Celestron Power Tank 7A

[DiamondSmiles]

Could anyone give me a rough idea how long a fully charged Celestron 7A Power Tank could run a Nexstar 8 SE for please?

Cheers

Ian

[msh1]

im not sure but a 17ah from maplins is cheaper i have got 2 nights viewing because i forgot to recharge and still had some power left

[brantuk]

I'm no electrical expert but this is my understanding. A 7ah battery should deliver one amp for 7 hrs - or 7 amps for 1 hr in theory. If your scope draws 1amp constantly it would last 7hrs theoretically. However - it needs to maintain a minimum voltage range (you can find that in your scope specs) which reduces as battery drains.

Once the voltage drops below a certain level the electronics start exhibiting apparent strange charcteristics - the goto might not be as accurate or it may swing off in the wrong direction. This is normal and doesn't indicate a dud scope or dud battery. It just needs charging back up.

Slewing in both planes simultaneously (eg with goto) causes the most drain - tracking only, considerably less. My 20ah powerpack has lasted in excess of six hours tracking with many goto's in between. I'm sure theres a formula for working out how long a 7ah one would last with your scope but I "guestimate" you'll get 2.5 to 3hrs with no problem.

Bear in mind temperature plays a part too - the colder it is the quicker it will drain. So to will additional gear - especially dew controllers and dew bands. I run the scope off the powerpack and other stuff from a PSU. I'm sure I'll be corrected but hope that gives you an idea

[TheThing]

What Kim said. I'm pretty sure he is right.

I run a RA drive only off a 17amp powertank and it outlasts my stamina to stay out.

TheThing

[Dunkster]

I've had several sessions lasting 4+ hours with my 6SE and C11+NEQ6 (independently!) where it hadn't exhausted the power tank. I'm a goto junkie, so they would have been slewing about plenty! Note that's without a dew heater though (lucky nights?)

[Stu]

I think dew strips are the killers, they do drain batteries relatively quickly.

The comments about cold are also spot on, if you can keep it warmer it will last longer.

Stu

[faulksy]

as kim said spot on a 7ah battery will give you 7 amps for 1 hour or 1 amp for 7 hours but as volts drop your go to might/will act strange also cold temps will drain the battery quicker. i wrapped my batterys in neoroprene to help fight this

[Eigen]

The only way to be sure would be to do a quick measure of current draw of the scope under different operations. Please see a thread I made on the forum pertaining to the SLT mount, won't be an exact comparison but should give you a ballpark value.

http://stargazerslounge.com/topic/156280-synscan-az-goto-current-draw-rough-data/

As you can see it depends mainly on operation. However, you must realize that just because the prescribed power source must but able to handle at least 1 amp, does not mean that the scope will draw 1 amp, that value is there to ensure a steady voltage supply at all possible current draws that are expected from the mount with a substantial safety margin to ensure precise tracking.

While just tracking the mount will draw little current, with max current occurring briefly during GOTO, when mount is moving on but alt/az, this however represents a small portion of observing sessions usually.

However, I would like to add that you will never get a true 7ah from the battery for a multitude of reasons. In addition due to the chemistry of the battery cold nights will decrease its performance and as a result it will drain faster.

If I had an 8SE mount on hand I would gladly run the tests for you, would take 5 minutes. So as of now, I can give little advice as I simply cannot speculate on the current draw of the 8SE mount.

Regards,

Eigen

[Hugechris]

I have the same mount and power source for the c6se and have run my scope for a good 3 hours for 2 nights in row without charging.

Most of the use has been tracking an object for some length of time with a bit of slewing in between.

You should not have any issues with the 8se for a few nights of normal viewing.

[Carbon Brush]

Sorry chaps. A 7Ah battery will generally not deliver 1amp for 7 hours.

Battery capacity, quoted by the manufacturer, is usually at the 20 hour rate and at 20C or thereabouts.

In other words a 7Ah battery will give 0.35A for 20 hours.

When you increase the current drawn, the capacity reduces.

Some manufacturers will specify the fall off, others keep quiet.

As every battery has the same chemistry and similar construction, you can make assumptions.

if you assume that by the time you take a current of 50% of the Ah figure, you are down to 50% capacity, that is a good approximation.

That means in this case you might expect 3.5A for 1 hour.

By reducing the current draw to less than the 20 hour rate, you do sometimes see an improvement in capacity over that specified.

Also, a cold battery has less capacity than a warm battery.

Unless stuck for size/weight, I would not bother with a small battery.

17Ah is not too heavy to lift.

Hope this is useful.

[kirkster501]

I run a CPC1100 with a Dew Not strip and controller off a 17Amp Maplin Jumpstarter in pic.

Had that running for ten hours with no issues whatsoever.

The golden rule with power tanks is to ALWAYS charge them after every use - without exception.

[LukeSkywatcher]

I have the same battery pack (Celestron 7ah) and the 8SE scope. Unfortunately i have not been able to give either one a good test drive due to weather. I have used it a couple of nights in a row for a couple of hours (say about 5 hrs) and it was still running as it should although i did notice that my maximum slewing speed (9) was starting to lag a bit. I'd say you could get the full 7 hrs use out of it but the last couple of hours will be a bit of a waiting game.

I like this pack because its small and light but i'd say you are better off going for a Maplins 17ah or similar, If for no other reason than they are cheaper then the branded ones from astro shops. Not to mention you get longer sessions with them and can run multiple power sources if you want such as laptops etc. A 7ah really wouldnt be good enough to allow this for longer then maybe a couple of hours?

[jonathan]

I would go with LukeSkywatcher on this - a couple of hours of enthusiastic goto operations with a dew heater running (which will be pretty much essential on an 8SE unless you are very lucky with the dew temp).

With this kind of battery you should try not to discharge them less than 50% otherwise it can damage the battery internals. A good charger / battery reconditioner could repair some of the damage; I have a Ring charger which I use on my Maplins 17Ah 5-in-1 tanks, it does a great job of keeping them in good working order; forget the silly little mains plug charger that comes with the 5-in-1, it is fairly useless as a battery charger. Any decent car battery charger will do a far better job, and quicker too.

[MikeWilson]

7Ah isn't much. Depending on your stamina for being outside it'll wear thin pretty quickly especially when you add things to it like dew straps/heaters and/or do a lot of slewing about.

Go with 17Ah as standard. You don't want to run any of the batteries down to flat plus they work less efficiently when cold, so bear that in mind!

All the best,

Mike