Powering my Scope

[Adamsavage]

I'm thinking of getting a battery booster power pack to power my scope. The only problem is my scope is using AC power, with a 3 prong plug. On the back of the scope motor is says 115V 60hz. I was told that it uses around 3watts of power. The smallest wattage inverter I could find was a 30watt one from Duracell. I'm not to sure about the quality of it however. The next step up would be a 75 watt one from the hardware store. How much would the efficiency effect the motor's accuracy ? What would be my best solution ?

MotoMaster Eliminator 700A Booster Pack

Duracell 30 Watt Inverter

MotoMaster Eliminator 75W Power Inverter


I could also just get a power back that already has a built in inverter.

Eliminator 300A/150W Power Box

[JustAFriend]

As long as you can provide the listed 3watts, you're fine.
Excess capacity just gives you breathing room; a good thing.

Unless you forsee powering other devices, just go with the 30w & booster and put the extra money into other toys.

[RickJ]

What is your scope? Most of today run on 120v via a power brick that outputs 12v dc to the scope. In that case no inverter is needed, just a 12v power cord. Inverters waste far more than 3 watts to generate 3 watts AC. Larger waste more power so if needed get the smallest if powering from a small batter like this.

When I did film work in the field I used a true AC scope and a home made inverter as a true AC scope drive is frequency controlled needing precise frequency control for photo work though not at all critical visually. I used a RV deep cycle battery of 80 amp hours as small units like this were often dead by sun up. If out for only a few hours it would work.

Rick

[Adamsavage]

It's a Meade 2080 8 inch. It's using a Equatorial Wedge and the motor a 115 Volt/60HZ synchronous motor. That's pretty much all I know about it. If it ran on DC power, then I wouldn't need an inverter and all that stuff. I would just get any
power pack really. I took a few pictures of the scope to show you what it looks like.

[mutleyeng]

yeah i was scratching my head about being 115v and needing an inverter, but then i remembered you had said summut about a 2080...which is going back a bit.

if you dont have a manual for it, i found this
http://homepages.spa.umn.edu/~vonder...0LX5manual.pdf

[Adamsavage]

I have the manual myself, the physical copy. I opened the back plate up and I got more info on the motor itself. It's listed on the motor that it's 120V 60HZ 4w Mod. 447 891x-1 91k 1/8RPM

[RickJ]

You will then need the inverter. Didn't realize it was such an old scope as you'd just bought it recently. AC motors are long gone from telescopes once stepper motors became affordable. For visual use, frequency accuracy is of little importance so most any should work as long as it is approximately 60 cycles. Just get a low power one to avoid unnecessary power losses. I have powered visual scopes with a vibrator inverter back in the days before transistors. Yeah, I've been at it that long.

Rick

[Adamsavage]

You will then need the inverter. Didn't realize it was such an old scope as you'd just bought it recently. AC motors are long gone from telescopes once stepper motors became affordable. For visual use, frequency accuracy is of little importance so most any should work as long as it is approximately 60 cycles. Just get a low power one to avoid unnecessary power losses. I have powered visual scopes with a vibrator inverter back in the days before transistors. Yeah, I've been at it that long.

Rick

That's quite long. I'm thinking of trading this one sometime this summer for a Celestron NexStar 8" SE. Yes, the GOTO is a lazy way of looking at the sky, however at the same time you spend less time finding and more time looking. I could still learn to find the object roughly. The scope would give me a general area on what I want to look at. The other plus side is it seems to be about half the combined weight of current scope and mount, this is a major advantage for moving it around outside my back yard. You also have the advantage of it being DC power, so there is no need for a inverter. I could have hours of fun, if I all I had to do was look at the object and not get frustrated trying to find it.

Do you think there any quality difference in the 8 inch SE, when compared to my scope that is almost as old as myself ?

[ShinAce]

If you do use the inverter, we should check its output frequency. I'm in Ottawa and have a meter for that. The wattage, as said, is going to be a non issue.

[Adamsavage]

If you do use the inverter, we should check its output frequency. I'm in Ottawa and have a meter for that. The wattage, as said, is going to be a non issue.

K, I will keep you mind when I get it. How do I figure out the scopes Ah ? I know how much amperage it's using now. I just take 4 watts divide it by 120 volts. I get 0.0333333333333333 Amps, but that doesn't tell me how much it would use in a hour.

[ShinAce]

K, I will keep you mind when I get it. How do I figure out the scopes Ah ? I know how much amperage it's using now. I just take 4 watts divide it by 120 volts. I get 0.0333333333333333 Amps, but that doesn't tell me how much it would use in a hour.

That's it, 0.03 Amps for one hour, so 0.03 amphours per hour. Or, 33 hours to use up 1 Ah. But a battery is not 120V.

There's a better way to do it. You use a multimeter set to measure the current being drawn from the battery. That way, you are taking into account the power wasted by the inverter, and any other power the scope uses. Just because the motor says 3 watts doesn't mean it actually uses 3 watts. It should average much less. There could be a built in fan to the scope, and the power needed to run the electronics.

So if the battery is a 12V - 5Ah (alarm system battery, about 30$) and you're measuring the current as being 0.5 amps(between the battery and the inverter), then the battery should last about 10 hours. However, a sealed lead acid will last many years if you never use more than say, half of it, and try to keep it charged. If you're going to run it until it's dead, you'll need a deep cycle battery(advisable if it's affordable for you).

[Adamsavage]

That's it, 0.03 Amps for one hour, so 0.03 amphours per hour. Or, 33 hours to use up 1 Ah. But a battery is not 120V.

There's a better way to do it. You use a multimeter set to measure the current being drawn from the battery. That way, you are taking into account the power wasted by the inverter, and any other power the scope uses. Just because the motor says 3 watts doesn't mean it actually uses 3 watts. It should average much less. There could be a built in fan to the scope, and the power needed to run the electronics.

So if the battery is a 12V - 5Ah (alarm system battery, about 30$) and you're measuring the current as being 0.5 amps(between the battery and the inverter), then the battery should last about 10 hours. However, a sealed lead acid will last many years if you never use more than say, half of it, and try to keep it charged. If you're going to run it until it's dead, you'll need a deep cycle battery(advisable if it's affordable for you).

There is no fan that I'm aware of, and I'm pretty sure there is no electronics. It's purely mechanical.

[RickJ]

The last small inverter I measured used a good amp just idling. Then the draw was about twice that of the power needed for the motor when very low. Efficiency improved at higher wattage levels. So a 4 watt motor would draw 8 from the battery (maybe 7 or so) plus the 12 watts idle for 19 to 20 total. That would be 20/12 amps or 1.67 amps. A 17 amp hour battery would last a night at that rate. But as mentioned you don't want to deep discharge such a battery. That greatly reduce the number of times it can be recharged. So does leaving it partly discharged. Always recharge upon return and never go below half capacity and it should last for many years. Otherwise you might not even get a year out of it. Depends on how often you discharge too deeply. I've seen estimates of a 10% capacity loss each time they are fully discharged.

There are two types of inverters out there. Cheap ones tend to be square wave while more expensive give a sine wave. Fortunately, for your purpose a square wave is not a problem. Also the measurements I gave were for a sine wave inverter and they are not as efficient. Thus, this is a case where cheaper might be better. Some devices can't tollerate a square wave as it has nasty harmonics that can do nasty things to some devices. Fortunately, a ac drive motor is not at all bothered by this.

For visual use frequency isn't much of an issue. Yes 60hz is on the nose but even 55 or 65hz will keep something near the center of a rather high power eyepiece for several minutes. By then you'll be moving on to something else anyway or changing eyepieces etc. That vibrator supply had horrid frequency control. As the battery drained it dropped considerably in frequency. As the power draw changed so did the frequency. Move in declination and listen to the buzz lower in frequency. Still, for visual use it worked great. Now for photographic use then exact frequency is needed and with an ac motor you need to control that. Dropping to 30 hz to move east and raising to 90 to move west for instance. Guiding would be done at 50hz and 70hz in my case. I'd drop the frequency ever so slightly when getting further from the meridian to compensate for atmospheric refraction (or raise it when rising toward the meridian). Such a drive could do things few of today's DC ones do. But then you can do things with the DC motors of today AC motors can't. Still a pain to use in the field. I changed as soon as such motors became available as well as control circuits for them.

Rick