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Will I need an extra power tank for dew heater/controller?


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I'm using the 3-in-1 Maplins Jumpstarter to power my 6SE, which is working just fine.

Although I have a dew shield already, at some point in the next few months I'm pretty sure I'm going to need to upgrade the protection to a dew strip and dew controller. I know I can get a cigarette lighter adapter so that I could plug both the scope and the dew controller into the adapter and, in theory at least, I could then use the one powertank to power both the scope and the dew heater.

But... and this is where I just don't have the technical knowledge... would the one powertank be enough to power both? If so, can anyone tell me how I work out roughly how many hours charge I'd have running both items? The scope on its own right now easily lasts 5-6 hours without even using half the charge, but I'm sure I've read that dew strips can really suck the power quickly?

Reason I'm asking now is I've just seen on another thread that the jumpstarters are currently on special offer at £19.99, which I think is a really good deal... so if I am going to need two, one for each, it may well be worth at least getting the powertank now.

Thanks all :glasses2:

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Hi Psychobilly, thanks for the speedy reply.

At the moment, they're ranging from an hour or so, to up to five/six hours at the weekend, clear skies permitting. Those long sessions have been when the weather has been fairly mild, and I'm not at all convinced I'll manage even half that in freezing winter temperatures, but I guess I'd like it to be the cold, or the clouds, that drives me inside rather than because I've run out of power.... :glasses2:

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The mounts can start to go a bit crazy as the battery voltage starts to drop... Realistically I wouldn't be looking to take more than say 10-12 AH out of one of these "17AH" units and remember that the charger only charges at 500mA so when you add in coulombic efficiency (around 70-80% for lead acid) a 10-12AH discharge is going to take around 24-30 hours to recharge...

Also remember that these batteries must not be left in a discharged state for any length of time afetr use and need to be recharged every few weeks even when they haven't been used

Peter...

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I am SO sorry, I think I understand some of what you've said, but I really am clueless when it comes to electricity/power supplies, etc so I may get this completely wrong, so please do bear with me (and forgive me if I use the wrong technical terms too!) :glasses2:

The first bit about taking no more than 10-12AH, is that referring to if I add up the amp values of the dew controller and the scope, it should total no more than 10-12 to be able to use both with the one powertank? The dew controller I was looking at says it's 5 amp, but I can't find the amp value for my mount anywhere.. is it likely to be over 5 amp, in which case would it be that fact alone would mean I'd need two power supplies?

Or, if both together make them less than 10-12ah, it would then come down to how long the charge in the powertank would last with both of them running off it. To feel happy about having just one power supply, I'd ideally want at least four hours minimum.

So I think from what you've said that it would be sensible to be using two separate power supplies, unless of course I have completely misunderstood everything and really it will be fine with just the one !!

And re the re-charging, yes, I had read about making sure to recharge regularly, even when not being used, so I do make sure I do this.

Thanks ! :rolleyes:

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Battery capacity is measured in amp hours AH..

you multiply the amps drawn by observing time to get an idea of how much capacity you need and then oversize the battery because you dont want to deeply discharge it. The battery voltage will fall off as it discharges...

Charging isnt 100% efficient so when charging it takes longer

Billy on the San Fran

.....

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If you observe from home why not buy a decent mains charger? RVO have a good selection.

That was actually something I seriously considered when I got the first powerpack for the scope.. but then I thought about the wire that would be trailing from the scope to inside the house and how clumsy I am at the best of times, and had visions of me tripping over the wire in the dark, taking me and my lovely telescope crashing to the ground.... I thought I'd best not :glasses2::eek::rolleyes:

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hi there a got the one of flo the skywatcher one i can use the goto scope for about 3 hours a night for about 8/9 days with the radio on and use in the torch on it as well it was not cheap but works a treat, can not say how long the other would work depends on the volts and amps it draws a guess,by the way in 3 years with my 12"never had a dew problem yet a do have the astrozap stuck on the end of the scope all the time

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I think I may have to win the clumsy award of the year then because I *have* tripped over my laptop lead a few times when I've had that out with me!! Luckily I just fell into the table those times and not the scope :rolleyes:

I think for the sake of £20 then I will grab another powerpack as I'm sure there'll be other things I can use it for to power even if I don't end up getting the dew heater/controller. Todd - like you I've been using a dew shield and so far that's been more than adequate. So for those items I definitely plan to wait until the shield isn't enough before spending out on those.

Thanks everyone for all the advice :glasses2:

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  • 2 weeks later...

My Aldi 17ah power tank/compressor is getting a bit old now, and while it will run my EQ5 mount for several hours, if I put my dew controller on, I'm lucky to get 3 hours. I measured the current they draw; the EQ5 takes about 1.6 amps when tracking, and my home-made band dew controller to wrap my 6 inch SCT takes 2.4amps full on, so in all approx 4 amps. So 17ah divided by 4amps is just over 4 hours observing, but as mentioned above as the voltage drops the mount does not like it (gives a dying beep and then the RA motor gives up making a funny whistling sound as if still trying to run, while the hand controller goes dimmer!). So I'm buying a seperate power tank for dew contol only, because I'm also getting a 2 eyepiece dew controller for my Binoviewers. The thing to consider is that if the battery gives up, you will have to go through re-aligning again, and if you were doing a long-exposure astrophotography session, you will have to re-start again, because the moment that tracking is lost, your photo session is over. With a seperate dew control battery, even if it dies, you still probably have a while before the scope/eyepieces cool down and dew starts to form again!

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I wouldn't bother with a battery pack, forget all the lights, bells and whistles that so often come with them and instead get yourself a leisure battery. Use at home to avoid trailing wires and therefore avoid having to buy transformers at extra cost. On the dew strip front, I would recommend buying the 'Dew-Not' brand which is made in the US and I believe is sold by one retailer Modern Astronomy. It doesn't use a heating element inside like the other strips, uniquely it uses a gel which offers a more even heat and here's the best bit, it draws significantly less juice from your battery. Received plenty of positive reviews on the US forum "Cloudy Nights" and one or two (including myself) use them on here. Might help with your amp calculations above.

James

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Is this the power tank? That's cheap.

Yep, that's the one, and yes it is a bit of a bargain, hence why I snapped up the extra one now in anticipation of needing it for the dew heaters. Promotion only lasts until tomorrow by the looks of things though, so if you need one, better get in there quick :)

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