7Ah powertank help needed

[Lee_P]

Any idea how long a 7Ah powertank (http://www.firstlightoptics.com/batteries-powerpacks/skywatcher-powertank-7ah.html) should keep an EQ3 (http://www.firstlightoptics.com/skywatcher-mounts/skywatcher-eq3-pro-synscan-goto.html) tracking for? I had a fully charged power tank but it only provided juice for around four hours. There was quite a bit of slewing, but by far the majority of the time was spent tracking. The powertank was sat on grass but it wasn't particularly cold so I wouldn't expect that to have drained it by much. I was rather hoping there would be enough power to keep it going all night, and then some. Any thoughts?

[keithatrochdale]

Hi

You might find this a better idea http://www.ebay.co.uk/itm/191036173976?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 even has a carrying handle.

Very easy to add http://www.ebay.co.uk/itm/Car-Cigarette-Lighter-Socket-3-Way-USB-Splitter-Adapter-/320551550103?pt=UK_Sound_Vision_Other&hash=item4aa25c7c97 on a short wire and a couple of crocodile clips http://www.ebay.co.uk/itm/Battery-Crocodile-Clips-25-Amp-Sold-in-Pairs-/131009662529?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item1e80c8ce41 do mark them red or black for easy identification.

[ronin]

Problem is that the battery in them is not intended for long slow drainage and if they get about half drained then the plates undergo damage and so work less efficently the next time, and the cycle repeats itself.

If they were actually designed for the use that they pertain to then they would have a bigger, deep cycle battery in them. However they cost more and need a slightly different style of charger. So the cheap bits get put in.

I would have said 3 hours maximum, but even that will be boarder line for plate damage.

If you intend to use a lead acid battery then work out how long you expoect to be stood outside using it, estimate the drain and add on at least 50% then get one that is sufficent for 4 or 5 times longer. So if you think it will be 1 amp for 6 hours then get something like a 40-50 amphour battery

From the idea that they get worse as used if you have used it previously and run it down to sort of half way then that will have caused less "in it" then the 7AH you were expecting, likely around 5AH or less now.

When people build their own they get a big deep cycle battery, and the reason is simple.

The little play ones fail, I would not expect nor use the 7AH specified items for more then 2 hours for anything like decent supply.

[Lee_P]

Thanks for the info. A golf buggy battery was recommended to me before, but I went for the Powertank figuring it would be a complete solution designed for the task. I feel a little ripped off if it can only provide power for a few hours! Regarding the suggested battery via eBay, how exactly would it connect to the 3-way cigarette lighter adapter? You say using wires and crocodile clips; can you be more specific? (Sorry, I'm not much good at electronics so really need it spelled out!) If you've got a picture that would be awesome. Thanks!

[RobH]

Unfortunately, 7 amp hours isn't much good for anything. It will give you 1 amp for 7 hours, 7 amps for an hour etc, so, not much. You need to go for a lot more than that.

I went completely OTT, and bought a 120 amp hour deep cycle leisure battery, which will run a big setup including cameras and dew bands, for a complete winters night from sunset to sunrise easily.

[keithatrochdale]

Thanks for the info. A golf buggy battery was recommended to me before, but I went for the Powertank figuring it would be a complete solution designed for the task. I feel a little ripped off if it can only provide power for a few hours! Regarding the suggested battery via eBay, how exactly would it connect to the 3-way cigarette lighter adapter? You say using wires and crocodile clips; can you be more specific? (Sorry, I'm not much good at electronics so really need it spelled out!) If you've got a picture that would be awesome. Thanks!

Hi

All that is needed is to cut off the cig plug that comes with it and then connect to the crock clips.

I do think the 7Ah powertanks are a big con and not fit for purpose.

[Scott]

I use this:

http://www.ebay.co.uk/itm/like/290804934997?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=108&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=108&ff19=0

[Lee_P]

Thanks for the advice; looks like I'll be getting one of those batteries and the clips that auspom suggests.

Another question: how much power does the EQ3 actually use? I would have assumed very little for tracking (those motors hardly move!) but I must be wrong. I'll also be hooking up a Nikon D700 to the battery. Would 22Ah be enough? Those batteries are pretty heavy..! 

[keithatrochdale]

It is difficult to gauge how much power the EQ3 actually use, it is dependant on a number of factors. How cold it is, how tight the bearings are tightened, what grease is used, how much weight is loaded on the mount, is it balanced well, etc

Now you have given a rough guide, assume the 7Ah battery had 6A of  charge and ran for 4 hours; so roughly 1.5A.

How much power does your Nikon use?

Personally I have a number of spare camera batteries from e-bay, so do not need to connect it to another power source. This also saves another wire to trip over, always a good idea.

[Lee_P]

Thanks for the tips. Not sure how much power the D700 uses, but it gets through its batteries fairly quickly. I'm leaning toward a 22Ah Lithium Polymer battery; pretty expensive, but compact. Those leisure batteries are heavy, and portability is an important factor for me. 22Ah should be plenty, I think...

[keithatrochdale]

One problem with Lithium Polymer or Iron is they do not like the cold, capacity can drop by a considerable ammount. They are also an expensive way to go. We use them a lot with R/C models, for powering the radio and also powering electrics motors.

The weight of a lead acid battery is not great, especially when you are used to carring scopes and mounts out!

Save your money too, lots of other bits to buy.