Please help with my DIY power box project

[antimorris]

I need some help with a DIY project and as you all are much more knowledgeable and adept at this sort of thing I thought I would run it by you to check my current knowledge, numbers, and plans.

Basically I want to make a portable power box for my astrophotography rig that I can use in the field or at home and will last me at least 2 full nights while running everything I want. At the same time I want something that I can replace the batteries on when need be without replacing the entire rig (as we move overseas and back with the military every few years and it seems every move leaves all my power packs dead and not holding a charge and its getting expensive replacing them, not to mention I don’t need things like car jumpers or radios on my astronomy power and it seems they all come with them)

What I am envisioning is a wooden box that has 12v power, 110v power, and possibly powered USB plugs (with an out-USB that I can connect to my laptop). I have seen similar setups here on the forum but the one I remembered seeing a year or two ago isn’t pulling up with my searches and if I recall correctly, there wasn’t exactly a step-by-step build either - just a picture.

It seems that Marine Deep Cycle batteries are the most common way to go with something like this but my knowledge of them is negligible so here are my initial questions.

1 - once this is all put together, how do you charge the Marine Batteries?

2 - I am trying to figure out exactly my power requirements. I am not very power-savvy so I would like you to look this over and tell me if I did this right . . . . on all my devices I looked in the specs for power and it gave me, for instance 12v, 0.8A ... does this mean that that specific device will draw 0.8A/Hr?

If so then here are my requirements:

Atik 314L+ 0.8 12v

CPC800 1.5 12v

Atik EFW2 0.22 12v

Starlight XPress Lodestar USB powered

Dell Inspiron Netbook 1.58 110v (30V requirement-power cord converts)

This brings the total to 4.1 Amps/Hr (if my above assumption is correct - if not: HELP!) ... if I want to assume 9hrs/night from when I turn everything on to when I turn it off then I need 36.9 amps per night so if I want 2 nights from the battery I would need at least a 75amp battery, correct?

3 - I know I will need an inverter to get the 110v outlets - is this going to change the power draw? If so, how do I factor that in? Should I do a second battery for the inverter?

4 - I would like to have everything fused and switched (on/off) as well as a power meter on the whole thing - any ideas of how to go about hooking that all up?

5 - I occasionally would like to be able to have enough extra power to plug in the dew controller, although I have an in-fork mod already done for that and would not need to always have that powered from this box I would like that extra availability. How much extra amperage should I factor in for this?

Once I sort all this out I plan on drawing something up and running the plan by you all before I start this project. Please sort me if my power assumptions are incorrect (nicely please I know I might be completely wrong - that is why I am asking kindly for help) ..... anything else I need to consider?

I know I am asking alot - please if you have it, impart your knowledge. It will be greatly appreciated!!!!

[Psychobilly]

Your going to need more than a 75AH battery to run two nights at 36.9AH/Night the Batteries don't like going below about 20% so a 110AH would be an absolute minimum...

The Current draw conversion for the Inverter will depend on the efficiency of the inverter... I would be inclined to drive the laptop for a 12V Laptop inverter (readiuly available) which will overall be more efficient and remove the 110V from the system...

[antimorris]

I have a 12V plug for the laptop and could plug it in that way, but even still I would like the 110v for the system even if I don't always use it. Better to have and not need philosophy ....

ok didn't know the 20% thing. I doubt I will ever do 2 full 9hr nights with no charging either, but I wanted to plan for the extreme so I don't have to make another one down the road. I will up my plans to a 110AH battery then.

Any other thoughts/corrections/ideas?

[James]

I suspect the figure you have for power consumption is a little on the low side but I'm not sure. (I'll go and do some sums unless someone else adds it up quicker).

Will you be at Kelling next week? If so I'll be bringing this battery box with me, you're welcome to come and have a look (I'll be on the blue field along with a large group of SGL members - pitch 266 I think).

I second Psychobilly's comments on the amount of power you'll need and as he says if you can avoid an inverter thats a good thing as they aren't particularly efficient.

James

EDIT: Of course by the time you have a 110Ah battery the portability side of things begins to suffer!

[Psychobilly]

Is still don't see the point of stepping the 12V battery up to 110v and then down to the typical 17-18V needed for the laptop ... keeping everything at a lower voltage is more efficient and more importantly makes things a lot safer...

Portability... you could always use a pair of 75AH batteries one in the "box" and another kept externally... more capacity overall weight is heavier but splits into more managable

lumps...

Oh and invest in a qaulity battery charger conditioner Optimate/Ctek etc...

Peter...

[antimorris]

I can use the 12V adapter I said I have for the laptop, but I have other things that I plug into the 110V occasionally (remember, I am American and only living over here) so even if I don't use it for the laptop (which now that you reminded me about the power step of it I will use the 12V for it) I would like to have the inverter included with plugs as an option for future other accessories

[Merlin66]

You'll need a trolley dolly to move all this stuff!

A car step up convertor 12V to 18V usually does the computer needs.

I like you do a LOT of moving around and I ended up with a collection of 20Ah gel cell batteries (and an electronic triple stage charger) as the solution. I also have a 12V to 240V AC invertor - I initially used it for the laptop, but after a few surprise dead batteries - is sucks power from a battery better than a Black Hole! I changed to the DC convertor - works 100%

HTH

[antimorris]

I already have a trolley I am planning the box so that it will fit onto the bottom of the scope buggy I have the whole setup on. As soon as I figure out the rest of my design and concept issues, I will post a picture of what I am envisioning and then I can hopefully get some help with the wiring questions

[pete_l]

Never underestimate the power in a tank of petrol. It's one of the most energy dense materials we have (short of using Plutonium )

What I'd suggest is a set of small, carry-able 12V batteries that you can take back to your car for charging at periods during the night(s). That means you'd want at least 3 batteries: one running the rig, one on "hot standby" to take over when you disconnect the flattened running battery and another one on charge.

The trick then is to design a battery system that allows you to have 2 batteries connected to your imaging rig at once, without anything bad happening. To do that, you'd need to connect each of the batteries to a suitably rated diode, and to power the rig from the output of the diode. That way you'd stop current flowing "backwards" into a less-charged battery when you connect up a fully charged one.

Of course, you'd also need the wherewithall to charge these batteries in the field - I have doubts that your car's alternator would be the best solution. Maybe others who know what they're talking about could chip in ...

[antimorris]

Ok here is my rough plan .... maybe this will help show you what I am thinking

[malc-c]

Given the weights and size... a generator would be better option.... would be a bit noisy and smelly though

[antimorris]

Malcolm -

I know a lot of people use a marine deep cycle battery for astro power - the overall box shouldn't be too much larger than the battery itself so I don't see this as a problem.

Maybe its more common to do this method in the US? I know quite a few people that do it there, I just can't find anyone with a how-to specific written up for their designs and when I ask I kinda get "I was just winging it and don't remember"