estes igniters minimum voltage

[François Paquette]

Hello everyone,

I would like in my next rocket to use an ejection charge that would be controlled electronically from an arduino nano via an altimeter. For that, I will use the igniter of estes mounted on a load cylinder holder. Has anyone ever done research on the minimum volt/amp to activate estes igniters ?


Do a 1200mAh 9 volt battery will be sufficient ?

 

[Jay Chladek]

Typically it was about 6 volts. Quest used 9 volt batteries in their launch controllers and 14.4V was what Pro Series 2 controllers could output with two battery packs. When in doubt, do a ground test to make sure the igniter fires as igniters cost a lot less than replacing a rocket.

 

[BEC]

Good advice. Estes has also made two launch controllers that used a 9V battery. The most recent was the "Astron II" controller. The battery had to be a high quality unit (Duracell or Energizer) in order for it to be reasonably reliable.

Wiring inside a rocket would be much shorter than that used by a launch controller, which will help. But ground testing is certainly indicated.

 

[jqavins]

How are you switching the circuit? Are you using an output from the Arduino to fire the charge directly, or using it to close a relay or switch a MOSFET or some such?

It's not voltage you need to consider, but current. Voltage measured at the ends of the starter's leads is tantamount to the same thing, but it's really the current that matters.

I couldn't find the technical details at Estes web site, but eRockets provides this:

• Minimum all-fire current: 2 A
• Maximum no-fire current: 0.5 A
• Nominal resistance: 0.6904 Ω

I'm disappointed that there is no tolerance given for the resistance, only the nominal value. I suspect the tolerance isn't more than 5%, but I could easily be all wet. Let's go with 10% to be on the safe side. Also, I'm skeptical that the resistance is actually known to four significant digits, but that's not important.

To be certain of firing you need at least 2 A with load resistance possibly as high as 1.1*0.69 Ω, so you need at least 1.52 V at the ends of the leads. But again, voltage is the wrong thing to focus on; just focus on the 2 A. What is the 9 V battery's internal resistance? What losses are there and is there a current limit in the switching method?

And if you are building in an on-board continuity test, be sure that the test current is under - well under - 0.5 A.

 

[jjwb22101]

A question for you - why are you using Estes igniters to activate an ejection charge? The standard method to do that is using an electric match, which is substantially less delicate, more reliable, and easier to activate than an Estes igniter.

 

[François Paquette]

thank you for your answer
a moffet will be used as a relay for ignition
tests will be done on the electric match and the christmas lights.
I will share the results of my ground test

 

[aeronaut]

I know this is an old thread, but power is another factor to consider. To deliver 2 A, the battery has to have a short term power level of at least 2 A times its voltage rating. This is probably why the 9 V cells weren't super reliable. Two of them in parallel would probably work very well.

Another way to reduce the battery size/power requirement is to put a capacitor in parallel with the battery. When the ignition switch is closed, the capacitor will dump its charge quite quickly, supplementing the battery's current. When the switch opens again, the capacitor will charge itself again to get ready for the next firing. One could reduce the strain on the battery by putting a resistor in series with the capacitor, so the capacitor charges slowly, but discharges quickly through the igniter alone. The only caveat here is that leaving the battery connected for many days will eventually drain it completely, so either a charging switch, or removing the battery between sessions is in order.

 

[BEC]

Interesting to have this thread pop up again. It makes me want to update two things:

First, Duracells and Energizers are no longer the go-to batteries for 9V controllers. There is much discussion in a 9V battery thread here and some details and numbers in my R&D report that was presented at vNARCON this year. What you want, these days, is a 9V battery that is either an alkaline marked “6LR61” somewhere on the package or a lithium-based 9V.

Second, perhaps Estes starter specs aren’t on their web site, but they are in every pack of engines on the instruction sheet. It looks like this:




These numbers did not change in the transition for the “Solar starters” to the “Startech starters”. I suspect that’s because the wires underneath the coating on the tip did not change. I got to see the desktop-sized machine that actually makes these when there was an Estes tour at NARAM-60. Pretty amazing device.

(hah — I just now noticed that they misspelled “current” on at least the version I took this picture of last November.)

 

[bjphoenix]

I checked a couple today and got 1.0 to 1.1 ohm. (although I can't vouch for the accuracy of my old VOM)

 

[BEC]

I checked a couple today and got 1.0 to 1.1 ohm. (although I can't vouch for the accuracy of my old VOM)

What does it read when you just touch the test tips together? This might not be correct practice, but I just subtract that value from the one displayed when testing the igniter (or whatever) to get a little closer. With that approach, I find the Estes ones to be pretty close to the 0.7 ohm value given on the motor instructions.

 

[lr64]

I checked a couple today and got 1.0 to 1.1 ohm. (although I can't vouch for the accuracy of my old VOM)

It might be more accurate to test a string of them in series, although that won't give you the variation between individual examples.

 

[sghioto]

From my testing a CR123A 3 volt battery will fire an Estes igniter reliably

 

[John Taylor]

Why use an Estes igniters at all? Like other said use an firewire electric match. It is very low current demand. Almost every Dual Deployment rocket uses electric matches. MUCH MORE RELIABLE.

 

[aeronaut]

I'm looking into the LiFePO4 cells (Lithium Iron Phosphate) as a candidate for the launch power source. They have a slightly lower voltage than the lithium polymer cells, but even a relatively small 18650 cell can deliver a massive current of 33 A, which would make them kind of dangerous if shorted. This is mostly due to a lower internal resistance. Through 0.7 Ohms this will produce a current of a little over 5.1 A, which should easily fire the igniter. Further, LiFePO4 cells are far less likely to catch fire when driven hard. They store less energy per volume vs. lithium polymer, but can dump the energy they have much faster. Sounds ideal, a single 18650 cell could drive the launch. I will post test results here after I get the cells (they are a special order item, about $4 each). Final bonus, 3.6 V can drive a small low voltage relay and power LEDs with minimal power loss to the current limiting resistors. I also might play around with making a low voltage DC welder out of several cells; short bursts of massive current could spot weld moderate thickness metals, but that's entirely another post.

Also, best practice to measure the resistance of a low resistance load is to put the ohmmeter across just a few millimeters of one of the leads, to measure the contact and lead resistances, and then put it across the device to get the total, and take the difference.

 

[lr64]

What could you possibly do with 33A? Many lipos can also deliver a lot of current, and some LiFePO4 cells can't. If you're worried about shorts, use a fuse or circuit breaker.