DIY Field battery - plans are ready, should I start?

[Obi Wan Ken00bi]

Dear SGL,

 

My plan is to do AP in the field, but for that I need a field battery / power tank. The ones you can buy seem nice, but there's nothing like a good DIY project right? Since I'm always running out of space to put things, I've decided the power tank will double as a small table and storage ;-)

 

Power needed:

12 V for Celestron CG5-Goto

8,1 V for Canon 50D

USB for tablet which I use for guiding (Dell venue pro 11)

12 V for red LEDs

 

The components ordered:

2 x DC-DC converter

12V cigarette plug

some on/off switches

2x DC plugs for mount & camera

LCD readouts (because that looks cool, haha)

DC to USB converter

Fuses

2 x red car LEDs

1 x 12V 18Ah lead acid battery (+charger)

I'm using 18mm and 3mm wood (what I have laying around) and black paint.

Here is the plan:

 

 

 

 

 

 

Couple of questions to all of you:

 

- Am I missing something mayor here? Any tips before I break out the power saw?

- Do I need a DC converter from the battery to my mount? (Don't want to blow up/ overpower the mount, but the battery should be 12Vdc )

- In your field experience, where to place my red car LEDs? (not in drawings yet)

- Capacity/ size of fuses per power circuit? I'm thinking 2A each....

 

Cheers!

[jambouk]

I'd get a battery with more capacity than 18 Amp hours. I'd look at 45 amp hour options.

James

[jambouk]

Have you factored in dew control when calculating the watts you need?

I'd also think about some sort of thermal insulation for the battery, even if this is 1inch of polystryene all the way around the battery.

James

[Obi Wan Ken00bi]

Great tip james! Thanks. I will add room for insulation! My imaging sessions will be short (3hours tops) and only one night per charge obviously. Also the tablet has its own battery so that will probably last a while as well. The problem is good batteries are expensive (especially here in Denmark) and I really want to try field AP out first. If I find my imaging time too short Ill buy the second 18Ah battery. I already have the first battery at home so cant exchange anymore....

[Obi Wan Ken00bi]

Btw how does dew affect power output?

[catman161]

I'm with James on that one. Factor in extreme drops in temperature causing problems with battery performance and you'd be better set to over engineer the project rather than under. I use a small 38 amp hour battery for a small grab and go alt-az setup in the field.

Sent from my iPhone using Tapatalk

[m.tweedy]

18ah lead acid=9ah usable without damage to battery.

my main concern would be dew control that will be the biggest draw. i have learned through "bitter" experience that batteries die quicker than you anticipate as there is always something not factored into the equation.

i prefer 2 batteries one for power so if the other that has the main draw of dew, camera etc dies you sill have a system that works and the camera can then be plugged into it. if you have one battery and it dies=game over.

[jambouk]

Dew doesn't affect power output per se, but dew forms when it's cold and most batteries don't like the cold, but what I meant was you need some form of electric dew heaters, and these can be energy consuming. If you are imaging, you don't want dew. Therefore you need dew control. You need to factor this in. There is information out there about how much power they draw; 0.3amp hours per inch of dew band springs to mind from a recent thread, but i might be making that up.

Also, if you are going to all this bother to make a nice unit for your power management, why not future proof as catman says, and go for a bigger battery, 38 sounds like a compromise.

You don't have to use leisure batteries, but if not, conventional car batteries don't like deep discharge so you need one with a good starting reserve. I've previously made a power pack for a mate with an old car battery the garage was going to chuck out, it was a 45 amp/hr one and i took a multi meter to test them all and took the one which still had well over 12v in it. Not all car batteries which garages replace are dead. I topped up the fluid, and gave it a lovely long trickle charge and it works like a dream. And it was free. Need to consider it contains acid though.

I though if i were to make another one, i'd wrap the battery itself in some kind of dew band just to trickle a little warmth into the battery on cold winter nights - no idea if this is necessary or not, but i liked the idea

James

[Obi Wan Ken00bi]

Ok this is all great feedback. Thanks for taking the time. Im not using dew control at the moment but will probably start getting into that as well so best prepare for that right.

I can exchange the battery for a 33Ah or 45Ah OR get an extra 18Ah...

[Obi Wan Ken00bi]

I've considered heating the battery too but then thought: increasing battery life by drawing power to heat itself.... that doesn't sound like energy effective, but maybe it is!

[jambouk]

I wouldn't get another 18amp hr one. I'd go for the largest capacity you can afford and carry - check the weights online and then mimic that weight with bags of sugar, small children; i suspect a 110amp hr might be the weight of a skinny teenager. But weight is a consideration. Not only have you got to lift it, and potentially lift it some height to get it into and out of the car, but also the floor of your unit needs to not fall out. Make sure the wheels on your mobile unit have sufficient load bearing capacity, and make sure they have a wide tread so don't just dig straight

Into soft ground. And factor in the weight if the unit fabric too and any other bits you'll stick onto it. And if future proofing, put plenty of power ports in, two is not usually enough.

James

[Blazar]

Power boxes are great..built mine in a tool chest. 75ah battery in the wheeled base, and the top toolbox housing the circuits etc, as well as the power outputs. I decided to not use vicar lighter sockets, and went for a more robust secure XLR plugs. Also now has dual USB for charging  phones, as well as powering a quark when doing solar. I power an AVX, as well as a 4 channel dew heater most of the time. The top also has a desktop that slots over the handle to sit the laptop on. I have not insulated the battery compartment and it seems to be fine. The build thread was here.

good luck!

[Obi Wan Ken00bi]

So I can exchange my current lead-acid battery:

http://www.batterinet.dk/shop/blybatteri-12-volt-1506p.html

For this one:

http://www.bauhaus.dk/marinebatteri-dual-12-volt-80-amp.html

Or go for the same type of lead acid type but then I only can afford a 45Ah

Not sure which type is best and all... 

[jambouk]

The 80Amp hour one looks like a leisure battery, so will tolerate the discharges better i think. But it is 19kg! That is quite heavy. How heavy is the 45amp hour one? From what you describe, 45amp hour would be sufficient for your needs for one night at least. But if you go camping and stat away for two nights, you may be wishing you got the 80 amp hour one... Hopefully someone else will help.

James

[Obi Wan Ken00bi]

The 80 Amp is NO AGM battery, so will require refilling and it vents more gas (right?) As I'm storing the battery in my basement in my house, I'd like the sealed lead acid AGM one's better. 

The AGM 45 aH is 14 kg so more manageable....

[jambouk]

14kg sounds better. 45 amp hours will be enough For your needs for the next few years i'm sure

[cjdawson]

Dear SGL,

My plan is to do AP in the field, but for that I need a field battery / power tank. The ones you can buy seem nice, but there's nothing like a good DIY project right? Since I'm always running out of space to put things, I've decided the power tank will double as a small table and storage ;-)

Power needed:

12 V for Celestron CG5-Goto

8,1 V for Canon 50D

USB for tablet which I use for guiding (Dell venue pro 11)

12 V for red LEDs

The components ordered:

2 x DC-DC converter

12V cigarette plug

some on/off switches

2x DC plugs for mount & camera

LCD readouts (because that looks cool, haha)

DC to USB converter

Fuses

2 x red car LEDs

1 x 12V 18Ah lead acid battery (+charger)

I'm using 18mm and 3mm wood (what I have laying around) and black paint.

Couple of questions to all of you:

- Am I missing something mayor here? Any tips before I break out the power saw?

- Do I need a DC converter from the battery to my mount? (Don't want to blow up/ overpower the mount, but the battery should be 12Vdc )

- In your field experience, where to place my red car LEDs? (not in drawings yet)

- Capacity/ size of fuses per power circuit? I'm thinking 2A each....

Cheers!

I wouldn't worry about 12v -12v conversion.   I know that my telescope runs quite happily from anything from 11-14 volts.

18Ah is an ok size for a battery, but it does not leave you any room to expansion.

I use an 80Ah leisure battery, (already pictured above) and run everything off it at the same time.

On my scope, I run the following items...

1. Telescope (12v)

2. 2*Dew heaters (12v)

3. SkyFi (6v)

4. SynGuider (5V)

5. EL Panel (12v, but only for short periods when taking Flats)

6. USB for charging iPhone and iPad.

In addition I have considered running a laptop from the battery (and indeed used to do so, but had problems with it and am glad to have stopped that - that's another story)

Your project looks good, but I'm not seeing and futur proofing.  I would hate to see you put in all the effort of making the box only to find out that you need to run more things from it, then have to remake it later.

Also, yes the battery does mean that the box gets heavy, to make that easier to manage my battery box is on wheels, with a handle.  Actually, my battery box is based on one of these.

http://tools.jcb.com/Home/Products/Tool-Storage/Site-System/Site-System.aspx?variation={0AC7F37C-EDFA-44C1-B929-5D11C7EFBACE}

On my box, I have a combined Volt and Ammeter, which I can switch on and off as desired.  I have 4 USB ports, 4 12V auto sockets, and a dedicated socket for the telescope. It also has terminals that I can use to charge the battery without removing it from the box.

The dedicated socket for the telescope has a cable that goes to a seperate box with the electronics for the dew heaters, dc-dc converter (12v - 5V).  This in turn sends the electric to a third box on the telescope itself that distributes the power to the various devices on my scope.

I have left room in my project to be able to add 8.1V for a DSLR, as well as another voltage for another device.

Hope this lot provides you with some ideas.  I'm going look into taking a series of photographs of the whole setup at the weekend (I'm at an astronomy event, so will have my telescope setup and running for most of the day)

[Obi Wan Ken00bi]

Good to hear, I've decided on the 45Ah.

Also, you guys have sparked my interest in dew control (when does this hobby ever stop!?!?!).

Commercially available stuff is too expensive, so i found this page:

http://www.deepskywatch.com/Articles/newtonian-dew-heater.html

He/she uses nichrome wire:

http://www.ebay.co.uk/itm/Nichrome-Wire-Resistance-Nickel-Chrome-Heating-Element-Hot-Cutting-Various-Sizes-/251550106470?var=&hash=item3a918e0366:m:mwLLt5nI5YsX9_bf7oqQpTQ

and suggest to use these babies:

http://www.ebay.co.uk/itm/LED-Switch-Dimmer-Adjust-PWM-Cotroller-For-Office-Lamp-Strip-Light-Efficient-8A-/141650296051?hash=item20fb03fcf3:g:BBsAAOSwPhdVPeVM

Any thoughts on this?

I am going to be using a GSO 8 inch newtonian, 8x50 finder with QHY5-II and a Canon 50D DLSR. I'm thinking of getting 4 of those cheap dimmer and some wire and just test some stuff out first..... 

[cjdawson]

Here's the page that I put together for the first version of my dew heater.

http://astronomy.cjdawson.com/projects/DewHeater.html

And here's the page for version 2.

http://astronomy.cjdawson.com/projects/PowerBox.html

The key difference for you from version 1 to version 2 is that I switch from a resister ladder to nichrome wire.   I'm still using the version 2 system to this day (but it's version 3 now)

I'd recommend using a couple of PWM circuits.  In reality, each of my PWM's use about 2A, so there's plenty of head room.

For my setup what I did was to put the Nichrome wire into heatshrink, then put that into a copper tube which I bent to fit right in front of the optics.  Since doing that, I've never had a problem with Dew on my main scope.

I've just added a second element for my Guidescope, so expect that I'll never have problems with that either.  Only time will tell.

Here's the link that I put up when I was making version 3 of my telescope power.

http://stargazerslounge.com/topic/250514-power-to-my-scope/

[Obi Wan Ken00bi]

Thanks cjdawson & James! Would love to get some pictures from your setup. Good to see more people make their own dew heaters as well as power tanks. also thanks for the link to your thread, it contains a lot of practical info which I'm gonna need  

I've changed the battery to 45Ah (dont want the exide one since it's not an AGM) and I'm going to make room on the frontpanel for future sockets and already ordered some more 12v sockets . Wouldn't have thought of this stuff myself, so really helpful. I will also make room for dew heaters

What do you think of the ebay PWM circuits? They say the idle power is 1 watt which is annoying.....

[Obi Wan Ken00bi]

What gauge of nichrome wire resistance shouyld I choose? 30 SWG or something?

[Obi Wan Ken00bi]

Hmm I'm going for 32

[cjdawson]

I just looked at the resistance wire that I used to make my heater elements, it's 28.

[cjdawson]

I'll go crazy with my camera on sunday when I have my setup all out on display.

[Obi Wan Ken00bi]

Haha you do that

since we have clouds all weekend here in Denmark ill go crazy on the CAD and change the design using all of your inputs

Have fun at the event! Hope you have some clear skies and a good time!