Help with 12v power and amperage

[RugbyRene (Rene)]

Hi all,

I need some help working-out my power needs.

I'm looking to hook up my scope to an existing 12v garden light transformer that used to power my deck lights but not anymore.

My rig will be controlled and powered by a Stellarmate Pro which is 12v 10amp. The current transformer I have is rated at 12v 105va max. So it's max output amperage is 8.75amps, which is below what the Stellarmate requires (everything else will be powered from the Stellarmate so all I need is 10amps). All my attached equipment comes in under 10amps.

Give the current transformer is 8.5 amps I'm assuming I'll need a bigger transformer to cover the amperage?

I have found a bigger transformer that is rated at 200va mx, which means it will output at 16amps which will more than cover my needs.

Just looking for a sanity check to make sure I'm thinking about this properly.

Rene

[Startrek (Martin)]

Hi Rene,
From your description I’m assuming your mount location is a fair distance from 230V mains (GPO or Power point ) ??

In regard to using an old garden light transformer for your Astro rig , I’d guess it was originally designed for static load ( lighting ) not transient load ( motors ) plus most mounts are fussy and require reliable stable voltage from a modern solid state power supply. Personally I wouldn’t use it.

Most rigs with all accessories only require a 12v 5amp rated power supply, so that Stellarmate 12v 10amp power supply is more than adequate to power most rigs. The Stellarmate 12v 10amp I saw on their website has a mains plug ( input ) and a twin 12v 10amp cable with unknown length ( output ) with a connector.

At my Obs down south my EQ8-R pro mount with 10” Carbon newt , filter wheel , guide camera , imaging camera , Kendrick dew controller and heaters , active 4 port hub, Laptop , led light panel and so on , draws less than 5amps at 12v. But my power point ( GPO ) is located in the Obs so my 12v cables to mount and accessories are short ( up to 5m ) so voltage drop is negligible.

It’s a different story if your mains ( GPO or power point ) is located a fair distance away from rig. You may have to run heavy duty 12v cables to your rig to minimise voltage drop or alternatively install a permanent GPO closer to your mount or the cheapest way , just run an extension lead out each night.
For a rough estimate you run up to 15m using 12v 5.0mm2 twin cable ( heavy duty ) for a total load of 5 amps ( which is most rigs ) and still keep within voltage drop limits.

Can you further describe your location of mount and mains location etc…

Martin

[Startrek (Martin)]

I read your post again and tell me if I’m barking up the wrong tree, if your using a Stellarmate as a power supply to your mount ( 230v AC to 12V DC , max load 10amps ) why are you talking about using your old garden light transformer ( 230v AC to 12v DC ) to power your mount ??

Mains 230V AC > 12V Power supply > Mount

I’m a bit lost !

[RB (Andrew)]

Originally Posted by Startrek

I read your post again and tell me if I’m barking up the wrong tree, if your using a Stellarmate as a power supply to your mount ( 230v AC to 12V DC , max load 10amps ) why are you talking about using your old garden light transformer ( 230v AC to 12v DC ) to power your mount ??

Mains 230V AC > 12V Power supply > Mount

I’m a bit lost !

Yes, me too.

[joshman (Josh)]

My understanding is that he is using a stellarmate pro to run his setup, and the stellarmate requires a power supply of 12V@10A (120W) for it to be able to do everything it says on the box.


I would not be looking at re-using the lighting transformer to power your mount, as mention it is designed for a very static load, and you're likely to experience some voltage collapse everytime you slew you mount.


While a bit of an expensive option, i use a Victron Blue smart Battery charger to power my mounts. They have a power supply mode where you can set a static voltage output upto 14vdc.
They also have short circuit detection where they will not output power if it detects a short circuit on the output.

[Startrek (Martin)]

Originally Posted by joshman

My understanding is that he is using a stellarmate pro to run his setup, and the stellarmate requires a power supply of 12V@10A (120W) for it to be able to do everything it says on the box.


I would not be looking at re-using the lighting transformer to power your mount, as mention it is designed for a very static load, and you're likely to experience some voltage collapse everytime you slew you mount.


While a bit of an expensive option, i use a Victron Blue smart Battery charger to power my mounts. They have a power supply mode where you can set a static voltage output upto 14vdc.
They also have short circuit detection where they will not output power if it detects a short circuit on the output.

I must be looking at the wrong Stellarmate which had a 230v mains input and 12v output. This unit is capable of powering everything , unless there’s an unkown bit of equipment outside of just the mount and accessories ??
Typically an EQ6-R mount with full 20kg payload tracks at around 0.9 to 1.1 amps @12v and slews around 1.8 to 2.0 amps @12v so there’s adequate spare capacity to run cameras , filter wheel , Focuser , heaters etc..as some of these are cycled loads.
I still don’t understand why he suggesting to use both Stellarmate and the old garden transformer, in addition to mentioning current ratings on both ?

I guess we can wait for a reply

M.

[joshman (Josh)]

Maybe?


I see this one:
https://bintel.com.au/products/stell...-pro-8gb-128gb


Which takes a 12v input through an XT60 connector.

[Startrek (Martin)]

Originally Posted by joshman

Maybe?


I see this one:
https://bintel.com.au/products/stell...-pro-8gb-128gb


Which takes a 12v input through an XT60 connector.

Good investigative work !!

Yeh this looks like what Rene is using and yes it does need a 12v 10amp regulated power supply to power it ( not included as per description notes )
So possibly he wants to use the old garden transformer to power it
Now we are getting somewhere !
What to use to power it is dependent upon how far in distance between mains ( GPO ) , the 12v 10amp regulated power supply ( either new or old garden transformer which I don’t recommend) the Stellarmate controller and the mount.

A simple sketch layout of equipment with distances in metres between ( or detailed descriptions) would be ideal for confirming power and cable requirements.

[joshman (Josh)]

I would not be concerned with the 230Vac distance, for this low power draw any appreciable distance is negligible. (120Wdc = 0.5A @ 240Vac + cable and conversion losses)


The 12 output is of real concern. this needs to be as short a run as possible with as large a gauge of cable as possible. And ideally you want to be powering a bit higher than 12v to ensure you overcome any voltage drop in the 12v cable, and the power supply needs to be able to maintain out put when the slew motors kick in.
I routinely power my setup at 13.5Vdc without issue.

[Startrek (Martin)]

Originally Posted by joshman

I would not be concerned with the 230Vac distance, for this low power draw any appreciable distance is negligible. (120Wdc = 0.5A @ 240Vac + cable and conversion losses)


The 12 output is of real concern. this needs to be as short a run as possible with as large a gauge of cable as possible. And ideally you want to be powering a bit higher than 12v to ensure you overcome any voltage drop in the 12v cable, and the power supply needs to be able to maintain out put when the slew motors kick in.
I routinely power my setup at 13.5Vdc without issue.

Yep , I was thinking more like if the 12v 10a power supply was not located close to the Stellarmate controller, say 15 to 20m away. Then Vd comes into play.
I ran a medium sized national electrical design , construct and maintenance company for 30 odd years ( commercial, retail and industrial) Now retired

[joshman (Josh)]

Originally Posted by Startrek

Yep , I was thinking more like if the 12v 10a power supply was not located close to the Stellarmate controller, say 15 to 20m away. Then Vd comes into play.
I ran a medium sized national electrical design , construct and maintenance company for 30 odd years ( commercial, retail and industrial) Now retired

I'm a Sparky by trade. I've noted appreciable Vd over very short distances (1-2m) at 12v on my own setups, the main culprit being undersized cabling, and weak power supplies.
I run minimum 12-16awg multi-strand flexible tinned automotive cable for all my main 12Vdc cabling runs (I'd need to confirm what my current setup is using), and these are kept to a minimum length.
My 12Vdc source is kept on the mount tripod.
Runs out to pieces of equipment (camera, flats panel, focuser, dew hearers etc) are usually in 18awg.

[acropolite (Phil)]

I doubt the garden transformer would be regulated or filtered as well as that it could well be AC output and not DC. Josh's suggestion of using a Victron charger is a good idea, reasonably inexpensive and can double as a battery charger if needed.