Wilga 35 and Rx battery question

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Robert Scott - 13 Sep 2006 00:58 GMT

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

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Doug McLaren - 13 Sep 2006 01:20 GMT

| 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.

Signature

Doug McLaren, dougmc@frenzied.us You can't teach a new mouse old clicks.

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Robert Scott - 13 Sep 2006 02:00 GMT

> | 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
[quoted text clipped - 3 lines]
> 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.

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.

> | How exactly does one decide for sure if an Rx pack needs replacing? Is
> the
[quoted text clipped - 10 lines]
> You might want to consider having two packs in your plane in parallel
> -- that's cheap insurance against most pack failures.

Thanks for the helpful information,
desmobob

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Robert Scott - 14 Sep 2006 02:12 GMT

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

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EtOH - 13 Sep 2006 20:45 GMT

> 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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Doug McLaren - 13 Sep 2006 22:28 GMT

| > 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?

http://www.rcbatteryclinic.com/parallel.html

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.

Signature

Doug McLaren, dougmc@frenzied.us
"The wheel is spinning but the hamster is dead."

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Model Forum / Radio Controlled / Air Models / September 2006

Wilga 35 and Rx battery question