[Raven 3] OK, LiPo gurus: How far in advance can I install my batteries?

Hi troops-

So how far in advance of a launch can I button up my AV bay? (I have a bay design that lets me attach the BP charges at the last minute so safety would not be compromised.)

In theory I could charge up my LiPos, install all the bits internal to the bay, and seal it up days in advance of a launch.

But would the batteries hold up? Have any of you done any work along these lines? Would a day be OK? Would a week be OK? Somewhere in between?

Anybody got an opinion here? Thanks...

In theory if you are using a traditional switch and not the magnetic switch you could keep it in there for a long time.

I would not trust it to be in there more then a day. Plus you need to keep in mind the temperature of the battery, if its in a tube in sunlight for even a day that could drastically effect the battery.

Ooh, good point; I should clarify: Magnetic switches. So there must be some minuscule current drain even when off.

I have been told by Adrian "A couple of days to a week"

That being said. I load mine up the day of the launch or night before.

I have actually used LiPo batteries that have been installed for over 6 mos. in the av-bay without a recharge. They still measured 4.2V so I just went with it and it worked fine. In my case it was connected with a physical switch though, not magnetic.

One of the great advantages of lithium chemistry is that it has very low self discharge. If you're using high quality, name brand batteries I wouldn't hesitate to let them sit for weeks before use.

I do it the day I launch.

dixontj93060 said:

I have actually used LiPo batteries that have been installed for over 6 mos. in the av-bay without a recharge. They still measured 4.2V so I just went with it and it worked fine. In my case it was connected with a physical switch though, not magnetic.

Click to expand...

Tim,

I think the OP is talking about the magnetic switches. They have a slight draw and would not last 6 months installed (been there, done that). I don't think the battery will drain itself unless there is a mag. switch in the circuit.

I'd definitely prefer not directly answer that question...........

However,,,,,,,,,

From flying RC aircraft and such,
I have experience with different battery chemistry's....
Pb and NiCad had the biggest memory problem.
If left on a "charger / maintainer" long term,
When they get down to the charger manufacturers preset voltage,
say 95% of peak, the charger automatically turns on and brings them up to say 98% or 99%
then shuts itself off. These chemistry's naturally discharge slowly and the charger turns back on.
After months of this ( winter storage ) you'd go to use the batteries, they show full charge
when you put them under load, as soon as they get down to
95% of peak they are "ready" to be charged again, and are dead.
NiMetal fixed this memory problem a little.
They were a little better, not much.
Lipo is different, they don't seem to self discharge much.
I have had lipo's sit on a shelf for months and they still show charged and still work,, fly the aircraft.
After a few months you don't get full capacity out of it, but it works fine.
After a few normal cycles the lipo's come right back to discharging and accepting their rated capacity...

What I am saying, I lived, I'm certain of it..
The reasons why I think if Bob Krech explained it you'd be better off...

Teddy

GRIFFIN said:

Tim,

I think the OP is talking about the magnetic switches. They have a slight draw and would not last 6 months installed (been there, done that). I don't think the battery will drain itself unless there is a mag. switch in the circuit.

Click to expand...

You are right. I love LiPo's because of the near zero discharge, but not so with a magnetic switch.

dixontj93060 said:

You are right. I love LiPo's because of the near zero discharge, but not so with a magnetic switch.

Click to expand...

I didn't know there was a drain at all from a magnetic switch...

I thought they were mechanical,,,
Guess not.......

Teddy

Question has been asked before, and it is a good one. If you are using an av-bay that uses a Featherweight magnetic switch, then you need to be careful--I think Adrian said no more than a couple of days out and the day of is even better (as cwbullet said). The mag switch has a draw on it even when not 'activated' so as to detect the passing magnet. The 24/29/38mm Featherweight av-bays as well as the Power Perch all use a magnetic switch. You can also buy the mag switch separately, and I would assume the same impact applies.

If you're using your Raven with a Lipo and a more traditional switch, like a Featherweight screw switch, then the timing is a lot less important--perhaps even weeks out depending on the size & discharge rate of the battery being used.

onebadhawk said:

I thought they were mechanical,,,
Guess not.......

Click to expand...

I also thought magnetic switches were mechanical, just a miniature version of a reed switch . Could someone explain how they work?

from the Featherweight site..

•Low quiescent current draw of under 3 micro-Amps. This switch can be left in standby for over a week without significantly draining even a tiny 135 mAhr lithium polymer battery.

Tony

dch said:

I also thought magnetic switches were mechanical, just a miniature version of a reed switch . Could someone explain how they work?

Click to expand...

It uses a Hall Effect switch which is an IC that detects a magnetic field. There's some additional logic to make it turn on or off with a "swipe" instead of just being on/off in the presence/absence of a magnetic field.

https://en.wikipedia.org/wiki/Hall_effect

The Featherweight magnetic switch products (including those used in the av-bays) draw micro-Amps of current from the battery to run the sensor that watches for a magnet passing by. When the magnet is detected, it turns on the switch and keeps it in that state until a magnet passes by again. The stand-by current is very, very small, but not zero. When I have tested with the very small batteries used in the Featherweight av-bay products (130 mAhrs), I think I remember the battery voltage going from 4.1V to 4.08 over the course of a couple of weeks. I have accidentally left batteries in an av-bay for a couple of months, and the altimeter still powered up fine. To be on the safe side, a few days is definitely no problem, but recharge if it has been more than a week or so.

-Adrian

Thanks Adrian and everyone who has replied. The real world experience is much appreciated. I'll load them up Thursday.

Adrian A said:

The Featherweight magnetic switch products (including those used in the av-bays) draw micro-Amps of current from the battery to run the sensor that watches for a magnet passing by. When the magnet is detected, it turns on the switch and keeps it in that state until a magnet passes by again. The stand-by current is very, very small, but not zero. When I have tested with the very small batteries used in the Featherweight av-bay products (130 mAhrs), I think I remember the battery voltage going from 4.1V to 4.08 over the course of a couple of weeks. I have accidentally left batteries in an av-bay for a couple of months, and the altimeter still powered up fine. To be on the safe side, a few days is definitely no problem, but recharge if it has been more than a week or so.

-Adrian

Click to expand...

What a detailed, in depth answer.......
With absolutely usable information......

Thank you,,,,

Can you tell me why lipo's don't self discharge like other battery chemistry's do ???
I've seen it for myself,,, but never understood it........

Teddy

LiPo's should not be stored fully charged for more than a week. If they are not going to be used for more than a week, they should be discharged to "storage charge" of 3.7 to 3.85 volts per cell. Most of the newer LiPo chargers have a "storage charge" mode in their menus. Storing the batteries above storage charge will cause them to swell and shorten their life. I learned this the hard way a few years ago and ruined a couple of 5S 4500 mah packs by leaving them charged.


Here's some discussion from the electric RC airplane fourms.

https://www.rctech.net/forum/rookie-zone/634865-lipo-storage-charge.html

https://www.rcgroups.com/forums/showthread.php?t=1615710

https://www.rcuniverse.com/forum/batteries-chargers-84/7428324-lipo-storage-charge.html


Rob

Rob Campbell said:

LiPo's should not be stored fully charged for more than a week. If they are not going to be used for more than a week, they should be discharged to "storage charge" of 3.7 to 3.85 volts per cell. Most of the newer LiPo chargers have a "storage charge" mode in their menus. Storing the batteries above storage charge will cause them to swell and shorten their life. I learned this the hard way a few years ago and ruined a couple of 5S 4500 mah packs by leaving them charged.


Here's some discussion from the electric RC airplane fourms.

https://www.rctech.net/forum/rookie-zone/634865-lipo-storage-charge.html

https://www.rcgroups.com/forums/showthread.php?t=1615710

https://www.rcuniverse.com/forum/batteries-chargers-84/7428324-lipo-storage-charge.html


Rob

Click to expand...

Wow,, very interesting........
That's another new one..........

I love my old computer charger........
It's a Thunder Power 610C...........
I've gotten great use out of it.........
This makes me think even more,,,,,,
it may be time to replace it.............

Teddy

onebadhawk said:

Wow,, very interesting........
That's another new one..........

I love my old computer charger........
It's a Thunder Power 610C...........
I've gotten great use out of it.........
This makes me think even more,,,,,,
it may be time to replace it.............

Teddy

Click to expand...

Teddy,

According to the TP website, the 610c has a storage charge mode, so you shluldn't need to replace it. TP makes awesome chargers . I have 2 TP 810CD's for my large LiPo's. I power them with two surplus server power supplies wired in series for 24 volts.


Rob

Whatttttttttt,,,,,,,,

I didn't even know it has a storage mode.........
How funny is that..........

Thank you very much Rob...........

Teddy