Moving an observatory dome

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 . 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.

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?

Reply to
W. eWatson
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[snip]

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*:

motx+ +--||-+-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 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 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... ;)

Reply to
Randy Day

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

Reply to
ehsjr
[snip]

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...

Reply to
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?

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

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

I hope not! :-)

Reply to
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.

Reply to
W. eWatson
[snip]

*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.

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.

Reply to
Randy Day

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

+----+----+---+->Z +----+----+---+->Z' | | | | | | | | |>| | | | X YX' Y'
Reply to
ehsjr
[snip]

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.

Reply to
Randy Day

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

Reply to
ehsjr

This might help.

Reply to
W. eWatson

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'?

Reply to
Randy Day

PWM=?

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

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?

Reply to
W. eWatson

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

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.

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?

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...

Reply to
Randy Day

Comments below.

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

Good tip.

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

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.

Reply to
W. eWatson
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It'll be great if it works; drop us a line and let us know!

Reply to
Randy Day

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

Reply to
W. eWatson

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