Written by Don Slusarczyk Jets Column As seen in the Fall 2018 issue of Park Pilot.
>> If you are an avid EDF (electric ducted-fan) pilot, the one thing you are fully aware of is the shorter flight times compared with most propeller airplanes that you fly at your local flying field. This means a full day of flying will require bringing a lot of charged batteries or having a means of charging batteries at the field. The field at which I fly is all electric, so it is quite common to see hoods popped up on cars, with chargers attached to the car batteries so that more flights can be made. I was never happy about the thought of having to use my car battery to charge my LiPo batteries. One reason is because I was always afraid of charging too many LiPo batteries and being stuck at the field with a dead car battery. The other reason is because I was afraid of a LiPo fire.
An HP server power supply can be easily converted to a 12-volt DC power supply.
Not too long ago, I witnessed a 3S 2,200 mAh LiPo start to emit smoke under a car hood while at the flying field. The owner was fortunately close enough to unplug it before the battery went up in flames, which could have caught his car on fire. To prevent any mishaps from occurring, I used a lawn mower battery for charging. Approximately 3 years ago, I went to a sealed SLA (lead acid) battery that had a 36 Ah capacity (the kind commonly used to power electric scooters or bikes). This allowed me to charge a decent number of batteries. For most park flying, that is probably a big enough battery for field charging. Throughout the years, I have started flying some EDF jets with larger 6S LiPos in the 4,000 to 5,000 mAh range. Those big packs will deplete the SLA battery after a few charges, so I decided to purchase a small 1,000-watt generator to charge the larger packs.
A dual set of banana plugs were soldered on and color coded for polarity.
The setup I am using now has a Sportsmen 1,000-watt generator (sportsmangenerators.com) as my main power source. It can be found online for approximately $230. This generator is fairly quiet at 56 dB. If you walk approximately 50 feet away when charging, you can barely hear it running. It is not as quiet as a similar-size Honda generator, but a Honda will cost close to $800, so the savings make up for the little extra noise in this application. The other item I bought was a power supply to run my chargers. The generator puts out 120 AC volts, just like a wall outlet. If your battery charger has an AC plug, you can plug your charger right into the generator and start charging; however, many DC-powered battery chargers have a higher charging watt capacity than the AC versions. If you want to parallel charge several packs at once, you will need a good 12-volt DC supply.
A 1K ohm resistor must be soldered to pins 33 and 36 for the supply to operate.
A high-watt, AC-to-DC power supply can be rather costly, but a computer power supply can be easily converted to DC power. Computer power supplies have changed throughout the years, and the newer versions used in computer servers have built-in cooling fans that are rather quiet. The one I use for field charging and for charging batteries in my modeling area is an HP DPS-1200FB power supply (www8.hp.com/us/en/home.html). It is rated for 12 volts and 66.7 amps (800 watts). I bought mine on eBay (ebay.com). They typically cost approximately $50 shipped. To convert it into a usable DC power supply, you will need to buy some 1-watt, 1K ohm, 1% film resistors. A bag of 10 should cost less than $5 shipped from eBay. The resistor must be soldered across pins 33 and 36 and installed for this type of power supply to work as a DC source.
A 3D-printed end cap was added to protect the end and still allow airflow.
Solder female 4 mm banana sockets to the positive and negative leads and add colored heat shrink to identify polarity. I added two sets of sockets so that I can run two chargers from the supply at one time if needed. Finally, a 3D-printed end cover was added to protect the connections and still allow airflow into the unit. The end-cap design was found on Thingiverse (thingiverse.com) and was specifically designed for this model power supply. With this generator and DC power supply, I can now fly all day and not worry about running out of batteries! -Don Slusarczyk [email protected]
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