Electric aeromodeling history
Following is a post by Simon Chaddock that I picked up on one of the modeling forums.
"I cannot claim to have matched the electric achievements of Col. Taplin but I did make a very light electric flyer in the early 1960s. Not RC but it did fly—just. 40-inch span, it weighed just 2.5 ounces complete! Apart from its ever-so-delicate light-weight construction the clever bit was the miniature bichromate battery, made by my dad.
"Not really a safe plane battery, as it used sulfuric acid as the electrolyte and potassium bichromate (a deep purple dye) as the depolarizer! It was, however, capable of producing a good burst of current (for a short time), so much so that the electrolyte could boil.
"In fact my dad made two batteries. The second battery (inset) was the same size (1 in × 1 in × 1.25 in) and weight (1 oz) as the first but more powerful, as it had five thinner plates per cell instead of three. It could deliver 6 amps at 2 volts for 10 seconds or 1 amp at 3 volts for a minute.
"It's so much easier to fly electric now!"
This begs the question: Who is or was Col. Taplin?
Reader Inquiries
Rebuilding a 5s LiPo pack as a 4s pack
Gary Ritchie of Olympia, Washington, wrote:
"Here is a question I'd like to see you address in a future column. Let's say you have a 5s LiPo pack and one cell goes bad. How can you safely disassemble the pack and rebuild it as a viable 4s pack?"
Technically, it can be done if you are proficient at desoldering. The problem is releasing the tabs from the cells that are usually interconnected by a small PC board. Those tabs are fragile and can be easily damaged if subjected to stress.
You will need some way to remove the solder. This is usually done with a tool called a solder sucker, or more properly a vacuum desoldering tool, available from most electronics suppliers. These cost less than $10 and are a must if you do much soldering on PC boards.
Heat Kills
Eric Richardson wrote:
"Having moved to Ft. Worth, TX from the upper Midwest, it's my practice to store my aircraft in the garage on trickle charge.
"Recently while pre-flighting I noticed one of my battery packs was below flight voltage—so I packed up and went home. I cycled all flight packs on my Triton and each failed to hold a charge.
"Question: what is the common practice or suggestion for storing batteries in hot climates? I'm guessing the high temperatures accelerated battery life as they were only 3 years old."
Storing on trickle charge in a hot environment will accelerate separator deterioration, meaning your packs will develop internal shorts. Don't store on trickle charge and don't store in a hot place. I remove my packs and store them in the refrigerator at about 40°F until I need them. Battery life is cut in half for every 17°F above room temperature (room = 68°F). So if you are storing at 90°F, you are cutting life substantially; mean time between failure is approximately seven years at normal conditions, and you'll see failures much sooner if stored hot.
Parallel Li-Poly Operation
There has been much discussion on RC forums—and almost the same amount of misinformation—particularly about charging. Li-Poly packs can be charged and discharged safely in parallel, as long as each pack has the same number of cells.
One caveat: charging packs in parallel is a problem if you want to balance at the same time. Don't attempt it! Although I strongly recommend balancing (and I do it on every charge), it's unnecessary on every charge. So if you want to bring up a couple of packs by charging them through the power lead at the field, you can feel reasonably confident you will not harm your packs. But make sure to balance them when you return to the shop.
I never recommend charging Ni-Cd or NiMH packs in parallel. Discharging in parallel is okay and is a good way to increase capacity if you need it.
Lithium packs are essentially constant-voltage-charge systems: you charge them to a fixed level (4.2 volts per cell). Ni-Cd and NiMH packs can be damaged unless the charge is controlled and set to terminate based on a voltage-peak profile. No Ni-Cd or NiMH packs are identical; one might peak before the other when in parallel. The one that peaks first starts declining in voltage, and the charger will try to increase current to that pack and limit current to the other. This situation can cause thermal runaway if the charger has enough current capacity.
LiFePO4 (A123) Update
Three years ago I built and installed my A123 packs made from 36-volt DeWalt packs. I am running them in 4S2P and 4S1P configurations and flying year-round here in Florida.
These packs have nearly 200 charge cycles and are still giving good capacity discharges, as shown in a photo comparing an early discharge (7/06) to one today (7/09). I do balance on each charge—not that I think they need it every time, but the FMA Direct Cellpro 10s does it anyway.
There is an excellent discussion by Ken Myers on his Electric Flyers Only website covering LiFePO4 technology. See the Sources section below for the address.
Is Your Glider-Launching Arm Getting Weak?
I was getting along fine launching my 2-meter sailplanes until a flying buddy, Andy Druga, fell in love with the Bird of Time. I was uncomfortable hand-launching this beauty, since Andy's skills in recovering from a bad launch matched the probability that I would not mess it up.
Triton EQ Chargers
You can review chargers when you receive them to make sure they meet all stated performance numbers. I reported on this in September's "The Battery Clinic" column.
Now that I have had the Tritons working on my charging bench for several months, serving a number of my charging requirements, I am happy to report that performance has been flawless.
One thing that has bothered some users is that the charge currents might not be what you select. The chargers are limited in the amount of power they can produce; therefore, if you are charging packs with a higher cell count, you cannot charge them at the maximum stated current rating. Discharge currents are power-limited too.
- The Triton 2 EQ is limited to 100 watts charging and 20 watts discharging.
- The Triton EQ is somewhat reduced: maximum charge power is 63 watts in DC mode and 50 watts in AC mode. Discharge is limited to 5 watts maximum.
The Triton 2 EQ manual covers this on page 19; the Triton EQ manual mentions it only in the specifications. This means that while the Triton 2 EQ states an 8-amp charge capability, you can use only 8 amps on packs with a voltage of no more than 12 volts. With higher voltages, the 100-watt power limit kicks in. The same is true for the Triton EQ. There is nothing wrong with your charger—just read the instructions.
The Triton 2 EQ and EQ follow the accepted peak-charge procedure, monitoring the voltage during the charge and sensing when it peaks. A discharge/charge cycle is shown. As the peak is reached, the charge current is pulsed, so sensing is between the open-circuit voltage and the charge voltage, which gives much more accurate termination than simply monitoring the voltage while on charge.
The curves were plotted using an inexpensive recording digital voltmeter with an RS232 connection to my shop computer. These instruments come in handy if you are doing battery investigations and your charger/discharger does not have a computer interface.
Dave Platt's First Electric
I had the opportunity to visit the Radio Control Association of Central Florida (RCACF) for its July 4 electric fly-in. It was well attended, considering temperatures exceeded 95°F.
Dave Platt, a master modeler, was there with what he claimed was his first venture into electric-powered flight. His original-design TWOCAN, a sleek twin-motor model, featured contra-rotating propellers, a military theme, and retracts. It delivered crisp performance.
Have a nice building season, you lucky dogs. We miss them here in Florida. MA
Sources
- The Battery Clinic
12219 NW 9th Ln. Newberry, FL 32669 www.hangtimes.com/redsbatteryclinic.html
- Electric Flyers Only
http://homepage.mac.com/kmyers/efo
- RCACF
Transcribed from original scans by AI. Minor OCR errors may remain.
