I took the trainer out Sunday for possibly the last session on skis since the snow is really melting fast. Had two great flights except for my usual prop-busting landings.....not real hard but hard enough to bump the front ski into the prop. I checked the receiver battery voltage ( a 1000 mah 4.8v ) and had 4.9v indicated with a load so I thought I was good to go. Fired up the plane did, my usual control check at full throttle, and was about to take off when I saw my horses run out into the pasture ( we had left the gate open ). So I shut down and gathered up the hay burners and got them back into the paddock. When I went back to start the plane for the last flight of the day I had no response at all on any of the servos. I checked the battery voltage and it was 0.79v. What would cause this sudden voltage drop? a short? I'm feeling mighty lucky that I didn't get airborne that last time but also a bit gun shy about batteries in general. Is there a way to get a back-up battery on board for this situation?

Thanks

Rufcut

Did you possibly leave the plane switched on while you were chasing the horses? It's odd for a pack to drop that much voltage unless it's left on or there is a short somewhere.

You can setup dual battery systems without too much trouble. Although I've never set up something like this on anything 60 and smaller because it's sometimes hard to find room for a second battery and the added weight isn't worth it. But you can run two batteries through two separate switches. Just plug them into two different channels in the receiver. This way a battery failure isn't a killer for the plane.

Ken

Thanks Ken,
I'm sure that the receiver switch was off because the first indication I had that all was not well was when I switched it on and did not get that little twitch from the servos. The plane is a Kadet Senior with a bunch of lead on the nose for balance so I can easily swap battery for lead. I have an extra 4.8v 4 cell 600mah battery. Can I use that with a new 4.8v 4 cell 1000 mah battery? Also, can I plug the extra battery into any open channel on the Rx?

Thanks again

Rufcut

Yes, you can use batteries with different capacities. You just need to make sure they are the same voltage. And yes, you plug the second battery switch into any available channel on the reciever.

Ken

Hi, Use caution when using two batteries with two switch harness plugged into the same receiver and turned on. This set up will only protect a model in the event of a battery failure caused buy an open cell or a broken solder joint seperating the cell in the pack creating an open circuit. if one battery shorts or discharges then since the second battery is connected to the battery circuit in the receiver then it will run down the back up battery. The only real way to correctly use two battery pack is by using a battery back up system that electronicly turns off the problem battery and ingages the back up battery. There is one available from EMS that works very well and has an LED thet turns on when/if the battery goes to the back up battery so you will know th check things out. There may be other systems out there but this is the only one I know of and they work.

I didn't realize it was that simple to get a back-up battery on board. It's always been pilot error that puts my models in the repair hangar. Loss of a plane because of equipment malfunction would be a real bummer, but I guess batteries do fail. Fortunately, I dodged a bullet this time. Where do I recycle these nicd's?

Rufcut

That EMS battery backer sounds like the ticket THERCAV8R. $45 sounds expensive but worth every nickel if it saves the model.

Thanks

Rufcut

There are quite a few trains of though about the devices. One is from the pattern folks that really rely on the KISS principal.. keep it simple stupid. (not meaning you.. just a term.. )

They contend that adding things add points of failure to your system. Most of them rely on a simple dual battery, dual switch, into separate RX channels as RCKen pointed out and shows in his drawing. They feel that any added point of failure will fail. Simple. They do not use the EMS device.

These guys have been at the pattern game for many years now, one has been flying RC and Control Line for around 40 years now and uses dual batterys on separate channels and each on a switch, for a long time now and does not have a lot of faith in added gizmos except perhaps a voltwatch.

I had a battery fail in flight on my Venus II, but I had two batteries set up as described. Before I took off for the third flight, both batteries checked out ok (quick look at the voltwatch). I took off, flew a tank, and landed. I then checked my batteries as I always do.. I check them before and after each flight.. and one checked bad. I swapped it out and recharged both to equalize them, and checked the bad battery. It had a bad cell. Happened in flight because, as I said, it was ok before the flight.

BTW, my process is this: I switch on switch #1 and check battery #1 on the voltwatch then switch off switch #1. I then switch on switch #2 and check battery #2 on the voltwatch. Then I switch on battery #1 so both are on and go flying (of course, if they check out ok).

So, yep, it can happen.. and will happen!! So, I use dual battery configs in most of my planes now, at least the larger ones.

CGr.

I never thought about using two batteries, thats a good idea, it dont over amp the rx though??

There is no such thing as over-amping anything (on powering RC receivers). The system draws as much current as it needs.

The dual battery actually puts the batteries in parallel which keeps the voltage the same but makes AVAILABLE more current. Batteries in series adds voltage. Batteries in parallel adds current.. but only makes it available as draw requires. If it is a 500 ma (mili-amps or .5 amps) system, it will draw 500 ma no matter if there is 5 amps available.

An 1100 mah battery pack consists of four 1.2 volt 1100 mah NiMh or NiCd batteries wired in series. + to - to + to -. and so on, as in a flashlight with a pair of D cells back to back with the + pole of the back dry cell touching the - pole of the one in front of it. Series.

Parallel means that all the + poles are tied together with all the - poles tied together and the output wires are taken anywhere from the + and - poles.

A dual pack in parallel makes 4.8 volts with an available current of 2200 ma.

Maybe the drawing will explain better.

CGr.

Cool, thanks CG

I had time this afternoon to pull the old battery out and found 3 dead cells and 1 with 0.75 volts. Just curious how 3 cells would suddenly go bad. There was no evidence of a short, no burn marks, no discoloration, nothing visible at all. This pack was about 6 years old. Is there a way to tell if a cell is open as opposed to shorted? Also, where do I recycle these dead batteries?

Thanks for all the feedback

Rufcut

Check your switch harness for a problem or ALL of your wiring to see if 2 wires (uninsulated) got together somehow. Sometimes the insulation gets pulled back near connectors and then the wires get together.

Most places that sell NiCd's may recyle them. Call around to places like Radio Shack, Best Buy or Circuit City. Even some large stores like Home Depot or Lowes.

Try to recharge the pack. I bet that it will recharge to proper voltage. However, it will have limited capacity. I always cycle my receiver batteries before each flying season and 1 or 2 times during the flying season. Last year I found a bad pack. It would charge up to full voltage but had limited capacity before dropping off. I will not use a battery that will not take at least 85% of its capacity. If you do not have a good battery cycler, I highly recommend getting one. Over charging NICDs will also reduce their capacity and they will show full initial voltage. This is another reason for cycling NICDs. Cold also reduces battery capacity. Todd

I use one battery on my planes. If its 6 yrs old I would say it was on its last leg before the horses got out and it was just luck you caught it when you did. I would take the lead out and add a bigger battery pack say 2000 mah or better. I run everything at 6 volts or 5 cells . makes the servos snappier and stronger. I use my 4.8 packs for testing now.

Yeah, that's what happened to one pack in my Venus II. I flew it three or so times one day then one of the two packs was just about dead. I'm glad it caught it, but also glad I had two battery packs in that plane that day.

Although it may.. could.. take a charge, it is not a battery I would rely on for flight. It may be fine for bench testing and other stuff, but not for flying. Replacement batteries are cheap enough that it just isn't worth the chance you will take using a questionable battery in flight.

CGr.

I put the dead pack on the charger for about 10 hours and had 1.3v under load. Tore the pack down and still had 3 dead cells and 1 at 1.3v. I'm going to give all the wiring a REAL close inspection before I load the new battery packs. Next, I'm going to buy a few lottery tickets 'cause I'm feeling lucky. I'll let you know Wednesday if I'm moving up to full scale. I have one more question and I'll quit flogging this horse. Should I cycle the new battery packs right out of the box or can I charge and fly a few times before I cycle them?

Thanks

Rufcut

You should always cycle new receiver battery packs.

If you find no problem with the wiring, attach the new battery and turn the system on and just let it set for 5 minutes. Move the controls occasionally. Then check the new battery. Repeat at 10,15m and 30 minute intervals. You may have a defective servo or receiver. You need to be sure that the only issue is your battery pack.

What is the mah of your battery?

Todd

I'll give that a try, Sawdust. What kind of voltage drop should I expect? The new pack is a 1000 Mah. I also have a new 600 mah pack that I was going to use as the back-up when the new switch harness gets here.

Rufcut

What you are looking for is a significant drop in voltage. Say below 4.8 volts. If you have a problem you will probably see it within the first 5 minutes. The best way to check this out is with a watt meter. Then you can actually see what the draw is.

Always test your voltage under a load.

Good luck.

Todd

Is there a chart that tells what the safe operating ranges are for batteries, i.e. 4.8v, 6v etc

There's a really easy way to calculate this on your own. Each NiCd cell should read around 1.3v (probably a little less) off the charger. Once the cells drop below 1.2v it's time to recharge.

CG is correct. There's no such thing as over-amping. mAh is simply a measurement of capacity with respect to time. 1000 mAh means that the battery can draw 1A (1000mA) for an hour, 500mA for two hours, etc... Voltage is like the force that pushes the current (amps) through the conductor. Too much voltage can cause damage, but that's it. The battery chemistry simply creates free electrons for power.

When testing, I usually put current meters in the airplane circuit to calculate how much draw there is. You don't have to, but I am finicky.

The reason the voltage drops is because it is mathematically linked to current. Voltage = current x resistance (V=IR) If you lower current while maintaining the load (resistance), then voltage drops.

As for the possible shorted battery draining the (still) good one, couldn't you just put two diodes in-line so that it doesn't do that. Granted, you would have to disconnect the battery to charge it. OR,,, it just came to me, how about if you simply made a single "Y" connector wire setup that has a diode in each line between the "Y" and the battery and then, put another termial on each "Y" section between the diode and the battery. Those would be your charging jacks and the single line would then connect into your receiver, switch line or whatever. Maybe I'm thinking too much.

... sling it in the bin and get a new one, its 5 years old so as mentioned previously, its probably had it anyway

I wouldn't do that. A forward biased silicon diode exhibits a voltage drop of around .7 volts. I would just say check your batteries often and don't worry about redundancy until your airplane costs the better half of 1 grand or is irreplaceable.