In search of the 'Perfect LiPo'

[dixontj93060]

Which trackers and/or altimeters have a feature designed to protect LiPo's?

Most all high use LiPo hobby electronics use a low-voltage safe circuit (RC planes/cars). In rocketry the Big Red Bee product series has used this feature for years. An excerpt from the FAQ page is below:

Are there any concerns regarding the battery?

YES: Lithium poly batteries can be destroyed if overcharged or over discharged. Always use an appropriate charger. NEVER discharge below 3 volts. Even though the BeeLine Transmitters have a low voltage shutdown feature, the battery can still be over discharged. Always turn the transmitter off when not in use.

 

[dixontj93060]

Tim,

Trackers yes, altimeters (used for recovery) should NEVER shut themselves off to protect the battery (but destroy the rocket or worse).

Actually, you are right, in haste I mis-spoke. My comment was directed at the Missileworks RTx tracker package, not the altimeter.

 

[Random Flying Object]

Tim,

Trackers yes, altimeters (used for recovery) should NEVER shut themselves off to protect the battery (but destroy the rocket or worse).

+1

I would rather loose a LiPo than fail a recovery. Same goes for tracking, my rocket is far more expensive than a LiPo pack.

 

[dixontj93060]

+1

I would rather loose a LiPo than fail a recovery. Same goes for tracking, my rocket is far more expensive than a LiPo pack.

You don't understand. At a 3V level likely your electronics isn't going to be working anyway. So why mess with a LiPo which can be dangerous at high and low voltages (and currents)? This in itself could destroy your electronics. A tracker is going to provide signal for 12+ hours in the first place, maybe more if you reduce the beacon frequency.

 

[Random Flying Object]

You don't understand. At a 3V level likely your electronics isn't going to be working anyway. So why mess with a LiPo which can be dangerous at high and low voltages (and currents)? This in itself could destroy your electronics. A tracker is going to provide signal for 12+ hours in the first place, maybe more if you reduce the beacon frequency.

I'm not sure I understand what would destroy my electronics? When the battery voltage drops too low for the electronics to operate they turn off. I just wouldn't want any type of safety system turning off my electronics just to save a LiPo pack.

 

[dixontj93060]

I'm not sure I understand what would destroy my electronics? When the battery voltage drops too low for the electronics to operate they turn off. I just wouldn't want any type of safety system turning off my electronics just to save a LiPo pack.

It is wholly dependent on the discharge rate. Yes, if your rocket has landed and is just sitting there for a few days, likely no problem except a ruined battery. On the other hand any anomaly in deploy or recovery that leads to fast discharge then you are at risk of battery-induced explosive fire event.

 

[Random Flying Object]

It is wholly dependent on the discharge rate. Yes, if your rocket has landed and is just sitting there for a few days, likely no problem except a ruined battery. On the other hand any anomaly in deploy or recovery that leads to fast discharge then you are at risk of battery-induced explosive fire event.

Something like setting the pyro duty cycle too long?

 

[dixontj93060]

Something like setting the pyro duty cycle too long?

Maybe, but more likely something different like what Adrian A. experienced in testing his Raven's design, i.e., shorting inside the motor chamber. He observed on more than one occasion, when a second stage is ignited apparently plasma fused wires together. Or in my case on one high performance rocket I had the av-bay fold and the charge wires stripped and twisted. Upon recovering the av-bay which landed close to the flight line, the LiPo was hot as h#!!. I pulled the offending wires off and threw the battery into a depression away from the pads and covered it best I could with dirt. Fortunately things didn't go further south and when I retrieved the battery toward the end of the launch day it was still intact although swollen and the plastic wrapping of the individual cells was clearly melted.

My concern is that it seems in general that rocketeers are not as well informed as R/C hobbyists on LiPo's. This makes sense as the R/C guys (and gals) have been using them far longer and utilize far bigger (read more dangerous) batteries. It would be good for everyone involved in rocketry to reference a document like this one from Duratrax that provide practical recommendations under a crash scenario (see info starting on page 3). Knowing what to do when things go awry is essential to safety at our launches.

 

[UhClem]

Maybe, but more likely something different like what Adrian A. experienced in testing his Raven's design, i.e., shorting inside the motor chamber. He observed on more than one occasion, when a second stage is ignited apparently plasma fused wires together.

This was also seen with the AltAcc Timer2. The SOIC8 packaged MOSFETs didn't take kindly to being attached to that load for their 1 second on times.

Easily worked around by inserting a resistor in series with the output. High enough to limit fault currents to safe levels but low enough so that the output current is still enough for the igniter.

 

[BayouRat]

I've been using these. The are currently back ordered because they are so darn popular. I usually buy 6 or so when they have them.
https://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=23135

I usually just heat shrink them to the board.

 

[bill2654]

Wow those Nano's are small.

 

[tim cubbedge]

Hey bayourat - where do you get that clear heat shrink?

 

[bill2654]

I got a couple of these from Hobbyking and I thought that these were small. I have tested these with MW RRC2 and Quarks and it will fire "Crazy Jims" lighters.
Also fits nice in a 29mm nosecone. I think this is the part# 9210000020 for this battery.

 

[Banzai88]

I got a couple of these from Hobbyking and I thought that these were small. I have tested these with MW RRC2 and Quarks and it will fire "Crazy Jims" lighters.
Also fits nice in a 29mm nosecone. I think this is the part# 9210000020 for this battery.
View attachment 286408

I use these extensively. Work great, cheap, and fast delivery.

 

[BayouRat]

Hey bayourat - where do you get that clear heat shrink?

Got it from Amazon. 1.5" Clear heat shrink tubing. I bought 10 feet of it for like $3.00. It works great! Although be careful heating your electronics. I put the heat gun on low and do it a little at a time!

Oops!!! Correction: It was 1.25" not 1.5" and it was 1 meter for $6.00 not 10'.

 

[BayouRat]

Got it from Amazon. 1.5" Clear heat shrink tubing. I bought 10 feet of it for like $3.00. It works great! Although be careful heating your electronics. I put the heat gun on low and do it a little at a time!

Oops!!! Correction: It was 1.25" not 1.5" and it was 1 meter for $6.00 not 10'.

 

[UhClem]

I usually just heat shrink them to the board.

That looks like a GPS patch antenna opposite the battery. If so that is not a good thing to do because the heat shrink will detune the antenna reducing performance. Actually, almost anything very close to the antenna will change its center frequency. I found that removing the heat shrink from the Big Red Bee GPS antenna improved signal acquisition time from about 15 seconds to nearly instant which is what is expected.

That may not seem like a big delay but it shows that the firmware is working a lot harder than it should just to capture a signal.