Battery and inverter for shed/observatory

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JP5

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#247851 26-Feb-2019 21:56

Hi all.

I have an observatory out in my paddock and I need some power in it so I can keep my laptop and telescope going for a few hours at night. Currently my plan is to setup a battery and inverter out there and just bring the battery back and charge it from the mains during the day as needed although it'd be nice to maintain the option of adding solar later. I don't have any electrical experience though so I'm hoping to get some feedback on my plan just to make sure I'm not missing anything.

From what I understand so far, I'm going to need the following equipment:

DC to AC Pure sine inverter (currently thinking 600w continuous)
12v Battery (thinking 120ah AGM)
Battery cabling (thinking AWG 4)
Fuse or circuit breaker (thinking 60A)

Am I missing anything so far?

As far as the inverter goes, I believe a pure sine one (as opposed to modified) is necessary if I want to power a laptop? My minimum power requirement is only about 200w (laptop 100w + telescope mount 50w + some headroom for efficiency) but I figured I'll go for 600w as I don't mind paying the cost and would like some headroom to power more stuff in future (tools, stereo). I don't believe anything I'll be plugging in will demand much in the way of surge rating so do I need to worry about that? Would there be any issue with this inverter?

For the battery I want to be able to get about 4hrs out of it at a time although more could be useful. I'm not sure what my optimum type of battery would be here but so far I'm thinking AGM would be good as they can discharge down to about 50%. If my calculations are correct I would get just short of 4hrs @ 200w with a 120AH AGM battery? I'm also considering lead crystal. Apparently they can discharge all the way down amongst a host of other benefits. I'm thinking I could get something like an 70ah lead crystal battery and even though it costs twice as much as an agm, apparently they can deliver about 3x the cycles so it sounds like a much more efficient option to me in the long run. Considering this.

The cabling to connect the battery and inverter is something I'm really not sure about. With a 600w inverter I believe I'll need cabling to handle 60A. The tables I've found online seem to contradict each other and while I probably only need 6 AWG wire I think I'll go with 4 AWG (21mm sq.) just to be on the safe side. Anything else I need to consider here? Do I need to worry about cable length at all if I keep them under 30cm? If I buy the cables individually, is there any difference between positive or negative wire?

When it comes to a fuse or circuit breaker - do I actually need one? Presuming that it would be prudent to have one anyway, I'm not sure what amperage rating I need. Do I need one that correlates to the surge rating on my inverter or the continuous? If the latter, then I believe 60A is what I need, correct? Is there any reason to go for a circuit breaker over just a fuse? And could someone please link me to a fuse that would be appropriate for this type of setup so I know what I'm looking for.

Anyway guys I'd appreciate any advice you can give. Thanks in advance :)

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#2187819 27-Feb-2019 06:51

why do you need cabling or the fuse? the inverter will have a way of connecting it to a battery (it should based on previous experience) and they have protection built into them.

a solar battery Charging system is pretty cheap these days so it might be worth getting on from the get go and just mounting it when it has sun most of the day.

rp1790

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#2187826 27-Feb-2019 07:36

You could just buy a kit

Solar Kits: http://sunnytech.co.nz/product-category/solar/solar-complete-kit/frame-panel-rv-package/ and a battery

Battery: http://sunnytech.co.nz/product-category/battery/

Inverter: http://sunnytech.co.nz/product-category/solar/dc-ac-inverter/

I've just bought a complete setup from these guys and they were very responsive, bought on Sunday, shipped Monday.

timmmay

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#2187834 27-Feb-2019 07:53

Those batteries are around 35kg, I don't think you want to be carrying it around.

Jase2985:

why do you need cabling or the fuse? the inverter will have a way of connecting it to a battery (it should based on previous experience) and they have protection built into them.

a solar battery Charging system is pretty cheap these days so it might be worth getting on from the get go and just mounting it when it has sun most of the day.

I've blown the fuse between the battery and the controller thingy on my small solar setup a few times while messing about reconnecting it. I guess it protected something.

Fred99

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#2187866 27-Feb-2019 08:51

JP5:

As far as the inverter goes, I believe a pure sine one (as opposed to modified) is necessary if I want to power a laptop?

Nope. I've never had any issue at all using cheap Jaycar modified sine wave inverters to power/charge laptops (Macbook and other) in a boat.

trig42

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#2187871 27-Feb-2019 09:05

AWG 4 cable is pretty thick stuff, don't see you needing that for connecting a battery to a 600W inverter.

If your 240V appliances are drawing 200W, that is ~1.2 Amps. The maximum a 600W inverter will draw maybe 5 Amps (depending on what it's surge is rated at). Just grab some cheap jumper cables and use them - they'll be rated at far more than you need.

ajbw

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#2187878 27-Feb-2019 09:15

I'm intrigued. I also have a solar-powered observatory. But my numbers are about two orders of magnitude lower than yours!
Are you sure you've got the power consumption numbers right ?

First off, the telescope. Astronomical telescopes are probably the lowest-geared objects on Earth. So they take almost no power. Meade used to supply a power-pack that took D-cells, for example. I ran my telescope from two cells out of a worn-out 3-cell Lipo quadcopter battery. It's been fine for the the last three years. Much better than the 12V lead-acid battery that preceded it.
The two cells are charged from a Dick Smith (remember them?) car battery windscreen-mounted solar charger, on the ground outside facing north, behind a bit of bent perspex to keep the rain off. It goes into a tiny DC-DC converter that takes the 12V and turns it into 8V at a max 1A (which it will never get to, because the solar panel max output is about 100mA).
Despite media hype, charging LiPo cells is much easier than charging lead-acid cells if you only charge them to 4.0 rather than 4.2 volts per cell. The added benefit is that they then last forever.

The whole setup cost about NZD50...

Second: the laptop. 100W? Do you have a fireproof lap :) ? At 100W a laptop would run for about half an hour on full charge. Have your worked out the average power consumption?

Why not just use the laptop on its own batteries? It worked fine for me.

Also consider that if you do run a lot of power, you will be creating warm air currents which can disturb the air (and hence the seeing) around the observatory.

It's quite possible that I have misunderstood your situation; in which case, please come back with some more detail!

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CJC

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#2187975 27-Feb-2019 11:58

Following on from ajbw, do you need to supply 240V? Because if the actual voltage requirements on each device are lower, then you could end up using a decent chunk of your battery (12V DC) to convert to 240V (AC), then back down to 19V (DC) just for the laptop.

JP5

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#2188066 27-Feb-2019 12:45

Well I'm glad I asked around here first because it seems I was heading down the wrong path!

You could just buy a kit

Solar is definitely an appealing option and those prices seem very good so I might just go for that. For now though I just want to work out my battery + inverter situation.

I've never had any issue at all using cheap Jaycar modified sine wave inverters to power/charge laptops

Good to know. From what I understand, the risk (if there is any significant one) is to the ac adapter anyway rather than the laptop itself.

If your 240V appliances are drawing 200W, that is ~1.2 Amps. The maximum a 600W inverter will draw maybe 5 Amps (depending on what it's surge is rated at). Just grab some cheap jumper cables and use them - they'll be rated at far more than you need.

Do the cable amperage requirements not need to be adjusted for 12v? So say 1200w surge @ 240v is only 5A but at 12v but the same amount of power @ 12v would require 100A? Is this not a big part of the reason 24v/48v are preferred over 12v in battery banks? I'll be very happy if I can get away with only using jumper cables so I'd appreciate a confirmation here.

I'm intrigued. I also have a solar-powered observatory. But my numbers are about two orders of magnitude lower than yours!
Are you sure you've got the power consumption numbers right ?

I have been overestimating here. I measured the power consumption of my laptop using one of those power meter wall plugs and at its maximum draw it'll take 100w but when I've just got the astro apps open it just sits between 45w and 60w. Uses about 30w when idle. It's a very inefficient laptop and the battery only lasts 90-120 mins which is not at all long enough. As for the mount, well the adapter says 2A @ 12v and I think it only uses that at full slew. It's average utilization is probably less than 1A. So in reality my average power requirements are probably below 100w.

With all that said though, I do still want more power capacity. It's not just a little observatory but more like a big shed so I'll definitely find more stuff to plug in over there. The laptop + scope mount is just the minimum I want to be able to power.

Following on from ajbw, do you need to supply 240V? Because if the actual voltage requirements on each device are lower, then you could end up using a decent chunk of your battery (12V DC) to convert to 240V (AC), then back down to 19V (DC) just for the laptop.

For the moment I don't need 240v. The laptop is 19v and the scope mount is 12v. If there's a cheap way I could do dc to dc off of a battery for both the scope and laptop I would consider at that. As mentioned above though, I do want to be able to plug in more stuff over there so 240v makes sense in that regard.

Thanks again everyone.

solutionz

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#2188127 27-Feb-2019 14:30

Have you tried searching for a (12v) car charger for you laptop? They're available for most models, no inverter needed then.

Fred99

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#2188279 27-Feb-2019 15:58

trig42:

AWG 4 cable is pretty thick stuff, don't see you needing that for connecting a battery to a 600W inverter.

If your 240V appliances are drawing 200W, that is ~1.2 Amps. The maximum a 600W inverter will draw maybe 5 Amps (depending on what it's surge is rated at). Just grab some cheap jumper cables and use them - they'll be rated at far more than you need.

Oh no it won't - I think you missed a decimal point. 600W/12v - it'll be drawing more than 50 amps at full 600W load. Cheap jumper cables aren't a great idea, you'd really need large terminals crimped on to the end of appropriate size cables, bolted on to the battery terminals, cable size dependant on length of cable.

SomeoneSomewhere

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#2188332 27-Feb-2019 18:01

As above, 600W at 12V is 50A plus losses.

For large cables that may be regularly disconnected, you want flexible cable for longevity, rather than solid/stranded as found in most mains wiring.

AWG is US sizing; unless you are buying the cable from overseas, expect metric sizes. Probably 10mm^2 or larger; you could probably get away with 6mm^2.

You may want a state-of-charge meter of some kind.

But a car charger would be my choice. Standing losses on inverters, especially large ones, can be significant.

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richms

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#2188424 27-Feb-2019 20:02

You can get some nice affordable pre-crimped cables with 50A anderson powerpoles on one end and rings on the other end off aliexpress, which would take care of your disconnects etc. - That will probably be enough for you.

Check the draw on the gear, If you want to minimize cabling losses get 24v stuff and a 24v inverter and 2 smaller batteries. 12 is a bit crap really and people only use it because that is what is in cars. You can get 24v led strip etc for your lighting there and remove any inverter losses on that.

Richard rich.ms

JP5

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#2194845 10-Mar-2019 00:06

Thanks for all the advice everyone. In the end I went for a solar setup from the outfit rp1790 ordered from. It all arrived very quickly and intact, although the battery has a little bit of sulfation around the positive terminal - is that something to worry about?

Anyway, I havent set it all up yet but I have a small wiring query. I have a 30A charge controller and I plan to use 10mm^2 cables to wire it to the battery. I'll also have a 32A breaker in between them as well. I'm just wondering that because the charge controller and inverter cable lugs will both be making contact at the battery terminals, does that mean I need wire between the battery and the charge controllers circuit breaker that matches the gauge of the wire between the battery and the inverter (50mm^2 as it's a 1200w inverter)? Or will I be fine with the 10mm wire?

Thanks.

SomeoneSomewhere

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#2194971 10-Mar-2019 11:24

10mm is fine. The circuit breaker will stop more than 32A (circuit breakers operate on long term averages or short term very high overloads, more than 32A can flow temporarily, yada yada yada) flowing in that portion of cable.

SomeoneSomewhere

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#2194972 10-Mar-2019 11:24

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