Cheap eBay Lithium 12V power source. Opinions needed.

[Micah-Jon]

Hi All,

First time poster and complete newbie here. I'm looking at purchasing my first telescope very shortly and require some advice/opinion about a power source.

I plan on purchasing an Orion SkyQuest XT10G which requires an external 12V power source. Pretty sure it shouldn’t draw any more than 2Amps. Anyone feel free to correct me here. At this stage I don’t plan on running any extra accessories just the scope.

After looking around I stumbled on this device on eBay:
http://www.ebay.com.au/itm/14000mAh-External-Portable-Battery-Power-Bank-backup-charger-Laptop-12v-16v-19v-/261423372212?pt=AU_MobilePhoneAcces sories&hash=item3cde0c17b4
It’s small, lightweight, puts out 12V @ 2Amp, has a Lithium Polymer internal battery and apparently good for 14AH

Feel free to post your opinions please.

[Nastyacidnoise]

Hi Micah. The capacity of these Lithium battery banks is commonly overrated, sometimes by a large margin. If it's truely 14Ah then it's a good deal, but there's definitely risk with this buy. The other quality consideration is that of the in-built charging circuit. Li-ion / Li-poly batteries are highly temperamental and can be ruined by inadequate charging regimes. In this case, you wouldn't know until it was too late. Sorry, this doesn't paint a rosy picture. At the end of the day it's only $130 and eBay is pretty good for returns.

As an alternative, you could look at Lithium batteries for motor cycles. I just did a quick search and found heaps available in Australia for around the same $. I suggest these over the backup charger packs because they're much more likely to be good quality (because of the high current drain required to start an engine). You would need a charger too, but all up you would be pretty certain of getting better bang for your buck.

Or if you're not afraid of a little DIY you could do what I did - make a high quality pack with batteries and a charger from a hobby supplier. As with motor vehicles, remote control gear needs to be high quality because of the massive amperage and physical demands that are placed on it. I've dealt with Hobbyking.com quite a bit for batteries. It's a pity that they don't make any 'off the shelf' 12v platforms.

Cheers,
Dane

[inertia8]

That doesn't seem very cheap at all to me.

I too was looking at the same scope, though I believe I will go for the manual option. For a power supply I was looking at a Sealed Lead Acid (SLA) battery, something in the 12-20ah range. Though smaller would be fine.. I use a 9ah in my R/C Plane Tote box, which is used to pump fuel and provide power to a starter motor and the glow plugs in the plane, in this use it lasts for months between charges.

I cannot imagine that the goto scope's motors would be continuously drawing very much power but happy for someone who has measured it to give the details.

For the $130 you are looking at with that Ebay pack you could get a decent SLA and put it into a box with an appropriately fused connection for the scope.

That said, something like the jump starter packs on sale at ALDI from time to time would be sufficient and provide you with something that can multitask. Fairly sure it's a 17ah SLA inside (will have to open and look) and they come with cigarette sockets, usb, an air compressor, lights and a nice gentle plug pack charger... and on the plus side, you can jump start your car to get yourself away from the observing site if your battery is found wanting in the cold of night!

[johnnyjetski]

Hi Micah jon
surprising such a small unit can put out that power,
I prefer the jump units just for the multi usage and the
cigarette lighter output, all for the same price or lower.
John

[The_Cat]

For a large range of LiPo batteries and very reasonably priced:

http://www.hobbyking.com/hobbyking/store/index.asp

Jeremy.

[julianh72]

The 14,000 mA.hr rating (if it's real!) would probably be measured at 5V (USB voltage) and relatively low average current, as used by the main devices that it is intended to power (mobile phones and tablets etc). While these things can pump out high current for short bursts, they can't always maintain high sustained current, due to problems with overheating etc. Also, their effective A.hr rating falls off at higher power demands (i.e. higher currents and higher voltages).

Remember that the total energy stored in a battery is approximately equal to the voltage times the average current (amps) times the duration.

Ignoring the reduced efficiency at high voltage / current, 14 A.hr @ 5 V is approximately equal to 70 W.hr - that's about right for a 450 g LiPo battery. http://en.wikipedia.org/wiki/Lithium_polymer_battery

However, when running at 12 V output, the best you could do is about 5.5 A.hr, which MIGHT give you three hours or so if you're lucky (assuming the thing can maintain a sustained output of 1 to 2 A @ 12 V without overheating).

The other thing to remember is how long will it take to recharge a 14,000 mA.hr battery via a USB cable? If you're lucky, you have a 2 A USB charger handy, so you can recharge it in 7 - 8 hours, but if you're trying to charge it off a typical 1 A phone charger or 500 mA computer USB port, it will take MUCH longer to recharge.

You'd be much better off with something like a 12 V Sealed Lead-Acid Battery (SLA). You can buy these (and suitable chargers) from places like JayCar - they're a lot cheaper, and will give you a genuine output of up to 20 A.hr or more at 12 volts and sustained currents of 1 - 2 A or more.

[julianh72]

I have a Celestron SLT GoTo AltAz mount. It's not as big as many of the "serious" mounts, but it's operating / power demand characteristics would be similar.

It only needs 100 mA or so to power the handset / controller, and the power demand of the motors depends on how fast it is slewing - the faster it is moving, the more juice it consumes. My SLT mount draws about 1.5 amps maximum @ 12 volts when slewing about both axes simultaneously at maximum speed, or about 1 amp if I slew about only one axis at maximum speed, but when tracking at normal sidereal rate, it only pulls about 500 mA @ 12 V.

I have a 7.2 A.hr / 12 volt SLA which I bought from JayCar for less than $30, and I can run the scope for quite a few evenings between charges. (I don't actually know how many hours in total I could get - I'm in the habit of recharging it every week or so, and it hasn't let me down yet!)

[Steffen]

I agree, $130 isn't exactly cheap. You'd get a very nice 40AH AGM deep-cycle battery for this kind of money. Of course, you couldn't just velcro that to the side of your Dob ;) and you'd need to add a decent charger.

Cheers
Steffen.

[Nastyacidnoise]

I second what Steffan has said - an AGM (absorbed glass matt) deep cycle lead acid battery is probably the best value. As with all Lead-acid batteries, they're heavy, but the weight could possibly be an advantage - if the dob base is sturdy enough to house the battery, then the extra mass could assist in keeping it stready.

Li-ion (& Li-poly) technology can be great. It will outlast a Lead-acid battery by many years if it's good quality. Unfortunately a lot of stuff on the retail market is poor quality.

If you do go with a battery that doesn't have it's own inbuilt charging circuit (often called a battery management system - BMS), do yourself a favour and get a decent charger. All battery types will break early if they're not charged properly. Batteryking.com sells units that can charge all kinds, for not a lot of $ (I have the old version of this one: http://www.hobbyking.com/hobbyking/store/__5606__Genuine_IMAX_B8plus_Charger _Discharger_1_8_Cells.html), but this one would be better if you only have mains power to charge from: http://www.hobbyking.com/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharg er_1_6_Cells_GENUINE_.html

Cheers,
Dane

[Micah-Jon]

Thanks for all the replies and advice guys.

I drove over to Melbourne on the weekend and purchased my scope from Bintel. I purchased a 240v power pack which will do for backyard viewing for now....

I'll put the battery purchase off till I can make up my mind :)

[raymo]

I have to disagree with Dane about his blanket assertion that a Li-ion
battery will outlast a lead acid one by many years. My Corolla battery
lasted 7.5 yrs in the car, and has been one of two batteries that I power my HEQ5 with for the two yrs since, and is still going strong.[ I changed it because it was having trouble holding charge while I was away on holiday for three weeks.] I changed my Astra battery 3 months ago at the ripe old age of 13yrs 7 months. My wife's closest friend has a 14 yr old Mazda
which still has the original battery going strong. I've been using motor
bike and car batteries[ mostly old ones] to power my scopes for over
30 yrs, and never had one let me down.
raymo

[mikerr]

I agree with raymo. See this thread ...

http://www.iceinspace.com.au/forum/showthread.php?t=76643

I,m still using an old car battery to power my setup.

Michael.