12v powering options

Hi I'm new to the board and in need of some help. Im an amature astrophotographer and dealing with 12v and 120v power sources. I need to keep my equipment using 12v's an not rely on a 12v to `120v converters these was battery life which I need the most. The equipment I am questioning is fairly easy but my knowledge is none. I need to power my usb hub and DSLR using a 12v power. I primarily use deep cycle batteries and I've posted this on astro forums but no one seems to give a hoot so no replies. Hopefully someone here can take a min or two to help me out. First is the slr I have been using a regular 120v dummy power to keep the slr going because external batteries are a pain to have to keep up with and in a middle of a shot the battery dies I lose time so this needs to change. The converter I need is a 12v to 7.4 2A. I've looked at several but I really have no idea of what to buy. I need to keep this inexpensive and simple to put together.

The other source is my USB hub. The hub is 5v - 3-3.5a. I'm only guessing that a 3A will surfice correct. What are my options and perferably placing these in a simple project box either plastic or aluminum will be fine. I'm not looking for nothing fancy just something simple and easy to maintain. I hope you can help because I've ran out of options

Your specification is somewhat vague.
Are you trying to run the DSLR and/or hub on 120V by boosting 12V to 120V or are you trying to eliminate 120V and convert 12V directly to 7.4V for the DSLR and 5V for the hub. I'm not sure what you mean by '120v dummy power', please explain.

A USB outlet is (should be) limited to 0.5A but something drawing that much is rare, what do you have plugged into your USB hub, it's likely you don't need anywhere near us much as 3 - 3.5A.

Brian.

First of all, the 7.4V and 5V loads have they got a common negative (earth) connection, if they have then the magic words are "12V buck convertor" like -> **broken link removed**
If the 7.4v and 5V need to be floating (no common connection) then the word are " 12 DC-DC convertor". Google is your friend.
Frank

ok a correction is made my mistake I'm trying to not have to use a 12v to 120v converter alas wanting to run a SLR and USB hub off of 12v's using smaller more efficient converters. This is my fault for not being exact on my descriptions. The 12v-120v is a waste of precious time during my runs because I loose hrs of battery time because of its consumption. Thus needing the smaller "buck" or appropriate converters to power the SLR which was stated at 7.4v 3a (I understand now about the 3.5a's not actually reaching that point). The usb hub is the other issue that I said needs a 12v to 5v 3a converter thus making the larger waste of money 12v to 120v converters left at home and can stay out longer because I'm not loosing as much energy going from 12v to a smaller output of 7.4 for the camera and 5v for the hub. I hope I'm looking at this correctly that its more efficient to reduce this amount and not having to increase 12 to 120 then back again a lot of it is wasted in between. I've rammbled enough but thank you and I'll keep this updated once its ordered and finished. Chuckey yes google is a friend but having a second opinion from one's who have had experience is a good learning process to avoid mistakes but everyone that has replied thanks for your responces.

Now we are getting somewhere.

What you are asking for is very 'do-able' and will save you wasting energy doing the double voltage conversion as well as eliminating extra equipment to lug around. Before suggesting the most effective way of dropping the voltage, we need you to answer Franks question in post #3. There is a big difference in the way you produce a floating and a common grounded supply. A floating supply has no ground connecton and can be wired almost anywhere at any time but it does require an isolating transformer. A common ground supply will have the two outputs you want but they are linked through a common ground connection, usually, the negative side of the supply. This type of supply is simpler and cheaper to build. If there is a connection between your DSLR and the USB hub you almost certainly want a common ground supply, let us know, or alternatively, draw a sketch of what connects to what so we can see where the grounds actually are.

Brian. (with a 16" Newtonian and DSLR)

Here are the 2 things that need to run off of 12v's:

1 http://www.amazon.com/gp/product/B003UNRHF0/ref=oh_details_o09_s00_i00?ie=UTF8&psc=1
2 http://www.amazon.com/gp/product/B004F38VFO/ref=oh_details_o03_s00_i02?ie=UTF8&psc=1

This is what is connected to the usb hub

1. 3tb hd
2 rj232 to usb adapter rj232's are used in the telescope community and haven't changed for years and laptops do not come with them anymore and the manufacturers have stated that they will not likely change This is used to control the telescope via laptop.
3 Meade DSI camera this for guide control using software (google PHD guiding software)
4 GPUSB this is used with PHD guiding software to send commands to the mount telling were to move again google PHD and GPUSB it will better explain it than I can sit here and type it

I tried to connect the 3 of the 4 pieces of equipment (I can leave out the rj232 and control the mount but its easier to control the mount via computer) but the laptop is very sluggish doing this for what ever reason I have no clue I guess the laptop isn't managed right (maybe another project?) The laptop I own and use is: an http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c03377414

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I will use the slr adapters "dummy battery" that is wired to the converter just by clipping it off and mount it into the converter thus removing the use for 120v's. The same for the USB hub using just the end that plugs in to the hub and again removing the 120v adapter. I think you understand what I'm trying to do. I could take a rechargable batter open it up remove the batteries and solder a couple of wires but the adapter already has this done and saves me a step. The hub the same way just clip off the end you'd plug into the 120v and use the existing wire.

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Brian I think you know what I'm talking about the 12v to 120v converter waste a ton of juice and a DSLR 120v adapter keeps the heat down in the camera than using rechargeable batteries They share a common ground and 99% chance I wont need a isolating transformer cause they both have 2 common outputs. I just need converters to run the 600D and on to run the usb hub (if its really needed) I tried to run the usb hub via usb that powers it but its sluggish (for what ever reason I plug the power in and its run normally)

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Wait a min gang I dug a little deeper in google and found this and its exactly what I'm looking for for the camera http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4938027

I just need to know what kind of converter

OK, it isn't much different from my system, I use KStars software, Synscan control and a EOS 450D camera.

To be honest, I find the battery in the camera is perfectly adequate for maybe 10 or more hours continuous use so the dummy battery unit is probably overkill but as you have it, you may as well use it. The main current draw on the camera is the flash unit and lens auto-focus motor which I doubt you would be using! So in reality you only need to cater for a smaller current, maybe 0.1A or even less.

The RS232 adapter will draw almost nothing, maybe 0.05A so that isn't a problem. I'm not sure about the GPUSB but assuming this is basically another RS232 adapter but with opto-coupled outputs, it shouldn't need more than say 0.1A maximum. The heavy draw will be the hard disk, is it powered entirely off the USB hub or does it have it's own power inlet? Most external drives use 12V through a small power socket, in which case you can hook that up to the 12V battery directly. The hub electronics themselves draw very little, no more than 0.1A in total.

Assuming the hard drive has it's own 12V feed and all you need is 7.4V for the camera and 5V for the rest, you can probably use one of those regulators on the Cloudynights web site to produce 7.4V then simply add two 3A rated diodes in series with the 7.4V to drop it to around 5V. It would make a very small and cheap supply, (~US$3) solution.

Brian.

ok I found what I'm needing look at this site: https://www.cloudynights.com/ubbthr...=1&PHPSESSID=a300f1794a64f734ca46b53aa82cdc81

except for the nicad battery the wiring is what I'm looking for to use with the camera. The usb hub that is a different story. The usb hub for some reason works better powered than relying on the usb powering the unit.

Looks good.
Your options are to get two of those regulators, join them both to the 12V battery and set one to give 7.4V output for the camera and the other to 5V for the USB hub, or-
Use one regulator, set to 7.4V to feed the camera and use that same 7.4V to also feed the hub through two diodes. The diodes will drop around 0.65V each so around 1.3V in total leaving 5.1V for the hub. That is well within allowed limits. Given their low cost, I would be inclined to use the two regulator solution.

Brian.

I ordered 2 and will await its arrival. I'll start a new thread with this and post it once everything is here. Thanks for your patience and understanding