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First session, battery dead?


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My equipment is outlined below. 

 

Tonight I was doing my first light just to test out all the components and it seems my batterypack is already dead after about 3-4 hours of getting darks, test exposures, and just having the tracking going.

 

Is this the normal battery capacity of a 17ah sky watcher batterypack or do I have a defective one? 

 

Its about 0 where I am and the battery pack has been sitting at the concrete right next to the mount.

 

When I went to check on it,  the camera had shut off and the power light on the mount was blinking.

So I checked the battery and the "needs charging" light was on.

The battery was fully charged(from yesterday) so it shoudlnt have depleted this fast even in around zero temperatures right? 

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Batteries lose performance in cold conditions so you would find it'll have apparently less capacity. Assuming it is a lead-acid battery from the 17AH rating, you'd also see voltage drop off once down below say 60-70% so in effect your 17AH would be more like 8AH in those conditions, perhaps. I may help if you can keep it off the concrete but even so the cold temps will still have its effect on performance.

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I'll get a converter from 230v-12v so I can run it off main. 

 

But still though. A completely new 17AH dedicated battery only lasting for darks and a few test exposures?  Sounds.. Weird. If thats natural, how do people even image at all during winter without main? 

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59 minutes ago, Pryce said:

If thats natural, how do people even image at all during winter without main? 

Just now completing the electrical system in my off-the-grid ROR observatory. The main components are a 200 Ah Gel battery powered by a 600 watt solar array connected to a 3000 watt pure sine wave inverter. When I was setting up on a tripod I used one of those power pack type batteries and it never lasted through the night.  Most folks suggest something in the neighborhood of a 100 Ah deep cell battery which will provide extra power for things like dew heaters, laptops, etc. Here's the 100 Ah version of my Renogy battery Amazon.com: Renogy Deep Cycle Hybrid Gel 12 Volt 100Ah Battery: Garden & Outdoor which weighs 29 kg but there are lots of different manufacturers to choose from. My 200 Ah battery weighs 58 kg not counting the box it's in which is another 14 kg. In terms of batteries, if it's something you can easily carry around with one hand it probably won't provide all the power you'll need for extended imaging sessions.

 

Battery.jpg

array.jpg

Wall 3.jpg

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Thanks for your replies guys!  Guess I just have to open the wallet again! 

Would probably be hard to get my hands on a suitable mains converter anytime soon though. Would a standard 230v-12v converter work or do I need somerhing more specific? 

In the meantime I guess I should take my darks using the in camera batteries and keep the mounts batterypack indoors until I'm ready to start imaging and then only bring it out once everything is ready to go.

 

Hopefully I'll get a few hours of imaging time before it drains the batterypack.

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Some things like the mount and dew heaters are 12 volt but other stuff like laptops and powered USB hubs will be 110 volt (in the US) or 230 in your case. You may want to get a mains power supply for the mount. I've heard this Celestron power supply will run an EQ6 but you would need to confirm that's true Amazon.com : Celestron 18778 AC Adapter (Black) : Telescope Accessories : Camera & Photo Then a converter like this could be used for accessories like dew heaters: Amazon.com: AstroAI AC to DC Converter, 10A/110Vto12V DC/120W/7.78FT, Car Cigarette Lighter Socket AC/DC Power Supply Adapter Transformer for Inflator, Car Refrigerator, and Other Car Devices: Automotive This way you could run everything off a multiplug outlet connected to a suitable extension cord connected to a nearby mains plug.

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Theres 2 outlets on the wall at work.  So a standard 230 to 12v converter and a normal extenstion for laptop should work fine for now then! At least thats all I can get my hand on at short notice.

 

But Ill invest in a dedicated mains PSU. I guess those just have a built in converter?

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5 minutes ago, Pryce said:

Followup.  Would it in that case be OK to use a 12v plug that branches out to two sockets or would that cause issues?

As long as you don't exceed the rating in amps of the single 12 volt socket, you could have as many branches as you like but you do need to know the amperage rating of the single socket and also the load of everything you'll have connected to be sure. If the 12 volt devices are labeled in watts instead of amps here's an online converter you can use: Watts to Amps (A) conversion calculator (rapidtables.com). Cheaper 12 volt sockets may only be rated for 5 amps which means you could only safely pull 60 watts (5 amps) continuous. On the other hand, if it's a heavy duty 12 volt, 30 amp socket, you could safely pull 360 watts (30 amps) continuous through multiple branches. If the devices are labeled in milliamps (mA) divide by 1000 to find the load in amps.

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On battery capacity. You do not necessarily get what is written on the box. This applies to any batteries.

For lead acid. A loss of capacity (identified in earlier posts) and increased internal resistance when cold is well known.
Next time you look for a car battery, there is a rating 'CCA'. cold cranking amps. A measure of how the battery will drive a starter motor on a cold day.

A lead acid battery capacity is usually quoted at the '20 hour' rate. In other words a 17Ah battery will provide 0.85 Amps for 20 hours.
However, when you draw a current higher than the 20 hour rate, the delivered capacity is lower.
For example a 17Ah battery delivering 8.5 amps not work for 2 hours. More likely 1 hour. In other words half the capacity.
The way capacity drops with higher load is similar between manufacturers. They all use essentially the same chemistry. It has been around for >100 years.

A further problem with lead acid is age related degradation. From the day of manufacture, the battery loses capacity. No matter how well you look after it, you can't beat this limit.
At high temperature, life is significantly shortened. This in terms of 0.085% daily degradation at 20C, doubling at 30C.
I am relying on memory here. I no longer use lead acid at work and have not done for years so 0.085% may not be correct, but the principle is valid.
So to get best life from your led acid battery, store it in a shed, but bring it into the house to warm before use.

Next you need to remember that lead acid has siginificant self discharge. think in terms of a top up charge if you have not used the kit for a month.

Finally. NEVER NEVER run a lead acid battery flat then leave it. The battery will 'sulphate' and give poor performance. Always recharge immediately after use.

Now you see why most people using lead acid for astro kit go for 100Ah or thereabouts leisure batteries. When they degrade, there is still enough capacity remaining for use.

Any new portable kit I construct or buy is always lithium battery powered.
Power to weight (and power to volume) is about 3x better than lead acid.
They work at low temperature.
Internal management electronics ensures you can't wreck them.
Self discharge rates are very low so you don't need to recharge when idle.
They are expensive, but they do last a long time.
Life tends to measured in charge/discharge cycles, rather than calendar. So for astronomy use, it is going to be several years.
Capacity degradation is fairly predictable. Often 70% remaining after 1000 cycles. 1000 nights of imaging(?)

HTH, David.

 

your

 

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3 hours ago, Pryce said:

Followup.  Would it in that case be OK to use a 12v plug that branches out to two sockets or would that cause issues?

Be careful with the multi-outlet adaptors as you often find the plug used has the positive (centre) not fully recessed so it is very possible to make accidental contact and short stuff, especially if the end makes contact with the mount body - a few tales of woe on fried mount electronics on here. Best to tape over or cap any plugs that you are not using just in case.

For the PSU, all the 12v gear you could in theory run off a single PSU if it has enough capacity. Best to add up what your load is and then add 50% or better double it and buy that rating. More expensive but you should see less issues esp during surge loads like slewing. My EQ5 goto is in theory max 2A during fast slew so I run that off a 5A PSU brick with no issues. I'm not imaging or using dew heaters tho.

As David above says, the newer tech batteries are better than lead ones, the LiFePo ones are much lighter for the same effective capacity and are not as maintenance sensitive, as in you do not need to keep them on a top-up/float charge. Downside is they are very expensive by comparison, at least at single unit pricing. I have thought to phase out the lead batteries in my UPS units but the LiFePo costs are a few times that of lead, tho they may well last the equivalent of 3x the replacement cycle (3-5 years) of the lead ones.

If you can keep the battery off the ground, perhaps in an insulated box, that may improve your runtime results a little if the battery was warmed up to room temp before you started.

Edited by DaveL59
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6 hours ago, Pryce said:

Would probably be hard to get my hands on a suitable mains converter anytime soon though. Would a standard 230v-12v converter work or do I need somerhing more specific? 

What do you mean by a 230v-12v converter, exactly? To power your kit from the mains, you will need a unit that converts mains power to regulated +12v DC.  There are hundreds of such things, ranging from power bricks to large bench supplies with screw terminal outputs.

If you can use mains power, that is likely to be the cheapest and most reliable method.  For powering a visual mount (and no dew heaters) I use a battery pack. It's quicker and safer than running an extension cable and the charge lasts for several sessions.

So your 17AH power tank went flat after about 4 hours? Without knowing the total load, I could not possibly comment on whether this is bad or normal.  What was powering the laptop? Laptops are a power hog.

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9 hours ago, Pryce said:

I'll get a converter from 230v-12v so I can run it off main. 

 

But still though. A completely new 17AH dedicated battery only lasting for darks and a few test exposures?  Sounds.. Weird. If thats natural, how do people even image at all during winter without main? 

All my imaging sessions have been in my backyard, so I've always used 12V PSUs off the main. As for visual at dark sites, my field battery is a Celestron LiFePO4 which is portable and hassle free. One full charge lasts several 2 - 3h sessions.

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8 hours ago, Cosmic Geoff said:

What do you mean by a 230v-12v converter, exactly? To power your kit from the mains, you will need a unit that converts mains power to regulated +12v DC.  There are hundreds of such things, ranging from power bricks to large bench supplies with screw terminal outputs.

If you can use mains power, that is likely to be the cheapest and most reliable method.  For powering a visual mount (and no dew heaters) I use a battery pack. It's quicker and safer than running an extension cable and the charge lasts for several sessions.

So your 17AH power tank went flat after about 4 hours? Without knowing the total load, I could not possibly comment on whether this is bad or normal.  What was powering the laptop? Laptops are a power hog.

230v is main here.

So basically I mean main to 12v converter.

 

The sky watcher 17AH battery was fully charged and completely new.  Only used inside for setup porposes.

And it only powered mount, camera and 2 dew heater straps. 

Computer ran off mains

Edited by Pryce
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Today I dug out a couple of dew heater bands (large and small) from my spares box and measured their resistances. Together they would consume 1.75 amps at 12 volts.  That would flatten a 17AH battery pack in about 9 hours.

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