Telescope Power Advice - save a fortune & buy an eyepiece!

[Pliadian]

One piece of advice.

Batteries will last a few hours - Dead money.

Ignore all these Astro Powerpacks. IGNORE!

I am an Electrical Engineer of over 25 years. This pays the bills so I can pursue my true passion of Astronomy.

So, you can all save a fortune on these powerpacks.

I am not saying some are good & some are bad.

The fact is, I understand electrons. Always have, always will.

All you need is this:

Buy a £20-£3012v 10-20Ah (Amps per hour) battery off ebay, new.

They are the mobility scooter type batteries.

Then spend £1 on a power connector from Maplin or similar with 2 meters of wire to take 10A. (Anything 1mm or 1.5mm wire is plenty)

Here is an example right now :  http://www.ebay.co.uk/itm/Mobility-Scooter-Battery-12V-12Ah-Wheelchair-Powerchair-Shoprider-/261228863880?pt=UK_Health_Beauty_Mobility_Disability_Medical_ET&hash=item3cd2742188

12Ah (Amps per hour) is more than enough for any scope. I have a 12" SCT and that only draws 4-5A at anytime. So having 12A on tap is an abundance.

I understand you can pay over £100 for some of these Powerpacks, but under all the plastic and a handy red light. There is a smaller battery than the one above, at 10x the cost.

Products can be about the 'frills' rather than the 'benefits'. IE - The reason you want power.

Save a fortune and it will last forever at a fraction of the cost.

You can even wait for weeks before you get a cheap charger too, the battery will last.

Save the cash and reward your new knowledge with an eyepiece too.

Clear Skies and love to the Altruist. AKA -  Astronomers (Us) x.

Scott.

[Pliadian]

One piece of advice.

Batteries will last a few hours - Dead money.

Ignore all these Astro Powerpacks. IGNORE!

I am an Electrical Engineer of over 25 years. This pays the bills so I can pursue my true passion of Astronomy.

So, you can all save a fortune on these powerpacks.

I am not saying some are good & some are bad.

The fact is, I understand electrons. Always have, always will.

All you need is this:

Buy a £20-£3012v 10-20Ah (Amps per hour) battery off ebay, new.

They are the mobility scooter type batteries.

Then spend £1 on a power connector from Maplin or similar with 2 meters of wire to take 10A. (Anything 1mm or 1.5mm wire is plenty)

Here is an example right now :  http://www.ebay.co.uk/itm/Mobility-Scooter-Battery-12V-12Ah-Wheelchair-Powerchair-Shoprider-/261228863880?pt=UK_Health_Beauty_Mobility_Disability_Medical_ET&hash=item3cd2742188

12Ah (Amps per hour) is more than enough for any scope. I have a 12" SCT and that only draws 4-5A at anytime. So having 12A on tap is an abundance.

I understand you can pay over £100 for some of these Powerpacks, but under all the plastic and a handy red light. There is a smaller battery than the one above, at 10x the cost.

Products can be about the 'frills' rather than the 'benefits'. IE - The reason you want power.

Save a fortune and it will last forever at a fraction of the cost.

You can even wait for weeks before you get a cheap charger too, the battery will last.

Save the cash and reward your new knowledge with an eyepiece too.

Clear Skies and love to the Altruist. AKA -  Astronomers (Us) x.

Scott.

Here is a PAIR of 7Ah for less. Shop around - http://www.ebay.co.uk/itm/PAIR-of-LUCAS-STAIRLIFT-BATTERIES-Brand-New-ALL-LIFTS/150861933686?_trksid=p2047675.m2109&_trkparms=aid%3D555001%26algo%3DPW.CURRENT%26ao%3D1%26asc%3D29%26meid%3D1840717902433269304%26pid%3D100010%26prg%3D1013%26rk%3D4%26rkt%3D15%26sd%3D261228863880%26

[Pliadian]

By the way.

I have nothing to do with any sale on ebay and from whom.

Just a sparky spreading the love x.

[Naemeth]

Good to know, thanks very much .

[knobby]

Don't they need charging fully before use?

[Pliadian]

They are supplied fully charged new. Always.

[Pig]

What about the usless air compressor you get with some of these chargers,   They have to be worth it for the annoyance factor

[Pliadian]

What about the usless air compressor you get with some of these chargers,   They have to be worth it for the annoyance factor

Like I say, 'frills' not 'benefits'. Old sales tactic of 'have this Rubbish as well for an extra £...'

Air compressor, for a scope? Unless you've got an inflatable observatory. That would be cool and worth the noise!

[Kropster]

The Ah figure is Ampere hours (Amps x hours) not Amps per hour.

Big difference.

[Rustysplit]

I got a replacement 22ah batt yesterday, and it needed a good 9hrs of charging before full, using a Ctek charger. So I would say, not always fully charged when supplied. Worth checking to protect your investment.

Very good advice though. Far cheaper and does the job.

[Pig]

Mine is a 37ah  with a built in inverter and USB.   I can run my Dew heater on full power, my GoTo scope slews fast plus its accurate and the laptop all at once for the price of £70, so it not all bad news with them

[Moonshane]

just so I underdstand it. I always thought that 12ah meant that you can run a 1amp draw for 12 hours and the bettery will then need recharging (OK I know you should not let it get right down) so surely your 4a draw will only last 3 hours, not enough for a full session? or have I got it wrong? my fan only draws 0.16a on my 7ah battery and lasts ages of course!

[Pig]

That's the way I understand it Shane

[Pliadian]

The Ah figure is Ampere hours (Amps x hours) not Amps per hour.

Big difference.

Yes their is a big difference but I won't explain it here.

Just to clarify, I am trying to state that Ah = time basically.

I won't go into the realms of Peukerts Law as batteries are more art than science. You can run all sorts of sums for load, conditions & % capacity of energy.

However I done this at college 25 years ago so you don't have to.

So more Ah = more time before needs a charge.

But that is obvious I suppose.

[Pliadian]

just so I underdstand it. I always thought that 12ah meant that you can run a 1amp draw for 12 hours and the bettery will then need recharging (OK I know you should not let it get right down) so surely your 4a draw will only last 3 hours, not enough for a full session? or have I got it wrong? my fan only draws 0.16a on my 7ah battery and lasts ages of course!

Just a rough example.

In reality it probably draws 1-2A and I have 'acquired' a 67Ah 12v industrial battery from an old machine at work.

This was already low at 12.45v and it has ran my Meade for (adding it up),,, roughly 40 hours powered up and or moving.

My Meade display has a power level indicator on it.

It was on 3 bars 1st time I plug in and it is Still on 3 bars after 40 odd hours.

Art not Science Batteries - 25years Electronic / Electrical Engineer. Still think it's witchcraft

[Pliadian]

Get a big one and forget it !

[Kropster]

The Ampere-Hour capacity is just that.

The number of Amps multiplied by the time in hous that that current can be supplied.

20 Ah battery  will supply 20A for 1 hour, or 2 A for 10 hours or 1mA for 20,000 hours.

Obviously these are ideal figures and reality will be less as the battery voltage drops, temperature changes and internal resistance causes power loss etc..

Basically, if you have lots of juice guzzling bits attached, you need a big capacity battery for a long observing session.

If all you run is a cooling fan, then a couple of AAs will do (almost!).

[Moonshane]

I suppose (assume) that any appliance will draw more when it starts than when it's running so the longer term draw will not be the same as the max.

[faulksy]

also worth mentioning external influences if its cold out this will bring the specific gravity down. i.e. battery power will drop

[Pliadian]

No. Its not.

This was boring back then. Were not going to Mars.

Just get a big un'.

[AstroTux]

The Ampere-Hour capacity is just that.

The number of Amps multiplied by the time in hous that that current can be supplied.

20 Ah battery  will supply 20A for 1 hour, or 2 A for 10 hours or 1mA for 20,000 hours.

Unfortunately this is not quite right.

One thing that a lot of people seem to misunderstand is that the rating of most SVLA batteries is given as the 20hr rating, ie. how much current can be drawn from the battery to make the charge last for 20hrs.

This means that a 20Ah battery will supply 1A for 20hr, but this is not a linear relationship. The same battery will only provide for around 12mins if 20A is taken from it, around 35 mins if 10A is taken from it and around 1hr 15mins if 5A is taken from it. Once the power drawn gets to 2A the same battery should last for about 9.5hrs, so is performing close to its rating.

Another thing to be aware of is that high currents will also discharge the battery to a much lower voltage - usually around 8 or 9 volts.

My advice would be that if you want your battery to provide enough power for your needs, then calculate how much current your rig takes and multiply that by 10 ( or better yet 20 ) and buy a battery of that rating. For example, if your entire rig ( mount, dew strips, camera, PC, etc. ) takes 5A then get a 50Ah or 100Ah battery.

From someone else who's spent far too much time in the electronics industry, hope this helps,

Alan

[Kropster]

Astro Tux, thanks for the correction. I was trying to keep things very simple.

As we don't live in a idealised world a lot of other factors come into play as you point out.

I would say buy cheap and buy big.

You pay a lot for extra bells and whistles that you really don't need.

[Gib007]

Agreed. £120 for a Skywatcher 17Ah battery and what is it doing now? It sits in the boot of my car until I get sick of it and dispose of it. My actual power source is an 85Ah Marine Deep Cycle battery. Together with a mains charger for it and a couple of leads for 12V supplies and £110. £10 cheaper than Skywatcher's 17Ah and I have 85Ah...

[jason.p]

So am I right in thinking that a car battery of around 60-70 Ah would be OK?

As I have mains power available what is the best way to get the 12V required?

Would a battery charger work?

Thanks

Jason

Sent from my GT-P5110 using Tapatalk 2

[Kropster]

I would say that you need to be extremely careful, if you use a car battery, that you make sure there is no chance of shorting the terminals accidentally.

Put it in a box and cover the terminals.

There is an enormous amount of stored energy that can do very nasty things if unleashed to quickly!