Thursday, September 5, 2013

LiPo Charging Station

The new hexacopter I am building will feature three 8000 mAh 6S Thunder Power batteries.  That's over $1,700 per set, and I plan on having two sets!  Now with that much capacity, my Accucel 6 would take forever to charge them.  And there is no way I am trusting $1,700 of batteries to a $23 charger.  Time to step up my charging game.  I figure Thunder Power must know how to charge their own batteries, so I selected their top of the line charger the 1430C.  It is capable of charging at a whopping 1000 watts!

Thunder Power 1430C

But to charge at that rate, you need a big power supply.  I chose the 1200 watt EFuel power supply.  It's good for 50 amps at 24 volts.  With that combination I should be able to charge a set of three batteries in parallel in about 30 minutes.

EFuel 1200 watt power supply

Now the charger and power supply are not delicate pieces of equipment.  But I would like to mount them inside a case for easy transport.  Also I would like to wire everything up once to reduce wear and tear on the connectors and minimize the chance of wiring something incorrectly.  I have this old equipment case that will fit everything nicely.  However am worried about the air circulation.  This stuff is likely to get very warm and I don't want to recirculate hot air into the equipment.  The best option is to mount everything onto a removable platform that will fit inside of the case for storage.

case for the charging system

I found an old street sign in my pile of materials.  I decided to bend it to fit the case.  The bent ends will serve as legs to allow for storage underneath the platform.  I tried to bend the sheet with my Harbor Freight bending brake.  I knew the brake wasn't rated for stock that thick but I figured I'd give it a try anyway.  Not a chance; the sheet wouldn't even budge.  So I clamped the sign to my steel bench and resorted to a 5 lbs mallet to "gently ease" it into shape.  Once bent to shape I trimmed the legs to bring the top to a height of 2 inches.

bad day to be a street sign

Next I disassembled the charger and power supply so I could punch mounting holes in them.  I guess I could have just zip tied them to the platform but I wanted a cleaner look than that.  I carefully chose the locations so that the screws would fit without touching any electrical contacts.  I then laid out the units on the platform, marked the mounting holes, and drilled the platform.

holes punched in bases

sign bent and ready to mount parts

Both units were held in place with 8-32 screws.  The power supply mounted easily.  I bolted down the base and then reassembled the unit.  The charger was a little more difficult.  Because the sides of the unit also act as the feet, I couldn't tighten down the charger until the unit was first reassembled.  So I put toothed lock washers under the screw heads so that I could tighten the nuts without access to the screw heads.

PSU and charger mounted to base
I decided to add a handle to make it easier to remove from the case.  I found a piece of aluminum bar and hand-bent it into shape in a vise.  The middle was sagging a little from the weight so screwed the handle into wooden blocks underneath the base.


wooden blocks for support

Next I needed to wire the charger to the power supply.  I could have just inserted the banana plugs into the binding posts.  But I wanted something a bit more permanent.  So I soldered some gold plated ring terminals to the charger wires and clamped them down in the binding posts.  Then I secured the wires to the base with cable clamps.  No need to worry about the wires coming out or someone hooking things up incorrectly.

ring terminals for binding posts

The charging system fits perfectly in the case.  Now it is nice and easy to transport which helps considering the system is pretty heavy.  A premium storage solution for a premium charging system.  I feel much better now knowing this $430 system is properly protected.

completed charging system

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