Skywatcher Motor focus power supply

[centroid]

I'm not sure which category this fits into, but hopefully its ok here.

Has anyone replaced the 9V PP3 battery in the SW hand controller with 12V external supply?

I have several 12V regulated Plug Top PSUs laying around, and if the hand controller is ok with 12V, then I would simply remove the battery, and fit a 5.5 x  2.1 socket to the hand controller, and supply it with 12V

I measured the current drawn from the battery, at just over 100mA.

I know that the motor would be fine running on 12V, but am not sure about the hand controller.

Edited September 20, 2021 by centroid

[malc-c]

I presume you are referring to the  DC motorised focuser that has a small black box with a speed knob and two in/out buttons that uses a PP3 9V battery?

To me I can't see any reason to try and power that by a 12v supply, with some form of 9v regulation, mainly as normally focus is something you typically do once  at the start of the session, or at most twice if temperature etc affects the image. You could in theory focus and then detach the cable entering the motor once focus has been set  

The problem is that the handset drains the battery if left in place, and often it will be flat by the time you come to use it in the next session.   I simply remove the battery once I've set focus, and place it by the mount for the next session (my scope is in an observatory, but that wouldn't make much difference in this instance), and this gives me decent use form a single battery

You may find that the hand controller can take 12v with out any regulation to 9v.  The use of a PP3 is probably more down to a PP3 being the more convenient size of battery to fit the handset and one that is close to the 12v requirement of the DC motor, so it's running the motor under voltage. You may find that you loose some of the fine control as you are running the motor at 25% higher voltage.

[centroid]

18 minutes ago, malc-c said:

I presume you are referring to the  DC motorised focuser that has a small black box with a speed knob and two in/out buttons that uses a PP3 9V battery?

To me I can't see any reason to try and power that by a 12v supply, with some form of 9v regulation, mainly as normally focus is something you typically do once  at the start of the session, or at most twice if temperature etc affects the image. You could in theory focus and then detach the cable entering the motor once focus has been set  

The problem is that the handset drains the battery if left in place, and often it will be flat by the time you come to use it in the next session.   I simply remove the battery once I've set focus, and place it by the mount for the next session (my scope is in an observatory, but that wouldn't make much difference in this instance), and this gives me decent use form a single battery

You may find that the hand controller can take 12v with out any regulation to 9v.  The use of a PP3 is probably more down to a PP3 being the more convenient size of battery to fit the handset and one that is close to the 12v requirement of the DC motor, so it's running the motor under voltage. You may find that you loose some of the fine control as you are running the motor at 25% higher voltage.

Yes, that is the one MaIcolm.

I found a a picture of the inside of the SW hand controller, and it doesn't appear to contain any 'sold state' devices. Just  two button switches, a couple of resistors, and a potentiometer, so pretty basic.

I note that the £79 Hitech controller uses a nominal 12V (standard13.2V ) supply, and they state that the motor is rated for up to 18V.

I found a comment on the Ice in Space forum, where one guy had ditched the 9V battery, and connected a 12V external supply, so it would seem to be ok to do this.

I could buy a 9V regulated plug-top PSU, but I have a least three regulated 12V DC plug top power supplies,  from old BT Broadband Home Hubs.

It is quite surprising that on a forum of this size, that as yet, nobody with the very popular SW motor focuser, appears to have moved away from the 9V PP3 battery supply. 🤔

Edited September 20, 2021 by centroid
typo

[malc-c]

Yes the innards are basic, it's just a DC speed controller akin to the old model railway controllers, but with low power transistors

I'm sure the 12v BT hub PSU would do the job, provided the DC is nice and smooth.  It's really going to be a case of trial and error...   I think the reason no one has done this is that it's another set of leads and a mains plug required for something that is only required for a few minutes use at the beginning of the session.   The use of a PP3 battery keeps wiring down to the minimum, and as mentioned, once focus is set the handset can be removed, reducing drag and weigh.

[Ouroboros]

39 minutes ago, malc-c said:

Yes the innards are basic, it's just a DC speed controller akin to the old model railway controllers, but with low power transistors

I'm sure the 12v BT hub PSU would do the job, provided the DC is nice and smooth.  It's really going to be a case of trial and error...   I think the reason no one has done this is that it's another set of leads and a mains plug required for something that is only required for a few minutes use at the beginning of the session.   The use of a PP3 battery keeps wiring down to the minimum, and as mentioned, once focus is set the handset can be removed, reducing drag and weigh.

Yes, I think that’s a fair point. I just make sure I’ve always got a spare 9v battery to swap in if needed. I’ve had one go flat on me which was a nuisance. Annoyingly you can’t adjust focus  manually if the battery is flat. I wonder whether an alternative is to use rechargeable 9V batteries - one on charge ready to go and one in the hand set.  Rechargeable 9v batteries and a charger are not too expensive. It might be worth investigating whether you can make a charger from your 12v supply if you like doing that sort of thing. 

[malc-c]

If removing the battery after each time the focuser is used so that it doesn't get drained is inconvenient  then the simplest mod to make would be to fit a small switch into the case if room permits.  An LED could be added to show the switch is on, and then once you've focussed turn the switch off to save battery.  

Edited September 20, 2021 by malc-c

[centroid]

My thinking is, that I have no need to operate the focuser from near the mount/scope, but from the summer house/shed via at least 6m of cable, and 12V supply,  would provide a little more 'oomph' than a PP3 battery. I tried the focuser indoors, via an 8m cable from a PP3 battery, and there was definitely a difference in torque, compared to using  the short curly lead, that comes with the handset.

Being operated from a fixed position within the summer house, adequate  mains power points are not an issue.

I'm sure that back in my previous imaging days (pre 2014), I used one of these SW units for a while, before upgrading to a stepper motor, and along with all of the 12V gear in the observatory, it ran off a 13.8 volt regulated linear PSU

I will experiment, and see how it goes.

 

[boulderbelly]

 Hi Mate  i have one of those and as you say it needs a bit of oomph...  i'm just running it with the PP3 and its ok for crawling to the point of focus,  as i have one attached to the rear top left of my 127 SLT tube  via the skywatcher supplied bracket fixed in  place permanently with Araldite 5 minute epoxy along with two custom cogs for the focuser and one for the motor  along with a rubber toothed belt   as i did not even dare drill holes for that motor bracket near the rear of the OTA next to the mirror.  the focuser  movement on the 127 SLT  is quite fine to focus so that too much either way it gets blurred  so the slow movement on the hand control suits me fine , the PP3 battery seems fine but i have never really used up all its power so dont know how far it would go before it ran out. I have 5M cables for the  focus motor extension cable & the starsense  hand controller along with the camera cables straight to my room window  and the skywatcher powertank connected   all that to the laptop through CPWI telescope control.  

Edited September 20, 2021 by boulderbelly
spelling error

[Tomatobro]

I have made radio controlled versions of the DC focus unit and I supply the motor with 12 volts PWM. I have tested the Hitec DC controller with 12 volts DC but I have not tested it at 13.8 volts

[centroid]

Sounds like a goer to me then 🙂. I don't intend to run the SW unit at 13.8V, but a 12V from a regulated 1 Amp plug top supply. I checked the output with no load, and its bang on 12V, so definitely regulated.

Just need to get a 5.5 x 2.1 panel mount socket to fit to the SW controller.

[banjaxed]

I converted my Skywatcher motor focuser to run off a 12v battery but it was a bit slow for me and not being able to use manual focus was a bit frustrating. My solution was to build my own motor focuser that uses a toothed drive belt that you can slide on and off the drive cog in a couple of seconds giving the advantage of both manual and motor focus. 

[malc-c]

Running long supply wires will result in voltage drop, so yes if you extended the battery connector wires then you would need to run it from 12-18v if you are 5m or more away.

[tooth_dr]

3 minutes ago, malc-c said:

Running long supply wires will result in voltage drop, so yes if you extended the battery connector wires then you would need to run it from 12-18v if you are 5m or more away.

I can confirm this. I extended my wires to about 2m and the 9v battery was not sufficient to power the motor. 12v should do the trick. 

[Ouroboros]

Now that’s funny init because I bought a ten metre cable so I could adjust focus while sitting in my warm room (shed) and it really made no discernible  difference to the operation of the motor. Mind you, it might depend on the charge in the battery. 

[malc-c]

An alternative is the HitecAstro USB controller for the SW DC focuser https://www.firstlightoptics.com/astronomy-cables-leads-accessories/hitecastro-dc-focus-controller.html

If you already have a 12v supply near the mount, and a USB up, then this is one alternative

[malc-c]

2 minutes ago, Ouroboros said:

Now that’s funny init because I bought a ten metre cable so I could adjust focus while sitting in my warm room (shed) and it really made no discernible  difference to the operation of the motor. Mind you, it might depend on the charge in the battery. 

More so the gauge and design of the wire used....

[centroid]

Ok, I have opened up the SW hand controller to see what it comprises, and it is indeed very simple.

Two push buttons, three fixed resistors (only two in this diagram), a small electrolytic capacitor, and an LM317 Voltage regulator.

The LM317 is rated at 3V min, and 40V max input voltage, so more than capable of handling a 12V input voltage.

If I use a 12V supply, I might have the change the R value, to get it to retain its current slowest speed.

I could of course just buy a 9V regulated plug top PSU with enough current capability to deliver the full 9V to the motor over a long cable, but there is no challenge in that. 😀

Edited September 20, 2021 by centroid
added diagram

[Laurieast]

17 minutes ago, Ouroboros said:

Now that’s funny init because I bought a ten metre cable so I could adjust focus while sitting in my warm room (shed) and it really made no discernible  difference to the operation of the motor. Mind you, it might depend on the charge in the battery. 

I have been running mine with the battery down 10 meters of telephone wire for years, and if your worried about manual focus, you can still do that, with slightly more effort than normal if you just unplug the handset, if the handset is plugged in it is very hard to turn.

[Tomatobro]

remote focus motor controller picture of what is inside

[boulderbelly]

On 20/09/2021 at 15:27, banjaxed said:

I converted my Skywatcher motor focuser to run off a 12v battery but it was a bit slow for me and not being able to use manual focus was a bit frustrating. My solution was to build my own motor focuser that uses a toothed drive belt that you can slide on and off the drive cog in a couple of seconds giving the advantage of both manual and motor focus. 

 amazon sell cogs and toothed belts in sets  thats how i went down that road.. the minute I touched the OTA it shook while i was manual focusing..  frustrating to say the least!!

[banjaxed]

56 minutes ago, boulderbelly said:

 amazon sell cogs and toothed belts in sets  thats how i went down that road.. the minute I touched the OTA it shook while i was manual focusing..  frustrating to say the least!!

I agree, even if your mount is not very stable the motor focuser makes a world of difference to stability.

[powerlord]

I just replace the grub screws with knurled bolts. that way, I can simply slacken then manually focus (via the other side of the focus axis which still has the knob) then tighen again.

It's especially useful if you are changing cameras, barlows etc and you've no idea where focus is - to quickly manualy whirl back and forth and get it approximately right, then tighten the bolt for fine adjustment.

simples ?

Edited September 21, 2021 by powerlord