Skywatcher Mount Power Woes (and a Way to Solve Them!)

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The HEQ5 with ED70 Doublet, Controlled via EQMod on a Microsoft Surface 2 Tablet

For the last couple of years, I’ve had a fair few instances of what I like to call ‘flash gremlins’ with my Skywatcher HEQ5 mount.  Before I start, I’d like to say I absolutely love this mount.  It’s been with me since the start of my deep-sky astro imaging journey back in 2012.  It’s consistently reliable, and when the gears had worn enough that it started not to be, a Rowan belt mod sorted it.  However, there’s one aspect of this, and other Skywatcher mounts (especially the otherwise fantastic AZ-EQ6 that my local Astro society uses), that continues to frustrate, and that’s power.  Basically, skywatcher mounts like power, and plenty of it.  They like to have the full whack of a fully charged battery to perform well – i.e. approxmately 12.5v or higher.  They can, according to the specs in the manual, work on between 11 and 15v, but truth be told, you always need to err towards the upper end of this range.  This is fine when powering from a sufficiently meaty PSU from the mains – I never get any issue when imaging at home and plugged in.  If, though, I decide to go into the field and use a battery, the story is quite different.

When the voltage being supplied to the mount drops below 12v, then you get the ominious ‘slow flash’ of the power light.   Batteries generally supply a highwer voltage when the current they have to supply is lower – i.e. if you only have one thing running on the battery, and as long as it’s not on its last legs, then you may be fine.  However, as soon as you ramp up the Amps being drawn, the voltage the battery can sustain generally drops, which can easily take it below this 12v threshold.  When you get the ‘flash’, the symptoms include issues with GoTo accuracy, issues when guiding, and general gremlins sneaking into the mix.   Some sessions can survive a whole night with the slow flash, whereas in others, the mount won’t play ball no matter what you do.  This has resulted in me toften tearing some of the little hair I have left out trying to sort the issue, or redistribute the power load somewhat to give the mount a higher share of the one battery.

I have precious little time to image as it is, with a good portion of it being eaten up with troubleshooting these sorts of issues.  I recently decided enough was enough, and decided to figure out a way to sort this once and for all.  The rules of the electricity gods state the the more voltage you supply, the fewer Amps the mount will need to draw.  In a nutshell there are two ways of doing this….

  1. Increase the voltage being supplied by (for example) placing two batteries in series to supply artound 24v, then use a step-down circuit to bring the voltage back down to the correct level (lets say 14.5v or so).
  2. Stay with the same supply, but use a step-up circuit to suck a bit more in the way of amps, and in turn maintain the higher voltage on the output.

I can safely say that both of these work well.  The first method was that chosen by a member of the Astro society to boost the power to the society AZ-EQ6.  Two of the batteries in the observatory were wired in series in order to up the output volatge to 24V.  This was then stepped down to approximately 14.5V, and now the mount has no power issues to speak of.  Job done!

However, due to the fact that humping two lead acid batteries is a little impractical for a mobile setup, I decided to investgate going the other way, and get more out of my single power source (a 67Ah AGM leisure battery).  On testing, this was actually dropping to 11.4V or so when slewing in both axes, and generally dropping from a high of about 12.5V to around 11.8V in about 30 mins when tracking/guiding.  The flash gremlins thrive in these conditions…

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Step-Up Circuit

On investigation, I managed to get hold of a step-up circuit for just under £7 from good old Amazon.   The link to the one I got is currently http://amzn.eu/8O53fbW, but depending on when you’re reading this, that link could have expired.  A quick search for DC-DC 150W Power Supply should bring up something similar.  The same units are also available all over ebay, but generally ship from Hong Kong, and with a spell of clear skies coming up, I wanted it double quick!  These little bundles of circuiry basically take an input voltage of anything between 10 and 32V, and will output anything from 12V-35V.  Basically, the output voltage needs to be approximately 2V or more higher than the input volatge.   The bigger the difference between the input and output volatges, the hotter the circuit will get, and if you’re boosting over about 30% of the potential capacity, then you need to install a fan to keep the whole lot cool enough.

 

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Circuit  mounted in it’s box

Luckily, my meagre boost of a few Volts from 11-12ish to around 14-15ish meant that this wasnt necessary.  I mounted the whole thing inside a small project box (dontcha love the transcent blueness of it!).  This particulr board has four M3 (I believe!) mounting risers installed which I used to do this.  In order to keep an close eye on the Voltage being supplied and the amps being drawn on the output, I installed a cheap panel-mount Volt/Ammeter.  This is more because I really dont want to over-Volt the mount and blow it to kingdom come, and so the Voltmeter allows me to keep an eye on this.

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Cheap Chinese Volt/Ammeter

 

The Ammeter allows me to see the Amps being drawn by the mount at any time.  The input to the power converter box is a 2.1mm power jack – the same used by the mount itself.  Using this means I can supply the power with the same 12v utility socket lead I use to power the mount directly.

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2.1mm Power Jack

The business end of the box sports a 12V utility/car lighter socket, and this allows another mount lead to be used on the output end.  I’m trying to keep leads as standard as possible, so it’d be quick to replace with one of the many spares I’ve collected over the years if something goes amiss.

 

To finish off, and before connecting to the mount, a small pot on the circuit needs to be tweaked to get the output Voltage correct.  I set this to 14.8V, to give a small margin for error, but still plenty of nice juicy Volts to keep the mount happy.  I did some testing, and took the Voltage on the input right down to 10V, and the output Voltage level stayed absolutely rock solid, but with a predicted effect on the amps being drawn from the input source.

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…in action

Generally, my battery supplies between 11.8V and 12.2V.  The lower the input volage, the more amps need to be drawn on the input to keep the voltage on the output up.

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Mounting Screws

What I was interested in was the difference in the Amps being drawn from the power source when supplying the mount with 11.8-12.2V directly, and when supplying the mount 14.8V via the new box.  I have a volt/ammeter on the power splitter box I use to supply the input, so could see what the whole lot was drawing.  Turns out the difference was fairly minimal in the big scheme of things.  When supplying via the step-up box, the mount would take about 0.25A (250mA) more when slewing at full speed in both Axes than when being supplied directly.  That’s a surefire win in my book!  When simply tracking, the difference was just 0.13A.   All this time, the voltage being output stayed absolutely steady.

And the flashing?  Consigned to the dustbin of gremlin history hopefully.  Certainly absolutely no sign of it during testing and subsequent first light use.

The jury is out on the long-term stability, but I currently have absolutely no reason to think that there will be any issues.  Here’s hoping!

UPDATE - 09/05/2018
I can happily confirm that after several sessions, the power box has performed admirably.  An 8-hour session out in the field, and several at home, and I haven’t had a single return of the flash gremlins.  I think I can safely say I can put this little issue to bed…

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8 Responses

  1. Emad Moussa says:

    I’m amazed how advanced you’ve become, Adam. Great stuff!! I’m getting back into astronomy once I’ve moved house, I’ll probably harras you with questions and stuff once that happened 😉

  2. Tony Williams says:

    I am using the step up module you describe and it works fine. I’ve also bought a voltmeter/ammeter to fix to the box but the wiring diagrams on the internet don’t seem to work with my setup. Could you possibly supply a basic wiring diagram for your meter please? If you could email me it at twastro@googlemail.com I would be very grateful.
    Cheers.
    Tony

    • Adam says:

      Hi Tony – Hi – Apologies for the late reply – for some reason I stopped receiving notifications of comments a while back – all sorted now

      No idea whether this will still be of use to you, but it may be to someone else. I seem to remember generally on these things, there’s a positive and negative set of thin wires (the supply for the meter) which you can stick in anywhere that supplies between about 4 and 30v on most of them. There’s then a thicker pair of positive and negative ammeter wires for wiring inline. Finally there’s a tap wire (usually yellow yellow) that you wire to a terminal where you want to to sample the volts. Where you wire this in will depend on what info you need. If I remember correctly, I wired the thicker + and – (black and red) inline to the negative output line (so the black wire to the output terminal on the step-up board, and the red wire to the actual negative terminal on your box that will be the one you connect your kit to. This means that the current flows through the ammeter on the negative line, as this is required for measurement of amps. The yellow wire then went to the output + terminal on the step-up board I believe, which provides a ‘tap’ for sampling the output voltage.

      Basically, the important things are:-

      1) The meter requires a supply (usually between 4 and 30v or similar) through the (usually) smaller black and red wired wires. this can go into either side, though probably the battery/input side is sensible.
      2) The ammeter part (usually thicker black and red wires) needs to be wired inline between the negative output of the step-down board and the negative input of your kit.
      3) The yellow wire needs to go to the positive output terminal of your step up board output to sample the output volts.

      Bear in mind this is from memory… It’s vitally important that you understand how to wire these things before using them on your actual kit. You must always check the output with a multimeter, and don’t put it near your kit until you’ve verified everything. If you wire it wrongly, you could blow the board or the volt/ammeter, which is annoying, but as long as you don’t connect to your kit before verifying the output voltage, your precious kit won’t be fried…! Again – fuses are also your friend in case of shorts etc…

      Lastly – always verify the output voltage with a trusted multimeter and compare it with the reported output voltage that appears on the little volt/ammeter box thing to verify it! These things are mass produced cheapies usually, and you shouldn’t trust your kit to it until you’ve verified the output voltage is correct (15V in this case) :).

      (disclaimer) Sorry to have to add this in, but all the above is based on my experience but YOU TAKE ALL THE RESPONSIBILITY FOR HOW YOU DO THIS FOR YOUR OWN PROJECTS! Make sure you understand what you’re doing and play around, verify and check everything away from your kit before connecting things up to power anything important. Your safety and the safety of your kit is your responsibility alone! (here ends the disclaimer!)

  3. Hello man! Greetings from Italy. I just purchased two of these step-up circuit boards to get rid of the woes you are writing about, and I will soon find a box to place one of them. I still have a question about the whole thing, something you dindn’t mentioned about: my step-up circuit is rated at 4A “only” (output/input?), which is enough to run my AZ-EQ6…but will the circuit fry once connected to my 65Ah 12 V battery? Forgive my scholastic english, and many thanks for your article, it was very useful to me!

    • Adam says:

      Hi – Apologies for the late reply – for some reason I stopped receiving notifications of comments a while back – all sorted now 🙂

      Nope – the circuit will only draw what it needs to form the battery. The 65Ah on the battery means that (in theory) it can supply 1A for 65 hours, or 2A for 32.5 hours etc etc. A battery (or power supply for that matter) doesn’t ‘push’ more amps than the load needs, so no need to worry about that. The only time this becomes an issue is if there’s a short somewhere that bridges the + and – terminals of the battery, which will cause a large current to flow through whatever is bridging it, and generally that results in something going bang :). In these cases, that’s where the fuses you should be including in your circuits come into play…

  4. Dermot says:

    Adam thanks for this article, I have just recently bought an EQ5 and have been thinking about power in the field. I will certainly use a voltage stabiliser as you’ve described so well, but I noted you use a 67 ah battery, is a battery of this size necessary ? It’s a sizeable thing to lug around along with everything else !!

    • Adam says:

      Hi – Apologies for the late reply – for some reason I stopped receiving notifications of comments a while back – all sorted now 🙂

      The size of the battery is mainly due to the fact it was a freebie! It’s 23kg, but never has to be lugged that far, so not a massive issue to be honest. When the time comes to replace it I’ll likely opt for something smaller, but again, if I get a bargain, then the weight isn’t the end of the world for me.

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