Power Supply

[nightsky]

Originally Posted by RAJAH235

Nightsky, the 12 volt/5 AMP, unit that I recommended is a 'regulated' one. (only 12 volts @ whatever load). Tis the best/cheapest option atm. L.
ps. The reason I suggested the 5 AMP one, was simply that you can use 'other stuff',(heaters), as well, without overloading it..

Hi thanks for your replies I did see the one you suggested the other day,and I have one of those which I use for my portable cooler/heater esky , I've beed told that the scope has a ,(not sure of the exact name of it,) but similar to the connection on a mobile phone, so my question is how and with what would I be able to use for a connection from that device to the scope thanks

[acropolite (Phil)]

Laurie is right on the money (as usual), buy the 12 volt switchmode from Jaycar, best value, smallest size, best regulated and most efficient. I have an LX 90 and am running a similar supply, works just nicely and they are small, not much larger than a cigarette packet. The socket on your meade is centre positive BTW.

[nightsky]

Hi everyone,I just got back from Jaycar and I bought this model
CAT. NO. MP3034 $47:95, it has 4 different size jacks including the one I need 2.5mm, the only thing I'd like to know now is , do I set it for negative or positive. Thanks
BTW my EXT 125 EC arrived yesterday

[RAJAH235]

I can only reply with, "Why did you not buy the recommended & cheaper 5 AMP unit when advised that anything less than 1.5 AMPS might not supply enough current"?
FWIW. The centre pin is usually POSITIVE, as Paul has already advised, but check with DMM first...
L.
ps. I only hope you do not burn out the smaller 800 mA unit.

[Karls48 (Karl)]

Hi all<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o:p></o:p>
While Switch mode Power Supplies are excellent choice for powering Telescopes, Focusers or Heaters, being small cheep and efficient, they are totally unsuitable for powering CCD cameras. Outputs of such Power supplies contain high frequency AC component that will show as increased noise on your CCD image. Even most basic linear Power Supply (Bridge rectifier, filter capacitor, voltage regulator, output capacitor) will do better job powering CCD camera then most expensive “switcher”.<o:p></o:p>
So, if your expensive CCD imaginer is outputting noisy image, have look on your Power supply first. <o:p></o:p>

[AndrewJ]

Gday Rajah

I have had an ETX125 for several years now, and it has run quite happily off a 500mA supply, though thats right on the limit at times
The ETX125, when slewing full speed in one axis draws about 250mA
and in both axes at the same time, about 480mA
Normal tracking operation draws about 80-100mA
The 800mA unit nightsky has bought will be OK.
( I still wouldnt have bought that one though )

I do agree a larger capacity plugpack for more accessories is a nice option, but in that case, you would really need to get one with banana plug outlets, or connecting the extra cables is going to be a pain.
I note the GH1379 appears to have a specialised connector, so he would have to cut this off to fit the correct 2.5mm DC plug anyway.
Whilst more expensive, the Desktop Regulated units MP3017 or 3434
look like a more flexible bet. Or even better, the MP3035, as it covers a more usable set of voltages than the MP3034

Lastly, i have been playing with testing dewheaters for RFI recently.
As a side effect of this, i "heard" the difference between switchmode and Transformer type plugpacks.
Whilst the switchmode units are much lighter,
they are more likely to fail when their capacitors blow.
( I now have two like this )
and they also put out a "lot" more RFI than the transformer units.
The latter hasnt affected my scope to date, but you never know.

Andrew

[acropolite (Phil)]

Karl, your comment on switchmode power supplies may have some relevance with regard to CCD sameras, however I doubt that you would find much, if any, high frequency ripple on most switchmode power supply outputs. Remember, the popular webcams used for planetary all run from USB ports, often powered from switchmode power supplies and PC soundcards also run from switchmode supplies. Many high end hi fi amps also use swich mode power supplies. A more likeley path for interference is RF. As Andrew points out, switchmode power supplies can produce high levels of RF interference, but it's not that hard to suppress such interference with some shielding, torroids and RF suppression caps on the output leads.

[AndrewJ]

Gday Acropolite

I would have to disagree on how easy it is to kill off the RFI from the switchmode "plugpacks". Also, the cheap plugpacks put out these days really dont have any RFI/HF ripple suppression in them.
The ones i have all show high freq artifacts in the output,
but you gets what you pays for.
I have tried shielding etc, but nothing saves me when using these units.
Its the leads from the pack to the device being powered that just radiate away. I have tried several forms of suppression beading, but nothing helps.
Better to just get a transformer style pack.

Note, The same effect is also present with ANY pwm dewheaters.
( Just detune an AM radio and put it near yr heater when running )
Whichever of the cables going to the heater is chopped, produces RFI.
If you have a nichrome wire heater, it also acts as a Radiator.
As i mentioned, this doesnt/hasnt affected my scope to date,
but it does screw up other things ( like cameras ), esp if the cables are run in parallel.

Andrew

[nightsky]

Originally Posted by RAJAH235

I can only reply with, "Why did you not buy the recommended & cheaper 5 AMP unit when advised that anything less than 1.5 AMPS might not supply enough current"?
FWIW. The centre pin is usually POSITIVE, as Paul has already advised, but check with DMM first...
L.
ps. I only hope you do not burn out the smaller 800 mA unit.

The only reason I did not buy the the one suggested was because I had asked in this form "How do I connect that to the scopes jack" and was told I would have to "cut" of the end (see Andrews reply)and attach the necessary lead from it to the scope, as I'm not mechanically minded and did not want to mess around with wires I give that one a miss, Also I was advised in this form to get at least "800mA" which the I bought is.I will only be useing it for the Telescope there will be no othe devices connected.the Laptop will be run directly from it's own adapter to the house power point extension cable.if anyone can suggest another model that I "DON'T have to mess around with cutting off wires,and it plugs straight into the scope please let me know, as I can always exchange the one I have, as I am still running the scope off 8AA battries. and thanks all for your replies BTW what does "DMM" stand for.

[RAJAH235]

Digital Multi Meter. L.

[Karls48 (Karl)]

Hi Acropolite. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o:p></o:p>
It is true that web cameras and sound cards works very good in extremely noisy environment, but they have been designed for it. We got Spectrum analyzer at work and I have seen noise presented on various switchers, ranging from tens of KHz to few MHz. Cheep imported switchers are usually worst. This noise is very difficult to get rid of because it is “common mode” meaning it is same on both outputs, positive and negative. Capacitor across the output will do nothing. The noise can be lowered by common mode choke, but not completely eliminated. Well designed and expensive switchers are pretty quite, but never as good as linear power supplies. Installers of security cameras almost never use switcher for camera installations for this reason. Even if switcher are more compact, cheaper and run cooler the linear power supply of same power output.<o:p></o:p>
Karl<o:p></o:p>

[Dennis]

Originally Posted by AndrewJ

Gday Acropolite
>snip
If you have a nichrome wire heater, it also acts as a Radiator.
As i mentioned, this doesnt/hasnt affected my scope to date,
but it does screw up other things ( like cameras ), esp if the cables are run in parallel.
Andrew

The Kendrick standard dew heater system at:

http://www.kendrickastro.com/astro/d...dardController

states:

"RFI (radio frequency interference) free. Absolutely necessary if you are into digital imaging!"

From memory, I understand that the Mk III standard controller may have contributed to RFI when used with ccd cameras, but this was fixed in the MkIV and onwards controller.

Cheers

Dennis

[Karls48 (Karl)]

Hi Andrew<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o:p></o:p>
This may help to reduce RFI from your switcher plug pack. It will work only if your PS is earthed. Connect 0.1uF to 0.47uF mono capacitor from negative output to the earth. Start with 0.1uF and do your test with AM radio and increase capacitor value if there is not improvement. Keep capacitor leads short. Then you may reduce RFI further by connecting 0.1uF capacitor across output terminals.<o:p></o:p>
Karl<o:p></o:p>

[nightsky]

Originally Posted by RAJAH235

Digital Multi Meter. L.

Thanks, another thing I have learnt 10000000000000 to go

[RAJAH235]

You're welcome. L.

[AndrewJ]

Gday Dennis

Re the Kendricks, i have seen the blurb, but havent seen a real unit yet
It states it uses PWM, and even if the unit itself is well shielded ( what i suspect they mean ), the cables going from it to the heater element, and the heater element itself can all act as radiators.
I have designed several PWM dewheaters ( passive and microprocessor controlled ). The units will run with pretty much no RFI when a load is close coupled. ( Ie a few inches max )
Put a lead from the controller to the heater element, ( and throw in 900mm of nichrome wire ) and it becomes a really nice RFI radiator.
Also, i dont know if the Kendricks switch on the high side or the low side.
Most use lowside switching, which means it is the earth return that is pulsing.
Hence to shield this setup, you need as a minimum, a three conductor connector. They only use RCAs so i doubt they are RFI free, when connected to an unshielded heater.
Need to get one to play with :-)

Gday Karl

All my cheapo plugpacks are unearthed.
However, i nearly always run my ETX off a battery, and to get constant supply, I have also have built a switchmode DC-DC boost convertor.
I can filter the output through an LC filter followed by a toroid with both lines wound "counter" to get rid of most of the common mode bits.
Its not perfect, but better than a cheap plugpack

Andrew

[AndrewJ]

Gday Nightsky

Whilst the adapter you have bought will work, the main detrimental comment that i have is the plug. It looks like the adapter has four plugs moulded into 1
If this is what plugs into the scope, i would be very wary of snags, and also shorting the exposed tips of the stereo type plugs, as these will be carrying 12V.

Looking at my current Jaycar catalogue, i would have suggested the MP3035 as a better deal, more current capacity and better voltage ranges, but it doesnt appear to come with an output lead or plugs.
You could always get a local sparky or auto electrician to knock up a lead with a 90deg 2.5 mm DC connector on it ( centre positive ), and get them to put a fuse in it at the same time.

Next best would be the MP3033 or MP3017, but both of those come with straight plugs, which will stick a long way out the side of the scope.
The MP3434 is shown having 90deg plugs, which is a much better all round fit into the scope, but the unit is expensive ( but has good capacity ).
Bintel sell a short 90deg power adapter ( $15) that fits into Meade scopes,
so if you got that ( and that plugs into the scope ), you could use the MP3033 to plug into it, and that will reduce the snagging possibility.
However, at that price, i would personally buy the MP3434, as it will be a much more versatile unit all round.

So my first choice, get the MP3035 ( or GH1379 ), and use the savings to pay someone to get a lead made up for it ( with fuse ).

Second choice, get the MP3434

Andrew

and after writing all that, i just noticed ( DSE ) have got a loose DC cable set
with 6 mixed 90deg adapter plugs ( M9603 for $13 ), that would connect directly to the MP3035s binding posts without needing any tools.
You still wont have a fuse, but you will have a much more flexible setup
and twice the current capacity.

[nightsky]

Originally Posted by AndrewJ

Gday Nightsky

Whilst the adapter you have bought will work, the main detrimental comment that i have is the plug. It looks like the adapter has four plugs moulded into 1
If this is what plugs into the scope, i would be very wary of snags, and also shorting the exposed tips of the stereo type plugs, as these will be carrying 12V.
The MP3434 is shown having 90deg plugs, which is a much better all round fit into the scope, but the unit is expensive ( but has good capacity ).
Andrew

Gday Andrew,
And after reading your suggestions and checking Jacar web site I've decided to ring them tomorrow and have the one I bought exchanged for the MP3434 much more straight forward for my needs, really glad you mentioned the 4 plugs on the one I have, never even thought of that, and it could be a problem. You know if Bintel had have had the Meade adapter in stock even though it was $80 + I would have paid for it, would have saved me and people like yourself in the group at lot of hassle and time,but when she said they have there own brand in stock for $100 + NO WAY.Anyway thanks very much for your reply and I'll let you and the Forum know the out come. This saga will soon come to a end

[Gama]

Originally Posted by cjmarsh81

Gama, I have heard of people using computer supplies as power supplies before. Did you have to put a load on the 5V side? I have heard you need to do this as the switching supply needs a load on 5V for some reason.

No, no load required.
Not any that i have ever used and owned in the last 20 years.
But everyones design is different.

It has no probs with my RCX-400 and its accesories attached.

[johnno]

Hi All,

I have followed this thread with great interest.

NIGHTSKY,

A lot of good advice here by people far more qualified than I,
I have just had a look at Meade's info on the ETX 125,and they say a set of 8 AA batteries,should last 20 hours.

You can take THAT with a grain of salt,BUT even if you only got half that time it would seem,the power requirements are quite low,as I initially thought.
8xAA batteries can supply a surprising amount of current,(for a short time),
and small amounts of Current for a surprisingly long time.

My reasoning,for the small current draw,was the use of AA batteries.

My reference to "get the polarity correct",has already been explained,IE,plug packs,often have a method of connecting + to the tip,or - to the tip,this HAS to be correct,or you WILL do damage.

Your Manual,should show you what is required.

IF,you are only running your scopes electronics,the 800 MA pack,should do the job,(Just)

As a retired Electronics tech,I hope I have not forgotten Too Much.

Regards.
John