12v portable power supply

[Marios (Marios)]

Originally Posted by MrB

Confirmed. At least for the ones I saw, obviously I can't speak for all of the various 'starter packs' out there.

When I was managing a Jaycar store we would get one or two customers a week chasing a replacement battery for their starter pack.
All of the old batteries were about half the weight of the equivalent sized replacement.

Generally SLI type batterys in those things good for a burst of energy to jump start and not much else. If you dont charge them regularly they die a quick death.

[guggle (Michael)]

Yesterday I spoke to someone at Battery World. He suggested a 12v 7AH AGM battery for around $39 (I think the brand was Panasonic) or 9AH for about $10 more plus $29 for a charger. At this stage I don't have any other accessories other than the fan at the bottom of my scope and probably won't get any more for a while, so I think I'll settle for the 9amp battery.

Thanks everyone for your input, it's great to get some good advice!

By the way, I mentioned the fan at the bottom of the scope. I asked what it was for when I bought it, but I've forgotten the reason. Would someone please refresh my memory..

Cheers, Michael.

[raymo]

Your primary mirror needs to be at or very near ambient temperature
to perform properly, so you should put the scope outside an hour or
so before you start viewing. The fan cools the mirror, so you don't
have to wait so long for the mirror to equalise. Until it equalises you will see some turbulence in your view, which is warmth from the mirror
rising up inside the scope.
raymo

[guggle (Michael)]

Thanks!

[Astro_Bot]

Forgive the information dump ...

Originally Posted by guggle

... plus $29 for a charger ... I think I'll settle for the 9amp battery

Power drawn by the fan will depend on size and design, but assuming it's a typical 80mm fan, it'll be around 3W. The NEQ6 in sidereal tracking draws 11W (I've measured it) and 22W at max slew speed, so that's 14W total for the majority of the time assuming the fan remains on. At 12VDC that's equivalent to 1.17A. I'll assume you're happy to go a bit over 50% depth-of-discharge for a battery you intend to replace maybe in a couple of years, so let's say 60% is the limit. With a 9Ah battery, to not exceed 60% discharge at 1.17A, you'll get around 5 hours usage*, less if you slew a lot.

For an AGM battery you should use a charger with AGM mode (they need different voltages). A 3-stage smart charger is recommended - bulk, absorption and float being the three stages. The charger should be sized for the Ah capacity of the battery to maximise life and not overheat the battery, though the acceptable range is fairly accommodating and opinions vary somewhat. The battery manufacturer should state the maximum initial current and (hopefully) afix it to the battery - do not exceed this. In the absence of this info, the rule of thumb is: charger rating (maximum current) = 0.3C, so for a 9Ah battery, the charger should have a rating of no more than 3A. However, AGM batteries are usually more tolerant of a higher initial current, and also going a bit smaller doesn't hurt too much.

* A note on capacity:

Typically, the manufacturer labels the battery with the C/20 capacity - that means when the battery discharges at a current of 1/20th it's capacity (which will take 20 hours). E.g. a "40Ah" battery only has 40Ah capacity when discharged at 2 Amps. Discharge faster and the capacity dwindles.

For a 9Ah battery, C/20 is 0.45A. Your equipment will draw more than twice this current, so the useful capacity will be less than 9Ah, which in turn, will shorten the run time. I don't know the specifics of the battery you're considering, but a rough guess would be a useful capacity reduction of 15-20% and a run-time reduction to 4 hours.

[guggle (Michael)]

Originally Posted by Astro_Bot

Forgive the information dump ...

No problem at all!! Thanks for the info!

[pfitzgerald (Paul)]

I've been thinking of a portable supply also. Does anyone have any thoughts/knowledge about one of these? I'm thinking that I'd be able to run my HEQ5-Pro, two Kendrick dew heaters and the Orion Autoguider camera off this in one go.

PS I'm not trying to HJ the thread, but thought it would be better to add here, rather than start a new thread. :-)

http://www.ebay.com.au/itm/Matson-MA...item19de097a1e

Matson MA44AH 44Ah 12V Portable Power Supply, Camping Power, Fridge

• Output Voltage: 12V DC & 5 Volt DC (USB)
• Type of battery: 2 x 22Ah high quality SLA batteries
• Dimensions: 260mm x 285mm x 255mm
• Weight: 16kg
• Output Media: 1x accessory (cigarette lighter) 12v, 15A socket, 1x merit 12v, 15A socket, 1 x 5v 2A USB port, 1x 50amp Anderson plug
• Protection: 2 x On/Off switch with LED indicators, 2x 15A manual resetable circuit breakers
• Digital voltage display: Battery voltage, current draw, charging current
• LED for: charging status, low voltage, fully charged
• Charging option: 12v DC charger, max 15A

[guggle (Michael)]

WOW! That's some serious power! A bit pricey for what I want now, but it might be useful down the track as I start to add gear. I also have considered the Celestron Power Tank which can be bought from Australian Geographic for about $200.

P.S. If you make a mistake in a post, you can edit it, rather that repost it.

[pfitzgerald (Paul)]

I actually double posted - unintentionally, and found that I couldn't delete the whole thing.

I'm currently using a Celestron Power Tank with my school's telescope. Initially I used it for running an EQ5 mount, but now use it for the dew heater only. When used for just running the scope I comfortably got four-five hours out of it if I ensured that it was fully charged before I started. I did notice that after several months of use its performance was starting to drop off a bit, but since running on mains power at home I haven't tried it on the mount for quite some time.

Paul

[Marios (Marios)]

Originally Posted by pfitzgerald

I've been thinking of a portable supply also. Does anyone have any thoughts/knowledge about one of these? I'm thinking that I'd be able to run my HEQ5-Pro, two Kendrick dew heaters and the Orion Autoguider camera off this in one go.

PS I'm not trying to HJ the thread, but thought it would be better to add here, rather than start a new thread. :-)

http://www.ebay.com.au/itm/Matson-MA...item19de097a1e

Matson MA44AH 44Ah 12V Portable Power Supply, Camping Power, Fridge

• Output Voltage: 12V DC & 5 Volt DC (USB)
• Type of battery: 2 x 22Ah high quality SLA batteries
• Dimensions: 260mm x 285mm x 255mm
• Weight: 16kg
• Output Media: 1x accessory (cigarette lighter) 12v, 15A socket, 1x merit 12v, 15A socket, 1 x 5v 2A USB port, 1x 50amp Anderson plug
• Protection: 2 x On/Off switch with LED indicators, 2x 15A manual resetable circuit breakers
• Digital voltage display: Battery voltage, current draw, charging current
• LED for: charging status, low voltage, fully charged
• Charging option: 12v DC charger, max 15A

Dont bother mate you are paying for the nice box and connecitons, plus the battery is a SLA not a Deep cycle AGM which is best for your application. You can get a 55AH AGM with a power tank box and you would be be better off. http://www.ebay.com.au/itm/AQUATRACK...p2054897.l4276

[pfitzgerald (Paul)]

Thanks for that Marios I'll look into it.

[Marios (Marios)]

Originally Posted by pfitzgerald

I actually double posted - unintentionally, and found that I couldn't delete the whole thing.

I'm currently using a Celestron Power Tank with my school's telescope. Initially I used it for running an EQ5 mount, but now use it for the dew heater only. When used for just running the scope I comfortably got four-five hours out of it if I ensured that it was fully charged before I started. I did notice that after several months of use its performance was starting to drop off a bit, but since running on mains power at home I haven't tried it on the mount for quite some time.

Paul

Those power tanks are waste of monet cheap SLA battery's that dont last the test of time. I strongly suggest you dont use the wall charger if you get a power surge on the mains it will fry youre board. There have been a few threads on tha thappening to people, stay with a battery for the scopes primary source.

[Marios (Marios)]

Originally Posted by pfitzgerald

Thanks for that Marios I'll look into it.

Chargers can be expensive make sure there AGM rated but you dont need a high powered one even 1 .25 amp Charger is good enough jus tmeans will take longer to charge generally over night.

[Astro_Bot]

Originally Posted by Marios

... with a power tank box and you would be be better off. http://www.ebay.com.au/itm/AQUATRACK...p2054897.l4276

That's the same box I have (I have 2). They're a tad cheaper at Repco (RRP $75 last time I looked and sometimes on sale for ~$50, which is what I paid). They may also be available at other stores.

[pfitzgerald (Paul)]

Thanks Guys - So I'm looking at:

One of these,
http://cgi.ebay.com.au/ws/eBayISAPI....tchlink:top:en

One of these,
http://www.ebay.com.au/itm/12V-55AH-...item2a301b4a15

And one of these
http://www.ebay.com.au/itm/PROJECTA-...item4178d08526

Would that be right? It will also need cables/adapters to the three bits of kit yes?

Paul

[Larryp (Laurie)]

Hi Paul
I think you can do much better than that price for the battery. There are sellers who market batteries that are more than 12 months old but are still new and unused, at big discounts, and these batteries are fine-I have been using 40Ah AGMs that I bought for $50.00 each, and they are fine

[Astro_Bot]

Originally Posted by Marios

...but you dont need a high powered one even 1 .25 amp Charger is good enough jus tmeans will take longer to charge generally over night.

Mainly, that's true - 1.25A would be fine for a 9Ah battery, or even larger.

But there's a technicality that's probably worth mentioning - lower rated chargers (that supply a low initial/maximum current) won't de-sulphate the battery as well as higher current chargers (though there are other factors such as age, temperature that come into play). For maximum life, the rating of the charger should be no less than 1/20th the nominal battery capacity.

If you only have one battery, there's no issue - just choose a suitable charger. Difficulties may arise if you use one charger for batteries of different capacity - then you'll have to pick a "happy medium" for your charger.

[Astro_Bot]

I concur with Laurie that the price for the battery is excessive - you can do much better - shop around.

[The_bluester (Paul)]

Yeah, I know that stuff. I bought it as it it was available and cheap and it has done the job for a couple of years so I have no complaints.