Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

petejw

Any Electronics Wizards out there? Circuit Advice

Recommended Posts

Hi

I want to build a multi voltage power supply to run scope, cameras, usb hub etc each device having different power requirements

I have done some searching round the internet and come up with the following circuit, can anyone provide any advice as to whether it is an OK design or have I got it completely round my neck (Wont be the first time) I have a 24Volt 10A regulated power supply and was looking to use this as the input.

I am sure I am not the only person to want to do this, are there designs out there, I dont want to reinvent the wheel

Any advice greatly appreciated

 

984756369_multisupply.thumb.png.99220ebf218af6ffedef37200a5a2185.png

Share this post


Link to post
Share on other sites

It would work, but it's very inefficient, and depending on your current draw, would require some beefy heatsinks. It's probably better to use buck converters, which properly specc'd will be better and more efficient and don't require heatsinks, especially for the 7.4v, which I take is for a DSLR camera ?  e.g. https://www.ebay.co.uk/itm/DC-DC-Step-Down-Converter-5-36V-to-1-25-32V-5A-Buck-Voltage-Regulator-UK/153809946953  &  https://www.ebay.co.uk/itm/LM2596S-DC-DC-Buck-Converter-Adjustable-Power-Supply-Step-Down-Module-5V-12V-24V/254234341174 (for camera)

  • Like 2
  • Thanks 1

Share this post


Link to post
Share on other sites

+1

  • Thanks 1

Share this post


Link to post
Share on other sites

Agreed, that's probably how I would have designed such a circuit when I did electronic engineering a long time ago, these buck convertors are the way to go nowadays, dont need any heatsinks due to the efficiency, whereas with that circuit you will need some decent size ones.

  • Thanks 1

Share this post


Link to post
Share on other sites

Buck converters are ideal for this.  Make sure each one has sufficient current rating and put a fuse on each individual output too :)

 

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

Yes, that's what I do.

Share this post


Link to post
Share on other sites

I would also be inclined to run the mount from a higher voltage source (e.g. 13.8V) and to over-spec its current requirements.

The reason is that there can be a significant voltage drop from the regulator in the power supply, through all the connectors and cables, to the actual mount motors. Especially if people use "cigarette lighter" type connectors. IMHO most of the "funny" problems that people have with their mounts  - controlling them in particular - can be traced back to the power supply. Whether an under-voltage as the motors start up, or noise from a switched mode PSU that was only ever designed to charge a laptop or strange things happening between the zero-volts common ground with their computer..

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

Thanks everyone for the feedback, really helpful, looks like a few buck converters are required and some fuses

Also, I would like to enclose the buck converters in a tidy box with different output sockets for different voltages and to also enclose an arduino focusser circuit. Has anyone come across any long thin project boxes that could be fitted to the mount.

Share this post


Link to post
Share on other sites

Definitely DC to DC converters are the way to go at those power levels.  Based upon your circuit diagram, your total output power requirement is 70 Watts with a maximum current draw of 7.5 Amps. The 24 Volt supply would therefore need to be rated for at least 180 Watts, and the linear regulators would need to capable of dissipating up to 110W.  Even if the DC to DC converters only had an efficiency of 80%, then the 24V supply rating would be reduced to a minimum of 88 Watts, and the total power dissipation would only be 17.5 watts.

Depending upon whether you go for off-the-shelf DC to DC convertors or decide to build your own, you may need to use a linear regulator to generate the 7.4 volt supply, but it you use a LDO type from say a 9 Volt output DC to DC converter, then any additional power dissipation will be minimal.

  • Thanks 1

Share this post


Link to post
Share on other sites

Buck converters can be set to any voltage up to a couple of volts below the input voltage.  But don't exceed the maximum input voltage (most seem to be 35v).  You can get step up buck converters too - useful if you want 24v from a standard 13.8v battery.

  • Thanks 1

Share this post


Link to post
Share on other sites
Posted (edited)
4 hours ago, petejw said:

Also, I would like to enclose the buck converters in a tidy box with different output sockets for different voltages and to also enclose an arduino focusser circuit. Has anyone come across any long thin project boxes that could be fitted to the mount.

A wise move. The circuit-board power converters are not rated for outdoor use, so they will need protecting from the elephants elements. They don't like moisture, high or low temperatures or insects crawling on them (which can be surprisingly conductive when electrified).
As for enclosures, Bitsbox have a selection at reasonable prices and honest P&P charges

Edited by pete_l
  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
Posted (edited)

Depending on your electronics skill you can make your own buck converters using the LM2596 which is the IC commonly used in the 3A ones you can buy. You just need a small inductor, schottky diode, two electrolytics plus two resistors to set the output voltage. Output voltage from 1.23V to 37V. Maximum i/p voltage of 40V and the input voltage must be at least 2V more than the input voltage. The ready made modules from China are cheaper though. 😀

The over-voltage protection zener diodes on the output need to be around a volt or so above the actual output votage to avoid them conducting in normal use, and need to be power devices, mounted on a heatsink, to take the power supply current for at least a minute or more to ensure the fuses will blow. 

1 hour ago, Gina said:

 You can get step up buck converters too.

Not wishing to be pedantic Gina, but buck converters only step down. Step-up converters are boost converters. 😉

Alan

Edited by symmetal
  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

As you like Alan but they are advertised as buck converters.  I can see your point though - buck means reduce.

  • Thanks 1

Share this post


Link to post
Share on other sites

I would try using a desktop computer power supply.  These are mains powered, switchmode,  and have outputs of +5v, +12v and usually other voltages like -12v. The +5v and +12v outputs will deliver several amps, depending on the supply rating.  The +5v is the regulated output so you should ensure this is sufficiently loaded.  All 0 volt returns are connected. The only bit you will have to make yourself is the 7.4 volt regulator circuit, powered from +12v.  And remember you will need to feed a signal into one of the connectors to make a computer PSU turn on.

  • Thanks 1

Share this post


Link to post
Share on other sites

A while back when I was using a Skywatcher NEQ6 Pro mount I found 12v from a PC ATX PSU was not quite sufficient.  I've used a 13.8v PSU since and no problem with that or the EQ8 I have now.

  • Thanks 1

Share this post


Link to post
Share on other sites

@Gina Yes, the Skywatcher manual recommends their 13.7V power supply. With the cabling and connectors it is easy to drop a Volt when the motors are drawing peak current at startup, so a 12V supply (at the source) would be right at the lower limit by the time it gets to the mount.

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

If you are dropping a volt over relatively short cables, then I'd be very suspect as to the suitability\quality\fabrication of those cables and connectors, leaving aside the power supply and its capabilities...

At home, I run all my gear from a PC PSU, which drives everything, i.e. the PC, USB hubs, mount, cameras, focusers etc. & I've never had any issues with insufficient power.

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
Posted (edited)

+12 volts is one of the nominal output voltages from a PC PSU - the exact level when measured by a digital multimeter may well be somewhat higher or lower - real example from working PC: 11.96v (varying slightly).  Sample output ratings: +5v = 30 amps, +12v = 15 amps.

Edited by Cosmic Geoff
  • Thanks 1

Share this post


Link to post
Share on other sites

Buck converters and flyback converters are cheap (reasonably), very efficient, widely available..lots of plusses. They still suffer slightly from output noise at the chopping frequency which might get in to the kit and cause banding issues on images....might be worth looking at some filters just to make sure what goes in to the camera is really clean. It's the one area where a linear regulator might still have a place.

I always use the metal box versions which helps contain noise issues. 

Mounts and dew heaters don't care about any reasonable amount of noise. 

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
Posted (edited)

If there is any risk that you can swap the polarity of the  input power connections (in the dark perhaps)I would add some polarity reversal protection. Just add a suitably rated relay and place a diode in the relay coil supply so if the power connections are accidentally reversed the relay will not close.  A few milliamps of extra current draw is a small price to pay to protect your kit.

So you are back in your favourite dark site and have set up your kit. What you do not know is that the last time you unplugged that 2.1mm power connector the positive wire broke off inside and is now touching the negative.

With the relay polarity protection you get the following. Connect the battery, no audible click from the relay, connections reversed.

swap and you get the click  no harm done

Connect and the relay buzzes. remember that shorted connector? The short pulls the voltage below the relay hold in voltage so the relay opens, voltage now recovers and relay closes and so on. Audible warning that something is not right. Disconnect and check.

same if input connection is poor and is causing a volt drop. 

 

Edited by Tomatobro
update
  • Like 3
  • Thanks 1

Share this post


Link to post
Share on other sites

Good idea but better to use non-reversible connectors.

Share this post


Link to post
Share on other sites

Just a diode in the positive supply will provide reverse supply protection.

  • Thanks 1

Share this post


Link to post
Share on other sites

The problem with adding a diode is that it drops about half a volt and carries the full current of the supply......and they can fail short circuit.

When battery power is the supply that half a volt can make all the difference.

  • Thanks 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By orfest
      Hi,
      I've been trying out astrophotography from home, where 220V socket is available with unlimited power.
      I want to be taking my setup to the field next year, but I'm wondering how to power all the devices.
      Current setup:
      The mount (10micron GM1000) needs 24V@3A (peak 4A). To get 24V@3A I need 12V@6A DSLR that can run from batteries, and I have lots of spare batteries on standby Raspberry Pi to control the devices, 5V@3A, equivalent to 12V@1.25A Dew Heater that I've just got, but never used, needs 12V@1A I'm considering some upgrades in the near future:
      An autofocuser, 12V. Power requirements should be minimal. Replace DSLR with a cooled camera, 12V. I don't know what I'll get, but top models need 3A. Don't know how much of it is used by cooling, and how much is used by the sensor. Questions:
      Is it safe to power the mount from a DC hub? My mount's manual says "Please don’t use unregulated power supplies because the output voltage of these units is not good enough to operate the mount.". I didn't find anything that says the warranty is void if not using the pre-approved power supplies. If I don't want to power the mount from the DC hub, how can I power the mount and the DC hub from the same battery? I saw these funny devices on Aliexpress but don't know if they are any good: https://www.aliexpress.com/item/32911966417.html What kind of batteries do you use to provide multiple Amperes to all the equipment all night long? Mount needs 6A (at 12V), cooled CMOS camera needs 3A, dew heater needs 1A, Pi needs 1.25A. That's 11.25A at 12V, which is 135W of power. The battery must be huge. I saw discussions of various DC hubs here:
       
    • By Nistelboy
      Hi all,
      I'm new to this forum but not particularly new to astronomy. 
      Anyway, I have an issue and I'm hoping that there is someone here who can help or at least point me in the right direction.
       
      I have a celestron advanced VX which I have now owned for probably 5 years or so, I lost a bit of interest in astronomy so all of my equipment went away and I have just recently started it all up again.
      Iwas powering the mount using an RAC heavy duty jump starter, which, admittedly, I haven't been keeping on charge! So there is a fair chance it is dead/on it's way out. So I purchased a talentcell 8300 from Amazon, it arrived today (12th) and I plugged in straight in to the mains to charge up, as soon as it was fully charged I plugged it in to my mount and nothing, literally nothing at all, no lights, no reponse, it's as if I had not plugged it in. So I plugged one of my RAC units in, one of them, when fully charged, will power the mount but not fully, the power LED comes on but the backlight on the HC does not and all I can see on the display is "boot start".
      I then tried to power the mount via the same 12v cable as I was using from the RAC units but with the power pack plugged in a charging too, this all worked exactly as expected, everything turned on, I can input into the HC and the motors all respond to input. I have noticed that the power LED on the 12v cigarette connector does dim dramatically as soon as I turn the avx on (when plugged in to the RAC pack). 
      I purchased the talentcell unit as I had noticed on other forums that people were using it for the same mount, it is rated as 12v and 6A output so all should be ok. I have not had a chance to check anything with my multimeter, and, honestly, I'm not that handy with one!
       
      Any help would be greatly appreciated 
       
      Many thanks

    • By willcastle
      Has anyone used the celestron lithium powertank (the small one, not the pro version) with a skywatcher HEQ5?
      It looks like it should be perfect but that is coming from someone who is relatively clueless
      From the skywatcher specs, it looks like the mount needs 2 amps of current, and the powertank supplies 3, so that should be good?
      It also looks like the power cable is a double-ended tip-positive 2.1 mm plug, so i assume that even though it doesn't have one of those 12V car battery inputs, it shouldn't matter right?
      (just to save people some time, i'm not going to bother with a lead battery / leisure battery / jump-start pack / etc)
    • By PlanetGazer
      I was hesitant to write this earlier, but I wanted to try all possible ways to get my new SkyWatcher 250P GOTO allgined, but to no avail.
      I have followed the instruction manuals of both the synscan and SW, and managed to get the message "alignment successful" multiple times on the handset or the app. The closest I got when I tried to dial a different star was a 20 to 25 degrees off on the azimth axis. Most times it's off by a margin on both axes.
      I have tried aligning around 30 times on more than 5 diffrenet occasions, different locations as well. I end up ignoring the thing and switch to navigating manually as the eager friends want to observe instantly, but we ran out of objectes and the planets are not close anymore, so I figured it's time to get deeper DSO's and sort out the GOTO.
      Here is what I do:
      • I level the scope to the zero reading on top of the base
      • I make sure the base is level with a spirit level I bought recently
      • I point the scope northish, but latley I bought compass to pinpoint north
      • I plug all equipments in and then switch on the power from a lead acid battery
      • I enter the date ( US fromat, month before day 😕 )
      • enter correct time zone obviously
      • the coordinates in the format of E 000 00 , N 00 00 
      • As for  elevation I use "my  elevation" app, not sure if it's accurate. Does this entry have to be that accurate?
      • I tried both brightest star and the 2 star align methods on the handset (which seems to be the same thing apart from the brightest method having an extra menu asking for which direction you are pointing at)
      I even used the synscan app and the synscan pro, and tried the 3 star align method. The app uses location and enters all data automatically
      •I use the top and right arrows as the last press before centring the star in the eyepiece as  recommended by the manual
       
      These are the steps I follow when I align , is there anythung I missed? Your kind help is much appreciated.
       
      Update: issue solved, check the reply in the second page
       
    • By masjstovel
      Hi,

      Background:
      There will probably be too much information below, but my level of knowledge in electronics is unfortunately low.
      I own a EQ-5 - upgraded to pro with synscan, a SW 150pds and a SSAG guidecam on a 9x50. I bought this with the purpose of AP. I have my telescope on the porch, so i can sit inside with the PC (5m distance) and power everything from the socket in the wall inside.
      I live in Norway where there is 230V 50hz AC in the wall.
      I have understood most telescope equipment (?) is powered by 12v DC.
      The mount came with a 12V "car-connector" which im sure people are familiar with. But i didnt wish to use this, so instead i bought a plug (European), which the picture below shows. It is like a multipurpose plug where i can choose 12V and also choose different "pc-style" connectors in the other end. 
      I am currently powering the mount via this plug to a 20m extension cord with 4 sockets. It's labeled "250V AC 50HZ". (picture below)
      I plug the USB3-powered SSAG straight to the computer. I plug the synscan controller to the computer with an adaptor to make it USB in the other end.


      So to the core of this post:
      I now have an ZWO ASI1600MM PRO (DC 12V 3A), with a 8 slot ZWO filter-wheel (USB2.0 powered - guess this connects to the camera). On its way.
      I also have a NEQ6 PRO on its way (12V 2A) - so no more EQ5 - but same power requirements.
      And lastly i have a HitecAstro 4 channel dew controller on its way (12V DC) - which i plan to use with a Omegon secondary mirror heating strap, SMALL (https://www.astroshop.eu/heater-bands-controls/omegon-secondary-mirror-heating-strip-small/p,56529#tab_bar_1_select), and maybe something else down the line. The strap uses 0,18amps the product specifications says.
       
       

      So....... With this setup, and from home like described: 
      1.
      -Plan is to use the 12v 2.25A adaptor-plug from the EQ5 on the NEQ6. 
      -Buy another one just like it, for the dew-controller. I dont know what Ampere it needs, but the dew-strap is only 0,18A.
      -Buy a upgraded 12V 3A (or 5A) for the ZWO ASI1600 and 5m USB3.0 to PC. 
      -Plug filterwheel to ZWO.
      -Plug guidecamera to PC as before - Or can this go straight to the ZWO? 
      -Plug the EQ6 via the Synscan ST4(?) to USB 5m to the PC. 
      So the mount, the ZWO and the dew-controller will go to the extension cord-cable drum outside which goes to the wall inside.
      The PC will go to the wall inside ofcourse.

      Can i do this?
      2.  If no: How should i do this?




       


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.