newbie question about batteries

[CharmingThunder]

 I've been into astronomy for a while now, but it's always been using manual telescopes (mainly a big dobsonian). I recently started considering upgrading to a goto mount and I'm looking at the EQ-5 with an 8-inch newtonian. I have a question regarding power supplies, the official skywatcher and celestron battery packs seem to be rather expensive for their power capacity, and I have an old 45ah car battery (It provides a steady 13.85V after testing with a multimeter). My question is what advantages do the official power supplies provide over the car battery? are there any downsides to using the car battery instead?

[brantuk]

In terms of the branded power supplies, which are way overpriced for what they are, you can get the same 17ah power supplies from Maplins for half the price (approx). Sometimes the branded ones have a radio or a choice of voltages (rarely needed) and flashing amber lights, search light, and other little extras - but if you don't have a need for that then they are way ott.

A lot of folks use leisure batteries from caravan and camping shops which give the same 12v but much longer amp hours (85ah, 110ah) - these are great when powering a lot of devices (mount, dew bands, cameras, filter wheels etc) - they last for full overnight sessions where a branded 17ah one would fail much quicker driving that lot.

Your 45ah car battery sounds ideal - though car batteries tend to be built to deliver large quick bursts of power (eg starting the engine) rather than long steady voltages over a period of time which is more suited to astro gear. So long as it stays over 12V for the duration of your sessions, then there's no harm trying it. Hth

[CharmingThunder]

43 minutes ago, brantuk said:

In terms of the branded power supplies, which are way overpriced for what they are, you can get the same 17ah power supplies from Maplins for half the price (approx). Sometimes the branded ones have a radio or a choice of voltages (rarely needed) and flashing amber lights, search light, and other little extras - but if you don't have a need for that then they are way ott.

A lot of folks use leisure batteries from caravan and camping shops which give the same 12v but much longer amp hours (85ah, 110ah) - these are great when powering a lot of devices (mount, dew bands, cameras, filter wheels etc) - they last for full overnight sessions where a branded 17ah one would fail much quicker driving that lot.

Your 45ah car battery sounds ideal - though car batteries tend to be built to deliver large quick bursts of power (eg starting the engine) rather than long steady voltages over a period of time which is more suited to astro gear. So long as it stays over 12V for the duration of your sessions, then there's no harm trying it. Hth

Thanks for the help! I'll probably try using the car battery at first, maybe look at a leisure battery if I have any issues. As I said I'm relatively new to powered mounts so I just wanted to make sure there wasn't something I was going to damage, these goto mounts are expensive!

[brantuk]

Sometimes folks plug their mounts into the car battery short term in an emergency if their regular battery packs run out. I've done it myself at star parties and not had any problems

[RayD]

I wouldn't use a car battery, they are shallow cycle and not designed for deep discharges without damage.  Generally they aren't sealed either, so you run the risk of spillage.

There's lots of sellers on eBay and Amazon of cheapish 17-22AH sealed deep cycle batteries, generally used for electric carts, wheelchairs and alike, so go for one of those, they aren't expensive and they will last much longer than a car battery (and won't spill on you).

http://www.ebay.co.uk/itm/Lucas-12V-20AH-Replace-17AH-18AH-19AH-21AH-22AH-Rechargeable-AGM-GEL-Battery/222039112019?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D37123%26meid%3Dc3baab5eac3c42a4adf1fd716b27c974%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D181301667306

[RayD]

Are you sure it's a car battery you have?  Normally car batteries have their output noted in Amps (220 for example) which is the cold cranking amps.  They are designed to delivery this very high current for very short periods.  However, deep cycle batteries, such as used in leisure vehicles, generally have their power noted in AH (45), which means they are designed to deliver lower currents over longer periods, but are also designed in such a way as a deep discharge, to say 80% DoD, will not damage them provided you charge them in a relatively short period after.

Your battery will work, but not for the long term, and if it is a vented battery (you can fill it with water) then it can spill what is basically a diluted sulfuric acid.

As Brantuk notes, the proprietary ones have little add ons, but you pay for those, and if you only want it to power a mount, then a simple small AGM or sealed lead acid is absolutely fine.

[Uplooker]

All good advice above about Leisure batteries. If you decide to get one, get a battery bigger than you think you will need. You will always want to power more stuff in the future as your interests and need change.

Also, most people end up using cigar plugs, because that is what most pre-made leads come with.

If you do stick with cigar plugs get ones that "lock" in, or consider XLR plugs as they are less likely to work loose. This is particularly important when powering a mount.

ATB

 

[CharmingThunder]

1 hour ago, RayD said:

Are you sure it's a car battery you have?  Normally car batteries have their output noted in Amps (220 for example) which is the cold cranking amps.  They are designed to delivery this very high current for very short periods.  However, deep cycle batteries, such as used in leisure vehicles, generally have their power noted in AH (45), which means they are designed to deliver lower currents over longer periods, but are also designed in such a way as a deep discharge, to say 80% DoD, will not damage them provided you charge them in a relatively short period after.

Your battery will work, but not for the long term, and if it is a vented battery (you can fill it with water) then it can spill what is basically a diluted sulfuric acid.

As Brantuk notes, the proprietary ones have little add ons, but you pay for those, and if you only want it to power a mount, then a simple small AGM or sealed lead acid is absolutely fine.

I pulled it from my brothers car after he bent the chassis on a dry stone wall a couple of years ago, so it's definitely a car battery. I dont think it's vented, but I'll check. The power is noted on top with "12V 45ah 880CCA"

23 minutes ago, Uplooker said:

All good advice above about Leisure batteries. If you decide to get one, get a battery bigger than you think you will need. You will always want to power more stuff in the future as your interests and need change.

Also, most people end up using cigar plugs, because that is what most pre-made leads come with.

If you do stick with cigar plugs get ones that "lock" in, or consider XLR plugs as they are less likely to work loose. This is particularly important when powering a mount.

ATB

 

Thanks for the advice. I'll probably get a leisure battery and use the car battery as a backup in any case, as I figure if I'm going to spend the money on the mount and telescope I may as well spend the extra to get a reliable battery

[brantuk]

You'll need a charger as well (unless you already have one).