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Old Jul 09, 2011, 04:00 PM
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Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
Build Log
My RC LiPo Field Charge Box

I'm building a small field box to house my battery charger, batteries and charge leads. I typically use Solidworks to plan and design my builds and this one is no exception.


---Purpose: I want to be able to charge my LiPos at the flying site (park or air field) without having to move and pack up my charging equipment from my flight box (which is somewhat large and heavy). I want a mostly self contained, small, and light(er) weight box I can load up easily for those quick trips to the park for some park flying.



---Materials:
1/4" (5mm) ply from Home depot
Edit: I'm now using 1/8" ply from the LHS. It's flatter and I think 1/8" will be strong enough.



---Equipment:
-Protek RC Prodigy 65AC http://www.amainhobbies.com/product_...rger-6S-5A-50W This charger has a low input voltage cut off so I'm not worried about over discharging my power source batteries.

-Two 4S 5000mAh LiPo batteries wired in parallel as a power source. These http://www.hobbyking.com/hobbycity/s...Warehouse.html or these http://www.hobbyking.com/hobbycity/s...Lipo_Pack.html are what I had in mind. Basically, any high capacity LiPo will do, I chose these as they are inexpensive. I'm going with 4S because my charger can handle 11v - 18v DC input. A 3S battery wouldn't be able to supply its full charge because it would get cut off at 11v. I would estimate that this power source would charge my 3S 2100mAh batteries 6 or 7 times. Both of my favorite park planes and the 450 clone I'm building all use the same batteries. With the 4 3S batteries I have now, that is potentially 11 flights before I'm out of juice.
I've changed this to using three 3S 5000mAh B-Grade LiPos http://hobbyking.com/hobbyking/store...dProduct=15512
Quote:
I've discovered that the low input voltage for my charger is only adjustable between 10 and 11 volts. So I've decided I'm going to use 3S batteries instead of 4S so that I don't have to keep checking my my input voltage manually to make sure I don't over discharge the batteries. 10 volts is a pretty good cut off for a 3S lipo anyway.

So because of this, I'm going to try some of those B-Grade LiPos from HK. http://hobbyking.com/hobbyking/store...dProduct=15512 Even at the full 5 amps my charger can do, it's only drawing about 2 to 3 C from a 3S LiPo. Plus, those batteries are super cheap!

I've done a little math in figuring out the cost effectiveness of each solution (4S and 3S)

The 4S 5000mAh is $23.65. 14.8v * 5Ah is ~ 74Wh at 3.1Wh/$1
The 3S 5000mAh is $16.58. 11.1v * 5Ah is ~ 56Wh at 3.4Wh/$1

Another factor is that particular 4S is on back order... so who knows that it'll come back, the closest battery to it is $29.99 and is on back order as well.

So now the plan is to use three 3S 5000mAh B-Grade LiPos.
-I have a couple of nice contura switches left over I'll use to turn the charger on and off.



---Design:
-Storage: It will have one lower drawer to hold my batteries. It's big enough to hold 10 of the 3s batteries I use. I don't have that many batteries, but that's just to give you guys an idea on its size. It has one upper drawer to hold my charging leads and maybe a couple of small tools I might use.

-Battery bank: There will be a compartment next to the upper drawer, but accessed from the rear that will house the three 3S 5000mAh batteries.

-Charger Tray: This is designed around my battery charger. It will allow my DC battery cables to be concealed and out of sight. It will also allow an AC cable to be plugged in, but stored out of sight when not in use. A cut out on the right box panel will allow access to the charge ports on the charger.

-TX holder: I didn't design them on Solidworks, but there will be posts on the top or back that I can hang my Transmitter on as well carrying handles on the box to facilitate easy transport.



---Youtube links:
http://youtu.be/QhS12TyZcAY?hd=1
http://youtu.be/ax8b-KBzy48



---Feedback: I'm looking for feedback on my design for possible improvements to the actual box. As well as comments and suggestions for my method of charging the batteries. Anyone else use high capacity LiPos as a source for charging other batteries?

I know some will suggest just using a car battery, which is what I currently do. I'd rather not have to load up a heavy car battery, or have to open the hood on my car and charge my batteries in the parking lot rather than close by on the flight line. Besides, if it ends up being a long day, and I just absolutely have to keep flying, I'll hook up to my car.
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Last edited by Libtekguy; Jul 24, 2011 at 08:45 PM.
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Old Jul 09, 2011, 04:07 PM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
To give you guys an idea on how my other builds have turned out. Here is my full size flight box I use for my nitro plane. I has a 60 oz fuel cell, 7Ah battery and electric fuel pump for fueling and some battery charging.
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Old Jul 09, 2011, 05:58 PM
KK4NZS
Nelapaty's Avatar
Virginia
Joined Sep 2006
1,484 Posts
Nice....I Like the color scheme
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Old Jul 09, 2011, 08:13 PM
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lipoflyer's Avatar
Australia
Joined Nov 2010
2,876 Posts
love the shark teeth. I just wonder if a handle would help you carry twice as much?
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Old Jul 10, 2011, 12:14 AM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
I've discovered that the low input voltage for my charger is only adjustable between 10 and 11 volts. So I've decided I'm going to use 3S batteries instead of 4S so that I don't have to keep checking my my input voltage manually to make sure I don't over discharge the batteries. 10 volts is a pretty good cut off for a 3S lipo anyway.

So because of this, I'm going to try some of those B-Grade LiPos from HK. http://hobbyking.com/hobbyking/store...dProduct=15512 Even at the full 5 amps my charger can do, it's only drawing about 1C from a 3S LiPo. Plus, those batteries are super cheap!

I've done a little math in figuring out the cost effectiveness of each solution (4S and 3S)

The 4S 5000mAh is $23.65. 14.8v * 5Ah is ~ 74Wh at 3.1Wh/$1
The 3S 5000mAh is $16.58. 11.1v * 5Ah is ~ 56Wh at 3.4Wh/$1

Another factor is that particular 4S is on back order... so who knows that it'll come back, the closest battery to it is $29.99 and is on back order as well.

So now the plan is to use three 3S 5000mAh B-Grade LiPos.
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Last edited by Libtekguy; Aug 28, 2011 at 06:51 PM.
Old Jul 10, 2011, 04:27 AM
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ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,796 Posts
Keep in mind that even though your charger will cutoff charging when the input voltage drops to 10 volts the charger will still draw some current from your source batteries. If you should fail to disconnect your source batteries (turn off power switch) when done charging the low current through your charger will discharge your source batteries. (Just like the ESC in your plane.)

Glen
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Old Jul 10, 2011, 11:40 PM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
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Quote:
Originally Posted by ggcrandall1 View Post
Keep in mind that even though your charger will cutoff charging when the input voltage drops to 10 volts the charger will still draw some current from your source batteries. If you should fail to disconnect your source batteries (turn off power switch) when done charging the low current through your charger will discharge your source batteries. (Just like the ESC in your plane.)

Glen
Agreed, that's why I have that switch on there. The charger doesn't have an on/off switch. The switch will disconnect power completely.
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Last edited by Libtekguy; Jul 23, 2011 at 07:41 PM.
Old Jul 23, 2011, 07:35 PM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
Started constructing the box today. I cut out the two side panels and bottom panel. I'm using 1/8" plywood from the LHS. I used 2'x4'x1/4" panels from Home Depot for my big box. They worked well, but these small 1'x2'x1/8" panels from A Main Hobbies are warp free and easy to work with. This project should go much faster than the big box.


I'm still thinking about how I'm going to finish the box. I've been thinking about Covering it in monokote, but I'm not sure how tough it'll be. Also, I've modified the design slightly so that it can nest inside the big box.
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Old Aug 28, 2011, 06:48 PM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
Some more progress

Made some more progress on my box. I cut out some more panels and started gluing them together. I started mocking up and drilling/cutting holes into the appropriate locations for wiring, switches and plugs.

I'm not real thrilled about how high up the switches are on the top panel, I'd rather have them centered. Because of the AC power cable getting in the way, and going lower on the panel would have made the mount too shallow of the switches, the switches are at only place they could be.

I just need to make a couple quick panels, the drawers, then fill/sand it, paint it (haven't decided one scheme yet though [I'm thinking a blue nosed mustang theme]), mount the rest of the electronics and it'll be done!
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Old Aug 28, 2011, 07:20 PM
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ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
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Looks pretty good so far. Have you given any thought about how you are going to carry it? Handles, etc?

Glen
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Old Aug 28, 2011, 10:33 PM
This we'll defend
Libtekguy's Avatar
United States, CA, Sacramento
Joined May 2011
68 Posts
Quote:
Originally Posted by ggcrandall1 View Post
Looks pretty good so far. Have you given any thought about how you are going to carry it? Handles, etc?

Glen
I got some handles from Home Depot that were not my first choice, but they were on sale for $.50 each, so I went with them. I'll post some pics when I get them mounted.
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Old Nov 11, 2011, 10:11 AM
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wareck's Avatar
France, Champagne-Ardenne, Francheville
Joined Aug 2009
21 Posts
Hi
Can you send to me the solidwork files?
I would like to adapt your field box to my charger...

Olivier
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Old Nov 11, 2011, 11:35 AM
KK4NZS
Nelapaty's Avatar
Virginia
Joined Sep 2006
1,484 Posts
Your wiring diagram looks similar to the one I will be building i will be using relays to switch between battery and powersupply..looks very clean good job on the design and building..
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