Power for SW 10" go to Dob

[Alderney]

Hi Guys
I am getting the scope in title. In the specs it says Power Supply 10 to 15 VCD 1Amp,2.1mm plug center positive. Is the 1Amp only for the hand controler or does this include slewing and tracking. I have been in contact with Jaycar and they said that their 7.2 Amp Hour 12V SLA battery would run it for aprox 7 hrs. Does this sound about right.

Dave.

[Steffen]

The 1 ampere is for the whole thing, the hand controller uses bugger all.

If you extract 7 ampere hours from a 7.2Ah SLA battery (like the Jaycar guy seems to suggest) the battery will be pretty much a write-off. That said, the mount will only draw 1A when slewing both axes, during tracking it'll use much less.

Look for an 18 or 20Ah battery, ideally a deep cycle AGM one. Those can be discharged down to 30% without affecting their lifespan, provided you recharge them properly.

Cheers
Steffen.

[julianh72]

I'm not sure that's correct for SLA batteries.

The actual effective capacity of an SLA depends on the average current drawn from it. E.g. for the Jaycar 7 Ah battery, they quote the following capacities:


20 hours @ 0.36 A = 7.2 Ah
10 hours @ 0.648 A = 6.48 Ah
5 hours @ 1.152 A = 5.76 Ah
1 hours @ 4.32 A = 4.32 Ah

http://www.jaycar.com.au/products_uploaded/SB2486.pdf

Most telescope mounts draw 1 amp (or significantly less) on average when tracking at sidereal rates (peaking at over an amp for full-speed slewing etc), so a 7 Ah SLA is probably good for 10 hours or so of constant use. (YMMV)

If you get in the habit of recharging every night or two, you should have no problems, and SLA batteries are very tolerant of shallow cycling:

"They do not suffer from the memory effect displayed by NiCad and NiMH batteries, and are therefore quite suitable for shallow cycling applications where they spend most of their time connected to a trickle or float charger. In fact unlike NiCad batteries, they prefer shallow cycling. This makes them much more suitable for emergency-standby applications such as UPSs and emergency lighting systems."
http://www.jaycar.com.au/images_uploaded/slabatts.pdf

Also:

"Although SLAs do prefer shallow cycling to deep cycling, they are nevertheless capable of supplying occasional heavy discharges without adverse effect."
...
"Generally speaking manufacturers recommend that SLA batteries are not stored in a discharged state, nor allowed to remain in such a state for very long."
[My emphasis]
http://www.jaycar.com.au/images_uploaded/slabatts.pdf

Nevertheless, SLA batteries are cheap enough that it is easy to buy an over-sized battery, just to be on the safe side.

[killswitch]

10 hours if you wanna discharge the battery near zero... which you do not want to do. SLA will not cope with constant deep cycles.

Always calculate using maximum draw to ensure extra headroom and avoid disappointments.

Aim for 14Ah or more, AGM if possible.

[5ash]

Jaycar sell a nice power supply 12v , 7.5amps for $39.95. , it's exactly the same as the one in bintels catalogue., but at a cheaper price. Here's the link to Jaycars catalogue
http://www.jaycar.com.au/productView.asp?ID=MP3575

I use one on my neq6 with no problems.
Regards philip

[coldknights]

That switch mode power supply Looks much the same that came with our 12v 110L camping fridge freezer ! They work great.

[Steffen]

That's right, the advertised capacity is only valid for slow discharge. The higher the discharge current the lower the capacity will be. Even with slow discharge you will not be able to extract more than half the capacity from an SLA battery without damaging it eventually.

AGM deep cycle batteries can be discharged a lot further, repeatedly, without flinching, that's why they're usually preferred as a power source in this kind of application (also in wheelchairs, golf buggies, etc).

Cheers
Steffen.

[Allan_L]

I use an 18 amp hour AGM deep cycle battery to power my SW 12" GoTo as well as 3 dew heaters and fan.

After 6 hours use, it still has plenty to go. Quickly recharges.
And it is small enough to sit on the front edge of the mount (so no cable tangle).

It is actually a Waeco 36 aH battery, that I opened up to find was comprised of two 18aH units. So I always have a spare if needed (eg on long Astro-Camps). [But it did cost just over $300].

http://www.fridgeandpower.com.au/fridge-accessories/battery-packs/waeco-battery-pack-raps36.html