polarity of the DC to
reverse the motor. If that's the case, you can
still use the controller for your AC motors,
but you'll need 2 relays and 4 diodes for *each
motor*:

So the relays are going to allow me to connect from the circuit board to
the contacts on the motor to set the motor in motion?

<view with monospaced font, i.e. courier>

motx+ +--|<------+-R
+-->|-+-R | e
| e | l
| l | a
- a v y
^ y - 2
| 1 | |
| | | |
motx- ------+-+--+-+

When Motx+ is positive, relay1 activates, and
when Motx- is positive, relay2 activates. Use
the relay contacts to activate the appropriate
motor circuits.

The fellow who gave me the idea for an inverter provided a schematic.
It's titled

MaxDome-II interface to ProDome to azimuth motor schematic featuring
soft start, PWM speed control and two isolated power supplies

It's to drive a much lighter weight dome (Prodome) than mine that uses
DC motors. It shows two (kind of odd) motors, 9-30v dc up to 50 A hooked
up to the circuit board with the two motors in parallel.

Additionally between the board and the motors is a 12V DPDT Relay for
motor direction control. Mot1+ and Mot1- go directly to the replay. It
has a 1A diode in the Mot1+ line. Apparently, running from this relay is
a SparkFun/Canakit 50A PWM DC motor soft start & speed control
(www.canakit.com) that shows duty cycle and frequency knobs. This device
has lines running to it with an Emergency kill switch, fused, and what I
think is a 9-30vDC battery. Connected to GND, BATT on the board is a
12v battery. There's Motor idle/run control relay just like the first
that is connected into the SparkFun and Emergency kill switch. I
probably can get details on this from him. He does this stuff with domes
for a living. I say probably because, I might start hearing the sound of
a cash register from him if I ask for too many details. He lives a
considerable distance from me. He's done work on my larger domes than mine.

PWM?

I once asked Grainger about a relay, not knowing what I really wanted
nor being able to describe the need accurately. They directed me to an
area that had probably 1000 relays! I might have better luck now that I
have a better idea of what's going on. I'll more likely go to McMasters
for the relay and some suitable inverter.

The inverter will need to be able to supply
enough power to run both motors at their rated
capacity.

Amazon lists the full load amperage for that
motor as 5 amps. Double that (at least) for 2
motors, and you're in the ballpark.

1200 Watt inverters are $100-250. Most of the
ones I saw are 1200W peak, not continuous.
You want 1200W continuous.

Oh, one more thing. 1200W/12v = 100Amps coming
out of your battery. You won't get much

The fellow suggests, IIRC, a 15 watt solar cell to keep the batteries
charged.

observation time from a car battery. Granted, you
won't be running both motors full-time, but even
one is asking a lot from a car battery. Maybe if
you connect the car...

I hope not!

 

[W. eWatson]

....
I likely read your previous e-mail, but with less knowledge than I have
now. I'm maturing on the subject. See my reply to Randy Day. I've heard
three different approaches to this topic. I might respond directly to you.

I do not have a recent electrical background, but from days long ago I
still have a reasonable amount of knowledge to read schematics, and take
on challenges like this. Although I think I've found a local guy who
might be able to take on this task. This is an interesting project, but
I have enough other projects going to want to get this one taken care of
by someone knowledgeable enough to carry it out with minor help from me.

 

[Randy Day]

So the relays are going to allow me to connect from the circuit board to
the contacts on the motor to set the motor in motion?

*IF* my assumptions are correct about
how your mot+, mot- outputs work, then
yes.

You need to determine if your controller
just switches motors on and off, or
whether it controls speed via PWM. The
circuit I sent you WON'T WORK with pwm.

My impression from your first posts was
that the dome sensor switched on the
dome motor (full speed) until the dome
moved enough that the sensor cut out.

You can use PWM'd mot outputs to
control relays, but you'll need more
than just diodes to do it.

The fellow suggests, IIRC, a 15 watt solar cell to keep the batteries
charged.

1200W / 15W = 80 hours of PEAK
sunlight to charge enough for 1 hour
of observation, maybe 2.

Your setup is significantly larger
than the ones using little DC motors
and light plastic domes. I don't think
solar is going to be enough.

 

[ehsjr]

[snip]

As I recall, you already have a working dome drive with AC motors.
If that's right, you have no need for an inverter, because you
already have an AC source capable of driving the motors. All you
need to do is use the new controller to activate relays. I posted
the solution way back. Here it is again, in a diagram:

IIRC, his idea was to run the thing off
solar, charging a battery with a panel,
then to the inverter. I don't think he's
crunched the numbers, though. He'll
need something like a week of good
sunlight to charge up for maybe an hour
or two of observing.

1/4hp motors suck a lot more
Kilowatt-hours than I think he realizes.

Still, your advice is good for when he
finds himself back on the grid...

The schematic works with either AC source - grid or
batteries/inverter. However, it is based on the assumption
of the existing switch having 3 contacts (SPDT), which he
mentioned. It could be a DPDT, like this:

AC------------------+
|
[Motor coil A]
|
+-------+-------+ +---+
| | | |
s1a |>| <| s1b |>| <| |
| | | |
| o---[Motor coil B]---o |
| |
AC-----+-----------------------------+

If the existing FWD/REV switch is a DPDT instead of the SPDT he
thinks he has, then the prior schematic doesn't apply. He'd
need something like this:

AC------------------+ +->X common
| |
[Motor coil A] [Motor coil b]
| |
+->Z common +->Y common

+----+----+---+->Z +----+----+---+->Z'
| | | | | | | |
|>| <| |>| <| | |>| <| |>| <| |
| | | | | | | |
| o->X Y<-o | | o->X' Y'<-o |
| | | |
AC--+--+------------------+ +------------------+
| Existing DPDT Switch | Added FWD/Reverse relay
| |
+---v Rev relay contact |
| --o-------------------+
| |
+---v Fwd relay contact |
--o-------------------+

FWD from controller-+-FWD/Reverse relay coil-+-gnd
| |
+-FWD relay coil---------+
|
REV from controller-+-REV relay coil---------+

X Y and Z are poles of the 3PDT interlock switch.

We're working on guesses about what he has and what the new
controller will do. A detailed specification would clear away
the guess work, but at least the schematics would work.

For solar, we are in _far_ worse shape. We don't know if his new
controller will work properly with some of the modified sine
inverters out there. We need an energy budget: how much can he
collect and how much does he need. To me, it seems pointless and
costly if he is already on the grid, which seems to be the case.
But then again, he hasn't said why he wants to use solar.

Ed

 

[Randy Day]

[snip]

The schematic works with either AC source - grid or
batteries/inverter. However, it is based on the assumption
of the existing switch having 3 contacts (SPDT), which he
mentioned. It could be a DPDT, like this:

There's an extra complication; he mentioned
PWM earlier. He didn't know if the
controller does pwm or not, but relays alone
won't work if it does.

 

[ehsjr]

[snip]

The schematic works with either AC source - grid or
batteries/inverter. However, it is based on the assumption
of the existing switch having 3 contacts (SPDT), which he
mentioned. It could be a DPDT, like this:

There's an extra complication; he mentioned
PWM earlier. He didn't know if the
controller does pwm or not, but relays alone
won't work if it does.

The documentation he cited for the controller mentions using relays:
"It is possible to connect other types of motors, such as AC motors,
using external relays. Please observe all electrical code regulations
when installing AC powered motor drives. "

Ed

 

[W. eWatson]

This might help.

<http://speckledwithstars.net/misc.html>

 

[Randy Day]

This might help.

<http://speckledwithstars.net/misc.html>

Ah, the PWM is a seperate module. With
your AC motors you wouldn't need the
PWM module, or the associated wiring.

The diagram I sent you should work;
with AC motors, you'd only need one
set of contacts on each relay: one
relay starts the motor 'forward' and
the other starts 'reverse'.

Are you planning to run the controller
off solar, and the motors off house
power, or do you think the whole thing
can stay 'off the grid'?

 

[W. eWatson]

PWM=?

Ah, the PWM is a seperate module. With
your AC motors you wouldn't need the
PWM module, or the associated wiring.

The diagram I sent you should work;
with AC motors, you'd only need one
set of contacts on each relay: one
relay starts the motor 'forward' and
the other starts 'reverse'.

Could you tell me on McMasters or DigiKey I might find the right relays?
How about the same for an inverter?

Are you planning to run the controller
off solar, and the motors off house
power, or do you think the whole thing
can stay 'off the grid'?

Solar cells and no use of electricity (off the grid).

Someone mentioned 5 amps. Am I going to run such a high current that
could make my little experiment dangerous?

 

[Randy Day]

PWM=?

Pulse Width Modulation. It's the method
used to vary the speed of DC motors.

Could you tell me on McMasters

What's McMasters?

or DigiKey I might find the right relays?

Do a search on 'relay' at DigiKey, select
coil voltage of 12v, contact voltage 125v
or 250v depending on the power in your area,
and contact current 10 amps (or larger).

That should bring up a few relays to choose
from.

You can use SPST, SPDT or DPDT relays;
they'll all work in your project.

How about the same for an inverter?

Choose one that can provide enough current
for both motors. If you estimate the motors
need 10A total, look for a 15A inverter to
give yourself a margin.

As I said before, look for a CONTINUOUS
output rating; lots of inverters list a
PEAK output rating.

Solar cells and no use of electricity (off the grid).

I guess my question is: do you think
solar and batteries will give you enough
viewing time (a couple of hours, max.), and
will the _days_ of recharge time between
viewings be acceptable?

Someone mentioned 5 amps. Am I going to run such a high current that
could make my little experiment dangerous?

You mentioned the model of your motor;
Amazon.com listed the max load current
as 5 amps. If you're comfortable
around house wiring you should be ok
hooking the relays up to your lever
switch.

This project is roughly comparable to
wiring up furnace motors...

 

[W. eWatson]

PWM=?

Pulse Width Modulation. It's the method
used to vary the speed of DC motors.

Could you tell me on McMasters

[/QUOTE]
McMasters is like Graingers. Both sell a lot of electrical components
from small to very big.

What's McMasters?


Do a search on 'relay' at DigiKey, select
coil voltage of 12v, contact voltage 125v
or 250v depending on the power in your area,
and contact current 10 amps (or larger).

That should bring up a few relays to choose
from.

You can use SPST, SPDT or DPDT relays;
they'll all work in your project.


Choose one that can provide enough current
for both motors. If you estimate the motors
need 10A total, look for a 15A inverter to
give yourself a margin.

As I said before, look for a CONTINUOUS
output rating; lots of inverters list a
PEAK output rating. Good tip.



I guess my question is: do you think
solar and batteries will give you enough
viewing time (a couple of hours, max.), and
will the _days_ of recharge time between
viewings be acceptable?

Everyone I've talked to about this has done it.

You mentioned the model of your motor;
Amazon.com listed the max load current
as 5 amps. If you're comfortable
around house wiring you should be ok
hooking the relays up to your lever
switch.

This project is roughly comparable to
wiring up furnace motors...

I'm searching for someone to do all this work, but in our small town of
15K they are not easy to come back. I'll do the az, if I can't find
someone. I had one guy come over and he seemed qualified motor and
electrical wise. Haven't heard back from him for 4 weeks. He seemed to
be having trouble estimating the cost. 4 days ago I recalled a guy I had
work on some non-electrical work in the obs. He has an EE, a motor
experience. I called him and he was all excited about it. I sent him the
Max Dome II manual, and some photos of how it looks in a similar obs.
Haven't heard back. I'll likely call him tomorrow. I'm leaving town in 3
weeks for a month of travel. This may have to wait for me to return. I
continue to put the pieces together.

Thanks for the tips.

 

[Randy Day]

Everyone I've talked to about this has done it.

It'll be great if it works; drop us a
line and let us know!

 

[W. eWatson]

It'll be great if it works; drop us a
line and let us know!

A fellow who knows his stuff is on his way over now to show me how he
thinks will work.