NOOB: Power requirements for composite igniters

[noise]

I'm getting ready to purchase my first composite motors and I was wondering if my launch controller will be sufficient for the composite igniters.

I'm using the Quest controller with the add on wire connected to two 6 volt lantern batteries wired in series.

Is this enough, or does it need the amperage of a larger battery?

 

[Rocketry nut]

According to Aerotech you need at least 12 volts and 3 amps. You also should have at least 30ft for up to G motors. So it sounds like you have 12 volts, but what about amps?

 

[noise]

I can't find that information posted anywhere, just voltage and mAh.

 

[Rocketry nut]

Originally posted by noise
I can't find that information posted anywhere, just voltage and mAh.

Give me the mAh and I can figure it out.

 

[jwagner61]

Lead acid batteries of similar size typically have CCA 's (Cold Cranking Amps) of around 50 A. While alkaline batteries have larger internal resistance, they can deliver 3 A for the few seconds needed to fire an ignitor.

A more immediate concern is whether you leads to the pad have low enough resistance.

 

[noise]

Originally posted by Rocketry nut
Give me the mAh and I can figure it out.

26000 mAh

 

[Brian -- PYH]

Its been a while since I took an Electrical Engineering course, but IIRC when dealing with DC batteries sources you will draw as much current as you need for the voltage given. In some cases this can exceed the limits of what the batteries are designed for and will cause them to get really hot and fail.

For the case of the igniters, your only drawing the current for a short time, just enough to cause the igniter to fire, shouldn't be a problem as long as you have some fairly fresh batteries. If you try it out and they don't light... you probably need some newer batteries... Car batteries work really well

The mAH rating on the batteries is just a measure of how much power is stored, not how much current can be drawn from the battery.

 

[noise]

Originally posted by jwagner61
Lead acid batteries of similar size typically have CCA 's (Cold Cranking Amps) of around 50 A. While alkaline batteries have larger internal resistance, they can deliver 3 A for the few seconds needed to fire an ignitor.

A more immediate concern is whether you leads to the pad have low enough resistance.

Well the quest controller wires are pretty thin, I assume that means higher resistance.

Maybe I just need to test out an igniter.

 

[Rocketry nut]

Originally posted by noise
26000 mAh

Dang is that for one or both. I have some electric r/c plane club members who could figure the exact stuff for you, but you really don't need that. That's 26 amps per hour which is more than enough. I have learned a lot in my r/c club about this stuff, but really don't need to get technical. So that will work, but thicker wires will help get more "juice" to the igniter.

My system has 16.8 volts and 4.2 amps an hour. This has lit everything from E-G just fine.

 

[noise]

Originally posted by Rocketry nut
Dang is that for one or both. I have some electric r/c plane club members who could figure the exact stuff for you, but you really don't need that. That's 26 amps per hour which is more than enough. I have learned a lot in my r/c club about this stuff, but really don't need to get technical. So that will work, but thicker wires will help get more "juice" to the igniter.

My system has 16.8 volts and 4.2 amps an hour. This has lit everything from E-G just fine.

That's for one, according to the energizer web site.

Actually I just realized my first composite may be launched from a club controller, but it's good to know.

I'm thinking a D13 in my Super Bird this weekend just to get rid of that nasty composite virginity.

EDIT: Oops, I mean D21, confusing my SU and RMS motors.

 

[Brian -- PYH]

Originally posted by Rocketry nut
That's 26 amps per hour

Actually, thats 26 Amp Hours.... not Amps per hour. Meaning the battery would last about 1 hour if you drew 26amps from it (though I would suspect that would ruin the battery as thats ALOT of current). Think of it more like you would get about 26 hours of battery life on a 1 Amp drain on the battery.

You should use the mAH ratings to gage battery life, not how much current you can draw from them. Most batteries unless designed for high current loadings will melt, explode, or fail in a bad way if you pull too much from them at once.

 

[Rocketry nut]

Originally posted by Brian -- PYH
Actually, thats 26 Amp Hours.... not Amps per hour. Meaning the battery would last about 1 hour if you drew 26amps from it (though I would suspect that would ruin the battery as thats ALOT of current). Think of it more like you would get about 26 hours of battery life on a 1 Amp drain on the battery.

You should use the mAH ratings to gage battery life, not how much current you can draw from them. Most batteries unless designed for high current loadings will melt, explode, or fail in a bad way if you pull too much from them at once.

Oops sorry about that. Sometimes I reread what I type and other times I don't.

I don't claim to know everything on the subject, but have learned maybe more than needed just by hanging around these club members. I get lost half the time, but pick enough up for what I need to know.LOL Anyway it should all work. Since your only pulling power for a few seconds at most, it won't ruin the battery.

 

[wildbluerocket]

.

 

[m85476585]

Originally posted by Brian -- PYH
Actually, thats 26 Amp Hours.... not Amps per hour. Meaning the battery would last about 1 hour if you drew 26amps from it (though I would suspect that would ruin the battery as thats ALOT of current). Think of it more like you would get about 26 hours of battery life on a 1 Amp drain on the battery.

You should use the mAH ratings to gage battery life, not how much current you can draw from them. Most batteries unless designed for high current loadings will melt, explode, or fail in a bad way if you pull too much from them at once.

I doubt you will ruin the battery. 26A is1C for a 26Ah battery, and most batteries can handle a lot more than 1C. Lithium polymer, for example (the only thing I could find info on), has a maximum discharge rate of somewhere around 10C with bursts up to 20C, which means that with a 26Ah Li-poly you could draw 260A for 6 minutes.

Although theoretically there is no limit to how fast a battery can discharge, internal resistance limits the rate, so you are not likely to draw enough current to damage the battery (with Li-poly you might because the internal resistance is so low, but not with 1-second bursts for igniters).

Edit: I read that NiCd batteries can also be discharged at 10C, but you might only get 80% of the total power.

 

[Zack Lau]

https://data.energizer.com/PDFs/alkaline_appman.pdf

According to this page, the internal resistance is likely to be around 0.2 ohms for each cell (D sized cell). With 8 cells for 12 volts, this is an total internal resistance of 1.6 ohms.

12volts/3 amps=4 ohms, the maximum resistance of entire wiring system

4 ohms-1.6 ohms =2.4 ohms.

The wiring and igniter, including the resistance of the clip leads, needs to have less than 2.4 ohms of resistance.

The application note suggests that if you are really lucky, you can get 16 amps out of one cell . But, I wouldn't count on all eight cells in two batteries being really good.

I'd suggest getting a sealed 12V gell cell battery for this application--you can buy a complete unit with charger relatively cheap.