Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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Does the Classic 18volt output actually put out 18 volts or can they put out a little more and still be within spec?
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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Kolenka
professor emeritus
Reged: 06/01/08
Posts: 593
Loc: Seattle Area, WA, USA
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That sentence is a bit confusing... do you mean "Does the Classic 18volt adapter actually put out 18 volts"?
If so, you should probably just stick to making sure it is 18 volts. LX200 scopes usually are not regulated all that well and you don't want to accidentally fry something.
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Meade 10" LX200R
Orion 80ED
Nagler 7T6, 9T6, 13T6, 17T4, 26T5
Canon XSi, TIS DMK 31AF03
Northwest Astro Photoblog
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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Sorry about the confusion....
Nothing in this world is perfect....120VAC can vary as much as 10V in either + or - directions.
I just assume the 18 Volt AC Adapter can vary and was just wondering by how much. Is 21 to 22 V out of the specification range of the adapter?
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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Joseph Gillman
Carpal Tunnel
Reged: 12/06/05
Posts: 2335
Loc: Boothwyn, PA
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If your scope needs say 12, or say, 18 volts, it's going to want that much *while it is drawing current (amps)* like during a slew. If you just plug it in to the wall and measure the tip, (without connecting it to the scope or drawing a load on it) it is going to measure more than 12 (or 18) on the voltmeter.
You are measuring 18 volts (or a little more) at the DC end of the plug after it has passed from the wall thru the transformer. 18V is DC not AC!
And Please don't do sticking metal voltmeter leads into the wall outlet! 
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Meade RCX400 30cm --
People dont like when I stick up for Meade but they're just jealous of my RCX 
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Gama
Vendor (Gama Electronics)
Reged: 08/23/05
Posts: 665
Loc: I come from the land downUnder
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I think he means the voltage stability with voltage input variations.
The word Regulated means just that.
If the supply is 18V DC regulated, it will maintain that voltage while the mains dips(to a percentage, or current is drawn up to its maximum). Switchmodes are very high effeciency supplies, Linear are very poor.
A voltage regulated supply will read X volts all the time, and will not matter if its loaded to its maximum current draw or unloaded. If its unregulated, thats a different ballgame. They are mainly linear supplies and they rate those supplies with the voltage at the current rating. So when the say 12V 3A unregulated, this means to get 12V it must be loaded down to 3 amps, so if you load it to 1 amp say, then the voltage could be as high as 18V or more. Not good for electronic circuits where stability is required.
Theo
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Skywatchr
Carpal Tunnel
Reged: 06/03/06
Posts: 1548
Loc: North-Central Pa.
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Steve, usually with "no load" the voltage will be a little higher. Once you put a load on it (turn the scope on), the voltage will drop to the specified voltage "under load".
If the power supply is regulated properly, the voltage will be very close, to withing a volt, of "spec".
Jeff
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18" F/5 Home-Built Dob. with Mike Dudley Mirror
Highly Modified Meade DS-16 in Roll Off Roof
6" F/15 Brass w/ D&G Lens on DS-16 Mount
DS-10 10" F/4.5 Newtonian
LXD650, LX200 Classic
Orange Tube C11
DayStar 0.45 with multiple ERFs
Vixen ED80sf
11x80 Meade, 20x80 Celestron binocs (Japan Made).
Lots of Naglers and 8mm and 13mm Ethos.
Gadgets and parts everywhere.
And a Wife that loves it as much as me!
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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OK..I understand ALL of that so far, except this:
"And Please don't do sticking metal voltmeter leads into the wall outlet!" How else is one to test the voltage?
So the next question:
Is the OEM AC Adaptor (spelled this way on the part) that is supplied with the 18VDC LX200 Classic a regulated adaptor? If so, then with an output of 21.5 volts the adaptor ic caput. If not, then with an output of 21.5 with no load, it is still in OK condition???
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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JAT Observatory
Space Freak
Reged: 02/20/05
Posts: 5607
Loc: Eastern PA
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Steve,
I would hope the Meade adapter is a regulated adapter but it wouldn't surprise me it if wasn't. In any case 21.5 volts (unloaded) seems a bit on the high side to me if it was my scope. I have a after market regulated adapter the I use to power my LXD-650 that runs at 18.5 volts unloaded and maintains 18 volts with a 2.0 amp load.
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-Marcus
The problem with free speech is even the stupid have a voice.
http://jatobservatory.org
12" LX200R on a Paramount ME
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Skywatchr
Carpal Tunnel
Reged: 06/03/06
Posts: 1548
Loc: North-Central Pa.
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Sticking probes into a receptacle is how I check the line voltage. The no-load voltage can be in the 21v range. Put a load on it like a light bulb, or a 12 volt motor (a heavier one, not a little fan) and then check the voltage. If it drops to around 18 or 19, it's fine. It's just not "well regulated". But I personally wouldn't like to use it on a Classic LX200 because the initial spike (before the voltage drops to "normal") could damage the voltage regulators in the scope.
Jeff
Quote:
OK..I understand ALL of that so far, except this:
"And Please don't do sticking metal voltmeter leads into the wall outlet!" How else is one to test the voltage?
So the next question:
Is the OEM AC Adaptor (spelled this way on the part) that is supplied with the 18VDC LX200 Classic a regulated adaptor? If so, then with an output of 21.5 volts the adaptor ic caput. If not, then with an output of 21.5 with no load, it is still in OK condition???
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18" F/5 Home-Built Dob. with Mike Dudley Mirror
Highly Modified Meade DS-16 in Roll Off Roof
6" F/15 Brass w/ D&G Lens on DS-16 Mount
DS-10 10" F/4.5 Newtonian
LXD650, LX200 Classic
Orange Tube C11
DayStar 0.45 with multiple ERFs
Vixen ED80sf
11x80 Meade, 20x80 Celestron binocs (Japan Made).
Lots of Naglers and 8mm and 13mm Ethos.
Gadgets and parts everywhere.
And a Wife that loves it as much as me!
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KnightDiver
member
Reged: 03/21/08
Posts: 33
Loc: SE Michigan
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This discussion is laced with lots of speculation and guesses. I'll try to give you some information that isn't speculation, unless I specifically state it is.
I just measured my AC adapter, the one that came with my LX200. It is rated at 18 volts at 2 amps. When it is unloaded (not plugged into the scope) and powered up (plugged into the wall) the output is indeed 21.5 volts.
This adapter is most definitely not regulated. There is no need for it to be regulated because the first circuit that this unregulated voltage sees when it enters the LX200 is a voltage regulator.
Now, it doesn't hurt to regulate a voltage twice, but it is not necessary. The voltage regulators inside the LX200 will do just fine by themselves.
There is no "initial spike" when an unregulated supply is connected to a loaded voltage regulator. I suppose with an oscilloscope you might see it momentarily go from the 21.5 volts to 18 volts when first connected. That will not harm a voltage regulator. They are rated for much higher input voltages before they fail. What does hurt a voltage regulator is generating too much heat. The power dissipated by the voltage regulator is determined by the voltage drop it has to regulate and the current it has to flow. So if you were to put, say, an unregulated supply that was 30 volts unloaded, that might cause the voltage regulator to overheat and fail. You have to calculate the current draw for the regulated voltage inside the LX200 and see if that current times the voltage drop from 30 volts to 5 volts (25 volts) is more than the regulator is rated for with the type of heat sink being used.
In fact, Meade designed the hand controller on the LX200 to use that heat from the voltage regulator to heat the controller itself. I suspect that is to keep the LCD warm enough to operate in below freezing air.
All that being said, I find that an old laptop computer power supply that outputs 18 or so volts is smaller and more efficient than the OEM supply from Meade. I also use a laptop supply designed to operate from 12 volts (in a car) when I'm running from my jump battery. They work great, are smaller, and generate less heat than the Meade supply.
I hope this clears things up a bit. If not, let me know and I'll try to be clearer.
Dave
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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Thanks, Dave....just exactly the info I was looking for.
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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Skywatchr
Carpal Tunnel
Reged: 06/03/06
Posts: 1548
Loc: North-Central Pa.
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The 7805CT regulators do fail from time to time. They are rated pretty good in terms of voltage. But I have had some pop using the Meade AC adapters. I use a regulated AC adapter now. Or I use a regulated DC adapter when away from house current. That's just my experience.
Jeff
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18" F/5 Home-Built Dob. with Mike Dudley Mirror
Highly Modified Meade DS-16 in Roll Off Roof
6" F/15 Brass w/ D&G Lens on DS-16 Mount
DS-10 10" F/4.5 Newtonian
LXD650, LX200 Classic
Orange Tube C11
DayStar 0.45 with multiple ERFs
Vixen ED80sf
11x80 Meade, 20x80 Celestron binocs (Japan Made).
Lots of Naglers and 8mm and 13mm Ethos.
Gadgets and parts everywhere.
And a Wife that loves it as much as me!
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KnightDiver
member
Reged: 03/21/08
Posts: 33
Loc: SE Michigan
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Quote:
The 7805CT regulators do fail from time to time. They are rated pretty good in terms of voltage. But I have had some pop using the Meade AC adapters. I use a regulated AC adapter now. Or I use a regulated DC adapter when away from house current. That's just my experience.
Jeff
I doubt that the Meade power supply had anything to do with your 7805 failures, but perhaps.
I have had a tantalum capacitor in my LX200 fail while using the Meade power supply. But I don't think the failure was related to that power supply.
Post hoc, ergo propter hoc?
Just my opinion.
Dave
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Joseph Gillman
Carpal Tunnel
Reged: 12/06/05
Posts: 2335
Loc: Boothwyn, PA
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Spoonsize, sorry, bad joke. I wouldn't go sticking leads into a wall outlet but that's just me.
My batteries and AC adapter for the RCX400 read about 13 volts in change (with fully charged battery) and "no load" and I have never had a problem with any Meade 12V scope. I don't recall measuring the volts on the 18v transformer I had for a LX200 CLassic.
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Meade RCX400 30cm --
People dont like when I stick up for Meade but they're just jealous of my RCX
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dwitek
member
Reged: 07/03/08
Posts: 83
Loc: White Lake, Michigan
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I just picked an Classic 1812 up the other day off eBay and it reads 18.27 volts with no load. Used it the other night for about 4 hours and when I was done it was still 18.27 volts unloaded.
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10" LX200 EMC Classic
Peterson Eye-Opener system
2" Dielectric Diagonal
JMI NGF Crayford focuser
Meade DSI Pro III
Piggybacked Stellarvue 80mm NHNG
I need an autoguider but don't want to tell my wife
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KnightDiver
member
Reged: 03/21/08
Posts: 33
Loc: SE Michigan
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Quote:
I just picked an Classic 1812 up the other day off eBay and it reads 18.27 volts with no load. Used it the other night for about 4 hours and when I was done it was still 18.27 volts unloaded.
Not sure how this fits into this discussion. However I would suspect that the 1812 is a regulated DC-to-DC converter. Most are.
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