Celestron 130SLT 12v battery question

[smuudge]

Hi everyone. Im guessing this has been discussed in some shape or form before. I have a 130SLT which i love (Astro Newbie here!) major downside is the battery consumption. I don't really want to go the cost of buying the Celestron power pack, i want a rechargeable battery i can sit neatly in the tray under the scope and then remove to recharge occasionally.

Question is would something along these lines be suitable for my scope?

http://www.amazon.co.uk/HQ-Universal-Sealed-Rechargeable-Battery/dp/B0013A7XOC/ref=sr_1_2?ie=UTF8&qid=1446465347&sr=8-2&keywords=12v+7ah+battery+%2B+charger

Thanks in advance.

[happy-kat]

I read of lion... rechargeable not lead batteries.

Hopefully you will get a knowledgeable reply soon.

[smuudge]

hi - can anyone help with this please!?

[will_w]

I'm interested in something similar and have been trawling through the Lithium Ion equivalents. What about something like this?

http://www.amazon.co.uk/ANNKE-Portable-18000mAh-capacity-multi-functional/dp/B015H2OUA6/ref=sr_1_11?ie=UTF8&qid=1447319082&sr=8-11&keywords=12v+annke#productDetails

[happy-kat]

This link is to a search on rechargeable battery goto, might find something.

http://stargazerslounge.com/index.php?app=core&module=search&section=search&do=search&fromsearch=1

I guess just got to pick the right voltage for your mount.

[smuudge]

I'm interested in something similar and have been trawling through the Lithium Ion equivalents. What about something like this?

http://www.amazon.co.uk/ANNKE-Portable-18000mAh-capacity-multi-functional/dp/B015H2OUA6/ref=sr_1_11?ie=UTF8&qid=1447319082&sr=8-11&keywords=12v+annke#productDetails

Hi Will, that looks pretty good to me. Do you have a 130SLT?

[smuudge]

This looks pretty good value. Would this do the job ? http://www.ebay.co.uk/itm/251893535778?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[happy-kat]

The second to last post on this thread is a related read.

http://stargazerslounge.com/topic/248336-how-do-you-power-your-mount/?fromsearch=1

[will_w]

Hi Will, that looks pretty good to me. Do you have a 130SLT?

Smuudge, I don't, but am waiting on delivery of a shiny new Orion 127 Mak and I'm keen to get a very portable setup, as I have dark sites within 15mins drive. I think the power demands of the motors / electronics would be similar to your scope. It all of course depends on the real power consumption of the devices to be run off the battery pack. For instance, the 8AH unit you show above might be limited, in that it can supply 96 watt hours only. A power hungry mount, a few heater bands, sundry phone or tablet, and that might go pretty fast. It strikes me that Lead Acid is proven, but heavy, and careful charging regime is required to keep battery health. LiPo is preferable, but expensive new tech still. Li-Ion could be a reasonable compromise, if it's up to the job. A lot of the Li-Ion battery packs are targeted at running laptops and charging phones, plenty of them are also touted for jump starting cars.

The question that remains for me - are Li-Ion batteries of approx. 15AH+ (with automatic discharge protection) suitable for the task of driving small/medium goto mounts + dew heating for 3 hrs+ of observing? Does anyone have experience of same?

[parallaxerr]

I'm a bit of a battery geek thanks to having spent years flying RC model aircraft/helicopters/quadcopters etc. Since I began in the hobby 25yrs or so ago, I've used most commercially available battery technologies on the market such as SLA, NiMH, NiCAD, LiFe, LiPo and so on.

When deciding on a battery to power anything, I consider the following...

1. Operating Voltage

The majority of our mounts are rated at 12V. This is a nominal voltage which means that actually it will operate at voltages above and below 12V although I do not recommend going much above. For instance, for grab & go quick setup, I use a 3S Lipo with only a 850mAh capacity (0.85Ah) to power my Nexstar SE as it can be attached to the mount arm negating any cable wrap issues. Fully charged, a 3S LiPo reads 12.6V and can be run down to 9.9V. I've yet to get the low voltage flashing screen on my mount, but it is noticeably slower to slew as voltage drops. This little LiPo safely powers my mount for two to three 3hr observing sessions. I also have a 4.5Ah SLA for longer sessions, I've never drained it flat.

 

2. Capacity

To accurately determine how long a battery will last, you need to know the power consumption of your mount. Whilst a Goto mount may draw close to 2A whilst slewing on both axes, in reality it will probably be closer to a few hundred milliamps while tracking, maybe less. To that end you may calculate that powering your mount alone, the 7.5Ah SLA you linked to could last in the region of 30hrs! BUT, discharge rate will have something to say about that...

3. Discharge rate

Different battery chemistries discharge at different rates. SLA batteries have a steep initial discharge rate before levelling out meaning your mount could be operating below 12V. In reality this is not a problem but it does mean that the voltage may drop below a usable level before you have used the full capacity. So, you will more likely get 5-6Ah out of that 7.5Ah battery.

Unless you're planning on adding heaters or getting into astrophotography, I'd recommend the SLA. They're cheap, robust, can be relatively deep cycled and are easily charged.

will_w

Due to the requirement for dew heaters, I'm currently building a new power supply using a 10Ah 4S LiPo which is 16.8V fully charged and can be run down to 13.2V. It will be regulated so the output will never drop below 12V. Usable capacity should be around 12Ah.

A 2" eyepiece and 4" objective heater band total less than 1A at max chat but will be run at less than that so I'd say yes, 15Ah+ should be more than enough!

[happy-kat]

Thank you the graph is very interesting.

[will_w]

parallaxerr, that is extremely useful info, thank you very much for that! Your setup is very tidy and looks smashingly functional!!

FWIW, I have to admit I'm put off by the cost of the LiFePo solutions right now, although they look technically superior to anything else. So, because I also love the idea of cables not wrapping, I will try out the Annke LiIon option I linked to above. I also find the cigar lighter socket a pretty cool idea, even though the tip for my mount is probably readily available with the jumper for many different 12v power packs.There are also very nice 12v units available from Aukey (up to 28.8AH) for similar money, but these definitely have more limited options on the breakouts. 

[parallaxerr]

That Annke option is certainly a lot of Amp hrs for the money I'd be in to one of those if it wasn't for my dew heater requirement. I also have two specialist chargers from my RC days that allow me to charge specialist batteries so I stand to save some money there. Will be interested to hear how it works out for you.

[Gfamily]

This doesn't meet your aim of having 'something that sits in the tray', because it's a lot heavier than a LiOn battery, but I bought a 40Ah leisure battery online (for about £45 as I recall) and I have adapted a 3-way car 'cigarette lighter' adapter so that I can power the scope and a laptop (and any future dew heater)  over several observing sessions without having to worry about 'did I recharge it last time'.

I carry it around in an Ikea "Frakta" bag ( http://www.ikea.com/gb/en/catalog/products/17228340/) and the weight isn't a problem because I'm rarely very distant from the car.

Charging is straightforward using a car charger. 

The advantage of this over a 'jump start' unit is that leisure batteries are designed for long slow discharges rather than the relatively short and relatively shallow discharges you expect with a 'get you home'  type device.