Goog 9V batteries for launching LPR and MPR

[RocketDestroyer]

I tested three different 9V batteries recently. I used a 2.5 Ohm resistor in the circuit to limit the current to something close to what my e-matches draw. In addition to measuring current I also measured the voltage under load. I also calculated the power the battery delivered to the load. I used a Tektronix digital oscilloscope and current probe to capture the first 8 mS of current draw. I used the average of the voltage and current after the initial spike when the circuit is first connected.

Here are my results...
Battery Volts Amps Watts
Ray o Vac Ultra Pro 4.12V 1.56A 6.43W
Duracell Duralock 6.68V 2.56A 17.11W
Energizer Lithium 6.44V 2.44A 15.71W*

* This was not a new battery. I had used it for at least a dozen flights ground tests. The rest of the batteries were brand new.

 

[neil_w]

This makes me so annoyed that I did my first launch with my daughter with a Rayovac; I've had perfectly fine success with them in other applications but here they are critically inferior. I wish this thread was around before I went with that battery, we could have had a much more enjoyable day of launches. Oh well!

 

[BEC]

Quick addendum: measured resistance of several different Estes Solar Igniters of various vintages all yielded values around 0.7 ohms.

 

[morlock]

Quick addendum: measured resistance of several different Estes Solar Igniters of various vintages all yielded values around 0.7 ohms.

That's interesting. I would have expected much more. I have to bring my recently deceased multimeter for repairing

 

[BEC]

I was a little surprised myself....since my homemade small igniters (Quickburst kits) tend to be about twice that. But the bridge wire on Estes igniters is pretty short.

Added later: I found this report https://www.psc473.org/howto/Igniter.pdf and it says that Estes igniters tested had an average resistance of 0.711 ohms, so I guess my crude measurement wasn't so far off.

 

[bobkrech]

I tested three different 9V batteries recently. I used a 2.5 Ohm resistor in the circuit to limit the current to something close to what my e-matches draw. In addition to measuring current I also measured the voltage under load. I also calculated the power the battery delivered to the load. I used a Tektronix digital oscilloscope and current probe to capture the first 8 mS of current draw. I used the average of the voltage and current after the initial spike when the circuit is first connected.

Here are my results...
Battery Volts Amps Watts
Ray o Vac Ultra Pro 4.12V 1.56A 6.43W
Duracell Duralock 6.68V 2.56A 17.11W
Energizer Lithium 6.44V 2.44A 15.71W*

* This was not a new battery. I had used it for at least a dozen flights ground tests. The rest of the batteries were brand new.

As stated above the resistance is ~0.8 ohms, so now do the same test with the real igniter, and run it as was done in the reference quoted above and see what you get and when the igniter actually burns. (The Energizer lithium may not be the same chemistry as a LiPo and/or may have a current limiter so beware of the results.)

Bob

 

[RocketDestroyer]

Energizer Lithium batteries are based on a Lithium Iron Disulfide (Li-FeS2) chemistry.

 

[j.a.duke]

I’ve taken a couple of old Estes controllers, added wire out the bottom and connected them to this:

12 volt 1.2ah SLA

Plenty of juice for a Cub Scout launch (50-60 flights). Also works great for clusters-plenty of power.

I charge it with this:

12v SLA Charger

I got started down this path when someone on one of the forums offered batteries that they pulled from equipment at work (I presume a hospital or similar) that are still good. I got some 2.3 and 5 amp hour batteries and my launches have been fast and reliable ever since. But those are heavy (about 1 pound per ah), so I went with a smaller battery for my personal launches, saving the bigger ones for Scouts and other mass launches.

Cheers,
Jon

 

[Flyfalcons]

My orange controller is finally starting to take 2-3 seconds to light off a motor. So I estimate that's around 50-60 launches on a Duracell 9V.

 

[BEC]

So you are well into reusable igniter territory then....as long as the bridge wire is intact you can reuse them.

 

[SirNomad]

I gave up and just got an 8 cell AA holder from Radio Shack with a snap connector. A little duct tape to hold it to the launch controller and we were good to go.

 

[BEC]

Just did a demo launch Tuesday night with the Astron II controller and the little lithium rechargeable in it. Instant ignition, bridge wire burnt through. Time will tell how it does over repeated use.