Wilga 35 and Rx battery question

The dirt strip airport where my club flies had an open house this weekend. Only a handful of planes flew in, but one was very interesting: a well-worn Wilga 35. I took some photos of it as it landed, taxied and parked. (I just tried to FTP some photo files to my web page so I could post a URL but my FTP program isn't cooperating.) Later on, the pilot started it up so I got grabbed my vidcam. He took off, circled the field a few times and landed. I was surprised to see our club president get out of the Wilga!

It seems one of the club members lost (literally) a Cap 232 gasser to an Rx battery failure earlier in the week. He had mentioned it to the Wilga pilot and the pilot offered to take him up to look for it. He declined! Another club member nearby was asked and he also declined!! Our club president didn't decline the offer though. Up they went. I was getting the video without knowing he was aboard or what they were doing. He spotted the model in a cornfield and called down to the club member by cell phone to direct him to it. What a neat thing!

When I got home, I decided to check the Rx battery in my 25% Giles 202. It's a 4.8V pack of KR-1400AE Sanyo Cadnica cells. After a discharge/charge cycle, the pack peaked at 5.79V with 1356mah of charge. Ten hours later, the pack was down to 5.2V. I was concerned that the voltage dropped by over a half a volt with no load present. Soft short, or nothing to worry about? I'll be ordering a new pack tonight to be safe.

How exactly does one decide for sure if an Rx pack needs replacing? Is the "80% of rated capacity" rule the main factor?

Thanks for any tips, desmobob

Reply to
Robert Scott
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| I was surprised to see our club president get out of the Wilga!

... and it wasn't until this point that I realized that 35 didn't refer to a 0.35 sized engine :)

| When I got home, I decided to check the Rx battery in my 25% Giles 202. | It's a 4.8V pack of KR-1400AE Sanyo Cadnica cells. After a discharge/charge | cycle, the pack peaked at 5.79V with 1356mah of charge.

5.79 volts while it's on the charger? Or off the charger? On would explain why it's slightly higher than I'd ever expect to see.

| Ten hours later, the pack was down to 5.2V. I was concerned that | the voltage dropped by over a half a volt with no load present. | Soft short, or nothing to worry about?

Hard to tell. Was it still on the charger? Perhaps the charger is slightly draining it.

Fresh off a charger, NiCd cells get around 1.41 volts each. That drops off slightly over time, but down to 1.3 volts with no load does seem sort of fast.

| I'll be ordering a new pack tonight to be safe. | | How exactly does one decide for sure if an Rx pack needs replacing? Is the | "80% of rated capacity" rule the main factor?

Some people use that. Some people just replace them after a few years. Some only replace them when the plane crashes.

It may be that your battery (or perhaps just some cells) have developed a much higher than normal self-discharge rate. And unfortunately, cycling doesn't really detect that unless you charge it up and then measure the discharge a few days later.

You might want to consider having two packs in your plane in parallel

-- that's cheap insurance against most pack failures.

Reply to
Doug McLaren

I hooked the pack to my SuperNova charger on discharge/charge and went to bed. In the morning, with the battery still connected but the charger "off" (automatic shut-off after peak-charging the pack) it read 5.79V. I unplugged the charger leads and went to work (7am). When I returned (5pm), the pack registered 5.2V on my expanded scale volt meter. At about 9pm, it's still at 5.2V. It seems that most of my smaller 600mah 4.8V packs read near the 6V mark when tested after charging; at or near the top of the meter's scale. The big pack's reading is barely in the green "good" zone.

Just for the heck of it, I peak charged the five year old 600mah pack I took out of a model and keep on the bench to run my servo set-up tool. It read right at 6V.

I will certainly replace the big pack. I did wonder if it's safe to fly with in the mean time or if I'd be playing Russian Roulette with my model, but I guess I won't take any chances.

Thanks for the helpful information, desmobob

Reply to
Robert Scott

How you do it? Do you need a special reciever or you do it the "electrical" way?

Reply to
EtOH

| > You might want to consider having two packs in your plane in parallel | > -- that's cheap insurance against most pack failures. | | How you do it? Do you need a special reciever or you do it the "electrical" | way?

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You can get fancier than this. Some people use devices that will automatically switch to the other pack if one pack goes back, but you don't need to do this.

Reply to
Doug McLaren

After much monkeying around and testing with the ESV and multi-tester, I believe the problem was with my switch harness. The battery pack checked out fine out of the model and showed a much higher voltage than it did last night (and it hadn't been charged again yet).

The switch harness has been replaced and further testing will ensue. :-)

Thanks for the help, Doug.

Good flying, desmobob

Reply to
Robert Scott

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