Charging at the flying field

Written by Don Slusarczyk
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 ( 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 ( It is rated for 12 volts and 66.7 amps (800 watts). I bought mine on eBay ( 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 ( 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



Good article. I've been using a similar power supply for several years to power my chargers at home and when I take my generator along to the field. Our field does not have AC power. I also encourage our members to be very careful when charging lipo batteries in their cars or under the hood. I have a large deep cycle battery in my airplane trailer and have banana jacks outside so all charging is done away from the vehicles. I built a box that houses two SLA (12ahr each) with banana jacks, a digital voltmeter a regulator for 1.5 volt glow driver and wiring that allows switching between 12 and 24 volts for the engine starter. This box also doubles as battery charger supply right on the flight line.

OK, where is the Sportsmen 1,000-watt generator available?

A quick internet search shows me it can be sourced at Sam's Club, Walmart, Camping World, and of course, Amazon.

I looked this up and found it's available thru Lowe's. Hope this is helpful.

Our club (Wasatch Aero Modelers) has installed Solar-powered charging stations on the East and West side of our North-South runway. The big trick we have found is to have large capacity deep discharge batteries in the system. We've had as many as 5 chargers on the system at once with no problems.

Using an automotive class battery for long duration applications is not recommended due to the design of the automotive battery. Automotive batteries are designed to discharge at high rates of current for a very short time; seconds at the most. Discharging at a few amperes for the times needed to charge LiPo and other flying batteries results in overdischarge of the plates and results as well as irreversible accelerated plate wear, potentially leaving you with an inoperable battery later - when you need it most to start your car.

A much better solution is the AGM (absorbed glass mat) designs that are not only good for spinning your electric starters for nitro planes, but they also have better long duration performance and service life for charging airplane batteries at the field. For higher capacity requirements and longer life, consider using a deep cycle marine/RV battery.

Another option is just a bigger lead-acid battery. Less energy storage than a generator, but more than a scooter battery. I got a 122ah deep discharge marine battery (about $110 at Walmart) and have never depleted it in a day. Some members with similar batteries have even connected them to their car alternator, so they never have to haul them to the garage for charging.

I have soldered 12 foot lampcord extensions to my chargers. This way I can have the charger and battery on the ground several feet away from my vehicle, not under the hood. I fly sailplanes, so running down my car battery doesn't ever seem to happen.

For several years I have been using solar charging to recharge flight packs at home and in the field. My setup runs on 12 and 24 VDC with two sets batteries and multiple flight chargers. The solar setup consists of a 100 watt solar panel and solar chargers. I use smaller UPS type gel batteries (4) all fits in a plastic toolbox about the same size as a flight box. So you connect the flight battery chargers directly to them and you don't have to worry if your car will start when your done flying.

You can get a 12 volt economy battery at Walmart for $ 49.99 plus tax. I run 4 DC chargers off mine at home.

Why not use a large capacity, deep cycle battery ( which you charge at home the night before you're going to be flying.....) to charge your batteries at the field ?

Going this route, it's a whole lot simpler, totally functional, QUIET, and Field-Proven.

Spend the $200.00 every six or seven years for a new deep cycle, keep it charged at home, and, at the Field, set up your charging station WELL AWAY ( 20 feet is fine....) from your vehicle. Keep a functional/tested fire extinguisher IN YOUR VEHICLE, but accessible in case of an 'accident'.

I too, many years ago, have run my car battery down, as well as had a charging battery begin to smoke in the back of my station wagon......that's how I started developing the simple system I now use.

No more run down car batteries.....or.......smoldering battery packs under your hood !

I rest my case.

This sounds too complicated, and too expensive! I use a charging system that fits in my "flight box" . Electric starts out from a 7AMP 12Volt battery I bought for $30. Electric goes into my Hobbico QUICK FIELD CHARGER. I plug my Equinox Li Po Cell Balancer into the Charger. Then I connect the Li Po battery to the appropriate plug, follow the instructions, and PERFECTLY QUIET charging begins, and ends with beeps from the quick field charger, DISSALLOWING an overcharge, fire, or too much heat. I could leave out the Cell Balancer 'till the end of the day, since I balanced them the previous day of flying. Being a propeller-type park flyer, it is all I need!

Thanks for the server supplies tips!

The idea of bringing a generator to the field to charge electric models strikes me as incredibly ironic. I’ve been flying electric since the early 1980s (back when it was hard to do) and one of the reasons I do is for the quiet. Now granted, with larger and more power-hungry models now being flown electrically, field charging can be a challenge and involves schlepping something heavy (I used to carry a group 24 deep cycle battery to the field and considered buying a group 27-sized one when I was really active and going to weekend-long events), but a gas-powered generator? Wow. :-)

Don’s idea is quite clever but perhaps a simpler, less expensive, and quieter idea is to use a deep cycle group 27 battery at the field and charge it when you get home. I leave mine in my van with a charger and just plug it in to charge and maintain it.

Another solution is to charge off a lead acid battery with a portable solar panel
connected to your lead acid battery to keep it charged.

Cheaper &. Less. Complex to use the battery ($25) to charge your flight packs and use generator to keep. Battery up.

Cheaper &. Less. Complex to use the battery ($25) to charge your flight packs and use generator to keep. Battery up.

we have a solar system at our field. we installed ourselves. two deep cycle marine batteries.
the complete set up was under $250.00. we run up to 6 chargers at a time. have never drained the two batteries. I highly recommend this type of system.

I have a 900 watt generator that is quite small and can power my two lipo chargers without any problems. This generator (Tailgator) will run for 4+ hours on a full tank so no problem at the flying site.

The CCRC club in Madera, CA just installed solar panels last week so we all can plug in our chargers and go nuts! Thanks CCRC (Aaron and Cruz)!!!

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