Altus Metrum LiPo Batteries

[Lord Rory Gin]

I was reading up on LiPO batteries for AM and came across this statement in their manual:

Spark Fun sells batteries that have a matching connector with the correct polarity. However, these batteries include an integrated current limiting circuit. That circuit will cause the battery to shut down when firing the igniter circuit. Do not use these batteries unless you remove the current limiting circuit.

I just happen to have Spark Fun's 400 mAh LiPOs and visually I can tell they have the limiting circuit board on them. Does this mean I can't use these batteries? Do I have to remove the circuit board for them to work? And lastly, WHY does this circuit cause the battery to shut down as above?

 

[roytyson]

I don't remember the exact reason Bdale told me, but yes, it is recommended to remove it. I do this for all of mine. Just peel the yellow tape off, snip off the wires (one at a time!), snip off the board, solder the wires back onto the tabs. The tabs are marked +-, just make sure they get put back on right. Cover with black tape. You will not have any issues.

 

[RocketDestroyer]

If you exceed a set current draw the protection circuit disconnects the battery from the electronics. Not something you really want to have happen during a flight. I believe the thinking was that it was better to sacrifice the battery to save the rocket.

Over current protection:
VDET3 Over current detection voltage 0.150±0.030V
IDP Over current detection current 2.5～4.5A
tVDET3 Detection delay time 10ms
Release condition Cut load

 

[GlueckAuf]

The LiPo overdischarge protection circuit reacts to large, over-the-threshold drains of current by shutting off current flow either permanently or briefly. Its aim is to prevent a chemical fire that can be rapid, intense, and difficult to extinguish. When an e-match is electrically ignited, it can draw a lot of current (especially if, as sometimes happens, its melting fuses the bridge wire carriers to the closed state after firing). Were this to trigger the protection circuit during the apogee event, the off or reset altimeter would be out of commission to fire the main chute charge. The rocket would, at best case, land much harder than usual and damage itself. Worst case, it could plunge dangerously fast and strike persons or property. And the bigger and heavier the rocket, the more consequential this main event failure could be. (The thud can be pretty sobering.)

A dual deployment altimeter's momentary closure of a firing circuit lasts for one second or less in the case of the three brands I've used. A dead short during this event would be unlikely to damage the LiPo, let alone cause it to catch fire (though it still wouldn't be good for the altimeter). Thus using small-capacity LiPo batteries (Perfect Flite recommended to me 125mAh or less) without the battery protection PCB is deemed best for our sport from a risk mitigation standpoint.

 

[cerving]

If you exceed a set current draw the protection circuit disconnects the battery from the electronics. Not something you really want to have happen during a flight. I believe the thinking was that it was better to sacrifice the battery to save the rocket.

Over current protection:
VDET3 Over current detection voltage 0.150±0.030V
IDP Over current detection current 2.5～4.5A
tVDET3 Detection delay time 10ms
Release condition Cut load

Since the all-fire current of most ematches is about 1A, if it's drawing that much current you probably have a dead short on the leads and it won't fire anyway... just my 2 cents.

 

[FredA]

Since the all-fire current of most ematches is about 1A, if it's drawing that much current you probably have a dead short on the leads and it won't fire anyway... just my 2 cents.

This has nothing to do with the all-fire current.

Once fired, a plasma ball is created that is nearly zero ohms.....a DEAD SHORT on your pyro output and real cause for concern.
Some flight computers sense this and PWM their outputs to protect their output devices.
Best practice IMHO is to use a 9V Alkaline battery who's internal resistance limits the current to about 4 Amps which almost all outputs can tolerate.

 

[jderimig]

Don't use a Lipo with a protection circuit and don't use a wimpy low mah Lipo to protect your altimeter. Your flight computer is a system, choose battery and computer that work together.

 

[Lord Rory Gin]

Don't use a Lipo with a protection circuit and don't use a wimpy low mah Lipo to protect your altimeter. Your flight computer is a system, choose battery and computer that work together.

That was my first inclination then I read this in their manual:
3.9. Using a Different Kind of Battery
TeleMini, TeleMega, EasyMega and TeleMetrum are only designed to operate off a single-cell Lithium Polymer battery and cannot be used with any other kind. Connecting a different kind of battery to any of these will destroy the board.

 

[roytyson]

That was my first inclination then I read this in their manual:
3.9. Using a Different Kind of Battery
TeleMini, TeleMega, EasyMega and TeleMetrum are only designed to operate off a single-cell Lithium Polymer battery and cannot be used with any other kind. Connecting a different kind of battery to any of these will destroy the board.

That battery will work just fine. you can use them all the way up to the 850mah, as long as you remove the board, OR just buy them from a rocket vendor or Altus Metrum website. Keith and Bdale would not continue selling them if they didn't work.

i buy the 850 sparkfun batteries if Im getting something else from digikey or just buy them from AM. The new boards that allow higher voltage batteries, I do use 2S batteries, but some of their older products only allow these 1S batteries.

 

[GlueckAuf]

Don't use a Lipo with a protection circuit and don't use a wimpy low mah Lipo to protect your altimeter. Your flight computer is a system, choose battery and computer that work together.

Just to clarify, the recommendation I received to use that "wimpy" 125 mAh LiPo I referenced came in a tech support email reply from the owner of Perfect Flight with regard to protecting the Stratologger CF. It's due, he wrote, to the possibility that an e-match might close the circuit upon firing and subject his device for a full 1 second to a potentially damaging dump of current if a large LiPo were used. He made it clear that he preferred his customers to use a 9V alkaline battery due to its protective, high internal resistance, but supported the use of low-capacity LiPo batteries NTE 125 mAh if the customer preferred to use that type of battery instead.

I've calculated that the Hyperion G3 and G5 2S 120mAh LiPo batteries I use with Stratologgers will, if fully charged, deliver up to about [edited] 40 single e-match firings at 5 amps each (and they’re usually just 2 to 3 amps), ALONG WITH up to 40 or so hours of continuously-on usage. That's more than enough capacity between recharges for this user.

 

[jderimig]

Just to clarify, the recommendation I received to use that "wimpy" 125 mAh LiPo I referenced came in a tech support email from the owner of Perfect Flight with regard to protecting the Stratologger CF. It's due, he wrote, to the possibility that an e-match might close the circuit upon firing and subject his device for a full 1 second to a potentially damaging dump of current if a large LiPo were used. He made it clear that he preferred his customers to use a 9V alkaline battery due to its protective, high internal resistance, but supported the use of low-capacity LiPo batteries NTE 125 mAh if the customer preferred to use that type of battery instead.

I've calculated that the 120mAh LiPo batteries I use with Stratologgers will, if fully charged, deliver up to about 46 e-match firings at 5 amps each, or up to 36 hours of continuous usage. That's more than enough capacity between recharges for this user.

Yes, a 9V battery will only deliver about 5A into a dead short because the internal resistance of the 9V alkaline is about 2 ohms which drops the voltage output to zero. The 120mah emulates the 9V alkaline with a similar high internal resistance that limits the current. But the small lipo is probably a more reliable package. Kudo's on the doing the calculations to understand the usage limits of that application.

 

[plugger]

I just happen to have Spark Fun's 400 mAh LiPOs and visually I can tell they have the limiting circuit board on them. Does this mean I can't use these batteries? Do I have to remove the circuit board for them to work? And lastly, WHY does this circuit cause the battery to shut down as above?

If you're looking to fire charges with that LiPo then 100% remove them. If you're looking to power a TeleGPS with them then the battery is fine as is.

The reason why it's recommended to remove them is that the protection circuit changed between prototyping the TeleMetrum and the release of the v1.0 boards/kits. And Altus didn't pick that up at the time. Some people (myself included) lawn darted rockets relying on v1.0 Telemetrums because of this issue and as a result the page was created on the Altus Metrum website recommending their removal.

 

[plugger]

Just to clarify, the recommendation I received to use that "wimpy" 125 mAh LiPo I referenced came in a tech support email from the owner of Perfect Flight with regard to protecting the Stratologger CF. It's due, he wrote, to the possibility that an e-match might close the circuit upon firing and subject his device for a full 1 second to a potentially damaging dump of current if a large LiPo were used. He made it clear that he preferred his customers to use a 9V alkaline battery due to its protective, high internal resistance, but supported the use of low-capacity LiPo batteries NTE 125 mAh if the customer preferred to use that type of battery instead.

I've calculated that the 120mAh LiPo batteries I use with Stratologgers will, if fully charged, deliver up to about 46 e-match firings at 5 amps each, or up to 36 hours of continuous usage. That's more than enough capacity between recharges for this user.

Adrian from FeatherWeight also recommends using 130 mAh LiPos for use with the Ravens. If you look at the Raven AV bays and the Power Perch you can see they're clearly designed for that battery size.

 

[Steve Shannon]

So why not simply add a current limit resistor when using lipos?

 

[jderimig]

So why not simply add a current limit resistor when using lipos?

On load not the source.

 

[Steve Shannon]

On load not the source.

Why? If people choose a different battery type because it has an internal resistance they don’t have a choice; it’s in the source. Are you concerned about brown outs causing a reset? If that’s the concern I would agree.

 

[FredA]

So why not simply add a current limit resistor when using lipos?

You could - you shouldn't have to with proper design - just that we don't know much about the designs.

 

[jderimig]

Why? If people choose a different battery type because it has an internal resistance they don’t have a choice; it’s in the source. Are you concerned about brown outs causing a reset? If that’s the concern I would agree.

Its just a terribly bad practice to degrade your power supply on electronics in the safety chain.