Frequently Asked Questions
Bob Aberle | [email protected]
Is it advisable to charge Li-Poly batteries in your car?
Also included in this column:
- Perry Pumps Web site information
- APP Powerpole High Current Battery Test Clamp
- "Foam-friendly" Krylon spray paint
- It could be your receiver crystal ...
This is the 35th monthly column in which I try to give you the best possible answers to questions you have written or E-mailed to me. Each new inquiry is given a sequential number for identification purposes. Many questions and answers have been posted to the AMA Web site at www.modelaircraft.org/mag/faq/index.asp. Unfortunately that posting stopped in August 2005 and will not continue until this section of the AMA Web site is revamped. In the meantime, if you can't find the subject matter you are interested in, drop me an E-mail or letter and I will try to assist you.
Q275
"I have a new Li-Poly battery charger and was surprised to see that the power input cable employs a 12-volt auto-type cigarette-lighter connector. This cable is intended to plug into the 12-volt accessory port that is supplied with most modern-day automobiles.
"My concern is that I am constantly hearing that you should remove your battery pack from your aircraft prior to charging and that you should never put that battery inside the passenger compartment of your auto during charging.
"If charging inside the car is a concern, why supply a connector that only works inside a car? What is your advice?"
A275
This is a good point. Yes, we do recommend that the battery be removed from the aircraft while it is being recharged. We also recommend that no battery be charged in the passenger compartment of a car.
Auto fires have started while a battery was being charged inside the passenger compartment. This is especially true when traveling (car in motion) and attempting to charge the battery pack simultaneously. You can't be watching that battery and charger and be driving at the same time.
I recently reviewed an electric-powered RC aircraft, and the balanced-type charger that was provided had a 12-volt auto cigarette-type connector on the input cable. I liked the charger and it did have a proprietary balancing connector, so I really wanted to use it.
The easiest fix proved to be a visit to my local RadioShack store, where I purchased a battery-terminal 12-volt DC adapter accessory outlet. It is catalog number 270-1527 and costs roughly $8.
The cable is approximately 20 inches in length. On one end is a pair of heavy-duty alligator clips you attach to the terminals of your auto battery (with the hood open, naturally). At the other end of the cable is the female, or mating, half of the cigarette-lighter plug.
Q279
"I wanted to relate a recent story to you. I had installed a new popular-brand single-conversion RC receiver into my new aircraft. When I made my first flight, I got the feeling that the controls were somewhat intermittent. There were times I commanded rudder or elevator on my sport/trainer aircraft and got no response. On one of my attempted flights I was about to hand launch the airplane when the electric motor stopped and the controls no longer worked. I realize it is hard to diagnose via E-mails, but do you have any ideas on this problem?"
A279
Normally I would tell you that solving your problem could be difficult without having a chance to look at the model's radio and power systems in person. After reading your description of the problem, one might assume it is a loose wire or, more likely, a loose connector. That is always one of the first things to check.
It is especially important to pull lightly on all the cable wires as they go into the connector housing. Sometimes a wire can break off a pin and you can't see it.
If after checking this you still have intermittent control I would try to substitute the receiver for a known-good receiver. If the intermittent problem disappears with the substitute receiver then you'll know that the receiver is the problem.
If substituting the receiver doesn't help, substitute the servos and see if that cures the problem. If still intermittent, check for corrosion inside the battery compartment, check wiring in the power system, and check for a loose or broken solder joint on the switch harness or speed-control connector. On glow-engine models check the battery harness and ignition switch or kill-switch wiring. On electric models, check the speed-control ground connection to the battery pack.
A good way to find an intermittent problem is to use a set of pen-tip probes taped to the servo leads and to the receiver pins. You can then lightly flex the wires as the receiver and servos are operating until you find the problem.
On several occasions I've found a small piece of solder or other metallic object that had lodged into the receiver connector and was causing a short. Removing it cured the problem.
Another possibility is that the receiver crystal may have a hairline crack. Single-conversion receivers with removable crystals can be especially susceptible to this. If you can, try replacing the crystal or taping it in place with clear tape so that it won't move.
However, a recent personal problem turned out to be something different that you might not expect or look for. It involves your receiver's crystal.
I have a new single-conversion RC receiver that is a popular brand and extremely lightweight. My radio system behaved exactly as you described at the flying field.
I did a little networking and learned that for some reason the pins on single-conversion receiver crystals have a much smaller diameter than crystals in a dual-conversion receiver. I also learned that the sockets for these "thin-pinned" crystals don't provide the best fit. As such, when plugged into the socket on the receiver, the crystal can actually "wobble" because it is so loose.
I examined the crystal in my receiver, and it was so loose that it fell out in my hand. I couldn't get at the socket pins to make them tighter, but I did come up with a fix. I wrapped tape around the entire receiver case several times, and that held the crystal tightly in place. My intermittent radio problem went away and I haven't had a problem since.
The message here is to not only check your wiring and connectors, but to check your crystal as well. If your crystal is soldered in place, that isn't going to be your problem. I'd like to hear from you readers if this suggestion proved to be helpful. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
